Oxidation Behavior of (Mo,Hf)Si₂-Al₂O₃ Coating on Mo-Based Alloy at Elevated Temperature

Area of Science:

• Materials Science
• Metallurgy
• Surface Engineering

Background:

• Molybdenum (Mo)-based alloys are crucial for high-temperature applications.
• Their oxidation resistance at elevated temperatures remains a significant challenge.
• Developing effective protective coatings is essential for extending alloy service life.

Purpose of the Study:

• To develop and evaluate a novel (Mo,Hf)Si2-Al2O3 composite coating for Mo-based alloys.
• To investigate the high-temperature oxidation behavior and protective mechanisms of the coating.
• To assess the coating's effectiveness in improving oxidation resistance at 1400 °C.

Main Methods:

• Fabrication of the (Mo,Hf)Si2-Al2O3 composite coating using slurry sintering.
• Isothermal oxidation testing of the coated alloy at 1400 °C.
• Characterization of microstructure, phase composition, and oxidation products using advanced techniques.

Main Results:

• The coating formed a double-layer structure: a MoSi2 inner layer and a (Mo,Hf)Si2-Al2O3 outer composite layer.
• The composite coating provided over 40 hours of oxidation protection at 1400 °C.
• A stable SiO2-based oxide scale containing Al2O3, HfO2, mullite, and HfSiO4 formed, exhibiting low oxygen permeability.

Conclusions:

• The (Mo,Hf)Si2-Al2O3 composite coating effectively protects Mo-based alloys against high-temperature oxidation.
• The formation of a stable, multi-component oxide scale is key to the coating's superior performance.
• This coating represents a promising solution for enhancing the durability of Mo-based alloys in extreme environments.