Effect of nano-size powders on the microstructure of Ti(C,N)-xWC-Ni cermets

Microstructural and compositional analyses of Ti(C,N)-xWC-20Ni cermets were performed to understand the dissolution behavior of nano-size Ti(C,N) and WC, compared with an ultra-fine and a micro-sized system. The WC content was varied from 10 wt% to 70 wt%. The rapid dissolution and reprecipitation of nano-Ti(C,N) powders induced the formation of a coreless microstructure. With an increase in the amount of WC, the concentration of W in the rims increased but was low compared with the ultra-fine or micrometer system. An inversion in W concentration between the inner rim and the outer rim occurred at similar to 40 wt% added WC. That is, the outer rim was richer in W than the inner rim. Powder size strongly affected the dissolution and precipitation of particles and was a major determinant of the final microstructure and compositions of the rims. Furthermore, a significant improvement in toughness in the case of simple nano systems was found, compared with that of the corresponding micrometer and ultra-fine systems (K-IC 10-12 vs. 6-10 MPa.m(1/2)). The coreless microstructure and the high fraction of rim phase in the nano system are responsible for this difference.