Change search
Refine search result
59606162636465 3051 - 3100 of 3228
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 3051.
    Yin, Jiaqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Morphology of Upper and Lower Bainite with 0.7 Mass Pct C2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48, no 9, p. 4006-4024Article in journal (Refereed)
    Abstract [en]

    There has been an on-going discussion on the difference in formation mechanisms of upper and lower bainite. Various suggestions have been supported by reference to observed morphologies and illustrated with idealized sketches of morphologies. In order to obtain a better basis for discussions about the difference in mechanism, the morphology of bainite in an Fe-C alloy with 0.7 mass pct carbon was now studied in some detail from 823 K to 548 K (550 °C to 275 °C) at temperature intervals of 50 K or less. The work focused on bainite seen to start from a grain boundary in the plane of polish and showing an advancing tip in the remaining austenite. The results indicate that there is no essential difference with temperature regarding the ferritic skeleton of feathery bainite. The second stage of bainite formation, which involves the formation of both ferrite and cementite, was regarded as a eutectoid transformation and the resulting morphologies were analyzed in terms of two modes, degenerate and cooperative eutectoid transformation. There was no sharp difference between upper and lower bainite. Ways to define the difference were discussed.

  • 3052.
    Yin, Jiaqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Widening of Laths in Bainite2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 11, p. 5294-5303Article in journal (Refereed)
    Abstract [en]

    Units of bainite in Fe-C alloys from the upper temperature range inherit their shape from Widmanstatten plates of ferrite, which are lathlike. The thickness increases by long-range diffusion of carbon and the length by short-range diffusion of carbon from the advancing edge of the tip. Both have been studied extensively and are fairly well understood. Widening growth seems to have been much neglected, but a study of some aspects of widening is now presented. The present report is the last one in a series of four morphological studies of bainite, isothermally formed in Fe-C alloys with 0.3 or 0.7 mass pct carbon, mainly in the upper temperature range. It contains a number of morphological observations made on cross sections of packets of bainite, and it elucidated a number of interesting questions about bainite and resulted in some proposals. The ferrite plates in a packet are nucleated as a group on a grain boundary, not each one separately on the side of a prior plate. Lengthening occurs by advancement of a short edge that is formed in close contact to the grain boundary. Widening of laths does not start spontaneously. It is initiated by a modification of the structure of the long edge of the lath. When it then moves, the lattice of the new ferrite is rotated relative to the ferrite formed by lengthening and the habit plane is different. In a section through the length direction, it is difficult to recognize what part of ferrite has formed by widening growth. Furthermore, it is proposed that the individual plates in a microstructure, previously used to illustrate subunits formed by repeated nucleation, were nucleated on a hidden grain boundary.

  • 3053.
    Yin, Jiaqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Widening of Laths in BainiteManuscript (preprint) (Other academic)
    Abstract [en]

    Units of bainite in Fe-C alloys from the upper temperature range inherit their shape from Widmanstätten plates of ferrite which are lath-like. The thickness increases by long-range diffusion of carbon and the length by short range diffusion of carbon from the advancing edge of the tip. Both have been studied extensively and are fairly well understood. Widening growth seems to have been much neglected but a study of some aspects of widening is now presented. The present report is the last one in a series of four morphological studies of bainite, isothermally formed in Fe-C alloys with 0.3 or 0.7 mass pct carbon, mainly in the upper temperature range.  It contains a number of morphological observations made on cross sections of packets of bainite. They elucidated a number of interesting questions about bainite and resulted in some proposals. The ferrite plates in a packet are nucleated as a group on a grain boundary, not each one separately on the side of a prior plate. Lengthening occurs by advancement of a short edge that is formed in close contact to the grain boundary. Widening of laths does not start spontaneously. It is initiated by a modification of the structure of the long edge of the lath. When it then moves, the lattice of the new ferrite is rotated relative to the ferrite formed by lengthening and the habit plane is different. In a section through the length direction it is difficult to recognize what part of ferrite has formed by widening growth. Furthermore, it is proposed that the individual plates in a microstructure, previously used to illustrate subunits formed by repeated nucleation, were nucleated on a hidden grain boundary.  

  • 3054.
    Yin, Jiaqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Leach, Lindsay
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    C-Curves for Lengthening of Widmanstätten and Bainitic Ferrite2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48, no 9, p. 3997-4005Article in journal (Refereed)
    Abstract [en]

    Widmanstätten ferrite and bainitic ferrite are both acicular and their lengthening rate in binary Fe-C alloys and low-alloyed steels under isothermal conditions is studied by searching the literature and through new measurements. As a function of temperature, the lengthening rate can be represented by a common curve for both kinds of acicular ferrite in contrast to the separate C-curves often presented in time-temperature-transformation (TTT) diagrams. The curves for Fe-C alloys with low carbon content show no obvious decrease in rate at low temperatures down to 623 K (350 °C). For alloys with higher carbon content, the expected decrease of rate as a function of temperature below a nose was observed. An attempt to explain the absence of a nose for low carbon contents by an increasing deviation from local equilibrium at high growth rates is presented. This explanation is based on a simple kinetic model, which predicts that the growth rates for Fe-C alloys with less than 0.3 mass pct carbon are high enough at low temperatures to make the carbon pileup, in front of the advancing tip of a ferrite plate, shrink below atomic dimensions, starting at about 600 K (323 °C).

  • 3055.
    Yin, Jiaqing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Leach, Lindsay
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hillert, Mats
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    C-curves for lengthening of Widmanstätten and bainitic ferriteManuscript (preprint) (Other academic)
    Abstract [en]

    Widmanstätten ferrite and bainitic ferrite are both acicular and their lengthening rate in binary Fe-C alloys and low alloyed steels under isothermal conditions is studied by searching the literature and through new measurements. As a function of temperature it can be represented by a common curve for both kinds of acicular ferrite in contrast to the separate C-curves often presented in TTT diagrams. The curves for alloys with low carbon content show no obvious decrease in rate at low temperatures down to 623 K (350 °C). For alloys with higher carbon content than 0.5 mass%, the expected decrease of rate as function of temperature below a nose was observed. An attempt to explain the absence of a nose for low carbon contents by an increasing deviation from local equilibrium at high growth rates is presented. It is based on a very simple kinetic model, which predicts that the rates for Fe-C alloys with less than 0.3 mass% carbon are high enough to result in an increasing deviation from local equilibrium on decreasing temperature, starting at about 773 K (500oC).

  • 3056.
    Yin, Litao
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. University of Science and Technology Beijing, China.
    Jin, Y.
    Leygraf, Christofer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Pan, Jinshan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Local probing & modelling of micro-galvanic corrosion of AI alloys2015In: European Corrosion Congress, EUROCORR 2015, Austrian Society for Metallurgy and Materials (ASMET) , 2015, Vol. 3, p. 1567-1567Conference paper (Refereed)
  • 3057.
    Ying, Yang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Inclusion Behaviour under a Swirl Flow in a Continuous Casting Process2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A swirl flow generated in a submerged entry nozzle (SEN) can effectively improve a flow pattern and heat transfer in a continuous casting process by using the methods of “swirl blade type” and “electromagnetic type”. In order to obtain a further in-depth understanding with respect to the effect of a swirl flow on a continuous casting process, the inclusion behaviour in a SEN and a mold was studied in the present work. Moreover, the use of electromagnetics was adopted for to generate a rotating electromagnetic field in a continuous casting process of steel. Specifically, an electromagnetic swirl flow generator (EMSFG) was placed around a SEN.

