Plasma Nitriding Conditions Research Articles

Machine learning-based model for fatigue behavior analysis of plasma nitrided AISI 304 steel

Surface treatments play critical role in fatigue behavior improvement of metals. In this study, a machine learning-based model was employed to analyze the effects of plasma nitriding as a thermal surface treatment on improving the fatigue behavior of AISI 304 steel. Experimental data, encompassing various plasma nitriding and fatigue loading conditions, were utilized to train different types of artificial neural networks including shallow neural networks and deep neural networks. The inputs to the model were the process parameters of plasma nitriding, including time and temperature, along with the stress amplitude in the fatigue test. The output parameter was the fatigue life. The findings demonstrated that employing deep neural networks led to higher accuracy in the predictions. Furthermore, the obtained results of conducted parametric analyses indicated that the optimal temperature range for achieving the highest fatigue performance lies between approximately 450-550 °C for more than 4 h.

Nitrogen Supersaturation into AISI420 Mold for Precise Machining

The plasma nitriding conditions and processing parameters were controlled to attain the high-density nitrogen ion and NH-radical populations and to form the nitrogen supersaturated layer into AISI420 type martensitic stainless steel mold substrate at 673 K for 14.4 ks and 28.8 ks. Thicker nitrided layer than 80 mm was attained for fine machining of the optical diffraction elements onto this nitrided AISI420 mold surface. The average hardness in this nitrogen supersaturated layer reached 1400 HV. After this hardness testing and microstructure analysis, the machinability test was performed to describe the ductile mode cutting behavior of nitrogen-supersaturated work by using the PCD (Poly-Crystalline Diamond)-chip tool. Higher average nitrogen solute content than 4 mass% was responsible for fine turning by PCD-chip and CVD (Chemical Vapor Deposition)-diamond coated cutting tools without any damages and for precisely finishing the mold surface with the lower maximum surface roughness than 10 nm on the machined mold surface. The low roughness and homogeneous machined surface profile proved that the nitrogen supersaturated AISI420 series stainless steel was adaptive as a stamping mold of chalcogenide glasses with high dimensional accuracy and demolding capacity.

Improvement Corrosion Behaviour of Lean Duplex Stainless Steel 2101 alloy in Ringer solution by Plasma Nitriding for Biomedical applications

“Plasma nitriding” is a surface hardening process that involves diffusion of the atoms of nitrogen onto the surface of metal under different plasma nitriding conditions. The new alloys used in the field of Biomedical applications are Lean Duplex Stainless Steel. The alloys of Lean DSS are corrosion resistant, lightweight, and have good mechanical properties such as fatigue strength, but in aggressive environments, they lack “wear resistance”. In a vacuum chamber of air (3 mbar), 400 V, and 30 mA, a lean duplex stainless steel (2101) alloy rod was plasma nitrided. The procedure of plasma nitriding was carried out at various times. The effect of plasma nitriding at different times (5, 10, 15, 20, 25) hrs on the chemical structure of LDX 2101 DSS alloy and the form of phases was investigated using OM, FESEM with EDS, XRD, and antibacterial test, tafel potential polarizaton and cyclic polarization for Orthopedic application. The results show that layers and phases S, Fe3N, and Fe2-3N were formed on the alloy’s surface, which would improve mechanical properties and corrosion resistance in Ringer solution at 37 °C.

Comprehensive analysis of pulsed plasma nitriding preconditions on the fatigue behavior of AISI 304 austenitic stainless steel

This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions. The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and durations. Results reveal that nitriding depth increased as process temperature and duration increase. The nitriding depth remarkably increased at 475°C for 8 h and at 550°C for 4 h. An austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite (S-phase) during low-temperature plasma nitriding. The S-phase was converted to CrN precipitation at 475°C for 8 h and at 550°C for 4 h. Surface hardness and fatigue limit increased through plasma nitriding regardless of process conditions. The best surface hardness and fatigue limit were obtained at 550°C for 4 h because of the occurrence of CrN precipitation.

