Active Screen Plasma Nitriding Research Articles

Interfacial alloying between expanded austenite and Ti(AlCu)N coating for enhanced cavitation erosion resistance

Duplex surface treatments, combining nitriding and PVD coatings, have been considered as potential solutions to enhance material cavitation erosion resistance. This study investigates 316 L stainless steels after active screen plasma nitriding (ASPN), Ti(AlCu)N coating and duplex-treatment (Duplex) for enhanced cavitation erosion resistance. We elucidate a ‘denitriding - nitriding’ alloying behavior in association with high-energy ion sputtering for the interface between the nitrided case and the Ti(AlCu)N coating in the duplex-treated 316 L surface. Comparing the cavitation erosion performance among ASPN, Ti(AlCu)N and Duplex, the lowest weight loss of the duplex-treated surface is attributable to the enhanced load-bearing capacity from the multilayer system and the strong coating adhesion (HF1) after metallurgical evolution at the interfacial zone.

Influence of screen height and bias voltage on the active screen plasma nitriding of shot-peened Ti-6Al-4V titanium alloy

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.

An investigation on nitrogen uptake and microstructure of equimolar quaternary FeCoNiCr high entropy alloy after active-screen plasma nitriding

Under nitrogen diffusion treatments, N-expanded austenite (γN) can form at the surface of self-passivating Fe-Cr, Ni-Cr, and Co-Cr alloys at low temperatures, which provides beneficial hardening and enhancements in wear resistance without reducing corrosion resistance. Given the wide research interests in multicomponent equimolar alloys, an equimolar quaternary FeCoNiCr high entropy alloy (HEA) was investigated after active-screen plasma nitriding at 430–480 °C in this study. Firstly, the formation of γN-FeCoNiCr case at 430 °C was demonstrated with the bright case appearance after metallographic etching, the lattice expansion under XRD, the FCC electron diffraction patterns and the shear bands under TEM. Secondly, the thick treatment cases at ∼9–16 μm first indicated that N interstitial diffusion was not sluggish in the FeCoNiCr surface. Thirdly, analogous to stainless steels, the onset of dark regions in the etched γN-FeCoNiCr case was owing to the formation of a cellular mixture of CrN + γ-(Fe, Co, Ni) nano-lamellae at elevated treatment temperatures. The residual bright regions in γN-FeCoNiCr at 480 °C showed ∼1–3 nm CrN nanoprecipitates with no substantial Cr segregation. Additionally, a significant nanocrystalline layer was seen at the topmost surface at 480 °C, which is most likely associated with the high substrate Cr content.

Effects of gas mixture on active screen plasma nitriding and post-oxidation of a 4140 steel

Plasma nitriding, followed by post-oxidation, is a surface treatment used to enhance the properties of steel parts. The primary objective of such treatments is to develop a magnetite-rich oxide phase on the previously nitrided surface, aiming to achieve increased wear and corrosion resistance. The active screen plasma treatment method offers an alternative to direct plasma treatments, where parts are shielded from direct exposure to active species. This approach helps prevent defects caused by electric arcing and reduces the risk of increased porosity. However, due to differences in kinetics between active screen and direct plasma methods, the parameters commonly used in direct plasma treatments are not suitable for achieving the desired outcomes with active screen plasma. In this study, we applied plasma nitriding and oxidation to AISI 4140 hardened and tempered steel workpieces using the active screen method, varying the O2:H2 ratio in the gas mixtures. Treated workpieces were subjected to reciprocating wear tests. Our findings demonstrate that for the active screen post-oxidation step to be successful, it is essential to increase the O2 content compared to the reference treatment parameters used for non-active screen methods. The highest O2 content investigated (40 %) facilitated the development of magnetite oxides over the nitrided surface. This resulted in remarkable improvements in wear resistance and a favorable reduction in the friction coefficient during our tribological tests.

Active screen plasma nitriding of laser powder bed fusion processed 316L stainless steel for the application of fuel cell bipolar plates

ABSTRACT 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.

