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 V-notch 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.

中文翻译：

---

增材制造 CrCoNi 中等熵合金的低温冲击和疲劳性能


对于承受快速和循环载荷的结构应用，冲击韧性和疲劳强度是决定材料适用性的关键特性。CrCoNi 中等熵合金 （MEA） 因其卓越的机械性能而受到关注。因此，在恶劣环境下评估这种合金的结构完整性至关重要。本研究研究了通过激光粉末床熔融 （LPBF） 加工的 CrCoNi MEA 在室温和低温下的影响和疲劳性能。夏比 V 型缺口冲击试验在 298 K、200 K 和 77 K 下进行，而高周疲劳试验在 298 K 和 150 K 下进行。结果显示，在所有温度下都具有出色的冲击韧性，尽管韧性会随着温度的下降而降低。在 298 K 时，简支梁冲击试样表现出更显着的变形，裂纹主要沿着晶界发展，而在 200 K 和 77 K 时，跨晶裂纹占主导地位。此外，LPBF CrCoNi MEA 在 150 K 下的疲劳性能与 298 K 下的疲劳性能相比显示出显着改善，这归因于疲劳过程中在较低温度下形成的变形孪晶的密度较高。这些发现表明，LPBF CrCoNi MEA 在低温下提供了有前途的冲击和疲劳性能组合，表明其适用于低温应用。