    First of all, two kinds of a full type EMSFG and a half type EMSFG were designed based on mathematical modeling. Then, distributions of a magnetic flux intensity in an EMSFG as well as distributions of a Lorentz force in molten steel were simulated. It was found that the EMSFG structure and electromagnetic parameters have an important effect on the magnetic flux intensity and Lorentz force distributions. For both a full type and a half type EMSFG, the magnetic flux intensity and Lorentz force increases as the magnetomotive force increases. Especially, for a full type EMSFG, the magnetic flux intensity is distributed evenly in molten steel. Moreover, the Lorentz force increases along a radial direction in the molten steel in the SEN. However, for a half type EMSFG, the magnetic flux intensity and Lorentz force decreases gradually towards the region without an EMSFG. Consequently, a full type EMSFG with a 44000 AT magnetomotive force and a 50 Hz frequency is more suitable to apply in the operation of an EMSFG under actual production conditions.

    Secondly, the flow field, the temperature field of molten steel and the inclusion behaviour in a SEN and a square bloom mold were simulated under the influence of a rotating electromagnetic field (swirl generator). Also, the influences of different inclusion parameters such as the densities, sizes and boundary conditions, on the inclusion behavior were studied. The results show that a flow pattern in a SEN can be characterized into three distinct flow regions: an accelerating flow of molten steel from an electromagnetic swirl flow generator (EMSFG) inlet to an EMSFG center, a decelerating flow of molten steel from an EMSFG center to an EMSFG outlet, and a recirculation flow of molten steel from an EMSFG outlet to an SEN outlet. In addition, it was found that light Al2O3 inclusion moves towards the rotational center by a centrifugal force, and that a swirl flow prevents nozzle clogging. Moreover, it was also found that the inclusion separation to a mold meniscus increased and that the inclusions trap into a solidified shell wall decreased by using a swirl flow.

     

     

  • 3058. Yokoya, S.
    et al.
    Jönsson, Pär G.
    KTH, Superseded Departments, Metallurgy.
    Sasaki, K.
    Tada, K.
    Takagi, Shigeo
    KTH, Superseded Departments, Metallurgy.
    Iguchi, M.
    The effect of swirl flow in an immersion nozzle on the heat and fluid flow in a billet continuous casting mold2004In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 33, no 1, p. 22-28Article in journal (Refereed)
    Abstract [en]

    A numerical analysis and a water model study of the mold region of a billet continuous caster was performed with a novel injection concept using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mold. The following results were found: A weak impinging flow can be observed near the corner of the mold wall, which results in the promotion of uniform heat and mass transfer all around across the plane, particularly at the casting corner. An upward flow directed from the vicinity of the nozzle outlet to the meniscus can be observed near the corner of the upper part of the mold, which leads to the active heat and mass transfer into the meniscus. A uniform velocity and heat distribution can be obtained within a short distance of 200 mm downward from the outlet of the nozzle. Quite different mold flow patterns are observed between the divergent and straight immersion nozzles. Heat and mass transport in the mold using the divergent nozzle is much more reasonable than that using the straight nozzle.

  • 3059. Yokoya, S.
    et al.
    Takagi, S.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Hallgren, Line
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Kholmatov, Shavkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Tsukaguchi, Y.
    Swirling flow effect in immersion nozzle on control of heat and mass transport in casting teeming2006In: 2006 TMS Fall Extraction and Processing Division, 2006, p. 485-498Conference paper (Refereed)
    Abstract [en]

    With increasing requirement of steel productivity and quality in continuous casting in the conventional casting system using an immersion nozzle, it is very difficult to establish a reasonable molten flow pattern. In order to overcome this difficulty, we propose a new method of imparting swirling motion onto the flow in the immersion nozzle and to control the flow pattern in the mold. Following results have been obtained during the studies. For the case of slab continuous casting mold: High amplitudes of oscillation with a period of 10 to 15 seconds are observed in the outlet flow of the immersion nozzle and meniscus flow in the conventional casting system, while these phenomena are remarkably suppressed using swirling motion in the immersion nozzle, which leads to very calm and uniform flow pattern at the outlets of the immersion nozzle, in the mold and on the meniscus in the mold; For the case of billet continuous casting mold: (1) heat and mass transfer near the meniscus can be remarkably activated compared with a conventional straight type immersion nozzle without swirl, and (2) Quite different mold flow patterns are observed between the divergent and straight immersion nozzles. Heat and mass transport in the mold using the divergent nozzle is much more reasonable compared to that of straight nozzle. The findings, mentioned above, are very useful to control the flow pattern in the slab, and billet continuous casters. Such effectiveness of swirling flow in the SEN on the mold flow has been put into practical use. As a result, remarkable progress on the quality and production of continuous casting products has been observed in practical application.

  • 3060. Yoshida, Suguru
    et al.
    Ushioda, Kohsaku
    Abe, Yoshio R.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Kinetic Model of gamma to alpha Phase Transformation at Grain Boundaries in B-Bearing Low Alloy Steel2012In: Tetsu to hagane, ISSN 0021-1575, E-ISSN 1883-2954, Vol. 98, no 9, p. 24-32Article in journal (Refereed)
    Abstract [en]

    The effect of Boron (B) on nucleation and growth of ferrite from austenite grain boundaries is examined theoretically assuming the junction of 4-austenite grain boundaries as dominant nucleation sites of ferrite. B segregates to the austenite grain boundaries and reduces the grain boundary energy and thereby retards the ferrite nucleation at the grain boundary. The retardation is expressed as a decrease of nucleation frequency due to an increase of activation energy for nucleation and the calculated value of the fraction of active nucleation sites is in satisfactory agreed with experimental results. The reduction of the austenite grain boundary energy, obtained by applying the Gibbs isotherm for adsorption to the B segregation, is of the same order of as the one which is deduced from results of calculation for decrease in the nucleation frequency based on experimental result. The growth of ferrite is calculated using DICTRA yielding both the volume fraction and the grain size of transformed ferrite as a function of time, which agreed with the experimental results. This suggests the slight influence of B on growth rate. However, the increase of the diffusion cell size due to B addition is considered to be the main reason for the subtle larger grain size of ferrite as compared with B-free steel, which is in good accordance with the experimental fact.

  • 3061. Yoshida, Suguru
    et al.
    Ushioda, Kohsaku
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Kinetic Model of the gamma to alpha Phase Transformation at Grain Boundaries in Boron-bearing Low-alloy Steel2014In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, no 3, p. 685-692Article in journal (Refereed)
    Abstract [en]

    The effect of boron on the nucleation and growth of ferrite at austenite grain boundaries is examined theoretically under the assumption that the junction of 4-austenite grain boundaries (i.e., the 4-grain junctions) are the dominant nucleation sites of ferrite. Boron segregates to the austenite grain boundaries and reduces the grain-boundary energy; it thereby retards ferrite nucleation at the grain boundary. The retardation is expressed as a decrease in nucleation density due to an increase in the critical activation energy for nucleation, and the calculated value of the fraction of active nucleation sites is in satisfactory agreement with the experimental results. The reduction of the austenite grain-boundary energy, which we obtained by applying the Gibbs isotherm for adsorption to the boron segregation, is of the same order of magnitude as the reduction is deduced from the results of calculations for a decrease in the nucleation density based on experimental results. The growth of ferrite was calculated using DICTRA, which yielded both the volume fraction and the grain size of transformed ferrite as functions of time; the results agreed with the experimental results. This agreement suggests that the influence of boron on the growth rate is negligible. However, the increase in the size of the diffusion cell due to the addition of boron is considered to be the main reason for the slightly larger grain size of ferrite compared with that in boron-free steel; this result is also in good agreement with experimental observations.

