Abstract The deformation and crack propagation behaviour have been comparatively investigated in a titanium alloy with bimodal microstructure (BM) and bilamellar microstructure (BLM). The results show that higher fracture toughness (58 MPa m1/2) was obtained for the BLM than that BM one (45 MPa m1/2). The deformed microstructure, crack initiation and propagation and surface damage morphology were observed by SEM and EBSD. Fatal cracks easily nucleated at the larger primary α phase, especially at the equiaxed αe/β interface and primary α lath (αl), and often grow along a straight line, which accelerated the crack propagation and leaded to non tortuous crack path in BM. For the BLM, slip hardly transferred the αl/βtrans interface due to the secondary α(αs) precipitation in the β lamellas. Cracks initiated at the boundaries of α colony and propagated with a zig-zag way, which leaded to a high branch and fluctuation of the crack of BLM and generated a relatively superior fracture toughness performance. These results indicate that a small amount of αl colony surrounded with βtrans matrix is beneficial to the improvement of fracture toughness, which can provide a good theoretical support to tailor the microstructure and mechanical performance of titanium alloys.

中文翻译：

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显微组织在α/β钛合金塑性变形和裂纹扩展行为中的作用

摘要 对双峰显微组织（BM）和双层显微组织（BLM）钛合金的变形和裂纹扩展行为进行了比较研究。结果表明，BLM 获得了比 BM 更高的断裂韧性（58 MPa m1/2）（45 MPa m1/2）。通过SEM和EBSD观察变形组织、裂纹萌生和扩展以及表面损伤形态。致命裂纹容易在较大的初生α相处形核，特别是在等轴αe/β界面和初生α板条（αl）处，并且往往沿直线生长，加速了裂纹扩展，导致BM中的非曲折裂纹路径。对于 BLM，由于 β 薄片中的二次 α(αs) 沉淀，滑移几乎不会转移 αl/βtrans 界面。裂纹起始于α菌落边界并以锯齿形方式扩展，导致BLM裂纹的高分支和波动，产生相对优越的断裂韧性性能。这些结果表明，少量αl菌落被βtrans基体包围有利于提高断裂韧性，为钛合金微观结构和力学性能的调整提供了良好的理论支持。