Plasma Nitrided Specimens Research Articles

Formation of Plasma-Nitrided Barrier Layers Against Hydrogen Absorption and Diffusion in Pure Iron

Hydrogen embrittlement is a serious problem for steels such as high strength steels. Reducing hydrogen absorption into steels is required for the prevention of hydrogen embrittlement. In order to improve the hydrogen absorption resistance into steels, a nitriding treatment is one of the effective ways among surface modifications because nitriding may increase the overpotential for the hydrogen evolution reaction on the surface and decrease hydrogen diffusivity in nitrided layers. In this study, the phase structure in the nitrogen compound layers for the pure iron specimens was controlled by plasma nitriding with different types of plasma gas and gas composition. The influence of ε-Fe2-3N and γ’-Fe4N phases on hydrogen absorption into the inside of the pure iron matrix through the nitrided layers was evaluated. During the hydrogen permeation tests, the plasma-nitrided specimens showed small permeation current values compared to the as-polished specimen when it reached the steady state. Especially, hydrogen absorption and permeation for the specimen with the compound layer containing ε-Fe2-3N were extremely inhibited. Hydrogen absorption and permeation behaviors in the nitrided pure iron specimens were discussed in terms of the catalytic activity and hydrogen diffusivity.

High-Temperature Wear and Frictional Performance of Plasma-Nitrided AISI H13 Die Steel

Plasma nitriding, a surface treatment technique, is gaining popularity, as it is environment-friendly and offers superior mechanical properties. This research studied the wear and friction performance of AISI H13 die steel after plasma nitriding in a gas mixture of N2:H2 at 20:80, 50:50, and 80:20 (volume ratio) at a fixed time and temperature. This work aimed to analyze the sliding wear performance of the plasma-nitrided tool die steel in hot-forming operations at higher loads. Scanning electron microscopy/electron-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD) techniques were used to study the microstructures of the H13 die steel pins after plasma nitriding. Wear tests were performed on a high-temperature tribometer under uni-directional sliding and dry conditions using a high-temperature tribometer under a 50 N load at various operating temperatures ranging from 25 °C to 600 °C. The results show that the plasma-nitriding process with N2:H2 at 20:80 improved the wear behavior of H13 steel. The friction coefficients and wear volume losses for all the plasma-nitrided specimens were less than those of the untreated die steel.

Mapping the Accouterment Effects of Plasma Nitriding on AISI 316L in Biomedical Applications

The present study aimed to critique the corrosion resistance of plasma-nitrided films of AISI 316L stainless steel with regards to their biomedical applications. The plasma nitriding process improves austenitic stainless steel’s micro-hardness and corrosion resistance. Austenitic stainless steel was treated at a temperature of 470 °C for 12, 24, and 36 h, to observe the outcomes of plasma nitriding. The corresponding microstructure, microhardness, depth of the nitrided layer, and electrochemical parameters were systematically characterized. The corrosion resistance of the plasma-nitrided specimens was gauged using the weight loss method in simulated body fluids (Phosphate-buffered saline (PBS), saline water, and ringer solution) by static immersion for 9, 18, and 27 days. Optimization was catalogued using the Taguchi method L27 orthogonal array to determine the optimum combination of plasma nitriding time and immersion time in simulated body fluid. The material characterization showed that the corrosion resistance of the plasma-nitrided specimens improved with longer nitriding times by Tafel polarization curves. Microhardness was observed at 12, 24, and 36 h as 1060, 1150, and 1220 HV0.1. SEM, with an energy-dispersive X-ray analysis (EDS) used to characterize the surface before and after plasma nitriding testing. It was concluded that CrN, which precipitates during processing and contributes to the loss of chromium from the surrounding matrix and the onset of a corrosive environment, is the primary cause of this behaviour.

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.

