Hot deformation behaviors of β phase containing Ti-43Al-4Nb-1.4W-based alloy

Flow behaviors and microstructures during hot compression of a Ti-43Al-4Nb-1.4W-based alloy containing β phase at various deformation conditions were investigated by physical simulations, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The dependence of the peak stress on the deformation temperature and the strain rate can be expressed by a hyperbolic-sine type equation. The activation energy for hot deformation of the alloy is determined to be 601.7 kJ/mol, which is closely related to microstructure and alloy composition. Microstructure analysis shows that both the fraction of dynamically recrystallized grains and the average size of spherical β phases increase with the decrease of Zener-Hollomon (Z) parameter. The dynamic phase transformation of β phases is apparently accelerated due to hot deformation, leading to the spheroidizing of irregular β phases. It is found that different deformation mechanisms are operated on hot deformation of the alloy, which is related to the value of Z parameter. At low Z, the dynamic softening mechanisms involve the main dynamic recrystallization (DRX) and twinning. At high Z, the DRX accompanied by the bending of lamellar colonies, γ grains and β phases would occur during hot deformation of the alloy. The existence of Y2O3 can also provide additional particle stimulated nucleation of DRX. Besides, the evolution of β phase during hot deformation plays an important role in the dynamic softening of the alloy.