The Influence of Titanium Addition on the High-Temperature Oxidation Behaviour of the Al0.7CoCrFeNi Alloy

In recent years, the development of advanced materials capable of withstanding extreme environments has become a key focus in materials science and engineering. High-entropy alloys (HEAs) are increasingly recognized as promising candidates for high-temperature applications due to their unique compositional flexibility and exceptional thermal stability. This study investigates the influence of titanium addition on the microstructure and oxidation resistance of the Al_0.7CoCrFeNi alloy, as titanium is known to affect diffusion processes and oxide scale stability at high temperatures. Alloys with different titanium contents (x = 0.05, 0.2, 0.5) were synthesised using the arc melting method and tested for high-temperature oxidation at 1000 °C for up to 1000 hours. Microstructural analysis revealed that low titanium additions (x ≤ 0.2) had minimal impact on the alloy’s biphasic, lamellar-dendritic structure, while higher titanium content (x = 0.5) led to significant morphological changes and elemental segregation. Results of oxidation kinetics showed that alloys with low titanium content maintained excellent oxidation resistance due to the formation of a stable Al2O3 layer. In contrast, the alloy with x = 0.5 exhibited rapid weight gain and poor oxidation resistance, attributed to the formation of porous, multilayered oxide scales dominated by Ti and Cr oxides. These findings suggest that while minor titanium additions do not significantly compromise oxidation resistance, excessive Ti content disrupts the formation of protective oxide layers, potentially limiting the alloy’s suitability for extreme temperature environments.