GH4742合金疲劳裂纹扩展行为

Fatigue crack growth behavior of GH4742 alloy

研究GH4742合金在室温、700℃及750℃的疲劳裂纹扩展行为。分析温度和应力强度因子对疲劳裂纹扩展寿命与速率的影响,利用扫描电镜观察不同温度下的疲劳裂纹扩展断口。采用背散射电子衍射(EBSD)技术分析合金裂纹扩展的晶体学机制。结果表明,随着温度的升高,合金的裂纹扩展寿命降低,裂纹扩展速率增加,沿晶断裂特征更明显。应力强度因子越大,裂纹扩展速率越大。在原始大变形晶粒中裂纹以穿晶方式沿着小角度晶界扩展,裂纹扩展到再结晶晶界时以沿晶扩展为主,其扩展方式取决于相邻晶粒的面间角和取向差。

The crack propagation behavior of GH4742 alloy was studied respectively at room temperature, 700 ℃ and 750 ℃. Fatigue fracture was observed by scanning electron microscopy(SEM). Effects of temperature and stress intensity factor(ΔK) on crack growth life and rate were studied. The electron back scattering diffraction(EBSD) technique was applied to investigate the crystallographic mechanism of crack propagation. The results show that with the increase of temperature, crack propagation life of the alloy decreases and crack propagation rate increases as well as the intergranular fracture characteristics is more obvious. Crack growth in the original large deformation grain is in a transgranular manner along a low angle boundary. While crack meets the recrystallized grain boundaries, the mode of fracture is mainly the intergranular expansion and the way of crack growth depends on the magnitude of the interfacial angle and the misorientation of adjacent grain plane.