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

Abstract

TiC reinforced Ti-based composite coatings were prepared on the Ti6Al4V surface via laser cladding with Ti6Al4V/NiCr-Cr 3 C 2 /Y 2 O 3 mixed powders. Influence of Y 2 O 3 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% Y 2 O 3 was added. In addition, the reinforcement TiC and the matrix sloid solution β-Ti were the main precipitated phases within the coating. The addition of Y 2 O 3 inhibited the generation of Ti 2 Ni at the grain boundary, however, promoted the generation of Cr 1.93 Ti 1.07 in the coating. With the addition of Y 2 O 3 , 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% Y 2 O 3 . Furthermore, some nano-sized β-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 β-Ti and TiC interface exhibited a semi-coherent relationship. Therefore, β-Ti can nucleate with TiC as the heterogeneous nucleation matrix. In the meanwhile, there was a certain dependent growth relationship between the β-Ti and TiC. • Y 2 O 3 addition eliminated cracks completely and reduced porosity of the coating. • Y 2 O 3 addition led to sufficient growth of the developed dendrite TiC. • Irregular Ti 2 Ni disappeared and Cr 1.93 Ti 1.07 precipitated in coating with Y 2 O 3 . • Y 2 O 3 addition resulted in severe regional segregation of Cr and Ni. • β-Ti can nucleate with TiC as the heterogeneous nucleation center.