Pulsed Plasma Nitriding Research Articles

Effect of Pre-treatment and Duration of Pulse Plasma Nitriding on Duplex Plasma Treatment by Physical Vapor Deposition of TiN on AISI D2 Steel

Effect of Pre-treatment and Duration of Pulse Plasma Nitriding on Duplex Plasma Treatment by Physical Vapor Deposition of TiN on AISI D2 Steel

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 %.

Pulsed plasma nitriding of high velocity oxy-fuel sprayed Inconel 625 coatings

A hardening of high velocity oxy-fuel sprayed Inconel 625 coating systems was performed by pulsed plasma nitriding treatment. After deposition of an Inconel 625 coating, samples were pulsed plasma nitrided at 520 °C for 12 h in a gas ratio of 3:1 N2 and H2 under a constant pressure of 2.5 × 102 Pa. Pulsed plasma nitriding improved the microhardness of the high velocity oxy-fuel sprayed Inconel 625 coating from 355 to 401 HV0.05. The high velocity oxy-fuel-sprayed Inconel 625 coating after pulsed plasma nitriding process showed excellent corrosion resistance as well as a reduction of both the friction coefficient and wear rate during the sliding phase in a 3.5 wt.% NaCl solution against sliding action of Al2O3 ball.

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.

Improved Mechanical Properties, Wear and Corrosion Resistance of 316L Steel by Homogeneous Chromium Nitride Layer Synthesis Using Plasma Nitriding

Here, pulsed plasma nitriding of AISI-316L austenite stainless steel is conducted in a narrow range of temperature 510-550 °C and simultaneous combination of expanded austenite phase, and homogenous, dense chromium nitride phase is attained in a single processing unit, with relative low-cost equipment and single-step processing. The results show a noteworthy enhancement in nanohardness at 530 °C, whereas best wear resistance is achieved by processing at 550 °C. A dual-layer structure is obtained constituted of expanded austenite phase covered by quite homogenous chromium nitride phase, which is probably responsible for the dramatic surface improvement. The wear mechanism is changed after plasma processing (abrasive to adhesive wear), and the friction coefficient is reduced and smoother, particularly for the sample treated at 530 °C. Interestingly, the corrosion resistance is also found to be enhanced, even in the presence of chromium nitride (which usually deteriorate the corrosion resistance), which is probably credited to the formation of fine-grained and homogeneous CrN layer over the expanded austenite phase. This study suggests that the development of homogenous CrN layer over the expanded austenite structure is highly valuable for mechanical and tribological features, and it enhances the corrosion resistance.

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.

Effect of ion peening and pulsed plasma nitriding on the structural properties of TiN coatings sputtered onto 100Cr6 steel

Ion peening with noble gas is typically used to generate lattice imperfections and a nanostructure within the bombarded metal surfaces. This might have therefore an impact on subsequent plasma nitriding, thus allowing for enhancing the adhesion and wear resistance of hard ceramic coatings deposited onto steel surfaces. In this work, the influence of pre-treating a 100Cr6 steel surface by Xe+ ion bombardment and pulsed plasma nitriding was investigated with respect to surface roughness, wear resistance and residual stresses of thin TiN coatings deposited by reactive ion beam assisted deposition.Xe+ ion bombardment was carried out using a 400 eV acceleration energy produced by a broad Kaufman cell and subsequent thermo-chemical nitrogen diffusion was accomplished at 520 °C. The results show that Xe+ ion bombardment intensifies nitrogen diffusion without inducing significant changes in the substrate topography. The combined pre-treatment with Xe+ ion bombardment and subsequent pulsed plasma nitriding leads to a reduction of compressive stresses in the TiN coatings. The presence of porosity in the white layer diminished the wear resistance.

Analysis of tribomechanical behavior of AISI 8620 steel treated by different plasma assisted processes

Abstract The tribomechanical behavior of AISI 8620 steel treated by different plasma-aided processes was investigated. In this study, we compared conventional plasma nitriding (CPN), pulsed plasma nitriding (PPN), plasma nitrocarburized (PNC), plasma oxynitriding (PON), and low-temperature plasma blued (LTPB). The microstructure of treated samples was characterized using X-ray diffraction, and the compound layer thickness was measured by optical microscopy. Vickers microhardness profiles were correlated with a reduction of friction coefficient in the treated samples. Wear test was performed on a pin-on-disc tribometer in dry-sliding conditions using a counter-face of WC-Co ball. Wear tracks on the ball and surface of the treated sample was analyzed with optical micrographs. LTPB process shows the best reduction of the friction coefficient of the amorphous carbon layer on the top of the surface.

