Influence of carbon sources on the sintering processes, microstructures, and mechanical proprieties of TiB2-reinforced ultrafine Ti(C,N)-based cermets fabricated via reactive spark plasma sintering

Abstract

TiB₂-reinforced ultrafine Ti(C,N)-based cermets are fabricated via reactive spark plasma sintering. This study investigates the effect of carbon sources on the sintering processes, microstructures, and mechanical properties of cermets derived from a Co-Ni-Y-Ti-BN-WC-VC-Mo₂C-TaC-C system. Results reveal that the sintering process involves both solid-state reactions and liquid-phase sintering stages. Compared to graphitic graphite and graphene, amorphous carbon black and nanocarbon exhibit higher reactivity and smaller particle sizes. This characteristic inhibits the CoTi and TiNi reactions but promotes the Ti-BN reaction, thereby reducing the shrinkage rate during the solid-state reaction stage. During the liquid-phase sintering stage, carbon dissolves into the molten metal and subsequently diffuses into preformed TiN to create Ti(C,N). The use of carbon black and nanocarbon facilitates greater consumption of carbon. Consequently, there is an increase in shrinkage rate during this stage, a reduction in residual carbon within the final sintered samples, and an enhancement in relative density. Moreover, C atoms present in the liquid phase would promote the diffusion of heavy metals into Ti(C,N). When graphite or graphene is used as a source of carbon, Ti(C,N) with a black core/Gy rim structure is obtained. In contrast, employing carbon black or nanocarbon encourages the diffusion of heavy metals toward the center of Ti(C,N). This behavior contributes to the achievement of weak core/rim-structured Ti(C,N) and coreless solid solution particles with finer particle sizes, respectively. As a result of these processes, the synthesized cermet attains an optimal hardness of 2145 HV and K_IC of 7.67 MPa·m^-1/2, along with a minimal wear depth of 8.19 μm.