Tribological behavior of duplex-coating on Vanadis 10 cold work tool steel

Powder metallurgy Vanadis 10 has an extensive range of applications as dies for extrusion and cold drawing. The tool surface is exposed to different requests (mechanical, chemical and tribological) and demands surface treatments to prolong its life. Few studies investigate the surface modification to optimize the tribological behavior of Vanadis 10. In this study, the combination of cryogenic treatment, two conditions of pulsed plasma nitriding and multilayer TiCN/AlTiN/CrAlTiN/CrN film deposition were evaluated. Pin-on-disc sliding tests were carried out at 0.1 m/s sliding speed, applied load of 10 N and sliding distance of 1000 m. The average hardness of all experimental conditions with multilayer film (2000 HV0.1) was approximately 2 times greater than the hardness of sub-zero treated Vanadis 10 (964 HV0.1). Plasma nitriding promoted the formation of Fe3N-ε compound layer in both experimental conditions. Cracks were observed in this layer. Duplex treatment does not guarantee satisfactory substrate-coating adhesion, because it depends on plasma nitriding conditions. Cryogenic treatment samples followed by plasma nitriding at 5% N2, 75% H2 and 20% Ar, presented higher dry sliding wear resistance in all tested conditions. This treatment is recommended for applications where Vanadis 10 requires high resistance to dry sliding wear.

LOW-TEMPERATURE NITRIDING BEHAVIOR OF COMPRESSIVE DEFORMED AISI 316Ti AUSTENITIC STAINLESS STEELS

The effects of compressive cold deformation under the quasi-static loads on the nitride formation, nitride layer growth and surface hardness properties were researched in this study. Martensite structure did not form in AISI 316Ti stainless steel as a result of quasi-static deformation. Diffusion layer did not form in all nitrided samples. Both the deformed and undeformed samples have only compound layer on the surfaces at the low-temperature nitriding conditions (400∘C, 7[Formula: see text]h). According to the X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and electron probe microanalysis (EPMA) results, S-phase and chromium nitride (CrN) were formed in the compound layers of the deformed samples. However, CrN did not form in the compound layer of the undeformed sample. The optical microscope (OM) results showed that the compressive cold deformation increased the nitrogen diffusion rate and led to thicker nitrided layer than the undeformed sample under the same plasma-nitriding conditions. All nitrided layers presented higher microhardness values ([Formula: see text][Formula: see text]HV) when compared with the untreated sample hardness. It was also verified that the deformation amount did not affect significantly the nitrided layer hardness.

Influence of the plasma nitriding conditions on the chemical and morphological characteristics of TiN coatings deposited on silicon

Titanium nitride (TiN) coatings were grown on silicon substrates by cathodic cage plasma deposition (CCPD). TiN coatings present interesting properties, such as high hardness, chemical and thermal stabilities, good thermal and electrical conductivities, and corrosion resistance, making them suitable for several technologically important applications. The influence of parameters such as plasma nitriding atmosphere, temperature, and time on the chemical and morphological characteristics of the deposited coatings was investigated by means of Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The results obtained by these characterization techniques revealed that the TiN coatings produced by CCPD presented high quality.

Corrosion Resistance of Plasma Nitrided and Nitrocarburized 42CrMo4 Steel

This article deals with comparison of corrosion resistance of 42CrMo4 steel used for breech mechanism in the armament production. Increasing of demands on materials used for armament production and in other industrial application leads to the innovation of technologies in the field of surface treatment especially wear resistance, surface hardness, running-in properties and corrosion resistance. For the evaluation of experimental NSS corrosion resistance tests samples of 42CrMo4 steel were compared with plasma nitrided and nitrocarburized one. Individual 42CrMo4 steel samples were subsequently metallographically evaluated and characterized by hardness and microhardness measuring. The results and comparison of corrosion resistance of not-surface treated steel samples with plasma nitrided and nitrocarburized showed significant differences of corrosion rate. Due to different plasma nitriding conditions, there are corrosion resistance differences evident between the plasma nitrided steel samples as well. The corrosion resistance evaluation is supplemented by the surface corrosion-free surfaces evaluation using the laser confocal microscopy.

