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 lamellar structure Ti-55531 alloy

摘要:

通过室温静态拉伸和扭转试验,结合TEM、SEM、OM等分析检测方法,系统研究了片层Ti-55531合金在拉伸和扭转两种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：拉伸曲线末端有明显的下降现象,而扭转曲线没有；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。

Abstract:

A combination of transmission electron microscopy, scanning electron microscopy and optical microscopy was used to study deformation and fracture behaviors of lamellar microstructure (LM) Ti-55531 alloy during tensile and torsion tests at room temperature. Results indicate that loading modes have a significant influence on deformation and fracture mechanisms of LM Ti-55531 alloy. First of all, the tensile stress-strain curve of LM Ti-55531 alloy is different from its torsion stress-strain curve. The stress could decline at the end stage of the tensile test, while it is not during the torsion experiment. Secondly, deformation mechanism of tensile test is a mix mode which combines dislocation slip, twinning and shear of secondary α_s phase, while deformation of torsion test are controlled predominantly by dislocation slips and shear. Thirdly, fractographs of tensile and torsion tested specimens seem to possess different morphologies. Fractographs of tensile specimens are cliffier than torsion specimens. The tensile samples show a ductile failure, including dimple, cleavage and inter-granular fracture mechanisms. The fracture of torsion specimen is still a mix mode type but with more shear dimples. At last but not the least, no matter samples under tensile or torsion loading, the failure of LM Ti-55531 alloy are controlled by the highest shear stress. And the shear stress has much more influence on the failure of LM Ti-55531 alloy than the rectangle stress.