Enhanced Oxidation Resistance of Ultrafine-Grain Microstructure AlCoCrFeNi High Entropy Alloy

Mayank Garg; Harpreet S Grewal; Ram K Sharma; Harpreet S Arora

doi:10.1021/acsomega.1c06014

Enhanced Oxidation Resistance of Ultrafine-Grain Microstructure AlCoCrFeNi High Entropy Alloy

ACS Omega. 2022 Apr 7;7(15):12589-12600. doi: 10.1021/acsomega.1c06014. eCollection 2022 Apr 19.

Authors

Mayank Garg¹, Harpreet S Grewal¹, Ram K Sharma², Harpreet S Arora¹

Affiliations

¹ Surface Science and Tribology Lab, Department of Mechanical Engineering, Shiv Nadar University, Greater Noida, Uttar Pradesh 201314, India.
² Centre for Inter-Disciplinary Research and Innovation, University of Petroleum and Energy Studies, Bidholi Via-Prem Nagar, Dehradun, Uttarakhand 248007, India.

Abstract

This work investigates the effect of ultrafine-grain microstructure on the oxidation behavior of AlCoCrFeNi high entropy alloy (HEA). The ultrafine-grain microstructure is obtained using stationary friction processing performed at two different rotational speeds, 400 and 1800 rpm, for 5 min duration. Processed samples demonstrate high depth of refinement (DOR) and ultrafine grain size (0.43-1 μm) at high rotational speeds along with significant phase transformations from BCC/B2 to FCC microstructure. Further, surface free energy of the ultrafine-grain microstructure is enhanced up to 35%. Oxidation kinetics of the ultrafine-grained sample is decelerated up to 12-48% in a temperature range of 850-1050 °C for a duration of 100 h. Chromia and alumina were the predominant oxides formed in almost all the samples oxidized at elevated temperature. In addition, spinel Co(Cr,Fe)₂O₄/Fe(Co,Cr)₂O₄ formation is also detected in the unprocessed oxidized samples. Processed samples rich in grain boundaries (GBs) promote internal oxidation to form Al-rich inner oxides. The enhanced oxidation resistance of the processed samples is attributed to the microstructural refinement and homogenization resulting in the formation of protective chromia followed by Al-rich inner oxides.