Plasma Nitriding Treatment Research Articles

Nanostructured multilayer Cr/CrN coatings on 316L stainless steel for proton exchange membrane fuel cell bipolar plates

Nowadays, hybrid surface modification approaches offer tailored solutions for improving the corrosion resistance and electrical conductivity of the bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs). In the present study, a combination of plasma nitriding and physical vapor deposition (PVD) processes was used to apply a nanometric Cr/CrN multilayer coating onto 316L stainless steel (SS316L) bipolar plates. The performance of the resulting plasma nitrided, PVD-coated, and combined plasma nitriding/PVD-coated SS316L BPPs was examined by phase and morphological characterizations, surface wettability measurements, interfacial contact resistance (ICR), and electrochemical investigations. Potentiodynamic and potentiostatic polarization evaluations, electrochemical impedance spectroscopy (EIS) and Mott-Schottky asessments were conducted on the coated samples in a simulated PEMFC cathode environment at temperatures of 25 °C and 75 °C. Results indicated that the Cr/CrN multilayer coating deposited on the plasma-nitrided 316L BPP exhibited a remarkable 100-fold improvement in corrosion resistance compared to the uncoated substrate. Also, the combination of nitriding and PVD resulted in a significant reduction of the ICR from 186 mΩ cm2 for the uncoated SS316L to 10.2 mΩ cm2 for the coated sample. Multilayer coatings based on the combination of plasma nitriding and PVD treatment can identified as promise candidates for BPP applications.

Improving the Anti-corrosion Property of FeCoNi High-Entropy Alloy Using Plasma Nitriding Treatment

Improving the Anti-corrosion Property of FeCoNi High-Entropy Alloy Using Plasma Nitriding Treatment

Exploring microstructural evolution, nitrogen depth profile, and dry wear performance in 31CrMoV9 steel through combined severe shot peening and plasma nitriding

The present study investigates the influence of severe shot peening (SSP) on the plasma nitriding behavior and sliding wear performance of 31CrMoV9 steel. Initially, the steel was austenitized at 880 °C, followed by oil quenching, and tempering at 520 °C for one hour. These samples were shot peened using high-carbon steel shots, resulting in an enhancement in surface hardness up to 447 HV, gradually converging to the initial martensitic hardness after 140 µm depth. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) scrutinized the initial and surface treated martensitic samples. Afterward, the plasma nitriding treatments were carried out at temperatures of 400 °C, 450 °C, and 500 °C for 8 hours in a 30% N2 + 70% H2 atmosphere and 300 Pa pressure. Microhardness testing, SEM, XRD, and glow-discharge optical emission spectroscopy (GDOES) evaluated both plasma nitrided (PN) and severe shot peened/plasma nitrided (SSP-PN) samples. Cross-sectional SEM observations revealed compound layer thicknesses of approximately 2.8 µm, 5.0 µm, and 6.3 µm for PN samples at 400 °C, 450 °C, and 500 °C, respectively. SSP-PN samples exhibited a substantial increase — roughly 71%, 44%, and 33% increase, respectively, compared to PN samples. GDOES analysis supported this trend and indicated enhanced nitrogen diffusion depth, particularly evident in SSP-PN samples at consistent temperatures. The XRD results showed the stability of Fe4N, Fe2–3N, and CrN phases at all three nitriding temperatures. Furthermore, the intensity of these phases increases with temperature and is augmented by the application of the SSP. Microhardness measurements indicated hardness escalation: from 775 HV to 980 HV at 400 °C, 932 HV to 1096 HV at 450 °C, and 1011 HV to 1205 HV at 500 °C due to SSP. Finally, the wear performance was investigated between the non-nitrided, SSP, PN, SSP-PN, samples. Initially, SSP led to decreased wear performance up to 500 m, followed by improved behavior up to 1500 m. At 400 °C, the SSP-PN sample exhibited a 12% lower wear rate than PN. At 450 °C and 1500 m, the SSP-PN sample displayed a 24% reduction, while at 500 °C, it showed a 27% reduction compared to PN. SEM observations indicated abrasion as the primary wear mechanism across all samples. The overall results indicated a significant similarity in the nitrogen depth profile, hardness depth, and wear performance between the SSP-PN sample at 450 °C and the PN sample at 500 °C. The fact suggested a potential reduction of approximately 50 °C in the typical plasma nitriding temperature for 31CrMoV9 steel as a result of the SSP process.

