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Purposes 38CrMoAl steel is often used as pistons in a hydraulic pump, its surface performance is especially important for long-life safe working. Wear is the main failure mode of pistons in a hydraulic pump. With surface strengthening treatment, it is able to break through its performance limit and realize high performance and reliable operation of a hydraulic pump. Methods In this work, the pattern and performance on the surface of 38CrMoAl steel has been regulated by a duplex treatment of surface texturing (ST) and active screen plasma nitriding (ASPN), aiming to achieve strengthening on its surface. Dimple texture with different shapes were first prepared on 38CrMoAl steel surface by laser processing technology. 38CrMoAl steel samples with and without textured surface have been treated by ASPN. A ball-on-disc friction and wear testing machine was employed to investigate the effect of surface texture-active screen plasma nitriding duplex treatment on the tribological behavior of 38CrMoAl steel. Findings The results show that ASPN layer is mainly built up by the phases of ε-Fe2-3N, γ′-Fe4N and CrN. The ASPN layer is compact, and free of obvious cracks and holes. Meanwhile, it is found that the uniform and continuous ASPN layer consists of a white bright layer and a diffusion layer. The hardness across surface to the inside of the ASPN layer has demonstrated a gradient distribution, where the highest hardness value is detected on the surface, and the hardness decreases as the distance from the surface increases. According to the dry sliding friction results of 38CrMoAl steel related samples against Al2O3 balls, the coefficients of friction of 38CrMoAl steel and ST＋ASPN-38CrMoAl steel are 0.40 and 0.36, respectively. The ST＋ASPN-38CrMoAl steel presents a 92.5% reduction in mass loss, as compared with 38CrMoAl steel. It can be concluded that surface texturing-active screen plasma nitriding duplex treatment endows the working surface of 38CrMoAl steel with enhanced tribological performance.

Laser powder bed fusion (LPBF) is capable to process complex flow field structures on 316L stainless steel (316L SS) bipolar plates, which is promising to improve the performance of proton exchange membrane fuel cell (PEMFC). However, insufficient corrosion resistance and relatively high interfacial contact resistance (ICR) hinder the widespread of LPBF-processed 316L SS bipolar plates. In this work, active screen plasma nitriding (ASPN) was used to modify 316L SSs fabricated by the LPBF process and forging, respectively. Results showed that the nitrided layer of LPBF-processed 316L SS (2000 mm/s, 300 W) exhibited the highest surface nitrogen concentration, thickest nitrided layer and highest average hardness. The ICR values decreased significantly after ASPN treatment. The corrosion current of nitrided LPBF-processed 316L SS (2000 mm/s, 300 W) was much lower than that of the nitrided forged 316L SS. By comparing multiscale microstructures between LPBF-processed and forged 316L SS, the ASPN mechanism of LPBF-processed 316L SS was proposed.

The plasma nitriding edge effect phenomenon is characteristic of parts with sharp edges. The intersection for the discharge of negative light of the two adjacent faces causes the apparition of this effect. In some cases, this effect causes disturbance to the general process. In this work, a sample with different angles of 30°, 60°, and 90° was analyzed. The sample was subjected to ion nitriding with and without the cathode grid to highlight the reduction of the edge effect on the non-uniformity appearing on the edges and corners of the parts. The effect of the active screen was also analyzed by hardness measurements in the area of the nitride edges and by SEM and EDX analyses in the mentioned areas. Additionally, the influence of active screens was studied by nanoindentation and scratch tests and by measuring the contact angle of coolants and liquid lubricants on the nitride surfaces with both methods. [ABSTRACT FROM AUTHOR]

Active screen plasma nitriding (ASPN) is a nitriding method that avoids the edge effects and arcing that occur during conventional direct current plasma nitriding (DCPN). Furthermore, applying voltage to a sample during ASPN allows the nitriding rate to be increased (S-DCPN). While steel is the predominant screen material, there are few reports of non-ferrous material screens. Therefore, in this study, we investigated the effect of a Ni screen on ASPN and S-DCPN. Low carbon steel S15C was treated by ASPN and S-DCPN using a Ni screen. A steel plate cold commercial (SPCC) screen was also prepared for comparison. Plasma nitriding was performed at 773K for 240 min under an atmosphere of 75% N2 + 25% H2 at a gas pressure of 200 Pa. After the nitriding treatment, X-ray diffraction (XRD), glow discharge optical emission spectrometry (GD-OES), cross-sectional microstructure observation, surface microstructure observation, Vickers hardness test, and corrosion test were performed. As a result, when the Ni screen was used for S15C steel nitriding, more nitrogen atoms diffused into the sample than that when the SPCC screen was used; furthermore, nickel atoms diffused within the samples treated by both ASPN and S-DCPN using the Ni screen. ASPN-treated samples had less surface hardness and were higher corrosion resistance when prepared using the Ni screen than the SPCC screen. S-DCPN-treated samples had greater surface hardness and were less corrosion resistance when prepared using the Ni screen than the SPCC screen. [ABSTRACT FROM AUTHOR]

Effect of active screen plasma nitriding (ASPN) on microstructure, hardness, and wear loss of 347H austenitic stainless steel (AuSS) was studied at various processing parameters. Scanning electron microscopy, x-ray diffraction (XRD), hardness, and wear tests were performed on samples. The XRD analysis showed the presence of S-phase (γN-expanded austenite) in samples nitrided at 350 °C and 400 °C. In contrast, samples nitrided at higher temperatures ranging from 450 to 550 °C showed the presence of various types of nitride phases in the nitrogen-enriched layer. The case depth and mass of nitrided samples increased with the increase in nitriding temperatures owing to the increase in diffusivity of nitrogen at a higher temperature. The wear loss of samples nitrided at higher temperatures was lower than those nitrided at lower temperatures due to the formation of a higher amount of hard nitride phase(s) in the nitrogen-enriched layer at temperature ≥ 450 °C. [ABSTRACT FROM AUTHOR]

