表面微喷丸对CuNi2Si合金疲劳短裂纹行为影响

在拉压载荷作用下，分别开展了CuNi₂Si合金微喷丸前后漏斗型圆棒试样的疲劳短裂纹复型试验；试验在预先确定的一系列载荷循环周次中断，以使用醋酸纤维膜对试样表面进行复型，进而采用逆序观察法获取了短裂纹萌生与扩展相关数据。分析结果表明:2种试样疲劳裂纹均萌生于试样表面，裂纹扩展受微观组织影响呈现曲折性增长, 整体表现出初期增长缓慢，后期裂纹长度迅速增长至试样断裂的趋势, 失稳扩展临界尺度约为750.0 μm; 微喷丸处理可以使裂纹增长模式由以晶间为主转为以穿晶为主，微喷丸前后断口形貌表现出巨大差异，相对未喷丸试样，微喷丸试样裂纹萌生位置呈现较大的晶体平面，无明显晶粒特征，裂纹源区面积较小，在疲劳过程中产生的纤维条纹数量较多，瞬断区韧窝形貌更为明显; 经微喷丸处理后，试样平均疲劳寿命提高约31.5倍，裂纹萌生和缓慢扩展阶段占比从整体疲劳寿命的60%增加至80%，可知微喷丸处理对于疲劳寿命的大幅提高主要体现在短裂纹的萌生和稳定扩展阶段，而这种强化效果主要受表面有效应力、硬度、晶界数目的共同影响，但该强化效果对疲劳裂纹扩展后期影响不大。 

Influence of surface micro shot peening on short fatigue crack behavior of CuNi2Si alloy

Under tension-compression loading, the fatigue short crack replica tests of funnel-shaped round bar specimens of CuNi₂Si alloy with/without micro-shot peening were carried out, respectively. Tests were interrupted at a series of predetermined load cycles to replicate the surface of the specimen with acetate film, and then the data related to short crack initiation and propagation were obtained by using the reverse order observation method. Analysis results show that the fatigue cracks of both types of specimens initiate on the surface. The crack shows a zigzag growth under the influence of microstructure. In general, it shows a trend of slow growth in the early stage followed by a rapid growth in the later stage until the fracture of the specimen, with a critical instability crack propagation size of about 750.0 μm. With the introduction of micro shot peening technology, the crack growth process changes from the intergranular mode to the transgranular mode. The fracture morphologies of specimens with/without micro shot peening are very different. Compared to un-peening specimens, micro shot peening specimens show a larger crystal plane in the crack initiation position without obvious grain characteristics. They show smaller crack source area, larger number of fatigue stripes produced in the fatigue process, and more obvious dimple morphology in the instantaneous fracture area. After micro shot peening, the average fatigue life of the specimens increases approximately 31.5 times, and the fatigue life proportion occupied by the stage of crack initiation and slow growth increases from 60% to 80%, indicating that the significant increase in fatigue life is mainly reflected in the initiation and stable propagation stage of short cracks. The strengthening effect is mainly affected by the surface effective stress, hardness, and the number of grain boundaries, but it has little effect on the later stage of fatigue crack growth. 3 tabs, 11 figs, 30 refs.