Glow Discharge Plasma Nitriding Research Articles

Tribo-Mechanical Behavior of Films and Modified Layers Produced by Cathodic Cage and Glow Discharge Plasma Nitriding Techniques

Two surface modification techniques, the glow discharge plasma nitriding (GDPN) and the cathodic cage plasma nitriding (CCPN), were compared regarding the mechanical and tribological behavior of layers produced on AISI 316 stainless-steel surfaces. The analyses were carried out at the micro/nanoscale using nanoindentation and nanoscratch tests. The nitriding temperature (°C) and time (h) parameters were 350/6, 400/6, and 450/6. Morphology, structure, and microstructure were evaluated by X-ray diffraction, scanning electron and optical interferometry microscopies, and energy-dispersive X-ray spectroscopy. GDPN results in stratified modified surfaces, solidly integrated with the substrate, with a temperature-dependent composition comprising nitrides (γ’-Fe4N, ε-Fe2+xN, CrN) and N-solid solution (γN phase). The latter prevails for the low treatment temperatures. Hardness increases from ~2.5 GPa (bare surface) to ~15.5 GPa (450 °C). The scratch resistance of the GDPN-modified surfaces presents a strong correlation with the layer composition and thickness, with the result that the 400 °C condition exhibits the highest standards against microwear. In contrast, CCPN results in well-defined dual-layers for any of the temperatures. A top 0.3–0.8 µm-thick nitride film (most ε-phase), brittle and easily removable under scratch with loads as low as 63 mN, covers a γN-rich case with hardness of 10 GPa. The thickness of the underneath CCPN layer produced at 450 °C is similar to that from GDPN at 400 °C (3 µm); on the other hand, the average roughness is much lower, comparable to the reference surface (Ra ~10 nm), while the layer formation involves no chromium depletion. Moreover, edge effects are absent across the entire sample´s surface. In conclusion, among the studied conditions, the GDPN 400 °C disclosed the best tribo-mechanical performance, whereas CCPN resulted in superior surface finishing for application purposes.

Characterization and Tribological Performance of Titanium Nitrides in Situ Grown on Ti6Al4V Alloy by Glow Discharge Plasma Nitriding

Characterization and Tribological Performance of Titanium Nitrides in Situ Grown on Ti6Al4V Alloy by Glow Discharge Plasma Nitriding

Structural, mechanical, and tribological properties of GLC film on a nitrided layer prepared in a glow-discharge plasma nitriding system

The structural, mechanical, and tribological properties of GLC film on a nitrided layer prepared in a glow-discharge plasma nitriding system were investigated. The gas composition (the ratio of C3H8 to H2) affects the thickness, microstructure, and surface roughness of the GLC film. The sp2 bond of the GLC film prepared in a glow-discharge plasma nitriding system is adjustable within the range of 71.36%–74.28%, which leads to an acceptable hardness (c. 10 GPa). The GLC film on the nitrided layer with gradient hardness contributes to a low coefficient of friction (0.12), and improved wear resistance. The GLC films prepared in 10 sccm C3H8 and 15 sccm H2 on the nitrided layer shows the best tribological performance due to the highest plastic index parameter (H/E) value of the duplex layers. The tribological behaviour of the duplex layer was assessed. This will guide the one-step preparation of GLC film and nitrided layer in an industrial plasma nitriding system in future work.

Corrosion Behavior Evaluation in Simulated Body Fluid of a Modified Ti–6Al–4V Alloy by DC Glow Plasma Nitriding

DC glow discharge plasma nitriding is the process of surface hardening through the spread of nitrogen atoms to the metal surface under special conditions of the plasma nitriding. Titanium and titanium alloys are the most common alloys used in medical applications. Titanium and its alloys are lightweight, corrosion resistant, and have good fatigue properties but lack wear resistance under aggressive environments. The plasma nitriding process was used for a titanium alloy (Ti–6Al–4V) rod with different parameters at a vacuum chamber of air (2 mbar), 680 volts and 30 mA. The plasma nitriding process was performed at different nitriding times (5, 10, and 15 h), and the effect of plasma nitriding was examined on the chemical compassion of Ti–6Al–4V alloy and the appearance of phases was studied by optical microscopy (OM), scanning electron microscopy and field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Tafel potential polarization, and cyclic polarization. The results indicate that the formation of layers and phases Ti2N and Ti2N3−x on a surface of the alloy were achieved, which would improve the surface characteristics of chemical corrosion in simulated body fluid.

