Wang Bohan, Cheng Li, Li Dongchun
Aeronautics Engineering College, Air Force Engineering University, Xi'an 710038, China.
Materials (Basel). 2021 Sep 15;14(18):5329. doi: 10.3390/ma14185329.
Ultrasonic fatigue tests of TC4 titanium alloy equiaxed I, II and bimodal I, II obtained by different forging processes were carried out in the range from 10 to 10 cycles using 20 kHz three-point bending. The results showed that the S-N curves had different shapes, there was no traditional fatigue limit, and the bimodal I had the best comprehensive fatigue performance. The fracture morphology was analyzed by SEM, and it was found that the fatigue cracks originated from the surface or subsurface facets, showing a transgranular quasi-cleavage fracture mechanism. EDS analysis showed that the facets were formed by the cleavage of primary α grains, and the fatigue cracks originated from the primary α grain preferred textures, rather than the primary α grain clusters. From the microstructure perspective, the reasons for better equiaxed high-cycle-fatigue properties and better bimodal ultra-high-cycle-fatigue properties were analyzed. The bimodal I fatigue life prediction based on energy was also completed, and the prediction curve was basically consistent with the experimental data.
对通过不同锻造工艺获得的TC4钛合金等轴I、II以及双态I、II进行了超声疲劳试验，试验在10⁶至10¹⁰次循环范围内采用20kHz三点弯曲进行。结果表明，S-N曲线形状不同，不存在传统疲劳极限，且双态I具有最佳的综合疲劳性能。通过扫描电子显微镜（SEM）分析了断口形貌，发现疲劳裂纹起源于表面或亚表面小平面，呈现穿晶准解理断裂机制。能谱分析（EDS）表明，小平面由初生α晶粒的解理形成，疲劳裂纹起源于初生α晶粒择优织构，而非初生α晶粒簇。从微观结构角度分析了等轴组织高周疲劳性能较好以及双态组织超高周疲劳性能较好的原因。还完成了基于能量的双态I疲劳寿命预测，预测曲线与实验数据基本一致。
