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Microstructural, Mechanical and Tribological Characterisation of CVD and PVD Coatings for Metal Cutting Applications
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis focuses on characterisation of microstructure and the resulting mechanical and tribological properties of CVD and PVD coatings used in metal cutting applications. These thin and hard coatings are designed to improve the tribological performance of cutting tools which in metal cutting operations may result in improved cutting performance, lower energy consumption, lower production costs and lower impact on the environment.  In order to increase the understanding of the tribological behaviour of the coating systems a number of friction and wear tests have been performed and evaluated by post-test microscopy and surface analysis. Much of the work has focused on coating cohesive and adhesive strength, surface fatigue resistance, abrasive wear resistance and friction and wear behaviour under sliding contact and metal cutting conditions.

The results show that the CVD deposition of accurate crystallographic phases, e.g. α-Al2O3 rather than κ-Al2O3, textures and multilayer structures can increase the wear resistance of Al2O3. However, the characteristics of the interfaces, e.g. topography as well as interfacial porosity, have a strong impact on coating adhesion and consequently on the resulting properties.  Through the deposition of well designed bonding and template layer structures the above problems may be eliminated.

Also, the presence of macro-particles in PVD coatings may have a significant impact on the interfacial adhesive strength, increasing the tendency to coating spalling and lowering the surface fatigue resistance, as well as increasing the friction in sliding contacts.

Finally, the CVD-Al2O3 coating topography influences the contact conditions in sliding as well as in metal cutting.

In summary, the work illuminates the importance of understanding the relationships between deposition process parameters, composition and microstructure, resulting properties and tribological performance of CVD and PVD coatings and how this knowledge can be used to develop the coating materials of tomorrow.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2012. , p. 83
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 934
Keyword [en]
Tribology, Friction, Wear, Coatings, CVD, PVD, Alumina, Metal cutting
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
URN: urn:nbn:se:uu:diva-172364ISBN: 978-91-554-8371-5 (print)OAI: oai:DiVA.org:uu-172364DiVA: diva2:516909
Public defence
2012-06-08, Claes Ohlsson-salen, Skomakargatan 1, Borlänge, 10:00 (Swedish)
Supervisors
Available from: 2012-05-15 Created: 2012-04-05 Last updated: 2012-08-01Bibliographically approved
List of papers
1. Nucleation and growth of CVD α-Al2O3 on TixOy template
Open this publication in new window or tab >>Nucleation and growth of CVD α-Al2O3 on TixOy template
(English)Article in journal (Other academic) Submitted
Abstract [en]

The microstructure, phase and chemical composition of TixOy templates used to  nucleate α-Al2O3 on Ti(C,N) coated cemented carbide have been elucidated using scanning electron microscopy, X-ray diffraction, Auger electron spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry. Further, the adhesive strength of the α-Al2O3-TixOy-Ti(C,N) interfaces was investigated using scratch adhesion testing.

 

The present study confirmed that the as-deposited template consisted of a Ti4O7 phase which during subsequent deposition of the Al2O3 layer transformed to a Ti3O5 phase and that the grown Al2O3 layer consisted of 100% α-Al2O3. Furthermore, the results showed that the lowest interfacial strength within the multilayer structure was exhibited by the Ti(C,N)-TixOy interface and that the transformation of Ti4O7 to Ti3O5 in the template resulted in formation of pores in the Ti(C,N)-template interface lowering the interfacial strength even more. The use of surface analysis techniques such as Auger electron spectroscopy and especially Time-of-Flight Secondary Ion Mass Spectrometry enabled trace element analyses using depth profiling to characterise the thin interfacial layers in detail.

Keyword
CVD, α-Al2O3, nucleation, template, adhesion
National Category
Materials Engineering
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-172446 (URN)
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2012-08-01
2. CVD of bonding and template layers for the nucleation of well adhering CVD a-Al2O3
Open this publication in new window or tab >>CVD of bonding and template layers for the nucleation of well adhering CVD a-Al2O3
(English)Article in journal (Other academic) Submitted
Abstract [en]

The microstructure, phase and chemical composition of a bonding-template layered structure used in order to nucleate α-Al2O3 on TiN/Ti(C,N) coated cemented carbide have been investigated using scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. Further, the adhesive strength of the coating multilayer interfaces was investigated using scratch adhesion testing.

