High strength and ductility in low-cost Ti–Al–Fe–Mn alloy exhibiting transformation-induced plasticity

In this study, Ti–4%Al–2%Fe–(1–4)%Mn alloys exhibiting transformation-induced plasticity (TRIP) were investigated using electron backscattering diffraction (EBSD). Fe, Al, and Mn are all low-cost elements with low melting points, making them suitable alloying elements for next-generation α + β titanium alloys with high strength and ductility. A pronounced solution temperature and Mn content dependence of the tensile behavior was observed. The solution temperature affected the β stability i.e., the kinetics of TRIP, because the Fe and Mn atoms (strong β stabilizers) were partitioned to the retained β phase during solution treatment in the α + β region. When the Mo equivalent content was between 8.4 and 10.4, the alloys exhibited an excellent combination of strength (>1.1 GPa) and ductility (>25%). On the other hand, solution treatment in the β region bestowed the same alloys with brittleness, even though the Mo equivalence was similar. During deformation, the alloys exhibited a stress-induced martensitic transformation followed by martensite coalescence. The transformation could increase the strain hardenability, but the coalescence could not. Experiments revealed that the coalesced martensite grains were propositional in size to the prior β grains. Solution treatment in the β region resulted in β coarsening, resulting in relatively low strain hardenability.