Active screen plasma nitriding (ASPN) is a nitriding method that avoids the edge effects and arcing that occur during conventional direct current plasma nitriding (DCPN). Furthermore, applying voltage to a sample during ASPN allows the nitriding rate to be increased (S–DCPN). While steel is the predominant screen material, there are few reports of non–ferrous material screens. Therefore, in this study, we investigated the effect of a Ni screen on ASPN and S–DCPN. Low carbon steel S15C was treated by ASPN and S–DCPN using a Ni screen. A steel plate cold commercial (SPCC) screen was also prepared for comparison. Plasma nitriding was performed at 773 K for 240 min under an atmosphere of 75％ N2 + 25％ H2 at a gas pressure of 200 Pa. After the nitriding treatment, X–ray diffraction (XRD), glow discharge optical emission spectrometry (GD–OES), cross–sectional microstructure observation, surface microstructure observation, Vickers hardness test, and corrosion test were performed. As a result, when the Ni screen was used for S15C steel nitriding, more nitrogen atoms diffused into the sample than that when the SPCC screen was used; furthermore, nickel atoms diffused within the samples treated by both ASPN and S–DCPN using the Ni screen. ASPN–treated samples had less surface hardness and were higher corrosion resistance when prepared using the Ni screen than the SPCC screen. S–DCPN–treated samples had greater surface hardness and were less corrosion resistance when prepared using the Ni screen than the SPCC screen. [ABSTRACT FROM AUTHOR]

Active screen plasma nitriding (ASPN) has recently emerged as an alternative nitriding technology with the potential to eliminate problems such as edge effect, arcing, and hollow cathode effects, associated with conventional direct current plasma nitriding technology. Amorphous hydrogenated carbon (a-C:H) is a thin film characterized by high hardness, a low friction coefficient, and superior wear resistance. However, the high residual stress of the a-C:H leads to poor adhesion between the a-C:H film and substrate. This study's objective was to investigate the properties of samples obtained by a duplex treatment (i.e., ASPN and a-C:H coating) of SUS304 austenitic stainless steel. The ASPN treatment was performed in 25% N2 + 75% H2 atmosphere for 5 h at 673 K under 600 Pa. An a-C:H film was coated using RF plasma-enhanced chemical vapor deposition in the presence of methane for 90 min. The results indicated that an a-C:H film with an S-phase interlayer formed after the duplex treatment of ASPN and a-C:H coating. Moreover, this treatment improved the adhesion and wear properties of the resulting sample.

In order to investigate the effect of the screen hole state of the active screen plasma nitriding (ASPN) process using Ti screen, low carbon steel S15C was treated by ASPN treatment and DC plasma nitriding treatment (S-DCPN) using the Ti screen with the hole diameter of Φ5 mm, 10 mm, and 20mm and the open area ratio of 0%, 15%, 35%, and 55%. Plasma nitriding was performed at 873K for 180 min at a gas pressure of 300 Pa under an atmosphere of 75% N2 + 25% H2. After the nitriding treatment, X--ray diffraction (XRD), surface microstructure observation, cross--section microstructure observation, wear test, Vickers hardness test, glow discharge optical emission spectrometry (GD--OES), and corrosion test were performed. As a result, the wear resistance of the ASPN--treated samples was improved under the condition that the deposit particles were small and the deposit layer was thick. In the cross--sectional microstructure of the S--DCPN--treated samples, a compound layer composed of iron nitrides and a diffusion layer in which γ'--Fe4N was precipitated by nitrogen diffusion were confirmed. The surface compound layer of iron nitrides was not formed when a screen with a hole size of 20mm and open area ratio of 55% was used. The results of SEM--EDX also confirmed the diffusion of titanium by S--DCPN treatment using a Ti screen. [ABSTRACT FROM AUTHOR]

The effects of screen height and bias voltage on the active screen plasma nitriding (ASPN) of Ti-6Al-4V titanium alloy were investigated in this paper. Before nitriding, the Ti-6Al-4V alloy was pretreated by shot peening to allow the ASPN performed at a low temperature of 500 °C. The ASPN process variables concerned in this paper included screen height (20 and 100 mm) and bias voltage (0, 400 and 1100 V). The results show that the increase in active screen height effectively increased the yield of nitride particles transferred to the specimen surface by expanding the screen sputtering area and promoted the thickening of the nitrided layer. When the bias voltage increased from 0 V to 1100 V, the nitrided layer thickness and surface hardness of the nitrided Ti-6Al-4V showed a tendency of increasing first and then decreasing. Among the three selected bias voltages (0 V, 400 V, 1100 V), the thickest and hardest nitrided layer was obtained at 400 V, which balanced better between the deposition of nitride particles and the sputtering thinning of the nitrided layer. Meanwhile, the thickness and hardness of the nitrided layer on the shot-peened Ti-6Al-4V specimens were greatly improved compared to the original specimen. The thickest (5.30 μm) and hardest (1672 HV) nitrided layer was obtained on the shot-peened specimen at ASPN 500 °C–20 h with a bias voltage of 400 V and a screen height of 100 mm. • A high active screen increased the thickness of the ASPN nitrided layer on Ti-6Al-4V alloy. • The increase in screen height expanded the sputtering area of the screen and increased the yield of nitride particles. • Among the three bias voltages (0 V, 400 V, 1100 V), the thickest and hardest nitrided layer was obtained at 400 V. • The bias of 400 V balanced better between the deposition of nitride particles and the sputtering of the nitrided layer. [ABSTRACT FROM AUTHOR]

Several process variants of plasma nitriding can be distinguished depending on the location of the voltage introduction. The aim of this study is to compare three different variants of plasma nitriding (DC plasma nitriding, active screen plasma nitriding, and active screening process with bias voltage application) extended by the study of the coverage of active screen on C45E unalloyed steel, using two different N2-H2 gas mixtures. The thickness of the compound layer was measured using a scanning electron microscope, the phase analysis was performed by an x-ray diffractometer, and the nitrogen contents were analyzed by glow discharge optical electron spectroscopy. The results showed that the layer thickness and the surface hardness were higher by using active screen-biased plasma nitriding with high N2 content gas mixture. Besides, the lid of the active screen did not influence significantly the chemical composition of the compound layer. [ABSTRACT FROM AUTHOR]