Microstructure and tribological performance of a dimpled gradient nanoscale TiN layer

The dimpled gradient nanoscale TiN (nano-TiN) layer was prepared on the pure Ti surface by the combined process of supersonic fine particles bombarding (SFPB) and glow-discharge plasma nitriding. A large numbers of dimples (30–40µm in diameter) homogenously distribute on the prepared nano-TiN layer surface and are beneficial to the reservation of oil and wear debris during friction process. The nano-TiN layer is about 25µm in thickness with a three-layered nanoscale structure and the grain size decreases sequentially from the outer layer to the inner one. The nano-TiN layer with higher mechanical properties displays enhanced friction and wear reducing effects compared to the SFPB-dimpled Ti surface.

Effect of honing gear hardness on microgeometry and surface quality improvement of straight bevel gears in PECH process

The present research is directed to investigate pulsed electrochemical honing (PECH) of bevel gears. Honing gears made of 20MnCr5 alloy steel were case hardened (found to have Vicker’s hardness value as 900 HV) using glow discharge plasma nitriding process. The hardened honing gear was used to finish workpiece gear made of same material. Unhardened honing gear having Vicker’s hardness value as 630 HV was also used to finish workpiece gears for comparison. The microgeometry of the workpiece bevel gear was evaluated using deviations in pitch, run-out and topology, while surface quality was evaluated in terms of surface finish, microstructure and microhardness. This research proves that the honing gear hardness is an important aspect for improving the surface quality and microgeometry of the gears. These improvements will enhance service life and operating performance of the PECH-finished gears and will reduce their noise level and chances of their premature failures.

Relación entre las propiedades mecánicas y tribológicas de Ti6AL4V ELI nitrurado mediante descarga intensa de plasma

En este trabajo se estudió el comportamiento tribológico, la rigidez y dureza, de la superficie de la aleación Ti6Al4V ELI después de llevar a cabo un tratamiento de nitruración por descarga intensa de plasma a temperaturas de 450, 480 y 520 °C. El par tribológico empleado fue metal-metal (pin de Ti6Al4V ELI - disco de Ti6Al4V ELI con tratamiento) para el respectivo cálculo del coeficiente de fricción. Los ensayos de nanoindentación se realizaron con una punta de ultra alta dureza de módulo de rigidez conocido, que permitió obtener la dureza promedio y el módulo de Young en GPa, de acuerdo con las normas ISO 14577 y ASTM G99-95 respectivamente. Para la caracterización del sustrato, se empleó microscopia electrónica de barrido, microscopia de fuerza atómica y difracción de rayos X, obteniendo así características importantes del comportamiento elástico-plástico, antes y después de aplicarse la nitruración a la aleación por descarga intensa de plasma

Optimization Study of Pulsed DC Nitrogen-Hydrogen Plasma in the Presence of an Active Screen Cage

A glow discharge plasma nitriding reactor in the presence of an active screen cage is optimized in terms of current density, filling pressure and hydrogen concentrations using optical emission spectroscopy (OES). The samples of AISI 304 are nitrided for different treatment times under optimum conditions. The treated samples were analyzed by X-ray diffraction (XRD) to explore the changes induced in the crystallographic structure. The XRD pattern confirmed the formation of iron and chromium nitrides arising from incorporation of nitrogen as an interstitial solid solution in the iron lattice. A Vickers microhardness tester was used to evaluate the surface hardness as a function of treatment time (h). The results showed clear evidence of improved surface hardness and a substantial amount of decrease in the treatment time compared with the previous work.

An exact calculation of the N2+ and H2+ influx at cathode surface in N2–H2 discharges

An exact calculation of N2+ and H2+ influx, at cathode surface in N2–H2 discharge, has been derived using electron impact ionization cross-section at plasma sheath boundary. The analytical formula is very convenient in practical applications. Through the analysis of experimental parameters for glow discharge plasma nitriding, the formula explains, why treatment in an N2–H2 mixture with H2 percentage ∼70% gives most enhanced result.

