Thickness Of Nitrided Layer Research Articles

Vacuum-arc Nitriding of Carbon Steels Having Low Tempering Temperature

Studies have been made into a new possibility of modifying the surface of steels having a low tempering temperature by nitriding them in a vacuum-arc gas discharge followed by heat treatment (heating, quenching and tempering). Generally, nitriding of hardened steels takes place at a temperature of about 500°C, and thus this process appears impossible for steels with tempering temperatures of the order of 200... 300°C. It is demonstrated here that a single ion-plasma nitriding of high-carbon steel with the composition of 0.9% C, 1% Cr, 1% Si, followed by heat treatment, provides the nitrided layer of 2.5 mm in depth, with the hardness between 9 and 11 GPa. Within the range of X-rays penetration, the nitride-hardened layer of the surface is defined as the nitrogen austenite-alpha ferrite mixture, which shows high wear resistance and impact toughness. This layer contributes, in particular, to three-/four-foldin crease in the operational life of cutting punches (made of this steel and used in the manufacture of metal sieves) as opposed to the punches that have undergone conventional heat treatment. After repeated nitriding of the same steel and its subsequent heat treatment according to standard technologies the nitrided layer thickness becomes nearly twice as large, and that allows for multiple regrinding of steel tools. A computer analysis of related publications entered into three International Databases (INIS, MSCI, SCOPUS) has been carried out.

The Controlled Compound Layer of Ni-Coated Nitrided Pure Iron.

In order not to sacrifice nitrided layer thickness and reduce brittle compound layer thickness, Ni-coated pretreatment was carried out with electrodeposition on a pure iron surface, followed by gas nitriding. The brittle compound layer thickness of duplex surface treated samples was reduced, and the nitrided layer thickness increased to 320 μm. The microhardness was 4 times harder, and the wear loss was reduced by 68% compared with the original material. The results indicate that Ni-coated pretreatment could effectively improve microhardness and wear resistance and realize the controlled microstructure of a brittle compound layer of pure iron without compromising nitrided layer thickness. Ni coating plays an important role in ammonia adsorption and decomposition, and in the transfer of active nitrogen atoms during nitriding.

Effect of elemental doping on the catalytic activity of ABO3 perovskite oxides during low-pressure gas nitriding

In order to optimize the catalytic activity of the LaFeO3 oxide during low-pressures gas nitriding, the elemental doping by chromium, nickel and cerium was applied in the present work. The effects of doped LaFeO3 oxides on catalytic nitriding efficiency were systematically investigated. A new catalytic feature was proposed to explain the differences in catalytic activity among ABO3 oxides. The microstructure, phase composition and thickness of nitrided layers were characterized by the optical microscope, scanning electron microscope, X-ray diffraction and micro-hardness tester, respectively. The chemical bonds on nitrided surfaces were carefully investigated by X-ray photoelectron spectroscopy. The first-principles calculation was applied to reveal the inner diffusion behavior of nitrogen atoms. The results show that all ABO3 oxides exhibit an excellent catalytic activity in low-pressure gas nitriding. The LaFeO3 and (La0.5Ce0.5)FeO3 oxide show the enhanced catalytic activity as nitriding time prolonging while the LaCrO3 and LaNiO3 oxide present an opposite phenomenon. It depended on the state of active oxygen on nitrided surfaces, which is affected by the valence of doped elements. A critical ratio of adsorbed oxygen to hydroxyl on nitrided surfaces was proved to be 1.33. Beyond this value, ABO3 oxides have a remarkable improvement on catalytic nitriding.

