Improve oxidation resistance at high temperature by nanocrystalline surface layer

Area of Science:

• Materials Science
• Surface Engineering
• Oxidation Science

Background:

• Conventional P91 steel exhibits a two-layer oxide scale (Fe3O4 outer, FeCr2O4 inner) during oxidation.
• Understanding scale formation is crucial for improving the oxidation resistance of heat-resistant steels.

Purpose of the Study:

• To investigate the effect of surface mechanical attrition treatment on the oxidation behavior of P91 steel.
• To characterize the oxide scale structure formed after treatment and identify changes in oxidation kinetics.

Main Methods:

• Application of surface mechanical attrition treatment to P91 steel.
• Oxidation experiments followed by detailed characterization of the resulting oxide scale.
• Analysis of diffusion mechanisms for Cr, Fe, and O within the oxide layers.

Main Results:

• A unique three-layer oxide scale (Fe3O4, FeCr2O4, (Fe,Cr)2O3) was observed, differing from the conventional two-layer structure.
• Enhanced diffusivity in the nanocrystalline surface layer led to rapid initial oxidation.
• The formation of a (Fe,Cr)2O3 inner layer inhibited diffusion in later stages, reducing the parabolic oxidation rate.

Conclusions:

• Surface mechanical attrition treatment significantly modifies the oxide scale structure of P91 steel.
• This modification leads to improved oxidation resistance by altering diffusion pathways.
• The study presents a new method to enhance steel oxidation resistance without changing its chromium content.