Active screen plasma nitriding of a Si-alloyed FeCrNi medium entropy alloy: High interstitial absorption and an anomalous Si-induced decomposition mechanism in N-expanded austenite

Nitrogen-expanded austenite (γN), also known as S phase, is a metastable, interstitial supersaturated phase, that has been extensively studied on AISI 304/316 stainless steel (SS) following N diffusion treatments at low temperatures. Substantial Cr segregation can occur in γN-304/316 under CrN formation at elevated treatment temperatures (typically at above 450 °C), resulting in degradation in corrosion performance. In contrast to 316 SS (mainly based on the Fe-Cr-Ni system), a FeCrNiSi0.5 medium entropy alloy (MEA) was investigated after active screen plasma nitriding (ASPN) at 430–480 °C in this study. Attributable to the equimolar Cr content in the substrate, the ASPN-treated MEA surface showed “excessive” N absorption, which was accompanied by severe surface micro-cracking and a topmost nanocrystalline layer. Nanoprecipitates (∼3-8 nm) can be seen in γN-MEA at treatment temperature as low as 430 °C. However, STEM-EDX analysis of those nanoprecipitates (∼5-30 nm) at 480 °C showed significant Si segregation without observable Cr redistribution, resulting in a uniform “greyish” etched treatment layer. The sluggish Cr segregation in the N-modified MEA surface could originate from both the minor Si addition (via Si-induced nanoprecipitation) and the high equimolar Ni/Cr content in the host matrix.

Columnar and nanocrystalline combined microstructure of the nitrided layer by active screen plasma nitriding on surface-nanocrystalline titanium alloy

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 Ti2N layer formed by nitrogen diffusion into the titanium substrate. The Ti2N 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.

Effects of Plasma Nitriding Temperature on the Properties of 1.3207 Type High Speed Steel

Active screen plasma nitriding on HS 10-4-3-10 high-speed steel specimens was performed at three different low nitriding temperatures while trying to keep the other nitriding parameters uniform. In addition, two extra samples were made to increase the treatment time. Optical microscopic investigation and microhardness testing were performed on the segments of the samples, and their qualitative composition was determined by energy-dispersive X-ray spectrometry. Based on the measurements, it is stated that the hardness of the surface can be increased 50% with active screen plasma nitriding.

Adhesion Enhancement on a Duplex DLC HiPIMS Positive Pulse Coating Performed by Active Screen Plasma Nitriding Pretreatment on 316L Stainless Steel Substrate

Diamond-like carbon (DLC) coatings have been the object of research interest due to properties such as excellent wear resistance, low coefficient of friction, high hardness, high elastic modulus, and biocompatibility. Despite this, DLC has poor adhesion properties, which makes it challenging to use in industrial applications. The application of DLC using the high-power pulse magnetron sputtering (HiPIMS) technique with positive pulses has been studied. Seeking greater DLC coating adherence, the application of a nitriding pretreatment prior to the DLC coating has been studied to improve its adhesion to AISI316L stainless steel soft metal substrates, employing active screen plasma nitriding (ASPN). The influence of the different pretreatment temperatures to reach the maximum levels of adhesion has been analyzed. Scratch methods have been employed to assess adhesion. The elemental composition, morphology, and roughness of the samples have been studied, as well as the behavior of resistance to wear and friction. The results show an improvement in DCL adhesion. Critical loads (LC3) increase at higher pretreatment temperatures, from 48 N for the DLC to 82 N for the ASPN + DLC. Pretreatment has also been shown to be effective in maintaining excellent dry wear resistance properties and a low coefficient of friction.

Active screen plasma nitriding of Fe-24Mn-2Al-0.45C TWIP steel: Microstructure evolution and a synergistic selective oxidation mechanism