Tribological and corrosion properties of plasma nitrided and nitrocarburized 42CrMo4 steel

This article deals with tribological and corrosion resistance comparison of plasma nitrided and nitrocarburized 42CrMo4 steel used for breech mechanism in the armament production. Increasing of materials demands (like wear resistance, surface hardness, running-in properties and corrosion resistance) used for armament production and in other industrial application leads in the field of surface treatment. Experimental steel samples were plasma nitrided under different nitriding gas ratio at 500 °C for 15h and nitrocarburized for 45 min at temperature 590°C and consequently post-oxidized for 10 min at 430°C. Individual 42CrMo4 steel samples were subsequently metallographically evaluated and characterized by hardness and microhardness measuring. The wear test “ball on disc” was realized for measuring of adhesive wear and coefficient of friction during unlubricated sliding. NSS corrosion tests were realized for corrosion resistance evaluation and expressed by corroded area and calculated corrosion rate. The corrosion resistance evaluation is by the surface corrosion-free surfaces evaluation supplemented using the laser confocal microscopy. Due to different surface treatment and plasma nitriding conditions, there are wear resistance and corrosion resistance differences evident between the plasma nitrided steel samples as well.

The Influence of Plasma Nitriding Period on Nitrided Layers Thickness

The plasma nitriding as a technology for finishing of material surface layers was carried out on selected material. The effect of plasma nitriding conditions on the thickness and hardness of nitrided layer was investigated. The influence of plasma nitriding period on the thickness of the plasma nitrided layers was comprehensively assessed on the C55 steels. Plasma nitriding was carried out on selected material at 500 °C under 280 Pa with a mixture atmosphere of H2 and N2 in the plasma nitriding equipment. The period of the plasma nitriding process was changeable from 5 to 20 hours. Measurements of the properties of nitrided layers of selected material were solved by using experimental methods in accordance with standards. The samples were characterized by GDOES spectrometry, optical microscopy, and hardness testing. The depths of the plasma nitriding layers were also detected using cross-sectional microhardness profiles. Relation between plasma nitriding period and a thickness of a nitrided layer was explained and has shown that microhardness and surface hardness of mentioned samples were significantly increased.

Corrosion Resistance of Plasma Nitrided Structural Steels

Plasma nitriding technology, based on plasma assisted nitrogen diffusion into the steel surface, mostly used for improvement of wear resistance and fatigue strength is well known. Additional benefit of plasma nitriding is heat and corrosion resistance improvement. This study is focused on evaluation of corrosion resistance of plasma nitrided structural steels under several nitriding conditions. Experiments were performed on structural steels CSN 41 2050 (C45E), CSN 41 4220 (16MnCr5) and CSN 41 5230 (DIN 1.7361). Selected structural steels were manufactured for experimental specimens (size of 80x50x4 mm), heat-treated and plasma nitrided under following conditions: T = 500 °C, process duration t = 10 and 20 h, p = 280 Pa, U = 510 V and variable gas mixture ratio of 3H2:1N2 [l/h] and 1H2:3N2 [l/h] for different compound layer phase composition. Corrosion tests were performed in the Liebisch GmbH & Co (S 400 M-TR) corrosion chamber in the mist of neutral sodium chloride dilution (NSS method), evaluated and documented in accordance to ISO 9227 standard and results compared to different plasma nitriding conditions. Under different plasma nitriding conditions were different nitride layer characteristics obtained. Nitride layers were by surface hardness (HV), metallographic testing and microhardness testing (HV0,05) classified. Using the microhardness testing were different values of microhardness and nitride layer depth detected. Metallographic testing and additional concentration profiles measuring (using GDOES method) displayed different compound layers thickness, which tends to be a significant factor to corrosion resistance of plasma nitrided structural steels.

Metallurgical response of an AISI 4140 steel to different plasma nitriding gas mixtures

Plasma nitriding is a surface modification process that uses glow discharge to diffuse nitrogen atoms into the metallic matrix of different materials. Among the many possible parameters of the process, the gas mixture composition plays an important role, as it impacts directly the formed layer's microstructure. In this work an AISI 4140 steel was plasma nitrided under five different gas compositions. The plasma nitriding samples were characterized using optical and scanning electron microscopy, microhardness test, X-ray diffraction and GDOES. The results showed that there are significant microstructural and morphological differences on the formed layers depending on the quantity of nitrogen and methane added to the plasma nitriding atmosphere. Thicknesses of 10, 5 and 2.5 µm were obtained when the nitrogen content of the gas mixtures were varied. The possibility to obtain a compound layer formed mainly by γ'-Fe4N nitrides was also shown. For all studied plasma nitriding conditions, the presence of a compound layer was recognized as being the responsible to hinder the decarburization on the steel surface. The highest value of surface hardness - 1277HV - were measured in the sample which were nitrided with 3vol.% of CH4.

