Mechanical Strength Evaluation of Superconducting Magnet Structures by HIP Bonding Method

MTC proposed that production of the International Thermonuclear Experimental Reactor (ITER) toroidal magnetic field coils support structure "Radial Plate (RP)" using the HIP diffusion bonding. HIP allows production cost reductions in materials and machining time. However, insufficient strength of the HIP diffusion bonded sections was an issue. In this study, changes in bonding strength and base material strength were investigated using HIP treatment temperatures as parameters. Mechanical property tests and microstructure observation of the cross sections at the bonded areas after HIP treatment were conducted and as a result it was found that the bonding strength equivalent to the mechanical strength of the base metal can be obtained at 1300[°C]. However, the yield strength at room temperature of the base material after HIP treatment decreased by 24%. Since crystal grain coarsening occurs due to heat input by HIP, design considerations are required to guarantee the specified strength. Furthermore, a full-size mock-up of RP segments was fabricated by HIP. It was confirmed that the yield strength and fracture toughness at 4 [K] at the bonded sections of the mock-up satisfied the specified values required for the RP and uniform quality was obtained. From this study, it was proven that HIP diffusion bonding can be applied to the fabrication of RP segments.