Two grades of duplex stainless steel, SAF 2205 and SAF 2507, were nitrided using an active screen plasma process carried out at 380 °C for 10 h and were characterized in terms of microstructure and hardness. Wear resistance was assessed by means of linear scratch tests, using loads below and above the critical load. Potentiodynamic polarization was used to analyze corrosion behavior in 0.6 M NaCl solution. X-ray diffractometry showed expanded austenite formation in all nitrided samples. The super duplex steel SAF 2507 showed much better scratch resistance, with low friction coefficient and greater toughness, as judged by the pattern of superficial cracks when it was tested above the critical load. The corrosion behavior of steels was also different, mainly in the active region, and nitriding had a more beneficial effect upon SAF 2507. The potential relative to the transpassive region was practically unaffected by the nitriding. [ABSTRACT FROM AUTHOR]

Abstract This study investigated the effect of nitriding time and temperature on the mechanical properties of the composite AlN/Fe 2-3 N coating deposited on the pure aluminium substrate using the novel Active Screen Plasma Nitriding (ASPN) method. ASPN treatment was performed for 2, 5, 10, 15 h at temperatures of 450,500, and 550 °C and Conventional Plasma Nitriding (CPN) treatment was carried out for 5 h at 500 °C. All treatments were performed at the 10 KHz frequency with 80% duty cycle on the Al1050 substrate under 20%H 2 +80%N 2 atmosphere. Phase and microstructure studies were performed using, respectively, the grazing incidence x-ray diffraction (GIXRD) system and the field emission - scanning electron microscopy (FE-SEM) system equipped with energy-dispersive spectroscopy (EDS) analyzer. The mechanical strength of the coating was evaluated by the roughness, nano-hardness, nano-scratch, and adhesion strength tests performed on coated and uncoated specimens. According to the results, the uncoated Al1050 specimen, the CPN-treated specimen, and the ASPN-treated specimen had a mean nano-hardness of 0.7 ± 0.1 GPa, 10.9 ± 0.6 GPa, and 9.6 ± 0.5 GPa, respectively. It was also found that the single-phase AlN coating has a better adhesion strength and scratch strength (L C3 = 12 N) than the composite AlN/Fe 2-3 N coating (L C3 = 10 N). Examination of scratch mechanisms in hard AlN and AlN + Fe 2-3 N coatings deposited on a soft aluminium substrate showed that the failures in these coatings are due to tensile-type Hertzian cracks. However, as the load increases, the substrate undergoes increasing deformation and failures shift to chipping and interfacial spallation. Graphical abstract Image 1 Highlights • Unlike CPN with only AlN phase as coating ASPN is with AlN and Fe 2-3 N complex. • The nano-hardness increased with the increase of treatment temperature and time. • Single-phase AlN get higher Adhesion/scratch strength rather than composite one. • Failures in nitride coatings is tensile-type Hertzian and forward chevron cracks. • In greater loads, chipping and interfacial spallation become main key failure cause. [ABSTRACT FROM AUTHOR]

Abstract Active screen plasma nitriding (ASPN) was performed on tempered 42CrMo4 low alloy steel samples. The effects of two technological parameters, namely 1) the hole size of the screen and 2) the open area ratio were investigated on the properties of the developed nitride layer. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and Vickers microhardness testing were used for the characterization of the surface. The thickness of the nitride layer, the microhardness and the length of the nitride diffusion zone and surface areal parameters like surface roughness, skewness, grain diameter and area were measured and correlated with the screen hole size and open area ratio. It was found that these two major technological parameters influence different aspects of the developed nitride layer. The layer thickness and surface skewness (connected to either a balanced surface with zero skewness or the appearance of hill-like complex structures with positive skewness) is more sensitive to the open area ratio, while the surface roughness is primarily a function of the hole size. The maximum surface hardness, the length of the nitride diffusion zone or the size (diameter and surface area) of the nitride grains did not show a strong correlation with either of these two parameters. [ABSTRACT FROM AUTHOR]

Abstract Plasma nitrocarburizing based on active screen technology using a carbon-fiber reinforced carbon active screen was applied in an industrial-scale unit for thermochemical surface treatment of austenitic stainless steel. This concept is based on the use of a solid-carbon-source for the generation of highly reactive process gases directly in the active screen plasma. In this work, plasma nitrocarburizing of AISI 316L stainless steel was performed by means of the variation of the precursor gases H 2 and N 2 in the range of 0% N 2 up to 100% N 2 without the use of any additional carbon bearing gas. For a set of H 2 -N 2 gas mixtures, the resulting reaction gas was monitored using infrared laser absorption spectroscopy (IRLAS). The four main stable species HCN, CH 4 , NH 3 and C 2 H 2 were detected. A detailed analysis of the surface microstructure resulting for each specific H 2 -N 2 precursor gas mixture was performed. This included glow discharge optical emission spectroscopy (GDOES), optical microscopy, micro hardness measurements, as well as X-ray diffraction analysis. The concentrations of hydrocarbons CH 4 and C 2 H 2 were most abundant in case of pure hydrogen plasma, and a carbon-expanded austenite layer with hardness values up to 600 HK0.01 and smooth hardness gradient resulted. The admixture of N 2 to the precursor gas significantly increased the concentrations of HCN and NH 3. Due to this, a duplex structure of nitrogen-expanded austenite γ N and carbon-expanded austenite γ C formed. With increasing content of N 2 up to 50% in the precursor gas, the resulting layer thickness increased and the hardness reached values up to 1300 HK0.01. At strong nitrogen excess in the precursor gas, the nitrogen concentration in the expanded austenite significantly increased, the Fe 2–3 (N, C) phase was formed, and simultaneously the layer thickness decreased. Structure and properties of the expanded austenite layer significantly changed by only varying the H 2 -N 2 ratio of the precursor gas mixture. Highlights • Plasma nitrocarburizing with carbon fiber reinforced carbon as solid carbon source. • Interaction of H 2 -N 2 plasma and carbon generates highly reactive species in-situ. • Reactive species provide surface activation, nitrogen and carbon uptake into steel. • H 2 -N 2 ratio variation in feed gas significantly effects N- and C-gradients in layer. • Infrared laser absorption spectroscopy for reaction gas monitoring [ABSTRACT FROM AUTHOR]