Changing the characteristics of the nitrided layer using three different plasma configurations

Direct current (DC) plasma nitriding offers some disadvantages, especially in parts with complex geometries, where the presence of edges is significant, such as gears, molds, and needle punched parts are strongly affected by this effect, leading to irregular formation of nitrided layers and high variation in surface hardness. To solve these problems two techniques were developed as alternatives, namely: pulsed plasma nitriding and cathodic cage nitriding. In this work, these three nitriding techniques were compared using AISI 1045 steel as substrate. Steel discs were nitrided with the purpose of evaluating the influence of these different plasma configurations on the characteristics of the nitrided layer. The treatments in the three techniques were carried out at the same pressure, temperature, time and gas atmosphere. The samples were characterized for the microstructure, microhardness and crystalline phases present. X-ray diffraction with grazing incidence was used to verify the order of the nitrites formed and to estimate the thickness of the single-phase layers. Differences between the configurations with respect to the occurrence of restriction rings, total thickness (xe + xγ') and relative (xe/xγ') compound layers were observed. Keywords: Plasma DC; cathodic cage; pulsed plasma; nitriding; GIXRD.

Cathodic Cage Plasma Pre-treatment of TiN-Coated AISI-304 Stainless Steel for Enhancement of Mechanical Strength and Wear Resistance

Although austenitic stainless steels (ASSs) are known for their superior corrosion resistance properties, the use of such materials in motion contact parts is limited due to their low wear resistance. Previous studies reveal that titanium nitride (TiN) coating of ASS significantly improves its hardness and surface morphology but not the wear resistance due to weak interfacing with the substrate. Since plasma nitriding is a flexible and multifunctional case-hardening process, an attempt was made to improve the wear resistance of TiN-coated AISI-304 stainless steel by subjecting it to pre-treatment by pulsed DC cathodic cage plasma nitriding (CCPN) in the abnormal glow region. The hardness of the TiN-coated steel samples (with and without CCPN pre-treatment) was measured using Vickers micro-hardness tester. This test revealed maximum hardness of 2284 HV after plasma treatment of TiN-coated steel. The untreated TiN-coated steel exhibited 10.6 times lower hardness than the plasma pre-treated TiN-coated steel (CCPN-TiN). XRD analysis of the untreated TiN-coated steel showed strong diffraction peaks of TiN (311) and (400) in the spectrum, whereas plasma pre-treated sample contained dominant peaks of TiN (111), (200) and (220). The ball-on-disk wear tester was used to investigate the wear behavior of the samples. Very small wear rate and friction coefficient were reported for CCPN-TiN-coated steel. The observed low wear rate was probably due to the development of a subsurface (i.e., nitrided surface) on TiN-coated steel during CCPN pre-treatment.

A Hybrid Plasma Treatment of H13 Tool Steel by Combining Plasma Nitriding and Post-Oxidation

Pulsed plasma nitriding and post-oxidizing process have been applied to hot work H13 tool steel to enhance the tribological properties (friction coefficient and wear rate). Nitriding was accomplished under specific conditions to generate a free white layer surface in order to avoid an abrasive wear mechanism. Post-oxidizing treatment was carried out in the same reactor after finishing the nitriding treatment; processing time was varied for 30 and 60 min. The morphology, phase’s composition and wear performance of duplex-treated samples were evaluated by scanning electron microscopy, x-ray diffraction analysis and pin-on-ball wear technique. The results show that the duplex treatment produces a bilayer arrangement constituted by an 80 μm diffusion zone with expanded martensite as the main phase underneath a 2–4 μm hematite–magnetite-oxidized layer. The duplex treatment modified the main wear mechanism of the nitrided sample from abrasive to plastic yielding. The changes in wear mechanisms resulted in a noticeable decrease, about 40%, in friction coefficient for oxidized samples in comparison with the nitrided-only sample. It was also established that the lowest friction coefficient values can be obtained when hematite is the main phase in the oxidized layer.

Investigating Tribological Characteristics of HVOF Sprayed AISI 316 Stainless Steel Coating by Pulsed Plasma Nitriding

In this study, surface modification of aluminum alloy using High-Velocity Oxygen Fuel (HVOF) thermal spray and pulsed plasma nitriding processes was investigated. AISI 316 stainless steel coating on 1050 aluminum alloy substrate by HVOF process was pulsed plasma nitrided at 793 K under 0.00025 MPa pressure for 43200 s in a gas mixture of 75 % N2 and 25 % H2. The results showed that the pulse plasma nitriding process produced a surface layer with CrN, iron nitrides (Fe3N, Fe4N) and expanded austenite (γN). The pulsed plasma nitrided HVOF-sprayed coating showed higher surface hardness, lower wear rate and coefficient of friction than the untreated HVOF-sprayed one.

