Search Results (33)

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 study systematically investigates the influence of nitrogen (N₂) flow rates and nitrocarburized (PNC) interlayers on the mechanical and tribological properties of TiAlN coatings deposited on 300M steel substrates via magnetron sputtering. The coatings were fabricated under three N₂ flow rates (30, 90, and 150 sccm), with microstructure evolution, elemental composition, and phase transitions analyzed using SEM, EDS, AFM, and XRD. The results indicate that the PNC/TiAlN composite coatings exhibited superior interfacial adhesion and load-bearing capacity compared to standalone TiAlN coatings, attributed to the graded hardness transition and stress distribution optimization at the coating–substrate interface. Nanoindentation tests revealed enhanced hardness and elastic modulus in PNC/TiAlN systems under high N₂ flow conditions. Tribological evaluations demonstrated that the composite coatings achieved lower specific wear rates (25.23 × 10⁻⁸ mm³·N⁻¹·m⁻¹) under 7.3 N, outperforming monolithic TiAlN coatings by mitigating abrasive wear and delamination. The synergy between N₂ flow modulation and nitrocarburizing pretreatment effectively optimized coating–substrate compatibility, establishing a robust framework for designing wear-resistant TiAlN coatings in extreme service environments. This work provides critical insights into tailoring PVD coating architectures for aerospace and heavy-load applications. Full article

Quench–polish–quench (QPQ) nitro-carburizing of AISI 4140 steel in a salt bath was performed in this study. Nitro-carburizing in a salt bath enhanced the formation of Fe-nitride on the outer surface layer. Moreover, the oxidizing treatment formed a thin oxide layer decorated on the outermost part of the QPQ-treated sample. The dense compound layer formed after nitro-carburizing in a salt bath consisted of refined granular Fe₃N and transformed to Fe₂N after post-oxidation treatment. Micro-shot peening (MSP) was adopted before QPQ treatment to increase the treated steel’s fatigue performance. The results indicated that MSP slightly increased the thickness of the compound layer and harden depth, but it had little effect on improving the fatigue strength/life of the QPQ-treated sample (SP-QPQ) compared to the non-peened one (NP-QPQ). A deep compressive residual stress (CRS) field (about 200 μm) and a hard nitrided layer showed a noticeable improvement in the fatigue performance of the QPQ-treated ones relative to the 4140 substrates tempered at 570 °C. The ease of slipping or deforming on the substrate surface was responsible for its poor resistance to fatigue failure. The cracking and spalling of the brittle surface layer were the causes for the fatigue crack initiation and growth of all of the QPQ-treated samples fatigue-loaded at/above 875 MPa. It was noticed that fatigue crack initiation at the subsurface inclusions was more likely to occur in the SP-QPQ sample fatigue-loading at 850 MPa or slightly above the fatigue limit. 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

In this work, we evaluated the impact of disc rotors of gray cast iron (GCI), nitrocarburized (NC), and superhard ceramic-coated (SCC) GCI on the brake wear PM emissions of passenger vehicles using dynamometric measurements. The brake emission factor (BEF) of the SCC was greatly reduced by more than a factor of 1/5 compared with those for the GCI and NC for both low-steel and non-steel friction materials. Surface topological and microstructural analyses confirmed that more severe wear was pronounced for the NC rotor compared with the SCC, as evidenced by large concave pits in the wear tracks. Analysis of the size-classified airborne PM suggests that reduced micron-sized particles, which originated from the GCI disc, were responsible for the lower BEF due to the increased hardness of the SCC. 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

Surface engineering of chromium-oxide-passivated alloys (e.g., stainless steels) by low-temperature infusion of interstitial solutes (carbon, nitrogen) from a gas phase requires “surface activation” by removing or perforating the passivating oxide film. We demonstrate a new approach for surface activation based on pyrolysis of a reagent powder, introduce advanced methodology to study its microstructure, and compare it to an established activation method. Rather than a bare alloy surface, stripped of its oxide, we find that an “activated” surface involves a reaction layer containing high concentrations of Cl, carbon, or nitrogen. We propose a model for the microscopic mechanism of surface activation that will enable future systematic development toward more effective process schemes. Full article

The corrosion resistance of Cr-containing alloy parts made by additive manufacturing can be significantly improved by a post-treatment of gas-phase-based infusion of concentrated interstitial solute (carbon and nitrogen). We demonstrate this universal approach for the example of low-temperature nitrocarburization by solid-reagent pyrolysis applied to Alloy 22 (UNS N06022) parts made by laser powderbed fusion. We show that the post-treatment improves the crevice-corrosion resistance of these parts, as well as the corrosion resistance of corresponding parts made from wrought Alloy 22 to surpass the maximum crevice corrosion test temperature specified in ASTM G48-D, whereas non-treated samples typically fail well below. Similarly, cyclic potentiodynamic polarization testing (ASTM G61-86) demonstrates that the post-treatment makes the additively manufactured alloy and the wrought alloy more corrosion-resistant than the non-treated wrought alloy. 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

A new method of surface modification based on the method of electrospark alloying (ESA) using carburizer containing nitrogen—carbon components for producing coatings is considered. New processes have been proposed that include the step of applying saturating media in the form of paste-like nitrogenous and nitrogenous-carbon components, respectively, onto the surface without waiting for those media to dry, conducting the ESA process with the use of a steel electrode-tool, as well as with a graphite electrode-tool. Before applying the saturating media, an aluminium layer is applied onto the surface with the use of the ESA method at a discharge energy of W_p = 0.13–6.80 J. A saturating medium in the form of a paste was applied to the surfaces of specimens of steel C22 and steel C40. During nitriding, nitrocarburizing and carburization by ESA (CESA) processes, with an increase in the discharge energy (W_p), the thickness, micro hardness and continuity of the “white layer” coatings, as well as the magnitude of the surface roughness, increase due to saturation of the steel surface with nitrogen and/or carbon, high cooling rates, formation of non-equilibrium structures, formation of special phases, etc. In the course of nitriding, nitrocarburizing and CESA processing of steels C22 and C40, preliminary processing with the use of the ESA method by aluminum increases the thickness, microhardness and continuity of the “white layer”, while the roughness changes insignificantly. Analysis of the phase composition indicates that the presence of the aluminum sublayer leads to the formation of the aluminum-containing phases, resulting in a significant increase in the hardness and, in addition, in an increase in the thickness and quality of the surface layers. The proposed methods can be used to strengthen the surface layers of the critical parts and their elements for compressor and pumping equipment. Full article

Nitriding can significantly increase the load carrying properties of gears. While the diffusion layer is primarily responsible for improving the tooth root and flank load carrying capacity, the compound layer mainly determines the tribological properties of the gear surface. In the present work, the influence of the compound layer on the tribological load carrying capacity of nitrided gears in the N/N pairing was investigated. For this purpose, compound layers with different thickness, porosity and phase composition were produced and their micro-pitting and wear behavior were investigated in load stage and speed stage tests. The test results confirm that the properties of the compound layer are decisive for the micro-pitting and wear resistance of nitrided gears. For a high micro-pitting resistance, the presence of pores in the near-surface area of the compound layer is of high importance, since no micro-pitting occurred as long as pores were present. With regard to the wear behavior, no dependence on the compound layer thickness or the porous zone thickness was found while the phase composition of the compound layer shows a decisive influence. Full article