 

The results show that the bonding-template layered structure, deposited on an inner TiN/Ti(C,N)/TiN structure, consists of a Ti(C,N,O) phase (bonding layer) and a Ti4O7 phase (template). The Al2O3 layer nucleated on the Ti4O7 template consists of 100% α-Al2O3. During the deposition of Al2O3 the Ti4O7 template transforms to a Ti(C,N,O) phase. Scratch adhesion testing shows that the interfacial strength within the bonding-template-α-Al2O3 multilayer structure is high and exceeds the interfacial strength displayed by the cemented carbide-TiN layer interface. AES depth profiling of the multilayer coating structure illustrates that diffusion of C, N, and O takes place during the deposition of the Ti(C,N,O) , Ti4O7 and Al2O3 layer.

Keyword
CVD, α-Al2O3, nucleation, template, bonding layer, adhesion
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-172453 (URN)
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2012-08-01
3. Abrasive wear of texture-controlled CVD α-Al2O3 coatings
Open this publication in new window or tab >>Abrasive wear of texture-controlled CVD α-Al2O3 coatings
2007 (English)In: Surface and Coatings TechnologyArticle in journal (Refereed) Published
Abstract [en]

In the present study the wear resistance of some CVD α-Al2O3 coatings with different growth textures, i.e. ‹0001›, ‹1012› and ‹1014› and a κ-Al2O3 coating have been investigated using a micro-abrasion test with diamond particles as the abrasive medium. The results show that the softer κ- Al2O3 coating shows a higher wear rate as compared with the textured a-Al2O3 coatings. Of the latter coatings, the  ‹1014› textured a-Al2O3 coating shows the lowest wear rate while the  ‹0001› and ‹1012› textured a-Al2O3 coatings show similar wear behaviour. Two different dominant wear mechanisms, i.e. micro cutting and micro chipping, were observed and the latter mechanism is believed to control the wear rate of the Al2O3 coatings investigated. The results obtained are discussed in relation to the dominant wear mechanisms of the coatings identified using scanning electron microscopy.

Keyword
Abrasive wear; CVD coating; A1203; Metal cutting; Coatings texture
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-172455 (URN)
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2012-08-01
4. Abrasive wear of multilayer κ-Al2O3 –Ti(C,N) CVD coatings on cemented carbide
Open this publication in new window or tab >>Abrasive wear of multilayer κ-Al2O3 –Ti(C,N) CVD coatings on cemented carbide
2007 (English)In: WearArticle in journal (Refereed) Published
Abstract [en]

In the present study the wear resistance of Κ-Al2O3-Ti(C,N) multilayer CVD coatings with different multilayer structures (8, 15, 32 layers of Κ-Al2O3 separated by thin Ti(C,N) layers) have been investigated using a micro-abrasion and a cutting test.

The results show that the wear rate of the Κ-Al2O3 multilayer coatings tend to decrease with decreasing layer thickness in the micro-abrasion test and decrease with increasing layer thickness in the cutting tests. The reason for this is mainly due to the difference in wear behaviour depending on temperature. The results obtained are presented in connection to the dominant wear mechanisms of the coatings which have been identified using scanning electron microscopy and energy dispersive X-ray spectroscopy. The potential of the micro-abrasion test in the characterisation of thin CVD coatings for cutting tool applications is discussed.

Keyword
Abrasive wear; CVD coating; Al2O3; Multilayer; Metal cutting
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-172458 (URN)
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2012-08-01
5. The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings
Open this publication in new window or tab >>The influence of surface defects on the mechanical and tribological properties of VN-based arc-evaporated coatings
2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 297, no 1-2, p. 1111-1119Article in journal (Refereed) Published
Abstract [en]

The influence of surface defects, i.e. droplets and craters, on the mechanical and tribological properties of arc-evaporated VxN coatings deposited on cemented carbide has been investigated in a scratching contact using a diamond stylus and a sliding contact using a stainless steel pin. Post-test characterisation using 3D optical surface profilometry and scanning electron microscopy was performed in order to investigate the mechanical and tribological response of the coatings. The results show that scratch induced coating cracking mainly is restricted to larger droplets showing a low interfacial bonding to the adjacent coating matrix. The influence of coating defects on the cohesive strength, i.e. the tendency to chipping of small coating fragments, was found to be relatively small. In contrast, the presence of defects may have a significant impact on the interfacial adhesive strength, increasing the tendency to spalling. In sliding contact, surface defects such as droplets and craters have a strong impact on the tribological behaviour of the coatings causing abrasive wear of the less hard counter material surface and material transfer to the coating, both mechanisms affecting the friction characteristics of sliding contact tribo system.

