Isothermal low-cycle fatigue and fatigue-creep of Haynes 230

Service temperature of airplane gas turbine engine combustors fluctuates between ambient to as high as 982 degrees C, during which structural constraints induce cyclic stresses and strains resulting in thermomechanical fatigue damage accumulation in the combustor liner. In order to substantially improve the current design methodologies or low-cycle fatigue (LCF) life predictions of such high-temperature components, it is essential to develop an experimentally validated advanced constitutive model. This requires a broad set of fatigue data of the combustor liner material, Haynes 230 (HA 230) - a nickel-based superalloy, to characterize its fatigue failure responses. Hence, a systematic set of isothermal experiments are conducted prescribing uniaxial strain-controlled loading cycles, with and without a compression peak strain-dwell, with and without a mean strain, at seven different temperatures in the range of 24-982 degrees C and at three strain rates. The experimental responses are critically examined to explore various fatigue failure responses of HA230, which is a complex material showing unique fatigue-creep, strain rate sensitivity, strain range dependence, temperature dependence and dynamic strain aging (DSA) properties. DSA is found to occur in the temperature domain 427-760 degrees C. Isothermal experimental responses at different strain rates show that HA 230 can be considered rate-independent at and below 760 degrees C. However, stress relaxation is observed at lower temperatures up to 649 degrees C during the peak strain-dwell period. Finally, fatigue lives of HA 230 from the isothermal experiments are found to decrease with increase in temperature. These experimental responses are presented and challenges in constitutive model development are discussed. (C) 2016 Elsevier Ltd. All rights reserved.