Microstructure and mechanical properties of the spark plasma sintered Ta ₂C ceramics

Single phase hexagonal α-Ta ₂C ceramics were synthesized by spark plasma sintering and using TaC and Ta as the starting powders. Effects of sintering temperatures and holding times on the densification process, phase formation, microstructure development, and mechanical properties of the α-Ta ₂C ceramics were investigated. Densification occurred in the temperature range of 1520-1675°C in less than 2.5 min. But completion of the Ta ₂C formation took about 40 min at 1500°C, and 5 min at 1900°C. The materials sintered at 1500°C consisted of fine equiaxed grains. The Ta ₂C grains grew anisotropic to form an elongated self-toughening microstructure at 1700°C. At 1900°C, the neighboring Ta ₂C individual crystals coalesced to form large Ta ₂C blocks to entrap the residual pores. Although higher flexural strength and fracture toughness were reached at 1700°C, the unstable microstructures of the Ta ₂C materials indicated limited applications at high temperatures.