Studies on thermal shock resistance of TiN and TiAlN coatings under pulsed laser irradiation

Abstract

TiN and TiAlN nitride coatings were deposited on WC/Co cemented carbide by cathode arc evaporation technique. The microstructural and fundamental properties of these nitride coatings were examined. Thermal shock tests were carried out on these nitride coatings by laser irradiation, and thermal shock behaviours were examined by scanning electron microscopy. Results showed that the major factors causing failure of these nitride coatings after laser irradiation were thermal stress and oxidation. The formation of cracks on the irradiated coating surface is attributed to the shrinkage and relaxation of thermal stresses during laser irradiation. The critical power density at which the coating is fractured is 20×108 W m−2 for the TiN coating and 45×108 W m−2 for the TiAlN coating. The coatings with Al (TiAlN) exhibited higher thermal shock resistance over the one without Al (TiN). Analysis of the repeated laser irradiated coating surfaces demonstrated that the TiN coating was composed mainly of crack networks, spallation and bulges, whereas the TiAlN coating experienced less damage than the TiN coating and showed a lot of cavities on the coating surface.