Comparative study of plasma nitriding and plasma oxynitriding for optimal wear and corrosion resistance: Influences of gas composition

The phase structures, microstructures, wear properties, and corrosion resistance of plasma nitrided and plasma oxynitrided 4140 steel were studied. The plasma nitriding was conducted on a mixture of nitrogen and hydrogen at 520 °C. Additional oxygen in the form of plain air was added during oxynitriding treatment in a fixed ratio of nitrogen and hydrogen at 520 °C. The influences of gas composition on properties of the nitrided layer and oxynitrided layer were investigated using an optical microscope, scanning electron microscope, profilometer, X-ray diffractometer, X-ray photoelectron spectroscopy, Raman microscope, micro and nano-indenters, a tribometer, and potentiodynamic polarization testing. Results of tests demonstrate that an iron oxide layer with nanocrystalline Fe 2 – 3 N phase distributed forms on the surface of plasma oxynitrided specimens. Oxygen addition leads to different phase compositions, microstructures, and thicknesses of surface layer, which result in differences in mechanical, wear, and corrosion properties of specimens. The plasma oxynitrided specimen with optimal properties was obtained at a certain gas composition (N:H:O = 1:1:0.175), which shows better wear property and corrosion resistance than plasma nitrided specimen.

Tribological behaviour of alternative surface modifications for cold rolling mill rolls

The present work used a new methodology proposed in previous work to analyse the tribological behaviour of coatings/surface modifications with potential to replace the carcinogenic hard chrome still applied in the rolls employed in cold rolling mills. For that, three surface modifications (chromium plating, electroless NiP coating, and plasma nitriding) were carried out on specimens that were previously either ground or surface textured by electrical discharge texturing. The specimens with electroless NiP coating presented the lowest friction coefficients, while plasma nitrided specimens showed the highest. A tribolayer rich in Nickel, Phosphorus, and Oxygen was found for the samples with electroless NiP coating on the surfaces of both the specimens and the counter-bodies, which was apparently responsible for providing low and stable friction coefficient values, as well as reduced wear rates.

Tribological analysis of plasma nitrided SS310 steel material for different process parameters

Abstract Surface modifications have been applied to metal in order to improve the mechanical, chemical and physical properties, such as wear and hardness. Surface modification is found on the part surface of the automobile parts like turbochargers. Surface modification of stainless-steel alloy by plasma treatment is achieved using different gases such as air, nitrogen, argon and helium. The objective of plasma surface modification is to enhance the surface wettability, reduce surface friction, to reduce the wear rate and to avoid surface crack propagation on the components, to improve of surface properties against wear and other factors. In this project SS310 material is selected as the base material which is used for turbocharger. This SS310 material is machined and undergone plasma nitriding at a temperature of 450 °C for 4 h. The plasma nitrided specimens have undergone different tests such as roughness, wear and hardness From all the test results, it is concluded that the material undergone heat treated plasma nitriding exhibits better mechanical and tribological properties such as roughness, hardness and wear resistance for the automobile components. This brings better service life of mating components in a successful way.

Investigation of the Surface Properties and Wear Properties of AISI H11 Steel Treated by Auxiliary Heating Plasma Nitriding

This paper presents an auxiliary heating method to maintain a uniform specimen temperature and precisely control nitriding temperature during plasma nitriding. The surface properties and wear properties of AISI H11 steel treated by auxiliary heating plasma nitriding are investigated. Firstly, the specimens with different diffusion layers and different hardness levels are fabricated through changing the plasma nitriding temperature. Secondly, the surface properties of the plasma-nitrided H11 steel specimens are characterized by a scanning electron microscope (SEM), X-ray diffractometer, metallographic microscope and microhardness tester. The results show that the surface hardness of the plasma-nitrided specimen is almost twice as high as that of the untreated specimen. The thickness of diffusion layer increases with the increase of nitriding temperature. However, the surface hardness firstly increases and then decreases with the increase of the nitriding temperature. Finally, the wear properties of untreated and plasma-nitrided H11 steel specimens are investigated under different friction conditions. The results show that the plasma-nitriding method can significantly improve the wear resistance of AISI H11 steel. The friction coefficient fluctuations of the plasma-nitrided specimens are all lower than those of the untreated specimens. In addition, the wear rates of the plasma-nitrided specimens rise along with load, and reduce along with the sliding speed and friction temperature.

