Small fatigue crack growth in a high entropy alloy

Abstract

High-entropy alloys (HEAs) contain a large amount of solid solution elements. This implies that the high capability of solid solution strengthening is expected to increase the resistance to fatigue crack growth. Therefore, we investigated the characteristics of microstructurally small fatigue crack growth of an HEA. In particular, we focused on microstructural fatigue crack growth behavior and associated scatter in crack growth rates. In this study, we used an equiatomic Fe-20Cr-20Ni-20Mn-20Co HEA and an Fe-18Cr-14Ni stable austenitic stainless steel. Rotating bending fatigue tests were performed at ambient temperature using smooth round bar specimens. The fatigue limits of the HEA and stainless steel were 250 and 200 MPa, respectively. The higher fatigue limit of the HEA was attributed to the solid solution strengthening. Furthermore, the scatter in crack growth rates of the HEA was more significant than that of the stainless steel owing to the temporal deceleration or non-propagation of the crack. In the stainless steel, as the crack length increased, the scatter in crack growth rates decreased. In contrast, in the HEA, even if the crack length increased, the scatter in crack growth rates remained significant As a factor that is perhaps related to the scatter characteristics, fatigue cracks with a length of approximately 500 µm in the HEA were highly deflected, compared to those of the stainless steel.