Fabrication of monoblock high heat flux components for ITER divertor upper vertical target using hot isostatic pressing diffusion welding

The monoblock concept is one of the most promising design concepts for high heat flux (HHF) components to be used in international thermonuclear reactor (ITER) divertor area. The fabrication of monoblocks is difficult due to the thermal expansion mismatch between copper alloy and tungsten. To overcome this problem, a Cu-OFHC compliant layer is used. A hot isostatic pressing diffusion welding (HIP-DW) technique is proposed. Diffusion welding experiments using flat samples were performed to determine suitable metallurgical conditions and HIP parameters for diffusion welding of W to Cu and Cu to CuCrZr alloy. A thin nickel interlayer providing metallurgical compatibility between W and Cu was tested. Diffusion welding of Cu to CuCrZr is limited by the Cu alloy ageing temperature, however a HIP diffusion brazing (HIP-DB) technique was successfully tested. Simultaneously, finite element modelling was used to improve the joint design: it was shown that the use of chamfered tiles allows reducing the high stress concentration on cooling.