Plasma Nitrided Layer Research Articles

Electrochemical Behavior of Plasma-Nitrided Austenitic Stainless Steel in Chloride Solutions.

The application possibilities of austenitic stainless steels in high friction, abrasion, and sliding wear conditions are limited by their inadequate hardness and tribological characteristics. In order to improve these properties, the thermochemical treatment of their surface by plasma nitriding is suitable. This article is focused on the corrosion resistance of conventionally plasma-nitrided AISI 304 stainless steel (530 °C, 24 h) in 0.05 M and 0.5 M sodium chloride solutions at room temperature (20 ± 3 °C), tested by potentiodynamic polarization and electrochemical impedance spectroscopy. Optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy are used for nitrided layer characterization. The experiment results confirmed the plasma-nitrided layer formation of increased micro-hardness related to the presence of Cr2N chromium nitrides and higher surface roughness compared to the as-received state. Both of the performed independent electrochemical corrosion tests point to a significant reduction in corrosion resistance after the performed plasma nitriding, even in a solution with a very low chloride concentration (0.05 mol/L).

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.

Titanium-modified plasma nitriding layer and enhanced properties for 42CrMo steel

In order to obtain a nitriding layer with thicker ductile diffusion layer and thinner brittle compound layer, plasma nitriding with titanium addition was carried out at 540 °C for 4 h for 42CrMo steel, the characteristic of titanium modified nitriding layer and the enhanced properties were systematically investigated by optical microscope (OM), scanning electron microscope (SEM), XRD, hardness tester and wear tester etc. The results show that titanium addition can effectively modify the characteristics of nitrided layer, and thus a plasma nitrided layer owning thicker ductile diffusion layer and thinner brittle compound layer and higher surface hardness can be obtained. Titanium addition can significantly decrease the compound layer and increase the effective hardening layer, and also greatly enhance the surface hardness, especially with the optimal amount of 0.8 g, the compound layer can be reduced from 19 μm to 10 μm, while the effective hardening layer can be increased from 225 μm to 370 μm. And the surface hardness can be enhanced from 703HV0.05 to 889HV0.05, more importantly, both wear resistance and toughness can be greatly promoted by the novel titanium modified plasma nitrided layer, attributed to the formation of dispersedly distributed TiN particles with very high hardness in the nitriding layer.

Dynamic response characteristics and damage mechanism of impact wear for deep plasma nitrided layer

The impact wear behaviour of deep plasma nitrided layer and its substrate (axle steel) were investigated. The nitrided layer had a 6 µm thick compound layer, and the effective case depth was 0.85 mm. Moreover, it introduced compressive residual stress with a maximum of 715.8 MPa at a depth of 511 µm. The nitrided specimens showed a lower energy absorption ratio and better impact resistance than the untreated specimens. Plastic deformation occurred in the initial test of the untreated specimens, but elastic deformation was predominant for the plasma-nitrided layer. The main wear mechanisms of the untreated samples were pitting, delamination and oxidation wear. In contrast, the plasma-nitrided specimens exhibited better oxidation resistance and slighter peeling-off than the untreated specimens.

Enhanced corrosion resistance and reduced cytotoxicity of the AZ91 Mg alloy by plasma nitriding and a hierarchical structure composed of ciprofloxacin-loaded polymeric multilayers and calcium phosphate coating.

