Microstructural assessment of fractional life approach to low-cycle fatigue at high temperatures

Abstract

Load- or strain-controlled cycles have been used to assess the low-cycle fatigue behaviour of the wrought Ni-Cr-base alloy IN 597, mainly at 850°C. Very large reductions in cyclic endurance were produced by the introduction of tensile dwell periods. Dwell periods of only a few seconds duration changed the mode of fracture from transcrystalline to predominantly intercrystalline with extensive grain boundary cavitation. Evaluation of the data by existing analytical procedures showed that a simple fractional life expression was suitable for both load- and straincontrolled cycling and gave cyclic endurance predictions within a factor of ± 2. Quantification of microstructural damage provided evidence supporting the fractional life concept.