High Temperature Deformation Behavior and Microstructure Evolution of Ti-4Al-4Fe-0.25Si Alloy

Hot deformation behavior of Ti-4Al-4Fe-0.25Si alloy with martensite microstructure was investigated by compression tests at temperatures of 1023 - 1173 K (alpha+beta phase region) and strain rates of 10(-3) - 1 s(-1). By analyzing the deformation behavior, plastic deformation instability parameters including strain rate sensitivity, deformation temperature sensitivity, efficiency of power dissipation, and Ziegler's instability were evaluated as a function of deformation temperature and strain rate, and they were further examined by drawing deformation processing maps. The microstructure evolution was also studied to determine the deformation conditions under which equiaxed alpha phase was formed in the microstructure without remnants or kinked alpha phase platelets and shear bands, these last two of which cause severe cracks during post-forming process. Based on the combined results of the processing maps and the microstructure analysis, the optimum alpha+beta forging conditions for Ti-4Al-4Fe-0.25Si alloy were determined.