Plasma Nitrided Samples Research Articles

Mössbauer spectroscopy study on the corrosion resistance of plasma nitrided ASTM F138 stainless steel in chloride solution

Plasma nitriding of ASTM F138 stainless steel samples has been carried out using dc glow discharge under 80% H 2–20% N 2 gas mixture, at 673 K, and 2, 4, and 7 h time intervals, in order to investigate the influence of treatment time on the microstructure and the corrosion resistance properties. The samples were characterized by scanning electron microscopy, glancing angle X-ray diffraction and conversion electron Mössbauer spectroscopy, besides electrochemical tests in NaCl aerated solution. A modified layer of about 6 μm was observed for all the nitrided samples, independent of nitriding time. The X-ray diffraction analysis shows broad γ N phase peaks, signifying a great degree of nitrogen supersaturation. Besides γ N, the Mössbauer spectroscopy results indicated the occurrence of γ′ and ε phases, as well as some other less important phases. Corrosion measurements demonstrate that the plasma nitriding time affects the corrosion resistance and the best performance is reached at 4 h treatment. It seems that the ε/γ′ fraction ratio plays an important role on the resistance corrosion. Additionally, the Mössbauer spectroscopy was decisive in this study, since it was able to identify and quantify the iron phases that influence the corrosion resistance of plasma nitrided ASTM F138 samples.

Effect of Plasma Nitriding Environment and Time on Plain Fatigue and Fretting Fatigue Behavior of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V fatigue test samples at 520°C in two environments (nitrogen and nitrogen–hydrogen mixture in a ratio of 3:1) for two time periods (4 and 18 h). Plain fatigue and fretting fatigue tests were conducted on unnitrided and plasma nitrided samples. Plasma nitriding degraded lives under both plain fatigue and fretting fatigue loadings. The samples nitrided in nitrogen exhibited superior lives compared with the samples nitrided in the nitrogen–hydrogen mixture, possibly due to the relatively higher hardness (and presumably lower toughness) of the nitrided layer of the samples nitrided in the nitrogen–hydrogen mixture environment. For those samples nitrided in the nitrogen–hydrogen mixture, those nitrided for 18 h exhibited superior lives compared with those nitrided for 4 h. This trend was observed for samples nitrided in nitrogen gas at lower stress levels only; the converse was true at higher stress levels of 550 MPa and 700 MPa under plain fatigue loading. However, under fretting fatigue loading, the plasma nitriding time did not influence the lives significantly.

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.

Plasma nitriding of 42CrMo low alloy steels at anodic or cathodic potentials

The nitriding of low alloy steel has been carried out at anodic potential in a space enclosed by an active screen that consists of two cylinders with different diameter. These two cylinders made up a hollow cathode in a discharge system. The difference in diameter of the two cylinders is about 8–10 mm to maintain strong discharge between them. They can also be heated rapidly to the required temperature for treatment. The sample to be nitrided was held at the same potential as that of the anode used in the discharge and heated through heat radiation from the hot cylinders and by electron bombardment. Electrons bombarded the surface of the sample even though the intensity of bombardment was low because of the anodic sheath. To illustrate the effect of the anodic potential on the nitriding a comparison was made between nitriding at anodic and cathodic potential (general plasma nitriding). The phase composition, the compound layer thickness and the surface topography of the nitrided layer, as well as its properties, were investigated using X-ray diffraction, scanning electron microscopy and microhardness tester. In particular, the corrosion properties of the untreated and plasma nitrided samples were evaluated using anodic polarization tests in 3.5% NaCl solution. The results showed that anodic plasma nitriding not only increased the surface hardness but also improved the corrosion resistance of the low alloy steel.

Novel plasma nitriding–oxidizing duplex treatment of AISI 316 austenitic stainless steel

In this work, plasma nitriding and plasma nitriding–oxidizing treatment have been performed on AISI 316 austenitic stainless steel. In order to evaluate its response to this treatment, their microstructures and wear resistance have been compared with conventional plasma nitrided. The treatment of plasma nitriding was performed at temperature of 450 °C for 5 h with gas mixture of N 2/H 2:1/3 whereas plasma nitriding–oxidizing was performed with the same parameters of plasma nitriding and temperature of 450 °C with gas mixture of O 2/H 2:1/5 for 15, 30 and 60 min. The structural, mechanical and tribological properties were analyzed using XRD, SEM, microhardness testing and pin-on-disk tribotesting. The results showed that oxidation treatment reduces wear resistance of plasma nitrided sample under high loads. Furthermore the tribological evaluation indicates that by increasing the oxidation time further reduction of wear resistance can be occurred. In addition, it was found that oxidation treatment after plasma nitriding provides an important improvement in the friction coefficient against a AISI 52100 steel pin and reduces surface roughness.

