片层Ti-55531合金的拉伸和扭转断裂失效行为

Tensile and Torsion Fracture Failure Behaviors of Ti-55531 Alloy with Lamellar Structure

通过室温静态拉伸和扭转试验,结合TEM、SEM等分析检测方法,系统研究了片层Ti-55531合金在拉伸和扭转载荷下的断裂失效行为。结果表明,片层Ti-55531合金在拉伸和扭转载荷下的断裂失效有显著的不同:拉伸变形受滑移、次生α_s的孪生及剪切共同控制,扭转变形主要受滑移和剪切控制,未发现有孪晶;拉伸断口较扭转断口陡峭,失效以微孔聚集为主,含少量穿晶解理和沿晶开裂的混合断裂机制;扭转断裂失效则以微孔聚集和剪切开裂为主,含部分穿晶解理的混合断裂机制。无论在拉伸还是扭转载荷下,片层Ti-55531合金的断裂失效面均由最大剪切应力产生,剪切力比正应力更易使片层Ti-55531合金损伤破坏。

Deformation and fracture behaviors of Ti-55531 alloy with lamellar microstructure（LM Ti-55531 alloy） were investigated during tensile and torsion tests at room temperature by transmission electron microscopy and scanning electron microscopy. Results indicate that loading modes have a significant influence on deformation and fracture mechanisms of LM Ti-55531 alloy. First of all, deformation mechanism of tensile tests is a mixed mode which combines dislocation slip, twinning of secondary αs phase and shear, while deformation of torsion tests is controlled predominantly by dislocation slips and shear. Secondly, fractographs of tensile and torsion tested specimens possess different morphologies. Fractographs of tensile specimens are cliffier than those of torsion specimens. The tensile sample shows a ductile failure, including microvoid coalescence, cleavage and inter-granular fracture mechanisms. The fracture of the torsion specimen is still a mixed mode type but with more shear dimples. No matter under tensile or torsion loading, the failure of LM Ti-55531 alloy is controlled by the highest shear stress. And the shear stress has much more effect on the failure of LM Ti-55531 alloy than the normal stress.