Microstructure evolution and properties of in-situ TiC reinforced titanium matrix composites coating by plasma transferred arc welding (PTAW)

In-situ TiC reinforced titanium matrix composites coating was prepared on the surface of Ti6Al4V by plasma transfer arc welding using pure Ti powder and Cr3C2 powder. The obtained TMCs coating is dense, no porosity and forms a good metallurgical bond with the substrate. There are obvious composition differences in the coating along the direction of temperature gradient: Mixture structures of TiC dendrites, β-Ti, needle-like α-Ti and TiCr2 phases were formed at the top of the coating due to heat accumulation and slow cooling rate, and the formation mechanism of these phases was analyzed in detail. The cavitation erosion resistance, corrosion resistance, microhardness and wear resistance of Ti6Al4V substrate and TMCs coating were compared and clarified. The TiC ceramic phase generated in situ is anchored by β-Ti, so that the TMCs coating is both tough and hard. The microhardness of the top of the coating reaches 1325 HV0.2, which is 4 times that of the substrate. In addition, the α-Ti + TiCr2 phase precipitates along the minimum mismatch crystal orientation and presents a certain crystallographic orientation relationship with β-Ti. The TMCs coating exhibits higher resistance to wear and corrosion than Ti6Al4V substrate. Therefore, the surface modified TMCs coating prepared in this study is expected to apply in the surface protection of Ti6Al4V under the working conditions of wear and sea water erosion corrosion in the field of ocean engineering.