Toughening Mechanisms of Lamellar TiAl Alloys Containing B2 Phase at Room Temperature

摘要:

通过三点弯曲断裂和卸载试验对含B2相TiAl金属间化合物的韧化机理进行研究，通过双缺口四点弯曲试验确定解理断裂的临界事件。通过扫描电子显微镜和能谱分析观察断口形貌和裂纹扩展路径。结果表明：(1) 3PB试验的载荷位移曲线为线性关系，B2相对裂纹的起裂无影响；(2) 块状B2相对裂纹的扩展有一定的阻碍作用，裂纹遇到B2相停止或绕过B2相继续扩展；(3) 解理断裂的临界事件为沿缺口根部开裂裂纹的扩展，穿层断裂对临界事件起着重要的作用；(4) 这种材料的韧化机理包括：块状B2相韧化，裂纹偏转，穿层断裂和剪切韧带韧化

Abstract:

Three point bending (3PB) fracture tests and unload tests of lamellar TiAl alloys containing B2 phase were carried out to investigate the toughening mechanisms of the TiAl alloy. Double notched 4PB tests were used to evaluate the critical event of cleavage fracture of this alloy. To observe the morphology of fracture surface and crack path, scanning electron microscope (SEM) and energy spectrum analyses were also carried out. The results reveal the following aspects: (1) The load-displacement curve of 3PB fracture tests presents linear elastic relationship, and B2 phase has no effect on the crack initiation. (2) B2 phase is an obstacle to the crack propagation. The crack is arrested by B2 phase at low applied load and bypasses the B2 phase by skipping over B2 phase or crosses B2 phase at high applied load. (3) The critical event of the cleavage fracture of a notched specimen is a propagation of the nucleated interlamellar crack at the notch root. And trans-lamellar propagation is the key factor affecting the whole process of cleavage fracture. (4) The toughening mechanisms of the current alloy include B2 phase toughening, crack deflection, shear ligament toughening and trans-lamellar toughening