High temperature deformation behavior of Ti-46Al-2Cr-4Nb-0.2Y alloy

The hot deformation characteristics of cast and hot isostatically pressed Ti-46Al-2Cr-4Nb-0.2Y (at%) alloy in the temperature range of 1100-1250°C and strain rate range of 0.01-1.0s^-1 using hot compression tests were studied. The processing map of the alloy at true strain of 0.5 was also developed on the basis of the dynamic materials model (DMM). The experimental results show that the flow stress decreases significantly with increasing deformation temperature and decreasing strain rate. Using the kinetic rate equation the stress exponent n and the apparent activation energy of deformation Q were determined as 4.47 and 400.4kJmol^-1, respectively. The efficiency values of power dissipation of the domain at strain rate below 0.4s^-1 show that the dynamic recrystallization occurring of γ phase in the alloy is easier in the wide deformation temperature range (1100-1250°C) due to low stacking fault energy. The fraction of new recrystallized grains increased with increasing the hot deformation temperature at a given strain rate. With the increasing of strain rate, the uniformity of microstructure was decreased. The domain defined by the temperature range of 1200-1230°C and the strain rate range of 0.01-0.05s^-1 which corresponds to a peak efficiency of about 60% is the optimal deformation condition of the alloy. Based on the optimal deformation conditions, a cylindrical sample was near isothermally forged. The microstructure and shape of pancake by forging was in good agreement with the prediction of processing map.