716 mV Open‐Circuit Voltage with Fully Screen‐Printed p‐Type Back Junction Solar Cells Featuring an Aluminum Front Grid and a Passivating Polysilicon on Oxide Contact at the Rear Side

This article reports the recent progress of p‐type back junction solar cells featuring an aluminum front grid and an n+‐type passivating polysilicon on oxide (POLO) contact at the cell rear side. The best cell has an efficiency of 22.6% and an open‐circuit voltage of 716 mV, independently confirmed by Institute for Solar Energy Research Hamelin (ISFH) CalTeC. The cell area is 244.5 cm2. The increase in the SiNx capping layer thickness at the cell rear side reduces the deterioration of passivation quality of the POLO contact by screen‐printed silver. This increases the open‐circuit voltage by 22 mV compared with cells with a thinner nitride layer thickness. The investigation with scanning electron microscopy shows that the damage of the POLO contacts underneath the screen‐printed metal contacts is avoided by increasing the SiNx capping layer thickness. A contact resistivity of 2 mΩ cm2 is measured using the transfer length method.

Plasma nitriding of AISI 431 steel: surface hardness - hardness profile [Nitruración por plasma del acero AISI 431: dureza superficial – perfil de durezas

The present research evaluated the effect of the nitriding time in plasma in the range of 5 to 15 hours, on the hardness profile of the cross section of stainless steel samples AISI 431; in addition to taking and differentiating the data on surface hardness, effective layer depth and nitride layer thickness. The nitriding process was by plasma, the process temperature was kept constant at 400 °C. The evaluated samples were machined (rolled and countersigned), and were left in one inch diameter and one inch in length. The times of 10 and 15 hours of nitriding time were obtained by accumulating time of 05 hours of nitriding per week; the hardness profiles were obtained by using the LECO model LMV-50V micro durometer; The ASTM E3-91 standard was used to collect the aforementioned hardness data, from these it was possible to determine that the maximum surface hardnesses are (1053, 1252 and 1327) HV-0.01, for nitriding times of (5,10 and 15) hours respectively, the average effective layer thicknesses were (37.75, 33 and 28.75) μm; while the nitride layer thicknesses were (4.9, 7.03 and 10.7) μm corresponding to times of (5, 10 and 15) hours respectively. The hardness in the core after the nitriding treatment was kept in the range of (275-277) HV-0.01. These values were determined by microscopic evaluation of the tested samples, the metallography reagent used was 3% Nital by electrolytic attack for 3 minutes in each case. The statistical analysis corresponded to Student's “t” tests, in the form of pairwise comparison, from which the non-significant difference between repetitions and the significant difference between the different levels of study were determined.

Structure and corrosion behavior of ultra-thick nitrided layer produced by plasma nitriding of austenitic stainless steel

An ultra-thick nitrided layer (>80 μm) was formed by hot wire enhanced plasma-assisted nitriding of AISI 316L austenitic stainless steel under the higher pulsed bias to investigate the structure and the corrosion performance. The phase structure, the cross-sectional morphology, the element distribution, hardness and modulus, as well as the corrosion behavior of the nitrided layer were investigated by XRD, SEM, EDS, nano-indentation tester and electrochemical workstation, respectively. The results showed that the nitrided layer was divided into two sub-layers: the upper thick layer composed of N-expanded austenite and CrN, and the lower thin layer mainly composed of γN with a trace of CrN precipitate. Nitrided at −400 V, CrN and high N-expanded austenite formed in the upper layer, which exhibited a high hardness and an excellent corrosion resistance. As the bias increased to −500 V, more nitrogen atoms precipitated as CrN phase and low N-expanded austenite phase began to form, the thickness of nitrided layer reached a maximum of 84 μm. To −600 V, high N-expanded austenite almost completely transformed to low N-expanded austenite, accompanied by the increase of CrN, which caused the thickness and hardness of the nitrided layer to decrease, and the pitting corrosion occurred at −4.1 mV.

Mathematical models of the change in composition of the inlet atmosphere for the assumed changes in the nitrogen potential

The development of gas nitriding and the systematic expansion of its scope of application in practice means that the issue of the production of nitrided layers on steels is still in the center of interest of industry and research centers from both a cognitive and application point of view. Research mainly focuses on determining the relationship between the construction of the nitrided layer and its production parameters. The condition of full control of the nitriding process effect is the control of the nitrogen availability of the nitriding atmosphere, which depends on the value of the nitrogen potential (Np) and the degree of ammonia dissociation (α). Shaping of these parameters is carried out by controlling and regulating the composition of the inlet atmosphere. Control and regulation of the inlet atmosphere composition is important in controlling the nitrogen availability of the nitriding atmosphere and, consequently, the kinetics of nitrided layer thickness increase. The article describes models for changing the composition of the three-component and two-component inlet atmosphere. Two variants of controlling and regulating the nitrogen potential are discussed: the composition of the two-component inlet atmosphere, dissociated ammonia-ammonia and the temperature function in the heating stage of the charge.

