On the precipitation during age hardening of CoCrFeMnNi with Al and Ti additions
(2026) Journal of Alloys and Compounds — Vol. 1050, p. 185757 (2026)
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Miotti Bettanini, Alvise 
- Abstract
- High entropy alloys (HEAs) based on Co-Cr-Fe-Mn-Ni transition metals with Al and Ti additions constitute a versatile system to generate complex microstructures. In this study, microstructures consisting of a ductile FCC matrix with hard BCC, sigma, and fine precipitates are obtained after thermo-mechanical treatments by varying the amounts of Al and Ti, specifically (CoCrFeMnNi)100-x(Al2Ti)x, x=6, 8, 10. Ageing is performed in the range of 650 to 850°C up to 160 hours. Additionally, the effect of ageing is compared between as-cold-rolled state and after solution treatment. Bulk hardness values ranges from 300 to 600 HV due to the precipitation of a (Cr, Fe, Mn)-rich sigma phase and a (Co, Ni, Al, Ti)-rich BCC phase, as characterized by nanoindentation, EBSD, and STEM. A higher content of Al/Ti increases the volume fraction of secondary phases, increasing hardness. During ageing, precipitation occurs in three stages with first the precipitation of a BCC secondary phase, second the concurrent precipitation of sigma and BCC phases, and third the formation of needle-like BCC precipitates. L12 precipitates have not been observed in the range of compositions and heat treatments investigated.
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Citations
Hilhorst, A., Miotti Bettanini, A., Callahan, M., & Jacques, P. (2026). On the precipitation during age hardening of CoCrFeMnNi with Al and Ti additions. Journal of Alloys and Compounds, 1050, 185757. https://doi.org/10.1016/j.jallcom.2025.185757 (Original work published 2026)