Microstructural evolution in Ti-6Al-4V during hot deformation

Evolution of microstructure and its effect on mechanical behaviour has been investigated in Ti-6Al-4V for different initial alpha and beta morphologies. Hot tensile tests were performed in the temperature range 720-920 degrees C and at strain rates of 10(-4)-10(-2)s(-1). The stress strain behaviour exhibited a maximum stress followed by a decrease in flow stress which was most pronounced at low temperatures, high strain rates and for the transformed beta microstructures, Optical microscopy of the transformed beta microstructures showed shearing and fragmentation of the a needles, particularly at high temperatures, leading to a softer microstructure of spherical alpha particles. In the as-received microstructure some rearrangement of the alpha and beta grains was observed. These results indicate that rearrangement of the microstructure is responsible, to some extent, for the development in flow stress seen in this alloy at high temperatures.