Sintering behavior of refractory materials by Field Assisted Sintering Technology (FAST)

Field assisted sintering technology is a promising solution for producing components of refractory materials. In this research, the effort is focused on sintering of tungsten carbide and tungsten metal in FAST. Tungsten carbide with 0.4 and 1.2 μn powder sizes were sintered successfully in FAST with density more than 98% of theoretical density, at the sintering temperature around 1500°C under pressure of 65 MPa. Furthermore, limited grain growth was observed in the sintered WC samples. For elemental tungsten, the relative density of 98.5% was achieved without binder phase, by sintering at 1900°C under pressure of 85 MPa for 30 minute. However, significant grain growth was observed in the sample. To minimize grain growth, two approaches were studied; 1) higher heating rate, and 2) addition of fine WC particles. By increasing heating rate from 100°C/min to 200 and 400°C/min, there was no benefit in reducing grain growth and the sintered density becomes lower associated with large deviation in temperature measurement. By adding 5 and 10 vol% WC into W powder, sintering phenomena was enhanced and relative density increased to 96.1% and 99.3% at relatively low sintering temperature, 1700°C 85 MPa for 5 minutes. WC particles in W matrix also exhibited grain growth inhibiting, which minimized the average grain size of W matrix to 3.1 μm, while the grain size of sintered pure tungsten with equivalent density was around 34.3 μm.