Study On Fabrication Of W/Cu/CuCrZr Plasma Facing Components In Controlled Nuclear Fusion Reactor

The divertor in the International Thermonuclear Experimental Reactor(ITER)is mainly made of W/Cu/CuCrZr laminated composites and joints.W is mainly used as the plasma facing material,CuCrZr is used as the heat sink material,and Cu is used as the middle layer to relieve thermal stress between W and CuCrZr.Therefore,the layered compositing and joining of W and Cu,Cu and CuCrZr are key technologies for the preparation of divertor.At present,the preparation methods of W/Cu and Cu/CuCrZr laminated composites and joints at home and abroad usually have extreme process conditions,which will produce large residual stress.In addition,these W/Cu and Cu/CuCrZr layered compositing and joining techonologies often need to use interlayer metals,which will decline the overall thermal conductivity of W/CuCrZr layered composites and joints.At present,the temperatures of Cu/CuCrZr layered compositing and joining technologies are higher than the optimal aging temperature of CuCrZr(475 °C),which will soften CuCrZr.In view of the above problems,this paper improves the surface energy of W through fabricating nanopores on W surface,and then compositing and joining of W to Cu.Then,Cu and CuCrZr were composited and joined by direct diffusion bonding at low temperature.The metallurgical bonding interfaces between W and Cu,Cu and CuCrZr have been successfully achieveed,and the W/Cu,Cu/CuCrZr and W/Cu/CuCrZr layered composite materials and joints have been obtained.The results are as follows:(1)Nanoporous oxide layer was prepared on W surface by two-step anodizing,then deoxidized in hydrogen atmosphere,and the nanoporous pure metal structure was formed on the surface of W.Then,Cu was electroplated or superimpositioned on W surface.The diffusion and alloying of W and Cu were realized by high temperature annealing close to melting point of Cu(the diffusion distance reached 25 nm).W/Cu layered composites and joints were successfully fabricated by compositing and joining of W-Cu annealed specimens to Cu.The average shear strength of W/Cu interfaces is about 101 MPa.(2)The thermodynamic model and calculation method of W/Cu direct alloying established by Miedema's theory and Alonso's calculation method in the previous work of our group were improved,and a new calculation method of surface energy and pressure energy was proposed.On this basis,the thermodynamic mechanism of W/Cu direct alloying based on fabricating nanopores on W surface was studied.The results show that it is feasible to realize W/Cu direct alloying based on fabricating nanopores on W surface in thermodynamics.The surface energy of W-Cu system has been greatly improved,which can be used as the thermodynamic driving force of direct alloying of W and Cu.(3)Cu/CuCrZr high strength layered composites and joints were successfully fabricated at 450 ? under 100 MPa for 180 min by rigorous treatment of the mating surfaces of Cu and CuCrZr.The average shear strength and shear strength of Cu/CuCrZr interface reach 128 MPa and 180 MPa.The Brinell hardness of CuCrZr did not obviously decrease,so the softening of CuCrZr was avoided.The diffusion distance between Cu and CuCrZr reached 15 um,and the effective bonding areas of the Cu/CuCrZr composite plates exceeded 97%.(4)Based on the above research results,two kinds of W/Cu/CuCrZr plasma facing components in ITER were fanricated,including W/Cu/CuCrZr monoblock components and W/Cu/CuCrZr/316 L stainless steel laminated composite components.