Investigation of evolution of γ N phase and its effect on conductivity and corrosion resistance of plasma-nitrided 316 L stainless steel bipolar plate for proton exchange membrane fuel cell

In this work, the evolution of γ N phase and its effect on conductivity and corrosion resistance of plasma-nitrided 316 L stainless steel bipolar plate was investigated. The results shows that a certain thickness of uniform γ N phase layer was formed after plasma-nitriding treatment. As the increasing in plasma-nitriding time, the thickness of γ N phase layer and nitrogen atoms in γ N phase layer was increased gradually. As the plasma-nitriding time was larger than 10 h, a large amount of cracks was formed in γ N phase layer because the nitrogen atoms were diffused into γ phase to cause the serious lattice distortion. When the plasma-nitriding time was reached to 24 h, the Fe4N compound was found on the sample surface. After plasma-nitriding treatment, the conductivity and corrosion resistance of the sample was obviously enhanced compared with the untreated sample. With the increasing in the thickness of γ N phase layer, the interfacial contact resistance (ICR) and corrosion current of the sample was gradually reduced. The ICR of the sample was reduced to 7 mΩ under 10 h condition. However, the formation of Fe4N compound and high roughness contributed to the increase of ICR of the sample under 24 h condition, its value was reached to 15 mΩ. When the plasma-nitriding time was larger than 10 h, the corrosion resistance of the sample became poor. The formation of cracks in γ N phase layer and the high surface roughness resulted in the degradation of corrosion resistance of the sample. Under 5 h condition, the comprehensive properties of the sample were the best. The ICR and corrosion of the sample were current conductivity and corrosion resistance of the sample were 15 mΩ and 5.1 μA cm−2, which were low 4 times and 15 times compared with the untreated sample.

Effect of Rapid Hollow Cathode Plasma Nitriding Treatment on Corrosion Resistance and Friction Performance of AISI 304 Stainless Steel.

Low-temperature plasma nitriding of austenitic stainless steel can ensure that its corrosion resistance does not deteriorate, improving surface hardness and wear performance. Nevertheless, it requires a longer processing time. The hollow cathode discharge effect helps increase the plasma density quickly while radiatively heating the workpiece. This work is based on the hollow cathode discharge effect to perform a rapid nitriding strengthening treatment on AISI 304 stainless steels. The experiments were conducted at three different temperatures (450, 475, and 500 °C) for 1 h in an ammonia atmosphere. The samples were characterized using various techniques, including SEM, AFM, XPS, XRD, and micro-hardness measurement. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were employed to assess the electrochemical behavior of the different samples in a 3.5% NaCl solution. The finding suggests that rapid hollow cathode plasma nitriding can enhance the hardness, wear resistance, and corrosion properties of AISI 304 stainless steel.

A detailed analysis of the structural, morphological characteristics and micro-abrasive wear behavior of nitrided layer produced in α (CP–Ti), α+β (Ti–6Al–4V), and β (TNZ33) type Ti alloys

The present work aimed to create a hard surface on a titanium surface via plasma nitriding to improve microhardness and wear properties of the as-cast (α-CP-Ti (CP–Ti), α+β-Ti6Al4V (Ti–Al–4V), and β-Ti-33Nb–33Zr (TNZ-33) samples. For the nitriding process, two temperature conditions (650 °C and 700 °C) were used. The presence of nitrides was evaluated by XRD. The microstructure and chemical composition were studied by electron microscopy and EDS. The roughness was evaluated by confocal microscopy. The microhardness and wear properties were analyzed using the Vickers microhardness and micro-abrasive wear test. Plasma nitriding led to the formation of TiN on CP-Ti, TiN, and Ti2N on Ti–6Al–4V, and TiN and ZrN on TNZ-33 samples. At 700 °C, the TiN increased on CP-Ti, while the Ti2N increased for Ti–6Al–4V and the ZrN increased for TNZ-33. The length of the nitride layer decreased when the temperature increased for CP-Ti and Ti–6Al–4V samples. However, for the TNZ33 alloy, the layer increased from 6.3 to 7.6 μm. The chemical analyses confirmed the presence of nitrogen on the substrate surfaces. After the nitriding process, all materials significantly increased the hardness. The hardness after plasma nitriding can be followed by: CP-Ti > TNZ-33> Ti–6Al–4V (at 650 °C); CP-Ti > Ti–6Al–4V > TNZ-33 (at 700 °C). The wear properties of all samples were improved after plasma nitriding treatment.