Improvement in Surface Properties of M50NiL Steel by Plasma Nitriding with Rare Earth Addition

The quenched M50NiL steel was plasma nitrided at 560 °C with and without rare earth (RE) addition. The effect of pure RE lanthanum (La) on the surface properties of plasma nitrided M50NiL steel was investigated using pin-on-disk tribometer. The treated surfaces were characterized using SEM equipped with EDS, XRD and microhardness tester. The results show that the presence of La obviously changes the surface morphologies and phase structures of the nitrided layers. The Fe4N phase appeared on the plasma nitrided surface is replaced by the LaFeO3 phase after introducing La into nitriding atmosphere. A suitable amount of La addition could accelerate the nitriding process by regulating the nitrogen concentration on the nitrided surface. The wear rates of plasma nitrided specimens are apparently lower than that of untreated one. The involvement of La could further reduce the wear rates of plasma nitrided specimens. The specimen plasma nitrided with La addition of 2.5 g demonstrates the best wear resistance with the wear rate of 3.01 ± 0.4 × 10−5 mm3/Nm. The transition of wear mode between adhesion and abrasion is mainly due to the differences in the phase structures and their proportion in the nitrided layers.

The effect of duplex surface treatment on erosion performance of QRO 90 Supreme steel

In this study, CrN and TiAlN thin films were deposited on plasma-nitrided QRO 90 Supreme hot work tool steel by physical vapor deposition process and analysed with regard to their erosion performance under hydro-abrasive erosion conditions. The as-received specimens were quenched to room temperature from 1050°C and tempered gradually at 605°C for 2 h and at 560°C for 4 h. These specimens were plasma-nitrided for 10 h at 500°C at a pressure of 250 Pa in a gas mixture of 80% N2 + 20% H2 and then coated with TiAlN or CrN coatings by cathode arc evaporation. The specimens were characterized by metallographic techniques, SEM, EDS and micro-hardness test. Plasma nitriding and duplex surface treatments significantly increased the hardness of the specimens and thus significantly reduced the erosion of the specimens. The hardnesses on the surface of plasma-nitrided, CrN-deposited and TiAlN-deposited QRO 90 steels were 1092 HV0.025, 2436 HV0.025 and 3578 HV0.025, respectively. TiAlN-coated specimens were about 17-fold harder than the as-received specimens and over 3-fold harder than the plasma-nitrided specimens. The erosion resistance of CrN-coated specimens was increased by a factor of 3.6 and 1.5 compared with that of the as-received and plasma-nitrided specimens, respectively. A brittle fracture phenomenon was observed on the eroded surface of the duplex-treated specimens while a ductile material removal was observed on the as-received and the tempered specimens. The plasma-nitrided specimens showed a mixed behaviour of ductility and brittleness.

Effect of gas mixture on tribological performance of plasma nitrided grey cast iron under dry and lubricated conditions

Grey cast iron is commonly utilized as an engineering material owing to its some properties such as its good machinability, ability to dampen vibrations, low-stress concentration, high thermal conductivity, good castability and low cost. Especially when this material is used as camshaft material, it can be exposed to wear because of its low wear properties. So, various surface treatment is applied to improve tribological properties of the grey cast iron. In this study, the grey cast irons were plasma nitrided under different gas mixture ratios for this aim. The structural, morphological and mechanical properties of plasma nitrided grey cast iron specimens were investigated by XRD, SEM, EDS and microhardness test. Also, tribological properties of unnitrided and nitrided specimens were characterized by tribotester under dry and lubricated conditions.

Effects of shot peening pre-treatment and plasma nitriding parameters on the structural, mechanical and tribological properties of AISI 4140 low-alloy steel

