Influence of Y2O3 addition on the microstructure of TiC reinforced Ti-based composite coating prepared by laser cladding

TiC reinforced Ti-based composite coatings were prepared on the Ti6Al4V surface via laser cladding with Ti6Al4V/NiCr-Cr3C2/Y2O3 mixed powders. Influence of Y2O3 on forming quality and microstructure of composite coatings was investigated systematically. The cracks were eliminated completely and the number of pores was drastically minimised when 2 wt% Y2O3 was added. In addition, the reinforcement TiC and the matrix sloid solution 8-Ti were the main precipitated phases within the coating. The addition of Y2O3 inhibited the generation of Ti2Ni at the grain boundary, however, promoted the generation of Cr1.93Ti1.07 in the coating. With the addition of Y2O3, the dendrites became largely developed and a large number of tertiary dendrites were found. Besides, a more obvious regional segregation appeared in the distribution of Ni and Cr elements in the coating with 2 wt% Y2O3. Furthermore, some nano-sized 8-Ti were distributed on the surface of small TiC particles in both coatings. Combined with the theoretical analysis of the two-dimensional mismatch degree, the 8-Ti and TiC interface exhibited a semi-coherent relationship. Therefore, 8-Ti can nucleate with TiC as the heterogeneous nucleation matrix. In the meanwhile, there was a certain dependent growth relationship between the 8-Ti and TiC.