Active Screen Plasma Nitriding Research Articles

Development of advanced duplex surface systems by combining CrAlN multilayer coatings with plasma nitrided steel substrates

Both modelling analyses and experimental work have recently confirmed that the failure of thin coatings on steel, especially under high loads for some demanding applications, is related to the lack of mechanical support from the substrate, which means that the exceptional hardness, toughness and wear resistance of state of the art PVD coatings cannot be fully exploited. To this end, two types of new duplex surface systems have been developed from this research: i) PVD (specifically Closed Field UnBalanced Magnetron Sputter Ion Plating, CFUBMSIP) CrAlN multilayer coating deposited on ex-situ, 20-h active-screen plasma nitrided (ASPN) steel samples, and ii) in-situ 3-h, high power medium frequency pulsed plasma nitriding (HPMFPPN) treatment, followed by a similar CrAlN coating, but performed in a serial, single batch process in an otherwise conventional CFUBMSIP equipment. The microstructures of these two duplex surface engineered systems were characterised using XRD and SEM, while their hardness, adhesion, load bearing capacity and tribological properties were compared by micro-hardness tests, scratch adhesion tests and pin-on-disc sliding wear measurements. Post-test examinations were conducted and the results confirmed that a hard coating on a nitrided substrate can fully exploit the advantages of both the nitrided sub-surfaces for increased load bearing capacity and of the PVD coating for increased hardness, high temperature stability and extreme wear resistance. Finally, the advantages and disadvantages of these two new duplex surface systems were compared and their potential applications were discussed.

Nanomechanical properties of duplex treated 42CrMo4 steel

Active screen plasma nitriding (ASPN) has attracted interest from researchers and industries as it can overcome several intrinsic problems in direct current glow discharge plasma nitriding such as arcing, hollow cathode, edge effects and the strong temperature dependence on the shape of the samples. In this study, an advanced duplex system based on ASPN and chromium nitride coating was synthesised on 42CrMo4 steels. The effects of ASPN on the mechanical properties, nanoimpact resistance and scratch resistance at different load ranges were investigated. The results show that the surface hardness H, reduced elastic modulus Er and the ratios of H/Er and H3/E2r can significantly be improved at the testing load range from 5 to 100 mN. The enhanced nanoimpact and scratch resistance can be well correlated to the improved H/Er and H3/E2r.

Active screen plasma nitriding enhances cell attachment to polymer surfaces

Active screen plasma nitriding (ASPN) is a well-established technique used for the surface modification of materials, the result of which is often a product with enhanced functional performance. Here we report the modification of the chemical and mechanical properties of ultra-high molecular weight poly(ethylene) (UHMWPE) using 80:20 (v/v) N2/H2 ASPN, followed by growth of 3T3 fibroblasts on the treated and untreated polymer surfaces. ASPN-treated UHMWPE showed extensive fibroblast attachment within 3h of seeding, whereas fibroblasts did not successfully attach to untreated UHMWPE. Fibroblast-coated surfaces were maintained for up to 28 days, monitoring their metabolic activity and morphology throughout. The chemical properties of the ASPN-treated UHMWPE surface were studied using X-ray photoelectron spectroscopy, revealing the presence of CN, CN, and CN chemical bonds. The elastic modulus, surface topography, and adhesion properties of the ASPN-treated UHMWPE surface were studied over 28 days during sample storage under ambient conditions and during immersion in two commonly used cell culture media.

Validity of “sputtering and re-condensation” model in active screen cage plasma nitriding process

The validity of “sputtering and re-condensation” model in active screen plasma nitriding for nitrogen mass transfer mechanism is investigated. The dominant species including NH, Fe-I, N2+, N-I and N2 along with Hα and Hβ lines are observed in the optical emission spectroscopy (OES) analysis. Active screen cage and dc plasma nitriding of AISI 316 stainless steel as function of treatment time is also investigated. The structure and phases composition of the nitrided layer is studied by X-ray diffraction (XRD). Surface morphology is studied by scanning electron microscopy (SEM) and hardness profile is obtained by Vicker's microhardness tester. Increasing trend in microhardness is observed in both cases but the increase in active screen plasma nitriding is about 3 times greater than that achieved by dc plasma nitriding. On the basis of metallurgical and OES observations the use of “sputtering and re-condensation” model in active screen plasma nitriding is tested.

