Effect of Nano‐Size Powders on the Microstructure of Ti(C,N)‐xWC‐Ni Cermets

Abstract

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 ∼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 (KIC 10–12 vs. 6–10 MPa·m1/2). The coreless microstructure and the high fraction of rim phase in the nano system are responsible for this difference.