Oxidation behaviour of PACVD-(Ti,Al)N wear resistance layers

Sputtered (Ti,Al)N hard coatings are successfully used for dry high speed c utting. These films show a lower oxidation rate than TiN or TiC coatings. I n our work (Ti,AI)N films were deposited on WC-6%Co substrates at a tempera ture of 490 degrees C by plasma-assisted chemical vapour deposition (PACVD) using a gas mixture of TiCl4/AlCl3/N-2/Ar/H-2. Investigation of microstruc ture, crystalline structure and chemical composition was carried out using SEM, WDXS, TEM, AES and XRD techniques. The chemical composition of the dep osited films showed a Al to Ti ratio of 1.33. The film thickness was 5.5 mu m. Films showed a fine crystalline size, the metastable fee crystal struct ure and a columnar growth. The film surface was under low compressive stres s up to several 100 MPa. For (Ti,Al)N/WC-Co compounds the oxidation behavio ur up to 1100 degrees C thigh temperature range) was studied. Therefore, sa mples were annealed or rapidly heated in air and under high vacuum conditio n using the laser shock method. The results show decomposition of the (Ti,A l)N structure to the TiN and the AlN phases at temperature values above 900 degrees C. Heating in air causes growing of a thin aluminum oxide layer at the film surface, which is a barrier for further oxygen diffusion to the a lumina-film boundary. Additionally, at temperatures above 900 degrees C oxi dation of the WC-6%Co substrate surface was obtained in regions of opened c racks and film delamination.