Nanomechanical properties of duplex treated 42CrMo4 steel

Active screen plasma nitriding (ASPN) has attracted interest from researchers and industries as it can overcome several intrinsic problems in direct current glow discharge plasma nitriding such as arcing, hollow cathode, edge effects and the strong temperature dependence on the shape of the samples. In this study, an advanced duplex system based on ASPN and chromium nitride coating was synthesised on 42CrMo4 steels. The effects of ASPN on the mechanical properties, nanoimpact resistance and scratch resistance at different load ranges were investigated. The results show that the surface hardness H, reduced elastic modulus Er and the ratios of H/Er and H3/E2r can significantly be improved at the testing load range from 5 to 100 mN. The enhanced nanoimpact and scratch resistance can be well correlated to the improved H/Er and H3/E2r.

Effect of Plasma Nitriding Parameters on the Wear Behaviour of AISI D6 Tool Steel

Abstract In the present investigation, the effects of plasma nitriding pressure and time on the structural and tribological characterization of AISI D6 grade cold work tool steel were studied. DC glow discharge plasma nitriding process under NH3 gas was performed at temperatures of 500 °C and at pressures of 150 Pa, 450 Pa and 800 Pa for durations of 2 h, 7 h and 10 h. The mass loss and the coefficient of friction were measured using a ball-on-disc wear test with 1.668 N, 4.143 N, and 9.113 N test loads. Cross-section and surface characterizations were evaluated using optical microscopy, SEM, and microhardness test techniques. The surface microhardness was found to increase with the nitriding time and the pressure. The wear resistance of the specimen strongly depends on the nitriding parameters and the applied test load in determining whether a plastic deformation of the surface layer has occurred or not.

Phase formation in selected surface-roughened plasma-nitrided 304 austenite stainless steel

Direct current (DC) glow discharge plasma nitriding was carried out on three selected surface-roughened AISI 304 stainless steel samples at 833 K under 4 mbar pressures for 24 h in the presence of N2:H2 gas mixtures of 50 : 50 ratios. After plasma nitriding, the phase formation, case depth, surface roughness, and microhardness of a plasma-nitrided layer were evaluated by glancing angle x-ray diffractogram, optical microscope, stylus profilometer, and Vickers microhardness tester techniques. The case depth, surface hardness, and phase formation variations were observed with a variation in initial surface roughness. The diffraction patterns of the plasma-nitrided samples showed the modified intensities of the α and γ phases along with those of the CrN, Fe4N, and Fe3N phases. Hardness and case depth variations were observed with a variation in surface roughness. A maximum hardness of 1058 Hv and a case depth of 95 μm were achieved in least surface-roughened samples.

Glow Discharge Plasma Nitriding of AISI 304 Stainless Steel

Glow discharge plasma nitriding of AISI 304 austenitic stainlesssteel has been carried out for different processing time underoptimum discharge conditions established by spectroscopic analysis.The treated samples were analysed by X-ray diffraction (XRD) toexplore the changes induced in the crystallographic structure. TheXRD pattern confirmed the formation of an expanded austenite phase(γN) owing to incorporation of nitrogen as aninterstitial solid solution in the iron lattice. A Vickersmicrohardness tester was used to evaluate the surface hardness as afunction of indentation depth (μm). The results showed clearevidence of surface changes with substantial increase in surfacehardness.

Effect of cathodic hydrogenation on the mechanical properties of AISI 304 stainless steel nitrided by ion implantation, glow discharge and plasma immersion ion implantation

Hydrogen embrittlement in austenitic stainless steels is restricted to the surface due to the low hydrogen diffusion in austenitic structures. The effect of three different nitriding processes: ion implantation (II), plasma immersion ion implantation (PI3) and glow discharge (GD), on the mechanical and structural properties of cathodically hydrogenated AISI 304 stainless steel were studied in the present work. Cathodic hydrogenation was made on untreated and nitrided samples. Surface microstructure after nitriding and hydrogenation was investigated by X-ray diffraction. Mechanical properties were measured by instrumented indentation. Surface crack formation and hardness decrease was observed in non-nitrided samples after cathodic hydrogenation. Hardness of nitrided samples decreases after hydrogen degassing but still has values higher than untreated samples. Comparative analysis of nitriding processes and working conditions indicated that glow discharge plasma nitriding process at 400°C or 450°C is the most adequate to avoid crack formation in steel surface after cathodic hydrogenation.

