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Article Dans Une Revue Journal of Applied Physics Année : 2023

Non-classical nucleation of ordered L12 precipitates in the FCC based Al0.25CoFeNi high entropy alloy

Résumé

The complex interplay between competing phase stabilities of FCC, L12, BCC, and B2 phases in the Al0.25CoFeNi (7Al-31Co-31Fe-31Ni in at%) high entropy alloy (HEA), leads to non-classical phase transformation pathways and resultant novel microstructures. Specifically, the competition between homogenous precipitation of L12 and heterogenous precipitation of BCC/B2 can be studied at a temperature of 500 o C in Al0.25CoFeNi alloy. Upon isothermally annealing the single FCC phase microstructure of this HEA at 500 o C up to 50 hours, the transformation initiates with the formation of a transient ordered L12 phase with minor Ni-Al enrichment, which is far-from equilibrium, as revealed by atom probe tomography, and can be considered as non-classical nucleation. The near equilibrium L12 phase eventually replaces the transient L12 during continued annealing at the same temperature. However, the resultant FCC+L12 microstructure is metastable because the true equilibrium for the Al0.25CoFeNi alloy at 500°C is a mixture of L12+B2 phases, as revealed by solution thermodynamics modeling. The higher nucleation barrier for the BCCbased ordered B2 phase coupled with the slower kinetics at 500 o C, leads to the homogeneous precipitation of L12, while the B2 phase appears to sluggishly grow from grain boundaries acting as heterogeneous nucleation sites.
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Dates et versions

hal-04160302 , version 1 (12-07-2023)

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Sriswaroop Dasari, Abhishek Sharma, Stéphane Gorsse, Advika Chesetti, Rajarshi Banerjee. Non-classical nucleation of ordered L12 precipitates in the FCC based Al0.25CoFeNi high entropy alloy. Journal of Applied Physics, 2023, 134 (1), pp.015102. ⟨10.1063/5.0138924⟩. ⟨hal-04160302⟩
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