Stress-induced martensitic transformation during cold rolling of metastable β Ti–5Al–5V–5Mo–3Cr alloy

Abstract

The present study focuses on modifying the microstructures and mechanical properties of a recently developed metastable β Ti–5Al–5V–5Mo–3Cr (Ti-5553) alloy through cold rolling technique. Three different degrees of deformations (5 %, 10 %, and 20 % thickness reductions) are employed on the as-cast Ti-5553 alloy. Microstructural analysis reveals presence of single β-phase in the as-cast alloy, which is further confirmed through X-ray diffraction technique. Cold rolling however activates different deformation mechanisms with increasing degree of rolling and hence evolve the microstructure as well. While the alloy subjected to the lowest extent of thickness reduction, deforms mainly via slip, that with the highest degree of rolling deforms through formation of slip lines, zigzag slip lines, and deformation bands. Overall, activation of specific twins such as {332} <113>β along the closed packed direction of the β matrix is noted for the optimally cold rolled specimen. Most interestingly, occurrence of stress-induced martensitic phase is also confirmed for all the cold rolled specimens with its volume percentage being directly proportional to the degree of deformation. This cold rolling imparted microstructural modifications also influence the local and global mechanical performance of Ti-5553 alloy. Highest values of hardness and compressive yield strength are noted for the Ti-5553 alloy cold rolled up to the highest extent. This systematic study is the first of its kind to report the influence of cold rolling on the stress induced martensite formation and hence establishes the processing-structure-property correlation for Ti-5553 alloy.