Microstructure, Wear Resistance and Oxidation Behavior of Ni-Ti-Si Coatings Fabricated on Ti6Al4V by Laser Cladding

Abstract

The Ni-Ti-Si composite coatings were successfully fabricated on Ti6Al4V by laser cladding. The microstructure were studied by SEM (scanning electron microscopy) and EDS (energy dispersive spectrometer). It has been found that Ti ₂Ni and Ti ₅Si ₃ phases exist in all coatings, and some samples have TiSi ₂ phases. Moreover, due to the existence of these phases, coatings presented relatively higher microhardness than that of the substrate (826 HV (Vickers hardness)) and the microhardness value of coating 3 is about twice larger than that of the substrate. During the dry sliding friction and wear test, due to the distribution of the relatively ductile phase of Ti ₂Ni and reinforcement phases of Ti ₅Si ₃ and TiSi ₂, the coatings performed good wear resistance. The oxidation process contains two stages: the rapid oxidation and slow oxidation by high temperature oxidation test at 800 °C for 50 h. Meanwhile, the value of the oxidation weight gain of the substrate is approximately three times larger than that of the coating 4. During the oxidation process, the oxidation film formed on the coating is mainly consisted of TiO ₂, Al ₂O ₃ and SiO ₂. Phases Ti ₂Ni, Ti ₅Si ₃, TiSi ₂ and TiSi were still found and it could be responsible for the improvement in oxidation resistance of the coatings by laser cladding.