Low-temperature active-screen plasma nitriding (ASPN) was applied in this study to improve the bending rigidity and corrosion resistance of a small-diameter thin pipe composed of austenitic stainless steel (SUS 304). The inner and outer diameters of the pipe were ϕ0.3 and ϕ0.4 mm, respectively, and the pipe length was 50 mm. The jig temperature was measured using a thermocouple and was adopted as the nitriding temperature because measuring the temperature of a small-diameter pipe is difficult. The nitriding temperature was varied from 578 to 638 K to investigate the effect of temperature on the nitriding layer and mechanical property. The nitriding layer thickness increased with an increase in nitriding temperature, reaching 15 μm at 638 K. The existence of expanded austenite (S phase) in this nitriding layer was revealed using the X-ray diffraction pattern. Moreover, the surface hardness increased with the nitriding temperature and took a maximum value of 1100 HV above 598 K. The bending load increased with an increase in the nitriding temperature in relation to the thicker nitriding layer and increased surface hardness. The nitrided samples did not corrode near the center, and corrosion was noted only near the tip at high nitriding temperatures of 618 and 638 K in a salt spray test. These results indicated that the bending rigidity of the small-diameter thin pipe composed of austenitic stainless steel was successfully improved using low-temperature ASPN while ensuring corrosion resistance.

The paper presents the structural characterization of γ′-Fe4N nitrides produced by active screen plasma nitriding (ASPN) processes. Experiments were performed on the Fe-Armco model material at 693, 773, and 853 K for 6 h. Investigation of the properties of the substrate was realized using scanning electron microscopy (SEM, SEM–EBSD/Kikuchi lines), energy-filtered transmission electron microscopy (TEM-EFTEM), X-ray diffraction (GID, grazing incidence diffraction, micro-XRD), and secondary ion mass spectroscopy (SIMS). Results have confirmed that the γ′-Fe4N nitrides’ structure and morphology depend considerably on the nitriding process’s plasma conditions and cooling rate. In addition to that, γ′-Fe4N nitrides’ formation can be correlated with the surface layer saturation mechanism and recombination effect. It has been shown that the γ′-Fe4N structure depends considerably on several phenomena that occur in the diffusive layer (e.g., top layer decomposition, nitrogen, and carbon atoms’ migration). Our research proves that the nitrogen concentration gradient is a driving force of nitrogen migration atoms during the recombination of γ′-Fe4N nitrides. Finally, realized processes have allowed us to optimize active screen plasma nitriding to produce a surface layer of fine nitrides.

High-entropy alloys (HEAs) were fabricated by powder metallurgy using gas-atomized powder and spark plasma sintering (SPS) followed by surface modification (plasma nitriding) of the sintered sample. Plasma nitriding forms nitride and induces solid-soluting of N; it enables the diffusion of N atoms by removing the passive film formed on the surface of alloys such as stainless steel, Al alloys, and Ti alloys, via the sputtering of cations during glow discharge. Therefore, plasma nitriding has the potential to process HEAs that contain strong oxidizing elements such as Cr, Al, and Ti. In this work, a sintered CoCrFeMnNi HEA was plasma-nitrided and its properties were subsequently evaluated. A uniform microstructure without segregation was obtained in the SPS sample, and its hardness and wear resistance were found to have improved. Analysis of the sample surface after nitriding revealed that an expanded face-centered cubic phase formed on the surface plasma-nitrided at 673 K and that a CrN phase formed on the surface plasma-nitrided at temperatures greater than 723 K. The surface hardness of the plasma-nitrided sample was 1200 HV or greater, and the wear resistance and pitting corrosion resistance were improved compared with those of the untreated sample.

Abstract Stainless steels, especially the austenitic grades, present a good corrosion resistance but poor mechanical properties. Nitriding can increase the surface hardness but typically at the expense of corrosion resistance. Besides, nitriding of inner surfaces is not straight forward, as control of the plasma there is challenging. This work has focused on the development of active screen plasma nitriding processes of inner geometries of the widely used AISI 316L austenitic stainless steel, with preservation of the corrosion resistance. The structure and composition of the nitrided surfaces were studied and corrosion resistance of the inner surfaces assessed. As a result of the study, a relation has been established between plasma treatment parameters, geometrical features and the corrosion resistance. Additionally, electro-tribological studies have been performed. It has been observed that wear resistance improved and that ECR (Electrical Contact Resistance) is a good indicator of the wear phenomena occurring along the test and potentially could be a useful and simple monitoring tool of the status of the surface and assist in defining safe and dependable operational lives. As part of the study, an equivalent electric circuit is proposed. In conclusion, treatment conditions for AISI316L inner tube surfaces have been defined, with corrosion resistance preservation and improved tribological performance, while ECR monitoring has been found insightful and informative of the evolution of the later. Highlights • Improvement of tribological features, without loss of corrosion resistance, in the 316L austenitic stainless steel • Short treatment times with high density plasmas, based on active screen plasma and the hollow cathode effect • Surface status monitoring by Electrical Contact Resistance (ECR) [ABSTRACT FROM AUTHOR]

