Comparison of TiN and Ti_1-xAl_xN coatings deposited on Al using plasma immersion ion implantation assisted deposition

TiN and Ti1-xAlxN coatings were deposited on Al substrates using the plasma immersion ion implantation and deposition technique, employing a filtered Ti and Ti0.5Al0.5 cathodic arc in a nitrogen atmosphere. Negative pulsed bias voltages between 0 to –4.0 kV were applied with varying duty cycles, at a constant time-averaged bias. Stress measurements using X-ray diffraction reveal an increase and then a decrease in the intrinsic compressive stress at increasing on-time bias, more pronounced for Ti1-xAlxN coatings. A bias dependent preferred orientation is observed for both the coatings, with [200] being the preferred orientation at higher bias. The hardness always reduces for TiN coatings with increase in bias, whereas for Ti1-xAlxN it shows a reverse trend. The results are qualitatively explained by the role played by Al in Ti1-xAlxN. The results indicate that the peak bias plays a more dominant role than time averaged bias.