Resistance sintering under ultra high pressure: a new approach to produce bulk nanocrystalline refractory metal

Several different types of commercially available grades of W and Mo powders with nano size (50 nm) and micro size (0.2-3 microm) were sintered by a novel sintering method named as resistance sintering under ultra high pressure in the absence of additive. The sintering effect was characterized through microstructure observation and testing the mechanical properties. It is finds that as very short sintering time (less than 1 min.) is needed, this novel method is an effective technology to fabricate nanocrystalline refractory metal. Density greater than 90% theoretical density was achieved, while the grain size still remained about 50 nm, this grain size is substantially smaller than previously reported. The sintering mechanism of this sintering method is very different from the conventional sintering methods and was primarily analyzed in this paper.