The effects of strain rate and temperature on the compressive deformation behaviour of Ti-6Al-4V alloy

The plastic deformation behaviour and compressive characteristics of Ti-6Al-4V alloy are investigated by means of compression tests under constant strain rates of 0.02, 0.1, and 1.0 s(-1) and at temperatures ranging from 25 to 500 degrees C. The height reductions, varying from 10 to 70% with intervals of 20%, are set to investigate the workability of this material. The flow stress data are analyzed in terms of strain rate and temperature sensitivities. A constitutive equation studying the dependence of the how stress on strain, strain rate and temperature is presented and evaluated. For microstructural analysis, the deformed specimens are polished and etched in order to analyze the characteristics of the deformation patterns. A scanning electron microscope is also used to observe the fracture appearance of failed specimens. The experimental results show that the flow stress decreases directly with the increasing of temperature and that the strain rate affects the how stress only slightly. Flow softening phenomena are observed at room temperature under a strain rate of 1.0 s(-1). When the reduction in height exceeds 50% at room temperature, inner cracks will initiate inside the specimen. Oblique outer cracks appear on the equatorial surface of the cylinder until the reduction in height increases to 70%. It is noticeable that the characteristics of the flow lines observed in the deformation pattern under isothermal conditions are similar to those of the Dead Metal Zone of non-isothermal deformation. Further, the fracture appearance tends to show that the formation of shear bands induces fragmentary failure. Finally, comparing the calculated flow stress and the measured flow stress, the results show that constitutive equation predicts an acceptable flow stress within a reasonable extent of error. (C) 1997 Elsevier Science S.A.