TA11钛合金超高周疲劳行为

利用常规疲劳试验方法获得TA11合金在不同温度,不同应力比下的3×10~7及1×108超高周疲劳极限,并采用三参数幂函数法获得合金超高周疲劳中值S-N曲线及其描述方程。研究发现:与传统1×10~7疲劳极限相比,TA11合金的超高周(3×10~7及1×108)疲劳强度表现出继续降低的趋势,这一趋势在负应力比(R=-1)下不太明显,在正应力比(R=0.1,0.5)下十分显著,并且室温下的降低幅度大于高温下的降低幅度;断口分析表明,室温下TA11合金试样的超高周疲劳裂纹均萌生于表面,高温下TA11合金试样的超高周疲劳裂纹萌生方式与应力比有关,R=-1和0.1时疲劳裂纹萌生于表面,R=0.5时疲劳裂纹萌生于内部;TA11合金试样的表面状态是导致其疲劳寿命分散的主要原因。

Very High Cycle Fatigue Behavior of TA11 Titanium Alloy

The conventional fatigue test method was used to obtain the very high cycle fatigue (VHCF) limits of 3×107 and 1×108 cycles for TA11 titanium alloy in different temperatures and stress ratios.Three parameter power function method was used to obtain the VHCF median S-N curves and equations.The results show that the VHCF strength of 3×107 and 1×108 cycles presented a continue reducing trend compared with the traditional 1 x 107 fatigue limit.This trend is not obvious in negative stress ratio (R=-1),but significant in normal stress ratio (R=0.1 and 0.5),and the reduction amplitude of room temperature tests was greater than that of elevated temperature tests.The fracture morphologies showed that the VHCF cracks initiat at the specimen surface of TA11 alloy in room temperature tests,and the VHCF cracks initiation ways in elevated temperature tests relate to the stress ratio.The cracks initiate at the specimen surface when R=0.1 and 0.5 but in the internal when R=0.5;The surface state of TA11 alloy specimens is the main cause of its fatigue life dispersion.