Exceptional cryogenic impact and fatigue properties of additively manufactured CrCoNi medium entropy alloy

For structural applications subjected to rapid and cyclic loading, impact toughness and fatigue strength are critical properties that determine material suitability. CrCoNi medium entropy alloys (MEAs) have garnered attention due to their exceptional mechanical properties. Therefore, it is essential to assess the structural integrity of this alloy under harsh environments. This study investigates the impact and fatigue properties of CrCoNi MEA processed via laser powder bed fusion (LPBF) at both room and cryogenic temperatures. Charpy Vnotch impact tests were conducted at 298 K, 200 K, and 77 K, while high-cycle fatigue tests were performed at 298 K and 150 K. The results show exceptional impact toughness at all temperatures, although toughness decreases as temperature drops. At 298 K, Charpy impact specimens exhibit more significant deformation, with cracks primarily following grain boundaries, while at 200 K and 77 K, trans-granular cracking dominates. Additionally, fatigue properties of LPBF CrCoNi MEA at 150 K show significant improvement compared to those at 298 K, attributed to the higher density of deformation twins forming at lower temperature during fatigue. These findings demonstrate that LPBF CrCoNi MEA offers a promising combination of impact and fatigue properties at cryogenic temperatures, suggesting its suitability for cryogenic applications.