Effects of minor yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloy

The effects of 0.3%(molar fraction,the same below)yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloywere investigated by simulated isothermal forging tests.The ingots with the nominal compositions of Ti-45Al-5Nb andTi-45Al-5Nb-0.3Y were prepared by induction skull melting.Simulated isothermal forging tests were conducted on Gleeble 1500Dthermo-simulation machine using a 6 mm in diameter and 10 mm in length compressive specimen at the deformation temperatures of1 100,1 150,1 200℃and strain rates of 1.0,0.1,0.01 s-1.The results show that yttrium addition remarkably improves hotdeformability of Ti-45Al-5Nb alloy.An appropriate hot deformation processing parameter of Ti-45Al-5Nb-0.3Y alloy is determinedas 1 200℃,0.01 s-1.The flow stresses are decreased by yttrium addition under the same compressive conditions.The activationenergies of deformation Q are calculated as 448.6 and 399.5 kJ/mol for Y-free and Y-containing alloys,respectively.The deformedmicrostructure observation under 1 200℃,0.01 s-1condition indicates that Ti-45Al-5Nb-0.3Y alloy shows more dynamicrecrystallization.The improvement of hot deformability of Ti-45Al-5Nb-0.3Y alloy induced by yttrium addition should be attributedto that the smaller the original lamellar colonies,the lower the deformation resistance and activation energy of deformation are,andthe more the dynamic recrystallization is.