Elimination of the Low Resistivity of Si Substrates in GaN HEMTs by Introducing a SiC Intermediate and a Thick Nitride Layer

We report the effect of a thick nitride layer on the high-frequency performance of AlGaN/GaN highelectron-mobility transistors (HEMTs) grown by metal oxide chemical vapor deposition (MOCVD) on a 6-inch Czochralski (Cz)-Si substrate. The thick nitride layer was grown via a 3C-SiC intermediate layer. A significantly low parasitic pad capacitance and a comparable cutoff frequency of 4.5 GHz for 2-μm gate length devices were achieved along with excellent electron transport characteristics, such as a mobility of ~2200 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V-s and a drain current density of 520 mA/mm. The extracted small-signal equivalentcircuit parameters also verified the accuracy of the measured cutoff frequency and parasitic capacitances.

N2/H2 Non-thermal Transferred arc Plasma Nitriding Treatment of Stainless Steel at Atmospheric Pressure

In the paper, a novel metal surface nitriding method is presented by using an atmospheric pressure non-thermal transferred arc plasma technique. In the N2/H2 plasma nitriding process, the surface of stainless-steel is treated by the arc root, which shows an irregular movement in a circle-like zone with about 5 mm diameter observed by high speed camera. The discharge has characteristics of high voltage and low current, and the gas temperature of the arc column plasma is only about 2900 K determined by the diatomic molecule N2+(B2Σu+ →X2Σg+ ) fitting method. It is found that the NH radical production in plasma plays an important role in the nitriding process. The thickness of nitrided layer can reach 60 μm after processing of 120 min under the optimal experimental conditions. The surface hardness of stainless-steel increased from 220 to about 1200 HV0.1 (Vickers hardness under the force of 0.1 kg) after plasma treatment. The treating saturation time for stainless-steel surface hardness reaching to 1200 HV0.1 is around 9 min.

The effect of novel composite pretreatment on performances of plasma nitrided layer

Novel composite pretreatment combining laser shock peening and pre-oxidation was primarily adopted prior to plasma nitriding for 42CrMo steel. Optical microscope, scanning electron microscope, vickers microhardness tester and wear tester were used to systematically investigate the innovative enhancement effect of novel composite pretreatment on the performances of plasma nitrided layer. The results showed that the surface characteristics of composite pretreated sample had the advantages of both laser shock peening and pre-oxidation, thus brought out much thicker nitrided layer with excellent performances. Compared with conventional plasma nitriding, the thickness of compound layer and effective hardening layer was increased 1.8 times under the same nitriding condition. Meanwhile, the surface hardness was much higher; reaching 750 HV0.05, and the wear resistance was significantly enhanced, with nearly 60% decrease of the width of abrasive mark, comparing with that by conventional plasma nitriding without pretreatment.

Rapid nitriding mechanism of titanium alloy by gas blow induction heating

This work characterized the surface-modified layers generated on a titanium alloy during gas blow induction heating (GBIH), so as to elucidate the rapid nitriding mechanism. The surface microstructures of GBIH nitrided specimens were analyzed by X-ray diffraction, micro-Vickers hardness testing, scanning electron microscopy and X-ray photoelectron spectroscopy. The data indicate that applying this process for only several minutes can forms nitrided layers on Ti-6Al-4V alloy surfaces, the characteristics of which are similar to those of layers produced by ordinary gas nitriding for several hours. The temperature inside the material was determined to be higher than that on the surface during GBIH nitriding. However, the thickness of the nitrided layer exceeded the estimated value based on the diffusion coefficient at this high internal temperature. This especially thick nitrided layer can possibly be attributed to eddy currents generated in the metal by the application of a high-frequency current. Passivation films on the surface of the Ti-6Al-4V alloy were found to be removed during GBIH nitriding, which is ascribed to the diffusion of oxygen atoms in the passivation film into the substrate. Thus, the data show that GBIH nitriding is able to modify a Ti-6Al-4V alloy within a short period of time based on the effect of an eddy current and the disappearance of the passivation film.