  • 3062.
    Yoshioka, Takanori
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ideguchi, Takahiro
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ohba, Yasuhide
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    The Effect of a High Al Content on the Variation of the Total Oxygen Content in the Steel Melt during a Secondary Refining Process2018In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 89, no 2, article id 1700287Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to clarify the mechanism of low total oxygen (T.O) contents in high-Al containing steel grades. Steel samples are taken from a ladle during an LF-RH process, and the compositions of both the steels and inclusions are determined. According to thermodynamic considerations, the low T.O contents of high Al steel grades are due to the low insoluble oxygen contents. Due to the high Al contents in a steel melt, thermodynamic driving forces of the Al2O3 modification are lower than those in ordinary Al-killed steels. Both the low thermodynamic driving force of the Al2O3 modification and the inclusion removal from the melts contribute to the low CaO contents in inclusions in high-Al steel melts. The contact angles of inclusions in high Al steel melts are higher than 90 degrees due to the low CaO content in inclusions. Therefore, the removal tendency of inclusions in high Al steel melts is kept high throughout an LF-RH process. Due to this high removal tendency, the T.O contents in high Al steel melts decreases remarkably during an LF refining process. Thereafter, they decrease further during the following RH treatment.

  • 3063.
    Yoshioka, Takanori
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Sanyo Special Steel Co., Japan.
    Shimamura, Y.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ohba, Y.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    The effect of a sulfur addition on the formation and behavior of cas inclusions during a secondary refining process without using a Ca-treatment2018In: International Symposium on Materials Processing Fundamentals, 2018, Springer International Publishing , 2018, Vol. Part F2, 2018, p. 3-13Conference paper (Refereed)
    Abstract [en]

    This study aimed to elucidate the effect of a sulfur addition on the formation and behavior of CaS inclusions in steel melts during a secondary refining process without a Ca-treatment. Samples were taken during production for two different steel grades, namely a low-S steel (S = 0.005%) and a high-S steel (S = 0.055%). Thereafter, the inclusion characteristics were determined using an SEM combined with an EDS. The results show that the CaO content in the inclusions decreased and the CaS content increased after a sulfur addition during an RH process for the high-S steel. Furthermore, CaS-covered inclusions were frequently detected in the high-S steel samples after the S addition. Thermodynamic calculations were also performed to compare the CaS formation behavior in the two steels. The results showed that a CaS phase can thermodynamically be formed in the high-S steel melt even without a Ca-treatment. Also, it was indicated that a CaS phase can be formed in two ways, namely a reaction between Ca and S and a reaction between CaO in inclusions and S. From the viewpoint of interfacial features, inclusions covered by a CaS phase are thought to possess low contact angles to steel melts. Therefore, CaS-covered inclusions tend to remain in a steel melt. According to the results of this study, CaS inclusions can be formed and deteriorate the castability of high-S containing steels even without a Ca-treatment.

  • 3064.
    Yoshioka, Takanori
    et al.
    KTH.
    Shimamura, Yuta
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ohba, Yasuhide
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mechanism of a CaS Formation in an Al-Killed High-S Containing Steel during a Secondary Refining Process without a Ca-Treatment2017In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, no 10, article id UNSP 1700147Article in journal (Refereed)
  • 3065.
    Younesi, S. R.
    et al.
    Amirkabir University of Technology.
    Alimadadi, H.
    Amirkabir University of Technology.
    Alamdari, E. Keshavarz
    Amirkabir University of Technology.
    Marashi, S. P. H.
    Amirkabir University of Technology.
    Kinetic mechanisms of cementation of cadmium ions by zinc powder from sulphate solutions2006In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 84, no 3–4, p. 155-164Article in journal (Refereed)
    Abstract [en]

    The cementation of cadmium ions by zinc powder was studied in a batch reactor at low and high concentrations at pH 5.2–5.4 and it is shown that the reaction is first-order. XRD and SEM analysis confirm that the deposited layer is metallic with no evidence of basic zinc sulphate or re-dissolution of cadmium. Dependence of the reaction constant on initial cadmium concentration proves the reaction mechanism. Different possible kinetic controlling models of cadmium ion (Cd2+) cementation from aqueous solution by zinc powder were studied with respect to initial cadmium concentration, temperature, zinc powder size and stoichiometric ratio. The experiments demonstrate that at initial cadmium concentrations > 1000 ppm, the ash diffusion control model prevails, while at concentrations < 500 ppm, the data has good agreement with the film diffusion model. For concentrations between 500 ppm and 1000 ppm, a combination of ash diffusion and film diffusion models controls the reaction rate. Based on numerical analysis, the calculated activation energies at high and low concentrations are 9.6 and 7.2 kJ/mol, respectively. Statistical data analysis was performed and different reaction rate constants were estimated from the equations for high and low initial cadmium concentrations.

  • 3066.
    Yu, Liang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dong, Yuan-Chi
    Li, Liaosha
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Existence of a solid solution between 3CaO center dot V(2)O(5)and 3CaO center dot P2O52006In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 6, p. 1097-1099Article in journal (Refereed)
    Abstract [en]

    In the present work, a solid solution of 3CaO - V2O5 and 3CaO (.) P2O5 was found below 1573 K. The solution could be described as 3CaO + xV(2)O(5) + (I - X) P205. The solid solutions at three compositions, namely, X = (1)/(3), X = (1)/(2), and X = (2)/(3), were synthesized. X-ray diffraction (XRD) patterns revealed that the crystals exhibited a rhombohedra structure. X-ray indexes at these compositions were reported.

  • 3067.
    Yuan, Kang
    et al.
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Jonnalagadda, Krisha Praveen
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Yu, Yueguang
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Li, Xin-Hai
    Department of Management and Engineering, Linköping University, S.
    Ji, Xiaojuan
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Shen, Jie
    Beijing General Research Institute of Mining and Metallurgy, Beijing, China.
    Thermal fatigue failure of thermal barrier coatings with a high-Cr MCrAIY bond coat2016In: Proceedings of the International Thermal Spray Conference (ITSC), 2016, Vol. 324, p. 273-278Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) were air-plasma sprayed onto Hastelloy X substrates. The TBCs consisted of a high-Cr MCrAlY (M for Ni and Co) bond coat and a yttria-stabilized zirconia (YSZ) top coat. The TBC samples were thermally cycled between 100 ºC and 1100 ºC with 1 hour dwell time at 1100 ºC. The thermal fatigue failure of the TBCs was investigated via microstructure analyses. The final fatigue failure of the TBCs was caused by the formation of interface-parallel cracks in the YSZ top coat. The formation of the cracks was found to be strongly related to the oxidation behaviour of the MCrAlY bond coat. The development of the oxide layers was therefore studied in detail. A thermokinetic model was also used to deepen the understanding on the elemental diffusion behavior in the materials.

