循环载荷对USSP处理TC4表层残余应力场影响研究

Effects of cyclic loading on residual stress field in TC4 after USSP treatment

摘要:

本研究采用超声喷丸技术(USSP) 处理TC4试样,再进行四点弯曲疲劳加载。采用X射线应力仪测试疲劳加载前后残余应力分布；利用TEM设备,对疲劳加载前后TC4组织结构进行表征。实验结果表明,经表面纳米化处理后,TC4合金的最大残余应力值已超过自身的屈服强度；当外加载荷高于疲劳极限时,残余应力场明显减弱；当外加载荷接近或小于疲劳极限时,循环周次与载荷的增减不再明显改变残余应力场；位错及位错胞在疲劳过程中发生了组态和数量的变化,位错密度的降低导致了残余压应力的松弛。

Abstract:

The ultrasonic shot peening (USSP) was used to treat TC4 surface, the samples were loaded by four-point-bending fatigue test, and residual stress distribution before and after fatigue loading was tested by X-ray stress tester. By TEM equipment, microstructure of TC4 before and after fatigue loading was characterized. The results showed that the maximum residual compressive stress of surface nanocrystallization TC4 exceeded its yield strength; When the loads were higher than fatigue limit, the residual stress released and the residual stress field decreased significantly; When the loads were close to or lower than the fatigue limit, the residual stress field tended to be stable and was no longer evidently altered with the change of cyclic time and loads; The configuration and quantity of dislocations and dislocation cells were changed in the process of fatigue, the decrease of the dislocation density resulted in the relaxation of residual compressive stress.