Hot deformation characterization of lamellar Ti-43Al-2Si alloy fabricated by cold crucible continuous casting

In order to investigate the hot deformation behavior of lamellar Ti-43Al-2Si (at%, similarly hereinafter) alloy with equiaxed colonies prepared by cold crucible continuous casting, the isothermal compression tests were carried out at different temperatures in the range of 1100–1250 °C using the strain rates between 0.001 s⁻¹and 1 s⁻¹with true strain of 0.8. A constitutive equation at elevated temperature and three-dimensional processing map of this alloy were established based on flow stress data at different temperatures and strain rates. The microstructures depended on deformation condition were observed by optical microscope (OM), backscattered electron (BSE) and electron back-scattered diffraction (EBSD). It was found that the deformation activation energy (Q) varied with the deformation temperature and strain rate, and average value was 451.15 kJ/mol which was much larger than that of the powder metallurgy TiAl-based alloy but smaller than that of the well directionally solidified (DS) microstructure TiAl-based alloy. Based on the processing map, the appropriate hot working domain of this alloy without deformed cracks was determined to be within the temperature window from 1150 °C to 1250 °C and in the strain rate range of 0.001–0.01 s⁻¹. The flow softening feature of the present alloy during deformation was noted and caused by synergetic effect of dynamic recrystallization (DRX), globularization and reorientation of lamellae. In addition, the Zener-Hollomom parameter played a key role on the DRX process.