Plasma Carburizing Research Articles

Hydrogen evolution on plasma carburised nickel and effect of iron deposition from the electrolyte in alkaline water electrolysis

Presence of carbon in electrodeposited nanocrystalline Ni-Fe-C cathodes renders a high electroactivity for hydrogen evolution reaction (HER) in hot alkaline solutions. In the present work carbon was introduced into nickel cathodes by plasma treatment in CH4+H2 gas mixture at 470°C. Electrochemical measurements were carried out in the solution of 25wt.% KOH (reagent p.a.) at 80°C. In some measurements the solution was pre-electrolysed to remove heavy metals. Carburisation resulted in a significant enhancement of catalytic activity of nickel for HER during short cathodic polarisation. Later, differences between the materials almost disappeared, evidently due to deposition of iron and of other heavy metals from the solution. Cathodes with iron deposits underwent an activation following anodic polarisation. It was proposed that the activating effect of iron can be associated with the formation of highly reactive iron during cathodic reduction of oxide species (probably Fe(OH)42−). The activating effect of prior anodic polarisation can be due to the formation of large amounts of oxide species which can undergo the reduction to reactive iron.

Effect of S-phase on the Hydrogen Induced Phase Transition and Hydrogen Embrittlement Susceptibility in AISI 304 Stainless Steel

S-phase produced by low temperature plasma carburizing treatment was studied for the feasibility in reducing the susceptibility to hydrogen embrittlement (HE) of metastable AISI 304 stainless steel. It is demonstrated by slow strain-rate tensile (SSRT) tests that samples with S-phase coatings have higher resistance to HE comparing with untreated counterparts. Meanwhile, “in situ” EBSD investigations have shown that hydrogen induced phase transition (HIPT) is suppressed by S-phase coatings, which is beneficial to improving the resistance to HE.

Investigation of plasma parameters in an active screen cage-pulsed dc plasma used for plasma nitriding

Active screen cage-pulsed dc plasmas are widely used in the material processing applications such as plasma nitriding, carburizing and nitrocarburizing. Specifically for plasma nitriding applications, a H2–N2 mixture is used. In this article, a study of the electron number density (ne), atomic nitrogen density ([N]), electron temperature and the excitation temperature is reported in the presence of an active screen cage-pulsed dc plasma. The ne and are determined here by a triple Langmuir probe, while [N] and are estimated by optical emission spectroscopy (OES). The two temperatures and their ratio are compared for different input parameters (such as applied power, gas pressure and H2 percentage). This study is useful in active screen cage plasma nitriding applications where only few plasma diagnostic measurements have been reported.

Investigation of the Influence of Electrolytic-Plasma Processing on Structural-Phase State and Mechanical Properties of the 40CrNiAl Alloy

It is shown that as a result of electrolytic plasma carburization is released from the solid solution carbides dispersed particles based alloy components, i.e. hardening occurs. Found that after processing the surface of the alloy samples 40CrNiAl modified form reinforced layers whose thickness depends on the time, temperature and processing of components of the electrolyte.

Analysis of sliding wear tests of plasma processed AISI 316L steel

In this paper, the influence of different plasma treatments on wear regime transitions during sliding wear tests carried out on AISI 316L steel was investigated. Selected plasma treatments included plasma nitriding, plasma carburizing and a sequential process involving plasma carburizing followed by plasma nitriding. During sliding wear tests, sharp transitions in frictional force were detected after the initial running-in period. These transitions in frictional force, which were measured as a function of sliding distance, could be correlated to different plasma-modified layers at the surface of the AISI 316L steel. They were also associated with concentrations of nitrogen and/or carbon along sample depths and also with instrumented indentation hardness–depth profiles. Once sliding distances that corresponded to such transitions were determined, additional tests were performed and then interrupted at these distances to record EDS (energy dispersive spectroscopy) composition maps of wear tracks. Additionally, both depth and wear volume of wear tracks were determined by stylus profilometry. Significant reductions in nitrogen and/or carbon contents were detected for each wear track analyzed, indicating that plasma modified layers were almost worn out for these sliding distances at which sharp transitions in frictional force were recorded. The smallest overall wear volume was measured for the sequentially treated sample, which exhibited the best wear resistance among all tested samples. Results indicated that transitions in friction coefficient were distance-dependent during sliding wear tests; this dependence could be attributed to variations in material hardness and/or concentration of interstitial solutes (carbon, nitrogen) in the austenite phase.