  • 3068. Yuan, Xiaoming
    et al.
    Zhang, Lijun
    Du, Yong
    Xiong, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Tang, Ying
    Wang, Aijun
    Liu, Shuhong
    A new approach to establish both stable and metastable phase equilibria for fcc ordered/disordered phase transition: application to the Al-Ni and Ni-Si systems2012In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 135, no 1, p. 94-105Article in journal (Refereed)
    Abstract [en]

    Both two-sublattice (2SL) and four-sublattice (4SL) models in the framework of the compound energy formalism can be used to describe the fcc ordered/disordered transitions. When transferring the parameters of 2SL disregarding the metastable ordered states into those of 4SL, inconsistence in either stable or metastable phase diagrams could appear, as detected in both Al-Ni and Ni-Si systems. To avoid such a kind of drawback, this behavior was analyzed and investigated in the Ni-Si and Al-Ni systems with the aid of first principle calculations. Furthermore, a new approach considering both the stable and metastable fcc ordered phase equilibria deduced from the first principles calculations was proposed to perform a reliable thermodynamic modeling for the fcc ordered/disordered transition. The Ni-Si system was then thermodynamically assessed using the presently proposed approach. The good agreement between the calculation and experiments demonstrates the reliability of the proposed approach. It is expected that the approach is valid for other systems showing complex ordered/disordered transitions.

  • 3069.
    Yuan, Xuemin
    Luleå tekniska universitet.
    Action of gases in control of pulp chemistry and flotation selectivity for a complex sulphide ore1995Licentiate thesis, comprehensive summary (Other academic)
  • 3070.
    Yuan, Xuemin
    Luleå tekniska universitet.
    Flotation selectivity, process modelling and simulation for a complex sulphide ore1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis covers research with different methods on the same fine-grained complex sulphide ore - Petiknäs - from the Skellefte Field in Northern Sweden. Mineralogical research results demonstrate that the degree of liberation of galena, rather than the chemical factors under the current flotation conditions, is the dominant factor affecting Pb grade and recovery, since galena has the same flotation as chalcopyrite if having the same degree of liberation. A novel approach for liberation pattern recognition is proposed based on multivariate statistical modelling and a four-parameter liberation model developed in this study. This approach opens up the possibility to use automatic pattern recognition and identification, and provides us with a quicker and more illustrative way to visualise mineral liberation characteristics. It is found that the effect of oxidising and reducing gases is only significant if the ore has been ground in a mild steel environment. The combination of mild steel grinding and prolonged aeration produces a slightly better selectivity between the copper minerals and zinc or iron sulphides compared with stainless steel grinding. However, this is at the expence of a slower flotation kinetics. For mild steel grinding, it is found that the copper flotation shows a marked potential dependence with a flotation "edge" at approx. +75mV (SHE). The pulp chemistry data show that mild steel grinding increases the surface oxidation of sulphide minerals, mobilising more sulphur into the pulp liquid. A combination of a galvanic interaction mechanism and a ferric leaching effect is probably responsible for the increased oxidation of sulphides after mild steel grinding. Also, theoretical calculations support that the hydrophobic entity responsible for chalcopyrite flotation with dithiophosphate is probably a surface percipate similar to the stoichiometric copper-collector compound. In batch flotation experiments, the first-order kinetic model with rectangular distribution of floatability is best fitted to the test data after stainless steel grinding only. For mild steel grinding, no traditional kinetic models are applicable. Redox potential has a profound effect on the flotation kinetics of chalcopyrite. In research on industrial kinetics, a similar phenomenon to mild steel grinding in batch tests is observed, i.e., there is no traditional kinetic model suitable to the full-scale kinetic data. Instead, the first-order classical kinetic model modified with a zero- time factor is found to give a simpler form and the best fit to the industrial data.

  • 3071.
    Yuan, Xuemin
    et al.
    Luleå tekniska universitet.
    Pålsson, Bertil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forssberg, Eric
    Flotation of a complex sulphide ore I.: Cu/Zn selectivity control by adjusting pulp potential with different gases1996In: International Journal of Mineral Processing, ISSN 0301-7516, E-ISSN 1879-3525, Vol. 46, no 3-4, p. 155-179Article in journal (Refereed)
    Abstract [en]

    To investigate the possibility of using gases with varying oxygen activity and their influence on copper-zinc selectivity, flotation tests were done in a mechanical laboratory cell on a fine-grained complex sulphide ore with high pyrite and pyrrhotite content. The pulp environment was modified by changing the grinding media and by using different gases in the pre-conditioning a flotation steps. A statistical design with two levels of grinding media, four levels of pre-conditioning, and three levels of flotation gas type, was used. It is found that the grinding environment is the most dominant variable influencing the flotation results. Strong interactions exist between the pre-conditioning type and the flotation gas for mild steel grinding. Such interactions, and even the direct influence of pre-conditioning and flotation gas type, are statistically insignificant for stainless steel grinding, which often gave good copper flotation. The Cu/Zn selectivity shows a strong dependence on the pre-conditioning type and flotation gases for mild steel grinding, but not for stainless steel grinding. The best Cu/Zn selectivity happens for the combination of 5% oxygen pre-conditioning and air flotation after mild steel grinding. It seems that galvanic reactions after or during the mild steel grinding facilitate surface oxidation of sulphides. A mechanism similar to ferric leaching is proposed. As expected, it was observed that the oxidising or reducing environment in the pulp, as measured by the pulp potential, has a strong influence on the flotation results.

  • 3072.
    Yuan, Xuemin
    et al.
    Luleå tekniska universitet.
    Pålsson, Bertil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forssberg, Eric
    Flotation of a complex sulphide ore. II.: Influence of grinding environments on Cu/Fe sulphide selectivity and pulp chemistry1996In: International Journal of Mineral Processing, ISSN 0301-7516, E-ISSN 1879-3525, Vol. 46, no 3-4, p. 181-204Article in journal (Refereed)
    Abstract [en]

    To investigate the possibility of using gases with varying oxygen activity and their influence on copper-zinc selectivity, flotation tests were done in a mechanical laboratory cell on a fine-grained complex sulphide ore with high pyrite and pyrrhotite content. The pulp environment was modified by changing the grinding media and by using different gases in the pre-conditioning a flotation steps. A statistical design with two levels of grinding media, four levels of pre-conditioning, and three levels of flotation gas type, was used. It is found that the grinding environment is the most dominant variable influencing the flotation results. Strong interactions exist between the pre-conditioning type and the flotation gas for mild steel grinding. Such interactions, and even the direct influence of pre-conditioning and flotation gas type, are statistically insignificant for stainless steel grinding, which often gave good copper flotation. The Cu/Zn selectivity shows a strong dependence on the pre-conditioning type and flotation gases for mild steel grinding, but not for stainless steel grinding. The best Cu/Zn selectivity happens for the combination of 5% oxygen pre-conditioning and air flotation after mild steel grinding. It seems that galvanic reactions after or during the mild steel grinding facilitate surface oxidation of sulphides. A mechanism similar to ferric leaching is proposed. As expected, it was observed that the oxidising or reducing environment in the pulp, as measured by the pulp potential, has a strong influence on the flotation results.