Influence of plasma nitriding on fretting wear behaviour of Ti–6Al–4V

Plasma nitriding was performed on Ti–6Al–4V samples at 520°C in two environments (pure nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 and 18h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using alumina ball counterbody. Plasma nitriding reduced the tangential force coefficient of Ti–6Al–4V. The samples nitrided for 4h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18h. The samples nitrided in nitrogen–hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in pure nitrogen. The samples plasma nitrided in nitrogen–hydrogen mixture for 4h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume and specific wear rate of the plasma nitrided samples were lower than those of the unnitrided samples. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume and specific wear rate at different loads.

Several plasma diffusion processes for improving wear properties of Ti6Al4V alloy

Different kinds of diffusion processes, plasma nitriding, oxidizing and oxynitriding as of a combination of other two, have been applied to Ti6Al4V alloy to evaluate the effect of treatment times (1 and 4 h) and temperatures (650 and 750 °C) on wear properties of the alloy. It was observed that a hard modified layer was produced on the surface of the alloy after each diffusion process. While TiN and Ti 2N phases form in the modified layer with plasma nitriding, mainly TiO 2 phase forms after plasma oxidizing treatment. The wear tests performed at different normal loads showed that all treated samples, except for nitrided and oxidized at 650 °C for 1 h, exhibited higher wear resistance than untreated Ti6Al4V alloy. The plasma nitrided samples showed adhesive wear. On the other hand, while the plasma oxidizing samples displayed adhesive wear at lower loads, wear mechanism changed to abrasive wear as the load increased because the oxide film which covers the surface was broken during the sliding at higher loads.

Comparison of Magnetron Deposited N‐Alloyed Stainless Steel Coatings and Low Temperature Plasma Nitrided Austenitic Stainless Steel

AbstractThis paper presents the results of a comparative scientific research concerning the properties of the S‐phase produced by plasma nitriding treatment and nitrogen alloyed austenitic stainless steel coatings deposited by a magnetron sputtering method assisted by a high voltage pulse discharge. The characteristics of the coatings (chemical composition, structure, and morphology) were evaluated by GDOES, XRD, and SEM investigations. Depending on the deposition parameters, the nitrogen content within the coating raised up to 31.5 at.‐%. At the same time, an increase in microhardness up to 1400 HV 0.1 was noticed. The corrosion tests were performed in Ringer's solution and the results were comparatively analyzed with plasma nitrided austenitic stainless steel samples considered as reference.

Comparison of conventional and active screen plasma nitriding of hard chromium electroplated steel

This paper considers the nitriding behavior of hard chromium electroplated steel by conventional plasma nitriding (CPN) and active screen plasma nitriding (ASPN) methods. Indentation test along the cross-section of the treated samples reveals that duplex treatment performed by two methods exhibits almost the same hardnesses. Furthermore, an increase in the time of plasma nitriding from 5 h to 10 h restores 30% of the hardness decline. Morphological studies show that surface particles formed on active screen plasma nitrided samples have orderly formed geometrical shapes while in conventional plasma nitriding they are in cauliflower shape. The reason for reaction between chromium and nitrogen seems to be the difference between thermal expansion coefficient of chromium oxide, chromium and steel substrate which results in partial breakdown of the oxide film. Moreover, the reducing of chromium oxide by hydrogen promotes the process. It looks as if nitriding treatment changes the corrosion behavior of the chromium coating from severe localized to uniform corrosion. Also active screen plasma nitriding treatment lowers the anodic dissolution 50–100 orders of magnitude which would be the result of full closure of surface microcracks.

Fretting wear behaviour of plasma nitrided Ti-6Al-4V fretted against unnitrided Ti-6Al-4V and alumina counterbodies

Ti-6Al-4V samples were plasma nitrided at 520°C in two environments (nitrogen and a mixture of nitrogen and hydrogen in the ratio of 3:1) for two different time periods (4 h and 18 h). Fretting wear tests were conducted on unnitrided and nitrided samples for 50,000 cycles using two counterbody materials (unnitrided Ti-6Al-4V and alumina). Gross slip prevailed at a normal load of 4.9 N while mixed stick-slip prevailed at 9.8 N. Tangential force coefficient values of plasma nitrided samples were lower than those of unnitrided samples. The tangential force coefficient nearly stabilised after thousand cycles in case of samples tested against Ti-6Al-4V counterbody. On the other hand, it showed a continuously increasing trend in case of specimens tested against alumina counterbody. The samples nitrided for 4 h exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided for 18 h. The samples nitrided in nitrogen-hydrogen mixture environment exhibited higher hardness and lower tangential force coefficient compared to the specimens nitrided in nitrogen. The samples plasma nitrided in nitrogen-hydrogen mixture for 4 h exhibited the highest hardness and the lowest tangential force coefficient. The wear volume of the plasma nitrided samples was lower than that of the unnitrided samples. Owing to tribochemical reactions, the wear volume of unnitrided and nitrided samples fretted against alumina ball was higher than that of the samples fretted against Ti-6Al-4V. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume at different loads.

