Effect of Nano-Dispersed Y2O3 on Oxidation Behavior of Mo-Ni-Si-Co Alloys Synthesized by Mechanical Alloying and Sintering

Abstract

The application range of Molybdenum (Mo) is greatly restricted by oxidation, necessitating the use of suitable alloying and dispersion techniques. Six distinct alloy compositions were synthesized via mechanical alloying as A1 (Mo80Ni10Si10), A2 (Mo80Ni10Co10), A3 (Mo80Ni10Si5Co5), A4 (Mo79Ni10Si10(Y2O3)1), A5 (Mo79Ni10Co10(Y2O3)1), and A6 (Mo79Ni10Si5Co5(Y2O3)1) (composition in weight percent), followed by conventional sintering at 1500 °C for 90 min in a continuous flowing H2 atmosphere. This study investigates the high-temperature oxidation behavior of these alloys reinforced with nano-dispersed Y2O3, focusing on oxidation kinetics, phase evolution, and thermodynamic stability. Oxidation tests conducted at 800 °C, 900 °C, and 1000 °C for 10 h reveal the formation of complex oxide phases, as identified by X-ray diffraction (XRD). Alloy A6 demonstrated the lowest specific weight change/unit area among the samples, indicating superior oxidation resistance attributed to a dense, stable oxide film. The formation of volatile MoO3 was significantly suppressed in Y2O3-containing alloys, due to its conversion into thermodynamically stable oxides. Thermodynamic considerations, supported by Molar volume and Pilling-Bedworth ratio (PBR) analysis, confirmed the protective nature of the oxide scales. The sin2ψ approach was utilized to calculate residual stresses in Mo-oxide layers using high-angle XRD (a Bruker D8 Advance XRD machine with Co Kα radiation). Morphological analysis revealed that a reduced porosity in alloy A6 effectively restricted oxygen diffusion pathways. Key oxidation reactions and intermediate oxide formation mechanisms were proposed, highlighting the role of Y2O3 in enhancing the oxide layer's mechanical integrity and chemical stability. These findings demonstrate that nano-dispersed Y2O3 significantly improves the oxidation resistance of Mo-based alloys through complex oxide interactions and phase stabilization mechanisms at elevated temperatures.