Plasma Electrolytic Nitrocarburizing Research Articles

Tribological Properties of Carbon Tool Steel after Plasma Electrolytic Nitrocarburizing

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.

The Effect of Plasma–Electrolytic Nitrocarburizing of a Medium Carbon Steel Surface on Friction and Wear in Pair with Tin–Lead Bronze

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.

Characteristics and properties of plasma electrolytic nitrocarburizing Ti (C, N) coatings on Ti6Al4V alloy

Titanium carbonitrides Ti(C,N) coatings were prepared by plasma electrolytic nitrocarburizing in an electrolytic solution containing ammonium nitrate, glycerol and ethanol. The coating consists of an outer compound layer and an inner diffusion layer with a total thickness of about 100μm. The compounds consist of Ti(C,N) and amorphous TiO2. The corrosion current density of the coating is almost an order of magnitude lower than that of Ti6Al4V substrate in 3.5% NaCl solution. The hardness of the coating is up to 2200HK0.025, which is 5~6 times greater than that of Ti6Al4V alloy. The coating itself is worn very slightly while the counter ball suffering serious abrasion during sliding against the SAE52100 counter ball. The PEN/C coating enhances the hardness, corrosion and abrasive resistances of Ti6Al4V alloy substantially.

Improved Wear Resistance of Low Carbon Steel by Duplex Surface Treatment Combining Cathodic Plasma Electrolytic Nitrocarburising and Anodic Plasma Electrolytic Polishing

Improved Wear Resistance of Low Carbon Steel by Duplex Surface Treatment Combining Cathodic Plasma Electrolytic Nitrocarburising and Anodic Plasma Electrolytic Polishing

Increasing the Hardness and Corrosion Resistance of the Surface of CP-Ti by Plasma Electrolytic Nitrocarburising and Polishing.

The possibility of increasing the hardness to 1420 HV and the corrosion resistance of the CP-Ti surface using a combined plasma electrolytic treatment consisting in anodic plasma electrolytic nitrocarburising in a solution of ammonia, acetone and ammonium chloride at 900 °C and subsequent plasma electrolytic polishing is shown. The morphology, surface roughness, phase composition, structure and microhardness of the modified layer were studied. The corrosion characteristics of the treated surface were studied through potentiodynamic tests and electrochemical impedance spectroscopy. It has been shown that an increase in the surface roughness has a negative effect on the corrosion resistance. The proposed plasma electrolytic polishing makes it possible to remove the outer porous oxide layer, providing increased corrosion resistance. The highest reduction in the corrosion current density, by 13 times compared to CP-Ti and by two orders compared to a plasma electrolytic nitrocarburising sample, is achieved after plasma electrolytic polishing in a solution of ammonium fluoride (4%) at 300 V for 3 min.

Features of Cathodic Plasma Electrolytic Nitrocarburizing of Low-Carbon Steel in an Aqueous Electrolyte of Ammonium Nitrate and Glycerin

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.

Increasing wear resistance of austenitic stainless steel by anodic plasma electrolytic nitrocarburising

The effect of plasma electrolytic nitrocarburising on the wear resistance of 12Cr18Ni10Ti steel was investigated. The phase composition of the modified layer and the surface morphology were studied using X-ray analysis and scanning electron microscope. The wear of the specimens was determined with dry friction of the lateral surface of a cylindrical specimen against a bearing steel disc (60 HRC). It is shown that anodic PEN/C of steel samples results in the formation of a hardened layer with a microhardness up to 370 HV due to its saturation with nitrogen and carbon followed by quenching. The wear resistance of steel enhances by 8.5 times after treatment in a solution of carbamide (12 wt. %) and ammonium chloride (10 wt. %) at 800 °C for 5 min with quenching in an electrolyte.

