Thermochemical modelling of the phase stability of coatings deposited from the gas phase
Final Report Abstract
By virtue of their physical, chemical, and mechanical properties (like high hardness, good abrasive and sliding wear resistance, and high temperature resistance) transition metal nitrides are widely used for wear protection of tools, dies, molds, as well as for components in the automotive and aerospace industry. Research into synthesis - structure - property relationships of Ti1-xAlxN (space group Fm3m, c henceforth) and their alloys, enables industrial applications including unlubricated metal cutting, with cutting temperatures exceeding 1000 °C3'4'5. In the system (Ti1-xAlx)N, the transformation from the metastable cubic phase, with excellent tribological properties, to the metastable hexagonal phase, with inferior coating properties, occurs in a range of 0.4 < x < 0.91, as reported by different authors. The reasons for the rather extensive variation in the critical aluminum concentration at which the hexagonal phase appears are not evident. The aim of this project was to contribute towards understanding the reasons for this rather extensive variation. We wanted to expand an existing thermochemical model, based on comparing the Gibbs energy of stoichiometric and defect free individual structures, by including variations in stoichiometry as well as the presence of grain boundaries. Based on ab initio calculations, we have shown that the chemical requirement for spinodal decomposition in the quasibinary c-TiN-c-AIN system is fulfilled over a wide composition and temperature range. We have also demonstrated that the phase stability of supersaturated c-Ti1_xAlxN not only depends on the chemical composition, but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit may be obtained by decreasing the number of Ti-Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configurational contribution to the total energy. This may in part explain the large variation of the metastable solubility limit reported in the literature. Furthermore, additional effects have been considered. The influence of sizes of the particles formed during spinodal decomposition and strain energy due to their different lattice parameter and elastic constants with respect to the remaining matrix on decomposition process and energetics has been described. Good agreement between the enthalpy output obtained from differential scanning calorimetry and values derived from ab initio and continuum mechanical based calculations for the occurring decomposition and transformation processes is obtained. Hence, all goals have been reached and we have already applied this methodology for other material systems.
Publications
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Energy distribution of 0~ ions during reactive magnetron sputtering, Appl. Phys. Lett. 89, 051502 (2006)
S. Mräz and J. M. Schneider
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Energy distribution of O" ions during reactive magnetron sputtering of transition metal oxide thin films, Third HIPIMS Days, 11-12. July 2006, Sheffield Hallam University, Sheffield, UK
J.M. Schneider
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Influence of the Al distribution on the structure, elastic properties and phase stability of supersaturated Ti1-xAlxN, J. Appl. Phys. 100, 094606 (2006)
P. H. Mayrhofer, D. Music, and J. M. Schneider
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Influence of the negative oxygen ions on the structure evolution of transition metal oxide thin films, J. Appl. Phys. 100, 023503 (2006)
S. Mräz and J. M. Schneider
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Reducing the impurity incorporation from residual gas by ion bombardment during high vacuum magnetron sputtering, Appl. Phys. Lett. 88, 191905(2006)
J. Rosen, E. Widenkvist, K. Larsson, U. Kreissig, S. Mräz, C. Martinez, D. Music, and J. M. Schneider
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Spinodal decomposition of Ti1-xAlxN; Experiments and modeling, International Conference on Metallurgical Coatings and Thin Films, May 1-5, 2006, San Diego, USA
P. H. Mayrhofer, H. Clemens, H. Eckerlebe, J. Sjölen, F. D. Fischer, H. J. Bohni, D. Music, J. M. Schneider, C. Mitterer, and L. Hultman
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Ab initio calculated binodal and spinodal of cubic Ti1-xAlxN, Appl. Phys. Lett. 88, 071922 (2006) Erratum: Appl. Phys. Lett. 90, 029902 (2007)
P. H. Mayrhofer, D. Music, and J. M. Schneider
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Comparative study on Ti1- XA1XN and Cr1-xAlxN, International Conference on Metallurgical Coatings and Thin Films, April 23-27, 2007, San Diego, USA
P. H. Mayrhofer, D. Music, and J. M. Schneider
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Energetic balance and kinetics for the decomposition of supersaturated Ti1-xAlxN, Acta Mater. 55, 1441 (2007)
P. H. Mayrhofer, F. D. Fischer, H. J. Böhm, C. Mitterer, and J. M. Schneider
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Energy distribution of O" ions during reactive magnetron sputtering of oxide thin films, 9th International Symposium on Sputtering & Plasma Processes (ISSP), 6-8 June, 2007, Kanazawa, Japan
J.M. Schneider
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Phase stability of Ti1-xAlxN and transition metal oxides, International Conference Materials and Austceram, 4-6 July 2007, Sydney, Australia
J.M. Schneider
