Effects of thermal annealing on phase transformation and microhardness of (Ti_xCr_yAl_z)N films

(Ti_xCr_yAl_z)N (x + y + z = 1) films with different atomic compositions were synthesized by the arc ion plating (AIP) method and annealed in vacuum from 700 to 1000 °C. The c-(Ti_0.10Cr_0.24Al_0.66)N and c-(Ti_0.27Cr_0.11Al_0.62)N films maintained the NaCl-type structure after annealing at 800 and 900 °C, respectively. While at 1000 °C, the structure of films was partially transformed into h-(Ti_xCr_yAl_z) N. The lattice parameter of films annealed at 1000 °C increased compared to those between 700 and 900 °C through possibly the diffusion of Al atoms from cubic to hexagonal grains. Due to the formation of the mixture phase by annealing at 1000 °C, microhardness of the film decreased from 31 to 24 GPa. In this paper, mechanical properties were determined using nanoindentation technique and microstructures, lattice parameter were investigated by X-ray and transmission electron microscopy. The observed phase transition was analyzed as a function of the annealing temperature.