Much effort has made to lessen the cytotoxicity and enhance the corrosion resistance of biodegradable magnesium alloys, for example, by depositing multilayered polymeric coatings containing hydroxyapatite. In this work, a hierarchical structure composed of ciprofloxacin (Cip)-loaded on polyacrylic acid (PAA) and poly (ethyleneimine) (PEI) as biocompatible polymeric multilayers and calcium phosphate coating as the top layer is formed by the sol-gel method on the AZ91 Mg alloy with an intermediate layer formed by nitrogen plasma immersion ion implantation. The thicknesses of the multilayered coating and nitrided layer (Mg3 N2 ) are 10μm and 140 nm, respectively. The corrosion current density decreases by 95.6% and the corrosion potential in the polarization curve shifts to the positive direction by 23%. The passivation process which occurs at defects by deposition of corrosion products mitigates both galvanic and localized corrosion. Slight increase in the contact angle and surface free energy, enhanced corrosion resistance, and reduced cytotoxicity are observed from the multilayered structure. The better corrosion resistance enables better control of release of Cip. Biological assessment indicates that the antibacterial activity against Escherichia coli is improved by 100% after culturing for 24 hr and the cell viability and noncytotoxic behavior of the coated AZ91 are enhanced as well. The corrosion behavior and biological results suggest that the strategy of using a hierarchical structure composed of Cip-loaded polymeric multilayers in conjunction with an intermediate plasma nitrided layer has large potential in the development of biodegradable orthopedic implants made of Mg alloys.

Plasma nitrided compound layers in sintered parts: Microstructures and wear mechanisms

The shape and dimensions of the component play an essential role in plasma nitriding processes, a surface treatment crucial for the powder metallurgy industry since salt bath and gas nitriding poorly interact with porous structures. When the geometry of the components contains cavities, holes, or even parallel flat surfaces, the hollow cathode effect (HCE) can be activated, and, as a consequence, microstructural transformations that develop columnar nitride compound layers and the formation of a N-rich eutectoid, the braunite, may occur. The tribological properties of nitride compound layers with microstructural characteristics induced by the hollow cathode effect were evaluated in this work. Hollow cylinders of sintered iron were plasma nitrided and the tribological behaviour was assessed via reciprocating dry sliding tests. Unlike the friction coefficient, which is high (~0.4) regardless of the surface treatment, the wear rate is strongly increased by the presence of columnar morphology (2.4x) and braunite layer (2.1x), which are at the origin of brittle mechanisms such as crack propagation and interaction, resulting in the detachment of the compound layer.

Combined Use of Surface Texturing, Plasma Nitriding and DLC Coating on Tool Steel

In cold rolling, a textured roll can be used to imprint a desired surface topography onto the sheet during rolling. This work proposes the use of diamond-like carbon (DLC) coatings to protect the surface topography of the rolls in replacement of the carcinogenic hard chrome. For that, hydrogenated amorphous carbon (a-C:H) was deposited on plasma nitrided tool steel, both for ground and textured specimens. Changes in surface topography due to DLC coating were assessed using a confocal microscope. Coating adhesion was evaluated using the method VDI 3198. The specimens were characterized using X-ray diffraction (XRD), microhardness test and scanning electron microscopy (SEM). The coating was characterized using Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). The results showed a soft multilayer coating consisting of a plasma nitrided layer for load support, a Si-rich interlayer to improve adhesion and an a-C:H top layer. DLC deposition reduced the roughness of the textured specimens. The coating resulted in relatively stable friction and good durability, with small damage and negligible wear even under dry sliding.

The separation of ε- and γ’-phases in the plasma nitrided layer by colour etching techniques

In this research, various etching reagents were tested on a quenched and tempered 42CrMo4 steel and an untreated C45E unalloyed steel sample, whichwere plasmanitrided for 4 h at 490 °C with 75% N2–25% H2 gas mixture. The aim is to find a reagent suitable for revealing and separating the two ε- and γ’-phases in the nitrided layer. Previously, the compound layer’s composition could only be identified by X-ray diffraction (XRD), a costly, time-consuming and not easily accessible process. Therefore, finding an alternative could be crucial for small businesses. Nital, Picral, Villela, and Oberhoffer’s reagents were investigated in the experiments. Scanning electron microscope (SEM) was used to observe the nitrided layer, and it was analysed by XRD to detect the formed phases and electron dispersive X-ray spectroscopy (EDS) was used to analyse the elemental composition. Nital is the most common used etchant in the industry, but Oberhofferwas found to be an excellent etchant to separate the two phases in a dual phases nitrided layer.

