The Yttrium Effect on Nanoscale Structure, Mechanical Properties, and High-Temperature Oxidation Resistance of (Ti0.6Al0.4)1-x Y x N Multilayer Coatings

As machine tool coating specifications become increasingly stringent, the fabrication of protective titanium aluminum nitride (Ti-Al-N) films by physical vapor deposition (PVD) is progressively more demanding. Nanostructural modification through the incorporation of metal dopants can enhance coating mechanical properties. However, dopant selection and their near-atomic-scale role in performance optimization is limited. Here, yttrium was alloyed in multilayered Ti-Al-N films to tune microstructures, microchemistries, and properties, including mechanical characteristics, adhesion, wear resistance, and resilience to oxidation. By regulating processing parameters, the multilayer period (I >) and Y content could be adjusted, which, in turn, permitted tailoring of grain nucleation and secondary phase formation. With the composition fixed at x = 0.024 in (Ti0.6Al0.4)(1-x) Y (x) N and I > increased from 5.5 to 24 nm, the microstructure transformed from acicular grains with aOE (c) 111 > preferred orientation to equiaxed grains with aOE (c) 200 > texture, while the hardness (40.8 +/- 2.8 GPa to 29.7 +/- 4.9 GPa) and Young's modulus (490 +/- 47 GPa to 424 +/- 50 GPa) concomitantly deteriorated. Alternately, when I > = 5.5 nm and x in (Ti0.6Al0.4)(1-x) Y (x) N was raised from 0 to 0.024, the hardness was enhanced (28.7 +/- 7.3 GPa to 40.8 +/- 2.8 GPa) while adhesion and wear resistance were not compromised. The Ti-Al-N adopted a rock-salt type structure with Y displacing either Ti or Al and stabilizing a secondary wurtzite phase. Moreover, Y effectively retarded coating oxidation at 1073 K (800 A degrees C) in air by inhibiting grain boundary oxygen diffusion.