Dwell effects in isothermal and thermo-mechanical fatigue of advanced materials

Effects of dwell-times in the isothermal fatigue (IF) and thermal-mechanical fatigue (TMF) behaviors of six advanced high temperature materials are investigated in this paper; two of which belonged to types SS 304L and SS 304 stainless steels, two tantalum alloys; T-111 and ASTAR 811C, pure nickel Ni 201 and a nickel based, single crystal superalloy PWA 1480. The SS 304 and 304L steels were found to be sensitive under tensile dwells, however, effect of dwell-times was found to saturate with the increase in strain range (inelastic or total) for all materials examined. At lower strain ranges the effects of dwell-times were found to produce lower lives than at higher strains as in the case of AISI SS 304 and two tantalum based alloys T-111 and ASTAR 811C. Trends in various normalized life curves were found to be near sigmoidal for ASTAR 811C, in which a typical inflection point could be found at nearly 0.2% inelastic strain range. Effects of dwell-times were more deleterious below that strain range and above 0.2% inelastic strain range the effects of dwell-times were nearly the same. Mechanistic aspects under different test conditions were summarized.