Search Results (14)

In this study, the process of electrolytic–plasma nitrocarburizing (EPNC) of 20-grade steel was investigated using various electrolytes and temperature regimes. At the first stage, optical spectral analysis of plasma emission during EPNC was carried out with spectral registration in the range of 275–850 nm, which allowed the identification of active components (Hα, CN, Fe I, O I lines, etc.) and the calculation of electron density. Additionally, the EPNC process was recorded using a high-speed camera (1500 frames per second), which made it possible to visually evaluate the dynamics of arc and glow discharges under varying electrolyte compositions. At the next stage, the influence of temperature regimes (650 °C, 750 °C, and 850 °C) on the formation of the hardened layer was studied. Using SEM and EDS methods, the morphology, phase zones, and the distribution of chemical elements were determined. Microhardness measurements along the depth and friction tests were carried out. It was found that a temperature of 750 °C provides the best balance between the uniformity of chemical composition, high microhardness (~800 HV), and a minimal coefficient of friction (~0.48). The obtained results confirm the potential of the selected EPNC regime for improving the performance characteristics of 20-grade steel. Full article

This work studied the effect of self-protective paste nitriding (SPN) and ion plasma nitriding (IPN) on the surface chemistry, microstructure, and nanohardness of AISI 304 and 316L stainless steels, with both treated at 440 °C for 5 h. Surface modifications analyzed using SEM and nanoindentation revealed distinct outcomes. SPN induced an oxynitriding effect due to the oxidation properties of the pastes, forming Fe₃O₄ and Fe_xC phases, while IPN produced an expanded austenite layer. Both methods enhanced surface nanohardness, but SPN showed superior results. For 316L SS, SPN increased nanohardness by 367.81% (6.83 GPa) compared to a 133.5% increase (3.41 GPa) with IPN. For 304 SS, SPN improved nanohardness by 26% (2.23 GPa), whereas IPN reduced it by 48% (0.92 GPa). These findings highlight SPN’s potential as an effective anti-wear treatment, particularly for 316L SS. The SPN process utilized a eutectic mixture of sodium cyanate and sodium carbonate, while IPN employed a N₂:H₂ (1:1) gas mixture. SEM analyses confirmed the formation of γ-Fe(N) phases, indicating dispersed iron nitrides (FeN, Fe₃N, Fe₄N). SPN’s simultaneous oxidation and nitrocarburization led to an oxide layer above the nitride diffusion layer, enhancing mechanical properties through iron oxides (Fe₃O₄) and carbides (Fe_xC). Comparative analysis showed that AISI 316L exhibited better performance than AISI 304, underscoring SPN’s effectiveness for surface modification. Full article

Under extreme conditions such as high speed and heavy load, 18Cr2Ni4WA steel cannot meet the service requirements even after carburizing and quenching processes. In order to obtain better surface mechanical properties and tribological property, a hollow cathode ion source diffusion strengthening device was used to nitride the traditional carburizing and quenching samples. Unlike traditional ion carbonitriding technology, the low-temperature ion carbonitriding technology used in this article can increase the surface hardness of the material by 50% after 3 h of treatment, from the original 600 HV_0.1 to 900 HV_0.1, while the core hardness only decreases by less than 20%. The effect of post-ion carbonitriding treatment on mechanical properties and tribological properties of the carburized and quenched 18Cr2Ni4WA steel was investigated. Samples in different treatment are characterized using optical microscopy (OM), scanning electron microscopy (SEM), optimal SRV-4 high temperature tribotester, as well as Vickers hardness tester. Under two conditions of 6N light load and 60 N heavy load, compared with untreated samples, the wear rate of ion carbonitriding samples decreased by more than 99%, while the friction coefficient remained basically unchanged. Furthermore, the careful selection of ion nitrocarburizing and carburizing tempering temperatures in this study has been shown to significantly enhance surface hardness and wear resistance, while preserving the overall hardness of the carburized sample. The present study demonstrates the potential of ion carbonitriding technology as a viable post-treatment method for carburized gears. Full article

