Fatigue performance of Hastelloy X at elevated temperature via small punch fatigue test

Abstract In this study, the fatigue behavior of Hastelloy X at 750 °C is investigated via load-controlled small punch fatigue (SPF) tests, which can overcome the restriction of the material. The fatigue characteristics of the SPF specimens can be reflected by the relationship among the load, number of cycles, and displacement. The displacement–cycle curves of the SPF specimens are segregated into three stages based on the increase in displacement per cycle: the rate of increase first decreases and then remains at a constant value, before finally increasing significantly. It is discovered that the development of the valley displacement per cycle may be associated with the maximum loads and cycle number, based on an empirical equation. Moreover, the area of the hysteretic load–displacement loops of the SPF tests increases gradually as the exerted loads increase and firstly decreases and then remains at a constant value as the cycle number increases. During the SPF tests, many short cracks are initiated and further developed into a circular main crack across the thickness, exhibiting a hexagonal fracture morphology due to localized stress and strain concentrations. Three different class life prediction models, i.e., the Gerber, Goodman and Smith-Watson-Topper average stress correction criterion (SWT–criterion) models, are employed to predict the SPF lives, among which the Gerber and Goodman models yield the higher prediction accuracy.