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  • 1.
    Abdul Abas, Riad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Hayashi, M.iyuki
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Thermal Diffusivity measurement of CMSX-4 alloy by Laser flash method2007In: International journal of thermophysics, ISSN 0195-928X, E-ISSN 1572-9567, Vol. 28, no 1, p. 109-122Article in journal (Refereed)
    Abstract [en]

    In the present work, thermal diffusivity measurements have been carried out on industrial samples of CMSX-4 nickel-base superalloy using the laser-flash method with emphasis on studying the effect of temperature and microstructure on the thermal diffusivity. The measurements were performed in the temperature range from 298 to 1623 K covering both solid as well as liquid ranges. Below 1253 K, the thermal-diffusivity values were found to increase with increasing temperature. Microstructural investigations of quenched samples revealed that below 1253 K, an ordered phase, usually referred to as the -phase was present together with the disordered fcc phase, often referred to as the γ phase. Between 1253 K and the solidus temperature, the phase was found to dissolve in the matrix alloy causing an increase in the disordering of the alloy, and thereby a small decrease in the thermal-diffusivity values. The thermal-diffusivity values of samples pre-annealed at 1573 K exhibited constancy in the temperature range from 1277 to 1513 K, which is attributed to the attainment of thermodynamic equilibrium. These equilibrium values were found to be lower than the results for samples not subjected to annealing. The thermal-diffusivity values of the alloy in the liquid state were found to be independent of temperature.

  • 2.
    Abdul Abas, Riad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Hayashi, Miyuki
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Thermal Diffusivity Measurements of some Industrially Important Alloys by a Laser Flash Method2007In: International journal of materials reseach, ISSN 1862-5282, Vol. 98, no 6, p. 535-540Article in journal (Refereed)
    Abstract [en]

    In the present work, thermal diffusivity measurements of three industrially significant alloys, viz. 90Ti.6Al.4V, stainless steel with 25Cr and 6Ni as well as plain carbon steel with 0.7 % carbon have been carried out as a function of temperature. The aim of this work is to study the effect of temperature and microstructure on the thermal diffusivities of these alloys. For the 90Ti.6Al.4V alloy, thermal diffusivity increases with temperature below 1225 K. Above this temperature, the values started decreasing probably due to the dissolution of Ti3Al intermediate phase in the matrix, which would result in an increase in the disorder of the structure. For 25Cr: 6Ni stainless steel, the thermal diffusivity is nearly constant up to about 700 K. Above this, there is an increase in the thermal diffusivities with temperature during the heating cycle, which was reproducible during thermal cycling. On the other hand, the slope of the curve increases above 950 K.

    In the case of the 0.7 % carbon steel, the thermal diffusivity shows a decreasing trend with temperature below the Curie point for the alloy, where the alloy consists of bcc + fcc phases. Above this point, only the fcc phase is prevalent and the thermal diffusivity was found to increase with temperature. Heat transfer is carried out by lattice vibration (phonons) as well as electrons. The contribution of electrons varies depending upon the type of alloy. In this study, the highest electron contribution was found in 0.7 % carbon steel, while the lowest was in stainless steel. The thermal conductivity values of these alloys are in good agreement with the calculated values using the model proposed by Mills.

  • 3.
    Abdul Abas, Riad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jakobsson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hayashi, Miyuki
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Studies on Graphitisation of Blast Furnace Coke by X-ray Diffraction Analysis and Thermal Diffusivity Measurements2005In: Steel research, ISSN 0177-4832, Vol. 77, no 11, p. 763-769Article in journal (Refereed)
    Abstract [en]

    High temperature XRD and thermal diffusivity experiments were employed to investigate the degree of graphitisation in blast furnace coke. The experiments were conducted between room temperature and 1473 K. X-ray diffraction studies were carried out in order to monitor the degree of graphitisation in the coke samples from the same campaign. In these cases, the degree of graphitisation was followed by the changes in the vertical dimension. The degree of graphitisation was found to be dependent on temperature. On the other hand, the graphitisation at each temperature was instantaneous, even at as low a temperature as 973 K and no dependency on time could be noticed. The thermal diffusivities of the coke samples taken from deeper level of the experimental blast furnace were measured using the laser-flash technique. The results from these measurements showed that thermal diffusivities increased with the degree of graphitisation, which in turn, can be affected by the level in the blast furnace at which the coke sample was taken. The present results indicate that the degree of graphitisation as followed by X-ray diffraction analysis as well as thermal diffusivities can be used to trace the thermal history of coke. DSC measurements show that the heat capacity of the coke increases with temperature towards the heat capacity of graphite, which could be due to the increasing the graphitisation degree of the coke.

