La₂O₃ Doped W-70Cu Composite Powder Prepared With Hydrothermal Method And Its Sintering Densification Process

W-Cu composite materials have both the properties of tungsten and copper,including: low thermal expansion coefficient,high melting point and high strength of tungsten component,while high thermal conductivity and electrical conductivity of the copper component.These characteristics make W-C u composite materials to be used as thermal deposition materials,ultra-high voltage electric contact materials and warhead materials,which are widely used in aerospace,electrical instrumentation industry and military industry.However,because the density and melting point of W and C u are quite different,as well as the intermiscibility is very poor,so the products fabricated via traditional powder metallurgy are easy to emerge defects like the inhomogeneous distribution of tungsten and copper,the poor relative density,the coarse grain size and so on,the mechanical and physical properties need to further improve.The key technology of W-Cu alloy with high properties lies in the preparation of homogenous distribution of elements,particle reinforced nano powder and the technology of sintering process.Therefore,this article use the Na2WO4 · 2H₂ O,Cu?NO3?2· 3H₂ O and La?NO3?3 · nH₂ O as raw materials to prepare La₂O₃ doped W-70 Cu precursor powder via hydrothermal-calcination method.By means of SEM,HRTEM,DTA/TG and XRD method for the phase,morphology and microstructure of composite powders have been characterized.The results showed that the best thermal reaction temperature of La₂O₃ doped tungsten copper via hydrothermal method was 180?,the best time was 25 h,and the best solution p H was 5.5.The powder was finer and not easy to agglomerate along with the increasing of La addition.While on the other hand,the particles of powder after calcination become uniform.The best dispersibility of powder calcined at 500 ? for 60 min with 2.0wt% La₂O₃ doping amount.The new phase La2?WO4?3 appeared in the as-calcined products.Besides,the precursor powder can get gather during the time increasing.The most uniform precursor powder prepared at 180? for 16 h.The results of the La₂O₃ doping W-Cu composite powder reduction process showed,the particles of reduced powders are quite inhomogeneous when adopted 775?×2h one-step reduction,and the C u phase is easy to gather with large size.When two-step reduction is applied,C u phase can be obtained at 400? for 30 min while fine and well distribution W-Cu composites powder can be obtained at 775? for 2h.Rare earth phase turned to be La₂O₃ by La2?WO4?3 at calcinination process,lanthanum oxide evenly distributed around the tungsten copper particles,cover and depart the tungsten-copper particles,which inhibited the nucleation,and refine the grain size.Compared to one-step reduction,W-Cu composite powder produced by two-step reduction has smaller particle size,more uniform particle distribution,better dispersion.Then W-70 C u alloy were prepared via CIP-hydrogen sintering and SPS sintering,respectively.The results showed,the higher temperature,the bigger copper grains.The relative density was 97.24% at 1090 ? and the hardness was 113 HB,electric conductivity was 71.4%IACS.Using SPS sintering,the optimum value is 950?×5min,the measured density was 97.86% and the hardness was 117 HB,electric conductivity was 74.8%IACS.The doped rare earth oxide La₂O₃ can refine the grain,balance the phases of tungsten and copper,in either way of sintering,thus improve the properties of relative density and hardness.In this article,nano composite powder prepared through the hydrothermal method can not only guarantee the uniformity of W,C u,La elements distributed in powder but also refined by the addition of La₂O₃,further improve the sinter activity of composite materials,cut down the sintering temperature,purify grain boundary,improve properties of materials,which has a high practical value.