Phase stability and kinetics of σ-phase precipitation in CrMnFeCoNi high-entropy alloys

Laplanche, Guillaume; Berglund, Sean P.; Reinhart, C.; Kostka, Aleksander; Fox, F.; George, E.P.

doi:10.1016/j.actamat.2018.09.040

Cited by 233 publications

(64 citation statements)

References 43 publications

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“…5. These peaks are often reported as being characteristic of the phase [19,27,28,45,46], and therefore, it is thought that the lightcontrast precipitates correspond to the phase.…”

Section: Crmnfeco15nimentioning

confidence: 99%

Effect of Co on the phase stability of CrMnFeCoxNi high entropy alloys following long-duration exposures at intermediate temperatures

2019

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The effect of Co on the phase stability of the CrMnFeCoxNi family of alloys, where the atomic ratio x = 0, 0.5, 1.5, has been experimentally established following 1000 hour heat treatments at 700 and 900˚C and up to 5000 hours at 500˚C. All the alloys were single phase fcc in the homogenised condition, except for CrMnFeNi which also contained bcc precipitates that remained present following exposures at 900˚C and 700˚C. The exposures at 900˚C and 700˚C also resulted in the formation of phase precipitates in the CrMnFeNi and CrMnFeCo0.5Ni alloys but not in the CrMnFeCo1.5Ni alloy. These data, in conjunction with results previously published in the literature, conclusively establish that Co stabilises the fcc matrix at elevated temperatures. However, at 500˚C, further bulk decomposition in the CrMnFeNi alloy was observed and produced a fine-scale intergrowth of a NiMn L10 phase and CrFe phase. Grain boundary precipitates were also observed following exposure at 500˚C in the CrMnFeCo0.5Ni and CrMnFeCo1.5Ni alloys. Four different phases were observed on the grain boundaries of the CrMnFeCo0.5Ni alloy (Cr carbide, , FeCo B2 and NiMn L10), whilst only two phases were found on the grain boundaries of the CrMnFeCo1.5Ni alloy (Cr carbide and NiMn L10). The experimental observations facilitated an assessment of the fidelity of current thermodynamic predictions of phase equilibria. All the phases predicted were observed experimentally and the stability fitted the experimental observations well. However, at lower temperatures, thermodynamic predictions were less consistent with experimental observations, underpredicting the extent of the B2 phase field and failing to predict the formation of the L10 phase.

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“…5. These peaks are often reported as being characteristic of the phase [19,27,28,45,46], and therefore, it is thought that the lightcontrast precipitates correspond to the phase.…”

Section: Crmnfeco15nimentioning

confidence: 99%

Effect of Co on the phase stability of CrMnFeCoxNi high entropy alloys following long-duration exposures at intermediate temperatures

2019

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“…The sigma phase is FeCr type with the space group of P4 2 mnm À1 . [3] The tetragonality (c/a) increases from 0.50 at 700 C to 0.513 at 1000 C. Another tetragonal phase is recognized as the MnNi-type phase (space group I4 mmm À1 ) where its tetragonality declines from 1.01 at 700 C to 0.95 at 1000 C. In other words, the tetragonal phase is formed at the starting stage of sintering, and it likely changes to the tetragonal phase as the temperature is raised. By considering the binary phase diagrams of Mn-V, Fe-V, Ni-V, and Co-V, [34] it is revealed that the composition range for the formation of tetragonal phases, especially the sigma phase, is relatively wide.…”

Section: Phase Evaluationmentioning

confidence: 99%

“…Mishra and Shahi [4] have observed that after 20 h of milling, the CrFeMnNiTi alloy could decompose into the FCC, BCC, and sigma phases and the alloy did not show any change in the phases even after vacuum annealing at 700 C. The phase separation was also reported in the AlCoCrFeNi HEA where the addition of Al, as a BCC stabilizer, caused not only a transition from FCC to BCC [1,17] , but also led to the formation of AlNitype and AlNi 3 -type (L1 2 ) phases. [1,11] As mentioned in the literature, one of the most important products of phase separation is the sigma (σ) phase, which is reported in several HEAs containing Fe-Cr and V. [3,16,18,19] The sigma phase, considered as a topologically close-packed (TCP) phase, has a tetragonal structure (space group P4 2 mnm À1 ) that contains 30 atoms per unit cell. [3] It has been reported that the sigma phase in the FeCoNiMnCr HEA is formed after annealing at temperatures below 1070 C. [3] Nonetheless, the formation of the sigma phase is affected by annealing conditions as well as the alloying elements.…”