  • 3073.
    Yuan, Xuemin
    et al.
    Luleå tekniska universitet.
    Pålsson, Bertil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forssberg, Eric
    Statistical intepretation of flotation kinetics in the flotation of a complex sulphide ore1995In: Konferens i mineralteknik: Luleå, 14-16 februari 1995 / [ed] Marianne Thomaeus; Eric Forssberg, MinFo , 1995, p. 51-61Conference paper (Other academic)
  • 3074.
    Yuan, Xuemin
    et al.
    Luleå tekniska universitet.
    Pålsson, Bertil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forssberg, Eric
    Statistical interpretation of flotation kinetics for a complex sulphide ore1996In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 9, no 4, p. 429-442Article in journal (Refereed)
    Abstract [en]

    Kinetic flotation models were applied to data from tests with reactive gases (hydrogen and sulphur dioxide) on a complex sulphide ore. The models were evaluated by statistical techniques, after non-linear regression on the model parameters. It is found that a first order model with rectangular distribution of floatability fits the test data very well. Statistical tests on copper, silver and lead kinetic data show that reactive gases have a greater influence on silver mineral flotation compared to copper-lead minerals. Sulphur dioxide generally gives higher ultimate silver recoveries than sodium bisulphite, and the magnitudes depend on the interactions between the modifiers and theflotation gases (5% H2 N2 and air). Correlation analysis suggests that silver flotation is probably determined by the floatability of a separate mineral such as tetrahedrite. Multivariate analysis on pulp chemistry data reveals that the pulp pH is the most significant variable among the pulp chemistry data, provided the grinding is iron free. The pH effect is attributed to the addition of sulphur dioxide. After autogenous or non-reducing grinding, the naturally-occurring variations in redox levels are too small to influence the flotation results, despite the tests being made with a complex sulphide ore.

  • 3075.
    Yuhua, Pan
    Luleå tekniska universitet.
    Mathematical modelling of fluid flow and heat transfer in steel ladles1999Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis work, three mathematical models, each of which is suitable for simulating a particular process in the operation of steel ladles, have been developed. Firstly, by using a finite-difference mathematical method (FDM), a one-dimensional numerical model for calculating heat transfer through ladle wall, bottom and top slag layer was established. This FDM model was used to provide transient and structure dependent heat loss fluxes for further modelling of fluid flow and heat transfer in steel ladles. Then, with a computational fluid dynamics (CFD) mathematical approach, a two-dimensional CFD model for simulating fluid flow and heat transfer in steel ladles during the holding period before teeming was developed. With this model the natural convection and thermal stratification phenomena occurring in steel ladles were investigated. Further, the two-dimensional CFD model was finally extended into a three-dimensional CFD model to include simulations on the fluid flow and heat transfer in steel ladles with drainage during teeming, so that the interaction between natural convection and drainage flow was examined. By using this three-dimensional CFD model, it is possible to predict the steel stream temperature during teeming which is important for further prediction and control of steel temperature in tundishes during continuous casting.

  • 3076. Yvell, K.
    et al.
    Grehk, T. M.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Forsberg, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Engberg, G.
    Microstructure development in a high-nickel austenitic stainless steel using EBSD during in situ tensile deformation2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, p. 228-237Article in journal (Refereed)
    Abstract [en]

    Plastic deformation of surface grains has been observed by electron backscatter diffraction technique during in situ tensile testing of a high-nickel austenitic stainless steel. The evolution of low- and high-angle boundaries as well as the orientation changes within individual grains has been studied. The number of low-angle boundaries and their respective misorientation increases with increasing strain and some of them also evolve into high-angle boundaries leading to grain fragmentation. The annealing twin boundaries successively lose their integrity with increasing strain. The changes in individual grains are characterized by an increasing spread of orientations and by grains moving towards more stable orientations with < 111 > or < 001 > parallel to the tensile direction. No deformation twins were observed and deformation was assumed to be caused by dislocation slip only.

  • 3077.
    Zachrisson, Jan
    et al.
    University West, Department of Engineering Science, Research Environment Production Technology West.
    Börjesson, Johan
    ESAB AB, Lindholmsallén 9, Box 8004, SE-40277 Gothenburg.
    Karlsson, Leif
    University West, Department of Engineering Science, Division of Manufacturing Processes.
    A new EBSD based methodology for the quantitative characterisation of microstructures formed by displacive fcc–bcc transformations2013In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, Vol. 45, no February, p. 45-54Article in journal (Refereed)
    Abstract [en]

    This work is concerned with a new methodology that can be used to quantify the degree to which grains in the microstructure are aligned in the form of packets. The methodology is based on a crystallographic definition of the term packet which is used to deduce the theoretically ideal misorientations of intra-packet grain boundaries. A misorientation distribution obtained from extensive EBSD mapping can thus be split into intra- and inter-packet misorientations and the corresponding fractions can be determined by integration. The theoretical framework of the methodology is explained and a step-by-step description of the procedure is given. Results from a trace analysis are provided to justify the assumptions made regarding habit plane and examples are included showing how the grain boundary network can be split into two separate parts, one for lath boundaries and the other for packet boundaries. Moreover, example weld metal microstructures along with the corresponding misorientation distributions as well as quantitative values of the microstructures are presented.

  • 3078.
    Zamani, Mohammadereza
    et al.
    Jönköping University, School of Engineering, JTH, Materials and Manufacturing. Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Iran.
    Amadeh, A.
    School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Iran.
    Lari Baghal, S. M.
    School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Iran.
    Effect of Co content on electrodeposition mechanism and mechanical properties of electrodeposited Ni-Co alloy2016In: Transactions of Nonferrous Metals Society of China, ISSN 1003-6326, E-ISSN 2210-3384, Vol. 26, no 2, p. 484-491Article in journal (Refereed)
    Abstract [en]

    Ni-Co coatings with various cobalt contents were electrodeposited from modified Watts bath. The effect of cobalt content on electrodeposition mechanism of the coatings was studied by electro-chemical impedance spectroscopy method (EIS). Surface morphology and crystallographic structure of the coatings were investigated by means of SEM and XRD. Mechanical properties of the coatings were determined using Vickers microhardness and tensile tests. It was found that with increasing the Co2+ ions in electroplating bath, the charge transfer resistance (Rct) of Ni-Co film increased whereas the Warburg impedence decreased. This may be due to enhancement in coverage of cathode surface by Co(OH)2 and higher diffusion rate of metal ions towards cathode surface, respectively. Also, with increasing the cobalt content in the bath, cobalt content in the alloy coating increased anomalously and (111) texture consolidated gradually. With increasing the cobalt content up to 45% in alloy coating, the grain size decreased and consequently, hardness and strength of the alloy increased. Further enhancement of cobalt content up to 55% led to a little decrease in hardness and strength. The maximum ductility was observed for Ni-25%Co coating due to relatively small grain size and compact structure. © 2016 The Nonferrous Metals Society of China.

  • 3079.
    Zamani, Mohammadreza
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. Jönköping University, School of Engineering, JTH, Mechanical Engineering.
    Al-Si Cast Alloys - Microstructure and Mechanical Properties at Ambient and Elevated Temperature2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Aluminium alloys with Si as the major alloying element form a class of material providing the most significant part of all casting manufactured materials. These alloys have a wide range of applications in the automotive and aerospace industries due to an excellent combination of castability and mechanical properties, as well as good corrosion resistance and wear resistivity. Additions of minor alloying elements such as Cu and Mg improve the mechanical properties and make the alloy responsive to heat treatment. The aim of this work is studying the role of size and morphology of microstructural constituents (e.g SDAS, Si-particles and intermetalics) on mechanical properties of Al-Si based casting alloy at room temperatures up to 500 ºC.

    The cooling rate controls the secondary dendrite arm spacing (SDAS), size and distribution of secondary phases. As SDAS becomes smaller, porosity and second phase constituents are dispersed more finely and evenly. This refinement of the microstructure leads to substantial improvement in tensile properties (e.g. Rm and εF). Addition of about 280 ppm Sr to EN AC- 46000 alloy yields fully modified Si-particles (from coarse plates to fine fibres) regardless of the cooling conditions. Depression in eutectic growth temperature as a result of Sr addition was found to be strongly correlated to the level of modification irrespective of coarseness of microstructure. Modification treatment can improve elongation to failure to a great extent as long as the intermetallic compounds are refined in size.

