Ti6321合金的拉-扭疲劳行为研究

Research on Behavior of Tensile-torsional Fatigue of Ti6321 Alloy

通过Ti6321合金的拉-扭疲劳试验,对0°和30°相位差的疲劳寿命进行对比分析,研究0°相位差时微裂纹和宏观裂纹扩展路径,并对疲劳断口进行分析。结果表明:相同Mises等效应力幅下,相位差为30°时疲劳寿命相对相位差为0°时的较低;受切应力主要作用,Ti6321合金表面萌生的微裂纹绝大部分分布在与试样轴向夹角20°~30°范围内,且随着等效应力幅增大,拉扭疲劳试样外表面萌生的微裂纹数量也随之增多,主裂纹在扩展过程中与这些微裂纹合并,使得其尖端发生与试样轴向呈小夹角方向急转弯,抑制了其向沿大夹角方向的最大正应力所在平面方向扩展的趋势,从而影响了宏观裂纹的扩展面角度;拉扭疲劳主裂纹在扩展过程中留下了明显的台阶状形貌,这是由于主裂纹在扩展过程中通过此区域时,各界面微裂纹扩展情况不同而造成的。

The fatigue life of Ti6321 alloy with phase differences of 0°and 30°is analyzed by tensile-torsional fatigue test.The propagation path of micro-cracks and macro-cracks at 0°phase difference is studied,and the fatigue fracture surface analyzed.Results show that axial-torsional fatigue life of Ti6321 alloy at 30° phase difference is shorter than that at 0° phase difference.The Ti6321 surface micro-cracks,mainly affected by shear stress,is initiated in the range of 20°~30° to axial direction.Besides,with the increase of equivalent stress amplitude,the number of initiated surface micro-cracks increases.And the main crack tip makes a sharp turn in the direction of small angle to axial direction due to the main crack and merges with micro-cracks during propagation,which restrains the main crack propagation along the maximum normal stress direction.The main axial-torsional fatigue crack,influenced by the micro-cracks,presents step morphology in the propagation zone.