载荷方式对双态Ti-55531合金变形和断裂的影响

Effect of Loading Type on Deformation and Fracture Behavior of Ti-55531 Alloy with Bimodal Microstructure

通过室温静态拉伸和扭转试验,结合TEM、SEM等分析检测,系统研究了双态Ti-55531合金在拉伸和扭转载荷下的变形和断裂失效行为。结果表明,载荷方式的改变对双态Ti-55531合金变形和断裂行为有显著的影响:该合金扭转剪切强度比抗拉强度低约300 MPa,表明该合金的断裂对扭转切应力的敏感性高于拉伸应力。拉伸和扭转变形时,合金主要都受滑移和剪切共同控制;高密度位错主要堆积在晶界α和等轴α_p的界面处。相对拉伸变形,扭转变形时等轴α_p产生的剪切滑移带数量更多。拉伸断口较扭转断口陡峭,拉伸断裂失效是以微孔聚集为主的穿晶断裂机制;而扭转断裂失效则是微孔聚集和剪切开裂的混合断裂机制。

A combination of transmission electron microscopy and scanning electron microscopy was used to study deformation and fracture behavior of Ti-55531 alloy with bimodal microstructure(BM Ti-55531 alloy)during tensile and torsion tests at room temperature.Results indicate that loading types have a significant influence on deformation and fracture behavior of BM Ti-55531 alloy.First of all,the tension strength is about 300 MPa higher than torsion strength of BM Ti-55531 alloy,and its ductilty of tension is also higher compared to torsional ductilty.It indicates that BM Ti-55531 alloy is more sensitive to torsional shear stress than to tensile stress.Secondly,deformation mechanisms of both tensile and torsion test are a mixing mode including dislocation slip and shear,while deformation of torsion test is predominantly controlled by shear.The interfaces between net-like grain boundaryα,primaryαand retainedβphases are easily filled with high density dislocations.Thirdly,fractographs of tensile and torsion tested specimens exhibit different morphologies.Fractograph of tensile specimen is cliffier than that of torsion specimen.The tensile sample shows a ductile failure,including microvoid coalescence and transgranular fracture mechanism.The fracture of torsion specimen is still a mixture type but with more shear dimples.