Electrospark Deposition Coatings Research Articles

Protective Heterophase Coatings Produced by Pulsed Electrospark Depostioin and High Power Impulse Magnetron Sputtering

In order to increase the service life of critical products made of refractory metals, the most effective is the use of protective coatings based on oxidation-resistant ceramic materials. Using an electrode/target made of heterophase HfSi2-MoSi2-HfB2 ceramics by electrospark deposition (ESD), high-power impulse magnetron sputtering (HIPIMS) technologies, as well as the combined ESD+HIPIMS technology, coatings were deposited onto molybdenum substrate (MCh-1 brand). Electrode materials and coatings were studied by the X-ray diffraction, the glow discharge optical emission spectroscopy, the X-ray spectral microanalysis, and the scanning electron microscopy. Combined ESD+HIPIMS technology made it possible to create a hard layer of oxidation-resistant ceramics on the surface of the substrate, which does not produce through cracks inherent in ESD coatings.

Influence of deposition voltage on tribological properties of W-WS2 coatings deposited by electrospark deposition

Electrospark deposition coatings were prepared with different deposition voltage on CrNi3MoVA steel substrates by using a W-WS2 sintered electrode and their tribological properties were investigated. The microhardness, roughness and tribological properties of the coatings were tested by using Vickers hardness tester, confocal laser scanning microscope and tribometer, and the morphologies, composition and phase structure were obtained by utilizing scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS) and X-ray diffraction(XRD). The results showed that with the increase of deposition voltage, the hardness and roughness of the coatings increase. The coatings remarkably increase the tribological properties of CrNi3MoVA steel, and among the three coatings deposited at 40 V, 60 V and 80 V, the coating deposited at 60 V has the smallest friction coefficient and the best wear resistance.

TaC-based wear-resistant coatings obtained by magnetron sputtering and electro-spark deposition for wedge gate valve protection

Ta–Zr–Si–B–C coatings were deposited by magnetron sputtering (MS) of a TaSi2–Ta3B4–(Ta, Zr)B2 multi-component target in an Ar + C2H4 gas mixture. TaC–Cr–Mo–Ni based coatings were obtained by electro-spark deposition (ESD) using TaC–Cr–Mo–Ni electrode. The composition and structure of the coatings were studied using scanning electron microscopy, energy-dispersive spectroscopy, glow discharge optical emission spectroscopy and X-ray diffraction. Mechanical and tribological properties of coatings were determined using nanoindentation and pin-on-disk tests. The study showed that the coatings have a homogeneous and defect-free structure, with the main structural component being the fcc-TaC phase. The MS coating exhibited a 30 % higher concentration of the TaC phase compared to the ESD coating. The TaC crystallite sizes for the MS and ESD coatings were 3 and 30 nm, respectively. The presence of a high fraction of the carbide phase and small crystallite size for the MS coating resulted in superior hardness (H = 28 GPa) compared to the ESD sample (H = 10 GPa). Both coatings exhibited similar values of the friction coefficient (about 0.15) and demonstrated reduced wear rates (<10–7 mm3/(N·m)). The deposition of coatings on a steel substrate led to a decrease in the friction coefficient by five times and the wear rate by four orders of magnitude. Pilot tests were conducted on coatings applied to wedge gate valve of shut-off devices used in the oil and gas industry for pumping liquids. The results indicated that the service life of the steel wedge gate valve increased by 25 and 70 % with deposited MS and ESD coatings, respectively.

Research Progress in Electrospark Deposition Coatings on Titanium Alloy Surfaces: A Short Review

The development process of electrospark deposition (ESD) technology is reviewed, and the principles and differences of ESD technology are discussed in this review. Based on the research status regarding the ESD of titanium alloys, the promotion effect of ESD technology on wear resistance, corrosion resistance, oxidation resistance at high temperatures, and the biocompatibility of titanium alloys was elaborated on. For example, with the use of ESD technology to prepare Ti–Al, TiN, Ni–Cr, and other hardening coatings with high hardness, the maximum hardness of the deposited layer is six times higher than that of the substrate material, which greatly reduces the loss of the material surface in the process of friction in service, and has a high wear–resistance effect. The preparation of a single–phase lamellar coating is more beneficial for improving the oxidation resistance of the substrate. Carbide and a nano–porous coating can effectively enhance the bone integration ability of implants and promote biocompatibility. The application of ESD technology in the surface modification of titanium alloys is reviewed in detail. Finally, the development direction of ESD technology for titanium alloys is proposed.

