Microstructure And Properties Control Of W-ZrC Alloys With Multi-scaled Interface Structure

For the plasma facing materials in the current fusion reactors,the tungsten based materials have the issues of low thermal load resistance,insufficient strength/ductility,low irradiation resistance/obvious sputtering corrosion and high hydrogen retention.The bulk W alloys were designed and fabricated with coexistence of multi-scaled interface structure:micrometer scaled similar columnar grain boundary interface,sub-micrometer ultrafine equiaxial sub-grain boundary interface and ultrafine nanoscaled phase boundary interface between refined dispersed strengthening nano particles and W matrix.The purpose is to synergistically improve the mechanical properties,high thermal load resistance,irradiation resistance/plasma sputtering corrosion resistance and decrease the hydrogen retention of W alloy.On this basis,the properties of tungsten-based alloy are further controlled by means of grain refinement,reduction of oxygen content and solution strengthening.Firstly,the microstructure of W-ZrC rolled alloys are controlled based on the size effect of tungsten powders.The commercial tungsten powder with grain size of 2.8 ?m and ZrC with the particle size of 50 nm were used for high-energy ball milling,then the billet was sintered at high temperature,and then the rolled alloy plate(2.8WZC)was obtained by hot rolling at high temperature with the deformation of 70%.By observing the microstructure,it is found that the mother-grain size is 17 ?m and the aspect ratio is 1.5,but the agglomeration of second phase particle is serious and the average particle size is 155 nm with the uneven distribution.By changing the initial grain size of tungsten powder,the tungsten powder with grain size of 0.5 ?m was selected.By using the same preparation process,the mother-grain size of the alloy plate(0.5WZC)was 9 ?m,the subcrystal size was-1 ?m,and the average size of the second phase particle was 51 nm.The distribution of the second phase particle was uniform,which was completely consistent with the system constructed.When the initial tungsten particle size is 0.2?m(0.2WZC),the average particle size of the second phase is 53 nm,but the distribution is not uniform.Based on the tungsten powder particle size effect to regulate the service performance of W-ZrC rolled alloy,the mechanical,thermal stability and thermal shock resistance of three alloy plates were characterized.It was found that the 0.5WZC had the highest initial recrystallization temperature(1500?),and the grain size only grew up to 70 ?m after full recrystallization.The DBTT of 0.5WZC is lower than 150?,the UTS is 932 MPa,and the annealing temperature is up to 1400?.The cracking threshold of 0.5WZC and 0.2WZC under transient thermal shock is 0.22-0.33 GW/m2,while that of 2.8WZC is lower than 0.22 GW/m2,which is closely related to the strength and plasticity.According to the grain size effect,the properties of the alloy were further controled from the perspectives of refining grain size,reducing the initial oxygen content of tungsten powder,and adding strengthening dissolved elements.When the particles were refined to submicron level by rapid sintering,the size of the nanoparticles was 24 nm,and the samples had higher hardness(590 Hv)and higher thermal conductivity(143 W/m·K).The ductile-brittle transition temperature of WZC prepared by oxygen content reduction is lower than 70?,the UTS at 70? reaches 1279 MPa,and the UTS at 150? reaches 1022 MPa,which is increased by?90 MPa compared with 0.5WZC of 932 MPa.The low temperature brittleness of WZC is further improved.However,the addition of solid solution element Re significantly increases the high temperature strength of the alloy.The ultimate tensile strength of the alloy at 400 ? is still 841 MPa,which is?200 MPa higher than that of WZC.Its excellent comprehensive properties come from the following effedts:fine grain strengthening achieved by rolling deformation,the nailing effect of the second phase particles,and the hysteretic diffusion effect of the solution elements.The tungsten-based alloy with multi-scale interface structure prepared in this paper has excellent comprehensive properties.The preparation method and design idea of the tungsten-based alloy provide ideas for engineering application of plasma materials in fusion reactor.