Combined plasma carburizing and nitriding of sprayed AISI 316L steel coating for improved wear resistance

Both low-temperature plasma nitriding and carburizing at treatment temperatures below 450°C are known to increase the surface hardness of a sprayed AISI 316L stainless steel coating to above 1000HV, while maintaining corrosion resistance, via production of a supersaturated solid solution of expanded austenite, known as the S-phase. In this work, we investigate combined plasma processes for nitriding and carburizing of sprayed AISI 316L coatings. The sequential process, with carburizing first, immediately followed by nitriding, did not produce a significantly thicker S-phase than that produced using plasma nitriding alone. In contrast, the simultaneous process, in which carburizing and nitriding were performed at the same time, was found to form a thick S-phase at 450°C. Vickers hardness and specific wear amount were improved considerably by both combined plasma processes. In addition, the thickness of the diffusion layers formed on the sprayed 316L coatings was inferior to that of the corresponding diffusion layers formed on AISI 316L steel plates; this was because the sprayed 316L coatings included oxide layers.

High temperature oxidation behaviour of plasma carburised Ni based single crystal superalloy with NiCoCrAlYHf high temperature oxidation protective coatings

The high temperature oxidation behaviour of plasma carburisation on Ni based third generation single crystal superalloy with NiCoCrAlYHf high temperature oxidation protective coating (HY5) is investigated in this paper. The Ni based third generation single crystal superalloy with single HY5 high temperature oxidation protective coating is compared to the plasma carburised samples. HY5 high temperature oxidation protective coating is deposited onto the single crystal superalloy by arc ion plating. The performance of diffusion during thermal cycling at 1100°C was studied. The microstructure and phase composition were examined by scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). The results show that by means of plasma carburisation into the HY5 high temperature oxidation protective coating, its microstructure can be made finer and more uniform, and its microhardness and adhesion to the substructure can be improved markedly. There were smaller quantities of topologically close packed phases (TCPs) and secondary reaction zones (SRZs) precipitated under coating in the single crystal superalloy.

Effect of Carburizing Atmosphere Proportion on Low Temperature Plasma Carburizing of Austenitic Stainless Steel

In this study, in order to explore a suitable method to obtain a better wear resistance and corrosion resistance of austenitic stainless steel, low temperature plasma carburizing technology has been studied. Research on the properties of austenitic stainless steel under different carburizing atmosphere proportion, with hardness, wear resistance and corrosion resistance as the properties characterization. The results shows that C3H8:H2=1:40 have better properties with the hardness of 950 HV0.05, the friction coefficient of about 0.25, which showed a better wear resistance. And also the corrosion rate of about 20.3g/m2·h showed a better corrosion resistance.

The Effect of Wear and Corrosion Resistance of Austenitic Stainless Steel on Plasma Carburizing

In this study, low temperature plasma carburizing technology as one of the surface hardening techniques has been applied to improve the mechanical properties of 304 austenitic stainless steel. Several low temperature process parameters were studied to focus on the structure and properties of the carburized layer. The results shows that carburizing at 450°C, C3H8: H2 = 1: 40, carburizing time 10h could get a better white layer, a better wear resistance and a reasonable corrosion resistance, which proved to be the optimal hardening treatment.

On the thermo-mechanical stability and oxidation behavior of carbon S-phase at elevated temperature and under tensile stress

The thermo-mechanical stability and oxidation behavior of S-phase are critical issues for some industrial applications at elevated temperatures owing to its metastable nature. In this study, the stability and oxidation behavior of carbon S-phase generated by plasma carburizing on AISI316 under both thermal and mechanical conditions was investigated for the first time. The experimental results demonstrate that when tested at a fixed temperature the thickness of the carbon S-phase layer increased with the stress applied to the tensile specimens during the thermo-mechanical stability tests. This indicates that tensile stress promotes the diffusion of carbon in the carbon-S-phase. The oxidation resistance of the carbon S-phase at 500°C is inferior to untreated AISI 316, which further deteriorated under tensile stress. The lattice expansion and high density of crystal defects in the S-phase and the applied tensile stress would facilitate the diffusion of oxygen and iron, thus promoting oxidation.