    Above 300 ºC, tensile strength, Rp0.2 and Rm, of EN AC-46000 alloys are dramatically degraded while the ductility was increased. The fine microstructure (SDAS 10 μm) has superior Rm and ductility compared to the coarse microstructure (SDAS 25 μm) at all test temperature (from room to 500 ºC). Concentration of solutes (e.g. Cu and Mg) in the dendrites increases at 300 ºC and above where Rp0.2 monotonically decreased. The brittleness of the alloy below 300 ºC was related to accumulation of a high volume fraction damaged particles such as Cu- Fe-bearing phases and Si-particles. The initiation rate of damage in the coarse particles was significantly higher, which enhances the probability of failure and decreasing both Rm and εF compared to the fine microstructure. A physically-based model was adapted, improved and validated in order to predict the flow stress behaviour of EN AC- 46000 cast alloys at room temperature up to 400 ºC for various microstructures. The temperature dependant variables of the model were quite well correlated to the underlying physics of the material

  • 3080.
    Zamani, Mohammadreza
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Al-Si Cast Alloys - Microstructure and Mechanical Properties at Ambient and Elevated Temperatures2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Swedish industry is a global leader in development and manufacture of automotive and aviation components where the usage of aluminium products is remarkable. In addition to manufacturing aluminium components, casting enables low-cost and low-emission production of complex geometry components with a range of sizes. Aluminium with Si as the major alloying element forms a class of alloys representing the most significant fraction of all cast products, for a wide range of applications due to an excellent combination of castability and mechanical properties, as well as good corrosion resistance, wear resistance and recyclability. The microstructure in Al-Si alloys strongly governs their mechanical properties. Several industrial practices such as eutectic modification and alloying are well-known to improve mechanical properties. Al-Si cast alloys generally suffer a lack of ductility and poor high temperature properties due to presence of either brittle or thermally unstable phases. The aim of this work is to study the explicit role of each microstructural constituent on the behaviour of Al-Si cast alloys at room and high temperatures. The results will accordingly highlight the potential for improvement in properties of such alloys.

    Casting defects have an immediate and negative effect on the properties of Al-Si alloys and reducing the overall level of defects substantially improves tensile properties. An increased cooling rate refines all microstructural features and reduces volumetric porosity which leads to substantial improvement in tensile properties (e.g. Rm and εF) at any test temperature. Modification of eutectic Si-particles (through Sr-addition) generally has a positive effect on alloy ductility. Depression in eutectic growth temperature as a result of eutectic modification was found to be strongly correlated to the level of modification irrespective of coarseness of the microstructure.

    Addition of transition metals (Ni-Ti-Zr-Cr-V) to Al-Si improves tensile strength, particularly at temperatures above 200 ºC caused by formation of thermally stable intermetallic compounds. Below 200 ºC however, a substantial potential for improvement through solute-reinforcement was obtained.

    A physically-based constitutive model with a wide validity range was successfully developed to describe the flow behaviour of Al-Si alloys at different temperatures, as a reliable input for finite element simulation. 

  • 3081.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    A Novel Approach for the Assessment of Eutectic Si Modification and Tensile Properties of Al-Si Cast Alloys2015Conference paper (Refereed)
    Abstract [en]

    This study presents a correlation between the depression in eutectic growth temperature, as a result of modification, and the tensile properties of Al-Si cast alloys. In order to study the role that Sr exerts on the solidification behavior, modification and mechanical properties, controlled solidification experiments accompanied with thermal analysis using three mold materials for various cooling conditions, and tensile testing were conducted on Al-Si alloys with several Sr levels (~ 35-500 ppm). The gradient solidification technique was applied to produce directional solidified tensile test specimens comprising low level of defects. The depression in growth temperature of eutectic Si was found to be correlated with the Sr additions and the tensile properties (e.g. elongation to failure and tensile strength). 

  • 3082.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Assessment of modification level in En AC-46000 aluminum casting alloy using thermal analysis and microscopic evaluation2015In: Light Metals 2015, 2015, p. 955-960Conference paper (Refereed)
    Abstract [en]

    The quantitative methods for controlling and predicting the level of Si modification in EN AC-46000 aluminum cast alloys were examined using thermocouples (thermal analysis) and optical microscopy (image analysis). A wide range of Sr, from 37 to 486 ppm, was added to the alloy. The alloys were cast using three different molds providing different cooling rate and consequently varied microstructure coarseness. Large difference in nucleation and growth temperature of unmodified and modified alloy was found irrespective of coarseness of microstructure. The depression in growth temperature of eutectic Si found to be strongly correlated to content of modification agent as well as modification level. Thermal analysis technique was realized as a non-biased, accurate and inexpensive approach for on-line prediction of Si modification level in the EN AC-46000 alloy cast under different cooling rate.

  • 3083.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH, Materials and Manufacturing.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Determination of Optimum Sr Level for Eutectic Si Modification in Al–Si Cast Alloys Using Thermal analysis and Tensile Properties2016In: International Journal of metalcasting, ISSN 1939-5981, E-ISSN 2163-3193, Vol. 10, no 4, p. 457-465Article in journal (Refereed)
    Abstract [en]

    This study presents a correlation between the depression in eutectic growth temperature as a result of Sr modification and the tensile properties of Al–Si cast alloys. In order to study the role that Sr exerts on the solidification behavior, modification and mechanical properties, controlled solidification experiments including thermal analysis were performed. Using three mold materials for different cooling rates, tensile testing was conducted on Al–Si alloys with various Sr levels (~35–500 ppm). The gradient solidification technique was used to produce directionally solidified tensile test specimens containing low levels of defects. The depression in eutectic Si growth temperature was correlated with the Sr additions and the tensile properties (elongation to failure and tensile strength).

  • 3084.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Aziziderouei, Mana
    The role of Sr on microstructure formations and mechanical properties of  Al-Si-Cu-Mg casting alloy2013Conference paper (Refereed)
    Abstract [en]

    The aim of the paper is to assess the role of Sr modification on eutectic Si, Fe-rich intermetallics and porosity and their responses to the mechanical properties of a commercial high pressure die cast alloy Al-Si-Cu-Mg with Fe level up to 1%. Tensile test samples with a variety of coarsenesses, containing different Sr levels were cast using the gradient solidification technique, that enables a study of the solely influence of Sr on microstructure and tensile properties. The modification altered the morphology and size of eutectic silicon, as well as the characteristics and distribution of Fe-rich intermetallic and porosity. The tensile test results indicate that eutectic Si modification is not a guarantee for improved mechanical properties due to the presence of a variety of Fe-intermetallics and porosity that tend to have a larger role on initiating and propagating cracks leading to premature failures in these commercial alloys.

  • 3085.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    EW Jarfors, Anders
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Effects of microstructure and defects on tensile and fracture behaviour of a HPDC component: Potential properties and actual outcome of En AC-44300 alloy2014In: Light Metals 2014 / [ed] J. F. Grandfield, John Wiley & Sons, 2014Conference paper (Refereed)
    Abstract [en]

    The aim of present work is to study the influence of microstructure and defects on the mechanical properties of a structural high pressure die cast (HPDC) component of a commercial Al-Si based foundry alloy, EN AC-44300. The alloy which contains mainly 12% Si and 0.7% Fe, is a successful application of a die-casting alloy for the automotive market. Tensile test specimens were extracted from both high pressure die cast components and from ones with comparable microstructures produced through gradient solidification technique, which offers specimens with low levels of defects. The microstructure and defects available in the component were well mapped via X-ray inspection system, optical and scanning electron microscopy.  The results clearly confirmed the components’ performance dependency to configuration of defects and Si morphology as well as revealed the potential of the alloy in terms of ultimate tensile strength and ductility.

