Computer simulation of nitrided layers growth for pure iron (original) (raw)
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Metallurgical and Materials Transactions A, 1995
Models were derived for monolayer and bilayer growth into a substrate in which diffusion of the solute governs the growth kinetics, as in gas-solid reactions, for example. In the models, the composition dependence of the solute diffusivity in the phases constituting the layers was accounted for by appropriate definition of an effective diffusion coefficient for a (sub)layer. This effective diffusion coefficient is the intrinsic diffusion coefficient weighted over the composition range of the (sub)layer. The models were applied for analyzing the growth kinetics of a 7'-Fe4N1_/monolayer on an c~-Fe substrate and the growth kinetics of an e-FezN~_z/y'-Fe4N~_~ bilayer on an a-Fe substrate, as observed by gaseous nitriding in an NH3/Hz-gas mixture at 843 K. The kinetics of layer development and the evolution of the microstructure were investigated by means of thermogravimetry, layer-thickness measurements, light microscopy, and electron probe X-ray microanalysis (EPMA). The effective and self-diffusion coefficients were determined for each of the nitride layers. The composition dependence of the intrinsic (and effective) diffusion coefficients was established. Re-evaluating literature data for diffusion in 7'-Fe4N~_x on the basis of the present model, it followed that the previous and present data are consistent. The activation energy for diffusion of nitrogen in 7'-Fe4Nl-x was determined from the temperature dependence of the self-diffusion coefficient. The self-diffusion coefficient for nitrogen in e-FezN~_z was significantly larger than that for T'-Fe4N l_x. This was explained qualitatively, considering the possible mechanisms for interstitial diffusion of nitrogen atoms in the close-packed iron lattices of the e and 7' iron nitrides.
A diffusion model for simulation of bilayer growth (ε/γ′) of nitrided pure iron
Materials Science and Engineering: A, 2004
The purpose of the present work is to apply a diffusion model based on Fick's laws in order to study the growth kinetics of ε and ␥ phases during the gas nitriding of pure iron. On the basis of experimental diffusion data, we have shown that it was possible to predict both the microstructural nature and thicknesses of nitrided layers as well as the nitrogen profile within the formed phases. This model has been validated by comparison of our simulation results with experimental data taken from the literature.
A simple diffusion model for the growth kinetics of γ′ iron nitride on the pure iron substrate
Applied Surface Science, 2005
A simplified diffusion model designed to predict the thickness, microstructure of nitrided layer on the pure iron, and the nitrogen profile is reported. The error function model based on Fick's laws was used to study the growth kinetics of g 0 phase during the gas nitriding process. The validity of the generated computer program was checked by comparing our simulation results with the experimental data taken from the literature and a fairly good agreement is achieved between calculated and experimentally measured values. #
MATEC Web of Conferences, 2014
This paper present mathematical model which developed to predict the nitrided layer thickness (case depth) of gas nitrided and plasma nitrided austenitic stainless steel according to Fick's first law for pure iron by adapting and manipulating the Hosseini's model to fit the diffusion mechanism where nitrided structure formed by nitrided AISI 316L austenitic stainless steel. The mathematical model later tested against various actual gas nitriding and plasma nitriding experimental results with varying nitriding temperature and nitriding duration to see whether the model managed to successfully predict the nitrided layer thickness. This model predicted the coexistence of ε-Fe2-3N and γ΄-Fe4N under the present nitriding process parameters. After the validation process, it is proven that the mathematical model managed to predict the nitrided layer growth of the gas nitrided and plasma nitrided of AISI 316L SS up to high degree of accuracy.