Keyword
Arc-evaporation, vanadium nitride, defects, cohesive and adhesive strength, friction
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-172461 (URN)10.1016/j.wear.2012.11.012 (DOI)
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2017-12-07Bibliographically approved
6. Mechanical and tribological properties of PVD-coated cemented carbide as evaluated by a new multi-pass scratch testing method
Open this publication in new window or tab >>Mechanical and tribological properties of PVD-coated cemented carbide as evaluated by a new multi-pass scratch testing method
2012 (English)In: Advances in Tribology, ISSN 1687-5915, E-ISSN 1687-5923, Vol. 2012, p. 305209-Article in journal (Refereed) Published
Abstract [en]

A new test method based on multi-pass scratch testing has been developed for evaluating the mechanical and tribological properties of thin, hard coatings. The proposed test method uses a pin-on-disc tribometer and during testing a Rockwell C diamond stylus is used as the “pin” and loaded against the rotating coated sample. The influence of normal load on the number of cycles to coating damage is investigated and the resulting coating damage mechanisms are evaluated by post-test scanning electron microscopy. The present study presents the test method by evaluating the performance of Ti0.86Si0.14N, Ti0.34Al0.66N and (Al0.7Cr0.3)2O3 coatings deposited by cathodic arc evaporation on cemented carbide inserts.

 

The results show that the test method is quick, simple and reproducible and can preferably be used to obtain relevant data concerning the fatigue, wear, chipping and spalling characteristics of different coating-substrate composites. Also, the small size of the test region (the radius of the circular scratch track can be as small as 0.5 mm) makes it possible to perform tests within small restricted areas. Consequently, the test method can be used as a virtually non-destructive test and e.g. be used to evaluate the fatigue and wear resistance as well as the cohesive and adhesive interfacial strength of coated cemented carbide inserts prior to cutting tests.

Keyword
Multi-pass scratch testing, PVD coatings, cemented carbide, spalling, surface fatigue, wear
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-172462 (URN)10.1155/2012/305209 (DOI)
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2017-12-07Bibliographically approved
7. Influence of the tool surface micro topography on the tribological characteristics in metal cutting – part I Experimental observations of contact conditions
Open this publication in new window or tab >>Influence of the tool surface micro topography on the tribological characteristics in metal cutting – part I Experimental observations of contact conditions
(English)Article in journal (Other academic) Submitted
Abstract [en]

The influence of surface micro topography of CVD α-Al2O3 coatings, deposited on cemented carbide inserts, on tribological characteristics in sliding contact and in metal cutting has been investigated using quenched and tempered steel as counter/work material. Pin-on-disc and turning tests were carried out and post-test characterization using 3D optical surface profilometry and scanning electron microscopy was performed in order to investigate the tribological response of the coatings. The results show that surface micro topography can have a significant impact on the tribological performance of Al2O3 coatings under initial and cutting contact conditions. For both kinds of tests the tendency for transfer of workpiece material strongly increases with increasing coating micro topography. In the pin-on-disc tests a smooth coating surface significantly reduces the friction coefficient.  In the turning tests the contact conditions at the flank face increases with decreasing micro topography. In contrast, no general conclusions can be drawn regarding the influence of coating micro topography on the contact conditions at the rake face. The resulting topography of the turned surface was found to increase with increasing coating topography.

Keyword
CVD, α-Al2O3, topography, friction, sliding contact, metal cutting.
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-173170 (URN)
Available from: 2012-04-19 Created: 2012-04-19 Last updated: 2012-08-01
8. Influence of the tool surface micro topography on the tribological characteristics in metal cutting – Part II Theoretical calculations of contact conditions
Open this publication in new window or tab >>Influence of the tool surface micro topography on the tribological characteristics in metal cutting – Part II Theoretical calculations of contact conditions
(English)In: WearArticle in journal (Other academic) Submitted
Abstract [en]

The tribological conditions at the contact between the cutting tool and the chip are of great importance when analyzing the machining process. By knowing the contact conditions on the rake face of the cutting tool the wear on the clearance and rake face may be predicted in terms of size and type of wear. A certain value of the surface stresses is often thought of as leading to a higher wear rate of the cutting tool and thus a shorter tool life. In this article two different methods for experimentally measuring the contact condition on the clearance and rake face of the cutting tool are presented and illustrated with results obtained while turning AISI 4140. Results are also obtained in terms of how the surface roughness value of the cutting tool influences the contact condition. It was found that the tool surface topography may have a significant impact on the tribological performance during machining.

Keyword
Turning, tribological conditions, contact condition, AISI 4140.
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-172465 (URN)
Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2012-08-01

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