Low- and high-energy plasma immersion ion implantation for modification of material surfaces

Low- and high-energy plasma immersion ion implantation (PIII) of nitrogen has been performed on austenitic stainless steel and high-carbon low-alloy steel to modify their surface properties. In the case of austenitic stainless steel, an expanded austenite layer with surface microhardness of 650 HV was formed with a thickness of 7–8 μm for an elevated treatment temperature of 400 °C, irrespective of the treatment energy. X-Ray photoelectron spectroscopy (XPS) investigations revealed that, at high energy, nitrogen is in a bound state and chromium nitride is formed in the subsurface region, followed by expanded austenite. In the case of high-carbon low alloy steel, the diffusion coefficient of nitrogen obtained by PIII is higher than that obtained by glow-discharge plasma nitriding. The results indicate that if implantation is followed by diffusion, low-energy PIII gives similar or better results than high-energy PIII as far as the treated layer thickness, phase formation and microhardness are considered. Low-energy PIII has a lower hardware cost and reduced sheath dimensions, and thus uniformity in surface modification is achieved.

A study of martensitic stainless steel AISI 420 modified using plasma nitriding

We studied martensitic stainless steel AISI 420, modified using glow discharge plasma nitriding. Microhardness measurements, X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to investigate the surface microhardness, crystal structure, microstructure and chemical bonding in the modified surfaces. High surface microhardness (∼1300 HV) over a case depth of about 60 microns is obtained. Glancing incidence X-ray diffraction (GIXRD) indicates the presence of a predominantly Fe 3N phase with dispersed CrN within 2–5 microns on the surface. In addition, using Bragg–Brentano geometry, we measured the presence of a minor phase of Fe 4N in the case depth. SEM confirms that the microstructure within 2–5 microns of the surface is different from that of the bulk. XPS shows nitride phase formation on the surface. AES measured over the cross-section of the case depth shows a direct relation of the increased surface microhardness to the high nitrogen content.

Low pressure plasma arc source ion nitriding compared with glow-discharge plasma nitriding of stainless steel

The nitrided layers produced by low temperature conventional d.c. glow discharge plasma nitriding and low pressure plasma arc source ion nitriding on AISI 304 austenitic stainless steel were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM) and microhardness testing. The surface nitrogen content was determined by electron probe microanalysis (EPMA) and energy dispersive X-ray analysis (EDX). The nitrogen content in the nitrided layer obtained using a low pressure plasma arc source is higher than that in the nitrided layer obtained by d.c. glow discharge plasma nitriding at 420°C. Microstructural analyses by XRD show that both treatments at the same temperature of ∼400°C lead to predominant formation of the f.c.c. nitrogen [N] solid solution phase γ N. However, the concentrations of N and the layer thickness of this phase are clearly different for the various treatments. There are substantial differences in microstructures and phases detected by TEM, which showed that the pure expanded austenite phase with a f.c.c. structure was formed in the nitrided layer for the low pressure plasma arc source, but for glow discharge plasma nitriding, the CrN+γ mixture was present in the nitrided layer even when nitriding at temperatures below 450°C. The reason for this is not clear. When the temperature was increased to 480–500°C, there was no evident difference in the microstructures and phases in nitrided layers obtained by both treatments. The nitrided layers all consisted of CrN+α-Fe phases. Both nitriding methods are able to harden the surface of austenitic stainless steel by nitrogen diffusion forming nitrided layers.