Plasma Nitriding of 20CrMo Steel with Nanostructured Surface Layer

A nanostructured surface layer was produced on an 20CrMo steel plate by means of ultrasonic shot peening (USSP) treatment. Plasma nitriding of the treated and un-treated sample were investigated by using structure analysis (X-ray diffraction, optical microscopy, and transmission electron microscopy ) as well as hardness measurements. It was found that a nanostructured surface layer sample developed a compound layer twice as thick as that in a coarse-grained sample under the same plasma nitriding conditions (530 oC for 6 h). In addition, the USSP nitrided sample exhibited higher hardness and thicker hardened surface layer in comparison with coarse-grained nitrided sample.

Plasma nitriding of AISI 304 austenitic stainless steel with pre-shot peening

AISI 304 austenitic stainless steel was plasma nitrided at the temperature ranging from 410 to 520 °C with pre-shot peening. The structural phases, micro-hardness and electrochemical behavior of the nitrided layer were investigated by optical microscopy, X-ray diffraction, micro-hardness testing and anodic polarization testing. The effects of shot peening on the nitride formation, nitride layer growth and corrosion properties were discussed. The results showed that shot peening enhanced the nitrogen diffusion rate and led to a twice thicker nitrided layer than the un-shot peening samples under the same plasma nitriding conditions (410 °C, 4 h). The nitrided layer was composed of single nitrogen expanded austenite (S-phase) when nitriding below 480 °C, which had combined improvement in hardness and corrosion resistance.

Ion nitriding of a superaustenitic stainless steel: Wear and corrosion characterization

Abstract The superiority of superaustenitic stainless steel (SASS) lies in its good weldability and great resistance to stress corrosion and pitting, because of its higher chromium, molybdenum, and nitrogen contents, when compared to general stainless steels. However, some of its applications are limited by very poor wear behavior. Plasma-nitriding is a very effective treatment for producing wear resistant and hard surface layers on stainless steels without compromising the corrosion resistance. In this work, UNS S31254 SASS samples were plasma-nitrided at three different temperatures (400, 450, and 500 °C), under a pressure of 500 Pa, for 5 h, in order to verify the influence of the temperature on the morphology, wear, and corrosion behavior of the modified surface layers. The plasma-nitrided samples were analyzed by means of optical microscopy, micro-hardness, X-ray diffraction, wear, and corrosion tests. Wear tests were conducted in a fixed ball micro-wear machine and corrosion behavior was carried out in natural sea water by means of potentiodynamic polarization curves. For the sample which was plasma-nitrided at 400 °C, only the expanded austenite phase was observed, and for the treatments performed at 450 and 500 °C, chromium nitrides (CrN and Cr2N) were formed in addition to the expanded austenite. Wear volume and Knoop surface hardness increased as the plasma-nitriding temperature increased. Higher wear rates were observed at high temperatures, probably due to the increment on layer fragility. The sample modified at 400 °C exhibited the best corrosion behavior among all the plasma-nitriding conditions.

The influence of the sputtering process on the constitution of the compound layers obtained by plasma nitriding

Using a relative simple experimental method, the sputtering rate has been measured under specific plasma nitriding conditions. The influence of gas composition and total pressure on the sputtering rate has been investigated. Depending on these factors, the sputtering rate varies in the range of 0.02–0.12 μm/h. The sputtered material has been analyzed as well. The results indicated that the phase constitution of this material is similar to that of the compound layer.