Effect of Pulse Repetition Time on Surface Properties of Pulsed Plasma Nitrided AISI 4340 Steel

Background/Objectives: Pulsed Plasma Nitriding (PPN) process is carried out on AISI 4340 steel at constant temperature and time. The key parameters which influence the nitrided compound layer properties in PPN are Pulse Duration (PD), Pulse Repetition (PR) time and Gas ratios of Hydrogen and Nitrogen. To obtain tailored properties of nitrided compound layer by varying the PR time and study the Microstructure, Crystalline phase formation and Wear properties and optimize the process parameters. Methods: In PPN process, PR time was varied from 100 μs to 500 μs and PD duration was fixed to 50μs. The nitrided samples were characterized by Optical Microscope, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Pin on Disc test. Findings: The decrease of PR time increases the formation of Iron Nitrides (Gamma nitride: γ-Fe4N and Epsilon Nitride: e-Fe3N) and it decreases when PR time is increased. Samples treated at PR-300 μs and PR-0 μs are observed with strong and weak intensities of Chromium Nitrides (Cr2N) respectively. The surface hardness is increased from 250±20 HV1 to 650±50 HV1, and the wear properties have increased by three times higher than base material. The nitrided properties are strongly influenced by PR time and the formation of Iron nitrides is inversely proportional to PR time. Novelty/Improvements: This investigation suggests that the PR time is a critical parameter for optimization of nitrided compound layer properties and the surface properties of AISI 4340 steel is improved by PPN process.

Evaluation of the Effect of Different Plasma-Nitriding Parameters on the Properties of Low-Alloy Steel

This work is concerned with the surface treatment (ion nitriding) of different plasma-nitriding parameters on the characteristics of DIN 1.8519 low-alloy steel. The samples were nitrided from 500 to 570 °C for 5–40 h using a constant 25% N2-75% H2 gaseous mixture. Lower temperature (500–520 °C) favors the formation of compound layers of γ′ and e iron nitrides in the surface layers, whereas a monophase γ′-Fe4 N layer can be obtained at a higher temperature. The hardness of this layer can be obtained when nitriding is performed at a higher temperature, and the hardness decreases when the temperature increases to 570 °C. These results indicate that pulsed plasma nitriding is highly efficient at 550 °C and can form thick and hard nitrided layers with satisfactory mechanical properties. The results show the optimized nitriding process at 540 °C for 20 h. This process can be an interesting means of enhancing the surface hardness of tool steels to forge dies compared to stamped steels with zinc coating with a reduced coefficient of friction and improving the anti-sticking properties of the tool surface.

Tribological properties and wear mechanisms of DC pulse plasma nitrided austenitic stainless steel in dry reciprocating sliding tests

Expanded austenite (γN), or S-phase, is a special phase of low-temperature nitrided austenite containing highly super-saturated nitrogen in the form of heterogeneous Cr-N nano-clusters. A nitrided layer of singe phase γN is known to provide austenitic stainless steel with combined high hardness, good wear resistance and superior corrosion resistance. This paper reports recent experiments on a comparative study of the sliding wear properties and wear mechanisms of nitrided austenite stainless steel AISI 316, with a special attention paid on worn surface structural evolutions induced by frictional heating and sliding deformation. The samples were prepared by DC pulsed plasma nitriding treatments of various time at a fixed power. Knoop micro-indentation has revealed hardening behaviour of the nitrided samples. The reciprocating ball-on-disc sliding wear and friction properties were investigated at ambient environment conditions using an alumina counterpart ball. The worn surfaces have been analysed by XRD, FEG-SEM and EDX to show wear induced changes in the crystalline characteristics and the wear mechanisms of tribo-oxidation, cracking, abrasive wear and ploughing deformation. Moreover, longitudinal cross-sectional foils of the worn samples have been prepared and analysed using TEM, to investigate the wear induced structural changes, including tribofilm formation, plastic deformation and delamination in depths of nano-scale.