The paper presents a structure of a nitrided layer formed with active screen plasma nitriding (ASPN) technique, which is a modification of plasma nitriding. The model investigated material was Fe Armco. The nitriding processes were carried out at 773 K for 6 h and 150 Pa. The main objective of this study was to confirm nitrogen migration effect and its influence on the nitride layer formation in different area of the layer interfaces (ε/ε+γ′/γ′). The results of the tests were evaluated using scanning electron microscopy (SEM, SEM/EBSD), transmission electron microscopy – electron energy loss spectroscopy (TEM-EFTEM), secondary ion mass spectroscopy (SIMS) and Wavelength Dispersive X-Ray Spectrometry (WDS). The analysis of the results suggests that the structures of the nitrided layers and nitrides morphology differ for various parameters and are dependent on the surface layer saturation mechanism for each of the temperatures and process parameters. New approaches in diffusion of nitrogen and carbon atoms and optimizing process were also analyzed. Nitrogen and also carbon transport in the sublayer was observed by several effects i.e. uphill diffusion effect which confirmed migration of the atoms in diffusive layer towards top surface (ε/ε+γ′ interface) and stress change effect in the nitrogen saturation area of the (Fe(C,N)+γ′) layer. Results showed in the paper might be used both for optimization of ASPN processes, modeling of nitrided layers formation mechanism and for controlling the nitrided layers morphology when nitriding different Fe based materials. [ABSTRACT FROM AUTHOR]

In this work, samples of St52 steel were plasma nitrided using an iron screen, in an N2: H2 gas mixture ratio of 4 : 1, at 500 and 550°C for 5, 10 and 15 h. The X-ray diffraction and optical microscopy methods were used for structural characterization of the coatings. Results indicated that the coatings were composed of Fe2-3N and Fe4N phases growing at longer deposition times. Moreover, the Fe2-3N phase was decomposed to Fe4N after 10 h of plasma nitriding. The erosion-corrosion behavior of nitrided coatings and a bare substrate were studied in various impact angles: 30, 45, 60 and 90 degrees. Polarization curves of the coated and uncoated samples were recorded between-900 to 600 mV, as a function of the slurry impact angle. Results showed that an active screen plasma nitriding method significantly enhanced the erosion-corrosion resistance of the St52 steel. Moreover, an impact angle of 30° on the sample surface yielded a lower weightloss whereas increasing the impact angle up to 90° caused more weight-loss due to the brittle characteristic of iron nitride coatings. According to SEM micrographs, by increasing the impact angle up to 90°, the depth of the removed mass increased substantially. [ABSTRACT FROM AUTHOR]

Active screen plasma nitriding (ASPN), a novel surface modification process, has been widely applied to improve various surface properties of austenitic stainless steels, such as wear resistance, electrical conductivity and corrosion resistance. All the improvement of surface properties attributes to the formation of a unique phase under low nitriding temperature, called S-phase. A “sputter – deposit – decompose –diffusion model” has been established to explain the formation of S-phase, however, the mechanism of nitrogen mass transfer to the substrate during ASPN still remains controversial. By comprehensively comparing the surface responds of three different surfaces (bare 316L stainless steel surface, Au-coated 316L stainless steel surface and Si wafer surface) during ASPN treatments, this paper provides the direct evidence and clarifies the mechanism of nitrogen mass transfer between the deposition layer and the substrate during ASPN treatment. [ABSTRACT FROM AUTHOR]

A nitrided case composed of expanded martensite and small quantities of hexagonal ε-Fe 24 N 10 iron nitrides was formed in a martensitic stainless steel by means of active screen plasma nitriding process. Nanoindentation tests were carried out in order to assess the mechanical properties and to obtain an energy dissipation coefficient defined as the ratio of plastic to total deformation energy. Friction coefficient, mechanical failure mode and critical load for damaging the nitrided case were determined using linear scratch tests performed at both linearly-increased normal force and constant normal force according to ASTM C1624 standard. The scratch test results showed that the groove features and the friction coefficient could be well correlated to the energy dissipation coefficient. The expanded martensite strongly decreased the friction coefficient in comparison to the non-nitrided martensitic stainless steel. The critical load was 14 N and tensile cracking was the mechanical failure mode of the nitrided case. [ABSTRACT FROM AUTHOR]

[Display omitted] • The TiN layer was formed by the deposition of nitride particles while the Ti 2 N layer was formed by nitrogen diffusion. • The Ti 2 N layer was an Al-depleted zone, which was a proof for its formation mode of nitrogen diffusion. • The TiN nanograins were maintained due to their high thermal stability during plasma nitriding of the shot-peened sample. • Some equiaxed TiN nanograins of the shot-peened sample grew into columnar grains due to competitive growth. The microstructure and formation mechanism of the nitrided layer by active screen plasma nitriding on surface-nanocrystalline TA17 titanium alloy were studied by TEM. The nitrided layer of both the original and shot-peened TA17 samples was composed of two sublayers: the outer TiN layer formed by deposition of titanium nitride particles and the inner Ti 2 N layer formed by nitrogen diffusion into the titanium substrate. The Ti 2 N layer was found to be an Al-depleted zone, which was a proof for its formation mode of nitrogen diffusion. Compared with the TiN layer of the original sample filled with columnar grains, the TiN layer of the shot-peened sample was composed of mainly equiaxed nanograins and a small amount of columnar grains. The large number of high-energy grain boundaries on the shot-peened surface provided numerous nucleation sites, resulting in the formation of equiaxed nanocrystalline TiN. During long term nitriding, most of the nano-scale TiN grains were maintained due to their high thermal stability, while the nano grains of the shot-peened substrate surface grew into microscale due to their low thermal stability. With the thickening of the nitrided layer, some equiaxed TiN nanograins grew into columns perpendicular to the substrate surface due to competitive growth. [ABSTRACT FROM AUTHOR]

In this research iron nitride coating was deposited on Al substrate using active screen plasma nitriding technique. Samples were plasma nitrided in an iron cage, at 550 °C, gas mixture of N 2 :H 2 % = 3:1 for 2.5, 5 and 7.5 h. The coatings were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Corrosion resistance of samples was investigated using polarization technique. Mechanical properties including nano hardness, wear performance and adhesion strength were also studied. Results showed that the coatings were mainly consist of Fe 2-3 N particles whose size increased by nitriding at longer time periods. Moreover, it was found that at longer coating times such as 7.5 h, the nitrogen atoms diffused into the Al substrate and formed a thin layer of AlN under the Fe 2-3 N coating. Formation of the AlN coating increased the corrosion resistance of the coated sample, but it was still poor compared to uncoated Al. On the contrary, mechanical features of coated Al improved by increasing the nitriding time. Finally, the mechanical characteristics of the deposited coatings were compared to those of conventionally plasma nitrided Al. Despite the higher hardness of the AlN coating, Fe 2-3 N showed superior scratch hardness and wear resistance. [ABSTRACT FROM AUTHOR]