Modeling of nitride layer formation during plasma nitriding of iron
Computational Materials Science, 1999
A generalized Wagner diusion model is used to analyze the layer formation and growth in de®nite experiments on plasma nitriding of pure iron. It is demonstrated that the model is able to predict the compound layer composition and can be used as a method for calculation of the eective diusion coecients in the ®rst sub-layer of the compound zone, providing that the concentration ranges and the eective diusion coecients of the nitrogen in the other sub-layers, as well as the total compound layer thickness as a function of time, are known. The model predicts the violation of the parabolic law of growth for both the compound and diusion zone of the plasma nitrided iron. Ó
Designing nitriding processes using simulator of the kinetics of nitrided layer growth
Journal of KONES, 2016
This article presents simulator of the kinetics of nitrided layer growth. Simulator of the kinetics of nitrided layer growth is an application, which supports new method of controlled gas nitriding called ZeroFlow. ZeroFlow method is used for nitriding selected car engine parts, such as crankshafts, camshafts, piston rings, poppet valve springs and discs, piston pins or nozzles for unit injectors. Through the use of simulation models, it is possible to develop the especially dedicated processes with specific parameters for each of this parts, which means that simulator of the kinetics of nitrided layer growth enables forming of nitrided layer with strictly defined properties: required phase structure with thicknesses of particular zones that occurs in it and required hardness distribution. Moreover, using simulation models this layers are obtained in the shortest possible time, which is connected with the lowest energy and gases consumption; therefore, nitriding process using ZeroFl...
Morphology and phase analysis of nitride layer on pure iron
THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIAL AND TECHNOLOGY (ICAMT) 2021
The pure iron sample was treated using gas nitriding at 1000 °C for 1 hour. The morphology and phase analysis of the nitride layer was characterized by scanning electron microscope and X-ray diffraction. The thickness of the nitride layer and average grain size were derived from the scanning electron microscope micrograph. The crystallite size was determined by X-ray diffraction using the Williamson-Hall method. The micrograph from the scanning electron microscope showed a nitride layer, a diffusion zone, and a narrow gap between them. The thickness of the nitride layer was 8.1 ± 0.5 μm with a visible gap in the diffusion zone of 1.5 ± 0.5 μm. The grain size in the diffusion zone increased, and some interstitial to the iron lattice and/or precipitate at the grain boundary were observed. The phase analysis of the nitride layer showed a single phase ε-Fe2N with a crystallite size number of 549 Å.
Microstructural evolution during nitriding, finite element simulation and experimental assessment
Applied Surface Science, 2013
A finite element simulation of nitriding is proposed in this paper, using the analogy between diffusion and heat conduction, to overcome the shortcomings of the classical internal oxidation model in predicting the kinetics of layer growth and nitrogen distribution during nitriding. To verify the model, a typical gas nitriding has been carried out on an axisymmetric specimen. Treated specimen has been characterized using optical microscopy (OM), scanning electron microscopy (SEM), micro-hardness and X-Ray diffraction (XRD) measurements. It was found that the so-called diffusion zone can be divided into two parts with different influence on the mechanical characteristics including residual stress and hardening. First layer which is a two phase region of ferritic matrix and ␥ (Fe 4 N) makes further improvement with respect to the second layer which is a solid solution of nitrogen in ferrite. The formation of that two phase region, which is not predicted by classical model, can be efficiently recognized by the proposed model. It is also proved that the model has the ability to consider the geometry dependency of layer growth and formation in nitriding.
The Stability of the Layer Nitrided in Low-Pressure Nitriding Process
Coatings
The kinetics of the nitrided layer thickness growth and its structure depend on the nitrogen flux from the atmosphere to the nitrided surface. A nitrogen flux to the surface is more significant than a diffusion flux into the substrate, during forming surface iron nitrides and the internal nitriding zone. For pure iron, nitrided under low pressure, cutting off the nitriding atmosphere creates a flux from the subsurface layer of nitrides to the surface. The purpose of this paper is to determine the direction of the nitrogen flux in a similar situation for steels containing nitride-forming elements, thus answering the question of the stability of the layer nitrided under such conditions. The surface of X37CrMoV5-1 steel was nitrided under low pressure (of 24 hPa) and annealed in a vacuum or nitrogen. The microstructure, thickness of the nitride layers nitrided layers, the thickness of the internal nitriding zone, surface hardness and stresses were examined. The highest values of the ni...