Plasma-source ion implantation compared with glow-discharge plasma nitriding of stainless steel

Abstract Plasma-source ion implantation (PSII) is a promising technology to overcome the line-of-sight limitations of beam-line ion implantation. Among the possible fields of commercial use, nitriding of stainless steels by plasma-source ion implantation seems to be one of the favourites. However, the technology of glow-discharge plasma nitriding (GDPN) is already being used commercially. Therefore, it remains to be determined whether PSII is more suitable to the demands of an industrial technology than GDPN. In particular, the incorporation rate of nitrogen during treatment has to be investigated, as the incorporation rate of nitrogen determines the depth of the nitrided layer for a given treatment time. For nitriding of stainless steel, PSII and GDPN were performed for the same treatment time of 2 h, using the same treatment voltage (700 V) and duty ratio (50%) during the nitriding process. The temperature during treatment was fixed at 380 °C and controlled by an isolated thermocouple. The only difference in the experimental conditions was the pressure, during treatment, of 0.1 Pa in the case of PSII and 500 Pa in the case of GDPN. Pure nitrogen as well as a nitrogen–hydrogen mixture was used as the feed gas. The resulting concentration profiles were determined by glow-discharge optical spectroscopy depth profiling to determine the nitrogen incorporation rate of both nitriding techniques. The surface properties were investigated by wear and hardness measurements. Both technologies yield the formation of a hard nitrided layer with an increased hardness. The highest nitrogen concentration and widest hardened layer was found in the case of PSII, using a nitrogen–hydrogen plasma.

High Resolution Electron Microscopy Characterization of Nitrides of Iron and Iron Alloys

A study of nitride-phase formation in alloys nitrided by glow discharge plasma nitriding was performed by high-resolution electron microscopy. The iron and steel samples were nitrided above and below the eutectoid transformation point (590 ‡C). After nitriding, the samples were annealed for several treatment times at 400 ‡C. The microstructure and identification of the iron nitrided phases formed by nitriding and annealing were investigated by x-ray diffraction (XRD), optical microscopy (OM) and mainly high resolution electron microscopy (HREM) in a JEOL-4000EX high resolution microscope at 400 kV. The results of the characterization show a surface e compact nitride layer, which is transformed into e + γ during cooling. The tempering process affects the surface hardness of the samples. After an initial increase relative to the untreated sample, the microhardness diminishes after long treatment times. This behavior is correlated with the αt’’ phase appearance, growth, and transformation.

Fatigue improvements of glow-discharge-plasma-nitrided steel rotary specimens

Wohler rotating—bending fatigue testing has been used to study the fatigue behaviour of plasma-nitrided steel for crankshafts with an elemental composition of 4.0% Ni, 2.0% Cr, 1.0% Mo and 0.18% C. The fatigue rotary specimens were machined from bars 12 mm in diameter of a steel for crankshafts. The test pieces were subsequently hardened and tempered to produce a core Vickers hardness of 275 HV. Then rotary specimens were glow-discharge-plasma-nitrided at a temperature of 480°C for a nitriding time of 25 h in two different mixtures of N 2 and H 2 at a pressure of 2.6 mbar, one group of specimens in a mixture with a dominant content of hydrogen (25%N 2–75%H 2), the other group in a mixture with a dominant content of nitrogen (75%N 2–25%H 2). The third group was left unnitrided. Evaluation of the specimens was performed by optical microscopy, X-ray diffractometry and microhardness measurements. Surface hardness was 750 HV (load, 0.3 kgf). A thin compound layer of γ-Fe 4N type with a thickness of 5 μm was identified. Microhardness profiles revealed diffusion zones extending over a region of 400 μm. Surface hardness, compound layer type and thickness and nitriding depth were independent of the two gas mixture types used. Fatigue testing was conducted employing a uniform frequency using an Amsler bending fatigue machine, where the number of stress changes is equal to the number of rotations. Specimens were tested for their temporary fatigue strength and endurance limit. Weibull probability functions were calculated for each stress level and these values were plotted in a logarithmic probability distribution diagram and approximated by a straight line. Glow discharge plasma nitriding improved the fatigue bending stress limit by a factor of 1.5, the limiting value of the number of stress changes by a factor of 5, and the endurance curve exponent by a factor of 2. Specimens treated in the mixture with a dominant content of H 2 had better properties than those treated in the mixture with a dominant content of N 2.