Influence of powder mixing processes and WC contents on microstructure, shrinkage behavior, and mechanical properties of WC-Si3N4 composites

Abstract

WC-Si3N4 composite structural material with excellent mechanical properties is essential for achieving high-strength connections between WC and Si3N4. Proper powder mixing process can significantly improve the mechanical properties of sintered samples. This study investigates the effects of two different ball milling methods: (1) mixing WC powder, Si3N4 powder, and sintering aid powders and then ball milling for 24 h (BM24); and (2) ball milling WC powder, Si3N4 powder, and sintering aid powders separately for 12 h and then ball milling in same jar for 12 h (BM12 + 12), as well as WC content on sintering shrinkage behavior of mixed powders. Furthermore, the bonding between the layers of one-time sintered sample of the WC-Si3N4 composite structure was investigated. The results showed that the microstrains of powders prepared by BM24 mixing process were greater than those of the powders prepared by BM12 + 12 mixing process. Shrinkage displacements and shrinkage rates during sintering of BM12 + 12 powders were greater than those of BM24 powders to varying degrees. Moreover, sintering temperature at which shrinkage rate of composite powders reaches its maximum value gradually increases as WC content decreases, while maximum value of shrinkage rate gradually decreases. Additionally, mechanical properties of all BM12 + 12 samples were better than those of BM24 samples. WC-Si3N4 composite structure sample sintered with BM12 + 12 powders had a smooth transition between the layers without any defects.