Near-Threshold Fatigue Crack Propagation in Sintered 304L Stainless Steel Compact with Network Structure Composed of High-Entropy CrMnFeCoNi Alloy

High-entropy alloys (HEAs) have several superior mechanical properties. However, for these alloys, there is a trade-off between tensile strength and fatigue-crack propagation resistance, as is the case for materials with a homogeneous microstructure. The purpose of the present study is to achieve both high-strength and fatigue-crack propagation resistance by using a bimodal structure. CrMnFeCoNi alloy and AISI304L powders with different particles diameters are mixed and then consolidated using spark plasma sintering to fabricate sintered compacts with a network structure composed of coarse-grained 304L surrounded by fine-grained HEA microstructure. Stress intensity factor K-decreasing tests are conducted at various force ratios in the ambient laboratory atmosphere to examine near-threshold fatigue-crack propagation in the sintered compacts. The ductility and threshold stress intensity range Delta K-th tested at a high force ratio for the sintered compacts are higher than that for a homogeneous fine-grained CrMnFeCoNi alloy. Fatigue cracks in the sintered compacts mainly propagate through the coarse-grained 304L microstructure, which has high-fatigue-crack propagation resistance near the threshold. Therefore, Delta K-th for the sintered compacts increases because the Delta K-eff,K-th, which is derived from the 304L without degrading the tensile strength, is higher than that for homogeneous fine-grained CrMnFeCoNi alloy.