Effects of solution temperature and cooling rate on microstructure and micro-hardness of a hot compressed Ti-6Al-4V alloy

The effects of solution temperature and cooling rate on microstructure and micro-hardness of a hot compressed Ti-6Al-4V alloy are investigated. The microstructure observations reveal the occurrence of static recrystallization during solution treatment. The lamellar alpha phases firstly decompose into the short-rod phases, and then gradually spheroidize. The increased solution temperature can accelerate the transformation of alpha grain boundary from the low-angle grain boundaries (LAGB) to the high-angle grain boundaries (HAGS). So, the growth and spheroidization of a grains become more and more obvious. Meanwhile, the precipitation of secondary alpha phases is promoted. The micro-hardness is significantly improved after the solution treatment, i.e., the micro-hardness undergoes the rapid decrease and slow increase with raising the solution temperature. In addition, the cooling rate has great impact on the microstructures and micro-hardness. With reducing the cooling rate, the mean size of equiaxed alpha grains and the thickness of lamellar alpha phases obviously increase.