In recent years, hybrid surface treatments which include plasma nitriding combined with pre-shot peening operations have been proposed for the improvement of nitriding efficiency. The main objective of this study is to characterize the effects of dual process on the friction and wear behavior of metallic materials. For this purpose, AISI 4140 steel samples were shot peened at various densities of 16, 20 and 24 A. The pre-treated samples were plasma nitrided at a temperature of 500 °C for 1 and 4 h. The structural and mechanical properties of samples were analyzed by XRD, SEM and microhardness tester. Wear tests were performed under dry sliding conditions to determine the tribological properties of the samples. This study showed that the shot peening treatment formed finer grains, compressive residual stresses on the surface and increased the diffusion kinetics of the samples. The surface hardness and residual stresses increased with increasing shot peening density. It was evidence that the finer grains, increased dislocation density and surface defects increased the case depth obtained from plasma nitriding by enabling easier diffusion of nitrogen. The depth of the diffusion zones in shot peened plus plasma nitrided specimens was found almost two times thicker than that of the diffusion zones in specimens treated only by plasma nitriding. The highest surface hardness values were obtained from pre shot peened and plasma nitrided samples in consequence of the interactive effect from nitride phases/layers and increased surface compressive residual stress. As a result, pre-shot peened plus plasma nitrided samples exhibited higher wear resistance than specimens treated only by shoot peening and hybrid treating in glow a discharge atmosphere.

High-temperature tribological studies of plasma-nitrided tool steels

ABSTRACTDuring hot forging/forming operations, the die surface and near surface region is subjected to severe wear. The failure of dies originates from the surface region. In this research work, plasma nitriding was done on two hot forming tool steels namely AISI H11 and AISI H13. The aim is to develop a hard and wear resistance surface required for hot forming operations. The mechanical and microstructural properties of the developed nitrided layer were critically examined. Thereafter the tribological characteristics of the untreated and plasma-nitrided specimens were studied on high-temperature pin-on-disc tribometer under the constant load of 25 N, sliding speed 0.5 m s−1, sliding distance of 1500 m at different temperatures ranging from room temperature to 600°C. The results showed that the main wear mechanisms is predominantly adhesive at room temperatures and 200°C and a combination of adhesive and abrasive at elevated temperatures (400°C and 600°C).

Study of plasma nitriding and nitrocarburising of AISI 430F stainless steel for high hardness and corrosion resistance

ABSTRACTIn order to improve both the hardness and corrosion resistance properties of AISI 430F stainless steel, plasma nitriding (PN) and nitrocarburising processes were carried out at different temperatures ranging from 350 to 500°C for 4 h. After PN, the nitrided layer was found to be thicker compared to that obtained by plasma nitrocarburising process. There was an increase in microhardness values by a factor of six to seven compared to the plasma nitrided and nitrocarburised specimens respectively, treated at 500°C. The electrochemical corrosion behaviour of the plasma nitrided and nitrocarburised AISI 430F specimens show that the plasma nitrided and nitrocarburised specimens treated at 400°C for 4 h showed better corrosion resistance and higher surface hardness than the untreated AISI 430F stainless steel specimens. This is mainly attributed to the presence of nitrogen in the modified layer existing as a solid solution in the ferrite phase.This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).

Influence of simultaneous aging and plasma nitriding on fatigue performance of 17-4 PH stainless steel

This paper investigates fatigue behavior of precipitation hardenable 17-4 PH stainless steel after simultaneous aging and plasma nitriding. For this purpose, “solution treated”, “aged” and “simultaneous aged and nitrided” specimens were compared in terms of hardness, phase analysis, residual stress and fatigue strength. Hardness values of aged specimens were recorded during aging process to find the optimum condition in terms of time and temperature for plasma nitriding at which specimens can be simultaneously nitrided and aged. Plasma nitrided specimens were analyzed for residual stresses, and its effect on mechanical properties including hardness and fatigue strength. The specimens that were plasma nitrided at lower temperatures had the highest core hardness. Increasing the nitriding temperature/time caused an increase in residual stress and, consequently, a higher surface hardness. Both nitriding and aging processes improved fatigue life by more than 40%. Plasma nitriding imparts beneficial effect mainly during high stress fatigue while aging treatment is more effective on low stress fatigue properties. Specimens nitrided at 500°C for 5h experienced longer fatigue life for high stress conditions while specimen aged/nitrided at 400°C for 10h exhibited the highest fatigue strength.