Quenched and tempered AISI 410 martensitic stainless steel specimens were active screen plasma nitrided in a mixture of 75% of nitrogen and 25% of hydrogen during 20 h at 400 °C. The microstructure of the nitrided case was characterized by optical microscopy, scanning electron microscopy and microhardness measurements. The phases were identified by X-ray diffraction and the nitrogen content as a function of depth was measured using wavelength dispersive X-ray spectrometer coupled to SEM. Nanoindentation tests were carried out in order to assess hardness ( H ), Young modulus ( E ), H / E and H 3 / E 2 ratios and the elastic recovery ( W e ) of the nitrided layer. Cavitation erosion tests were carried out according to ASTM G32 standard during 20 h, with periodical interruptions for registering the mass losses. Additional cavitation erosion tests were performed to identify the wear mechanisms in both specimens, through assessment of the evolution of the damage on the surface, in a scanning electron microscope. A ~28 µm thick, 1275 HV hard nitrided case formed at the surface of the martensitic stainless steel, composed of nitrogen supersaturated expanded martensite and hexagonal ε-Fe 24 N 10 iron nitrides. The expanded martensite decreased 27 times the mass loss shown by the non-nitrided stainless steel and the erosion rate decreased from 2.56 mg/h to 0.085 mg/h. The increase in cavitation erosion resistance can be mainly attributed to the increase in hardness and to the elastic response of the expanded martensite. The non-nitrided specimen changed from initially ductile to brittle behavior, exhibiting two different modes of material detachment. The first mode was characterized by a great degree of plastic deformation, fatigue and ductile fracture. The second failure mode could be associated to brittle fracture by cleavage mechanisms. In contrast, the wear mechanism observed in the nitrided specimen was brittle fracture without evident plastic deformation. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cell (PEMFC) has attracted considerable interest because of its superb performance, and many researches are focused on the development of high-performance, long-life bipolar plates. Stainless steel bipolar plates offer many advantages over the conventional graphite bipolar plates, such as low material and fabrication cost, excellent mechanical behaviour and ease of mass production. However, the insufficient corrosion resistance and relatively high interfacial contact resistance (ICR) become the major obstacles to the widespread use of stainless steel bipolar plates. In this work, active screen plasma nitriding (ASPN), a novel plasma nitriding technique, was used to modify the surface of 316 austenitic stainless steel. A variety of analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), glow discharge optical emission spectrometer (GDOES), were employed to characterize the nitrided samples. The results reveal that a nitrogen supersaturated S-phase layer has been successfully produced on the surface of all nitrided 316 stainless steel samples. The interfacial contact resistance (ICR) value can be decreased dramatically after ASPN treatment and the corrosion resistance can also been improved. In addition, better corrosion resistance can be achieved by active screen plasma nitriding with a stainless steel screen than with a carbon steel screen. This technique could be used to improve the performance and lifespan of bipolar plates for fuel cells. [ABSTRACT FROM AUTHOR]

A novel active screen plasma nitriding (ASPN) process provided excellent temperature homogeneity in the load and showed further progress in the control of nitriding potential. In addition to a variation of the nitrogen partial pressure in the process gas commonly used in the conventional plasma nitriding, the applied bias power strongly impacted the nitriding results. In the present work, an application of both methods for the control of nitriding potential in the ASPN process was systematically investigated for a wide range of process parameters to meet the treatment requirements for different types of engineering steel. A two-stage technique based on proper choice of process temperature and required nitriding potential in each stage has been applied in the ASPN process to avoid unnecessary compromises between sufficient thickness of the compound layer, the maximum case hardness and the acceptable nitriding hardness depth. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Active Screen Plasma Nitriding (ASPN) treatment on the surface-cellular compatibility of an inert aluminosilicate glass surface has been investigated. ASPN is a novel surface engineering technique, the main advantage of which is the capacity to treat homogeneously all kind of materials surfaces of any shape. A conventional direct current nitriding unit has been used together with an active screen experimental arrangement. The material that was treated was an ionomer glass of the composition 4.5SiO2–3Al2O3–1.5P2O5–3CaO–2CaF2. The modified glass surface showed increased hardness and elastic modulus, decreased surface roughness. The incorporation of nitrogen-containing groups was confirmed using X-ray photoelectron spectroscopy. The modified surface favoured attachment and proliferation of NIH 3T3 fibroblasts. [Copyright &y& Elsevier]

Highlights: [•] Active screen plasma nitriding of ultra-high molecular weight poly(ethylene). [•] Nitrogen-containing functional groups incorporated into surface. [•] NIH 3T3 fibroblast attachment and proliferation over 28 days. [•] Extensive spectroscopic and visualisation study of polymer surface. [ABSTRACT FROM AUTHOR]

The subject of the research is optimization of the parameters of the Active Screen Plasma Nitriding (ASPN) process of high speed steel planing knives used in woodworking. The Taguchi approach was applied for development of the plan of experiments and elaboration of obtained experimental results. The optimized ASPN parameters were: process duration, composition and pressure of the gaseous atmosphere, the substrate BIAS voltage and the substrate temperature. The results of the optimization procedure were verified by the tools' behavior in the sharpening operation performed in normal industrial conditions. The ASPN technology proved to be extremely suitable for nitriding the woodworking planing tools, which because of their specific geometry, in particular extremely sharp wedge angles, could not be successfully nitrided using conventional direct current plasma nitriding method. The carried out research proved that the values of fracture toughness coefficient K are in correlation with maximum spalling depths of the cutting edge measured after sharpening, and therefore may be used as a measure of the nitrided planing knives quality. Based on this criterion the optimum parameters of the ASPN process for nitriding high speed planing knives were determined. [ABSTRACT FROM AUTHOR]

