Anisotropy influence on flow behaviour and plastic instability of Ti6Al4V sheets deformed in a wide range of temperatures and strain rates

摘要

Ti6Al4V sheets are usually difficult to form at room temperature as a consequence of their reduced number of slip systems. The heating of the alloy below the p-transus temperature is recognized to enhance its formability, reducing the flow stress and increasing the ductility. However, the effect of the sheet anisotropy on the material flow behaviour and plastic instability at varying temperature and strain rate has not been studied systematically, yet. To this aim, uniaxial tensile tests were carried out in a wide range of testing temperatures (from room temperature to 800°C) and strain rates (0.01, 0.1, 1 s~(-1)) to assess the anisotropy effects. Strain hardening, strain rate sensitivity, and Lankford coefficients were evaluated as a function of the testing parameters and sample orientation. Furthermore, a numerical model of the uniaxial tensile tests was developed and calibrated making use of the Barlat-Lian-1989 yield criterion and a hardening rule, which was adapted to take into account the anisotropic behaviour at different temperatures. It was proved that the developed model was capable of predicting the strain localization in the sample gauge length due to plastic instability as well as its thickness distribution at varying temperature and strain rate.