The effect of plasma electrolytic polishing on the surface properties of nitrocarburised steel

The effect of anodic plasma electrolytic polishing on the characteristics of low carbon steel (0.2 % C) after nitrocarburising was investigated. The formation of the modified layer including a hardened diffusion layer and a surface oxide layer occurs as a result of anodic plasma electrolytic nitrocarburising in an aqueous solution of glycerol (8 %), ammonium nitrate (5 %) and ammonium chloride (15 %) at 850 °C. Conducting a plasma electrolytic polishing of the surface leads to the removal of a loose part of the oxide layer (predominantly FeO), which affects the reduction the surface roughness of 2 times. The rate of the weight loss of steel in this process is 0.5 mg/s. The corrosion current density in a 3.5 % sodium chloride solution decreases from 41.0 μA/cm2 in an untreated sample to 32.6 μA/cm2 in the steel after nitrocarburising and polishing during 30 s and to 22–24 μA/cm2 when the second operation lasted 60-300 s due to the protective action of the nitride zone and the dense part of the oxide layer. Wear test shows that plasma electrolytic polishing enhances the wear resistance of a nitrocarburised sample by 1.8 times.

Wear mechanism of medium carbon steel after its plasma electrolytic nitrocarburising

This article considers the change in the tribological characteristics of medium carbon steel after its anodic plasma electrolytic nitrocarburising in a carbamide electrolyte. Phase and elemental composition of the nitrocarburised layer was studied using X-ray analysis and nuclear backscattering of protons. Optical and electron microscopes were used to observe friction tracks. It has been found out that the wear process in nitrocarburised samples is followed by plastic displacement of the metal in the friction contact zone according to the molecular-mechanical and fatigue theory of wear and application of the Kragelsky criterion. It has been shown that an increase in the sliding velocity of 0.5 m/s to 1.5 m/s results in a linear decrease in the friction coefficient from 0.65 to 0.45. The minimum wear rate is achieved after nitrocarburising of steel at 750 °C for 7 min and a sliding speed of (0.4–0.55) m/s. Anodic nitrocarburising increases the wear resistance of steel by 40% compared to quenching at a sliding speed of 0.9 m/s.

Preparation and corrosion resistance of hybrid coatings formed by PEN/C plus PEO on AZ91D magnesium alloys

A novel surface modification technique is developed to further improve the corrosion resistance of AZ91D magnesium alloys. Hybrid coatings were fabricated successfully by a combination of plasma electrolytic nitrocarburizing (PEN/C) and plasma electrolytic oxidation (PEO) on magnesium alloys. The microstructures, element distribution and phase compositions of the coatings were analyzed by SEM, EPMA and XRD, respectively. The potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) were employed to evaluate the corrosion resistance of the coatings. The results show that PEN/C process predominantly depends on the adsorption and diffusion effects of the active atoms of [N] and [C], and it creates a good substrate surface with predesigned chemical composition to get newly born phases, such as SiC and Si3N4 with excellent properties, in the following hybrid coatings. PEN/C pretreatment also provide a favorable microstructure to enlarge the coating thickness and to make the coating more compact for the hybrid coatings followed. There exists an overlapping phenomenon regarding coating thickness rather than piling up layer by layer during the formation of the hybrid coatings. The hybrid coatings exhibit more excellent corrosion resistance than both single PEN/C modified layers and single PEO coatings. Particularly, the hybrid coatings can provide relatively superior long-term corrosion protection and suppress the occurrence of the localized corrosion for AZ91D substrates. It is worth noting that the key of this investigation is keeping the PEO process unchanged for both PEO treatment only and PEN/C + PEO combining procedure.

Increasing wear resistance of Ti6Al4V alloy by anodic saturation with carbon and nitrogen

In this paper, anodic plasma electrolytic nitrocarburising (PEN/C) was applied to Ti6Al4V alloy. This treatment was carried out in electrolyte containing ammonia (5 wt.%), acetone (5 wt.%) and ammonium chloride (10 wt.%) during 5 min at treatment temperature from 750 to 900°C. There were investigated the alloy microhardness, surface roughness and wear resistance. It was shown that the PEN/C results in saturation of studied alloy with oxygen, nitrogen and carbon include formation TiO2 with rutile structure and solid solution in titanium of nitrogen and carbon. This structure provides an increase in microhardness of the surface layer up to 940 HV by sealing the crystal lattice. Surface roughness Ra of treated samples decreases by 1.2–1.4 times and wear resistance increases by 9–10 times after PEN/C. Friction coefficient of PEN/C samples was reduced by 1.5-fold after treatment at 750°C.

