Correlation between arc evaporation of Ti–Al–N coatings and corresponding Ti0.50Al0.50 target types

Abstract

Ti–Al–N, which has been proven to be an effective protective coating for machining application, is one of the most studied ternary transition metal nitrides systems. Here, the Ti–Al–N coatings were deposited from three different target types (TiAlN_1: powder metallurgical (PM) Ti0.50Al0.50 target produced from powders with grain sizes between 45 and 150μm, TiAlN_2: PM target produced from powders with grains sized below 45μm and TiAlN_3 for smelting (SM) target) by cathodic arc evaporation in order to investigate the effect of target types on the structure, mechanical and thermal properties of arc evaporated Ti–Al–N coatings. For Ti–Al–N coatings deposited from PM targets, the TiAlN_2 coating has higher deposition rate, concentration of metallic macro-particles and hardness than TiAlN_1 coating. Additionally, decreasing Ti and Al grain sizes of PM targets has a deteriorative effect on the thermal stability and oxidation resistance of Ti–Al–N coatings, where TiAlN_2 coating exhibits an earlier w-AlN formation by ~100°C during thermal annealing in Ar and thicker oxide scale during exposure to air at 850°C. The utilization of SM target causes an obvious drop in hardness and oxidation resistance for TiAlN_3 coating, which exhibit similar concentration of metallic macro-particles and thermal decomposition process with TiAlN_1. Therefore, the best cutting performance is obtained by TiAlN_1 coated inserts allowing for the overall mechanical and thermal properties of coating.