The Effect of the Transformation of ε-Fe2-3N into γ′-Fe4N Phase on the Fatigue Strength of Gas-Nitrided Pure Iron

The effect of the iron nitride phases, ε-Fe2-3N and γ′-Fe4N, on the fatigue strength was investigated. Pure iron was used to observe only the effect of nitride, excluding the effects of factors, such as residual stress, depending on the alloy composition and microstructural change according to working on the fatigue strength. In this work, ε and γ′ phases were respectively grown at a time on the surface of the pure iron specimens using the appropriate nitriding potential KN, the mixture rates of ammonia and hydrogen gases, at same temperature of 570 °C according to the Fe-N Lehrer diagram. Another γ′ phase was prepared by first growing the ε phase and then transformed from ε phase into γ′ phase by changing the KN at the same temperature of 570 °C in the 2-stage gas nitriding. The fatigue strengths of the iron nitride consisted of ε and γ′ phases, γ′ phase, and γ′ phase grown by the 2-stage gas nitriding were evaluated, respectively. As a result, first, it can be seen that the diffusion layer of ε phase was deeper than γ′ phase, but fatigue strength was lower. On the other hand, fatigue strength of both the γ′ phases are higher than that of the ε, and the fatigue strength of γ′ phase nitride grown by 2-stage gas nitriding was almost similar to that of γ′ phase nitride grown at a time, i.e., fatigue strength was not significantly related to diffusion depth and depended on nitride phases in this study. Secondly, we cannot clearly conclude that there was the difference in fatigue strength according to the thickness of nitride layer consisted of γ′ phase. However, it is clear that when ε phase was transformed to γ′ phase, fatigue strength had the same level as γ′ phase formed at one time.

Particularities of metallographic preparation for the analysis of thin layers and coatings. Foundry production and metallurgy

The article deals with the issues of determining the thickness of layers and coatings for various purposes in metallographic research. The role of the material for filling metallographic sections in determining the layer thickness is demonstrated. It is shown that when filling the sample with plastic masses, the error in determining the layer thickness can be 0.2...0.4 microns, which is significant for thin layers. Sample preparation options for determining the thickness of titanium nitride layers with a thickness of 1 microns or less are considered. It is shown that with the optimal method of sample preparation, it is possible to visualize a layer less than 1 microns thick, and also determine its thickness in the image processing program.

Low-pressure gas nitriding of AISI 304 austenitic stainless steel: reducing the precipitation of chromium nitrides

In this study, low-pressure gas nitriding (gas pressure of 0.01 MPa) was conducted to produce a thicker nitrided layer with high hardness and anti-corrosive properties on AISI 304 austenitic stainless steel. The effects of nitriding temperature and duration on the microstructure and surface property of nitrided layers were systematically evaluated by using optical microscope, X-ray diffraction, elemental analysis, microhardness test and potentiodynamic polarization tests. The samples were also treated under conventional gas pressure of 0.1 MPa for comparison. The results show that the low-pressure gas nitriding could restrain the precipitation of chromium nitrides effectively, which is beneficial for obtaining a thicker nitrided layer. Although the activation energy of nitrogen diffusion for low-pressure nitriding (220 kJ mol−1) is higher than that for the atmospheric pressure nitriding (196 kJ mol−1), the thickness of nitrided layers for low pressure nitriding could reach to a comparable value as that for the conventional atmospheric pressure nitriding. More importantly, the surface toughness and corrosion resistance of nitrided layers could be improved by low-pressure nitriding, which is mainly attributed to the optimized nitrogen content in nitrided layers and the reduced precipitation of chromium nitrides under low-pressure.

