Co-existence of γ'N phase and γN phase in nitrided austenitic Fe-Cr-Ni alloys - II: A pragmatic modeling approach

Che, H.L.; Christiansen, Thomas; Lei, Ming; Somers, Marcel A. J.

doi:10.1016/j.actamat.2022.118094

Cited by 8 publications

(4 citation statements)

References 42 publications

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“…The broadened peaks were essentially formed by two phases of Fe 4 N-like ordered expanded austenite (γ′ N ), and the disordered expanded austenite (γ N ), which have been well confirmed in previous experimental work [9]. The ordered γ′ N phase appeared as nano-sized antiphase domains near the surface at high N concentration [13]. For the nitrided Fe-Cr-Ni alloys with more than about 12 wt% Cr, there is no clear concentration and lattice parameter break between the γ N and γ′ N phases, but only the disordered and ordered transition of the N arrangement.…”

Section: Structure Of Nitrided Layersupporting

confidence: 85%

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Gradient self-organized dislocation in expanded austenite layer during low-temperature nitriding

Che

Liu

et al. 2023

Mater. Res. Express

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A typical nitrogen expanded austenite layer is formed by plasma-based low-energy nitrogen ion implantation (PBLEII) on AISI 304L austenitic stainless steel at a moderate temperature of 380° C. The dislocation self-organization structure in the nitrogen expanded austenite layer is characterized as an evolution from partial and Lomer-Cottrell dislocations in the inner layer near the interface to multilayer stacking faults in the outer nitrided layer. The self-organized dislocation density and forms are essentially dependent on the plastic deformation, strain-gradient, and nitrogen-related stacking fault energies, respectively, due to the constrained expansion in the nitrided layer. As the nitrogen concentration in the austenitic matrix increases, the stacking fault energy gradually decreases, resulting in the transformation of the defect from Lamer-Cottrell dislocations to a multilayer stacking faults. The appropriate stress, which is associated with orderly stress relief during dislocation self-organization, preserves the integrity of the nitrided layer with a combinedly improved in wear and corrosion resistance. Nitriding-induced dislocation self-organization is basically explored as the formation mechanism of the nitrogen expanded austenite layer, contributing to development of the specific low-temperature nitriding austenitic steel.

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Section: Structure Of Nitrided Layersupporting

confidence: 85%

“…The higher the Cr content in an octahedral interstice, the stronger the Cr-N interaction. Combined with the subsequently formed Fe 4 N-like LRO, the supersaturated N concentration could reach more than 30 at.% [9,13].…”

Section: Structure Of Nitrided Layermentioning

confidence: 99%

Gradient self-organized dislocation in expanded austenite layer during low-temperature nitriding

Che

Liu

et al. 2023

Mater. Res. Express

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“…The nature of this expanded phase is still an open question. Many studies carried out with different analytical techniques suggested that a preferential bonding of N with Cr atoms occurred [110][111][112] and that Cr-N short-range order (SRO) regions were present together with regions having a γ -Fe 4 N-like long-range order (LRO) region, indicated as γ N [113][114][115][116]. Further details on the structure of the expanded austenite are reported in [22,24,33].…”

Section: Microstructure and Characteristics Of The Modified Surface L...mentioning

confidence: 99%

The Corrosion Behavior in Different Environments of Austenitic Stainless Steels Subjected to Thermochemical Surface Treatments at Low Temperatures: An Overview

Borgioli

2023

Metals

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Low-temperature thermochemical treatments are particularly suitable for use in the surface hardening of austenitic stainless steels without impairing their corrosion resistance. In fact, when using treatment media rich in nitrogen and/or carbon at relatively low temperatures (<450 °C for nitriding, <550 °C for carburizing), it is possible to inhibit the formation of chromium compounds and obtain modified surface layers that consist mainly of a supersaturated solid solution, known as expanded austenite or S-phase. It has been observed that this hard phase allows the enhancement of corrosion resistance in chloride-ion-containing solutions, while the results were contradictory for chloride-free acidic solutions. This overview aims to discuss the corrosion behavior of low-temperature-treated austenitic stainless steels, taking into account the different microstructures and phase compositions of the modified layers, as well as the different test environments and conditions. In particular, the corrosion behavior in both chloride-ion-containing solutions and chloride-free solutions (sulfuric acid, sulfate and borate solutions) is discussed. The analysis of the international literature presents evidence that the microstructure and phase composition of the modified layers have key roles in corrosion resistance, especially in sulfuric acid solutions.

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“…In the outer surface zone, with the highest N content, a long-range ordering (LRO) among the N atoms occurs in addition to the short-range ordering (SRO) of N and Cr atoms; and in the subsurface zone, with the lower N content, only the SRO of N and Cr atoms is encountered. These zones are dubbed γ′ N and γ N , respectively [3,4]. The Fe 4 N-like LRO γ′ N phase is obtained as small ordered domains separated by antiphase boundaries.…”

Section: Introductionmentioning

confidence: 99%

Pancake-like antiphase domains in perfect nitrogen-expanded austenite by TEM characterization

Che,

Yang,

Lei

2023

Mater. Res. Express

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Elongated superstructure diffraction spots were observed in perfect nitrogen-expanded austenite without stress or plastic strain, which was prepared by plasma-based low-energy nitrogen-ion implanting Fe-Cr-Ni austenitic alloy foils at low temperature of 380 °C. The Fe4N-like ordered nitrogen-expanded austenite (γ′N) antiphase domains formed in the disordered nitrogen-expanded austenite (γ N) matrix. Only the high Cr-content alloys presented elongated diffraction spots. The reconstruction of the diffraction spots strength distribution shows an elongated egg-shape in reciprocal space. This elongation corresponded to a pancake-like antiphase domains distribution in matrix, which was confirmed in dark field images as a lamellar structural feature. The Cr-N short-range ordering (SRO) and anisotropic elastic module rather than the constrained strain in the γ N phase layer determine the formation of γ′N antiphase domains.

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Co-existence of γ'N phase and γN phase in nitrided austenitic Fe-Cr-Ni alloys - II: A pragmatic modeling approach

Cited by 8 publications

References 42 publications

Gradient self-organized dislocation in expanded austenite layer during low-temperature nitriding

Gradient self-organized dislocation in expanded austenite layer during low-temperature nitriding

The Corrosion Behavior in Different Environments of Austenitic Stainless Steels Subjected to Thermochemical Surface Treatments at Low Temperatures: An Overview

Pancake-like antiphase domains in perfect nitrogen-expanded austenite by TEM characterization

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