TC4钛合金超高周疲劳性能研究

On the ultra-high cycle fatigue behavior of titanium alloy TC4

应用基于压电超声疲劳技术开发的20kHz超声疲劳拉压试验系统，在室温下完成了对称载荷作用下TC4钛合金的超高周疲劳试验，并分析了次表面断裂的试件断口。结果表明：疲劳循环大于10 7周次时，试件仍会发生疲劳断裂，且疲劳强度会随循环次数的增加而下降，不存在明显的疲劳极限；TC4钛合金断口呈现“类鱼眼”形貌，能谱分析未观察到裂纹源处夹杂物的存在；疲劳断面的粗糙度随与疲劳源区距离的增大而减小，裂纹在后期扩展速率较快，并伴随少量塑性变形。该TC4钛合金次表面疲劳裂纹的产生是由其微观组织的不均匀或晶粒内部的滑移带导致的。

Applying a 20kHz ultrasonic fatigue tension and compression experimental system developed based on piezoelectric ultrasonic fatigue technology, an ultra-high cycle fatigue experiment was carried out for titanium alloy TC4 under condition of symmetrical loading and at room temperature, and specimen＇s fracture surface due to subsurface fracture was analyzed. Results show that when fatigue cycle is more than 10 7 , fatigue fracture still occurs, and fatigue strength decreases with the increase of cycle number, there is not obvious fatigue limit of specimen. The morphology of TC4 titanium alloy fracture surface presents ＂fish-like＂ shape. Inclusions in crack source area is not observed by energy spectrum analysis. The roughness of fracture surface decreases with the increase of distance to fatigue source area, and crack propagation rate is faster in the later stage and is accompanied by a small amount of plastic deformation. The fatigue cracks on subsurface of TC4 titanium alloy are caused by the microstructures inhomogeneity or slip bands inside the grains.