Phase transitions in PACVD-(Ti,Al)N coatings after annealing

(Ti,Al)N wear resistance layers were deposited on WC–6% Co substrates by plasma assisted chemical vapour deposition (PACVD). The film composition was 21.0 at% Ti, 28.0 at% Al, 48.0 at% N, 1.5 at% O and 1.5 at% Cl. lm–substrate compounds were investigated after long as well as short time thermal treatment. In this paper we study the (Ti,Al)N films after annealing for 1 h in vacuum or air at 700°C up to 1100°C. logy and damages of the films were detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Phase transitions in the films were examined by X-ray diffraction; the chemical analysis was done using Auger electron spectroscopy and WDXS. mental results show film decomposition of the metastable fcc-(Ti,Al)N phase in fcc-TiN and hcp-AlN phases after annealing at temperatures above 900°C. There is only a small decrease in the Cl content measured at annealing temperatures up to 1000°C. Additionally in air, the oxidation of the (Ti,Al)N film is observed, which results in the development of an alumina layer at the film surface, whereas a titanium oxide sublayer is not found. The oxidation process is accompanied by partial film damages by crack formation and delamination effects.