Wear performance of different nitride-based coatings on plasma nitrided AISI M2 tool steel in dry and lubricated conditions

AISI M2 high speed tool steel is one of the widely used materials in the machining industry. The most common problems of this material are wearing of the cutting edge and adhesion of the work materials to the tool during the machining operations. To overcome these disadvantages, single and duplex surface treatments combining a diffusion process and a thin film ceramic coating are performed. In this study, various nitride-based coatings (TiN, TiCN, AlTiN and CrN) were deposited on untreated and plasma nitrided AISI M2 high speed tool steel specimens using cathodic arc physical vapour deposition (CAPVD) technique. The plasma nitriding treatment was performed in 50%N2−50%H2 gas mixture at 500°C for 2h. The influences of different surface treatments on structural properties of AISI M2 steel were investigated by means of field emission scanning electron microscope, X-ray diffractometer, focused ion beam milling system, microhardness tester and optical profilometer. The tribological properties of specimens were examined in dry and cutting fluid conditions by using reciprocating sliding wear test with Al2O3 ball as a counter material. According to tribological test results, the solely coating treatment was more effective in improvement of the wear resistance of AISI M2 high-speed tool steel rather than duplex treatment. The lowest worn volume was obtained from the solely CrN coated surface. Whereas under cutting fluid condition, solely TiN and TiCN coated surfaces showed higher wear resistance. It was also observed that the friction coefficients of all specimens tested in boron-containing cutting fluid were lower and quite stable compared with dry sliding condition.

Rolling Contact Fatigue Failure Mechanisms of Plasma-Nitrided Ductile Cast Iron

Rolling contact fatigue (RCF) of a nitrided ductile cast iron was investigated. Flat washers machined from a pearlitic ductile cast iron bar were quenched and tempered to maximum hardness, ground, polished and divided into four groups: (1) specimens tested as quenched and tempered; (2) specimens plasma-nitrided for 8 h at 400 °C; (3) specimens plasma-nitrided and submitted to a diffusion process for 16 h at 400 °C; and (4) specimens submitted to a second tempering for 24 h at 400 °C. Hardness profiles, phase analyses and residual stress measurements by x-ray diffraction, surface roughness and scanning electron microscopy were applied to characterize the surfaces at each step of this work. Ball-on-flat washer tests were conducted with a maximum contact pressure of 3.6 GPa, under flood lubrication with a SAE 90 API GL-5 oil at 50 °C. Test ending criterion was the occurrence of a spalling. Weibull analysis was used to characterize RCF’s lifetime data. Plasma-nitrided specimens exhibited a shorter RCF lifetime than those just quenched and tempered. The effects of nitriding on the mechanical properties and microstructure of the ductile cast iron are discussed in order to explain the shorter endurance of nitrided samples.

