Abstract High-temperature fatigue test was performed to study the effects of laser peening (LP) on the fatigue behavior of Inconel 718 nickel-based alloy at high temperature. Compressive residual stress (CRS) induced by LP was investigated at both room and high temperature. Microstructural evolution was also studied before and after LP process. The macro- and micro-fracture morphologies in fatigue crack initiation (FCI) region, fatigue crack growth (FCG) region and finial rupture (FR) region of LPed samples with different laser power densities at different temperatures were systematically analyzed. The results showed that LP process can enhance the fatigue life of IN718 nickel-based alloy at both room and high temperature. Excessively high temperature (e.g. 800 °C) may result in a sudden decrease in the fatigue life of LPed samples due to the weakening of grain boundaries and oxidation damage. The losing of coherent strengthen between γ″ phase and matrix was another reason for the rapid reducing of fatigue life. Compared to the untreated samples, the crack source transferred from the surface to deeper layer indicated that LP can retard the crack initiation on the metal surface, which is conducive to enhance the final fatigue life. Some direct evidence, such as the decreased distance between the parallel fatigue striations, the tortuous crack growth path in the LPed specimen confirmed the retarding effects of LP on the FCG. The mechanism of microcracking and the dynamic plastic behavior of LPed specimens during high-temperature fatigue test of IN718 nickel-based alloy were also discussed.

中文翻译：

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激光喷丸对Inconel 718镍基合金高温疲劳寿命及断裂的影响

摘要 通过高温疲劳试验研究激光喷丸处理对Inconel 718镍基合金高温疲劳行为的影响。在室温和高温下研究了由 LP 引起的压缩残余应力 (CRS)。还研究了 LP 工艺前后的微观结构演变。系统分析了不同激光功率密度的LPed样品在不同温度下疲劳裂纹萌生（FCI）区、疲劳裂纹扩展（FCG）区和最终断裂（FR）区的宏观和微观断裂形貌。结果表明，LP工艺可以提高IN718镍基合金的室温和高温疲劳寿命。温度过高（例如 800 °C) 可能会由于晶界减弱和氧化损伤而导致 LPed 样品的疲劳寿命突然下降。γ″相与基体之间失去相干强度是疲劳寿命迅速降低的另一个原因。与未处理样品相比，裂纹源从表面转移到更深层表明LP可以延缓金属表面的裂纹萌生，有利于提高最终疲劳寿命。一些直接证据，例如平行疲劳条纹之间距离的减小，LPed 试样中曲折的裂纹扩展路径，证实了 LP 对 FCG 的阻滞作用。还讨论了IN718镍基合金高温疲劳试验中LPed试样的微裂纹机理和动态塑性行为。