双峰结构纯钛的低周疲劳性能研究:试验和模拟

Study on Low-cycle Fatigue Performance of Pure Titanium with Bimodal Structure:Experiment and Simulation

通过低温轧制和退火热处理在纯钛的微观组织中引入了双峰晶粒分布,对双峰结构纯钛(BM-Ti)的拉伸性能和低周疲劳性能进行了系统地研究,结果表明,相比于原始粗晶纯钛(CG-Ti)和超细晶纯钛(UFG-Ti),双峰结构纯钛表现出高屈服强度(634.4 MPa)和高均匀伸长率(7.2%)的优异强韧匹配性能。然而,双峰结构并不能有效提高纯钛的低周疲劳寿命。循环过程中,双峰结构纯钛的粗晶粒区域承担了大部分的塑性变形,大量位错在粗晶粒内部进行堆积,并逐渐分割晶粒导致粗晶粒细化。通过晶体塑性有限元法模拟了双峰结构纯钛的低周疲劳行为,引入了累积塑性应变以评估疲劳过程中的损伤,发现双峰结构纯钛的异质界面处由于应变不相容性更容易导致疲劳裂纹的萌生。

The bimodal-grained distribution was introduced into the microstructure of pure titanium through cryo-rolling combined with annealing heat treatment.The tensile properties and low-cycle fatigue properties of bimodal pure titanium(BM-Ti)were systematically studied.Compared to the original coarse-grained pure titanium(CG-Ti)and ultra-fine grained pure titanium(UFG-Ti),BM-Ti exhibited excellent strength-ductility matching properties with high yield strength(634.4 MPa)and high uniform elongation(7.2%).The results of low-cycle fatigue experiments indicate that the bimodal structure cannot effectively improve the fatigue life of pure titanium.During the cycling process,the coarse-grained area of BM-Ti bore most of the plastic deformation,and a large number of dislocations accumulated within coarse grains,gradually dividing the grains and leading to the refinement of coarse grains.The low-cycle fatigue behavior of BM-Ti was simulated by crystal plasticity finite element method,and accumulated plastic strain was introduced to evaluate the damage during the fatigue process.It was found that the heterogeneous interface of BM-Ti is more prone to fatigue crack initiation due to strain incompatibility.