Surface treatment of Ti and Ti composites using concentrating solar power and laser

Titanium and its composites are widely used in implants of bones and teeth. Besides mechanical properties also surface characteristics are very important in these biomaterials. Very important are properties such as surface topography, roughness, chemistry, and surface energy, wettability, and Ti oxides or Ti nitride layers thickness. The concentrated solar power was used successfully to nitride Ti Grade 2 and powder metallurgical Ti prepared from hydrogenated dehydrogenated Ti powder. The nitriding experiments were performed under nitrogen atmosphere at different temperatures and time in SF40 (40kW horizontal solar furnace) at PSA, Spain. Concentrated solar energy has been shown to be an economical alternative to conventional gas nitriding techniques in electric furnaces, CVD, PVD, plasma nitriding, or laser treatments. It has been observed that the solar process represents a significant reduction of the heating time to several minutes (up to 5 minutes at temperature range 500-1000 °C), a clean and non-polluting high-temperature process. The formation of continuous and homogeneous surface layers of TiN, Ti2N and their mixture according to the nitriding temperature was investigated using X-ray diffraction and electron microscopy. Laser surface treatment is of great significance in modifying surface morphology and surface and near-surface region microstructures. Effects of lase treatment parameters on machined surface morphology, surface roughness and chemistry are analyzed in this study and discussed from the point of view of application in dental implantology. The current advances of our research group in application of laser-treated powder metallurgy prepared Ti-based materials are analyzed and discussed.

The diffusion behavior and surface properties of catalytic nitriding with LaFeO3 film prepared by the sol-gel method

In the present work, LaFeO3 film prepared by the sol-gel method was applied to realize the catalytic plasma nitriding for 38CrMoAl steel. The plasma nitriding treatments were conducted at 520 °C for 4, 8 and 12 h. The plasma nitriding without LaFeO3 film was set as a normal group. The microstructure, phase structure, mechanical and tribological properties of the plasma nitrided layers with and without the LaFeO3 film were investigated in comparison. The LaFeO3 was proved to be effective for accelerating plasma nitriding because it suppresses the formation of the compound phase and layer. Moreover, the LaFeO3 has a positive effect on the surface mechanical and tribological properties. Interestingly, the effect mechanism was varied during the nitriding process, which was discussed based on the experimental results.

Effect of high-speed steel surface nitriding treatment on adhesion and wear resistance properties of nitrogen-doped diamond-like carbon coatings

Based on the principle of hollow cathode, diamond-like carbon (DLC) coatings were deposited on high-speed steel by plasma enhanced chemical vapor deposition (PECVD). The mechanism of the experimental parameters on the adhesion and wear behavior of the multilayer coatings, prepared by plasma nitriding substrate and DLC N-doping, were systematically investigated via Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), micro-Vickers tester, friction and wear tester analysis. It was found that the deposition speed and structure of DLC coatings can be efficiently improved by different contents of N doping. With the increase of nitrogen content, the content of sp3 bond in DLC coating first increased to 60.82 % and then decreased to 58.73 %. Meanwhile, the friction coefficient of DLC coating first decreased and then increased. Combined with plasma nitriding treatment for substrate, the wear resistance of DLC coating was effectively improved by optimizing the hardness gradient between the coating and the substrate. Under the same friction conditions, the wear rate was reduced by about 50 %, while the adhesion of DLC coating was improved from HF4 to HF1 in comparison with non-nitriding and non-N-doping DLC coatings. It was revealed by the mechanistic-based model that the resistance by nitriding layers played a more important role than an increase in coatings thickness due to the reasonable hardness gradient in resisting deformation. Based on the N-doped DLC + DLC structure, the surface hardness of the coating gradually increased to 1970.9 HV. The hard outer layer provided sufficient load-carrying capacity and wear resistance during the friction process, thus decreasing the generation of wear debris and the depletion of coating.

