Kinetics of Densification and Grain Growth of Pure Tungsten During Spark Plasma Sintering

The kinetics of densification and grain growth of tungsten during spark plasma sintering (SPS) was studied under isothermal conditions. The results show that using SPS, high-density (>97 pct) pure tungsten can be produced without the addition of sintering aids. The estimated sintering exponent (m = 0.4 ± 0.03) suggests that the rate-controlling mechanism of sintering is diffusion along the grain contacts into the interparticles neck region. The activation energy of tungsten self-diffusion was calculated (Q = 277 ± 15 kJ/mol) in the temperature range 1523 K to 1773 K (1250 °C to 1500 °C). The activation energy is smaller than the values in previous studies using conventional sintering. This suggests that there may be some differences in the sintering conditions and mechanisms during SPS processing compared to conventional sintering. Grain-growth kinetics was studied in the range 1873 K to 2073 K (1600 °C to 1800 °C) and classified as normal grain growth according to the estimated grain-growth exponent (m = 2 ± 0.2). The grain-growth activation energy was calculated as 231 ± 15 kJ/mol.