Microstructure and performance of functionally graded Ti(C,N)-based cermets prepared by double-glow plasma carburization

Ti(C,N)-based cermets were subject to double-glow plasma carburization which substantially improved the surface hardness. The microstructures were studied using scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX). It was found that the double-glow plasma carburization introduced a graded surface zone enriched in carbonitride phase and deficient in binder phase. The microstructure of the surface zone of the carburized cermet was different from that of the as-sintered cermets. Besides the carbonitride grains with typical core–rim structure, the amount of smaller grains without obvious rim phase increased greatly, and some carbonitride grains adjoined and congregated with each other. The formation of the graded layer was due to the high carbon activity in the surface region during carburization, which caused the titanium, molybdenum and tungsten to transport outwards and forced the nickel to transfer inwards. After double-glow plasma carburization, the surface hardness was increased greatly and the hardness distribution along the depth was in accord with the binder distribution.

S1160205 硬化した交互欠歯車を用いた動的熱電対法による歯面温度計測に関する研究([S116-02]伝動装置の基礎と応用(2),機素潤滑設計部門)

It is very important to know the surface temperature of gears in operation. However, measuring the surface temperature of gears in operation is difficult. As an effective means to measure the surface temperature, method of using dissimilar metals is known. The voltage proportional to surface temperature was produced by contacting dissimilar metals. In this study, S55C and SUS304 were selected to dissimilar metals. Both dissimilar metals were heat-treated and surfaces were hardened. SUS304 was performed plasma carburizing process and S55C was performed induction hardening. There were very few measurement examples of the surface temperature by using hardened dissimilar metals in the previous studies. In order to remove the influence of the number of tooth in operation, the gear of two sheets were made into the one structure meshed by turns (combined lacked gear). When making the gear of two sheets into one structure meshed by turns, the problem of accuracy arose. However, surface temperature is measured almost successfully by combined lacked gear by SUS316 plasma carburizing process and S55C induction hardening.

Design and characterisation of a new duplex surface system based on S-phase hardening and carbon-based coating for ASTM F1537 Co–Cr–Mo alloy

Co–Cr–Mo alloys are one of the most widely used metallic biomaterials for metal-on-metal joint prostheses. However, concerns over increased revision rates mainly due to nano-sized wear debris have been raised. This study was aimed at enhancing the friction, wear and load-bearing properties of Co–Cr–Mo alloys by developing a new duplex surface system combining super hard and wear-resistant S-phase layer with self-lubricating, low-friction carbon-based coating. To this end, ASTM F1537 Co–Cr–Mo alloy surface was plasma carburised (PC) at 450°C and then coated with a carbon-based GiC coating. The microstructures of the duplex and single treated (PC or GiC coating) Co–Cr–Mo surface systems were characterized and their mechanical, tribological and corrosion properties were evaluated. The results showed that the new duplex surface system exhibited a high load bearing capacity, a low friction coefficient, excellent wear resistance and good corrosion behaviour.

An Investigation of Carburized Layers on Austenitic Stainless Steels

In this study, low temperature plasma carburizing of austenitic stainless steels has been studied, with the aim to improve the hardness and wear resistance of austenite layers. Austenitic stainless steels were plasma carburized at 450°C, using C3H8 as carbon carrier gas. Depth profiles of hardness, hardness distribution and the friction coefficient of carburized layer were measured. The results show that carburized layers range from 10 to 20μm, causing the improvement of the hardness and wear resistance of the surface of austenitic stainless steels.

Low temperature plasma carburizing of AISI 316L austenitic stainless steel and AISI F51 duplex stainless steel

In this work an austenitic AISI 316L and a duplex AISI F51 (EN 1.4462) stainless steel were DC-Plasma carburized at 480ºC, using CH4 as carbon carrier gas. For the austenitic AISI 316L stainless steel, low temperature plasma carburizing induced a strong carbon supersaturation in the austenitic lattice and the formation of carbon expanded austenite (γC) without any precipitation of carbides. The hardness of the carburized AISI 316L steel reached a maximum of 1000 HV due to ∼13 at% carbon supersaturation and expansion of the FCC lattice. For the duplex stainless steel AISI F51, the austenitic grains transformed to carbon expanded austenite (γC), the ferritic grains transformed to carbon expanded ferrite (αC) and M23C6 type carbides precipitated in the nitrided case. Hardness of the carburized case of the F51 duplex steel reached 1600 HV due to the combined effects of austenite and ferrite lattice expansion with a fine and dispersed precipitation of M23C6 carbides.

