激光冲击对GH742镍基合金疲劳短裂纹扩展的影响

Influence of laser shock processing on short crack growth of GH742 nickel-base alloy

对GH742镍基高温合金紧凑拉伸件预制裂纹,并分别进行1次及3次搭接激光冲击处理,利用复型技术和光学显微镜研究了镍基合金的裂纹起源、裂纹分布及尺寸演化全过程。结果表明,未作激光冲击强化试样形成的是沿晶裂纹,晶界处大量位错塞积群造成很高的应力集中;而经激光冲击强化后试样在远离冲击强化区域以裂纹群的形式萌生,且大约集中在同一时段萌生,疲劳后期萌生的新裂纹条数不多,且激光冲击作用的次数越多,裂纹扩展速率越小,激光冲击处理产生的强化效应能大大降低裂纹扩展速率,在某些强化区还能明显提高应力强度因子门槛值。

Cracks were prefabricated on compact tension specimen of nickel-base alloy GH742. Laser shock process was carried out once and overlapped three times. The whole crack initiation process, distribution and size evolution of the alloy were studied with replica technique and optical microscope. The results show that intergranular cracks are created in samples without laser shock processing（ LSP）, and great numbers of dislocation accumulation groups at the grain boundary leads to high stress concentration. While samples with LSP the cracks initiate in the form of crack groups in regions distant from shocking and strengthening zone, and in the same period of time for initiation. There are not many cracks created after fatigue, and their propagation rate decreases as LSP times increase. The effect of LSP can reduce the propagation rate of cracks greatly, and raise the factor threshold of stress intensity significantly in some strengthened regions.