Study on the Fast Nitriding Process of Active Screen Plasma Nitriding

Abstract A new nitriding technology using active screen plasma nitriding (ASPN) was carried out in order to increase the nitriding speed of AISI 5140 steel. The fast nitriding process is based upon the different solubility and diffuse rate of nitrogen atoms in austenite and in ferrite of steel respectively. First, the nitriding samples were heated above the eutectoid temperature for a few minutes to dissolve a large amount of nitrogen and form a nitrogen-rich layer on the surface of the nitrided samples. Then, the nitriding temperature was decreased below the eutectoid temperature and kept the temperature for a long time to make the dissolved nitrogen in the nitrogen-rich layer diffuse into ferrite. The two different nitriding processes were carried on alternately. Experimental results indicate that the fast nitriding process not only enhances the nitriding speed remarkably, but also keeps the high hardness of the nitrided layer. The new fast nitriding technology with nitrogen-rich layer can be explained with “absorption- diffusion” model.

プラズマ窒化処理技術の最近の発展

Recent developments in plasma nitriding heat treatment technology were reviewed. The feature of plasma nitriding technology was introduced. Moreover, characteristics of the S phase, which was formed at 673 to 723 K in plasma nitriding of austenitic stainless steel, were explained. Finally, a new nitriding technology, — active screen plasma nitriding technology, was also explained.

Surface modification of ferritic stainless steel by active screen plasma nitriding

Plasma nitriding is a surface modification process with a low environmental impact. Active screen plasma nitriding (ASPN) is one of the new plasma nitriding technologies, and can eliminate problems related to conventional direct current plasma nitriding (DCPN). In this study, ferritic stainless steel SUS430 samples were treated by ASPN to increase their wear resistance without decreasing their corrosion resistance. ASPN was performed in a nitrogen-hydrogen atmosphere with 25%N2 + 75%H2 for 18 ks at 623 K, 673 K, 723 K, 773 K, and 823 K under 600 Pa using an SUS304 screen. When the sample was treated at 673 K by ASPN, the pitting corrosion resistance and wear resistance of its surface were improved because of the formation of the Sα phase and a deposited layer containing Ni on the sample surface.

Optimization of the ASPN Process to Bright Nitriding of Woodworking Tools Using the Taguchi Approach

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 Ic 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.

Effects of conventional and active screen plasma nitriding on properties of electroless Ni–B coating

In the present study, the properties of nitrided electroless Ni–B coatings prepared by conventional plasma nitriding and active screen plasma nitriding were investigated. For this purpose, electroless Ni–B coatings were deposited from an alkaline bath on AISI 4140 substrates. Then, some of the prepared coatings were plasma nitrided by conventional method and the other ones by active screen method under the same conditions. Microstructure, morphology, microhardness and wear resistance of the coatings were evaluated. Based on the results, post-treatments change the amorphous as deposited coating structure to a crystalline one, which increases microhardness and wear resistance. Employing plasma nitriding treatment on the coatings results in higher microhardness and superior wear resistance than conventional heat treatment. The sputtering of iron atoms during plasma nitriding process can be the main reason for these results. In addition, active screen plasma nitriding demonstrates less surface roughness and superior wear resistance than conventional plasma nitriding.

