Fatigue strength of Inconel 625 plate and weldments used in the DIII-D configuration vacuum vessel

The Doublet III-D vacuum vessel will enable fusion experiments with large dee-configuration plasmas in the tokamak device at GA Technologies Inc. The vessel is a welded structure of Ni-Cr-Mo-Nb alloy Inconel 625, in the forms of mill-annealed plate and sheet. An emphasis was placed on spceifying material with small grain size to enhance fatigue resistance. Fatigue strength was determined by tension-compression axial strain cycling of specimens excised from stock plate 25 mm thick. In addition, tests were conducted on gas-tungsten-arc weldments. The strain ranges and the resulting alternating, which produced fatigue lives between 103 and 106 cycles, were determined in the test program. Comparisons are presented with published data obtained using the rotating-beam test method. A discussion is also presented on the effect of the grain size on fatigue strength