Possibility of increasing wear resistance of steel by combining anodic plasma electrolytic treatment

The opportunity of enhancement of the wear resistance of steel by combining anodic plasma electrolytic saturation of steel with interstitial elements followed by, quenching and plasma electrolytic polishing was shown. The samples of low-carbon steel were subjected to plasma electrolytic nitrocarburising. The samples of medium carbon steel were subjected to plasma electrolytic boriding. The formation of the modified layer including a hardened diffusion layer and a surface oxide layer occurs as a result of diffusion saturation. After nitrocarburising and boriding the steel samples were polished in an aqueous solution of ammonium sulphate. Conducting the surface polishing results in the removal of a loose part of the oxide layer (predominantly FeO), which reduces the surface roughness more than a half. Wear testing reveals that wear resistance of steel samples after polishing is higher than nitrocarburising ones of 1.8 times and boriding ones of 21.5 times.

Anodic plasma electrolytic nitrocarburising of Ti6Al4 V alloy (SMT31)

ABSTRACT The structure of Ti6Al4 V alloy, its microhardness, surface roughness and corrosion resistance after anodic plasma electrolytic nitrocarburising (PEN/C) in an electrolyte containing carbamide and ammonium chloride were investigated. An X-ray diffractometer and a scanning electron microscopy were used to characterise the phase composition and structure of the modified surface. The effect of processing temperature on the corrosion resistance of the PEN/C samples was examined by means of potentiodynamic polarisation in Ringer’s solution. It was found that the PEN/C provides the formation of the external oxide layer (rutile) and a solid solution of carbon and nitrogen in titanium with martensite structure after quenching in the electrolyte. The microhardness of the layer is 740 HV; the surface roughness decreases from 1 to 0.63 μm. Corrosion resistance in Ringer’s solution does not deteriorate after anodic PEN/C at low temperature.

Effects of pulse frequency and duty cycle on the plasma discharge characteristics and surface microstructure of carbon steel by plasma electrolytic nitrocarburizing

A plasma electrolytic nitrocarburizing (PEN/C) process was used to produce a protective coating on the surface of 45# carbon steel under a pulsed direct current power mode in a urea electrolyte. The effects of pulse frequency and duty cycle on the microdischarge characteristics and coating microstructure were investigated. The results show that the pulse frequency has a small effect on the breakdown voltage. However, the micropore size in the formed worm-like feature of the sample surface increases with increasing pulse frequency. Carbide, nitride and oxide phases were identified in the PEN/C layers. The microhardness increases with increasing pulse frequency. Increasing duty cycle results in a gradual decrease of the breakdown voltage. At low duty cycles, both crater-shaped regions and worm-like features were observed. However, the microhardness of the formed PEN/C layers exhibits a minute variation, in spite of the increase of the duty cycle.

Anodic plasma electrolytic nitrocarburising of VT22 titanium alloy in carbamide and ammonium chloride electrolyte

The structure of alpha- and beta-titanium alloy VT22, its microhardness, surface roughness, wear and corrosion resistance after anodic plasma electrolytic nitrocarburising in an electrolyte containing carbamide and ammonium chloride were investigated. An X-ray diffractometer and a scanning electron microscope were used to characterize the phase composition and structure of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a ball-on-disc tribometer under lubricated testing conditions. The effect of processing temperature on corrosion resistance of the plasma electrolytic nitrocarburising samples was examined by means of potentiodynamic polarization in Ringer’s solution. It was shown that the anodic nitrocarburising provides saturation of the titanium alloy with oxygen, nitrogen and carbon and the formation of TiO2 with a rutile structure and a nitrogen/carbon solid solution in titanium. The anodic plasma electrolytic nitrocarburising at all treatment temperatures diminishes the wear rate of the titanium alloy samples and the surface roughness. Friction coefficient of treated samples can be reduced by 4.7 times. The anodic nitrocarburising results in an enhanced corrosion resistance since the corrosion potential increases by an order of magnitude.

Effect of plasma electrolytic nitrocarburizing on phase composition of 0.3C-1Mn-1Si-Fe steel

By transmission diffraction electron microscopy, study of the changes in the phase composition arising in 0.3C-1Mn-1Si-Fe steel upon plasma electrolytic nitrocarburizing with increasing distance from the modified surface is performed. It is found that, with increasing distance from the surface, the list of carbonitride phases and their volume fraction are reduced. The morphology of the steel matrix is changed.

