The international experimental fusion project (ITER) has now entered its construction phase. The engineers building the facility will have to integrate and test all essential fusion power reactor technologies and components while demonstrating the safety and environmental acceptability of fusion. As part of this, developing a systematic and thorough framework for the toroidal-field (TF) jacket is extremely important.
As part of this work, a team from the Chinese Academy of Science has now published an extensive observation and analysis of structural transformation for the ITER TF jacket after tensile test at cryogenic temperatures with a phase transformation from γ-austenitic phase to α’-martensite. They found with decreasing the temperature, less external energy is needed to induce the γ-α’ phase change. The maximum volume fraction of α’-martensite phase occurred at fracture and a gradual transformation of γ into α’ occurs parallel the longitudinal direction. Overall microanalysis revealed intersections of deformation bands, dislocation channels and twins on {111} plane as the favorable sites can promote the generation of α’-martensite phase. Their observations may also serve as a guide to predict phase instabilities in TF jacket tube under stress at 4.2 K.