Phase constitution control of plasma nitrided layer and its effect on wear behavior under different loads

Plasma nitriding was conducted at different nitrogen ratio under the same nitriding condition of 510 °C and 4 h for AISI 4340 steel in this study, the phase constitution of nitrided layer was controlled by adjusting nitrogen ratio and its effect on wear behavior under different loads was investigated. The results showed that the phase constitution of plasma nitrided layer could be precisely controlled by adjusting nitrogen ratio, a compound-free nitrided layer, single γ′ phase and ε + γ′ dual-phase compound layer was obtained at nitrogen ratio of 15%, 20% and 25%, respectively. And it was found that the hardness increased gradually for compound-free nitrided layer, single γ′ phase and ε + γ′ dual-phase layer. More importantly, it was found that the wear resistance was closely related to the phase constitution of nitrided layer under different loads, the best wear resistance under light load of 200 g was obtained for the sample with ε + γ′ dual-phase layer due to the highest hardness; whereas the best wear resistance under heavy load of 400 g was obtained for the sample with single γ′ phase layer due to its excellent combination of hardness and toughness. Meanwhile, the mechanisms of phase constitution control and wear behaviors of nitrided layer under different loads were revealed.

The effect of novel composite pretreatment on performances of plasma nitrided layer

Novel composite pretreatment combining laser shock peening and pre-oxidation was primarily adopted prior to plasma nitriding for 42CrMo steel. Optical microscope, scanning electron microscope, vickers microhardness tester and wear tester were used to systematically investigate the innovative enhancement effect of novel composite pretreatment on the performances of plasma nitrided layer. The results showed that the surface characteristics of composite pretreated sample had the advantages of both laser shock peening and pre-oxidation, thus brought out much thicker nitrided layer with excellent performances. Compared with conventional plasma nitriding, the thickness of compound layer and effective hardening layer was increased 1.8 times under the same nitriding condition. Meanwhile, the surface hardness was much higher; reaching 750 HV0.05, and the wear resistance was significantly enhanced, with nearly 60% decrease of the width of abrasive mark, comparing with that by conventional plasma nitriding without pretreatment.

Characterization and growth kinetics of plasma nitrided layer fabricated on Incoloy 901 superalloy

The phase composition, microstructure, mechanical performance and growth kinetics of nitrided layers on Incoloy 901 (IN-901) at 460– 610 °C were investigated. XRD results indicated that CrN, γ-FeNi, γN and Ni4N were the main phase compositions of the nitrided layer. The formation of Ni4N took longer duration or higher temperature than those of CrN and γN. EDS results suggested that the content of Cr in the nitrided layer was larger than that in the substrate, while fewer Ni and Fe entered the nitrided layer from the matrix. The kinetic studies showed that the weight and thickness of the nitrided layer significantly increased with the increase of nitriding temperature, and the diffusion activation energy of IN-901 was calculated as ~153 kJ/mol (1.6 eV). Micro-hardness and sliding tests proved a high surface hardness (up to ~1892 HV0.025) and a low friction coefficient (~0.22) of the nitrided IN-901.

Analysis of the Surface Treatments Effect on the Creep Behavior of Ti-6Al-4V Alloy

Abstract This paper compares the creep behavior of Ti-6Al-4V alloy after different surface treatments, the plasma nitriding using Plasma Enhanced Chemical Vapor Deposition (PECVD), and the deposition of SiC thin films with Cr interlayer using High Power Impulse Magnetron Sputtering (HiPIMS). A microstructural characterization was performed with Scanning Electron Microscopy (SEM), Scanning and Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS) techniques. The creep test was performed at a constant load from 500 to 600 °C and 125 to 319 MPa, and a fractographic analysis was performed. The EDS analysis of the plasma nitrided layer indicated the nitrogen presence of the compounds TiN and Ti2N and an increase in the iron concentration. Creep test results in both conditions indicated an increase in the creep resistance. Plasma nitrided condition indicated the lowest creep rate and lesser elongation, making it the most suitable in applications that require a low dimensional distortion.