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

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

Effect of nitrogen incorporation on 1/f noise performance of metal-oxide-semiconductor field effect transistors with HfSiON dielectric

Nitrided hafnium silicate is the leading candidate for possible replacement of SiON as a gate dielectric. 1/f noise characteristics of plasma and thermally nitrided Hf-based high-dielectric constant (high-k) gate dielectrics were investigated. Plasma nitrided samples showed less noise than thermally nitrided samples. The mobility fluctuation component of 1/f noise was found to show a strong process dependence, specifically on the nitridation technique. Increase in the number of Coulomb scattering sites due to the additional Si–N bonds near the high-k/Si interface is suggested as the reason for this dependence. This work represents the first investigation on the effect of different nitridation methodologies on low-frequency noise mechanisms in ultrathin (∼2 nm) Hf-based high-k nMOSFET (metal-oxide-semiconductor field effect transistor).

Plain fatigue and fretting fatigue behaviour of plasma nitrided Ti-6Al-4V

Fatigue tests with and without fretting against unnitrided fretting pads were conducted on unnitrided and plasma nitrided Ti-6Al-4V samples. Plasma nitrided samples exhibited higher surface hardness, higher surface compressive residual stress, lower surface roughness and reduced friction force compared with the unnitrided specimens. Plasma nitriding enhanced the lives of Ti-6Al-4V specimens under both plain fatigue and fretting fatigue loadings. This was explained in terms of the differences in surface hardness, surface residual stress, surface roughness and friction force between the unnitrided and nitrided samples.

Improvement of corrosion and wear resistances of AISI 420 martensitic stainless steel using plasma nitriding at low temperature

The influence of low temperature plasma nitriding on the wear and corrosion resistance of AISI 420 martensitic stainless steel was investigated. Plasma nitriding experiments were carried out with DC-pulsed plasma in 25% N 2 + 75% H 2 atmosphere at 350 °C, 450 °C and 550 °C for 15 h. The composition, microstructure and hardness of the nitrided samples were examined. The wear resistances of plasma nitrided samples were determined with a ball-on-disc wear tester. The corrosion behaviors of plasma nitrided AISI420 stainless steel were evaluated using anodic polarization tests and salt fog spray tests in the simulated industrial environment. The results show that plasma nitriding produces a relatively thick nitrided layer consisting of a compound layer and an adjacent nitrogen diffusion layer on the AISI 420 stainless steel surface. Plasma nitriding not only increases the surface hardness but also improves the wear resistance of the martensitic stainless steel. Furthermore, the anti-wear property of the steel nitrided at 350 °C is much more excellent than that at 550 °C. In addition, the corrosion resistance of AISI420 martensitic stainless steel is considerably improved by 350 °C low temperature plasma nitriding. The improved corrosion resistance is considered to be related to the combined effect of the solid solution of Cr and the high chemical stable phases of ɛ-Fe 3N and α N formed on the martensitic stainless steel surface during 350 °C low temperature plasma nitriding. However, plasma nitriding carried out at 450 °C or 550 °C reduces the corrosion resistance of samples, because of the formation of CrN and leading to the depletion of Cr in the solid solution phase of the nitrided layer.

Langmuir probe characterization of nitrogen plasma for surface nitriding of AISI-4140 steel

Abstract Langmuir probe measurements are carried out to characterize a 50 Hz ac generated nitrogen plasma as a function of filling pressure (2–5 mbar) under constant power level. Plasma nitriding of AISI-4140 steel is executed for different time durations (2, 6, 10, and 14 h) at filling pressures of 2 and 3 mbar, keeping the input power at 100 W and substrate temperature at 300 °C. The plasma nitrided samples are characterized for their surface properties by using X-ray diffractometer (XRD) and Vickers microhardness tester. Results demonstrate the formation of nitrogen infused ferrite phase (α N -Fe) owing to the inclusion of nitrogen in the original iron lattice as interstitial solid solution. Significant increase in the surface hardness is observed when samples are treated for 14 h at a filling pressure of 2 mbar. The rapid decrease in the hardness value with increase in imposed load suggests the formation of the skinny modified layer.

