Electrical resistance flash sintering of tungsten carbide

Abstract

This work explores the possibilities for the ultrafast sintering of binderless tungsten carbide by electric/pressure assisted sintering. A limited voltage (3–4 V) in AC condition was applied to WC powder compact in combination with uniaxial pressure. The thermal insulating ceramic die allows the ultrafast heating (104 °C/min) of the powder compact which undergoes a rapid transition of its electrical properties, from negative to positive dependence of resistivity on temperature, i.e. from NTC to PTC behaviour. Such effect is fundamental for inducing a thermal runaway phenomenon associated with ultrarapid temperature increase and massive electric power dissipation, thus inducing very rapid sintering. The relationship between electrical properties of tungsten carbide and the possibility to achieve “flash sintering” conditions to complete densification in a couple of seconds was investigated. At the optimal conditions of 3.5 V and 4 MPa pressure, pure WC sinters up to 95% in less than 10 s. Longer sintering time after the flash improves only slightly the density, despite a significant energetic consumption. It is also shown that if larger pressure is applied, the flash event duration and final density decrease.