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.