The effect of plasma electrolytic nitrocarburizing on the wear resistance of carbon tool steel in friction couples with hardened steel and lead-tin bronze is considered in order to study the mechanism and type of wear, as well as the influence of structural and morphological characteristics of the surface on them. The microgeometry of friction tracks and its change with an increasing duration of friction tests are analyzed. The equilibrium roughness is determined, which is optimal for the friction couple and ensures minimal wear. The optimal values of the plasma electrolytic nitrocarburizing parameters, which provide the lowest values of the friction coefficient and wear rate, have been determined. The phase and elemental composition of the surface layer was studied using X-ray diffraction analysis and EDX analysis. The relationship of the microstructure of the nitrocarburized layer of tool steel with the friction coefficient and weight wear is established. Full article

The possibility of increasing the durability of steel pins working against bronze bushings through plasma–electrolytic nitrocarburizing of the surface of medium carbon steel is shown. The phase composition, microhardness, morphology, and surface roughness were studied. Tribological tests were carried out under dry friction conditions according to the shaft-pad scheme. It has been established that plasma–electrolytic nitrocarburizing of the surface of medium carbon steel at a temperature of 700 °C for 5 min leads to a decrease in the friction coefficient by 2.3 times, the weight wear of steel by 24.9 times, and the wear of the bronze counterbody by 5.9 times. At the same time, the contact stiffness increases by 2.6 times. Type of wear: wear with dry friction and plastic contact. The changes in tribological characteristics are associated with the high hardness of the hardened steel surface combined with the effect of dispersed nitrides and iron carbonitrides. Full article

The technology for duplex treatment of a commercially pure titanium surface is expected to increase hardness and wear resistance. This technology consists of sequential nitrocarburizing and polishing of the product in plasma electrolysis. The mechanism of duplex processing is revealed; it consists of strengthening the surface layers under diffusion saturation and controlled formation of the surface relief. The possibility of controlling the characteristics of the modified surface by combining various plasma technologies is shown. The morphological features of the surface and the surface layer after treatment were studied. The microhardness of the modified layer and the tribological properties of the surface were measured. It has been established that the samples with the highest surface layer hardness and a small thickness of the oxide layer on the surface have the highest wear resistance. After nitrocarburizing at 750 °C for 5 min, wear resistance increases by 4.3 times compared to pure material. If subsequent polishing is carried out at a voltage of 275–300 V for 3–5 min in chloride and fluoride electrolytes and 5–10 min in a sulfate electrolyte, then wear resistance can be further increased. This is achieved by removing the porous outer oxide layer. Full article

Recent technological development of utilizing an active screen made of solid carbon for plasma-assisted thermochemical diffusion treatments opens up new possibilities for control over the in situ generated treatment environment to guarantee reproducible treatment conditions and material responses. Until now, the investigations of active-screen plasma nitrocarburizing (ASPNC) using an active screen manufactured from solid carbon focused on the influence of a single treatment parameter variation on the material response. In this systematic study, experiments were conducted to vary the H₂-N₂ feed-gas composition while varying the bias plasma power. The experiments served to better understand a simultaneous variation in the mentioned parameters on the resulting treatment environment and material response during ASPNC of AISI 316L austenitic stainless steel. Therefore, nitriding and carburizing effects in the expanded austenite layer can be obtained. It is shown that an increased nitriding effect, i.e., nitrogen diffusion depth and content, was achieved in case of biased conditions and for H₂-N₂ feed-gas compositions with higher N₂ amounts. On the contrary, an increased carburizing effect, i.e., carbon diffusion depth and content, was achieved in nonbiased conditions, independent from the H₂-N₂ feed-gas composition. Full article

