Sintering mechanism of TiB2 reinforced Ti(C,N)-based cermet during reaction spark plasma sintering

Abstract

TiB2 reinforced Ti(C,N)-based cermet was produced by the reaction spark plasma sintering of Co, Ni, Ti, C, BN, Mo2C, WC, and TaC mixtures. To understand the mechanism of reaction sintering, systematic investigation on the microstructure evolution and displacement variation rule was carried out. In addition, the influence of C/BN molar ratio on the microstructures and performances of cermet was investigated. Except an initially increased pressure, three densification patterns were found. The first method was the CoTi, TiNi, and Ti-BN diffusion reactions, resulting in a shrinkage of 22.06%. The second pattern was the viscous flow and dissolution-reprecipitation, which corresponded to the synthesis of Ti(C,N) and TiB2. In this process, the shrinkage ratio was increased by 35.62%. The final densification mainly originated from the viscous flow of metallic binder. It contributed to the transformation of macrovoids into microvoids, and an increased displacement of 30.10%. With the increasing of C/BN ratio, more C atoms diffused into Ti(C,N). Furthermore, core/rim structure-Ti(C,N) and coreless (W,Mo,Ta,Ti)(C,N) were fabricated. However, the microvoids in cermets enhanced. As a result, the hardness and fracture toughness first increased and then decreased. Results from this work are helpful to understand the reaction spark plasma sintering technique, and can enrich the preparation method of cermet.