DEFORMATION AND MICROSTRUCTURE DEVELOPMENT DURING HOT-PACK ROLLING OF A NEAR-GAMMA TITANIUM ALUMINIDE ALLOY

Deformation behavior and microstructure development during hot pack rolling of the near-gamma titanium aluminide alloy Ti-45.5Al-2Cr-2Nb (atomic percent) were established. Deformation behavior was investigated through rolling at various nominal furnace temperatures and parallel modeling studies using a finite difference approach to predict temperature transients during workpiece transfer from the furnace and during the rolling operation itself. Agreement between measured rolling pressures and predictions based on a rule-of-mixtures (ROM) average of the flow stresses of the pack components (at the predicted temperatures and strain rates within the roll gap) was excellent. As-rolled microstructures were interpreted in terms of the Ti-xAl-2Cr-2Nb pseudobinary phase diagram, predicted temperature transients during rolling, and the static (no deformation) phase-transformation behavior of the program material. These results demonstrated the strong influence of furnace preheat temperature on microstructure development, as well as the tendency for temperature transients due to radiation heat losses and roll chilling to suppress phase transformations.