Abstract
Thermal cycles consisting of 1623 K peak temperature and 270∼0.4 K/s cooling rate were applied for nine kinds of Ti-6 Al-4 V alloys of 0.17 mass % to 2.35 mass % oxygen content, which made using the arc-melting furnace, to fundamentally investigate the effects of cooling rate and oxygen content on the microstructure and the hardness of Ti-6 Al-4 V alloys. These experiments made clear that the critical cooling rates to create a martensitic microstructure and a grain boundary α became higher with increasing the oxygen content of Ti-6 Al-4 V alloy, and that the hardness of Ti-6 Al-4 V alloy was increased with an increase in oxygen content and/or cooling rate of Ti-6 Al-4 V alloy. Furthermore, a new concept of characteristics of surface hardened layer of Ti-6 Al-4 V alloy investment casting was presented, based on the above mentioned experimental results.
