Sinter-ability of nanocrystalline tungsten powder

The relationship between the green density and as-sintered density of nano-tungsten compacts

“…Previous works, and our own experience, have shown that it is nearly impossible to obtain high green density of compacts at room temperature for nano tungsten powders made by high energy milling [14][15][16][17][18]. Using common uniaxial or isostatic pressing, with pressures up to 1 GPa, it is very difficult to press nano-W powders to high green density, more than 40% of theoretical density, due to the large amount of surface area, strength and brittleness.…”

“…The low green density compacts require sintering at high temperatures and long times to achieve full densification. Unfortunately, the onset temperature for W grain growth during sintering nano W powders is in a very low temperature range, 800-900°C [14,16]. At 1000 °C, W grains with a starting size of ~20 nm can grow to a size of about 300 nm in 1 hour, but with a relative density less than 90%.…”

“…Compared with the alternative pressure-assisted rapid consolidation techniques, the press-sinter route has advantages in removing impurities and economic benefits [13]. Prior models and experiments showed that a potential presssinter route, unitizing ultrahigh compaction pressure and low sintering temperatures, could preserve nanosized grains [13][14][15]. Johnson predicted that a starting W particle size of 40 nm, an ultrahigh compaction pressure of 2560 MPa and a sintering temperature of A C C E P T E D M A N U S C R I P T…”

Experimental and numerical analysis of the particle size effect on the densification behaviour of metal injection moulded tungsten parts during sintering

“…The maximum relative density achieved was 98.5%, which was for the sample sintered at 2000°C, 85 MPa for 30-min holding time. Recently, Wang et al [12] reported that nanocrystalline W powder can be sintered to near full density at a temperature as low as 1100°C under a H 2 atmosphere without external pressure. Prabhu et al [13] led an experimental investigation with anther sintering heating mode; microwave sintering has been studied using as-received W and activated W powder.…”

Initial-stage Sintering Kinetics of Nanocrystalline Tungsten

“…[1,2] Nanocrystalline tungsten has been sintered at a low temperature of 1973 K (1700°C) with 95 pct theoretical density in comparison with a high conventional sintering temperature ( ‡2773 K (2500°C)) for microcrystalline tungsten. [3] Recently, Wang et al [4] reported as low a sintering temperature as 1373 K (1100°C) for nanocrystalline tungsten powders in hydrogen atmosphere without pressure, which was further reduced to 1273 K (1000°C) using spark plasma sintering (SPS). [5] Nanocrystalline tungsten powder of submicron sizes was also used to produce near fully dense (above 99.7 pct theoretical density) tungsten heavy alloy.…”