Abstract
From the required characteristics of structural material for high response excitation superconducting generators, precipitation hardened Ni base alloys such as Inconel 718, were considered as candidate materials. To improve weldability and make a large size ingot, the chemical composition range of 4.0≤Nb+Ti≤4.5% was determined. Based on the above chemical composition, a thinwalled forged ring, welded at the center, was manufactured. Material strength and physical property tests were conducted systematically from 4K to room temperature for base metal and weld metal of this ring. From the material strength tests, as expected, the material strength rose with falling temperature, but ductility and toughness were almost constant for both of these materials. Also, it was shown that if the sample was re-annealed and aged after welding, original characteristics of the base metal were recovered in this precipitation-hardened material. The physical properties of thermal expansion, electrical resistivity, and magnetization, were also measured. From the comparison of mechanical and physical properties of this material with those of Inconel 718, it was clarified that the differences of characteristics of these materials were closely related with chemical compositions of Nb+Ti and Ni, respectively.
