On the nature of a peculiar initial yield behavior in metastable β titanium alloy Ti-5Al-5Mo-5V-3Cr-0.5Fe with different initial microstructures

The compressive yielding phenomenon of titanium alloys is not as focused and sufficiently ascertain as the tensile yielding phenomenon. In the present work, the peculiar compressive yielding behavior and the different dynamic responses of three different initial microstructures (single β, clavate α and lamellar α) were investigated in an attractive metastable β titanium alloy Ti-5553 using electron microscopes/crystallographic calculation/crystal plastic finite element simulation. Results reveal that the distinct compressive yielding behavior, steep peaks of sudden drop in the initial stage (very small true strain ˜0.03) of stress loading have appeared in the compression stress-strain curves except for the lamellar α initial microstructure. Dislocation slip is the essential mechanism of the initial yielding behavior. Interlaced multiple-slip bands formed in the single β initial microstructure during the warm deformation process. A small quantity of single slip bands was observed in the deformed clavate α initial microstructure. The abundant varied nano/ultrafine α_s precipitates were nucleated dynamically and dispersedly in all the three deformed initial microstructures. The multiple-slip bands formation and substantial nanoscale α_s result in the highest peak of flow stress for single β initial microstructure. The compressive slip bands are formed early in the elastic – plastic deformation stage. As the increasing strain, the sample showed a significant compressive bulge, or eventually forming a strong adiabatic shear band or crack. These results are expected to provide a reference for the study of deformation behavior and mechanical properties of metastable β titanium alloys.