Effect of oxygen content on the phase transformation of Ti-5Al-2.5Fe alloy during continuous cooling

Abstract

The effects of oxygen content on the p to a phase transformation of the Ti-5AI-2.5Fe alloy during continuous cooling were investigated by varying the oxygen content between 0.08 - 0.41 wt%. Dilatometer tests were performed at cooling rates of 0.05 - 100°Cls combined with microstructure observation to examine phase transformation mechanisms and resulting microstructure. Our results showed that oxygen acted as a strong a phase stabilizer by increasing β-Transus temperature, and promoted diffuse-controlled a phase transformation with hindering martensitic transformation. Depending on the oxygen content, the different transformation mechanism led to a distinct difference in microstructure evolution. As an oxygen content increased, a phase was developed in thicker lath forms and was globularized at a slow cooling rate, whereas the formation of acicular-shaped a phase was significantly reduced. Hardness behavior after cooling was discussed in the light of microstructure morphology and possible precipitation formation. Based on the analysis results, continuous cooling transformation diagrams of the investigated alloys were established.