IMPROVEMENT OF WEAR RESISTANCE OF SHREDDER BLADES USED IN A REFUSE-DERIVED FUEL (RDF) FACILITY BY PLASMA NITRIDING

Refuse-derived fuel (RDF) is a kind of renewable energy source to produce energy for replacement of fossil fuels. Aggressive working conditions in RDF facilities cause the shredder blades to wear out quickly. So, the purpose of this paper was to study the effect of plasma-nitriding process on wear resistance of shredder blades made of AISI D2 tool steel in the service condition of RDF facility. Shredder blades were commercially available from two different suppliers (A and B suppliers). These hardened shredder blades were plasma-nitrided in the mixed nitrogen and hydrogen atmosphere at a volume ratio of 3:1 at 450∘C for 12, 18 and 24[Formula: see text]h at a total pressure of 250 Pa. Characterisation of plasma-nitrided layers on the shredder blades was carried out by means of microstructure and microhardness measurements. Wear tests of plasma-nitrided shredder blades were performed under actual working conditions in the RDF facility. Wear analysis of these shredder blades was conducted using three-dimensional (3D) optical measuring instrument GOM ATOS II. The compositional difference of the shredder blades provided by A and B suppliers played an important role on the nitrided layer. The case depth of A-blades significantly increased with increasing plasma-nitriding time. However, the case depth of B-blades was fairly lower at the same nitriding time and only slightly increased with increasing plasma-nitriding time. Plasma-nitriding process significantly improved the surface hardness of the shredder blades. Maximum surface hardness values were achieved at nitriding time of 18 h for both blades. In this case, this increase in surface hardness values was above 100%. At nitriding time of 24[Formula: see text]h, the maximum surface hardness of A-blades significantly decreased, whereas this decrease in surface hardness of B-blades was the negligible value. The wear test results showed that plasma-nitriding process significatly decreased the wear of shredder blades; 18 h nitriding for A-blades and 24[Formula: see text]h nitriding for B-blades had better wear-reducing ability in the service condition of RDF facility. In these cases, the decreases in the total volume wear loss for A- and B-blades were 53% and 60%, respectively.

Microstructure and properties of plasma nitrided layers on Ni-based superalloy Ni-20Cr

Ni-base superalloy Ni20Cr was plasma-nitrided at low temperature of 450 °C. Microstructural characteristics of the case layer were investigated by X-ray diffraction (XRD), optical microscopy (OPM) and scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A thin nitrided layer of about 4 μm was produced on the nitrided Ni-based superalloy which exhibited “featureless” appearance in OPM and SEM observations without strong etched regions, usually representative of nitride precipitation. Nevertheless, XRD revealed the nitrided layer contained an expanded austenite γN phase and CrN precipitates. TEM image of the nitrided layer exhibited the Moiré patterns resulting from overlapping of the γN phase and CrN lattices. It was suggested that the nature of the nitrided layer was a N-saturated matrix in which nanometric CrN precipitates dispersed. The orientation relationship between CrN and γN corresponded to Baker-Nutting relationship: (100)CrN // (100)γ; [001]CrN // [001]γ. The small lattice expansion and distortion occurred on the γN phase due to lower solubility of nitrogen in the austenite containing high Ni content, compared to the Fe-rich alloy. Lower saturation of nitrogen in the γN phase and precipitation of CrN in the γN phase are attributed to the repulsion of excessive nitrogen by nickel and the trapping effect of nitrogen played by chromium. The nitrided surface was found to be a three-time increase in hardness. Tribological behavior of nitrided Ni-based superalloy was improved significantly due to increased surface hardness. The corrosion resistance of nitrided Ni-based superalloy was not deteriorated but a little improvement in spite of the precipitation of nanometric CrN in γN phase as the matrix of case-layer.

