Preparation and high temperature oxidation resistance of laser deposited Ti5Si3/MoSi2/Mo5Si3 reinforced α-Ti/NiTi composite coatings

Abstract

Three kinds of composite coatings with different proportion of preplaced Ni-Mo-Si powders were fabricated on Ti6Al4V alloy by laser depositing to enhance the high temperature oxidation resistance. The microstructures of composite coatings were studied by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The microhardness of composite coatings was measured by Vickers microhardness tester. The samples of composite coatings and Ti6Al4V alloy underwent isothermal oxidation tests at 800 °C, and the oxidation mechanism was analyzed by thermodynamics and kinetics. Results indicate that composite coatings mainly include Ti5Si3, MoSi2 and Mo5Si3 as enhanced phases and α-Ti/NiTi as matrix, and have metallurgical bonding with substrate. With the increase of Ni content in composite coatings, the inter-metallic compounds α-Ti/NiTi matrix increased and the hard phase Ti5Si3 refined. The average microhardness of composite coatings is 2.6, 2.4, 2.3 times of that of Ti6Al4V alloy, respectively. Oxidation mass gain of the coatings are 5.6%, 12% and 57.9% of that of the substrate at 800 °C for 100 h, respectively, and oxide scales of the coatings are continuous and dense, showing good oxidation resistance at high temperatures.