Phase stability, mechanical properties and thermal stability of Y alloyed Ti–Al–N coatings

The increasing demand for Ti1 − xAlxN protective coatings, especially when applied on cutting and milling tools, trigger further studies to enhance their wear performance at high-temperature conditions. To obtain requirements such as high oxidation and corrosion resistance and simultaneously high hardness and elasticity, the formation of quaternary alloys with 4d–transition metals such as yttrium (Y) is a promising approach. In order to study the impact of varying Al and Y content on the industrially preferred cubic structure of Ti1 − xAlxN, several Ti1 − x − yAlxYyN coatings were deposited using a plasma-assisted reactive magnetron sputtering process. Decreasing Y and Al content favour the formation of the single phase cubic structure. The thermal stability of coatings with single-phase cubic structure was carried out by annealing experiments in vacuum and ambient atmosphere. An increase in hardness of about 10% can be assigned to age-hardening effects which result in its hardness maximum of ≈ 32.4 GPa for Ta = 1200 °C for Ti0.51Al0.47Y0.02N. The formation of wurtzite structured AlN can be observed for annealing at temperatures above 1100 °C. Oxidation experiments (20 h at ≈ 850 °C) result in the formation of the typically layered oxide scale (Al2O3 and Ti-rich oxides) on top of the Ti1 − x − yAlxYyN coating. For Ti0.51Al0.47Y0.02N, the consumed nitride layer thickness is with ≈ 20% of the ~ 3.5-μm film thickness, the minimum of the coatings investigated. In contrast to this, Y free coatings are fully oxidised after 20 h annealing in ambient atmosphere at ≈ 850 °C.