Research On Joining Of Carbon And Tungsten Based Plasma Facing Materials To Heat Sinks

Joining of carbon and tungsten?W?plasma facing materials?PFMs?to heat sink materials?including copper alloy and steel?is of great importance in fusion reactor applications.However,the joining meets difficulty due to their large differences in physical properties.In this study,joining of graphite/CuCrZr,W/CuCrZr and W/stainless steel 301?SS301?has been realized with Cu-22TiH₂ filler.The microstructure and mechanical properties of joints have been characterized.The interface evolution of joints has been discussed.It is expected that this study can provide technical reference for the fabrication of carbon and W plasma facing components.For the graphite/CuCrZr joints brazed using Cu-22TiH₂ filler and Cu foil as filler,a TiC reaction layer is formed between the filler layer and graphite substrate,and inter-diffusions occur at the interfaces of Cu-22TiH₂/Cu foil and Cu-22TiH₂/CuCrZr.The structure of joint,graphite/Ti C/Cu based solid solution?Cu?s,s??+Ti-Cu intermetallics/Cu interlayer/Cu?s,s?+Ti-Cu intermetallics/CuCrZr alloy,is obtained.The average shear strength of the joints is 95%of the graphite strength,indicating that the Cu foil could benefit the relaxation of thermal residual stresses in joints.For the W/CuCrZr joints brazed with Cu-22TiH₂ filler,no inter-diffusions occur between the W substrate and the filler.The filler layer is mainly composed of Cu?s,s?,TiCu₄,TiCu and Ti₂Cu phases.The microhardness of the W substrate is similar to that of as-received(463 HV_0.1),but the microhardness of CuCrZr is about 80 HV0.1,drastically lower than that of as-received,mainly caused by the recrystallization and grain growth.The hardness of the filler layer is 133±17 HV_0.1,higher than that of CuCrZr but lower than that of Ti-Cu intermetallics.For the W/SS301 joints brazed with Cu-22TiH₂,the filler layer in the joining area is mainly composed of Cu?s,s?,and intermetallic Ti-Cu and?Fe,Cr?₂Ti phases.Furthermore,a diffusion layer containing?-phase is developed adjacent to the SS301 substrate,and a wave-like reaction layer of?Fe,Cr?₂Ti is formed between the filler layer and the?-phase layer.The hardness of SS301 substrate decreases to 275 HV_0.1 due to the recrystallization and grain growth during the joining process.The hardness of the filler layer and?Fe,Cr?₂Ti reaction layer is 358±8 HV_0.1 and 475±22 HV_0.1,respectively,whereas the?-phase layer obtains the highest microhardness(571±23 HV_0.1)in the joints.The average shear strength of both W/CuCr Zr and W/SS301 joints is higher than 95MPa,indicating the favorable bonding between Cu-22TiH₂ filler and substrates,which contributes to potential applications in the fabrication of plasma facing components.