Low-temperature Sintering Of The Y₂O₃dispersion Strengthened W-based Alloy With Ultrafine Grain And High Density And Microstructure Control

With high melting point,low sputtering rate,high thermal conductivity,low tritium inventory,high strength at elevated temperatures and low thermal expansion,tungsten-base materials have been widely applied in many fields,such as aerospace industry,engineering and nuclear industry.However,high-density sintered products are always difficult to be get.Moreover,serious embrittlement in several aspects including low-temperature brittleness,recrystallization brittleness and irradiation induced brittleness is the main drawback to limit the application of tungsten-based materials,especially as the structural materials.In this paper,W-Y₂O₃ alloy was prepared by wet chemical method and subsequent SPS sintering.The codeposition mechanism of Y³⁺ions and tungstic acid particles was studied firstly.And on this basis,anionic surfactant SDS and macromolecular compound PVP were applied to prepare high-quality powder precursor with ultrafine W grains and homogeneously distributed Y₂O₃.Using this powder precursor,fine grained W-Y₂O₃ alloy with high density can be produecd via SPS sintering.The effect of SDS and PVP on the properties of the alloy is discussed and interface states in the alloy are analysed.The main conclusions are obtained as follows:?1?According to the HSAB principle,coordination reaction can occur quickly between hard acid Y³⁺ions and hard base white tungstic acid particles.The activity source of white tungstic acid particle attribute to W-OH bonds on its surface.Y³⁺ions can displace H⁺ions in hydroxyl groups and then form thermodynamically stable coordination complex with oxygen atoms,promoting the codeposition of Y³⁺ions and tungstic acid particles.?2?Powder precursor with ultrafine W grains?about 20 nm?and homogeneously distributed Y₂O₃ was prepared successfully.By sintering this high-quality powder precursor,tungsten-based alloy with fine grain?650 nm?and high density?99%?was produced.Besides,high-density Y₆WO₁₂2 nanoparticles are embeded within W grains and these Y₆WO₁₂2 nanoparticles are generated by diffusion reaction of W atoms.Thus,one can see that anionic surfactant SDS have remarkable dispersion effect on Y³⁺ions during chemical reaction,which can make Y₂O₃ play their role of inhibiting W grain growth as much as possible.Moreover,the refining effect of PVP on powder precursor can effectively improve the W grain size uniformity after sintering.?3?The Y₆WO₁₂2 particles distributed within W grain keep coherent relation with W matrix.Chemical ordering effect of these coherent particles create backstress when they are cut by dislocations,strengthening the alloy.Besides,these interior particles can enhance the strain hardening rate of material and then improve the ductility.The oxide particle distributed at W grain boundary is Y₂O₃ whose interface possess a 10nm of diffusion layer containing W atoms.However,the amount of W atoms diffusing into the submicron Y₂O₃ particle is limited in the larger space during SPS and thus no W-Y-O new phase is generated.In addition,most of the W/W grain boundaries in alloy belong to high-angle grain boundaries.The presence of high-angle grain boundary is responsible for increasing yield strength and strain hardening.