Preparation And Sintering Densification Behavior Of Ultrafine/Nano W-La₂O₃Composite Powder

Tungsten with high melting point, high density, high sputtering threshold, high thermal conductivity and mechanical properties at high temperature, low thermal expansion coefficient and tritium retention, is widely used in the defense industry, the nuclear industry and the aerospace field. But at the same time, the densification difficulties, low temperature brittleness, recrystallization brittleness and neutron irradiation brittleness defect, limit the application of tungsten and its alloy. In this paper, by sol spray-calcination reduction method, ultrafine/nano-scaled W-La2O3composite powder with high sintering activity is prepared. Fine grained W-La2O3alloy high density is prepared through densification process control. The powder preparation process and mechanism, densification behavior are studied to optimize alloy sintering process. The effect of La2O3on the properties of the alloy are discussed, the main conclusions are obtained as follows:(1) By sol spray-calcination reduction method ultrafine/nano-scaled W-La2O3composite powder is prepared. The particle size is fine and uniform, and shows a thinning trend with the increase of La2O3content. The particle size and grain size of W-0.7La composite powder are0.1μm and56nm. Appropriate milling can reduce the particle size, improve the uniformity of powder. The lattice distortion and dislocation density of powder raise with the milling time increasing.(2) After sintering, La2O3exists in the form of La-W-0second phase. When the sintering temperature is lower than1700℃, the second phase particle phase changes barely. Second phase particles distributes and disperses on tungsten grain boundaries, impedes the migration of grain boundaries and densification. As the sintering temperature increasing, the second phase particles and tungsten react. The excess surface energy kept and high temperature act as driving force.the grain boundary migrate rapidly and densification accelerate.(3) Ultrafine/nano composite powder with high sintering activity can be sintered at low temperature. By strengthening the densification process at low temperature (1000～1500℃),and reducing the residence time of sintering at high temperature, fine grained W-La2O3alloy with high density is obtained. the second phase particle size has no obvious change, in which W-0.7La has a bending strength of the best (548MPa) and most fine grain group fabric (8.7μm)respectively.