1240MPa级Ti-38644高锁螺栓的拉伸疲劳增寿机理

用扫描电镜和能谱观测分析Ti-38644高强钛合金高锁螺栓的拉伸疲劳断口,揭示了高锁螺栓的疲劳裂纹萌生和扩展的微观特征和疲劳增寿机理。结果表明,Ti-38644高强钛合金高锁螺栓的疲劳断口包括疲劳裂纹萌生区、扩展区和瞬断区:疲劳裂纹从螺栓头下圆角滚压薄弱部位表面萌生,随后在基体中呈放射性扩展;进入扩展区后裂纹的尺寸由微观扩展至宏观,以疲劳条带扩展机制为主,同时也存在解理断裂。头下圆角处的变形层对Ti-38644高锁螺栓的疲劳寿命有显著的影响,变形层使Ti-38644钛合金高锁螺栓的疲劳寿命明显提高。通过微观组织与疲劳寿命的对比,探讨了Ti-38644钛合金高锁螺栓疲劳强化的作用机理。

Mechanism of Fatigue Life Enhancement for 1240 MPaHi-lock Bolt of Ti-38644 Ti-alloy

The tension-tension fatigue fracture for Hi-lock bolts of Ti-38644 high strength Ti-alloy has been investigated using SEM and EDS in order to reveal the microscopic characteristics of crack initiation and crack propagation, as well as the mechanism related with fatigue life enhancement. The fatigue fracture zone for Hi-lock bolt of Ti-38644 Ti-alloy can be divided into three parts: fatigue crack initiation zone, crack propagation zone and instant break zone. The fatigue cracks initiate from the surface of weak part under the bolt head, then radially propagate in matrix. The sizes of fatigue cracks display a transition from microscopic to macroscopic, once in the propagation zone. The fatigue band extension becomes the main mechanism, meanwhile, the typical features of cleavage fracture can be observed. The fatigue life for Hi-lock bolt of Ti-38644 Ti-alloy is significantly affected by deformation layer at the fillet, which may enhance the fatigue life-time for the Hi-lock bolts of Ti-38644 Ti-alloy with such deformation layer. The mechanism of strengthen anti fatigue has also been discussed by comparing the microstructure observation data and fatigue test results from different Hi-lock bolts of Ti-38644 Ti-alloy.