EBSD characterization of the eutectic microstructure in hypoeutectic Fe-C and Fe-C-Si alloys

Kante, Stefan; Leineweber, Andreas

doi:10.1016/j.matchar.2018.01.032

Cited by 8 publications

(5 citation statements)

References 39 publications

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“…The experimental observation that solvent-dispersible, size-controlled metal carbide nanocrystals can be isolated, while maintaining the metal ratios, following a thermal decomposition reaction of PBA is intriguing. The formation of the metal from the carbide follows classical metallurgic pathways via a kinetically slow carbon diffusion process, − as defined by the Pitsch–Petch relationships. − The ability to isolate high-surface-area metal carbides is important in catalysis, where the experimental results provide a convenient strategy to form foam-like mesostructures or size-controlled nanocrystals that are potential catalyst candidates. Although the isolation of metal carbide and metallic phases has been previously reported by solid-state thermal decomposition routes, the ability to isolate both nanocrystal compositions and define the mechanistic attributes of the reaction when carried out lyothermally has not been reported. − Although catalysis was not investigated in this manuscript, the demonstration that controlled PBA decomposition can lead to size, shape, and metal ion ratio-controlled metal carbide (and metal) formation provides a convenient pathway for new catalyst development.…”

Section: Discussionmentioning

confidence: 99%

Prussian Blue Iron–Cobalt Mesocrystals as a Template for the Growth of Fe/Co Carbide (Cementite) and Fe/Co Nanocrystals

et al. 2019

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Controlling the composition, size, and morphology of transition-metal carbides and metals is important for product selectivity in industrial catalytic processes, such as in the Fischer–Tropsch synthesis (FTS). The formation of iron–cobalt carbide nanocatalysts can enhance selectivity in the FTS process if the iron to cobalt ratios are controlled. Unfortunately, this is difficult to achieve in nanocrystals due to ion migration, differences in formation rates, and the requirement of perfect critical nuclei to form prior to the growth of the nanocrystal in colloidal synthesis. In this manuscript, a mixed metal iron–cobalt Prussian blue analogue (PBA) mesocrystal is shown to act as a template for isolating pure phase iron–cobalt carbide and iron–cobalt alloy nanocrystals. The formation of the individual nanocrystals from the heterometallic mesocrystal occurs through sequential decomposition and recrystallization events. The steps in the interconversion are observed by in situ and ex situ analytical techniques allowing a mechanism for carbide and metal formation to be proposed. The synthetic route is scalable and likely to be extendable to a wider range of bimetallic materials using the diverse range of Prussian blue analogues (PBAs) reported in the literature.

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Section: Discussionmentioning

confidence: 99%

Prussian Blue Iron–Cobalt Mesocrystals as a Template for the Growth of Fe/Co Carbide (Cementite) and Fe/Co Nanocrystals

et al. 2019

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“…[17] The microstructure of white-solidified Fe-3.5 wt% C-1.5/3 wt% Si alloys, having C and Si contents typical of cast irons, is mainly composed of coarse eutectic cementite plates, θ-Fe 3 C 1Àz (Table 1), embedded in ferrite and pearlite. [20,21] The latter result from the decomposition of primary and eutectic γ-Fe during cooling after solidification. In addition, a minor volume fraction of Fe 23 Si 5 C 4 -type silicocarbide (Table 1) is contained in the alloys.…”

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confidence: 99%

Nitriding of White‐Solidified Fe–C–Si Alloys: Diffusion Path Concept Applied to Inhomogeneous Microstructures

