OXIDATION RESISTANCE OF (TI,AL,SI)N COATINGS IN AIR

(Ti, Al)N and (Ti, Al, Si)N coatings were annealed in air at temperatu res ranging from 500 to 900 degrees C. The Ti.35Al.65N and Ti.62Al.38N form a protective superficial layer of Al2O3, protecting the underlyi ng nitride from further oxidation. Despite its higher aluminium conten t, the Ti.19Al.81N and the Ti.27Al.73N develop a homogeneous oxide lay er for all the oxidation temperatures, exhibiting the lowest oxidation resistance, very similar to that of AlN. The Ti.70Si.30N forms a homo geneous oxide layer, with an oxidation resistance similar to that of T i.62Al.38N. The Ti.62Al.26Si.12 forms a two-phase scale as in the Ti.6 2Al.38N, but the oxidation resistance is slightly lower. The Ti.27Al.5 3Si.20N shows, for temperatures below 800 degrees C, the formation of a homogeneous oxide layer, while for temperatures between 800 and 900 degrees C, an Al enrichment at the top layer is observed, which is res ponsible for a better oxidation resistance at 850 degrees C than that at 750 degrees C. (C) 1998 Elsevier Science S.A.