  • 3086.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH, Materials and Manufacturing.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Ghassemali, Ehsan
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Effect of cooling rate and eutectic modification on texture and grain structure of Al-Si-Cu-Mg die cast alloy2016In: La Metallurgia Italiana, ISSN 0026-0843, Vol. 108, no 6, p. 5-8Article in journal (Refereed)
    Abstract [en]

    The effect of cooling rate and eutectic modification on texture evolution and grain structure of an Al-Si-Cu-Mg die cast alloy were investigated using optical microscopy (OM) and electron backscatter diffraction (EBSD) techniques. Directional solidification technique was utilized to produce as-cast specimens having low level of casting defects with controlled microstructural scale: specimens with average SDAS of 10 and 25 µm. Mode of solidification, cooling rate and eutectic modification did not induce any significant texture in the microstructure. An increase in cooling rate resulted in reduction grain size. High degree of grains orientation randomness was found in high cooling rate regardless of modification treatment.

  • 3087.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Jarfors, Anders
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    High Temperature Tensile Deformation Behaviour and Failure Process of an Al-Si-Cu-Mg Cast Alloy: The Microstructural Scale Effect2015In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 86, p. 361-370Article in journal (Refereed)
    Abstract [en]

    In this study the high temperature tensile deformation behavior of a commercial Al–Si–Cu–Mg cast alloy was investigated. The alloy was cast with two different cooling rates which resulted in average secondary dendrite arm spacing of 10 and 25 μm, which is typical of the microstructure scale obtained from high pressure die casting and gravity die casting. Tensile tests were performed at different strain rates (10− 4 s− 1 to 10− 1 s− 1) and over a wide temperature range from ambient temperature to 500 °C. The fine microstructure had superior tensile strength and ductility compared to the coarse microstructure at any given temperature. The coarse microstructure showed brittle fracture up to 300 °C; the fracture mode in the fine microstructure was fully ductile above 200 °C. The fraction of damaged particles was increased by raising the temperature and/or by microstructure coarsening. Cracks arising from damaged particles in the coarse microstructure were linked in a transgranular-dominated fashion even at 500 °C. However, in the fine microstructure alloy the inter-dendritic fracture path was more prevalent. When the temperature was raised to 300 °C, the concentration of alloying elements in the dendrites changed. The dissolution rates of Cu- and Mg-bearing phases were higher in the fine microstructure.

  • 3088.
    Zeng, Yigen
    Luleå tekniska universitet.
    Optimisation of vibration sensor location for an industrial ball mill1994In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 8, no 4, p. 475-482Article in journal (Refereed)
    Abstract [en]

    Ball mills play an important role in both energy consumption and metal wear in mineral processing plants. To maintain high operating efficiency, the material transportation inside the tumbling body has to be monitored in time. It is known that the vibration signal pattern varies corresponding to the operating state of the mill. Besides the basic vibration signature from the rotary drum and machine assembly, the tumbling of steel balls and the material are the major vibration sources. Since the steel balls and the material are unevenly distributed along the rotating axis the vibration sources are spread widely. The location of the vibration sensor has to be optimised to obtain representative signals for the process. Nine locations on the trunnion bearings and the bearing for the pinion axis have been investigated to select the best place for situating a vibration sensor. The vibration signal was picked up by an accelerometer in the form of time-domain waveform, which was firstly recorded by a DAT deck and then digitised by an oscilloscope. The digital signal processing and system identification were performed using software specially developed for an IBM compatible personal computer. The power spectra from different locations were studied and one best sensor location was recommended for picking up a representative signal from the ball mill. More sensors on different bearings are required for mapping the whole picture of the milling state.

  • 3089.
    Zeng, Yigen
    Luleå tekniska universitet.
    Vibration signal analysis in comminution1994Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Comminution accounts for a significant part of the energy consumption and metal wear in powder manufacturing industries and as a result, it is a major cost factor. To maintain high efficiency, the operating parameters must be monitored and adjusted promptly to optimal values. In practice, it is either difficult or laborious and time consuming to measure most of the parameters involved, therefore, a quick and economic way to monitor the parameters of interest is essential for system control. Vibration signals from comminution devices (ball mills) were picked up using piezoelectric accelerometers andlor an acoustic microphone. The source signals were amplified and digitised for an IBM compatible PC. The time-domain waveforms were transformed into frequencydomain power spectra. Finally, the vibration signals were reduced, using multivariate data analysis, to a few "latent" variables which could then be related to the physical parameters. Signal analyses were performed with the DSP4ME toolbox (MatLab) on a PC. Since the vibration signal pattern varies correspondingly with the operating state of an equipment, a technique based on the vibration signal analysis have been widely used in fault-detection for heavy machines. Most of the analytical instruments for this purpose are based on hardware, which make them inflexible and hard to adopt for other purposes. Moreover, there is no routine for signal identification and model building. To overcome all these disadvantages, a strategy based on a simple hardware, but a complex computer software was used for the vibration signal analysis both in the laboratory scale and industrial grinding operations. Various operating parameters from the comminution process were predicted by measuring and processing vibration signals. Since the signal measurement can be made on-line, this technique provides accurate and fast information for the control system to adjust the operating parameters to optimal values.

  • 3090.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Application of digital signal processing and multivariate data analysis to vibration signals from ball-mill grinding1993In: Transactions of the Institution of Mining and Metallurgy Section C - Mineral Processing and Extractive Metallurgy, ISSN 0371-9553, E-ISSN 1743-2855, Vol. 102, no Jan-Apr, p. 39-43Article in journal (Refereed)
    Abstract [en]

    During mechanical grinding high-intensity vibration is emitted that contains information on the operating state of the mill. To study the influence of operating parameters on the vibration signature tests were performed with a laboratory ball-mill. Five operating parameters were considered: mill speed, powder filling (as a percentage of voidage), pulp density, grinding period, and pulp temperature. Vibration signals were detected by an accelerometer, amplified by a portable vibrometer and recorded with a digital audio tape recorder. A digital oscilloscope was used to convert the signals into an IBM-compatible data format.

  • 3091. Zeng, Yigen
    et al.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Application of vibration signal measurement for monitoring grinding parameters1994In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 8, no 6, p. 703-713Article in journal (Refereed)
    Abstract [en]

    Vibration signal measurements are discussed for monitoring operating parameters in a laboratory-scale ball mill. The vibration signal was first picked up with an accelerometer, amplified by a vibrometer and then transmitted to a DAT recorder during the entire testing period. The signal on the DAT recorder was resampled and converted into IBM compatible personal computer readable data format using a digital oscilloscope. The vibration signal analyses included rms estimation, power spectral estimation, waterfall plot, principal component analysis and stepwise multiple regression analysis. Clear differences in the rms and the spectra are found for different grinding conditions. Three principal components described about 95% of the total variation in the spectra. Each principal component was related mainly to one to three major frequency bands. Close correlation was found between the vibration signal and grinding parameters. Therefore, an alternative method can be developed for monitoring the operating parameters in a ball mill.

