Characterization of the CuCrZr alloy and the Cu/ss joints for ITER first wall

As the ITER first wall material, Cu-alloy should satisfy the ITER specification for the material. The alloy would be influenced not only by thermo-mechanical process but also by the neutron radiation. It is thus necessary to study the effect of heat treatment on the microstructure and mechanical properties of the alloy. Besides, as a heat sink material, the alloy would be bond to a support back plate of 316LN steel in the FW panel. Mockups of Cu/ss joints have been fabricated by a hot isostatic pressing (HIP) process. The interface needs to characterize to understand the bonding mechanism. According to the material specification for the supply of CuCrZr-ITER Grade alloy plates for the ITER First Wall, CuCrZr alloy was prepared by vacuum melting. Ingots were then forged and hot-rolled to 13-18 mm thick plate. Samples were cut from the plates. They were solid solution annealed at 960-1040 degree C for 30 minutes, followed by aging at 475 degree C and 580 degree C. Tensile tests were conducted at RT and 250 degree C. The microstructure of the alloy was analyzed. Results showed the significant effect of the heat treatment on the microstructure and the tensile strength. For the Cu-SS joining, the HIPing method showed promising. Bonding strength was measured by tensile test at RT and the interface was observed by SEM. No defects at the interface were found by optical microscopy and SEM observation. However, the grains of Cu-alloy in the vicinity of interface are inhomogeneous, fine grain near the interface but very large ones in the faraway area. EDS analysis shows the change of alloy element content and microstructure across the interface. (authors)