Spark plasma sintering of tungsten–yttrium oxide composites from chemically synthesized nanopowders and microstructural characterization

Nano-crystalline W-1%Y2O3 (wt.%) powder was produced by a modified solution chemical reaction of ammonium paratungstate (APT) and yttrium nitrate. The precursor powder was found to consist of particles of bimodal morphology i.e. large APT-like particles up to 20 lm and rectangular yttrium containing ultrafine plates. After thermal processing tungsten crystals were evolved from W–O–Y plate like particles. spark plasma sintering (SPS) was used to consolidate the powder at 1100 and 1200 _C for different holding times in order to optimize the sintering conditions to yield high density but with reduced grain growth. Dispersion of yttrium oxide enhanced the sinterability of W powder with respect to lanthanum oxide. W–1%Y2O3 composites with sub-micron grain size showed improved density and mechanical properties as compared to W–La2O3 composites. Sample sintered in two steps showed improved density, due to longer holding time at lower temperature (900 _C) and less grain growth due to shorter holding time at higher temperature i.e. 1 min at 1100 _C.
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