应力比对热等静压Ti-6Al-4V钛合金疲劳裂纹扩展速率的影响

采用标准C(T)试样测定热等静压Ti-6Al-4V钛合金在应力比R=0.1、0.4和0.7的条件下疲劳裂纹扩展速率,获得相应条件下的疲劳裂纹扩展数据,绘制了对应的裂纹扩展速率与应力场强度因子(da/dN-ΔK)关系曲线,并结合疲劳裂纹扩展路径和断口形貌分析探究应力比R对热等静压Ti-6Al-4V钛合金裂纹扩展速率的影响。结果表明,随着应力比R的增大,裂纹扩展门槛值ΔKtn减小。相同ΔK下,裂纹扩展速率da/dN随应力比R一同增大,致使da/dN-ΔK关系曲线向左上移动;裂纹能够穿过等轴晶α相和纤薄的α片层结构呈直线型扩展,遇到较厚的α片层结构时,裂纹偏转并沿原始α片层方向继续扩展,最终发生断裂;断口由预裂区、稳态扩展区和快速断裂区构成,分别对应于疲劳裂纹扩展的三个阶段。

Effect of Stress Ratio on Fatigue Crack Growth Rate of Hot Isostatic Pressing Ti-6Al-4V Titanium Alloy

The fatigue crack growth rate of hot isostatic pressing Ti-6Al-4V titanium alloy at different stress ratios (R=0.1, 0.4 and 0.7) was studied by standard C(T) specimens. Then obtained the data of fatigue cracks growth rate and plotted the relationship between crack growth rate and stress field strength factor. The effects of stress ratio R on the fatigue crack growth rate was investigated by combining the fatigue crack growth path and fracture morphology analysis. The results show that as the stress ratio R increases, the crack growth threshold ?Kth decreases. Under the same ?K condition, the crack growth rate da/dN increases with the stress ratio R, causing the da/dN-?K relationship curve to move to the upper left. The crack can extend linearly through the equiaxed alpha phase and the thin alpha layer structure. When a thick alpha layer structure is encountered, the crack deflects and continues to expand along the original alpha layer, eventually breaking.The fracture is composed of a pre-crack zone, a steady-state extension zone and a rapid fracture zone, corresponding to three stages of fatigue crack growth.