  • 4.
    Aune, Ragnhild E.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sridhar, S.
    Hayashi, Miyuki
    Viscosities and Gibbs energies: On a common structural base2004In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 22, no 5/6, p. 369-378Article in journal (Refereed)
    Abstract [en]

    The present paper reviews the extensive work carried out with respect to the modeling of viscosities of high temperature melts carried out in the Division of Metallurgy, Royal Institute of Technology (KTH), Stockholm, Sweden. This work was inspired to a great extent by a past collaboration with Professor Ken Mills at Imperial College, London, UK. A thermodynamic approach based on Richardson's theory of ideal mixing of silicates, was used to predict the viscosities of binary silicates. The second derivative of In eta with respect to composition was used to predict the setting of ordering in a homogeneous silicate melt during cooling as it approaches the liquidus temperature. The paper clearly demonstrates the powerfulness of the thermodynamic approach to physical properties of high temperature melts.

  • 5.
    Hayashi, Miyuki
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Abdul Abas, Raid
    KTH, Superseded Departments, Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, Superseded Departments, Materials Science and Engineering.
    Effect of crystallinity on thermal diffusivities of mould fluxes for the continuous casting of steels2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 4, p. 691-697Article in journal (Refereed)
    Abstract [en]

    The thermal diffusivities of mould flux having the glassy and crystalline states were measured as a function of temperature by the laser flash method to obtain the relationship between the thermal diffusivity and the degree of crystallization. The thermal diffusivities of the liquid mould flux were also measured to compare the data with those of the solid samples. The thermal diffusivity increases roughly linearly with an increase in the degree of crystallization. The thermal diffusivities of glassy and liquid samples having the ratios of NBO/T 1.48, 1.65 and 2.11 exhibit roughly the same values of 4.6 x 10(-7) m(2)s(-1) and 4.0 x 10(-7) m(2)s(-1), respectively. It is considered that because the silicate network is largely broken down, there is not a significant change of the structure for these samples.

  • 6.
    Hayashi, Miyuki
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Abdul Abas, Riad
    KTH, Superseded Departments, Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, Superseded Departments, Materials Science and Engineering.
    Effect of Crystallinity on the Thermal Diffusivity of Mould Fluxes for the Continuous Casting of Steels2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 4, p. 691-697Article in journal (Refereed)
    Abstract [en]

    The thermal diffusivities of mould flux having the glassy and crystalline states were measured as a function of temperature by the laser flash method to obtain the relationship between the thermal diffusivity and the degree of crystallization. The thermal diffusivities of the liquid mould flux were also measured to compare the data with those of the solid samples. The thermal diffusivity increases roughly linearly with an increase in the degree of crystallization. The thermal diffusivities of glassy and liquid samples having the ratios of NBO/T=1.48, 1.65 and 2.11 exhibit roughly the same values of 4.6*10-7 m2 s-1 and 4.0*10-7 m2 s-1, respectively. It is considered that because the silicate network is largely broken down, there is not a significant change of the structure for these samples.

  • 7.
    Hayashi, Miyuki
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sano, Nobuo
    Fredriksson, Patrik
    KTH, Superseded Departments, Materials Science and Engineering.
    Evaluation of thermodynamic activity of a metallic oxide in a ternary slag from the sulphide capacity of the slag2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 11, p. 1783-1786Article in journal (Refereed)
    Abstract [en]

    The correlation between the activity of a metallic oxide in a ternary slag system and the sulphide capacity of the slag was investigated. The solubility of sulphur in the binary systems CaO-SiO2 and Al2O3-CaO along with its sulphide capacity of the Al2O3-CaO-SiO2 system respectively have been used to estimate the activities of CaO at the compositions of some Al2O3-CaO-SiO2 intermediate compounds. Estimation has been carried out assuming that the Gibbs free energy of fusion for the ternary composition is additive of those for pure substances. The estimated values of the activities are in good agreement with the measured values. This correlation is not only used to evaluate the activity but also, by comparing the estimated activities with the measured ones, it is possible to elucidate the applicability of Henry's law to the activity of a metallic sulphide and to determine the order in the affinity of a cation to sulphur between two metallic oxides in a slag.

  • 8. Nagata, K.
    et al.
    Fukuyama, H.
    Taguchi, K.
    Ishii, H.
    Hayashi, Miyuki
    KTH, Superseded Departments, Materials Science and Engineering.
    Thermal Conductivity of Molten Al, Si and Ni Measured under Microgravity2004In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 22, no 5-6, p. 267-273Article in journal (Refereed)
    Abstract [en]

    The thermal conductivities of molten Si, Ni, Al and their alloys have been measured by means of the nonstationary hot wire method under 1 G and microgravity of 10-5 G. A Mo wire was used as the heating wire and coated with alumina by the electrophoretic deposition to prevent an electric current leakage through the melts. Natural convection in the melts was suppressed by measuring the thermal conductivity under the microgravity of 10-5 G using the drop shaft facility of the Japan Microgravity Center. Moreover, the free surface of the melts was covered with a ceramics plate to prevent Marangoni flow. The thermal conductivity of molten Si is about 10 Wm-1K-1, and that of molten Al is 47 Wm -1K-1 at 1260 K. The thermal conductivity of molten Al-30 mass% Si alloy is about 30 Wm-1K-1, and that of molten Ni is 5 Wm-1K-1 at 1773 K. The thermal conductivities of some molten metals are discussed on the deviation from the Wiedemann-Franz law.

1 - 8 of 8
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