Assessment of the High-Temperature Oxidation Performance of Ti-Based Systems via a Novel Combinatorial Approach

Poor oxidation performance and subsequent surface embrittlement are the important stumbling blocks and life-limiting factors that have often limited the use of Ti-based alloys in elevated temperature structural applications. However, neither the mechanisms associated with evolution of oxide layers nor the effects of oxygen on the microstructure of the material are well-understood. To better explore the influence of composition (as a determining factor) on the oxidation behavior of titanium, several binary and ternary Ti-based systems were prepared in the form of compositionally graded specimens and subsequently exposed to still-air at 650°C. A suite of the state-of-the-art characterization techniques were used to assess, as a function of the local average composition: the structure and composition of the oxide; the oxide adherence and porosity; the thickness of the oxide layers; the depth of oxygen ingress; and microstructural evolution of the base material just below the surface but within the oxygen-enriched region. After this fashion, it is possible to better understand the role that composition has on the formation of oxides and the evolution of structure near the surface. Importantly the aforementioned comparative assessments are independent of experimental variability regarding time, temperature, and atmosphere which would otherwise yield to misleading results specifically in the oxidation stages predominantly associated with the establishment of an oxygen concentration gradient in the metal substrate.