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The effect of nitrogen vacancies on initial wear in arc deposited (Ti-0.52,Ti- Al-0.48)N-y, (y < 1) coatings during machining
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Univ Lorraine, France.
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.ORCID iD: 0000-0003-4577-0976
Univ Lorraine, France.
Univ Lorraine, France.
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2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 358, p. 452-460Article in journal (Refereed) Published
Abstract [en]

Nitrogen deficient c-(Ti0.52Al0.48)Ny, y = 0.92, y = 0.87, and y = 0.75 coatings were prepared in different N-2/Ar discharges on WC-Co inserts by reactive cathodic arc deposition. The microstructure of the y = 0.92 coating show that spinodal decomposition has occurred resulting in the formation of coherent c-TiN- and c-AIN rich domains during cutting. The y = 0.87 and y = 0.75 coatings have exhibited a delay in decomposition due to the presence of nitrogen vacancies that lowers the free energy of the system. In the decomposed structure, grain boundaries and misfit dislocations enhance the diffusion of elements from the workpiece and the substrate (e.g. Fe, Cr, and Co) into the coatings and it becomes more susceptible to crater wear. The y = 0.87 sample displays the highest crater wear resistance because of its dense grain boundaries that prevent chemical wear. The y = 0.92 sample has the best flank wear resistance because the decomposition results in age hardening. The y = 0.75 sample contains the MAX-phase Ti(2)AIN after cutting. The chemical alteration within the y = 0.75 sample and its high amount of macroparticles cause its low wear resistance. The different microstructure evolution caused by different amount of N-vacancies result in distinctive interactions between chip and coating, which also causes difference in the initial wear mechanism of the (Ti,Al)/N-y coatings.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA , 2019. Vol. 358, p. 452-460
Keywords [en]
Wear mechanism; Nitrogen vacancies; (Ti, Al)N; Spinodal decomposition; MAX-phase; Cathodic arc
National Category
Manufacturing, Surface and Joining Technology
Identifiers
URN: urn:nbn:se:liu:diva-154689DOI: 10.1016/j.surfcoat.2018.11.062ISI: 000456762300054OAI: oai:DiVA.org:liu-154689DiVA, id: diva2:1292647
Note

Funding Agencies|European Unions Erasmus Mundus doctoral program in Materials Science and Engineering (DocMASE); Swedish Research Council [2017-03813, 2017-06701]; Swedish government strategic research area grant AFM, LiU [2009-00971]; VINNOVA (FunMat-II project) [2016-05156]

Available from: 2019-02-28 Created: 2019-02-28 Last updated: 2019-05-27
In thesis
1. Phase stability and defect structures in (Ti,Al)N hard coatings
Open this publication in new window or tab >>Phase stability and defect structures in (Ti,Al)N hard coatings
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This study highlights the role of nitrogen vacancies and defect structures in engineering hard coatings with enhanced phase stability and mechanical properties for high temperature applications. Titanium aluminum nitride (Ti,Al)N based materials in the form of thin coatings has remained as an outstanding choice for protection of metal cutting tools due to its superior oxidation resistance and high-temperature wear resistance. High-temperature spinodal decomposition of metastable (Ti,Al)N into coherent c-TiN and c-AlN nm-sized domains results in high hardness at elevated temperatures. Even higher thermal input leads to transformation of c-AlN to w-AlN, which is detrimental to the mechanical properties of the coating. One mean to delay this transformation is to introduce nitrogen vacancies.

In this thesis, I show that by combining a reduction of the overall N-content of the c-(Ti,Al)Ny (y < 1) coating with a low substrate bias voltage during cathodic arc deposition an even more pronounced delay of the c-AlN to w-AlN phase transformation is achieved. Under such condition, age hardening is retained until 1100 ˚C, which is the highest temperature reported for (Ti,Al)N films. During cutting operations, the wear mechanism of the cathodicarc-deposited c-(Ti0.52Al0.48)Ny with N-contents of y = 0.92, 0.87, and 0.75 films are influenced by the interplay of nitrogen vacancies, microstructure, and chemical reactions with the workpiece material. The y = 0.75 coating contains the highest number of macroparticles and has an inhomogeneous microstructure after machining, which lower its flank and crater wear resistance. Age hardening of the y = 0.92 sample causes its superior flank wear resistance while the dense structure of the y = 0.87 sample prevents chemical wear that results in excellent crater wear resistance.

Heteroepitaxial c-(Ti1-x,Alx)Ny (y = 0.92, 0.79, and0.67) films were grown on MgO(001) and (111) substrates using magnetron putter deposition to examine the details of their defect structures during spinodal decomposition. At 900 ˚C, the films decompose to form coherent c-AlN- and c-TiN- rich domains with elongated shape along the elastically soft <001> direction. Deformation maps show that most strains occur near the interface of the segregated domains and inside the c-TiN domains. Dislocations favorably aggregate in c-TiN rather than c-AlN because the later has stronger directionality of covalent chemical bonds. At elevated temperature, the domain size of (001) and (111)- oriented c-(Ti,Al)Ny films increases with the nitrogen content. This indicates that there is a delay in coarsening due to the presence of more N vacancies in the film.

The structural and functional properties (Ti1-x,Alx)Ny are also influenced by its Al content (x). TiN and (Ti1-x,Alx)Ny (y = 1, x = 0.63 and x = 0.77) thin films were grown on MgO(111) substrates using magnetron sputtering technique. Both TiN and Ti0.27Al0.63N films are single crystals with cubic structure. (Ti0.23,Al0.77)N film has epitaxial cubic structure only in the first few atomic layers then it transitions to an epitaxial wurtzite layer, with an orientation relationship of c-(Ti0.23,Al0.77)N(111)[1-10]ǀǀw-(Ti0.23,Al0.77)N(0001)[11-20]. The w-(Ti0.23,Al0.77)N shows phase separation of coherent nm-sized domains with varying chemical composition during growth. After annealing at high temperature, the domains in w-(Ti0.23,Al0.77)N have coarsened. The domains in w-(Ti0.23,Al0.77)N are smaller compared to the domains in c-(Ti0.27,Al0.63)N film that has undergone spinodal decomposition. The results that emerged from this thesis are of great importance in the cutting tool industry and also in the microelectronics industry, because the layers examined have properties that are well suited for diffusion barriers.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. p. 49
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1996
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-157078 (URN)9789176850411 (ISBN)
Public defence
2019-06-18, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
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Supervisors
Available from: 2019-05-27 Created: 2019-05-27 Last updated: 2019-05-27Bibliographically approved

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