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Abstract
Under nitrogen diffusion treatments, N-expanded austenite (γN) can form at the surface of self-passivating Fe-Cr, Ni-Cr, and Co-Cr alloys at low temperatures, which provides beneficial hardening and enhancements in wear resistance without reducing corrosion resistance. Given the wide research interests in multicomponent equimolar alloys, an equimolar quaternary FeCoNiCr high entropy alloy (HEA) was investigated after active-screen plasma nitriding at 430–480 °C in this study. Firstly, the formation of γN-FeCoNiCr case at 430 °C was demonstrated with the bright case appearance after metallographic etching, the lattice expansion under XRD, the FCC electron diffraction patterns and the shear bands under TEM. Secondly, the thick treatment cases at ∼9–16 μm first indicated that N interstitial diffusion was not sluggish in the FeCoNiCr surface. Thirdly, analogous to stainless steels, the onset of dark regions in the etched γN-FeCoNiCr case was owing to the formation of a cellular mixture of CrN + γ-(Fe, Co, Ni) nano-lamellae at elevated treatment temperatures. The residual bright regions in γN-FeCoNiCr at 480 °C showed ∼1–3 nm CrN nanoprecipitates with no substantial Cr segregation. Additionally, a significant nanocrystalline layer was seen at the topmost surface at 480 °C, which is most likely associated with the high substrate Cr content.
Original language | English |
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Article number | 113593 |
Journal | Materials Characterization |
Volume | 208 |
Early online date | 22 Dec 2023 |
DOIs | |
Publication status | Published - 1 Feb 2024 |
Bibliographical note
AcknowledgementThe authors would first like to thank the financial support from Smart Factory Hub (ESIF 06R1702266). The authors acknowledge Prof. Bin Liu at Central South University for providing the materials. The authors also wish to acknowledge the EPSRC ‘Friction: The Tribology Enigma’ Programme Grant (grant number EP/001766/1) and The Henry Royce Institute for Advanced Materials, for access to the JEOL JEM-F200 (funded through EPSRC grant EP/R00661X/1).
Keywords
- Surface alloying
- Plasma nitriding
- Expanded austenite
- High entropy alloys
- Microstructure
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- 1 Finished
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ERDF_Smart Factory Hub (SmartFub)
Dong, H., Essa, K., Attallah, M., Anthony, C., Saadat, M., Cai, B., Pham, D., Kong, M. C., Dimov, S., Castellani, M., Hood, R., Shepherd, D., Soo, L., Gao, N., Espino, D., Dearn, K., Herreros, M., Thomas-Seale, L., Hemida, H., Al-Dadah, R., Tsolakis, A., Jangi, M., Cummins, G., Wang, Y. W., Zeraati Rezaei, S. & Hajiyavand, A.
DEPT FOR COMMUNITIES & LOCAL GOVERNMENT, Yamazaki Mazak Uk Ltd, The Manufacturing Technology Centre Ltd, HMK Technical Services Ltd, KEYENCE (UK) Ltd, Laser Lines, Lasea Sa, Rolls Royce
1/10/18 → 30/06/23
Project: Other Government Departments