Revealing the correlation between microstructure and fatigue crack growth behaviors in Ti–6Al–3Nb–2Zr–1Mo alloy
Revealing the correlation between microstructure and fatigue crack growth behaviors in Ti–6Al–3Nb–2Zr–1Mo alloy
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DOI：
10.1016/j.msea.2022.143406
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发表时间：
2022-07
期刊：
影响因子：
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通讯作者：
Pengfei Yang;Qi Sun;Xue-chao Zheng;Xue Mi;L. Chai;Minhao Zhu
中科院分区：
文献类型：
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作者：
Pengfei Yang;Qi Sun;Xue-chao Zheng;Xue Mi;L. Chai;Minhao Zhu
采用电子背散射衍射（EBSD）、电子沟道衬度（ECC）和力学性能测试相结合的方法，研究了Ti-6Al-3 Nb-2 Zr-1 Mo合金的显微组织特征与疲劳裂纹扩展（FCG）行为之间的关系。在原始材料的α+β相区等温1h后，分别采用水淬（WQ）、空冷（AC）和炉冷（FC）工艺制备了3种不同显微组织的试样。da/dN-Δ K曲线表明，AC试样的抗疲劳裂纹扩展能力最差，疲劳裂纹扩展率（FCGR）最高。这些样品的相应的FCG路径也进行了系统的检查。结果表明，WQ试样和FC试样的裂纹分叉和偏转都比AC试样严重。对于具有WQ显微组织的样品，由β相转化而来的不同α变体之间具有高取向差角的边界可能会成为阻碍位错运动和滑移传递的障碍，有利于二次裂纹的萌生。同样，在FC试样中不同α相之间的边界处产生的应变不相容性也可能促进裂纹分叉的发生。相比之下，在AC样品中，包含具有相同晶体取向的α变体的α菌落更可能在β转变晶粒内形成，导致很少的二次裂纹形成。此外，一个修改的数学模型，评估裂纹偏转和分叉的FCGR的共同影响。研究表明，裂纹分叉是有效降低主裂纹尖端应力强度因子，进而减缓疲劳裂纹扩展速率的主要因素。
In the current work, the correlation between microstructural features and fatigue crack growth (FCG) behaviors in Ti–6Al–3Nb–2Zr–1Mo alloy is investigated by a combination of electron backscatter diffraction (EBSD), electron channeling contrast (ECC) and mechanical tests. Three kinds of samples with different microstructures are prepared by water quenching (WQ), air cooling (AC) and furnace cooling (FC) after isothermal holding for 1h in α+β phase region of the as-received material. Theda/dN-ΔKcurves indicate that the FCG resistance ability of the AC sample is the worst, resulting in the highest FCG rate (FCGR). The corresponding FCG paths of these samples are also examined systematically. And the results show that the crack bifurcation and deflection in both the WQ sample and the FC sample are more serious than that in the AC sample. For the sample with the WQ microstructure, boundaries with high misorientation angles between different α variants transformed from β phase may act as an obstacle to hinder the dislocation movement and slip transfer, favoring the secondary crack initiation. Similarly, the strain incompatibility generated at the boundaries between different α phases in the FC sample may also promote the occurrence of crack bifurcation. In contrast, in the AC sample, α colonies that contain α variants with the same crystal orientation are more likely to be formed inside β transformation grains leading to few secondary cracks forming. Furthermore, a modified mathematical model is developed to evaluate the co-effect of the crack deflection and bifurcation on the FCGR. It is suggested that the crack bifurcation is the main factor that can effectively reduce the stress intensity factor of the main crack tip, and in turn slow down the FCGR.