损伤容限型TC4-DT钛合金近门槛区疲劳裂纹扩展行为研究

研究了双态组织、片层组织TC4-DT钛合金在近门槛区的疲劳裂纹扩展行为,通过扫描电镜观察裂纹扩展路径及断口微观特征,研究了等轴初生α相含量对TC4-DT钛合金在近门槛区疲劳裂纹扩展速率的影响,讨论了TC4-DT钛合金的疲劳裂纹扩展行为和断裂方式。结果表明:随着等轴初生α相含量的降低,TC4-DT钛合金在近门槛值区的da/dN-△K曲线逐渐向下偏折,裂纹扩展速率明显降低,在Paris区出现转折点现象且转折点对应的△Kt值逐渐增大;片层组织在近门槛区的裂纹扩展路径曲折,疲劳裂纹扩展速率显著降低,表现出更好的损伤容限性能。

Near-threshold Fatigue Crack Propagation Behavior of TC4-DT Damage Tolerance Titanium Alloys

The fatigue crack propagation behavior was investigated for the TC4-DT titanium alloy with bimodal and lamellar microstructure, developed by (a+b) annealing treatment and b annealing treatment, respectively. The effect of microstructure on fatigue crack growth rates of TC4-DT titanium alloy has been discussed by SEM analyses of fracture morphology and crack propagation paths in the two different microstructures. The results show that for the bimodal microstructure, the fatigue crack growth rate lowers with decrease in the content of primary a phase, and the turning point in the curve tends to move to the right. The lamellar microstructure exhibits tortuous crack paths and fatigue crack propagation resistance, which indicates that the lamellar structure has better damage tolerance compared with bimodal structure.