Tensile and torsion fracture failure behaviors of Ti-55531 alloy with lamellar structure

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 α_s 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.