Unusual Iron Nitride Formation Upon Nitriding Fe-Si Alloy

Meka, Sai Ramudu; Schubert, Andreas; Bischoff, E.; Mittemeijer, E. J.

doi:10.1007/s11661-020-05713-4

Cited by 14 publications

(19 citation statements)

References 47 publications

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“…Upon nitriding Fe-1.0/2.3wt pctSi alloys, e has been observed at nitriding conditions only allowing for the formation of c¢ in pure a-Fe. [33,34] A higher Si solubility in e as compared to a negligible solubility in c¢ was assumed to promote the formation of e. It seems uncertain whether the reported phase mixtures containing e and c¢ represent a state of equilibrium. * Upon nitriding Fe-3.5wt pctC-1.5/3wt pctSi alloys also at conditions only allowing for c¢ formation in pure a-Fe, STEFAN KANTE and ANDREAS LEINEWEBER are with the Institute of Materials Science, TU Bergakademie Freiberg, Gustav-Zeuner-Str.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, little is known about the formation sequence of e and c¢ as well as the microstructure evolution of compound layers containing both nitrides in Fe-Si-base alloys. [30,34,36] Microstructure investigations were largely focused on c¢ in Si-rich ferrite. c¢ plates were observed, which protrude from the compound layer into the diffusion zone, [33,34,[36][37][38] and which are referred to as plate-type c¢ in the present work.…”

Section: Introductionmentioning

confidence: 99%

“…[30,34,36] Microstructure investigations were largely focused on c¢ in Si-rich ferrite. c¢ plates were observed, which protrude from the compound layer into the diffusion zone, [33,34,[36][37][38] and which are referred to as plate-type c¢ in the present work. Moreover, a ''tooth''-like morphology of c¢ has been described.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, a ''tooth''-like morphology of c¢ has been described. [34] This ''tooth''-like c¢ is composed of two R3-related c¢ grains which exhibit the Nishiyama-Wassermann orientation relationship (OR) with a-Fe (Table II). In contrast to ''tooth''-like c¢, crystallographic features of the more frequently reported plate-type c¢ in Fe-Si alloys have not been studied.…”

Section: Introductionmentioning

confidence: 99%

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Fe Nitride Formation in Fe–Si Alloys: Crystallographic and Thermodynamic Aspects

Kante

Leineweber

2021

Metall Mater Trans A

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A Fe–3wt pctSi alloy was gas nitrided to study the effect of Si on the Fe nitride formation. Both ε-Fe3N1+x and γ′-Fe4N were observed at nitriding conditions only allowing to form single-phase γ′ layers in pure α-Fe. During short nitriding times, ε and γ′ simultaneously grow in contact with Si-supersaturated α-Fe(Si). Both nitrides almost invariably exhibit crystallographic orientation relationships with α-Fe, which are indicative of a partially displacive transformation of α-Fe being involved in the initial formation of ε and γ′. Due to Si constraining the Fe nitride growth, such transformation mechanism becomes highly important to the nitride layer formation, causing α-Fe-grain-dependent variations in the nitride layer morphology and thickness, as well as microstructure refinement within the nitride layer. After prolonged nitriding, α-Fe is depleted in Si due the pronounced precipitation of Si-rich nitride in α-Fe. The growth mode of the compound layer changes, now advancing by conventional planar-type growth. During nitriding times of 1 to 48 hours, ε exists in contact with the NH3/H2-containing nitriding atmosphere at a nitriding potential of 1 atm−1/2 and 540 °C, only allowing for the formation of γ′ in pure Fe, indicating that Si affects the thermodynamic stability ranges of ε and γ′.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fe Nitride Formation in Fe–Si Alloys: Crystallographic and Thermodynamic Aspects

Kante

Leineweber

2021

Metall Mater Trans A

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“…Since the magnetic performance of existing Fe atomic structure still has much room for improvement, especially its density of residual magnetization, researchers tried to further nitride them with NH 3 . Iron-nitride clusters, including Fe 2 N, Fe 3 N 1 + x , Fe 4 N and Fe 16 N 2 (x = 0, 1, 2...), have been under intense research due to particularly strong magnetism and interest in their formation origin [20,21]. In general, nitriding process needs a high temperature condition, which is bound to have adverse effects on the previous atomic layers.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Enhancement and Nitriding Process of Fe Atomic Layers on Si (111)-7×7-CH3OH Surface

Ding

Gong

et al. 2021

Preprint

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Fe atoms were steamed on Si(111)-7×7 surface, which had been saturated by CH3OH. Aim to greatly enhance the magnetic performance, nitriding experiments were implemented and adjusted on the existing linear Fe clusters. First of all, the dissociation of CH3OH adsorption process was deducted in detail, which laid a good foundation for the better use of surface quasi-potential. Further to solve the coming problems like weak linearity and low nitriding effect, the formation mechanism of iron-nitride was explored. Atomic layers of Fe deposition are confirmed as the key to NH3 dissociation process (at room temperature). Specifically, the higher Fe atomic layer contacted by NH3, the weaker influence of surface quasi-potential. With the introduction of Ar, Fe deposition could be controlled at 1-2 atomic layers, result in good NH3 dissociation and nitriding efficiency. Combing with magnetic performance result, the density of residual magnetization is improved from 1.5E-0.5 emu to 7.0E-0.5 emu, forming an obvious linear structure. It is also proved that our new linear iron-nitride clusters will maintain good stability with the improvement of nitriding efficiency.PACS: 07.79.Cz; 81.15.-z; 75.75.Fk

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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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Unusual Iron Nitride Formation Upon Nitriding Fe-Si Alloy

Cited by 14 publications

References 47 publications

Fe Nitride Formation in Fe–Si Alloys: Crystallographic and Thermodynamic Aspects

Fe Nitride Formation in Fe–Si Alloys: Crystallographic and Thermodynamic Aspects

Magnetic Enhancement and Nitriding Process of Fe Atomic Layers on Si (111)-7×7-CH3OH Surface

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

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