Development of High Strength Tungsten/Oxide Dispersion Strengthened Ferritic Steel Joints by Innovative Thermal Stress Relaxation Technique Based on Phase-Transformation-Induced Creep Deformation

抄録

The realization of fusion reactors rests on the function of the blanket systems with high thermal efficiency consisting of armor and structural materials. The fabrication of the blanket requires upgrade of bonding technology which makes the components reliable. The combination of tungsten and oxide dispersion strengthened ferritic steel (ODS-FS) is considered to be adequate for the application to the fusion diverter components. The issue of diffusion bonding of tungsten with ODS-FS is to reduce thermal stresses caused by a large difference in thermal expansion coefficient between the two materials. In this study, an innovative thermal stress relaxation methodology during cooling has been newly proposed as a key technology in joining, which is based on the phenomenon of γ→α phase transformation-induced creep deformation of low carbon steel inserted between tungsten and ODS-FS. In the cooling pattern where the joint was slowly cooled at a rate of approximately 1.6℃/min from 800℃ to 600℃. The application of the technology to the diffusion bonding of tungsten/ODS-FS resulted in a very high bonding strength of 480 MPa, which has never been achieved so far by the conventional bonding methodologies.