Hydrogen Entry into Pure Iron Treated By Plasma Nitriding

In order to prevent hydrogen embrittlement of steels, it is effective to decrease the amount of hydrogen entry into steel matrix under atmospheric corrosion environments. In this study, the nitrided layer was formed in the surface of pure iron by plasma nitriding to inhibit the hydrogen entry, and the hydrogen permeation tests were conducted to clarify the barrier effect of nitrided layer on the hydrogen entry into pure iron. Pure iron sheets of 1 mm thickness with 99.99 mass% purity were used as the specimens. The specimens were heat-treated at 1173 K for 18 ks and then furnace-cooled. The surfaces of the specimens were polished with diamond paste down to 1 μm. Plasma nitriding was performed in a nitrogen-hydrogen atmosphere composed of 75 % N2 and 25 % H2 for 3.6 ks at 673 K and at 600 Pa. The one side of the specimens was nitrided by masking another side. Figure 1a shows the cross-sectional image of the specimen etched with 3 % nital solution after the plasma nitriding. The layer with a different etching behavior from the matrix was observed in the surface region. The thickness of the surface layer was ca. 2.8 μm. Figure 1b shows the XRD patterns of the plasma-nitrided specimen. The peaks assigned to ε-Fe2-3N and γ ’-Fe4N were detected. The peaks of ε-Fe2-3N were larger than that of γ ’-Fe4N, suggesting that the surface layer was mainly composed of ε-Fe2-3N phase. In order to investigate the property of hydrogen entry in the surface of the nitrided specimen, the hydrogen permeation tests using the Devanathan-Stachurski cell1 were carried out. The hydrogen entry was conducted by galvanostatic polarization at −100 μA (i c) in deaerated boric-borate buffer solution with 0.01 M NaCl (pH 8.45) for 10.8 ks. The Pd-coated surface of the specimens in the hydrogen detection side was polarized at 0.2 V vs. SHE in deaerated 0.1 M NaOH solution. Figure 1c and 1d show time variation of the potential on the hydrogen entry side and the hydrogen permeation current density (i p), respectively. In the initial 30 s, the potential of both the untreated and the nitrided specimen drastically decreased to approximately the same value (ca. −0.75 V vs. SHE). In the case of the untreated specimen, the permeation current drastically increased to ca. 300 nAcm-2 in the period from 0.5 to 1.0 ks. After that, it gradually increased and reached to 450 nAcm-2 at 10.8 ks. On the other hand, the permeation current of the nitrided specimen slightly increased to 10 nAcm-2 in the period from 1.6 to 4.0 ks and stayed at ca. 10 nAcm-2 from 4.0 to 10.8 ks. The hydrogen permeation test revealed that the plasma nitriding treatment strongly inhibited the hydrogen entry into pure iron under the cathodic polarization. 1. M. A. V. Devanathan, and A. Stachurski, Proc. Roy. Soc. A, 270, 90 (1962). Figure 1

Fatigue crack growth analysis of plasma nitrided AISI 4140 low-alloy steel: Part 1-constant amplitude loading

The compact tension (CT) specimens manufactured from AISI 4140 steel were plasma nitrided at 400°C, 500°C and 600°C for 1 and 4h in a gas mixture of 50% N2 and 50% H2. CT specimens were subjected to fatigue crack growth under constant amplitude loading in order to analyze the effect of plasma nitriding on fatigue crack growth (FCG). The crack sizes of specimens were correctly detected by a digital image monitoring system. Also, the structural and mechanical properties of specimens were characterized by XRD, SEM, optical microscopy and 3D profilometer and microhardness tester. The structural and mechanical examinations showed that the surface hardness, layer thicknesses and surface residual stresses continuously increased with increasing plasma nitriding time and temperature. It was found that plasma nitriding improved the FCG life of the material due to the formation of compressive residual stresses and nitride layers in surface and near-surface regions. Additionally, the highest FCG increase rate was obtained from 500°C to 4h plasma nitrided specimen with respect to untreated specimen. The formation of compound layer and braunite layer constrained the continuous increase of FCG life because of increasing embrittlement and cracking tendency of nitride layers.

ステンレス鋼のスパッタエッチングにより形成した多機能微細突起物の圧縮強度におよぼすプラズマ窒化の影響

Argon ion sputter-etching of SUS420J2 martensitic stainless steel and SUS316 austenitic stainless steel were carried out to form fine protrusions on the specimen surface by using a radio-frequency magnetron sputter-apparatus. Plasma-nitriding was applied to the protrusions by using nitrogen gas of 0.53 Pa mixed with argon gas of 0.67 Pa at a power of 50 W for 1.8 ks. Micro-Vickers hardness tests on cone-shaped protrusions with diameter of about 20 μm formed on the SUS420J2 steel showed that the compressive strength of protrusion tip of the plasma-nitrided specimen is almost four times larger than that of the as-sputter-etched specimen. Nanoindentation tests on quasi-columnar protrusions with sizes smaller than 500 nm formed on the SUS316 steel showed not only much scatter of indentation force vs depth curves but also irregular changes of gradient of the curves. This means that an inhomogeneous contact of the indenter on the protrusions with different heights, sizes and spaces as well as a discontinuous deformation of protrusions occur with progress of indentation. Although the true compressive strength of one protrusion is not obtained directly by usual hardness tests, a measure of the deformation resistance of a group of protrusions can be obtained from the hardness that is extrapolated to zero indentation area on the indentation area vs hardness curve. The compressive resistance of the plasma-nitrided protrusions is almost six times as large as that of the as-sputter-etched ones.