2021

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Gray-solidified cast irons are frequently used to manufacture machine and engine parts due to their low cost, good compressive strength, and high damping capacity. [1,2] Their use is, however, often limited by poor surface hardness and corrosion resistance. Both can be notably improved by a duplex surface treatment developed in recent years. [3][4][5][6] First, the surface of the cast iron is remelted, e.g., by an electron beam or plasma arc. This produces a white-solidified, ledeburitic [7,8] surface layer, which is hard and abrasion-resistant. Afterward, the material is nitrided to enhance the corrosion resistance by the formation of a dense surface layer composed of the main Fe (carbo)nitrides, γ 0 -Fe 4 (N,C) and ε-Fe 3 (N,C) 1þx (Table 1), denoted compound layer. Note that nitriding without remelting leads to less favorable microstructures because coarse graphite particles contained in gray-solidified cast irons are detrimental to the compound layer formation. [3,4,[9][10][11] Although the general advantages of the previously described duplex treatment have been demonstrated, the nitriding behavior of the white-solidified surface layers turns out to be complex and incompletely understood. [12][13][14][15][16][17][18][19] The research of the current authors [12,18,19] aims at elucidating the complex nitriding behavior of the remelted surface layers by controlled gas nitriding of white-solidified Fe-3.5 wt% C-0/1.5/3 wt% Si alloys, serving as model alloys for commercially available ferritic cast iron grades subjected to remelting and nitriding. Note that, in contrast to ferritic cast irons, pearlitic cast irons often contain non-negligible additions of Mn and Cu, which may additionally affect the nitriding behavior. [17] The microstructure of white-solidified Fe-3.5 wt% C-1.5/3 wt% Si alloys, having C and Si contents typical of cast irons, is mainly composed of coarse eutectic cementite plates, θ-Fe 3 C 1Àz (Table 1), embedded in ferrite and pearlite. [20,21] The latter result from the decomposition of primary and eutectic γ-Fe during cooling after solidification. In addition, a minor volume fraction of Fe 23 Si 5 C 4 -type silicocarbide (Table 1) is contained in the alloys. [22][23][24] The distribution of Si in the white-solidified microstructure is very heterogeneous. The Si/Fe atomic ratio in the eutectic and pearlitic θ is u Si,θ < 3 Â 10 À4 and, here, considered negligible, say u Si,θ ! 0. [12] The Si/Fe atomic ratio in Fe 23 Si 5 C 4 is u Si,Fe 23 Si 5 C 4 % 0.22; however, it might take also values slightly different from 0.22 due to a possibly mixed Fe/Si site [23,24] and extended lattice defects affecting the composition. [22] The Si content in α-Fe relates to the Si content of γ-Fe, which is affected by Si segregation during solidification. The Si content in the center of γ-Fe dendrites is typically similar to the Si content of the alloy, while the outer rim of dendrites and last-to-freeze regions are enriched in Si. [25] The Si content in eutectic γ-Fe is higher

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“…At high temperature, cementite is non-stoichiometric and contains carbon vacancies [23,45,46]. These vacancies are quenched-in due to fast cooling after solidification and lead to characteristic changes in the cementite lattice parameters (results presented elsewhere [10]). At low temperature, cementite is approximately stoichiometric.…”

Section: Thermal Stability Of the Eutectic Cementitecoarsening And Grmentioning

confidence: 96%

“…The portion of rod eutectic, however, varies with the solidification technique (see below). More detailed information on the microstructures of mold-cast and remelted M3.5 and M3.9 and of the remelted conventional cast irons is presented in the literature [10,14]. Moreover, Xray diffraction and microscopic investigations indicate the existence of another phase in the alloys with high silicon content -especially in M4.4 and C4.4.…”

Section: Microstructure and Hardness Of White-solidified Low-alloy Camentioning

confidence: 99%

“…White-solidified low-alloy cast iron is characterized by a microstructure, which forms upon the metastable cementite/austenite eutectic reaction. The metastable eutectic microstructure is frequently referred to as ledeburite and has been extensively investigated [1][2][3][4][5][6][7][8][9][10]. Ledeburite is characterized by two growth morphologies, i. e. elongated alternating plates of cementite and austenite as well as austenite rods embedded in a cementite matrix [1].…”

Section: Introductionmentioning

confidence: 99%

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Low‐temperature annealing and graphitizing of white‐solidified low‐alloy cast irons

Kante

Leineweber

Holst

et al. 2019

Materialwissenschaft Werkst

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Hypoeutectic iron‐carbon and iron‐carbon‐silicon model alloys as well as conventional cast irons GJL‐250mod and EN‐GJS‐600‐3 have been produced and processed by different solidification techniques, i. e. mold casting, electron beam surface remelting and melt spinning. The white‐solidified alloys exhibit different degrees of microstructural refinement indicated by a secondary dendrite arm spacing of 0.3 μm–12 μm. The effects of microstructural refinement and silicon content on the hardness as well as on coarsening of cementite and graphitizing at temperatures of 540 °C to 670 °C have been investigated. The hardness of the as‐solidified alloys increases with decreasing secondary dendrite arm spacing and increasing silicon content. High silicon content effectively retards coarsening of pearlitic cementite, and thus is beneficial to retain the hardness at small thermal load. On the downside, high degree of microstructural refinement and high silicon content promote and accelerate graphitizing at temperatures > 600 °C. The results are discussed in terms of the applicability of a recently developed two‐step surface treatment for cast irons, i. e. electron beam remelting followed by nitriding.

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EBSD characterization of the eutectic microstructure in hypoeutectic Fe-C and Fe-C-Si alloys

Cited by 8 publications

References 39 publications

Prussian Blue Iron–Cobalt Mesocrystals as a Template for the Growth of Fe/Co Carbide (Cementite) and Fe/Co Nanocrystals

Prussian Blue Iron–Cobalt Mesocrystals as a Template for the Growth of Fe/Co Carbide (Cementite) and Fe/Co Nanocrystals

Nitriding of White‐Solidified Fe–C–Si Alloys: Diffusion Path Concept Applied to Inhomogeneous Microstructures

Low‐temperature annealing and graphitizing of white‐solidified low‐alloy cast irons

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