Active screen plasma nitriding (ASPN) is commonly used when regular surface hardening is necessary. The ASPN technique produces a more homogeneous surface coating than direct current plasma nitriding (DCPN) due to different process principles. The term active screen in plasma nitriding refers to a cathodic cage with a defined geometry. The purpose of this work was to study the differences between ASPN using a hemispherical cathodic cage and ASPN using a normal cylindrical cathodic cage. Following some trials using similar parameters, the tests were carried out with three conditions: with DCPN, with a cylindrical cathodic cage in ASPN and with a hemispherical cathodic cage in ASPN. X-ray diffraction and scanning electron microscopy analysis together with energy dispersive spectroscopy were applied to characterise the nitrided layers. The nitrided layers are not the same for each of the conditions used. The ASPN with a hemispherical cathodic cage produced a layer of almost Fe3N alone, while the other processes gave significant amounts of Fe4N in the nitrided layer. Scanning electron microscopy analysis showed different surface morphology for each condition. [ABSTRACT FROM AUTHOR]

Abstract: Deposition of CN-based films by a novel version of active screen plasma nitriding, aiming at surface modification of polymers, is reported. The approach relies on the use of pure graphite as the grid material, which was found to act both as an active screen and as a dry source of carbon atoms for the synthesis of thin films consisting mainly of a stoichiometric CN layer with columnar-type structure and dome-like nanostructured morphology. [Copyright &y& Elsevier]

Abstract: Active screen plasma nitriding is a new and common method for deposition of Iron nitride. Since techniques such as Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD) and Plasma Assisted Chemical Vapor Deposition (PACVD) are usually applied in order to deposit the titanium nitride and each of these methods has its own problems, in this research active screen plasma nitriding method was introduced as a novel approach for deposition of nano sized titanium nitride. H11 tool steel samples were coated by plasma nitriding method at 550 °C for 5, 7.5 and 10 h, using three gas mixtures consisted of H2/N2 = 3, 1 and 1/3. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) were employed to investigate the coating properties such as grain size, layer thickness and chemical composition. Results showed that the proportion of H2 in the gas mixture was a crucial point in order to obtain a perfect coating. By increasing the coating time, the grain size and the layer thickness increased. XPS results showed that the coating was mainly consisted of TiN + TiN0.1 together with a small amount of TiO4. [Copyright &y& Elsevier]

UNS S31803 duplex stainless steel (DSS) was nitrided using the active screen plasma nitriding (ASPN) technique at temperature ranging from 400 to 450°C. Microstructures and corrosion properties of the untreated substrate and AS plasma nitrided specimens were analyzed by means of X-ray diffractometry, scanning electron microscopy, microhardness measurement, anodic polarization test, and wear test using a ring-on-disc tester. The result shows that ASPN specimen surface nitrided at 420°C consisted of a dual phase nitrided layer of nitrogen expanded austenite (γN or S-phase) and expanded ferrite (αN), which considerably improved the hardness, wear, and corrosion property of the UNS S31803 duplex stainless steel. For ASPN specimens nitrided at 435°C or 450°C, precipitated nitrides of Fe3N, Fe4N and chromium nitride (CrN) appeared in the nitrided layer. The results showed that the wear and corrosion resistance of the specimen nitrided at 420°C for 10 h were exceedingly improved, and the specimen exhibited the least wear mass loss and corrosion current density. [ABSTRACT FROM AUTHOR]

Abstract: The nanocrystallization process of amorphous Fe73.5Si13.5B9Nb3Cu1 was investigated by active screen plasma nitriding (ASPN) treatment at temperatures ranging from 410°C to 560°C for 3h in two gas mixtures of 75% N2–25% H2 and 25% N2–75% H2 at 5mbar atmosphere. The amorphous ribbons were then annealed under vacuum at the same time and temperatures mentioned above. The structure of the samples was analyzed using various techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Microhardness measurements, electrical resistivity and Vibrating Sample Magnetometer (VSM) were used to study mechanical, electrical and magnetic properties of the samples, respectively. It was observed that the ASPN treatment leads to finer grain size and higher crystalline volume fraction and modifies the structural features of Fe(Si) phase. The Fe(Si) lattice parameter for the nitrided samples decreased up to 520°C, indicating that Si atoms form a solid solution in α-Fe and it was raised at 560°C, due to Si ex-solution in the Fe(Si) phase and the formation of more nitrided phases. In ASPN treatment, the lowest magnitude of coercivity and the maximum saturated magnetization were obtained at 440°C in 75% N2–25% H2 and at 560°C in 25% N2–75% H2 gas mixtures, respectively. Our proposed method (ASPN treatment) increased the microhardness and electrical resistivity of the samples. [Copyright &y& Elsevier]

A feasibility study of active screen plasma nitriding (ASPN) of Ti6Al4V titanium alloy was conducted using a CP-Ti cage as the active screen under various process conditions. The process variables included active screen setup parameters (two different potentials of 0%-bias and 100%-bias), treatment temperature (750 and 850°C), gas mixture (10/90, 25/75, 50/50 and 100/0 of N2/H2) and treatment time (10 h) under 1·5 mbar pressure. The samples were characterised by X-ray diffraction, optical microscopy, scanning electron microscopy, microhardness and surface roughness tests. The experimental results have demonstrated that Ti–6Al–4V alloy can be treated by ASPN using a Ti screen. A Ti nitride compound layer consisting of TiN followed by Ti2N was formed on top of the surface and an Al rich layer was formed between the Ti nitride layer and the α-Ti case. The surface hardness of the samples nitrided at 750 and 850°C was 800 and 1400 HV respectively. [ABSTRACT FROM AUTHOR]

Abstract: 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 5h to 10h 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. [Copyright &y& Elsevier]