Simultaneous duplex process of TiN coating and nitriding by active screen plasma nitriding

Nitriding steel sample SACM 645 was nitrided by active screen plasma nitriding (ASPN) using a titanium screen to form simultaneously TiN coating/nitrogen-diffusion layer on the sample surface. ASPN experiments were carried out using a DC plasma-nitriding unit. The sample was placed on the sample stage in a floating potential and a cathodic potential. A titanium double screen was mounted on the cathodic stage around the sample stage. ASPN treatments at 0%-bias and 100%-bias were performed in a nitrogen–hydrogen atmosphere with 75% N2+25% H2 for 0–54 ks at 873K under 100Pa. After nitriding, the nitrided microstructure was examined with a scanning electron microscope, glow discharge optical emission spectroscopy and X-ray diffraction studies. In addition, the hardness of the surface and the cross‐sections of the nitrided sample were measured using a Vickers microhardness tester under a 0.1-N load. The thickness of the TiN layer grew linearly with increasing nitriding time. In this case, the deposition rate of the TiN layer was 0.22μm/h. The nitrided layer formed by ASPN at 100%-bias consisted of a TiN compound layer followed by a nitrogen-diffusion layer.

Effect of active screen plasma nitriding pretreatment on wear behavior of TiN coating deposited by PACVD technique

Titanium based alloys are used extensively for improving wear properties of different parts due to their high hardness contents. Titanium nitride (TiN) is among these coatings which can be deposited on surface using various techniques such as CVD, PVD and PACVD. Their weak interface with substrate is one major drawback which can increase the total wear in spite of favorite wear behavior of TiN. Disc shaped samples from AISI H13 (DIN 1.2344) steel were prepared in this study. Single TiN coating was deposited on some of them while others have experienced a TiN deposition by active screen plasma nitriding (ASPN). Hardness at the surface and depth of samples was measured through Vickers micro hardness test which revealed 1810Hv hardness as the maximum values for a dual-layered ASPN–TiN. Pin-on-disc wear test was done in order to study the wear mechanism. In this regard, the wear behavior of samples was investigated against pins from 100Cr6 (Din 1.3505) bearing steel and tungsten carbide–cobalt (WC–Co) steel. It was evidenced that the dual-layer ASPN–TiN coating has shown the least weight loss with the best wearing behavior because of its high hardness values, stable interface and acceptable resistance against peeling during wearing period.

Differences in nitrided layer between classic active screen plasma nitriding and active screen plasma nitriding with hemispherical cathodic cage

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 proces...

THE EFFECT OF ACTIVE SCREEN PLASMA NITRIDING TREATMENT ON STRUCTURAL, MECHANICAL AND MAGNETIC PROPERTIES OF NANOCRYSTALLINE FINEMET-TYPE ALLOY

The Active Screen Plasma Nitriding (ASPN) treatment of Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 alloy was investigated for 3 h at 480 °C and 560 °C in various N 2- H 2 gas mixtures at 5 mbar atmosphere. The amorphous ribbons were then annealed under vacuum at the same time and temperatures. The samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Microhardness measurements and Vibrating Sample Magnetometer (VSM). 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 was higher than that for the annealed samples due to the diffusion of nitrogen into the Fe ( Si ) phase and the formation of Si - N precipitates. In ASPN treatment, the lowest magnitude of coercivity and the maximum saturated magnetization were obtained at 480 °C and 560 °C, respectively, in 75% H 2-25% N 2 gas mixture. ASPN treatment increased the microhardness of the samples.

Investigations on the active screen plasma nitriding process

This study presents the mechanism of nitrogen transfer in a large scale active screen plasma nitriding (ASPN) unit. The active screen provides a homogeneous temperature distribution within the workload as well as an arcing tendency is reduced, since the plasma is moved from the treated work pieces to the active screen. In order to study the mechanisms in detail, plasma diagnostics is necessary. The applied diagnostic methods for analyses of the excited process gas synthesised by the active screen include mass spectrometry and infrared diode laser spectroscopy (TDLAS). Together with a metallurgical characterisation of nitrided steels a better understanding of the chemical phenomena in the N2-H2 plasmas is achieved. Various N2/H2 gas mixtures and variable bias activation powers at the pressure of 200 Pa were investigated. It was found that even during heating up in nitrogen free process gas exited nitrogen (atomic or molecular) releases from the active screen. Infrared diode laser spectroscopy has been used as a diagnostic methode to measure the concentrations of the stable NH3 molecules downstream the plasma source. The ammonia production turns out to depend on the mixtures of N2-H2 and the current input of the bias activation. The results are discussed with the plasma parameters measured by the electrostatic probe. Thus, a contribution to the interpretation of the mass transfer in ASPN process has been realised.