  • 3092.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Application of vibration signals to monitoring crushing parameters1993In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 76, no 3, p. 247-252Article in journal (Refereed)
    Abstract [en]

    Vibration measurements for fine crushing have been performed on a laboratory scale jaw crusher on dolomite. The original vibration signal was sensed by an accelerometer and stored on a DAT recorder during the whole testing period. The vibration signal was resampled and converted into an IBM PC compatible data format with a digital oscilloscope. The time-domain vibration signal was analyzed with the aid of a digital signal processing technique. The crushing process can be inspected by replaying the sample of the time-domain waveform. The variation of the vibration pattern was described by a few `latent' variables obtained by principal component analysis. Relations were established between the crusher setting, the product size and the latent variables by multiple regression. Measurement of the vibration signal provides a new strategy for monitoring crushing processes.

  • 3093.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Effect of powder filling fraction on particle size and energy consumption in coarse grinding1991In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 20, no 5, p. 300-304Article in journal (Refereed)
    Abstract [en]

    Particle size distribution, power draw, and energy consumption have been compared between rod and ball mills under laboratory dry batchwise grinding conditions. A parabolic-sine equation has been used to describe the particle size distributions of ground products and it fit satisfactorily with the particle size data. Based on this equation, the effects of the powder filling fraction and other operating parameters on the product fineness have been analyzed mathematically. The power draw and the energy consumption have also been related to the operating parameters. It was found that the maximum power draw occurs when the powder filling fraction is about 0.6 and 0.5 for the rod and ball mills respectively. The specific energy consumption of the rod mill is smaller than that of the ball mill under coarse grinding conditions.

  • 3094.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Effects of mill feed size and rod charges on grinding performance1992In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 69, no 2, p. 119-123Article in journal (Refereed)
    Abstract [en]

    The effects of mill feed sizes and the rod charges on ground product fineness, energy utilization and energy consumption have been investigated on a rod mill under dry batchwise grinding conditions. The effect of reducing mill feed size on product fineness decreases with grinding time, while the effects of different composition of rod charges are very small. Smaller rod diameter, coarser mill feed size and shorter grinding time will increase the energy utilization. The energy consumption in batch grinding is described by the Bond method. Using smaller rod diameter and reducing the mill feed size will optimize energy use in coarse grinding.

  • 3095.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Effects of mill feed size on product fineness and energy consumption in coarse grinding1991In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 4, no 5-6, p. 599-609Article in journal (Refereed)
    Abstract [en]

    The effects of some grinding parameters on the product fineness and the energy consumption under dry batchwise coarse grinding conditions are studied on rod and ball mills. A parabolic-sine equation is suitable to describe the particle size distribution. The constants in the equation are related to the grinding parameters, which permits a mathematical analysis. A relation between energy consumption and grinding parameters is also established, and the grinding effects in the rod and ball mills are compared.

  • 3096.
    Zeng, Yigen
    et al.
    Luleå tekniska universitet.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Effects of operating parameters on vibration signal under laboratory scale ball grinding conditions1992In: International Journal of Mineral Processing, ISSN 0301-7516, E-ISSN 1879-3525, Vol. 35, no 3, p. 273-290Article in journal (Refereed)
    Abstract [en]

    Experiments were performed under batchwise wet grinding conditions with dolomite. The vibration signal was received by an accelerometer and transmitted to a vibrometer. The vibration signal was first stored on a Digital-Audio-Tape recorder in voltage format during the grinding tests. The original signal was then resampled and converted into data format for an IBM or compatible personal computer by a digital oscilloscope. The Root-Mean-Square and the power spectrum were estimated on the time-domain vibration signal. A partial correlation analysis was applied to the frequency-domain spectrums to detect the non-zero correlation between the frequency bands and the operating parameters in grinding. A stepwise regression analysis was used to locate the key frequency bands for describing the changes of a particular operating parameter. After vibration analysis, the operating parameters in grinding, e.g., the mill speed, the powder filling, the pulp density, the pulp temperature and the batchwise grinding time were found to be strongly correlated with a few frequency bands. It is therefore possible to develop an efficient method for monitoring the operating parameters in grinding based on the vibration signal.

  • 3097.
    Zeng, Yigen
    et al.
    Luleå tekniska universitet.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Energy benefits by reducing mill feed size using fine crushing1991In: Konferens i mineralteknik: Luleå, 5-7 februari 1991 / [ed] Börje Sköld; Eric Forssberg, MinFo , 1991, p. 111-125Conference paper (Other academic)
  • 3098.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Energy consumption in fine crushing and dry rod grinding1992In: Minerals & metallurgical processing, ISSN 0747-9182, Vol. 9, no 2, p. 69-72Article in journal (Refereed)
    Abstract [en]

    Fine crushing and rod grinding have been investigated using a laboratory-scale jaw crusher and a rod mill. The net energy consumption in both crushing and grinding was evaluated from torque measurements. An empirical relationship was established between energy consumption, particle size and operating parameters. When the mill feed size is reduced, through fine crushing, to about 80% passing 3 mm, the energy consumption will be minimized in a comminution chain of fine crushing and coarse rod grinding. The results in fine crushing were compared with a large-scale test.

  • 3099.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Monitoring grinding parameters by signal measurements for an industrial ball mill1993In: International Journal of Mineral Processing, ISSN 0301-7516, E-ISSN 1879-3525, Vol. 40, no 1-2, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Mechanical grinding emits a high-intensity vibration signal that contains information on the mill operating state. Vibration signals from the mill are presented in the form of both mechanical vibration and acoustic pressure. To apply these source signals to monitoring of grinding parameters, industrial scale grinding tests were performed with an iron ore at LKAB, Malmberget. Three operating parameters were considered: the feed rate, the mill feed size and the pulp density of mill discharge. The measured response parameters were the ground product size, the power draw and the pulp temperature. The source signals of the time-domain waveforms were simultaneously sensed by accelerometer and microphone so as to obtain a "stereograph" of grinding. The signals were first stored on a DAT recorder and then converted into digital format by an oscilloscope. The digitised waveforms were transformed into frequency-domain spectra by power spectral estimation. The variations on the power spectra can be described by a few "latent" variables derived by principal component analysis. Finally, close relations were established between key grinding parameters and "latent" variables by multiple regression. Using signal measurements, an automatic and efficient strategy can be developed to monitor operating parameters for the control system in a ball grinding circuit.

  • 3100.
    Zeng, Yigen
    et al.
    Luleå University of Technology.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Monitoring grinding parameters by vibration signal measurement: a primary application1994In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 7, no 4, p. 495-501Article in journal (Other academic)
    Abstract [en]

    Grinding plays an important role on energy consumption and subsequent separation stage in a mineral processing plant. To maintain higher grinding efficieny, the operating parameters must be continuously monitored and adjusted close to the setup of the optimal operating conditions. It is difficult and expensive to trace the frequent variations of the grinding parameters by traditional methods in commercial scale operation. Since mechanical grinding emits strong vibration signals, it can be picked up commercially available instrument in the form of time-domain waveform. The variations of the vibration signals were governed by the changes of the grinding state. A primary application was studied based on the industrial scale measurements, where the mechanical vibration was picked up by an accelerometer and acoustic pressure changes by a microphone. The digitised time-domain source signals were processed by digital signal processing technique. The variable grinding parameters were the power draw, the feed rate, the pulp density, and the particle sizes of the mill feed and the ground product. By principle component analysis and parameter identification, the variations of the grinding parameters were related to the changes of the source vibration signals. By vibration measurement, a new alternative could be developed for monitoring the operating parameters in grinding.

59606162636465 3051 - 3100 of 3228
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf