The role of interstitial oxygen in microstructural evolution and mechanical behavior for titanium alloys:A review

Interstitial oxygen is the most influential impurity element in titanium alloys and plays a central role in determining their structural stability and mechanical performance. Although it was traditionally regarded as a detrimental impurity because of oxygen-induced embrittlement, the recent advances in atomic-scale characterization, alloy design and additive manufacturing have revealed that oxygen can also function as a powerful alloying element capable of regulating phase stability, defect interactions and microstructural evolution across multiple length scales. Unlike previous reviews that mainly focus on strengthening effects or specific alloy systems, this article provides an integrated perspective linking oxygen-mediated phase transformation, microstructural evolution and mechanical behavior across different classes of titanium alloys. We begin with examining how oxygen alters phase stability and transformation pathways, including α stabilization, martensitic transformations (α′ and α″), and the formation and stability of ω phase. A summary of oxygen-mediated microstructural evolution in α, α+β, and metastable β titanium alloys follows afterwards. The effects of oxygen on deformation behavior and the associated strengthening mechanisms are subsequently analyzed, with particular emphasis on the intrinsic interplay between strengthening and embrittlement. Those emerging concepts such as oxygen-induced nanoscale ordering, oxygen–defect interactions, and heterogeneous microstructural design are also highlighted. Finally, the key challenges and future research directions for oxygen-enabled alloy design are discussed. By integrating the insights from atomic-scale mechanisms to macroscopic mechanical behavior, this review aims to establish a unified framework for understanding oxygen-modulated structure–property relationships and to provide a guidance for the development of next-generation high-performance titanium alloys.