Structure and mechanical properties of TiAlN-WNx thin films

A combinatorial method was employed to grow TiAlN-WNx films by DC sputtering as well as by High Power Pulsed Magnetron Sputtering (HPPMS) where the W concentration was varied between 10-52 at.% and 7-54 at.%, respectively. Experiments were paired with ab initio calculations to investigate the correlation between composition, structure, and mechanical properties. During all depositions the time averaged power was kept constant. As the W concentration was increased, the lattice parameter of cubic TiAlN-WNx films first increased and then decreased for W concentrations above approximate to 29 at.% (DCMS) and approximate to 27 at.% (HPPMS) as the N concentration decreased. Calculations helped to attribute the increase to the substitution of Ti and Al by W and the decrease to the presence of N vacancies. Young's modulus and hardness were around 385-400 GPa and 29-31 GPa for DCMS and 430-480 GPa and 34-38 GPa for HPPMS, respectively, showing no significant trend as the W concentration was increased, whereas calculations showed a continuous decrease in Young's modulus from 440 to 325 GPa as the W concentration was increased from 0 to 37.5 at.%. The presence of N vacancies was shown to increase the calculated Young's modulus. Hence, the relatively constant values measured may be understood based on N vacancy formation as the W concentration was increased. HPPMS-deposited films exceed DCMS films in Young's modulus and hardness, which may be a consequence of the larger degree of ionization in the HPPMS plasma. It is reasonable to assume that especially the ionized film forming species may contribute towards film densification and N vacancy formation. (C) 2011 Elsevier B.V. All rights reserved.