The effect of aluminum on the microstructure and mechanical properties of arc-evaporated Ti1-xAlxN coatings deposited on cemented carbide substrates

The effect of aluminum contents (x) on the microstructure and mechanical properties of cathodic arc evaporated Ti1-xAlxN coatings was investigated. The coatings were deposited on mirror-polished plates of cemented carbides from mixed powder metallurgical Ti1-xTAlxT targets with xT = 0.50, 0.55, 0.60 and 0.66. The depositions were performed in a N2 atmosphere maintained at a working pressure of 5 Pa and at a bias voltage of -100 V. Glow discharge optical emission spectroscopy (GDOES), X-ray diffraction in glancing angle mode (GAXRD) and nano-indentation were used to characterize the chemical composition, the microstructure and the mechanical properties of the coatings. The results deduced from GDOES data analysis show that the coatings have a slightly higher aluminum contents than the targets used to deposit the coatings. The aluminum content was found to influence the phase composition, microstructure and mechanical properties of the coatings. The phase composition of the coatings changed from predominantly single-phase fcc-Ti1-xAlxN for x between ~0.5 and ~0.6 to dual-phase fcc-Ti1-xAlxN and w-AlN for x~0.66. For coatings with x < 0.6 the stress-free lattice parameter decreases with increasing x, whereas the hardness maintains a constant value of ~23 GPa. Further increasing the aluminum content is followed with an abrupt decrease in hardness by ~7 GPa. (Author)