An investigation on microstructural and mechanical properties of powder metallurgical TiAl alloy during hot pack-rolling

The microstructural and mechanical properties of powder metallurgical (PM) Ti-47Al-2Cr-0.2Mo alloy plates under various hot pack-rolling conditions were investigated. The PM TiAl plates show recrystallized and duplex microstructure. The dynamic recrystallization mainly occurred in beta phase at the beginning of deformation, and a large amount of dislocations and sub-grains formed in gamma phase. The dynamic recrystallization of gamma phase is the main mechanism for the flow softening in the later stage of the hot rolling. The optimum parameters for hot rolling PM TiAl are obtained by adjusting temperatures, speeds and reduction per pass. Based on the microstructures after a certain reduction, a roll-speed-increase hot rolling is developed for effectively producing TiAl alloy plates. Once fine and uniform duplex microstructure was obtained after the first stage of deformation, the TiAl alloy can be further rolled at a lower temperature, higher speed and larger reduction per pass. The ultimate strength, yield strength and elongation of the plate fabricated though the new process are 682 MPa, 639 MPa and 1.32%, respectively, which are higher than those of plated produced by the constant-speed rolling. (C) 2014 Elsevier B.V. All rights reserved.