Effect of nitrogen vacancies on the growth, dislocation structure, and decomposition of single crystal epitaxial (Ti1-xAlx)Ny thin films

• Published in: Acta materialia 2021-01, Vol.203, p.116509, Article 116509
• Main Authors: Calamba, K.M., Salamania, J., Jõesaar, M.P. Johansson, Johnson, L.J.S., Boyd, R., Pierson, J.F., Sortica, M.A., Primetzhofer, D., Odén, M.
• Format: Article
• Language: English
• Subjects: Nitrogen vacancies; spinodal decomposition; Thin Films; TiAlN system
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2020.116509

The effect of varying nitrogen vacancies on the growth, microstructure, spinodal decomposition and hardness values of predominantly single crystal cubic phase c-(Ti1-xAlx)Ny films was investigated. Epitaxial c-(Ti1−xAlx)Ny films with y = 0.67, 0.79, and 0.92 were grown on MgO(001) and MgO(111) substrates by magnetron sputter deposition. High N vacancy c-(Ti1−xAlx)N0.67 films deposited on MgO(111) contained coherently oriented w-(0001) structures while segregated conical structures were observed on the films grown on MgO(001). High resolution STEM images revealed that the N-deficient growth conditions induced segregation with small compositional fluctuations that increase with the number of N vacancies. Similarly, strain map analysis of the epitaxial c-(Ti1−xAlx)Ny (001) and (111) films show fluctuations in strain concentration that scales with the number of N vacancies and increases during annealing. The spinodal decomposition coarsening rate of the epitaxial c-(Ti1−xAlx)Ny films was observed to increase with decreasing N vacancies. Nanoindentation showed decreasing trends in hardness of the as-deposited films as the N vacancies increase. Isothermal post-anneal at 1100 °C in vacuum for 120 min revealed a continuation in the increase in hardness for the film with the largest number of N vacancies (y = 0.67) while the hardness decreased for the films with y = 0.79 and 0.92. These results suggest that nitrogen-deficient depositions of c-(Ti1-xAlx)Ny films help to promote a self-organized phase segregation, while higher N vacancies generally increase the coherency strain which delays the coarsening process and can influence the hardness at high temperatures. [Display omitted]