Technological Processes for Increasing the Cavitation Erosion Resistance of Nimonic 80A Superalloys.

Nickel-based superalloys are frequently used to manufacture the components that operate under cavitation erosion conditions, such as aircraft gas turbine construction, nuclear power systems, steam turbine power plants, and chemical and petrochemical industries. Their poor performance in terms of cavitation erosion leads to a significant reduction in service life. This paper compares four technological treatment methods to improve cavitation erosion resistance. The cavitation erosion experiments were carried out on a vibrating device with piezoceramic crystals in accordance with the prescriptions of the ASTM G32-2016 standard. The maximum depth of surface damage, the erosion rate, and the morphologies of the eroded surfaces during the cavitation erosion tests were characterized. The results indicate that the thermochemical plasma nitriding treatment can reduce mass losses and the erosion rate. The cavitation erosion resistance of the nitrided samples is approximately 2 times higher than that of the remelted TIG surfaces, approximately 2.4 times higher than that of the artificially aged hardened substrate, and 10.6 times higher than that of the solution heat-treated substrate. The improvement in cavitation erosion resistance for Nimonic 80A superalloy is attributed to the finishing of the surface microstructure, graining, and the presence of residual compressive stresses, factors that prevent crack initiation and propagation, thus blocking material removal during cavitation stresses.

To determine the effect of plasma nitriding treatment 56 on screw loosening and surface topography of different 78 implant-abutment screw systems with and without thermocycling: An in vitro study.

The aim of this study was to evaluate and compare the effect of plasma nitride-treated abutment screws of two different implant systems on screw loosening and surface topography with and without thermocycling. This was an in-vitro experimental study. Fifty-two abutment screws (Group A: 26 Genesis and Group B: 26 Bredent) underwent plasma nitride treatment and were subdivided into two groups, one without thermocycling and one with thermocycling. Dynamic load was applied and detorque values were evaluated for determining the screw loosening using "independent t-test" with the help of IBM SPSS Statistics 20 and scanning electron microscopy was done to check for surface topography. Inter- and intragroup comparisons were done using independent t-test (SPSS: Statistical Package for the Social Sciences software version 20). Plasma nitriding treatment genesis implant system abutment screw showed more screw loosening (P < 0.05) and surface roughness as compared to bredent with and without thermocycling. From the present study, it was shown that plasma nitride-treated abutment screws decreased the occurrence of screw loosening favoring the bredent implant-abutment system more than the genesis implant-abutment system.

Study of Surface Modification of Niobium Caused by Nitriding and Cathodic Cage Deposition

In this work, plasma nitriding (PN) and cathode cage plasma deposition (CCPN) treatments were carried out with temperatures of 400 and 450 °C to evaluate the modifications caused on the surface of pure niobium samples. XRD, SEM, Vickers microhardness, and sphere-disk analyses were used to characterize the coatings’ composition, morphology, hardness, and wear resistance. The results showed that the treated samples increased hardness and wear resistance, with the sample submitted to CCPN at 450 °C presenting the best tribological behavior.

Investigation on the machinability of nitriding mold steel by applying in-situ laser assisted diamond cutting

Mold steel is a typical material in precision molding for the massive production of optical lenses. It has the outstanding mechanical properties and superior corrosion resistance. However, it is a huge challenge for ultra-precision diamond cutting mold steel due to the active chemical affinity between the diamond tool and steel, which causes the deteriorated surface integrity and catastrophic tool wear. In this research, we adopted a novel hybrid machining technology, which is in-situ laser assisted diamond cutting (In-situ LADC), for ultra-precision machining nitriding mold steel. Pulsed plasma nitriding treatment provides a dense nitrided compounds layer in workpiece surface to suppress the chemical reaction between the iron atom of steel and carbon atom of diamond. Furthermore, the surface nitriding layer is softened by the laser radiating to improve the machinability of workpiece. Experimental results showed that the laser thermal effect obviously decreased the hardness and elastic modulus of nitrided layer, which enhanced the material removing in ductile mode. Compared with the ordinary cutting (OC), the machined surface roughness Ra is decreased from 29 nm to 12 nm. The maximum profile error PV is also decreased from 161 nm to 64 nm. The mechanism of tool wear was changed from the rapidly abrasive wear to mildly adhesive wear, which significantly increased working life by 29 %.