Improvement of the slurry erosion resistance of an austenitic stainless steel with combinations of surface treatments: Nitriding and TiN coating

The combination of different surface treatments for improving the erosion resistance of an AISI 304 stainless steel was studied. Six kinds of sample conditions were tested in a slurry composed of distilled water and SiC particles: High temperature gas nitriding (HTGN), low temperature plasma nitriding (expanded austenite), high temperature gas nitriding followed by a PVD-TiN coating, low temperature plasma nitriding followed by a PVD-TiN coating as well as PVD-TiN coated and uncoated samples in the solubilized condition. The erosion tests were performed during 6 h in a jet-like device with a normal angle of incidence and an impact velocity of 8.0 m/s. Wear rates were assessed by accumulated mass loss measurements and through analysis of scanning electron microscopy images of the worn surfaces. The results were related to the microstructure and hardness of the surface to establish a ranking of the different surface treatments. After the first few minutes of testing cutting of the surface occurred in the solubilized, in the HTGN and in the low temperature plasma nitrided AISI 304 samples, whereas TiN coated samples did not show any cutting marks, although some indentation marks could be observed. The TiN coated samples showed wear resistances one order of magnitude greater than the solubilized, HTGN and low plasma nitrided samples.

Reliability degradation of HfSiO gate dielectric layers: influence of nitridation

In this work we investigate the effect of nitridation on HfSiO’s degradation under positive constant voltage stress. A comparison between decoupled plasma nitridation, annealing in NH 3 and no nitridation is made. Stress induced leakage current dominates a wear-out phase before the final hard breakdown, regardless of nitridation. However, this progressive breakdown phase is more pronounced in NH 3 annealed samples resulting in 60 times gate current increase after 10 years, 3 times higher compared to decoupled plasma nitridation and no nitridation. On the other hand, a shorter wear out phase is responsible for faster breakdown in plasma nitrided samples.

Effect of plasma nitriding of electroplated chromium coatings on the corrosion protection C45 mild steel

Plasma nitriding is a promising posttreatment technique to create a nitride layer on electroplated chromium coatings for improving their corrosion resistance. In the present study, the effects of plasma nitriding on the corrosion properties of electroplated chromium/C45 mild steel were investigated using electrochemical characterization. The chromium plated samples were nitrided using a pulsed direct current glow discharge in an NH 3 atmosphere. The polarization curve measurement results showed that the plasma nitrided samples exhibited more positive corrosion potentials ( E corr), smaller corrosion currents ( I corr), and evident passivation when compared with unnitrided chromium plating/substrate system. The high value of E corr and low value of I corr imply an improvement of the corrosion resistance of the coating/substrate system after plasma nitriding.

The Corrosion Behaviour of Austenitic 316L Stainless Steel After Low-T Plasma Nitridation in the Physiological Solutions

We studied the corrosion properties of low-T plasma-nitrided 316L austenitic stainless steel in the physiological solutions. The plasma nitridation was performed at different gas compositions of N2–H2 mixture at temperatures from 400 to 5008C for 1 h. The potentiodynamic anodic polarization measurements were performed in the physiological saline and Hank’s solutions at the room temperature. The corrosion resistance is dependent on the microstructure of plasma-nitrided austenitic stainless steel and the chemical composition of physiological solution. The pitting potential tends to increase without CrN precipitation, otherwise the pits are clearly seen on the plasma-nitrided samples. The S-phase formation in the microstructure improves the corrosion resistance.

A comparative study of single and duplex treatment of martensitic AISI 420 stainless steel using plasma nitriding and plasma nitriding-plus-nitrogen ion implantation techniques

Martensitic AISI 420 is a high chromium mold steel which is suitable for tools for molding corrosive plastics. In this study, micro-pulsed plasma nitriding and plasma nitriding + nitrogen ion implantation techniques have been used to improve the surface hardness and tribological properties of AISI 420 substrates. Firstly polished-AISI 420 samples are nitrided at 530 °C for 15 h at a pressure of 10 mbar. Then nitrided samples are implanted with nitrogen ions to a dose of 2 × 10 17 ions/cm 2. Mechanical characterization of both of the modified and unmodified samples has been carried out by means of nano-hardness, wear resistance, friction coefficient and surface roughness measurements. It is found that the nano-hardness, wear resistance, friction coefficient and surface roughness values improve 1.6, 3.5, 1.4 and 10 times for plasma nitrided samples, and 2.0, 4.6, 1.1 and 9 times for plasma nitrided-plus-N + ion implanted samples, respectively, in comparison with unmodified AISI 420 samples. Both the plasma nitriding process and the plasma nitriding-plus-N + ion implantation treatment sample results are also compared. The improvement of the samples modified using nitriding-plus-N + ion implantation process is found to be better than that of samples modified by the nitriding process.