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Metals
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Segregation Phenomena in Alloys Systems
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Segregation Phenomena in Alloys Systems

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (27 November 2020) | Viewed by 16362

Special Issue Editor

Prof. Dr. Mohammad Jahazi

E-Mail Website
Guest Editor
Ecole de Technologie Superieure, Département de Génie Mécanique, Montreal, Canada
Interests: manufacturing processes-materials-mechanical properties; hot deformation processes: forging, rolling, extrusion, superplastic forming; new joining processes: fsw, lfw, ebw, tlp; microstructure characterization and modeling; optimization of mechanical properties; phase transformation, recrystallization and prepcipitation in metallic materials; heat treatment
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The most important characteristic of an alloy is the presence of one or more elements in its composition. This presence is at the origin of the significant changes in the properties of the alloy, in particular, its mechanical properties. High strength steels, nickel-based superalloys, and titanium or aluminum alloys could contain up to 20 different alloying elements, which are critical engineering materials that owe their extraordinary properties to the interactions between the elements and their impact on phase formations, phase transformation, and microstructure evolution. However, the differences associated with the inherent nature of each element result in the formation of localized regions with different chemical compositions than the nominal one of the alloys during the subsequent processing operations, such as solidification, solid state forming, and heat treatment. Segregation refers to the formation of such local chemical heterogeneities, and is one of the biggest challenges faced when processing multicomponent systems. Segregation could be responsible for the formation of cracks; undesirable second phases; changes in the transition temperature; the modification of physical, microstructural, and mechanical properties of the final product; and result in quality reduction or even the rejection of the part.

Segregation is classified according to its scale of occurrence on microsegregation, which corresponds to the chemical inhomogeneities at the scale of the interfaces (e.g., dendrites and grain boundaries), while macrosegregation is usually observed in large-size cast products such as ingots and slabs, and can extend in the range of centimeters or meters. In recent years, with the advent of new manufacturing technologies, such as additive manufacturing, as well as the request for ever larger size castings, the impact of segregation on product quality has become highly important.

In this context, it is of great importance to better understand the mechanisms influencing the occurrence of segregation at different scales, especially knowing that there are very little data on the effect of the different process parameters on alloying element segregation behaviors. Segregation studies require both experimental and simulation investigations. The role of experimental methods is to provide information about segregation behaviors. However, this task is more complicated in the case of large-size ingots, where the experimental studies are very costly and time consuming, or at a very small scale, such as additive manufacturing, where several cycles of solidification and heat treatment operations are applied during the fabrication of one single part. The use of simulation tools would allow for reducing of cost and the rapid identification of the influence of each parameter. Nevertheless, simulation studies require the use of reliable and representative thermophysical and thermomechanical input data. However, the determination of these parameters is not easy, because of their dependence on the chemical composition, temperature, and cooling rate.

The main objective of this Metals Special Issue is to cover the significant scientific and technical challenges of experimental or simulation studies related to segregation phenomena in alloys.

Prof. Mohammad Jahazi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Segregation
  • Chemical heterogeneity
  • Interfaces
  • Equilibrium segregation
  • Non-equilibrium segregation
  • Macro-segregation
  • Micro-segregation
  • Diffusion

Published Papers (4 papers)