Influence of plasma nitriding treatment on the micro-scale abrasive wear behavior of AISI 4140 steel

• Nitriding treatment leads to a reduction in the volume of wear and the specific wear coefficient. • Nano nitrides phases formed on the surface of the material. • Microstructural parameters and the number of phases influence the micro-abrasive wear behavior. • The hard layer of nitrides increased the AISI 4140 steel hardness more than 2.5 twice. Plasma nitriding was performed on AISI 4140 steel for various times. Untreated and plasma nitrided AISI 4140 steel were microstructurally, mechanically and tribologically characterized. The nitrided compound layer, consisting of ε-Fe 2-3 N and λ-Fe 4 N phases, was approximately of 5.0 μm thick. Microhardness of treated steel for 3 h was significantly higher than that of the untreated. The ball cratering test revealed that abrasivity of the treated samples decreased with the nitriding time due to an increasing in micro-strain values, quantify of nitrided phases, and the formation of nanocrystalline size of nitrides.

Fatigue crack growth rate of AISI 4140 low alloy steel treated via shot peening and plasma nitriding

In this study, the effects of conventional shot peening (CSP), severe shot peening (SSP), and plasma nitriding (PN) on the fatigue crack growth (FCGR) of AISI 4140 low alloy steel were investigated. FCGR tests were performed on axial fatigue equipment, associated with slow-motion camera and COD gauge. As a result of the experiments, an improvement of 8% in CSP, 15% in SSP, and 5,5% in the PN operations were observed on the number of cycles of all specimens at 30 mm crack length. Particularly for SSP treatments, hardness, compressive stresses, and the creation of nano-crystallization on the surface provide the most effective improvement in FCGR behavior. Additionally, for PN, formation of nitrogen diffusion and effective hardness improvement showed positive results in FCGR behavior. CSP and SSP (particularly SSP) behaved dominant on the improvement of FCGR performance compared to PN treatment. The formation of two-phase brittle structural white layer on the surface prevented the effective FCGR improvement.

Improvement on pitting wear resistance of gears by controlled forging and plasma nitriding

In the present investigation, the use of a bainitic steel for forged gears applications and the suitability of different plasma nitriding treatments is discussed. The gears were forged, machined, ground, polished, and nitrided at 500 °C with three sets of N2–H2 gas mixtures, containing 5, 24, and 76 vol.% N2, to develop a nitrided case of approximately 300 μm depth. Gears were characterized before and after the nitriding concerning the phase composition, microstructure, microhardness, fracture toughness, and residual stresses states. Pitting wear tests were performed on a standard Forschungsstelle für Zahnräder und Getriebebau (FZG) test rig. The nitrided gears with 24 and 76 vol.% N2 formed a biphasic compound layer of ε-Fe2-3(C)N and γ′-Fe4N. As the volume fraction of nitrogen in the gas mixture was decreased, the detected content of γ′-Fe4N in the compound layer increased, but a monophasic compound layer was only reached with 5 vol.% N2. The nitrogen rich gas composition increased the surface hardness and decreased the fracture toughness of the compound layer, as they have more ε-Fe2-3(C)N. The diffusion zone of the different nitrided surfaces showed residual compressive stresses. The best performance was obtained in the nitrided gears with 24 vol.% N2, due to the better combination between the surface hardness, fracture toughness, residual stresses, and compound layer thickness. The nitrided gears with 24 vol.% N2 have ten times improvement over the non-nitrided gears, while the nitrided gears with 5 and 76 vol.% N2 have an improvement of three point seven and five point four times.

