Influence of cooling rate on ω phase precipitation and deformation mechanism of a novel metastable β titanium alloy

This work investigated the effect of cooling rate (water quenching and air cooling) on the precipitation of omega phase after solution treatment in beta-phase region, and its effect on the mechanical properties in a novel metastable beta titanium alloy (Ti-5Mo-3Cr-Fe-3Zr). The initial microstructures, phase composition and deformation-induced microstructures have been investigated using SEM, EBSD, XRD, and TEM. The phase composition of water-quenched alloy and air-cooled alloy are beta, alpha '', and omega phase. The size and volume fraction of omega phase of air-cooled alloy are larger than that of water-quenched alloy, resulting in an increase in tensile strength and a decrease in ductility. Deformation mechanisms of Ti-5Mo-3Cr-Fe-3Zr alloy with different cooling rate change from stress-induced omega phase transformation and dislocation slip to only dislocation slip. The stress-induced omega lamellas parallel to [1-11](beta) direction along the [0001](omega 1) direction, which is formed by {112}(beta)< 111 >(beta) slip. Dislocations can cut through the encountered omega phase to form omega-free deformation bands, which accounts for the ductility.

Automated summary

This study investigated the effect of cooling rate on the mechanical properties of a beta titanium alloy, revealing that air-cooled alloy had larger omega phase size, higher tensile strength, but lower ductility compared to water-quenched alloy. The deformation mechanisms of the alloy also varied with cooling rate, showing a transition from stress-induced omega phase transformation to only dislocation slip.