Nanoindentation hardness of compositionally modulated Ti/TiN multilayered films

摘要

A detailed study of microhardness of multilayered films has been strongly needed to reveal effects of film layer structures and deposition conditions on the film hardness. A nanoindentation method is a useful method to investigate mechanical properties of thin films prepared on substrate materials. In this respect we have deposited a several types of Ti/TiN multilayered films and estimated their hardness by a nanoindentation method. The desired compositional modulation was obtained by changing the fllw rate of N_2 gas periodically using a computer system. The modulation period has been varied from 10 to 40 nm by changing a flow rate control pattern. The total thickness of the film was about 500 nm including the underlayer of the TiO_2(50nm)/Ti(50nm) multilayer for all samples with different modulation period. Substrates used in the experiment were borosilicate glass and not heated during film deposition. The compositional distribution toward to the film depth orientation was estimated by Auger electron spectroscopy. The dynamic hardness of the films has been estimated by a nanoindenter as a function of the modulation period. It was found that there existed an optimum modulation period of 20 nm to enhance the film hardness by multilayer structure. The maximum value of microhardness obtained for the optimum modulation period was 29 GPa, which was much larger than that of the monolithic TiN coating of 15 GPa. The hardness measurement results show that the behavior for dynamic hardness was different from that for plastic deformation hardness obtained.