Effect of pre-existing carbides prepared by different heat treatments on the nitriding behaviour during a carburizing and nitriding duplex treatment of an M50NiL steel

This article reports the effect of pre-existing carbides prepared by different heat treatments on the nitriding behaviour during a carburizing and nitriding duplex treatment of an M50NiL steel. The goal was to achieve an improved understanding of the relationship between the pre-existing carbides and nitriding behaviour. The M50NiL steel was carburized at 950 °C, heat treated at different quenching temperatures (ranging from 1000 to 1150 °C) and tempering temperatures (ranging from 500 to 580 °C), and finally nitrided at 500 °C. The surface layers were characterized by means of X-ray diffraction (XRD), laser scanning confocal microscopy (LSCM), scanning electron microscopy (SEM), Vickers microhardness measurement and transmission electron microscopy (TEM). The results show that the formation of intergranular precipitates was greatly related to the presence of pre-existing carbides, which led to a change in the carbon content in the matrix and showed different dissolving capacities. The compound layers consisted of γ′ (Fe4N) and ε (Fe2-3N) phases as well as a minor amount of Fe3O4. The pre-existing carbides had no effect on the composition of the compound layer. For the diffusion of nitrogen, a density of pre-existing carbides that was too high or too low was unfavorable, as it greatly decreased the thickness of the nitrided layer. At the quenching temperature of 1100 °C and the tempering temperature of 540 °C, the thickest nitrided layer herein and a good hardness distribution were obtained, which was attributed to the optimum density of pre-existing carbides. This study provides information regarding how to obtain a thick nitrided layer by controlling pre-existing carbides during the duplex treatment of M50NiL steels.

STRUCTURE AND CORROSION RESISTANCE OF VACUUM-ARC MULTI-PERIOD CrN/Cu, ZrN/Cu, AND NbN/Cu COATINGS

The structure and properties of vacuum-arc multi-period composite coatings of the MeN/Cu system (where Me is Cr, Zr, and Nb) are studied. It was found that at the smallest nanolayer thickness (about 8…10 nm) of composites in the layers of all systems, only a phase with an fcc lattice is formed, without a pronounced texture in the nitride layers. For ZrN and CrN, the phases with an fcc lattice are equilibrium, and for NbN, they are nonequilibrium. An increase in the thickness of nitride layers leads to the appearance of a texture in ZrN/Cu and CrN/Cu systems and the formation of an equilibrium ε-NbN phase in the layers of the NbN/Cu system. Tests for corrosion resistance in the environment of the formation of chloride ions showed that the coatings are anodic reaction. The best corrosion properties were obtained for coatings with the smallest layer thickness (about 8…10 nm).

Nitriding of steels of various structural classes manufactured by laser additive technologies

The authors have conducted a comparative analysis of diffusion layers of steels of various structural classes manufactured by complex technology including laser remelting of powder material and plasma nitriding. Parameters of diffusion layers of bainitic steel (Fe – 0.09 % C – 1 % Cr – 2 % Ni – 1 % Mo – 1 % Cu) and martensitic steel (Fe – 0.25 % C – 13 % Cr – 2 % Ni) manufactured by direct laser deposition (DLD) and austenitic steel (Fe – 0.03 % C – 17 % Cr – – 14 % Ni – 3 % Mo) manufactured by selective laser melting (SLM) were investigated. During plasma nitriding at 540 °C for 24 h of martensitic and austenitic steels, diffusion layer of 140 – 160 μm was formed, additionally maximum microhardness of surface layer was 800 HV0.1 and 1050 HV0.1 and it is almost constant on thickness of 100 μm. Diffusing layer of bainitic steel is 900 μm and its microhardness monotonously decreases from the surface. Reinforcing phases of nitrided layer were determined by X-ray analysis: γ′ (Fe4N) is fixed in the bainitic steel, γ′ and CrN are fixed in martensitic and austenitic steels. Moreover on the surface of austenitic steel solid nitrided layer is formed. The influence of heat treatment after laser remelting of powder material was also studied. It was determined, that despite decreasing of crystal structure defects after heat treatment, the thickness of nitrided layer changes slightly. Also the authors have investigated the influence of porosity of austenitic steel on the thickness of nitrided layer. It was shown, that porosity of 0.5 – 2.0 % doesn’t result in changing of diffusion layer’s thickness.