In this study, Fe-24Mn-2Al-0.45C twinning-induced plasticity (TWIP) steel was investigated after active screen plasma nitriding (ASPN) at 350–480 °C. Up to 450 °C, the ASPN-treated TWIP steel showed a double-layered structure, with a topmost Fe4N-type γ’ layer and an underlying interstitial solid solution. The underlying nitrogen interstitial solid solution obtained on ASPN-treated TWIP steel can be identified as γN(i), being expanded austenite with small lattice expansions at low nitrogen (and carbon) absorption levels. However, the 480 °C ASPN-treated TWIP steel surface is composed of an unexpected MnO-containing ferritic topmost layer and a thick underlying γN(i) layer, which corresponds to a hardness-depth profile different to those obtained at 350–480 °C. Hence, we propose and elucidate a selective oxidation mechanism (that occurred alongside nitrogen inward diffusion) on TWIP steel during ASPN treatment, which can be attributed to (a) an elevated treatment temperature that allowed Mn migration, (b) a processing atmosphere with low oxygen partial pressure, and (c) a high-Mn substrate chemical composition with low Al/Mn (or Si/Mn) ratio.

Processing and interpretation of core-electron XPS spectra of complex plasma-treated polyethylene-based surfaces using a theoretical peak model.

Interpretation of X-ray photoelectron spectroscopy (XPS) spectra of complex material surfaces, such as those obtained after surface plasma treatment of polymers, is confined by the available references. The limited understanding of the chemical surface composition may impact the ability to determine suitable coupling chemistries used for surface decoration or assess surface-related properties like biocompatibility. In this work, XPS is used to investigate the chemical composition of various ultra-high-molecular-weight polyethylene (UHMWPE) surfaces. UHMWPE doped with α-tocopherol or functionalised by active screen plasma nitriding (ASPN) was investigated as a model system. Subsequently, a more complex combined system obtained by ASPN treatment of α-tocopherol doped UHMWPE was investigated. Through ab initio orbital calculations and by employing Koopmans' theorem, the core-electron binding energies (CEBEs) were evaluated for a substantial number of possible chemical functionalities positioned on PE-based model structures. The calculated ΔCEBEs showed to be in reasonable agreement with experimental reference data. The calculated ΔCEBEs were used to develop a material-specific peak model suitable for the interpretation of merged high-resolution C 1s, N 1s and O 1s XPS spectra of PE-based materials. In contrast to conventional peak fitting, the presented approach allowed the distinction of functionality positioning (i.e. centred or end-chain) and evaluation of the long-range effects of the chemical functionalities on the PE carbon backbone. Altogether, a more detailed interpretation of the modified UHMWPE surfaces was achieved whilst reducing the need for manual input and personal bias introduced by the spectral analyst.

Effects of Nickel Screen on Active Screen Plasma Nitriding

Effects of Nickel Screen on Active Screen Plasma Nitriding

Effects of Nickel Screen on Active Screen Plasma Nitriding

Effects of Nickel Screen on Active Screen Plasma Nitriding

Duplex treatment of active screen plasma nitriding and amorphous hydrogenated carbon coating

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.

Enhancing the Corrosion Resistance of Austenitic Steel Using Active Screen Plasma Nitriding and Nitrocarburising.

AISI 316L steel was subjected to active screen plasma nitriding and nitrocarburising. The processes were carried out at 440 °C for 6 h. The nitriding process employed an atmosphere of nitrogen and hydrogen, while nitrocarburising was carried out in nitrogen, hydrogen and methane. The processes yielded structures consisting of nitrogen and nitro-carbon expanded austenite, respectively. Microhardness was measured via the Vickers method, surface roughness using an optical profilometer, microstructure by means of light microscopy, while a scanning electron microscope (SEM) served to determine surface topography. Phase composition, lattice parameter and lattice deformation tests were carried out using the X-ray diffraction (XRD) method. Corrosion resistance measurements were performed in a 0.5 M NaCl solution using the potentiodynamic method. The produced layers showed very high resistance to pitting corrosion, while the pitting potential reached 1.5 V, a value that has not yet been recorded in a chloride environment. After the passive layer was broken down, there was a clear deceleration of pitting in the nitrocarburised layer. It was found that in the case of nitro-carbon expanded austenite, pits are formed much slower compared to the nitrogen austenite layer.

