EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Cyclic loading leads to failure of the material in over 90% of cases. Therefore, it is important to develop materials with a high fatigue strength and to understand them in detail. High-entropy alloys (HEAs) have a great potential for application under cyclic loading, as they exhibit both high fatigue strength and fracture toughness. In addition to these positive characteristics, the fatigue threshold of these alloys can be enhanced specifically by tailoring the microstructure to inhibit crack growth. The combination of equal-channel angular pressing (ECAP) and a subsequent heat treatment is a suitable method to achieve such a tailored microstructure. This has already been studied in detail on conventional Al and Cu alloys. For the promising HEAs, however, the relation between ECAP processing and the resulting microstructure is still far unexplored. In the present study, 3 ECAP passes were performed on the cast HEAs CrFeCoNi and CrMnFeCoNi in a 120° die. The ECAP billets were examined both before and after heat treatment by quasi-static tensile tests and microstructural investigations using scanning transmission microscopy (STEM) and electron backscatter diffraction (EBSD). Further, the threshold against crack propagation was determined for the ECAP-processed CrFeCoNi and CrMnFeCoNi both with and without a subsequent heat treatment using a resonant testing machine at a load ratio of R = 0.1. The results of this study show a significant influence of the microstructure of CrFeCoNi and CrMnFeCoNi HEAs produced by severe plastic deformation and subsequent heat treatment on the fatigue threshold. The understanding of this relation allows for a tailored microstructure of the investigated HEAs in order to increase the fatigue threshold.