Section: Introductionmentioning

confidence: 99%

“…[1,11] As mentioned in the literature, one of the most important products of phase separation is the sigma (σ) phase, which is reported in several HEAs containing Fe-Cr and V. [3,16,18,19] The sigma phase, considered as a topologically close-packed (TCP) phase, has a tetragonal structure (space group P4 2 mnm À1 ) that contains 30 atoms per unit cell. [3] It has been reported that the sigma phase in the FeCoNiMnCr HEA is formed after annealing at temperatures below 1070 C. [3] Nonetheless, the formation of the sigma phase is affected by annealing conditions as well as the alloying elements. [20] According to the literature survey, in the multiphase HEAs, each constituent phase has a significant role in the overall properties of the alloy.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, the experimental evidence on this composition has proved that the formation of the second phase in addition to the solid solution matrix seems to be inevitable. [3][4][5] As a result, each HEA with new composition needs to be studied in terms of phase formation and the factors that affect phase stability.…”

Section: Introductionmentioning

confidence: 99%

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Microstructural Characterization of Mechanically Alloyed FeCoNiMnV High Entropy Alloy Consolidated by Spark Plasma Sintering

et al. 2019

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The microstructure and phase evolution of the mechanically alloyed FeCoNiMnV high entropy alloy during spark plasma sintering are examined. The milled powders are sintered at different temperatures ranging between 500 C and 1000 C. A multiphase structure is produced during the sintering process. The produced alloy experiences different types of decompositions and phase formations as the sintering temperature is raised. During sintering at different temperatures, the body centered cubic and face centered cubic (FCC) phases are transformed to new FCC and tetragonal phases. According to the results, V does not show the tendency to dissolve into the structure and the tetragonal phases, mainly composed of V and Mn, tending to be formed in addition to the FCC solid solution. Sintering at 900 C results in the grain size of about 220 nm, attaining the highest hardness of about 450 HV. The sintered alloy at 1000 C shows the highest relative density (about 98%) with an average grain size of about 580 nm. The phase formation is predicted and evaluated by different criteria, and the consistency between the theoretical and experimental results is explained.

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Microstructure and Mechanical Properties of Face‐Centered‐Cubic‐Based Cr‐Free Equiatomic High‐Entropy Alloys

Liu

Zhang

et al. 2020

Adv Eng Mater

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High‐entropy alloys (HEAs) with face‐centered‐cubic (FCC) structures, e.g., the typical CrMnFeCoNi HEA, have a strong tendency to precipitate brittle sigma phases, as Cr is a strong sigma stabilizer. To develop HEAs with alleviated concerns of sigma phases, Cu for Cr in the Cr‐Mn‐Fe‐Co‐Ni HEA system is substituted to form a Mn‐Fe‐Co‐Ni‐Cu system. The quinary alloy and its quaternary subsets are investigated all in as‐cast state. Microstructure evolution, phase constituent, and tensile properties at room temperature are studied. The HEAs have multi‐phase FCC structures with slightly different lattice constants and spherical Cu‐rich particles are observed in most systems. All alloys exhibit dendrite‐like morphology with Cu segregation in interdendritic regions due to the solute partitioning. The investigated HEAs show good strengths, large elongations, and work hardening capability. The strengths are attributed to combined mechanisms, especially the precipitation strengthening by Cu‐rich particles. The findings provide some model HEA systems for further usefully guiding design in the widely compositional space of Cr‐free HEAs.

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Phase stability and kinetics of σ-phase precipitation in CrMnFeCoNi high-entropy alloys

Cited by 233 publications

References 43 publications

Effect of Co on the phase stability of CrMnFeCoxNi high entropy alloys following long-duration exposures at intermediate temperatures

Effect of Co on the phase stability of CrMnFeCoxNi high entropy alloys following long-duration exposures at intermediate temperatures

Microstructural Characterization of Mechanically Alloyed FeCoNiMnV High Entropy Alloy Consolidated by Spark Plasma Sintering

Microstructure and Mechanical Properties of Face‐Centered‐Cubic‐Based Cr‐Free Equiatomic High‐Entropy Alloys

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