AISI 316L austenitic stainless steel samples were nitrided by active screen plasma nitriding (ASPN) at anodic and floating potentials respectively. The microstructures, morphologies, phase structures, microhardness and corrosion resistance of the nitrided layers were characterised. Experimental results show that austenitic stainless steel treated at both potentials can obtain the same precipitation free nitrided layer of S phase structure on the surface, which exhibits not only high hardness but also good corrosion resistance. A great variety of particles in the active screen space play an important role in the ASPN of austenitic stainless steel. The neutral particles sputtered from the active screen by positive ions are the primary nitrogen carrier from atmosphere to matrix surface in nitriding process. In the atmosphere of little oxygen and more hydrogen in the vacuum chamber, the surface passive film can be cleaned out by many kinds of particles bumping its surface, such as the particles sputtered from the active screen, the energetic neutral species in the plasma flow through the screen towards the samples, and even the electrons moving towards the anode samples affected by the electrical field. [ABSTRACT FROM AUTHOR]

Abstract: The active screen plasma and DC plasma nitriding of the low alloy steel 722M24 are investigated. Experimental results showed that the metallurgical characteristics and hardening effect on 722M24 steel nitrided by AS plasma nitriding at both floating potential and grounded potential were similar to those nitrided by DC plasma nitriding. Particles sputtered from the active screen and deposited on the specimen surface play the role of the nitrogen carrier in AS plasma nitriding. XRD and high-resolution SEM analysis indicated that the particles with sizes in sub-micron scale were Fe x N (x >2). Based on metallurgical analysis and Optical Emission Spectrometer (OES) experimental results, an AS plasma nitriding model has been proposed considering that AS plasma nitriding is a multi-stage process, involving sputtering, physical adsorption, desorption, diffusion and deposition. [Copyright &y& Elsevier]

The effect of a substrate bias and prenitride plasma etching on the nitriding response of four steel substrates is investigated in a two factor two level full factorial experimental design. The steels investigated were P20 (M200, plastic mould steel), H13 (W302, hot work tool steel – as received), 4140 (preheat treated nitriding steel) and 1020 (CS1020, bright mild steel). The nitriding response was determined from surface and cross-sectional hardness measurements. Nitrogen depth profile measurements were obtained using glow discharge optical emission spectroscopy. Considering the main effects, the results show that without a worktable bias during the nitriding step there is effectively little or no nitriding response in most of the materials. The prenitride plasma etch did not produce a significant surface hardness response in all steels except H13, where a prior etch substantially increased surface hardness and influenced the hardness depth profile. The bias also significantly increased the nitrogen wt-%. The plasma etch also influenced the near surface nitrogen wt-% concentrations, however the practical implications of this require further investigation. [ABSTRACT FROM AUTHOR]

Abstract: Active screen plasma nitriding (ASPN) is a novel surface modification technique that has many capabilities over the conventional DC plasma nitriding (CPN). In this study, 30CrNiMo8 low-alloy steel was active screen plasma-nitrided under various nitriding parameters such as active screen set-up parameters (different screen hole sizes, mesh sheet and plate top lids) and treatment temperature (520, 550 and 580°C), in the gas mixture of 75% N2+25% H2 and chamber pressure of 500Pa for 5h. The properties of the nitrided specimens have been assessed by evaluating composition of phases, surface hardness, compound layer thickness and case depth using X-ray diffraction (XRD), microhardness measurements and scanning electron microscopy (SEM). It was found that the screen hole size and top lid type (mesh or plate) play an important role in transition of active species (nitrogen ions and neutrals) toward the sample surface, which in turn can affect the nitrided layer hardness and thickness. Treatment at higher temperature with bigger screen hole size resulted in a thicker compound layer and higher layer hardness. The compound layers developed on the samples treated under different conditions were dual phase consisting of γ′-Fe4N and ε-Fe2–3N phases. [Copyright &y& Elsevier]

Low-temperature active-screen plasma nitriding (ASPN) was applied in this study to improve the bending rigidity and corrosion resistance of a small-diameter thin pipe composed of austenitic stainless steel (SUS 304). The inner and outer diameters of the pipe were ϕ0.3 and ϕ0.4 mm, respectively, and the pipe length was 50 mm. The jig temperature was measured using a thermocouple and was adopted as the nitriding temperature because measuring the temperature of a small-diameter pipe is difficult. The nitriding temperature was varied from 578 to 638 K to investigate the effect of temperature on the nitriding layer and mechanical property. The nitriding layer thickness increased with an increase in nitriding temperature, reaching 15 μm at 638 K. The existence of expanded austenite (S phase) in this nitriding layer was revealed using the X-ray diffraction pattern. Moreover, the surface hardness increased with the nitriding temperature and took a maximum value of 1100 HV above 598 K. The bending load increased with an increase in the nitriding temperature in relation to the thicker nitriding layer and increased surface hardness. The nitrided samples did not corrode near the center, and corrosion was noted only near the tip at high nitriding temperatures of 618 and 638 K in a salt spray test. These results indicated that the bending rigidity of the small-diameter thin pipe composed of austenitic stainless steel was successfully improved using low-temperature ASPN while ensuring corrosion resistance. [ABSTRACT FROM AUTHOR]

The paper presents the structural characterization of γ′-Fe4N nitrides produced by active screen plasma nitriding (ASPN) processes. Experiments were performed on the Fe-Armco model material at 693, 773, and 853 K for 6 h. Investigation of the properties of the substrate was realized using scanning electron microscopy (SEM, SEM–EBSD/Kikuchi lines), energy-filtered transmission electron microscopy (TEM-EFTEM), X-ray diffraction (GID, grazing incidence diffraction, micro-XRD), and secondary ion mass spectroscopy (SIMS). Results have confirmed that the γ′-Fe4N nitrides' structure and morphology depend considerably on the nitriding process's plasma conditions and cooling rate. In addition to that, γ′-Fe4N nitrides' formation can be correlated with the surface layer saturation mechanism and recombination effect. It has been shown that the γ′-Fe4N structure depends considerably on several phenomena that occur in the diffusive layer (e.g., top layer decomposition, nitrogen, and carbon atoms' migration). Our research proves that the nitrogen concentration gradient is a driving force of nitrogen migration atoms during the recombination of γ′-Fe4N nitrides. Finally, realized processes have allowed us to optimize active screen plasma nitriding to produce a surface layer of fine nitrides. [ABSTRACT FROM AUTHOR]