Applicability study of Friction-Stir Process on Cu and its irradiation resistivity

Hamaguchi, Dai; Tanigawa, Hiroyasu; Ozawa, Kazumi; Fujii, Hidetoshi*; Morisada, Yoshiaki*

Friction-Stir Process were applied to OFCCu in order to evaluate the applicability of the process to mechanically strengthening pure-Cu and possible structural improvement on CuCrZr alloy. In this study, the tool rotational speed was varied from 50 to 500 rpm in order to clarify the effect of rotational speed on the process. The result showed the achievement of very fine grain structure at the rotational speed of 100 and 200 rpm and also the hardness increase to about 1.5 time higher within the stir-zone than that of the base metal at the most. However, the result also revealed that the rapid decrease of the hardness toward a depth direction and relatively shallow stir-zone depth compared to a length of the pin. This can be explained as post-annealing effect due to a good thermal conductivity of a pure-Cu. To avoid the effect, we are considering to introduce compulsory cooling system during the process, which application is more important to a CuCrZr alloy because more rapid cooling and lower thermal diffusion to base metal are required.