The possibility of using an aqueous non-toxic electrolyte of ammonium nitrate and glycerin for the cathodic plasma electrolytic nitrocarburizing of low-carbon steel is considered in this paper. Surface morphology and roughness, element and phase compositions, and microhardness of the modified layer were investigated. Kinetic calculations of the processes of nitrogen and carbon diffusion into the steel surface are proposed, taking into account their mutual influence. Wear resistance was studied under dry friction conditions with tool alloy steel as a counter-body. Corrosion studies are performed using potentiodynamic polarization curves in 3.5% sodium chloride solution. The plasma electrolytic nitrocarburizing in an aqueous electrolyte with ammonium nitrate and glycerin is established to increase surface hardness up to 980 HV due to the formation of a nitrocarburized layer with 1.35 ± 0.12% carbon and 0.32 ± 0.08% nitrogen concentration. The influence of erosion in electrolyte plasma and high-temperature oxidation on the morphology and surface roughness is shown. The presence of a dense oxide layer, low surface roughness, and high hardness of the diffusion layer favor a decrease in the friction coefficient by 1.3 times, weight wear by 1.8 times and corrosion current density by 1.4 times. Full article

For rapid surface engineering of Cr-containing alloys by low-temperature nitrocarburization, we introduce a process based on pyrolysis of solid reagents, e.g., urea, performed in an evacuated closed vessel. Upon heating to temperatures high enough for rapid diffusion of interstitial solute, but low enough to avoid second-phase precipitation, the reagent is pyrolyzed to a gas atmosphere containing molecules that (i) activate the alloy surface by stripping away the passivating Cr${}_2$O${}_3$-rich surface film (diffusion barrier) and (ii) rapidly infuse carbon and nitrogen into the alloy. We demonstrate quantitatively that this method can generate a subsurface zone with concentrated carbon and nitrogen comparable to what can be accomplished by established (e.g., gas-phase- or plasma-based) methods, but with significantly reduced processing time. As another important difference to established gas-phase processing, the interaction of gas molecules with the alloy surface can have auto-catalytic effects by altering the gas composition in a way that accelerates solute infusion by providing a high activity of HNCO. The new method lends itself to rapid experimentation with a minimum of laboratory equipment. Full article

The effect of a controlled oxygen admixture to a plasma nitrocarburizing process using active screen technology and an active screen made of carbon was investigated to control the carburizing potential within the plasma-assisted process. Laser absorption spectroscopy was used to determine the resulting process gas composition at different levels of oxygen admixture using O₂ and CO₂, respectively, as well as the long-term trends of the concentration of major reaction products over the duration of a material treatment of ARMCO^® iron. The short-term studies of the resulting process gas composition, as a function of oxygen addition to the process feed gases N₂ and H_2, showed that a stepwise increase in oxygen addition led to the formation of oxygen-containing species, such as CO, CO₂, and H₂O, and to a significant decrease in the concentrations of hydrocarbons and HCN. Despite increased oxygen concentration within the process gas, no oxygen enrichment was observed in the compound layer of ARMCO^® iron; however, the diffusion depth of nitrogen and carbon increased significantly. Increasing the local nitrogen concentration changed the stoichiometry of the ε-Fe₃(N,C)_1+x phase in the compound layer and opens up additional degrees of freedom for improved process control. Full article

Stainless steel-based WC composite layers fabricated by a laser cladding technique, have strong mechanical strength. However, the wear resistance of WC composite layers is not sufficient for use in severe friction and wear environments, and the corrosion resistance is significantly reduced by the formation of secondary carbides. Low-temperature plasma nitriding and carburizing of austenitic stainless steels, treated at temperatures of less than 450 °C, can produce a supersaturated solid solution of nitrogen or carbon, known as the S-phase. The combined treatment of nitriding and carburizing can form a nitrocarburizing S-phase, which is characterized by a thick layer and superior cross-sectional hardness distribution. During the laser cladding process, free carbon was produced by the decomposition of WC particles. To achieve excellent wear and corrosion resistance, we attempted to use this free carbon to form a nitrocarburizing S-phase on AISI 316 L stainless steel-based WC composite layers by plasma nitriding alone. As a result, the thick nitrocarburizing S-phase was formed. The Vickers hardness of the S-phase ranged from 1200 to 1400 HV, and the hardness depth distribution became smoother. The corrosion resistance was also improved through increasing the pitting resistance equivalent numbers due to the nitrogen that dissolved in the AISI 316 L steel matrix. Full article

