Ti-6Al-4V合金的超高周疲劳行为

采用超声疲劳实验分别确定了双态和网篮两种组织的Ti-6Al-4V合金的疲劳寿命(S-N)曲线,并用SEM观察疲劳断口.结果表明,两种组织合金的S-N曲线均保持下降趋势,在105-109cyc间不出现水平段,不存在传统意义的疲劳极限,断口形貌分析表明,随着应力幅的降低,二者的裂纹萌生位置都发生了由试样表面到内部的转变.与加载频率为25 Hz时的疲劳实验结果进行比较后发现,超声疲劳加载条件下,疲劳强度提高,疲劳寿命延长,且频率对网篮组织合金疲劳性能的影响大于对双态组织的影响.

Ultra-high cycle fatigue behavior of Ti-6Al-4V alloy

The fatigue S-N curves of Ti-6Al-4V alloys with the bimodal and basketweave microstructures were determined between 10~5-10~9 cyc using the ultrasonic fatigue testing system under a loading frequency of 20 kHz.The fracture surfaces of specimens were investigated with SEM.The results show that the S-N curves of Ti-6Al-4V with two kinds of microstructures continue to decrease with increasing the number of cycles and have no horizontal asymptote in the regime of 10~5-10~9 cyc, so no conventional fatigue limits exist for Ti-6Al-4V with the two microstructures.SEM analysis shows that the crack initiation sites change from the surface to interior of specimens with decreasing the load amplitude,and therefore formed a bimodal failure distribution.The fatigue lifetime is higher under the frequency of 20 kHz as compared with that under the frequency of 25 Hz.Especially,the fatigue behavior of the basketweave microstructure shows more pronounced frequency effect than that of bimodal microstructure.