Metastable β-titanium alloys have attracted considerable interest for structural
applications, owing to their superior specific strength and the ability to
obtain enhanced ductility through phase transformations induced by deformation.
Nevertheless, in recently developed Ti-Zr-Al-V alloy systems, the interactions
among dislocation slip, strain-induced martensitic transformation, and the
consequent work-hardening response remains largely unclear. Under
room-temperature uniaxial tension, this work systematically investigates how the
microstructure evolves and how the alloy deforms for a metastable β-type
Ti-42Zr-12Al-4V (at.%) alloy. To track the progression of strain-induced α″
martensite and dislocation activity across varying strain levels, techniques
including quasi-in-situ scanning electron microscopy (SEM) and electron
backscatter diffraction (EBSD), transmission electron microscopy (TEM), and
focused ion beam (FIB) were employed. Findings indicate that the dominant
strengthening mechanism stems from the strain-induced α″ martensite blocking
dislocation motion, alongside dislocation cross-slip. Although the martensite
volume fraction rises with increasing strain, its growth rate diminishes at
higher strains. The martensite and the β matrix exhibited a clear Burgers-type
orientation relationship, namely [001]α″//[110]β.
Moreover, the appearance of martensite inside both primary and secondary slip
bands generates a dynamic Hall-Petch effect, which reduces the dislocation mean
free path and thereby supports continued strain hardening. These results provide
deeper insight into the transformation-induced plasticity (TRIP)-assisted
deformation mechanisms active in β-type titanium alloys and could guide the
development of strong yet ductile materials.