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

摘要

The increasing demand for Ti_(1-x)Al_xN 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 Ti_(1-x)Al_xN, several Ti_(1-x-y)Al_xY_yN 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 agehardening effects which result in its hardness maximum of ≈32.4 GPa for T_a = 1200 °C for Ti_(0.51_Al_(0.47)Y_(0.02)N. 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 (Al_2O_3 and Ti-rich oxides) on top of the Ti_(1-x-y)Al_xY_yN coating. For Ti_(0.51)Al_(0.47)Y_(0.02)N, the consumed nitride layer thickness is with ≈20% of the ~3.5-μmfilm thickness, theminimumof the coatings investigated. In contrast to this, Y free coatings are fully oxidised after 20 h annealing in ambient atmosphere at ≈850 °C.