Anode plasma electrolytic nitrocarburizing of steel in an aqueous electrolyte based on glycerol, ammonium nitrate, and ammonium chloride

The mechanism of transport of saturating components from the electrolyte into the treated material during the anode nitrocarburizing of steel in an electrolyte containing glycerol, ammonium nitrate, and ammonium chloride has been described. The effect of the electrolyte component concentrations and treatment conditions on the pattern of formation and properties of the diffusion layers has been determined. The possibility of preparing a nitrocarburized layer with a thickness of up to 0.2 mm and a surface microhardness of up to 870 HV has been shown.

Surface Modification of Low-Carbon Steels by Plasma Electrolytic Nitrocarburising

This study investigates the effect of the plasma electrolytic nitrocarburising conditions and electrolyte composition (NH4Cl, NH4NO3 and glycerol) on steel structure and properties. The cross-sectional microstructure, composition and phase constituents of a modified layer are characterized. The thickness of each layer is determined by carbon and nitrogen diffusion, anode dissolution, and oxidation that occur simultaneously. These processes are affected by the concentration of electrolyte components. The aqueous solution containing NH4NO3, NH4Cl and glycerol enables to obtain the modified layer with the thickness of 0.20 mm and hardness of 930 HV, the decrease in the surface roughness from 1.01 to 0.15 µm, the corrosion rate by a factor of 4.4 and the weight loss after lubricate wear testing by a factor of 14.

Modification of steel surface by plasma electrolytic saturation with nitrogen and carbon

The effect of the electrolyte composition with ammonia, acetone, and ammonium chloride on the structure and properties of low carbon steel was studied in anode plasma electrolytic nitrocarburising. An X-ray diffractometer, a scanning electron microscopy (SEM) and an optical microscope were used to characterize the phase composition of the modified layer and its surface morphology. Surface roughness was studied with a profilometer–profilograph. The hardness of the treated and untreated samples was measured using a microhardness tester. The sources of nitrogen and carbon are shown to be the products of evaporation and thermal decomposition of the electrolyte components. It is established that the influence of concentration of ammonia, acetone, and ammonium chloride on the size of the structural components of the hardened layer is explained by the competition of the anode dissolution, high-temperature oxidation and diffusion of the saturating component. The electrolyte composition (10–12.5% ammonium chloride, 5% acetone, 5% ammonia) and processing mode (800 °C, 5–10 min) of low carbon steels allowing to obtain the hardened surface layer up to 0.2 mm with microhardness 930 HV and with decrease in the roughness (Ra) from 1.013 to 0.054 μm are proposed. The anode plasma electrolytic nitricarburising is able to decrease friction coefficient of the treated low carbon steel from 0.191 to 0.169 and wear rate from 13.5 mg to 1.0 mg.

Formation of Diffusion Layers by Anode Plasma Electrolytic Nitrocarburizing of Low-Carbon Steel

The structure of the low-carbon steel after plasma electrolytic nitrocarburizing in the electrolyte containing acetonitrile was investigated. The cross-sectional microstructure, composition, and phase constituents of a modified layer under different processing conditions were characterized. It is shown that the electrolyte that contained ammonium chloride and acetonitrile provides the saturation of steel with nitrogen and carbon and the formation of the Fe4N and FeN0.05 nitrides, Fe4C carbide and other phases. The nitrogen diffusion decreases the austenitization temperature and results in the formation of martensite after the sample cooling in the electrolyte. The formation of a carbon and nitrogen source in a vapor-gas envelope (VGE) is investigated. The proposed mechanism includes evaporation of acetonitrile in the VGE, its adsorption on an anode with the following thermal decomposition, and also the acetonitrile reduction to amine with subsequent hydrolysis to ethanol that is determined with the use of chromatographic method. The aqueous solution that contained 10 wt.% NH4Cl and 10 wt.% CH3CN allows one to obtain the nitrocarburized layer with the thickness of 0.22 mm and microhardness up to 740 HV during 10 min at 850 °C. This treatment regime leads to the decrease in the surface roughness of steel R a from 1.01 μm to 0.17 μm.