The Sigma Phase

Hall, E. O.; Algie, S. H.

doi:10.1179/imr.1966.11.1.61

Cited by 199 publications

(11 citation statements)

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“…Whilst the phase is routinely observed in structural metallic systems incorporating Cr additions, such as Ni-based superalloys and stainless steels, its chemical composition is known to vary from system-to-system [13,18,19]. Crystallographically, the phase consists of close packed atomic layers separated from each other by large interatomic distances and arranged in a body centred tetragonal structure, which is responsible for the embrittling nature of the phase [13,18,19]. Generally, it is believed to form with the AxBy formula, in which x and y are approximately equal [18,19].…”

Section: Introductionmentioning

confidence: 99%

“…Crystallographically, the phase consists of close packed atomic layers separated from each other by large interatomic distances and arranged in a body centred tetragonal structure, which is responsible for the embrittling nature of the phase [13,18,19]. Generally, it is believed to form with the AxBy formula, in which x and y are approximately equal [18,19]. In structural metallics, Cr has been identified as the major forming element, and is found in the phase in concentrations of ~ 50 at.%.…”

Section: Introductionmentioning

confidence: 99%

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On the prediction and the formation of the sigma phase in CrMnCoFeNix high entropy alloys

Christofidou

McAuliffe

Mignanelli

et al. 2019

Journal of Alloys and Compounds

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The almost limitless variations in potential compositions of high entropy alloys necessitates the use of computational methods when attempting to optimise for any given application. However, the accuracy of the current thermodynamic approaches commonly being used for this purpose remains under debate, as relatively few validatory studies have been performed. Within the CrMnFeCoNi family of alloys, the formation of the phase and how it is influenced by compositional variations is of particular interest for elevated temperature structural applications. Here, the role of Ni on the formation of the phase has been studied through a systematic series of CrMnFeCoNix alloys, 0 x 1.5, following 1000 hour exposures at temperatures typically found to promote formation. Ni was found to have a significant effect on the phase stability of these alloys, suppressing the phase such that a single solid solution phase was the only stable phase in the CrMnFeCoNi1.5 alloy, whilst the CrMnFeCo alloy formed the phase during solidification. The corresponding thermodynamic predictions varied dramatically from the experimentally observed microstructures, indicating that the underlying databases require further optimisation. Interestingly, it was found that a relatively simple electronic structure based approach, New PhaComp, provided much more accurate predictions of the observed phase formation in the CrMnFeCoNix and CrMnxFeCoNi systems and could be manipulated to obtain formation temperatures. As such, this method could be extremely useful to those wanting to design CrMnFeCoNi high entropy alloys that are free from the phase.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the prediction and the formation of the sigma phase in CrMnCoFeNix high entropy alloys

Christofidou

McAuliffe

Mignanelli

et al. 2019

Journal of Alloys and Compounds

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“…The above-presented description showed how complex metallurgical processes can take place in DSS. The application temperature of DSS is limited at maximum 280–325 °C due to the appearance of the undesirable precipitations [3,9,10,11,12,13,14,15,16,17,18].…”

Section: Introductionmentioning

confidence: 99%

“…DSS has four grades with different pitting resistance equivalent numbers (PREN) which can characterize the corrosion resistance of the steel: lean DSS (PREN < 35), standard DSS (PREN 35–40), super-duplex stainless steel (SDSS) (PREN 40–45), and hyper-DSS (PREN > 45) [3,9,10,11,12,13,14,15,16,17,18].…”

Section: Introductionmentioning

confidence: 99%

Complex Study of Eutectoidal Phase Transformation of 2507-Type Super-Duplex Stainless Steel

Mészarós

Bögre

2019

Materials

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The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat treatment for the eutectoidal phase transformation. Samples were cold rolled at seven different rolling reductions which was followed by heat treatment at five different temperatures. The second sample set was prepared to determine the activation energy of the eutectoidal decomposition process using the Arrhenius equation. Samples were cold rolled at seven different rolling reductions and were heat treated at the same temperature during eight different terms. A third sample set was made to study how another plastic-forming technology, beside the cold rolling, can influence the eutectoidal decomposition. Samples were elongated by single axis tensile stress and were heat treated at the same temperature. The results of the first and the third sample sets were compared. The rest δ-ferrite contents were calculated using the results of AC and DC magnetometer measurements. DC magnetometer was used as a feritscope device in this work. Light microscope and electron back scattering diffraction (EBSD) images demonstrated the process of the eutectoidal decomposition. The thermoelectric power and the hardness of the samples were measured. The results of the thermoelectric power measurement were compared with the results of the δ-ferrite content measurement. The accurate value of the coercive field was determined by a Foerster-type DC coercimeter device.

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“…22) Kim et al 23) reported that the addition of a small amount of Ce (55110 ppm) to HDSSs results in the homogeneous distribution of Ce in the alloy matrix and delays the precipitation of secondary phases by reducing the diffusion rates of Cr, Mo, and W. Park et al 24) showed that partially substituting W for Mo retarded the formation of the · phase in FSSs. This was due to an increase in the tendency of formation of a » phase with a higher nucleation efficiency and lower growth rate than those of the · phase.…”

Section: )mentioning

confidence: 99%

Effect of Cu on the Precipitation of Deleterious Phases and the Mechanical Properties of 27Cr–7Ni Hyper Duplex Stainless Steels

et al. 2014

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Cu addition to the base alloy reduces the total amount of deleterious phases such as chromium nitride and sigma and chi phases. In particular, Cu addition to the base alloy results in pronounced suppression of the amount of sigma phase whereas it slightly facilitates the precipitation of chromium nitride and chi phase along the phase boundaries and within ferrite grains. During the initial stage of aging, the preferential precipitation of chromium nitride and chi phase seems to be closely associated with the retardation of the precipitation of the sigma phase. The preferential precipitation of chromium nitride and the chi phase inhibits the nucleation and growth of the sigma phase by depleting the Cr adjacent to the chromium nitride particles and depleting the Mo and W adjacent to the chi phase. Thus, the addition of Cu to the base alloy reduces its embrittlement owing to the delayed precipitation of these deleterious phases.

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The Sigma Phase

Cited by 199 publications

References 0 publications

On the prediction and the formation of the sigma phase in CrMnCoFeNix high entropy alloys

On the prediction and the formation of the sigma phase in CrMnCoFeNix high entropy alloys

Complex Study of Eutectoidal Phase Transformation of 2507-Type Super-Duplex Stainless Steel

Effect of Cu on the Precipitation of Deleterious Phases and the Mechanical Properties of 27Cr–7Ni Hyper Duplex Stainless Steels

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The Sigma Phase

Cited by 199 publications

References 0 publications

On the prediction and the formation of the sigma phase in CrMnCoFeNix high entropy alloys

On the prediction and the formation of the sigma phase in CrMnCoFeNix high entropy alloys

Complex Study of Eutectoidal Phase Transformation of 2507-Type Super-Duplex Stainless Steel

Effect of Cu on the Precipitation of Deleterious Phases and the Mechanical Properties of 27Cr&ndash;7Ni Hyper Duplex Stainless Steels

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Effect of Cu on the Precipitation of Deleterious Phases and the Mechanical Properties of 27Cr–7Ni Hyper Duplex Stainless Steels