Fatigue properties of plasma nitriding for dental implant application

Statement of problemFatigue failure of implant components is a common clinical problem. Plasma nitriding, an in situ surface-strengthening method, may improve fatigue properties of dental implants. PurposeThe purpose of this in vitro study was to evaluate the effect of plasma nitriding on the fatigue behavior of implant systems. Material and methodsThe preload and friction coefficient of plasma nitrided abutment screws, as well as settlement of the implant-abutment interface, were measured. Then, the reverse torque values and pullout force were evaluated after cyclic loading. Finally, the fatigue properties of the implant system were investigated with static fracture and dynamic fatigue life tests, and the morphology of the fracture on the surface of the implant system was observed. ResultsThe plasma nitriding treatment reduced the friction coefficient; increased the preload, settlement value, reverse torque values, pullout force, and static fracture load; and prolonged fatigue life. Furthermore, abutment screws with plasma nitriding treatment showed a different fatigue fracture mode. ConclusionsPlasma nitriding improved mechanical performance and may be a suitable way to optimize the fatigue behavior of dental implants.

Physical and Mechanical Characterization Study of Thin Nitriding Layers Produced by Plasma on Low Alloy Steel

The present study has been conducted in order to obtain iron nitrides layer on AISI4140 steel by using plasma nitriding treatment. As one of several parameters of this process, the nitrogen rate ranging from 10 to 70% with a step of 20% was chosen. The structure, the morphology, the thickness and the hardness of iron nitrides layer were investigated. As a result, the improvement of surface hardness of nitrided steel was identified related with the increase of compound layer thickness due to the increase of activation rate. The steel substrate treated at high activation rate presents hardness 3 times higher than that of untreated steel.

Effect of plasma nitriding on tribological properties of nickel‑boron-nanodiamond electroless coatings

This study is an effort to investigate the synergic effect of nano-diamond (ND) addition and plasma nitriding (PN) treatment on tribological and structural properties of nickel‑boron (NiB) coatings. NiB/ND nanocomposites containing different amounts of NDs (0.0, 0.1, 0.5, and 1.0 g/L) were produced in an electroless bath. Then, plasma nitriding was conducted on the samples for 1 h at 400 °C in an N2-H2 environment. To study phase analysis and examine the surface morphology of the samples, X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were utilized. The wear behavior and friction were determined under the normal load of 10 N using the pin-on-disk method. The surface roughness, microstructure, and microhardness were also assessed. The results showed that, as the ND concentration increased, the amorphous structure of as-plated (AP) Ni-B transformed to a semi-crystalline one. Moreover, the amorphous structure of the as-deposited NiB/ND coatings changed to a crystalline one after plasma nitriding, which resulted in a higher hardness value. NiB/0.5ND coating showed the highest hardness value (1523 HV0.1) and the highest wear resistance (0.8×10−10 Kg/N.m). The smoothest wear trace with no visible cracks is related to the worn surface of PN NiB/0.5ND sample, suggesting that the NiB/ND nanocomposite can be a promising candidate for surface engineering processes.

Effect of electric potentials on high‐temperature plasma nitriding of 2Cr13 stainless steel with active screen assisted

AbstractThe influence of electric potentials on the characteristics of modified layers with plasma nitriding of 2Cr13 stainless steel at a high temperature was investigated. Three active screens were placed on the cathodic plate. Three groups of 2Cr13 stainless steel samples were set with cathodic, anodic, and floating potentials. Samples were nitrided at 500 °C for 5 h in an ammonia atmosphere. The treated samples were analyzed using x‐ray diffraction, scanning electron microscopy with energy dispersive x‐ray spectroscopy, surface roughness tester, and atomic force microscopy. It is proved that nitriding treatments can be suitably carried out at three electric potentials, but the corresponding modified layers take on different microstructure, morphology, and hardness behaviors. It found that the three nitrided samples are mainly composed of the ϵ−Fe2‐3N and γ’−Fe4N phases. The order of thicknesses of the nitrided layers is: floating &lt; anodic &lt; cathodic potential. The results also demonstrated that electric potentials play essential roles in the corrosion resistance and tribological properties in plasma nitriding treatment. Because there is no visible precipitation of chromium nitride in the modified layer, the corrosion resistance of the floating nitrided sample is better than that of the other two samples.