High-Temperature Deformation Behavior and Microstructure Evolution of Ti64 Microalloyed with Rare-Earth Scandium.

The isothermal compression experiments of annealed rare earth microalloyed Ti64-xSi-ySc alloys were carried out on an MMS-100 thermal simulator in the temperature range of 800-950 °C and strain rate range of 0.01-10 s⁻¹. The Arrhenius constitutive models of the alloys were established, and it was found the deformation activation energies of Ti64, Ti64-0.25Si, Ti64-0.3Sc, and Ti64-0.25Si-0.3Sc alloys were 497.65 KJ/mol, 485.6 KJ/mol, 549.13 KJ/mol, and 494.98 KJ/mol, respectively. Indicating the addition of scandium can increase the thermal deformation activation energy, which was unfavorable to the processing performance of the alloys, while silicon reduced the thermal deformation activation energy. The hot processing maps of materials demonstrated that the optimal processing area of Ti64 and Ti64-0.25Si alloys were in the range of temperature 850-950 °C and strain rate 0.01-0.1 s⁻¹, while Ti64-0.3Sc and Ti64-0.25Si-0.3Sc alloys were more desirable for thermal deformation at the temperature range of 800-900 °C and the strain rate of 0.01-0.1 s⁻¹. Based on electron backscatter diffraction (EBSD) characterization, scandium as an α phase stabilizing element that can refine the recrystallized grains and raise the strain storage energy, which improved the efficiency of power dissipation but expanded the instability region on the hot processing maps of the alloys, while silicon as a β phase stabilizing element reduced the instability region. [ABSTRACT FROM AUTHOR]