Effect of Active Screen Plasma Nitriding on Mechanical Properties of Spheroidal Graphite Cast Iron

Spheroidal graphite cast iron is a material with a wide range of uses such as in automobile parts. By applying active screen plasma nitriding (ASPN) treatment, the use of spheroidal graphite cast iron is expanded, and it can be expected to be used under special load conditions. In this study, we evaluated the effect of ASPN treatment on the mechanical properties of spheroidal graphite cast iron. With ASPN treatment, a nitride layer was formed on the sample surface and a diffusion layer was formed further inside the nitride layer. The thickness of nitride layer increased as the treatment temperature increased. The hardness was improved by ASPN treatment. The abrasion resistance was improved by ASPN treatment, and longer treatment time resulted in higher abrasion resistance. The fatigue strength was improved by ASPN treatment, and longer treatment time resulted in higher fatigue strength. ASPN treatment also improved the corrosion resistance.

Application of Active-Screen Plasma Nitriding to an Austenitic Stainless Steel Small-Diameter Thin Pipe

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.

Nitriding of titanium by hollow cathode assisted active screen plasma and its electro-tribological properties

Titanium presents good corrosion resistance, a high strength-to-weight ratio, but poor tribological properties. However, these can be enhanced by nitriding processes.Hollow cathode assisted active screen plasma has proved to be an effective and fast nitriding technique. In this work, the effect of process parameters (hollow cathode induced temperature and plasma intensity, electrical bias…) on the resulting surface microstructure (XRD, SEM/EDS), finishing and hardness of titanium (TiGr4) have been studied. Additionally, the electro-tribological properties have been evaluated on a ball on cylinder reciprocating configuration.The results show that hollow cathode assisted active screen plasma nitriding of titanium can produce titanium nitride surfaces with thicknesses far exceeding those typical in PVD coatings. Moreover, higher plasma processing intensities can generate same layer thicknesses at lower temperatures, minimizing the deleterious effect on grain size growth. Finally, monitoring of the electrical contact resistance can provide valuable information concerning the evolution of the status of the surfaces.

Investigation of Surface Properties of EN8, EN24, and EN41B Low Alloy Steel Treated by Active Screen Plasma Nitriding

In this work, active screen plasma nitriding (AS_PN) of EN8, EN24, and EN41B low alloy steel was carried out to improve its surface properties. The process parameters of 500 °C temperature for 4 h with the gas flow in the ratio of H2:N2 = 1:1 were used for the treatment. The improvement in the surface was assessed by the microhardness as well as characterized by SEM and XRD. The microhardness measurements reveal an increase in surface hardness by more than 4, 3.4, and 2.7 times from the base material for EN41B, EN8, and EN24. The compound zone/layer ranges from 4.9 microns (μm) for EN8 to as high as 9.1 microns (μm) for EN41B after nitriding. On analyzing the nitride layer thickness through SEM, the results found from microhardness measurement were confirmed. The XRD results also approve the predominant development of γ'-Fe4N and ɛ-Fe2–3 N phases on the treated sample surface, although its compound layer surges with different nitride forming elements. Further, SEM analysis also reveals a white layer formation without transformed austenite (γ). Further, EDS analysis was also performed on the treated samples. Finally, a comparative corrosion study for AS_PN treated and bare (untreated) material samples were done to find the influence of the treatment.

New ASPN High Efficiency Treatment of ASTM M2 Steel

Abstract Plasma nitriding treatments are applied to achieve excellent surface properties on steel parts and tools. Active screen plasma nitriding (ASPN) does not have the defects presents in direct nitriding plasma treatments (DCPN). However, ASPN require much longer processing times to develop surface layers as deep as those of DCPN. This work presents the development of a biased ASPN treatment system, to investigate the possibility of achieving greater efficiency. The treatments were performed on ASTM M2 steel samples using the same processing parameters in 4 different configurations: DCPN, ASPN and 2 active screen plasma nitriding with biased specimens voltage: one was called bright bias, because biased voltage is high enough to develop a plasma glow on the samples, and the other bias, where no plasma glow sheath is seen on the samples. The active screen dark biased treatment presented the best results. These results could be understood by the electromagnetic field generated by the bias source promoting the deposition of nitrogen ions on the surface of the part being treated. Therefore, it was demonstrated that the use of dark bias voltage in the active screen treatment in larger reactors is fundamental to achieve good nitriding results in smaller times.