Microstructural evolution of a ductile metastable β titanium alloy with combined TRIP/TWIP effects

Herein, we investigated the microstructural evolution of a metastable β Ti-12(wt%)Mo alloy under tension, exhibiting combined phase transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects. The deformed samples were analyzed by X-ray diffraction (XRD), optical microscopy (OM) and transmission electron microscopy (TEM) until fracture. Lamella-like {112}〈111〉 nano-twinning was observed at the onset of plastic deformation. Upon straining, {332}〈113〉 twinning and stress induced martensitic (SIM) β->α″ transformation were both identified locally in the deformed β matrix as primary mechanisms. Secondary mechanisms such as 2nd twinning and 2nd SIM, were then observed in the primary β twins. At the end of the uniform plastic deformation, a complex deformation microstructure was observed, showing highly disturbed matrix induced by a high volume fraction of twins and occurrence of multiples secondary mechanisms. Resultant macroscopic mechanical properties of the material display a combination of very high ductility (45%), high strength and superior strain-hardening behavior.