Surface properties and tribocorrosion behaviour of a thermal sprayed martensitic stainless steel coating after pulsed plasma nitriding process

In this work, the effects of pulsed plasma nitriding on HVOF-sprayed martensitic stainless steel coating were investigated. Martensitic stainless steel coating was pulsed plasma nitrided at 793 K under 0.00025 MPa pressure for 43200 s in a gas mixture of 75% N2 and 25% H2. The pulsed plasma nitriding resulted in not only an increase in the surface hardness, but also improvement of dry sliding wear and tribocorrosion resistance of the HVOF sprayed martensitic stainless steel coating because of the Cr, Fe3, and Fe4 N phases. However, the corrosion resistance of the HVOF-sprayed martensitic stainless steel decreased notably by nitriding process.

Direct Current and Pulsed Direct Current Plasma Nitriding of Ferrous Materials a Critical Review

Abstract Nowadays, the improvement of ferrous materials performance is a problem of high interest. One of well-known wear- and corrosion properties improving technique is plasma nitriding, in which elemental nitrogen is introduced to the surface of a metal part for subsequent diffusion into the material. As a result, a compound, “white” layer and a diffusion zone are formed at the detail’s surface. Most of the authors positively describe the effects of surface ion nitiding. On the other hand, there are also reports on adverse effects of direct current and pulsed direct current plasma nitriding on ferrous materials performance. Therefore, an attempt to provide comprehensive summary on direct current and pulsed direct current ion nitriding and its influence on ferrous materials’ mechanical and corrosion properties has been made. According to the results, some of the technique drawbacks are hard to avoid in mass production.

Corrosion Resistance of the Inconel 740H Nickel Alloy after Pulse Plasma Nitriding at a Frequency of 10 kHz

The microstructure and corrosion resistance of the CrN, Cr2N layer produced by pulse plasma ion nitriding at a frequency of 10 kHz on the Inconel 740H nickel superalloy were examined. The microstructure of the layers were characterized by light microscope and scanning electron microscopy. The corrosion resistance was examined by the impedance and potentiodynamic methods in a 0.1 M Na2SO4 solution and an acidified (pH = 4) 0.1 M NaCl solution at room temperature. The layer obtained, about 4.5 μm thick, contains CrN, Cr2N phases. It is continuous on the entire cross-section of the sample and adheres well to the substrate. However, in the chloride environment it constitutes an inhomogeneous cathodic coating for corrosion and thereby intensifies pitting corrosion of the material. In chloride-less environment, on the other hand, the layer has no essential effect on the corrosion rate of the Inconel 740H nickel alloy.

Improving the Abrasive Wear Resistance of a Microalloyed Steel by Plasma Nitriding

The aim of this work was to study the micro-abrasive wear resistance of an API 5L X-70 microalloyed steel plasma nitrided under different conditions of time and temperature. Pulsed DC plasma nitriding experiments were performed under a treatment atmosphere of 10%N2 + 90%H2, at temperatures of 410, 440 and 470 °C and for nitriding times of 1, 3 and 5h. The results show that plasma nitriding performed at 440 °C and 1h led to the formation of a compound layer constituted mainly of ε-Fe2-3N nitride and a diffusion zone with large needle-like nitride, offering the highest wear resistance. The amount of γ’- Fe4N phase was found to increase with the plasma nitriding time, decreasing the wear resistance of the material.

A Study on Formation and Growth Mechanism of Nitride Layers During Plasma Nitriding Process of Plastic Injection Mold Steel

Ion nitriding modifies composition of surface layer in steel used in plastic mold application and this consequently improves their lifecycle. In this study, pulsed plasma nitriding technique was used to produce a protecting hard layer on AISI P20 steel at three process temperatures of 450°C, 500°C, and 550°C for durations of 2.5, 5, 7.5, and 10 h at a constant gas mixture of 75% N2–25% H2. Surface morphology was studied by optical and scanning electron microscope and the phases formed on the surface layer were determined by X-ray diffraction (XRD). Elemental depth profile was measured by techniques including energy dispersive spectroscopy, wavelength dispersive spectrometer, and glow discharge spectroscopy and for identifying hardness profile, microhardness variations from surface to core of samples were recorded. Results showed that, thickness of compound layer of plastic mold steel AISI P20 was negligible. Moreover in ion nitriding of AISI P20, nitride were formed and grown in some preferred directions and upward diffusion of carbon and downward diffusion of nitrogen occurred during ion nitriding of AISI P20. XRD results showed that, ϵ-nitride is the dominant phase after plasma nitriding in all strategies. Furthermore, ion nitriding improved hardness of AISI P20 up to three times and as time and temperature increased, hardness and hardness depth of diffusion zone increased considerably.