Effects of Al content on hardness, lattice parameter and microstructure of Ti_1-xAl_xN films

Ti_1-xAl_xN films were synthesized by the arc ion plating method using Ti_1-xAl_x alloy targets with differing Al contents. X-ray diffraction patterns from films indicated that the NaCl structure for x≤0.6 changed into wurtzite structure for x≥0.7. For films with x≤0.6, the lattice parameter decreased in proportion to the x value, and correspondingly, the hardness gradually increased from ~2000HV for x=0 up to 3200HV for x=0.6. On the other hand, the hardness of films with x≥0.7 abruptly deceased from ~3000HV for x=0.7 to 1400HV for x=1. Further, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that the films with x=0.6 had a typical columnar structure with grain sizes of 100-200nm. While for films with x≥0.7, a columnar structure disappeared and excess Al atoms did not segregate at the grain boundaries as AlN, but Ti and Al were uniformly dissolved and distributed as nitride grains with wurtzite structure.