The formation mechanism of in-situ TaC/Ni0.9Ta0.1 composites prepared by pressureless reactive sintering

The in-situ Tantalum Carbide (TaC)/Ni0.9Ta0.1 composite was fabricated by pressureless reactive sintering method using Nickel (Ni), Tantalum (Ta) and graphite as raw materials. The formation mechanism was investigated through analyzing the phase and morphology evolution process during the reactive sintering process. Results showed that Ni, Ta and graphite completely reacted and dense TaC/Ni0.9Ta0.1 composite was obtained. With the increase of temperature, the solid-phase diffusion of atoms occurs at the interface of Ni, Ta and graphite, leading to the formation of Ni3C, Ni2Ta, Ni3Ta, Ni0.9Ta0.1 and TaC. Meanwhile, the reaction [Ta] (Ta atoms in Ni3Ta) + [C] (C atoms in Ni3Ta)TaC in Ni3Ta takes place, due to the high affinity between Ta and C atoms. The intermediate products Ni3C, Ni2Ta and Ni3Ta vanish, and the composite is consisted of Ni0.9Ta0.1 and TaC before the appearance of liquid phase. The formation of TaC included two ways, namely the diffusion of C into Ta particles and the reaction [Ta]+[C] = TaC in Ni3Ta. Ni0.9Ta0.1 was also generated through two ways, i.e., the diffusion of Ta into Ni and the transformation of Ni3Ta. The liquid phase sintering of composite occurs at about 1320 °C, and the optimum sintering temperature was about 1380 °C.