Sintering behavior and grain growth of tungsten and tantalum with nano tungsten carbide powder

Sintering behavior of tungsten (W) and tantalum (Ta) powders were investigated by field assisted sintering technology (FAST). The results show that tungsten powder (0.6-0.9 μm) was sintered to around 99% relative density at 2000°C under 85 MPa pressure for 30 minutes. The same density was achieved in tantalum powder (5.3 μm) sintered at 1850oC under 55-75 MPa pressure for 5 minutes. However, the corresponding grain sizes were 22.2 μm for tungsten, and above 50 μm for tantalum. With 10 vol% nano WC additive, 99% relative density was achieved at lower sintering temperature in both materials (1700°C for W and 1750°C for Ta). Furthermore, sintered grain size was reduced to 2.9 μm for W and less than 10 μm for Ta, when WC additive was used. X-ray diffraction results revealed that some W reacted with WC and formed W₂C phase, which remained after sintering. Ta ₂C phase was detected in the Ta samples with WC additive.