Dwell sensitivity fatigue behavior of high temperature materials

The dwell sensitivity fatigue behavior of six high temperature materials is examined in this paper: two stainless steels, 304L and 304, two tantalum alloys, T-111 and ASTAR 811C, pure nickel Ni 201 and a single crystal nickel-base superalloy, PWA 1480. The stainless steel alloys were found to be tensile dwell sensitive; however, a saturation in dwell sensitivity was found with the increase in strain range for all materials examined. At lower strain ranges the dwell cycles were producing lower lives than at higher strains, as found in the case of AISI SS 304 and two Ta based alloys, T-111 and ASTAR 811C. Trends in various normalized life curves were found to be strain dependent for ASTAR 811C, in which < 0.2% inelastic strain range, dwell effects were more deleterious than above it. Mechanistic aspects under different test conditions were summarized.