The formation of ω phase severely impairs the mechanical properties of metastable β-Ti and β-Zr alloys, causing embrittlement and loss of ductility, yet its transformation kinetics remain poorly understood. Using molecular dynamics simulations, we examine how chemical ordering influences the β→ω phase transformation in Zr-Nb alloys. Our results reveal that the nucleation of the ω-phase is influenced not only by the concentration of alloying elements, but also by the degree of chemical ordering along ${\langle 111\rangle }_{\beta }$ directions, with Nb atoms occupying two out of every three ${\left\{111\right\}}_{\beta }$ planes. Notably, in rapidly quenched Zr-10%Nb alloys, enhanced local chemical ordering leads to larger ω precipitates with their crystallographic orientation directed by the ${\langle 111\rangle }_{\beta }$ ordering of Nb atoms. This interaction results in nanosized, morphologically distinct athermal ω phases, facilitated by local ${\langle 111\rangle }_{\beta }$ ordering. The propensity for ω-phase formation in chemically ordered regions arises from a reduced shear modulus and lower transformation barriers. These insights provide valuable guidance for understanding microstructural control in developing high-performance titanium and zirconium alloys.

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• Solid-solid transformations
• Structural phase transition
• Solid solutions
• Transition metal alloys
• First-principles calculations
• Molecular dynamics