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Abstract
Nitrogen-expanded austenite (γN), also known as S phase, is a metastable, interstitial supersaturated phase, that has been extensively studied on AISI 304/316 stainless steel (SS) following N diffusion treatments at low temperatures. Substantial Cr segregation can occur in γN-304/316 under CrN formation at elevated treatment temperatures (typically at above 450 °C), resulting in degradation in corrosion performance. In contrast to 316 SS (mainly based on the Fe-Cr-Ni system), a FeCrNiSi0.5 medium entropy alloy (MEA) was investigated after active screen plasma nitriding (ASPN) at 430–480 °C in this study. Attributable to the equimolar Cr content in the substrate, the ASPN-treated MEA surface showed “excessive” N absorption, which was accompanied by severe surface micro-cracking and a topmost nanocrystalline layer. Nanoprecipitates (∼3-8 nm) can be seen in γN-MEA at treatment temperature as low as 430 °C. However, STEM-EDX analysis of those nanoprecipitates (∼5-30 nm) at 480 °C showed significant Si segregation without observable Cr redistribution, resulting in a uniform “greyish” etched treatment layer. The sluggish Cr segregation in the N-modified MEA surface could originate from both the minor Si addition (via Si-induced nanoprecipitation) and the high equimolar Ni/Cr content in the host matrix.
Original language | English |
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Article number | 157137 |
Number of pages | 12 |
Journal | Applied Surface Science |
Volume | 624 |
Early online date | 25 Mar 2023 |
DOIs | |
Publication status | Published - 1 Jul 2023 |
Keywords
- Surface alloying
- Plasma nitriding
- Medium entropy alloys
- Expanded austenite
- Microstructure
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Dive into the research topics of 'Active screen plasma nitriding of a Si-alloyed FeCrNi medium entropy alloy: High interstitial absorption and an anomalous Si-induced decomposition mechanism in N-expanded austenite'. Together they form a unique fingerprint.Projects
- 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