Laser nitriding of titanium surfaces for biomedical applications

In this paper, titanium nitrides were produced on commercially pure titanium samples by laser nitriding processes, with the goal of improving bio-compatibility and corrosion resistance. To identify the critical set of laser nitriding processing parameters (a combination of both laser scanning parameters and the N2 content processing gas), mouse MLO-Y4 cells were utilized for bio-compatibility evaluation, and simulated body fluid was used for electrochemical behavior examination to characterize corrosion performance. The modified surfaces were also characterized with scanning electron microscope, X-ray diffraction, and nano-indentation techniques to reveal the connections between the bio-compatibility/corrosion resistance performance and the nitrided layer composition, thickness, and surface roughness. For improved bio-compatibility and corrosion resistance performance, a dense and thick titanium-nitride dendritic layer is desirable, which can be formed in a pure N2 environment, together with a high laser energy density.

Characterization of surface layer formed by gas blow induction heating nitriding at different temperatures and its effect on the fatigue properties of titanium alloy

Gas blow induction heating (GBIH) nitriding was carried out for Ti–6Al–4V alloy at different temperatures, and its effect on surface characteristics, wear resistance and fatigue properties was investigated. The microstructures of the specimen surface were characterized using optical microscopy, laser microscopy, X-ray diffraction, micro-Vickers hardness tester, and nano-indentation tester. It was found that the surface characteristics of titanium alloy varied with increasing the treatment temperature of GBIH-nitriding. In this study, a nitrogen diffusion layer was formed on the titanium alloy surface GBIH-nitrided at 1073 ​K. A nitrogen compound layer and diffusion layer were created at the treatment temperature of 1173 ​K, which suppressed the wear loss to under one tenth that of the substrate. In order to examine the fatigue properties of the treated alloy, fatigue tests under four-point bending were performed. The fatigue strength of the Ti–6Al–4V alloy GBIH-nitrided at 1173 ​K was 234 ​MPa lower than that of the mirror-polished alloy. The decrease in the fatigue strength is due to the formation of the compound layer with a Young’s modulus approximately twice that of the substrate, and the grain coarsening from 7 ​μm to 300 ​μm. The results indicate that a thick nitrided layer with high hardness and the close Young’s modulus to the substrate improved the fatigue strength of the Ti–6Al–4V alloy.

ANALISIS PENGARUH WAKTU TAHAN SALT BATH NITRIDING TERHADAP KETEBALAN NITRIDE LAYER DAN KEKERASAN PERMUKAAN PADA MATERIAL SUH35 (JIS: SUH35)

Time is a parameter that is very influential on the productivity and product quality from the nitriding process. This study aims to find out how much effect of the holding time in salt bath nitriding process to the nitride layer thickness and surface hardness of SUH35 material. This salt bath nitriding process used chemical salt with cyanide content (CNˉ) 1.5% - 4.5%, and cyanate content (CNOˉ) 28% - 32%. The workpiece used in this study is a cylindrical SUH35 material with diameter 5 mm. Temperature that used for salt bath nitriding process is 580 ° C with a variation of the holding time is 20 minutes, 25 minutes and 35 minutes. From this study, results of the data obtained are, with a holding time 20 minutes the average thickness of the nitride layer SUH35 material is 12.74 µm and the average surface hardness is 556.96 Hv. With a holding time 25 minutes the average thickness of the nitride layer SUH35 material is 16.07 µm and the average surface hardness is 792.18 Hv. With a holding time 35 minutes the average thickness of the nitride layer SUH35 material is 20.17 µm and the average surface hardness is 989.94 Hv.