Hot-pressed Ti-Al targets for synthesizing Ti_1-xAl_xN films by the arc ion plating method

Ti and Al powders were mixed with identical atomic ratios and hot-pressed at 650, 800, 950, 1100 and 1250 °C, respectively, for the use of targets in the arc ion plating (AIP) method. As the sintering temperatures increased, the target density monotonously increased and the porosity correspondingly decreased. Chemical analysis by X-ray diffraction indicated that pure Ti and Al phases decreased and intermetallics such as TiAl₃ and Ti₃Al phases were formed at 800-950 °C. Over 950 °C, the amount of the intermetallics decreased and finally TiAl phase was formed. Next, the Ti-Al targets were arc-discharged in nitrogen plasma and Ti_1-xAl_xN films were deposited on mirror-polished cemented carbide substrates. The targets with lower density, sintered at 650 and 800 °C, did not easily trigger and keep stable arc-discharge during the deposition. As a result, synthesized Ti_1-xAl_xN films had a larger number and size of droplets which were not only circular but were also irregular shapes. Although microstructures of Ti-Al targets were quite different, all films mostly consisted of Ti_0.5Al_0.5N with the NaCl structure and similar hardness with approximately 3000 HV. Further, all Ti_0.5Al_0.5N films had the same columnar cross-sectional structures and the growth rate was approximately 17 μm/h.