Microstructure evolution and formation mechanism of graded cemented carbide with cubic-carbide-free layer prepared with TiN or Ti(C,N) free powder mixture

The graded cemented carbide with cubic-carbide-free layer (CCFL) in the surface layer is synthesized by employing TiN or Ti(C,N) free initial powder mixture as well as nitridation-denitridation sintering procedure. Six types of alloy samples at different nitridation and denitridation sintering stages are prepared via interruption of sintering procedure at a certain temperature and direct cooling in furnace. Subsequently, the microstructure, element distribution and phase composition of these samples are analyzed by SEM, EPMA,XRD techniques respectively. Moreover, the microstructure evolution during nitridation and denitridation sintering stages is investigated, the formation mechanism of CCFL and Co-enriched layer are analyzed. The research results contribute to illuminate the formation process of CCFL, also offer instruction for adjusting the starting mixture composition and sintering procedure in a positive direction.