Youqiang Xing

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.

Periodic nano-ripples structures fabricated on WC/Co based TiAlN coatings by femtosecond pulsed laser

Abstract Periodic nano-ripples structures were fabricated by femtosecond laser scanning on WC/Co based TiAlN coatings. The surface morphology, ripples dimension and changes in the element content of samples irradiated with different processing parameters were analysed. The results show that the formation and quality of ripples are largely determined by pulse energy, scanning speed and scanning spacings. The 3 μJ pulse energy, 500 μm s−1 scanning speed and 5 μm scanning spacing induce best quality ripples on TiAlN films among all experimental conditions. The period of ripples formed on TiAlN films gradually increases with increasing pulse energy, scanning speed and scanning spacing, which is smaller than the laser wavelength. With the high pulse energy and low scanning speed, TiAlN films could be removed, and ripples with period of 480–600 nm are formed on cemented carbide substrates. Concentration and distribution of all constitutive elements in the irradiated area are gradually changed with increasing pulse energy.