Surface Strengthening of Ti-6Al-4V Alloy by Glow Plasma Carbonization Process

A glow plasma carburizing technique was applied to strengthen the surface of the Ti-6Al-4V alloy. The alloy was carburized at 950 °C and 30∼35 Pa for 3 h using plasma of Ar gas. Graphite rod was employed as carbon supply to avoid the hydrogen brittleness which is common in traditional gas carbonization. The carburized layer was examined by an optical microscope (OM), field emission scanning electron microscope (FESEM), and X-ray diffractometer (XRD). The wear resistance under ring-block wear testing and the surface hardness were evaluated and compared to those for the untreated material. Results show that a carburized layer (416 μm thick), mainly composed of TiC and V8C7, is found. These hard carbides contributed to the imrovement of the hardness and wear resistance.

Surface hardness improvement of plasma-sprayed AISI 316L stainless steel coating by low-temperature plasma carburizing

Low-temperature carburizing below 773K of austenite stainless steel can produce expanded austenite, known as S-phase, where surface hardness is improved while corrosion resistance is retained. Plasma-sprayed austenitic AISI 316L stainless steel coatings were carburized at low temperatures to enhance wear resistance. Because the sprayed AISI 316L coatings include oxide layers synthesized in the air during the plasma spraying process, the oxide layers may restrict carbon diffusion. We found that the carbon content of the sprayed AISI 316L coatings by low-temperature carburizing was less than that of the AISI 316L steel plates; however, there was little difference in the thickness of the carburized layers. The Vickers hardness of the carburized AISI 316L spray coating was above 1000HV and the amount of specific wear by dry sliding wear was improved by two orders of magnitude. We conclude that low-temperature plasma carburizing enabling the sprayed coatings to enhance the wear resistance to the level of carburized AISI 316L stainless steel plates. As for corrosion resistance in a 3.5 mass% NaCl solution, the carburized AISI 316L spray coating was slightly inferior to the as-sprayed AISI 316L coating.

Time dependence of microstructure and hardness in plasma carbonized Ti–6Al–4V alloys

Ti–6Al–4V alloy was treated by plasma carburizing process at 950 °C for different durations of 1 h, 2 h, 3 h, and 4 h. Plasma carburizing was performed in pure Ar gas under 32 ± 2 Pa. Graphite rod was employed as carbon supplier. Optical microscope (OM) observations showed a carburizing layer formed after carburizing. Further FESEM examinations and XRD analysis confirmed that the carburizing layer consists of a TiC/α-Ti mixed layer and a thin compound (TiC) layer on the mixed layer. With increasing the carbonizing time, the thickness of the carburizing layer increased and the specimen treated at 950 °C for 3 h obtains maximum values of the hardness.

Effect of Hybrid Surface Treatment Composed of Plasma Nitriding and DLC Coating on Friction Coefficient and Fatigue Strength of Stainless Steel

This study was conducted to investigate the effect of hybrid surface treatment composed of plasma nitriding and DLC (diamond-like carbon) coating on the friction coefficient and fatigue strength of stainless steel JIS SUS316. The obtained results were compared with the results of the previous study which investigated the effect of hybrid surface treatment composed of plasma carburizing and DLC coating. Plasma nitriding as a pretreatment was more effective to decrease the friction coefficient of DLC-coated stainless steel than plasma carburizing because the hardened layer with greater hardness supported the DLC layer. The mechanical properties were unaffected by both hybrid surface treatments. Plasma nitriding improved the fatigue strength of stainless steel more than plasma carburizing. DLC coating slightly improved the fatigue strength of the plasma-nitrided material; however, its effect was more significant on the plasma-carburized material. [doi:10.2320/matertrans.M2012426]

Electrochemical Stability of Magnesium Battery Current Collectors in a Grignard Reagent-Based Electrolyte

The electrochemical stabilities of several electrodes were investigated by cyclic voltammetry and chronoamperometry in a tetrahydrofuran solution containing phenylmagnesium chloride and aluminum chloride. The existence of chloride ions in the electrolyte caused pitting of affordable, non-noble metal electrodes at high potentials and crucially lowered their corrosion resistance. In contrast, Pt and glassy carbon electrodes exhibited high corrosion resistance. Since Pt is expensive and bulk glassy carbon is not flexible, these two materials are not suitable current collectors in commercial batteries. A considerable improvement in corrosion resistance was confirmed when glassy carbon coatings were formed on the affordable electrodes by plasma carburization, which can be one solution to this corrosion problem.