Densification and mechanical properties of tantalum carbide and tantalum diboride ceramics.

摘要

A systematic study on densification behavior of TaC by hot pressing over a range of temperatures from 1900°C to 2400°C revealed the microstructural development as a function of hot pressing temperature. Grain growth started around 2350°C while the relative density reached 95%. Grain growth became rapid at 2400°C and resulted in entrapped porosity which prevented further densification. The addition of a small amount (0.36 wt% to 0.78 wt%) of an oxide reducing additive, such as B4C and/or C, significantly enhanced the densification of TaC, achieving 98% relative density at 2200°C. However, the onset temperature for rapid grain growth was also reduced. The competition between densification and grain growth inhibited the achievement of full density. Grain growth was pinned by adding excess B4C. Near full density was obtained for TaC with 1 or 2 wt% B4C additions by hot pressing at 2100°C without observable grain growth. However, it was found that grain growth was pinned by the new phases including TaB2 and C (instead of B4C) formed by the reaction between TaC and B 4C. The achievement of near full density allowed for mechanical property measurements.;The formation of refractory TaB2 in the TaC-B4C system has raised the interest in studying the densification and mechanical properties of TaC-TaB2 composites. However, the mechanical properties of TaB2 have not been reported in the literature and a considerable amount of discrepancy exists. Therefore, a study of the basic mechanical properties of TaB2 was also completed. Phase pure TaB2 was synthesized by reducing Ta2O5 using B4C and graphite at 1600°C, having an average particle size of 0.4 mum. The TaB 2 was hot pressed to 98% relative density at 2100°C with an average grain size of 5.3 mum. Mechanical properties were measured on hot pressed TaB2.