Synergistic effect of local chemical fluctuation and oxygen-induced nanodomains on stress-induced martensitic transformation in Ti-Nb-O alloys

Ti-Nb-O superelastic alloys are promising biomedical materials, yet their practical application is limited by insufficient mechanical strength and limited recoverable strain. Although oxygen (O) doping and local chemical fluctuations (LCF) are known to affect stress-induced martensitic transformation (SIMT) and thus the mechanical response of Ti-Nb-O alloys, their synergistic regulation effect and underlying atomic-scale mechanisms remain unclear. In this study, these mechanisms are systematically investigated by molecular dynamics (MD) simulations. A customized interatomic potential was constructed for Ti-Nb-O alloys by extensively sampling the α, β, and α” phases containing interstitial O atoms. The simulations revealed that the formation of LCF is energetically favorable, and O clustering in Nb-lean regions leads to the formation of nanodomains that generate lattice strains opposing the local atomic distortion required for SIMT. LCF facilitates early nucleation of the α” phase in Nb-lean regions but inhibits its propagation into Nb-rich regions, while O-induced nanodomains further hinder SIMT. As a result, SIMT is spatially localized, leading to an increased stress threshold for continuous phase transformation. These findings provide an atomic-scale framework for tailoring the macroscopic superelastic response of Ti-Nb-O alloys.