Effect of aging on tensile and fracture behavior of a metastable Ti-15 V–3Cr–3Al–3Sn β-titanium alloy

This study aims to investigate the mechanical behaviors of Ti–15 V–3Cr–3Al–3Sn (Ti-15333), a metastable β titanium alloy. Thermomechanical processing of the alloy sheet in its as-received state included solution treatment at 800°C, followed by varying aging temperatures from 450°C to 700°C. As the aging temperature rises, α precipitation increases with a fine, uniform distribution attained at 500°C to 550°C. Increased aging temperature and time causes precipitation not only at grain boundaries but also intra-granularly with morphology change from globular to lath. However, if the temperature goes above 600°C, the α phase starts to coarsen. Aged samples showed an upward trend in tensile strength that peaked and then declined, while % elongation showed an inverse trend, with optimal properties observed after 6 h aging at 500°C and 550°C. This is consistent with the idea that mechanical properties evolve alongside microstructure. The examination of the local fracture surface of aged tensile specimens using EBSD revealed a random texture. KAM value reflecting dislocation density rose with both aging temperature and duration, with its highest average reported for 6 h aging condition at 500°C and 550°C, aligning with peak level of α precipitation. The size, shape, and size distributions of α precipitates also had a pronounced impact on the fracture modes observed in the specimens. The likelihood of cleavage-like fractures occurring was higher in the under and peak-aged specimens when compared to the over-aged counterparts at 600°C and beyond. This tendency suggests that the over-aged specimens, featuring coarse α platelets, should exhibit decreased resistance to deformation and higher ductility, which is indeed the case. Investigation and analysis of different microstructures and mechanical properties obtained under different aging conditions can aid in summarizing the principles under laying deformation and fracture mechanisms of metastable β titanium alloy, potentially enhancing the service life of components and providing a foundation for alloy fabrication with customized microstructure.