Exploring the impact of Ti/Al on L12 nanoprecipitation and deformation behavior in CoNiFeAlTi multi-principal element alloys through atomistic simulations

A Esfandiarpour and ADS Parmar and S Bonfanti and P Sobkowicz and BJ Lee and M Alava, JOURNAL OF ALLOYS AND COMPOUNDS, 1035, 181580 (2025).

DOI: 10.1016/j.jallcom.2025.181580

Recent experimental studies on CoNi-based multi-principal element alloys (MPEAs) have demonstrated high strength and ductility, attributed to the formation of stable L12 nanoscale precipitates. However, the fundamental mechanisms behind such impressive properties in these complex alloys are not well understood. In this work, we investigate the effects of Ti and Al concentrations on the formation of L12 precipitates in (CoNiFe)84(Al8Ti8), (CoNiFe)86(Al7Ti7), (CoNiFe)88(Al6Ti6), and (CoNiFe)94(Al4Ti2) MPEAs using hybrid molecular dynamics/Monte Carlo (MD/MC) simulations and a developed MEAM interatomic potential for the CoNiFeTiAl system. Additionally, we study the effect of L12 precipitation on the mechanical properties and stacking fault energy of these MPEAs using MD. Our hybrid MD/MC simulations show that (CoNiFe)86(Al7Ti7) alloy exhibits the highest amount of L12 nanoprecipitates. We find that L12 precipitation increases the stacking fault energy, with higher Al and Ti contents leading to greater increases. Tensile simulations reveal that L12 precipitates enhance yield strength, with alloys exhibiting higher precipitation showing increased flow stress. We also investigate dislocation-nanoprecipitate interactions with different precipitate sizes in (CoNiFe)86(Al7Ti7) alloy. Larger nanoprecipitate sizes result in stronger dislocation pinning. Dislocation-precipitate interactions indicate that dislocations predominantly shear through 4-8 nm precipitates instead of looping around them (Orowan mechanism), which enhances strength while maintaining good ductility. Although the lattice mismatch between the L12 nanoprecipitate and the matrix is low (0.139 %), the significant difference in stacking fault energy between the L12 nanoprecipitate and the matrix results in stronger dislocation pinning. This fundamental understanding can guide the compositional design of MPEAs with tailored properties by controlling nanoscale precipitation.

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