三种组织TC17合金的疲劳裂纹扩展行为研究

Study on the Fatigue Crack Growth of TC17 Titanium Alloy with Three Mcrostructures

摘要:

本文通过对TC17合金进行常规锻造、β锻造和“β区预变形+(α+β)区大变形”,获得了等轴组织、网篮组织和球化组织三种典型显微组织,并通过裂纹扩展速率测试研究了不同显微组织对TC17合金疲劳裂纹扩展速率的影响。结果表明,显微组织对TC17合金的疲劳裂纹扩展速率具有显著影响,网篮组织的抗裂纹扩展能力最优,球化组织次之,等轴组织最差,基于断裂力学和Paris公式,建立了三种典型组织TC17合金的疲劳裂纹扩展寿命预测模型,对预测模型的分析发现,三种组织的长裂纹扩展寿命仅占疲劳总寿命的极小部分,控制裂纹起始(形核和短裂纹扩展)更为重要,提高抗疲劳裂纹扩展能力的意义在于提高临界裂纹长度。

Abstract:

Three typical microstructures for TC17 titanium alloy, i.e. equiaxed microstructure, basket-waved microstructure and globularized microstructure, are obtained by conventional forging, beta forging and “beta pre-forging+subtransus forging”, and Fatigue crack growth rates of TC17 samples with the three microstructures are tested in order to evaluate the influence of different microstructures. The results reveal a significant dependence of microstructure on fatigue crack growth rate for this material. Basket-waved microstructure has an excellent fatigue crack growth resistance, followed by globularized microstructure, while the equiaxed microstructure shows the poorest propagation resistance. On the basis of fracture mechanics, prediction models for fatigue crack growth life based on Paris equation are developed respectively for the three different microstructures. The models suggest that the propagation life for the large crack in the three microstructure accounts for only a very small proportion of the total fatigue life, hence the control of crack initiation is more important. Superior propagation resistance means a longer critical crack length, which is easily testable in practice.