初生 α 相对Ti6242s合金在保载疲劳载荷作用下微区塑性变形的影响

Effect of Primary α-Phase on Micro-area Plastic Defor-mation of Ti6242s Alloy Under Dwell Fatigue

摘要:

分析Ti-6Al-2Sn-4Zr-2Mo-0.1Si（Ti6242s）合金的组织特征和疲劳性能的关系。微观组织定量分析结果显示，不同温度固溶处理对初生α相的比例和形貌有明显影响，这些微观结构特征的变化对Ti6242s合金的室温拉伸性能和低周期疲劳性能有轻微的影响，但是对室温保载疲劳和保载疲劳敏感性有明显影响。随后分析证实了Ti6242s合金在保载疲劳载荷作用下存在相对较强的应力集中和不均匀微区塑性变形情况。而且，通过对疲劳失效断口形貌分析也证实了Ti6242s合金在室温保载疲劳下形成小平面特征和附近的准解理断裂区域特征，相关测试结果恰好对应等轴初生α相和附近的软相/软晶粒的微观组织应力应变分布表征结果。因此，在具有较低体积分数等轴初生α相的合金中形成相对较低程度的微区不均匀塑性变形，有助于降低裂纹萌生的概率并延迟裂纹扩展，从而改善保载疲劳性能。

Abstract:

The relationship between microstructure characteristics and fatigue properties of Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti6242s) alloy was investigated. According to the microstructure quantitative analysis results, the solution treatments at different temperatures have an obvious effect on the proportion and morphology of primary α-phase. The changes in microstructure characteristics slightly influence the tensile property and low-cycle fatigue property of Ti6242s alloy at room temperature, whereas the dwell fatigue life and the fatigue sensitivity index are sensitive to these changes. Additionally, it is verified that the relatively strong stress concentration and inhomogeneous micro-area plastic deformation occur in the Ti6242s alloy under dwell fatigue load. Moreover, the characteristics of small plane regions and the surrounding quasi-cleavage regions in the Ti6242s alloy under dwell fatigue load at room temperature are formed through the analysis of fatigue failure fracture morphologies. The related experiment results are in good agreement with the stress-strain distribution characterizations of microstructures of equiaxed primary α-phase and the surrounding soft phase/grain. Accordingly, the relatively low inhomogeneous micro-area plastic deformation in the alloy with equiaxed primary α-phase of low volume fraction is beneficial to reduce the probability of crack initiation and can delay crack propagation, thus improving the dwell fatigue property.