Corrosion Behavior of Plasma-Nitrided 904L Austenitic Stainless Steel in Hydrofluoric Acid

A new type of high-chromium nickel molybdenum super austenitic stainless steel, 904L, has excellent corrosion resistance in acidic environments. However, the service life of 904L decreases significantly in a mixed acid system that includes hydrogen fluoride and sulfuric acid. In this article, different plasma nitriding processes were used to modify the surface of 904L stainless steel. X-ray diffraction was used to analyze the phase composition after nitriding; scanning electron microscopy and atomic force microscopy were used to examine the surface morphology after nitriding; electrochemical noise and electrochemical methods were used to study the localized corrosion behavior and the damage mechanism of the ion nitride layer; and the effect of the plasma nitride layer on the corrosion resistance was explored. The results show that with increasing nitriding time, the thickness of the nitride layer increased. Ion nitriding resulted in the coarsening of the 904L austenitic stainless steel surface. A long nitriding treatment time resulted in the precipitation of CrN in the modified layer, depleting the chromium from the matrix and remarkably reducing the corrosion resistance.

Analyse of Tribological Properties of Layers Created by Plasma Nitriding + DLC

Plasma technology of deposition of thin layers is currently the commonly used technology serving to influence the surface properties of various materials (metals, polymers, ceramics, etc.). The great advantage of applied thin layers is that although they can significantly change the surface properties of coated materials, their advantageous volumetric properties are preserved. The experimental part of work describes the evaluation of the properties of duplex system of the plasma nitrided layer with DLC coating and confronts them with the properties of plasma nitrided layers and polished surfaces. 42CrMo4 and 17Ni4CrMo steels were chosen for experiment. Experimental part deals with the practical analysis of the determination of tribological properties of thin film-substrate (specifically nitrided layer-DLC coating). The tribological properties of selected steels were evaluated using the Pin on Disc method. Modified layer formed by duplex system PN+DLC showed up to 8x lower coefficient of friction than nitrided or only polished surface.

Development in plasma surface diffusion techniques of Ti-6Al-4V alloy: a review

Ti-6Al-4V alloy has been widely used as an important structural material in aerospace, automotive, and chemical and biomedical industries due to its high specific strength and excellent corrosion resistance. However, the poor tribological properties and low resistance to high temperature oxidation limit extensive applications of the alloy. Plasma surface diffusion treatments, including plasma carbonizing, plasma nitriding, and plasma alloying treatments, contribute to improve wear resistance and the anti-oxidation property of the alloy by introducing other elements into the surface of the alloy to form hard surface layers under low pressure conditions. In this review article, the developments in microstructure and properties of the layers generated by the three techniques were reviewed systematically. In particular, the development in the phase determination of the plasma-nitrided layer was analyzed. New approaches in accelerating the diffusion of atoms and optimizing process were analyzed in detail.

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.

Increasing of Durability of Surfaces by Plasma Nitriding Process

This article deals with properties of plasma nitrided layers in depth. The redistribution of alloy elements and C-N in depth of nitrided layers was analysed. The plasma nitriding process was used for creation of nitrided layers [1]. The nitrided layers were applied to 32CrMoV12-10 steel used for stressed machine parts. Samples were subsequently evaluated by metallographic, OES, hardness and microhardness methods. The results of measurement showed connection between chemical composition of alloying elements after chemical-heat treated process and universal hardness, microhardness.

Kinetics and wear behaviour of M50NiL steel plasma nitrided at low temperature

The quenched M50NiL steel was plasma nitrided at 460°C for different time to investigate the effects of the duration time on the microstructure, microhardness and wear resistance of the nitrided layers. The results show that the plasma nitrided layer depth increases with increasing nitriding time. The plasma nitrided layer includes only the diffusion layer without compound layer. The main phases in the nitrided surface layer are nitrogen expended α′-Fe and γ′-Fe4N. The microstructure of the nitrided layer is refined. The wear resistance of the nitrided samples can be improved significantly by plasma nitriding. The sample nitrided for 4 h possesses the highest wear resistance, due to its relatively smooth surface and ultra-fine grains in the nitrided layer.