Improving the mechanical properties of steels using low energy, high temperature nitrogen ion implantation

The use of nitrogen ion implantation to increase the surface hardness of structural steels is well documented. Traditionally this involves the use of high energy nitrogen ion beams (approximately 100 keV), with a relatively low beam current density because high energy beams are necessary to produce the required penetration into the material to achieve a significant depth of hardened material. Hardening needs to occur in a region whose size is comparable with the scale of the deformation associated with the tribocontact. 100 keV nitrogen ions typically penetrate into steels only about 0.1 μm and the range of possible tribological applications is thus restricted by this shallow treatment depth. In plasma nitriding processes the nitrogen ions approach the substrate with much lower energies but the ion currents are sufficiently high to cause considerable substrate heating. In this study an ion beam process has been used which more closely approximates plasma nitriding conditions. This involves the use of comparatively low energy nitrogen ion beams (1–2 keV), with higher beam current densities and, where necessary, additional heating to increase the sample temperature to approximately 400 °C at the surface. Secondary ion mass spectrometry has been used to assess the extent of nitrogen diffusion into a range of steels. The nitrogen penetration depth (and profile shape) depends both on the ion beam parameters and the structure and composition of the steel. Additional experiments conducted with a supplementary supply of nitrogen gas in the form of a vacuum chamber backfill demonstrate that increasing the nitrogen supply can increase nitrogen take-up for some materials. For a 30 min implantation at 263 μA cm −2 the penetration depth was a substantial fraction of a micrometre and is greater than the profile produced by high energy implantation in some cases. The hardness of the implanted steels can be correlated with the extent of nitrogen take-up, the amount of diffusion during implantation and softening induced by annealing of the steel substrates. Considerable hardening is achieved for some steels (e.g. M2 high speed steel) whereas for other steels the improvements are less obvious (e.g. 304 stainless). These observations are discussed in the light of the nitridability of the steels.

Plasma-nitrided α-β Ti alloy: layer characterization and mechanical properties modification

Beyond continuous efforts to develop advanced processing methods or new directions in surface modification, the foundation for assessment of appropriate surface layers still remain very challenging. In this context, Ti6Al4V α-β alloy was investigated mainly after plasma nitriding by nitrogen or by a nitrogen mixture with hydrogen and/or argon. The current study objectives consist in gradually developing some aspects of the microstructure and property relationship. As such, the study centred on the characterization of refined layers as well as confronting critical questions of how layers and interfacial microstructure might affect the near-surface mechanical properties (i.e. microhardness, fatigue resistance and crosion). In particular, the effects on fatigue behaviour are emphasized by utilizing single edge notched specimens and fatigue stepdown techniques. It is found that two distinct sublayers, comprising σ-Tin and σ-Tin + ε-Ti 2N phases, were formed with alloying elements in a segregated zone, followed by a solid solution of N in the Ti. Here, the far field affected zone extended up to about 20μm. It was observed that the formation of the uppermost sublayer (σ-TiN phase) with a composition including H, NH, and N, as well as Ti depleted of Al ar. 'V, has a strong effect on the layer properties. A microhardness value as high as 29.4 GPa (3000 kgf mm −2) was obtained with significant improvements in the erosion resistance and fatigue life. It was found that in some controlled plasma nitriding conditions the fatigue life for crack initiation increased by more than a factor of 3. Accordingly, the cyclic crack initiation behaviour is described, revealing substantial influences due to crack tip field perturbations, or fracture resistance modifications. Finally, the role of extrinsic crack tip shielding effects as related to closure or to the local effective driving force for microcracking onset is elaborated.

Plasma nitriding of powder metal steel

The influence of plasma nitriding conditions (temperature, process duration, gas mixture, pressure) on the surface layer microstructure and on the compound and diffusion layer properties at the surface of chromium alloyed powder metal steel samples has been studied. A rather high surface hardness of 710 HV 5 and 890 HV 0.3 is achieved. This is a consequence of the compound layer being formed very rapidly as a result of a high content of alloying elements in the powder metal steel matrix. The nitriding layer grows in accordance with the diffusion nature of the nitriding process reaching 200 and 700 μm after 3 and 16 h, respectively. In spite of the fact that the diffusion layer continues to grow steadily with the time, the compound layer thickness reaches a saturation level after only 6 h of around 7 μm. The compound layer is continuous over the entire surface of the samples, including voids, thus giving rise to potentially very good wear properties.

The fatigue characteristics of Plasma Nitrided three Pct Cr-Mo steel

The plasma nitriding conditions necessary to treat a three pct Cr-Mo steel with and without the formation of a surface compound layer have been investigated and the influence of this compound layer on the fatigue limit is described. The nitrided case depth has been varied as a function of time at a constant temperature of 480 °C and the corresponding rotating bending fatigue strength evaluated. This data has been used to develop a simple model to describe the influence of the case depth on the fatigue limit.