This study presents a comprehensive exploration of the fatigue response in the very high cycle fatigue (VHCF) regime for an additively manufactured (i.e., laser powder bed fused) A20X aluminum alloy. Although the need for high-performance materials with exceptional fatigue qualities has increased dramatically, the VHCF behavior of Al-Cu-Mg-Ag-TiB (A20X) structures remains largely unknown. A series of ultrasonic fatigue tests were performed to assess the prolonged fatigue life of the A20X alloy (in the VHCF domain where the number of cycles to failure is beyond 10 million cycles). The VHCF response, assessed through ultrasonic fatigue testing, was investigated by examining the stress-life (S-N) curves in a statistical framework, the fatigue crack initiation and propagation behavior, and the fracture surfaces. An asymptotic trend was experimentally found at 10 cycles, with a stress amplitude of 110 MPa for stress-relieved (SR) and 125 MPa for artificially aged (T7) materials, indicating the presence of an endurance limit. Furthermore, fracture surfaces showed the typical fisheye morphology, with a fine granular area (FGA) containing an internal crack-initiating site. The findings of this paper can assist in optimizing fatigue and durability design allowable for applications for extended fatigue life in the VHCF domains.

中文翻译：

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激光粉末床熔融 Al-Cu-Mg-Ag-TiB2 (A20X) 合金的极高循环疲劳：应力消除和时效处理

本研究对增材制造（即激光粉末床熔融）A20X 铝合金在极高循环疲劳 (VHCF) 状态下的疲劳响应进行了全面探索。尽管对具有卓越疲劳性能的高性能材料的需求急剧增加，但 Al-Cu-Mg-Ag-TiB (A20X) 结构的 VHCF 行为仍然很大程度上未知。进行了一系列超声波疲劳测试，以评估 A20X 合金的延长疲劳寿命（在 VHCF 领域，失效循环次数超过 1000 万次）。通过检查统计框架中的应力-寿命 (SN) 曲线、疲劳裂纹萌生和扩展行为以及断裂表面，研究了通过超声波疲劳测试评估的 VHCF 响应。实验发现在 10 个循环时渐近趋势，应力消除 (SR) 材料的应力幅度为 110 MPa，人工时效 (T7) 材料的应力幅度为 125 MPa，表明存在耐久性极限。此外，断裂表面呈现出典型的鱼眼形态，具有包含内部裂纹起始位点的细颗粒区域（FGA）。本文的研究结果有助于优化疲劳和耐久性设计，从而适用于 VHCF 领域中延长疲劳寿命的应用。