Effect of cooling process on the α phase formation and mechanical properties of sintered Ti-Fe alloys

Titanium sintered compacts can be strengthened by adding iron due to both its high solid solution strengthening effect and its ability to stabilize the bcc beta phase. However, these outcomes may be changed by the cooling rate and the amount of iron added, both of which influence the microstructures and properties of the sintered compact. This study presents the sintered properties of Ti-xFe (x = 3, 5, and 7 wt.%) sintered at 1150 degrees C under vacuum and then cooled with different cooling schedules. The results indicated that all alloys reached about 96% relative densities. Higher holding temperatures (740 and 640 degrees C) in the alpha + beta region after sintering increased the tensile strength and hardness due to the higher amounts of the beta phase and the acicular alpha precipitates inside the beta. With holding at a lower temperature of 550 degrees C, the amount of beta phase decreases and no secondary alpha precipitates were observed in the beta phase. No TiFe compound was observed in any of the sintered parts, even with a slow cooling rate, indicating that iron is a very strong beta phase stabilizer that can suppress the eutectoid reaction at 595 degrees C. These changes in microstructure result in significant changes in mechanical properties. (C) 2011 Elsevier B.V. All rights reserved.