A Unifying Review of Breakaway Oxidation in Early Transition Metals at High Temperatures

Early transition metals from Groups IV to VI are critical for maintaining structural integrity at high temperatures. However, their performance is often limited by breakaway oxidation, the transition from initially protective oxide growth to accelerated, non-protective oxidation. Despite decades of research, the underlying mechanisms remain unresolved, even within individual metals. This review argues that the shared oxidation characteristics of these metals warrant a unified assessment to constrain the mechanistic space and guide focused future studies. Experimental and theoretical evidence across Ti, Zr, Nb, Ta, and W is synthesized to identify critical gaps in current understanding. This unified perspective suggests that breakaway may arise from coupled instabilities at the metal-oxide interface involving oxygen dissolution into the metal, defect-rich monoxides, and growth-induced stresses that promote cracking and porosity. In addition, alloying and processing strategies proposed to enhance the oxidation resistance of these metals are synthesized. Finally, the influence of early transition metals on the oxidation performance of emerging refractory high-entropy alloys is discussed, highlighting the broader significance of the mechanistic insights developed in this review. These insights are particularly timely given the urgent demand for oxidation-resistant materials in ultra-high temperature applications.