Effect of Temperature on Low-cycle Fatigue Properties of Ni-base Superalloys for HTGR

Abstract

In order to obtain fundamental information on the effect of test temperature on the low-cycle fatigue properties of two Ni-base wrought alloys, namely Inconel 617 and Hastelloy XR, a set of strain controlled fatigue tests has been carried out at temperatures up to 1000°C in air and partly in vacuum under a fully reversible triangular and a strain-hold waveforms.
Cyclic hardening behaviors were observed at temperatures up to 800°C. The fatigue life was reduced with increasing temperature. At high temperatures above 800°C the following results were obtained. The difference of lives between in air and vacuum became larger. The intergranular failure was dominant and the range of transition temperature from transgranular to intergranular was 600800°C depending on the strain range and waveform.Experimental fatigue lives for both alloys were shorter than fatigue lives predicted by the universal slope method and 10% rule.
Thus, the effects of creep deformation and high temperature oxidation on the fatigue properties were significant at high temperatures.