高强韧Ti-3Al-5Mo-4Cr-2Zr-1Fe合金低周疲劳性能研究

Study on Low Cycle Fatigue Behavior of Ti-3Al-5Mo-4Cr-2Zr-1Fe Alloy with High Strength and Toughness

摘要:

本文通过室温下应变控制疲劳试验研究了高强韧Ti-3Al-5Mo-4Cr-2Zr-1Fe钛合金的低周疲劳性能，结果表明：在高应变幅值下（Δεt/2=1.0%，1.2%，1.4%，1.6%），合金的循环应力幅值表现为初始循环软化，而后趋于循环稳定；在低应变幅值下（Δεt/2=0.6%，0.8%），合金的循环应力响应表现为循环饱和特征。断口形貌观察发现：应变幅值为0.6%时，疲劳裂纹源只有一处，在断口表面分布有大量细小的二次裂纹。当应变幅增加到1.6%时，组织中发现多处疲劳裂纹源，二次裂纹的数量明显减少，但长度和宽度明显增加。透射电镜结果表明：在低应变幅值下（Δεt/2=0.6%），在αp/β界面处出现大量的位错堆积，在此处易产生应力集中导致微裂纹形核。而在高应变幅值下（Δεt/2=1.6%），在αp相中有明显的变形不均匀性，在αp相内出现大量的位错缠结和位错碎片，并且在αs相中出现一些位错塞积，但在β基体中没有明显的位错堆积情况。

关键词:低成本钛合金;低周疲劳;循环软化;循环稳定

Abstract:

In the present work, low cycle fatigue (LCF) behavior of Ti-35421 titanium alloy with bimodal microstructure consists of lath α (αp) and βtrans were investigated by strain-controlled mode at room temperature. Results indicated that the cyclic stress amplitude of the bimodal microstructure Ti-35421 alloy show cyclic softening at first, then reach to cyclic stability at high strain amplitude (Δεt/2=1.0%, 1.2%, 1.4%, 1.6%). However, the cyclic stress response was characterized by cyclic saturation at low strain amplitudes (Δεt/2=0.6%, 0.8%). One of fatigue crack source was found by fracture morphology observation when Δεt/2=0.6%, while a large number of small secondary cracks occurred on the surface. On the contrary, multiple fatigue crack sources generated when the strain amplitude increased to 1.6%, the number of secondary cracks reduced, but the length and width of the secondary cracks increased significantly. TEM results indicated that a large number of dislocations generate at the αp/βtrans interface at the low strain amplitude (Δεt/2=0.6%), which might lead to micro-crack nucleation due to the stress concentration. Meanwhile, at high strain amplitude ( Δεt/2=1.6%), deformation inhomogeneity phenomena happened in the αp phase, a large number of dislocation tangles and dislocation debris formed in the αp phase, and some dislocation pile-ups formed in the αs phase, which is not founded in the β substrate.

Key words:Low-cost titanium; Low cycle fatigue; cyclic softening; cyclic stability