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 alpha + beta 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 beta stability i.e., the kinetics of TRIP, because the Fe and Mn atoms (strong beta stabilizers) were partitioned to the retained beta phase during solution treatment in the alpha + beta 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 beta 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 beta grains. Solution treatment in the beta region resulted in beta coarsening, resulting in relatively low strain hardenability.