Active screen plasma surface modification of polycaprolactone to improve cell attachment

To tailor polycaprolactone (PCL) surface properties for biomedical applications, film samples of PCL were surface modified by the active screen plasma nitriding (ASPN) technique. The chemical composition and structure were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The wettability of the surface modified polymers was investigated by contact angle and surface energy methods. Biocompatibility of the prepared PCL samples was evaluated in vitro using MC3T3-E1 osteoblast-like cells. The degradability was assessed by determining the self-degradation rate (catalyzed by lipase). The results show that ASPN surface modification can effectively improve osteoblast cell adhesion and spreading on the surface of PCL. The main change in chemical composition is the exchange of some carboxyl groups on the surface for hydroxyl groups. The active-screen plasma nitriding technique has been found to be an effective and practical method to effectively improve osteoblast cell adhesion and spreading on the PCL surface. Such changes have been attributed to the increase in wettablity and generation of new hydroxyl groups by plasma treatment. After active-screen plasma treatment, the PCL film is still degradable, but the enzymatic degradation rate is slower compared with untreated PCL film.

Linear Ion Source에 의해 증착된 Diamond-Like Carbon(DLC) 박막의 질화층 형성에 따른 밀착력 특성 연구

Diamond-like carbon (DLC) has many outstanding properties such as low friction, high wear resistance and corrosion resistance. However, it is difficult to achieve enough adhesion on the metal substrates because of weak bonding between DLC film and the metal substrate. The purpose of this study is to enhance an adhesion of DLC film. For improving adhesion, the substrate was treated by active screen plasma nitriding before DLC film deposing. Nitrided substrates were investigated by Glow Discharge Spectrometer (GDS), Micro-Vickers Hardness. DLC films were deposited on several metals by linear ion source, and characteristics of the films were investigated using nano-indentation, Field Emission Scanning Electron Microscope (FESEM). The adhesion was measured by scratch tester. The adhesion of DLC films was increased when nitriding layer was formed before DLC deposition. Therefore, the adhesion of DLC film can be enhanced as increasing the hardness of materials.

Characterization on Duplex Treated Coating Fabricated by Laser Cladding and Active Screen Plasma Nitriding

In order to enhance the performances of laser remanufacturing part, we combined laser cladding with active screen plasma nitriding duplex treatment to repair metal part. The microstructure, phase structure and micro-hardness of duplex treated coating were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and micro-hardness tester. Wear tests were carried out on reciprocating wear tester under dry sliding condition. The results show that the white layer and the nitrogen diffusion layer were formed after nitriding treatment. The duplex treated coating consists mainly of γ-Fe, CrN, Fe4N and Fe3N. The duplex treated coating improved not only surface hardness but also wear resistance.

Carbon nitride film deposition by active screen plasma nitriding

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.

Nitriding of high speed steel

Current practice when nitriding high speed steel (HSS) cutting tools is to avoid embrittlement of the cutting edge by limiting the depth of the diffusion zone. This is accomplished by reducing the nitriding time and temperature and eliminating any compound layer formation. However, in many applications there is an argument for generating a compound layer with beneficial tribological properties. In this investigation, results are presented of a metallographic, X-ray diffraction and X-ray photoelectron spectroscopy analysis of nitrided HSS surface layers generated using active screen plasma nitriding and reactive vapour deposition using cathodic arc. These results are discussed in the context HSS cutting tool performance when machining under built-up edge conditions.

A new method for deposition of nano sized titanium nitride on steels

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 H 2/N 2 = 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 H 2 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 + TiN 0.1 together with a small amount of TiO 4.