Low-temperature plasma nitrocarburizing treatments are applied to improve the surface properties of austenitic stainless steels by forming an expanded austenite layer without impairing the excellent corrosion resistance of the steel. Here, low-temperature active screen plasma nitrocarburizing (ASPNC) was investigated in an industrial-scale cold-wall reactor to compare the effects of two active screen materials: (i) a steel active screen with the addition of methane as a gaseous carbon-containing precursor and (ii) an active screen made of carbon-fibre-reinforced carbon (CFC) as a solid carbon precursor. By using both active screen materials, ASPNC treatments at variable plasma conditions were conducted using AISI 316L. Moreover, insight into the plasma-chemical composition of the H₂-N₂ plasma for both active screen materials was gained by laser absorption spectroscopy (LAS) combined with optical emission spectroscopy (OES). It was found that, in the case of a CFC active screen in a biased condition, the thickness of the nitrogen-expanded austenite layer increased, while the thickness of the carbon-expanded austenite layer decreased compared to the non-biased condition, in which the nitrogen- and carbon-expanded austenite layers had comparable thicknesses. Furthermore, the crucial role of biasing the workload to produce a thick and homogeneous expanded austenite layer by using a steel active screen was validated. Full article

This paper is devoted to the possibilities of the utilization of chosen chemical heat treatment technologies on steels used for manufacturing highly stressed components of military vehicles and weapons systems. The technologies chosen for this research are plasma ferritic nitrocarburizing and ferritic nitrocarburizing in a gaseous atmosphere. These technologies were applied on a steel equivalent 1.5752 (i.e., CSN 41 6426), which is suitable for carburizing. Chemical composition of the steel was verified by optical emission spectrometry. An observation of a microstructure and an assessment of the parameters of obtained white layers were performed by optical microscopy. Morphology and porosity of the surface were observed by electron microscopy. The depth of diffusion layers was evaluated in accordance with ISO 18203:2016(E) from the results of microhardness measurements. A friction coefficient was obtained as a result of measurements in accordance with a linearly reciprocating ball-on-flat sliding wear method. Wear resistance was assessed by employing the scratch test method and a profilometry. The profilometry was also utilized for surface roughness assessment. It was proved that both tested chemical heat treatment technologies are suitable for surface treatment of the selected steel. Both technologies, ferritic nitrocarburizing in plasma and a gaseous atmosphere, are beneficial for the improvement of surface properties and could lead to a suppression of geometrical deformation in comparison with frequently utilized carburizing. Moreover, the paper presents a procedure that creates a white layer-less ferritic nitrocarburized surface by utilizing an appropriate modification of chemical heat treatment parameters, thus subsequent machining is no longer required. Full article

Active screen plasma nitrocarburizing (ASPNC) increases the surface hardness and lifetime of austenitic stainless steel without deteriorating its corrosion resistance. Using an active screen made of carbon opens up new technological possibilities that have not been exploited to date. In this study, the effect of screen power variation without bias application on resulting concentrations of process gas species and surface modification of AISI 316L steel was studied. The concentrations of gas species (e.g., HCN, NH₃, CH₄, C₂H₂) were measured as functions of the active screen power and the feed gas composition at constant temperature using in situ infrared laser absorption spectroscopy. At constant precursor gas composition, the decrease in active screen power led to a decrease in both the concentrations of the detected molecules and the diffusion depths of nitrogen and carbon. Depending on the gas mixture, a threshold of the active screen power was found above which no changes in the expanded austenite layer thickness were measured. The use of a heating independent of the screen power offers an additional parameter for optimizing the ASPNC process in addition to changes in the feed gas composition and the bias power. In this way, an advanced process control can be established. Full article