Controllable Preparation And Low Temperature Sintering Characteristics Of Oxide-tungsten Composite Nanopowders

Tungsten-based alloys have many excellent properties such as high hardness,high melting point,high thermal conductivity and low thermal expansion coefficient,high thermal shock resistance and low radiation,so they are considered as the most promising plasma facing materials in nuclear fusion.However,traditional tungsten-based alloys have some problems,such as coarse grains,low temperature brittleness and recrystallization brittleness.Current research focuses on the second phase dispersion strengthening and fine grain strengthening to improve above problems.In order to prepare high performance Y₂O₃ dispersion strengthened tungsten based alloys,from the aspects of physical doping and chemical doping by“bottom-up”in-situ synthesis,high-quality W-Y₂O₃ composite powders were prepared by the freeze-drying and hydrothermal synthesis technology,and its low-temperature sintering characteristics were analyzed and discussed.Freeze drying is a physical homogeneous doping process of precursor powder elements from bottom to top.The average grain size of W-Y₂O₃ composite powders prepared by freeze-drying method with liquid nitrogen pre-freezing is only 14 nm.After low temperature sintering,W-Y₂O₃ alloys possess average W grain size of 410nm,high relative density of 98.1%,dispersed Y₂O₃ particles(<50 nm),and thus high hardness of 690±32 HV_0.2.It is because that the formation of second phase nano-Y₂WO₆particles(<20 nm)can adsorb oxygen impurities resulting in the purification and strengthening of W matrix.At the same time,Y₂WO₆ particles and W matrix show coherent and semi-coherent interfaces to strengthen their phase boundaries.Furthermore,the dispersant was introduced into the freeze-drying process,and corresponding average W grain size of W-Y₂O₃ composite powders is 9 nm.After low temperature sintering,W-Y₂O₃ alloys possess average W grain size of 210 nm,high relative density of 97.8%,dispersed Y₂O₃ particles(<50 nm),and thus high hardness of 721±31 HV_0.2.Hydrothermal synthesis is a chemical homogeneous doping process of precursor powder elements from bottom to top.Results show that the Keggin structure of raw materials AMT is destroyed during the hydrothermal synthesis at 170?,resulting in the formation of many W-OH bonds.Then the W-OH bond reacts with Y³⁺to form the W-O-Y bond,which is a co-deposition process in which element are uniformly doping.The average grain size of W-Y₂O₃ composite powders is 15 nm.After low temperature sintering,W-Y₂O₃ alloys have average W grain size of 210 nm,high relative density of 98%,dispersed Y₂O₃ particles(<50 nm),and thus high hardness of726±25 HV_0.2.Blue ammonium tungsten bronze(NH₄)_xWO₃ was synthesized as tungsten source by hydrothermal synthesis at 220?.The average grain size of W-Y₂O₃ composite powders is 15 nm.After low temperature sintering,W-Y₂O₃ alloys possess average W grain size of 200 nm,high relative density of 97.8%,dispersed Y₂O₃ particles(<150 nm),and thus high hardness of 733±37 HV_0.2.