PHASE STABILITY AND OXIDATION MECHANISM DIVERGENCE IN Al₃₀Cr₁₅Ni₁₅Si₁₀Ti₃₀ HIGH-ENTROPY ALLOY AT 1000 °C

Mudassar Hussain; Junsen Wang; Abdillah Sani Mohd Najib; Nor Akmal Fadil; Jing Liu; Tuty Asma Abu Bakar

Mudassar Hussain Materials Research and Consultancy Group (MRCG), Department of Materials, Manufacturing & Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia. https://orcid.org/0000-0003-1362-9150
Junsen Wang Guangdong Provincial Key Laboratory of New Energy Materials Service Safety, College of Materials Science and Engineering, Shenzhen University, Shenzhen, Guangdong, P.R. China.
Abdillah Sani Mohd Najib Materials Research and Consultancy Group (MRCG), Department of Materials, Manufacturing & Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia.
Nor Akmal Fadil Materials Research and Consultancy Group (MRCG), Department of Materials, Manufacturing & Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia.
Jing Liu Guangdong Provincial Key Laboratory of New Energy Materials Service Safety, College of Materials Science and Engineering, Shenzhen University, Shenzhen, Guangdong, P.R. China.
Tuty Asma Abu Bakar Centre of Advanced Composite Materials, Universiti Teknologi Malaysia,81310 Johor Bahru, Johor, Malaysia.

Keywords: Al-Ti-rich AlCrNiSiTi high-entropy alloy, phase stability, high-temperature oxidation, TiO2 formation, limited oxidation resistance

Abstract

AlCrNiSiTi high-entropy alloys (HEAs) are promising candidates as next-generation competitors to Ni-based superalloys and refractory alloys, offering low density and notable phase stability for high-temperature applications. However, their oxidation performance at elevated temperatures showed limitations due to complex oxidation behaviour. This study investigates the phase stability and oxidation response of an as-cast Al₃₀Cr₁₅Ni ₁₅Si₁₀Ti₃₀ HEA at 1000 °C for 100 hours. A systematic characterisation and performance evaluation framework is adopted, encompassing X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC). Structural and elemental investigations revealed the formation of nonprotective multielement oxides. The oxide scale is dominated by rapid, extensive TiO₂formation, resulting in a porous, poorly adherent surface layer. Beneath this, a discontinuous Al₂O₃ sublayer forms with dispersed (NiCr)₂O₃ and SiO₂, but it fails to develop into a continuous protective scale. As a result, the alloy exhibits a relatively high total mass gain of 2.1 mg cm⁻², significantly higher than alloys capable of forming a continuous Al₂O₃ barrier (<1 mg cm⁻² under similar conditions). Oxidation kinetics exhibit a clear three-stage parabolic behaviour, with rate constants of , , and mg² cm⁻⁴ h⁻¹ for the early, intermediate, and late stages, respectively. A global parabolic rate constant of mg² cm⁻⁴ h⁻¹ reflects the overall diffusion-controlled oxidation process. However, DSC analysis up to 1400 °C confirms the absence of solid-state phase transformations, aside from the melting peaks of individual phases, thereby identifying the melting range of the alloy. The findings highlight pronounced phase stability but limited oxidation resistance, emphasising the need for compositional tuning for extreme-temperature applications.