Evolution of interfacial microstructure and oxides of CLAM steel by hot compression bonding

Abstract

The development of the joining process is essential for the application of China low activation martensitic (CLAM) steel as the structural material for fusion reactors. In the present study, the hot compression bonding (HCB) for CLAM steel was carried out under different parameters. The effects of different strain rates, temperatures, strains and holding time on the evolution of interfacial microstructure and oxides were investigated. Compressed at 1000 °C with 5% deformation, some micron-size continuous oxides distributed along the flat interface. The interfacial oxides were broken and decomposed as the deformation increased to 20%, their average size was reduced to 400 nm. With the bonding temperature increasing, more interfacial grain boundaries (IGBs) could cross the original bonding interface and flat interface became wavy. Compressed at 1000 °C/20%, the interfacial oxides consisted of fcc-structured spinel MnCr2O4 and enriched in Si and Ta oxides. The MnCr2O4 oxides would decompose preferentially after 0.5 h holding treatment at 1100 °C. Only a small number of oxides rich in Si and Ta elements remained at the original bonding area after 2 h holding treatment. Compressed at 1100 °C/20%, the bonding interface was completely replaced by the migrated grains after 2 h holding treatment and no large-size oxides could be observed. Moreover, the tensile strength and elongation at room temperature of the joint were comparable to those of the base material.