Microstructure and oxidation-resistance of Til-x-y-zAlxCryYzN layers grown by combined steered-arc/unbalanced-magnetron-sputter deposition

Cation-substituted Til-x-y-zAlxCryYzN alloys, with y = 0.03 and z = 0.02, have been shown to offer greatly enhanced high-temperature oxidation resistance compared to presently used TiN and Til-xAlxN films. Layers (3 mu m thickness) were deposited by unbalanced magnetron sputter deposition onto austenitic stainless steel and M2 high-speed steel substrates which had been ion etched in situ using a steered Cr-metal-ion cathodic are discharge at an Ar pressure of 6 x 10(-4) mbar (0.45 mTorr). The metal ion-etching promoted initial local epitaxy on individual substrate grains while the overall film texture evolved through competitive growth to (111) in Ti0.44Al0.53Cr0.03N alloys and (200) in Ti0.43Al0.52Cr0.03Y0.02N. Although Ti0.44Al0.53Cr0.03N layers exhibited a columnar microstructure similar to that previously observed in Til-xAlxN alloys, the addition of 2 mol% YN resulted in significant grain refinement giving rise to a more equiaxed structure. The Knoop microhardness of Ti0.43Al0.52Cr0.03Y0.02N alloys was HK0.025 = 2700 kg mm(-2) compared to 2400 kg mm(-2) for Ti0.44Al0.53Cr0.03N. The onset of rapid oxidation, as determined from thermo-gravimetric measurements, ranged from approximate to 600 degrees C for TiN to 870 degrees C for Ti0.46Al0.54N to 920 degrees C for Ti0.44Al0.53Cr0.03N to 950 degrees C for Ti0.43Al0.52Cr0.03Y0.02N. (C) 1997 Elsevier Science S.A.