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Research

12 pages, 3187 KiB  
Article
Kinetics of Arsenic Surface Segregation in Scrap-Based Silicon Electrical Steel
by Darja Steiner Petrovič
Metals 2021, 11(1), 1; https://doi.org/10.3390/met11010001 - 22 Dec 2020
Cited by 2 | Viewed by 2332
Abstract
The segregation kinetics of surface-active, residual elements are investigated in an in situ study of annealing scrap-based silicon electrical steel sheet where the arsenic (As) surface segregation is highlighted. During annealing in the temperature range of 300–950 °C, different kinds of interactions between [...] Read more.
The segregation kinetics of surface-active, residual elements are investigated in an in situ study of annealing scrap-based silicon electrical steel sheet where the arsenic (As) surface segregation is highlighted. During annealing in the temperature range of 300–950 °C, different kinds of interactions between the segregated residual elements were observed. Attractive interactions between the segregands produced co-segregation, e.g., between Sn and Sb, whereas repulsive interactions resulted in site competition, e.g., between Sn and As. These competing interactions are strongly time dependent. In spite of there being twice as much Sn compared to As in the bulk material, the As prevailed in the surface enrichments of the polycrystalline silicon steel at 950 °C. The intensity of the As surface segregation in the temperature range 800–950 °C is proportional to the calculated amount of γ-austenite phase in the (α + γ) steel matrix. The detected phenomenon of the As versus Sn site competition could be valuable for the texture design and surface engineering of silicon steels with a thermodynamically stable two-phase (α + γ) region. Full article
(This article belongs to the Special Issue Segregation Phenomena in Alloys Systems)
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27 pages, 5208 KiB  
Article
Effect of the Microsegregation on Martensitic and Bainitic Reactions in a High Carbon-High Silicon Cast Steel
by Alejandro Daniel Basso, Isaac Toda-Caraballo, Adriana Eres-Castellanos, David San-Martin, José Antonio Jimenez and Francisca G. Caballero
Metals 2020, 10(5), 574; https://doi.org/10.3390/met10050574 - 28 Apr 2020
Cited by 4 | Viewed by 5007
Abstract
Casting processes show some weaknesses. A particular problem is presented when the workpiece needs to be subjected to heat treatments to achieve a desired microstructure. This problem arises from the microsegregation phenomena typically present in cast parts. The effect of the microsegregation on [...] Read more.
Casting processes show some weaknesses. A particular problem is presented when the workpiece needs to be subjected to heat treatments to achieve a desired microstructure. This problem arises from the microsegregation phenomena typically present in cast parts. The effect of the microsegregation on the martensitic and bainitic transformations has been investigated in a high carbon-high silicon cast steel, with the approximate composition Fe-0.8C-2Si-1Mn-1Cr (in wt. %), which was poured into 25 mm keel block-shaped sand molds. The microsegregation maps of Cr, Si, and Mn characterized by electron probe microanalysis (EPMA) show that interdendritic regions are enriched while dendrites are impoverished in these elements, implying that their partition coefficients are lower that the unity (k < 1). As-quenched martensitic and austempered bainitic microstructures (at 230 °C) were obtained and analyzed after applying an austenitization heat treatment at 920 °C (holding for 60 min). The thermal etching method used to reveal the prior austenite grain size showed a bimodal grain size distribution, with larger grains in the dendritic regions (≈22.4 µm) than in the interdendritic ones (≈6.4 µm). This is likely due to both the microsegregation and the presence of small undissolved cementite precipitates. Electron Backscatter Diffraction (EBSD) analysis carried out on the martensitic microstructure do not unveil any differences in misorientation distribution frequency and block size between the dendritic and interdendritic zones related to the microsegregation and bimodality of the austenite grain size. On the contrary, the bainitic transformation starts earlier (incubation time of 80 min), proceeds faster and bainitic ferrite plates are longer in the dendritic zones, were prior austenite grains are larger and impoverish in solute. The presence of these microsegregation pattern leads to the non-uniform development of the bainitic reaction in cast parts, modifying its kinetics and the resulting microstructures, which would probably have a major impact on the mechanical properties. Full article
(This article belongs to the Special Issue Segregation Phenomena in Alloys Systems)
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12 pages, 4663 KiB  
Article
Method of Verification of Carbon Segregation Ratio Determined with Experimental Methods
by Jan Falkus, Katarzyna Miłkowska-Piszczek, Paweł Krajewski and Tomasz Ropka
Metals 2020, 10(4), 499; https://doi.org/10.3390/met10040499 - 10 Apr 2020
Cited by 3 | Viewed by 3073
Abstract
The problem of macrosegregation of alloying elements occurring during cast strand solidification in the continuous casting process is still valid; it is the subject of numerous experiments and theoretical considerations. A large percentage of this research is dedicated to carbon segregation, which, for [...] Read more.
The problem of macrosegregation of alloying elements occurring during cast strand solidification in the continuous casting process is still valid; it is the subject of numerous experiments and theoretical considerations. A large percentage of this research is dedicated to carbon segregation, which, for understandable reasons, is vital for the production of high-carbon steels. The background knowledge on the mechanism of segregation occurrence indicates that it is a very complex effect, and a broad range of factors influencing the continuous casting process need to be considered. Therefore, it is difficult to translate information (provided by complex models of metal flow through a diphase area at the solidification interface of a cast strand) into practical engineering recommendations to reduce the macrosegregation effect. The presented study shows the latest research related to the carbon macrosegregation effect for selected high-carbon steel grades cast with a continuous caster. Problems related to the recording of the effect concerned have been pointed out. The second part of the paper presents the influence of selected casting parameters on carbon macrosegregation intensity when casting 160 × 160 billets with a six-strand caster. In this case, the main subject of the research was the influence of the casting speed on macrosegregation intensity. In the following step, an attempt was made to find the relationship between the cast strand structure and the distribution of carbon content on its cross-section. The ultimate objective of the presented study was to find an answer to the question on the technological capabilities of restricting the segregation effect. Full article
(This article belongs to the Special Issue Segregation Phenomena in Alloys Systems)
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17 pages, 5826 KiB  
Article
On the Impact of Microsegregation Model on the Thermophysical and Solidification Behaviors of a Large Size Steel Ingot
by Chunping Zhang, Mohammad Jahazi and Paloma Isabel Gallego
Metals 2020, 10(1), 74; https://doi.org/10.3390/met10010074 - 02 Jan 2020
Cited by 6 | Viewed by 3475
Abstract
The impact of microsegregation models on thermophysical properties and solidification behaviors of a high strength steel was investigated. The examined microsegregation models include the classical equilibrium Lever rule, the extreme non-equilibrium Scheil-Gulliver, as well as other treatments in the intermediate regime proposed by [...] Read more.
The impact of microsegregation models on thermophysical properties and solidification behaviors of a high strength steel was investigated. The examined microsegregation models include the classical equilibrium Lever rule, the extreme non-equilibrium Scheil-Gulliver, as well as other treatments in the intermediate regime proposed by Brody and Flemings, Clyne and Kurz, Kobayashi and Ohnaka. Based on the comparative analyses performed on three representative regions with varied secondary dendrite arm spacing sizes, the classical equilibrium Lever rule and non-equilibrium Scheil scheme were employed to determine the thermophysical features of the studied steel, using the experimentally verified models from literature. The evaluated thermophysical properties include effective thermal conductivity, specific heat capacity and density. The calculated thermophysical data were used for three-dimensional simulation of the casting and solidification process of a 40 metric ton steel ingot, using FEM code Thercast®. The simulations captured the full filling, the thermo-mechanical phenomena and macro-scale solute transport in the cast ingot. The results demonstrated that Lever rule turned out to be the most reasonable depiction of the physical behavior of steel in study in large-size cast ingot and appropriate for the relevant macrosegregation simulation study. The determination of the model was validated using the experimentally measured top cavity dimension, the thermal profiles on the mold outside surface by means of thermocouples, and the carbon distribution patterns via mass spectrometer analysis. Full article
(This article belongs to the Special Issue Segregation Phenomena in Alloys Systems)
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