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为分析微粒子喷丸工艺对等温淬火球墨铸铁(ADI)超高周疲劳性能的改善情况,利用旋转弯曲疲劳试验机开展了ADI 109循环周次疲劳试验。对比分析了经微粒子喷丸处理前后试样的疲劳性能,并利用扫描电镜对断口表面进行观察,分析了其超高周疲劳破坏行为。结果表明:未喷丸和喷丸处理后ADI的S-N曲线均表现为典型的阶梯下降型,且在超高周区域没有传统疲劳极限。微粒子喷丸可显著提高原始材料高周阶段的疲劳强度,超高周阶段的疲劳强度也有一定程度的提升。断口观察显示,超高周阶段两种试样均起裂于内部的缩孔或石墨球,并且部分断口表面可观察到粒状亮面GBF(granular bright face)区域。微粒子喷丸所引入的硬化层及残余压应力迫使疲劳裂纹萌生位置向内部转移。通过降低裂纹萌生位置的应力可改善旋转弯曲条件下超高周阶段的疲劳强度。
In order to analyze the improvement of ultrahigh-cycle fatigue performance of the as-quenched nodular cast iron (ADI) by the particle-shot peening process, the cyclic fatigue test of ADI 109 was carried out by using the rotating bending fatigue tester. The fatigue properties of the samples before and after the shot peening were compared and analyzed. The surface of the fracture surface was observed by scanning electron microscopy, and the fatigue failure behavior was analyzed. The results show that the S-N curve of ADI shows the typical step-down type without peening and shot peening, and there is no traditional fatigue limit in the ultra-high-frequency region. Particle shot peening can significantly improve the fatigue strength of the high-cycle stage of the original material, and the fatigue strength of the ultra-high cycle stage also has a certain degree of improvement. Fracture observation showed that both samples in the ultrahigh-frequency stage started to crack in the internal shrinkage cavity or graphite sphere, and the granular bright face GBF (granular bright face) area could be observed on the part of the fracture surface. The hardening layer and residual compressive stress introduced by the shot peening force the initiation of fatigue crack initiation to the interior. The fatigue strength of the ultrahigh-cycle stage can be improved by reducing the stress at crack initiation.