Synthesis, Wear and Corrosion of Novel Electrospark and Electrospark–Electrochemical Hybrid Coatings Based on Carbon Steels

The electrospark deposition (ESD) technique is a low-heat-input process that has great potential for coating applications and the restoration of damaged high-value parts. Carbon steels are commonly used as a substrate material for ESD coatings. However, we demonstrated that carbon steels could be used successfully as the electrode tool for the ESD process. Furthermore, ESD coatings commonly have a high as–deposited roughness. In view of this, in order to reduce the roughness of the ESD coatings, electrodeposition as a tool to alter surface morphology was investigated. Hence, the micro-leveling power of several electrolytes for Ni, Fe-W, Fe, and Cr electrodeposition were evaluated. The maximum leveling effect was detected for Ni electroplated from the Watts electrolyte. Thus, the novel hybrid coatings based on an ESD layer and a subsequent layer of electrodeposited Ni were obtained. ESD layers were obtained by using the following electrode tools as anodes: several types of carbon steels (St20, St30, and St45), alloys T15K6 (WC + TiC + Co), CuNiZn; and NiCr. The morphology and structure of the obtained hybrid coatings with an electrodeposited Ni top-layer was analyzed and compared to ESD coatings from the point of view of their wear and corrosion behavior. The wear rate of the novel ESD coatings based on carbon steels was comparable with coatings obtained using the NiCr electrode tool. Moreover, for all the studied cases, the corrosion resistance of the hybrid coatings was higher than for their ESD counterparts and close to electrolytic chromium.

Obtaining of Metal-Matrix Alloys Based on Ni-Al for ESD Coatings Formation

The experimental results of obtaining complex-alloyed intermetallic alloys by the method of liquid-phase self-propagating high-temperature synthesis (SHS) and their subsequent use for the formation of wear-resistant coatings by the method of electrospark deposition (ESD) are submitted. Metal oxides Cr2O3, NiO, CoO and mineral concentrate containing a larger part of ZrO2 in its composition were used as a melt charge for the SHS experiments. Alloys based on Ni-Al system dopped with Cr, Zr, Co, and C were obtained. It was established that extra addition of C led to the refinement of the alloys microstructure (3-5 times). ESD coatings were formed on steel 45 using the obtained alloys as anode material. The coatings formed by using the alloys doped by Co, Zr, Cr and extra addition of C (0.4 wt%) proved to be maximum wear resistant.

Investigations on microstructure, oxidation, and tribological behavior of NiCoCrAlYTa/Y2O3 blade tip protective coating produced by electro spark deposition over a wide temperature range

NiCoCrAlYTa/Y2O3 coatings were prepared on two nickel-based superalloys by electro spark deposition (ESD). The ESD coatings “inherited” the microstructure of the substrate, which depended on the orientation of the substrate and the primary solidification phase of the coating. Columnar crystal structure had fewer grain boundaries, better high-temperature bearing capacity, and a more uniform “glaze” layer than equiaxed crystal structure, which allowed it to exhibit better oxidation resistance and wear resistance. The competition between the lubrication/wear reduction of the “glaze” layer and the plowing caused by hard oxide particles influenced the tribological behaviors of both. The difference in cutting performance between the two coatings is related to the oxidation behavior of the coating and the structure of the “glaze” layer.

Multi-Criteria Optimization of Automatic Electro-Spark Deposition TiCrNiVSi0.1 Multi-Principal Element Alloy Coating on TC4 Alloy

In this work, TiCrNiVSi0.1 coatings were prepared on TC4 alloy by CNC-controlled automatic electro-spark deposition (ESD). The TOPSIS-based Taguchi method was applied for multi-criteria optimization of ESD coating quality. Frequency (f), capacitance (c), and electrode moving speed (v) were considered process parameters for optimizing the coating quality criteria, which included coating thickness, coating coverage, and porosity in the coating. The optimized parametric setting of the ESD process (f = 700 Hz, c = 270 μF, v = 150 mm/min) was obtained. MPEA coatings with a thickness of about 70 um, a coverage rate almost reaching 100%, and porosity as low as about 1% were prepared. The wear- and burn-resistance functions of the TiCrNiVSi0.1 ESD coatings were investigated. The wear rates of the coating at room temperature and 400 °C are one-sixth and one-fourth of the TC4 alloy, respectively. A TiCrNiVSi0.1 alloy coating was deposited and significantly improved the burn resistance of the TC4 alloy.

Abrasive and Erosive Wear of TI6Al4V Alloy with Electrospark Deposited Coatings of Multicomponent Hard Alloys Materials Based of WC and TiB2

In the present work, abrasive and erosive wear of wear-resistant composite coatings with a complex structure and different phase compositions deposited on titanium surfaces was studied. The coatings were obtained by electrospark deposition (ESD) using two types of hard-alloy compositions: WC–TiB2–B4C–Co–Ni–Cr–Si–B and TiB2–TiAl reinforced with dispersed nanoparticles of ZrO2 and NbC. The influence of the ESD process parameters on the roughness, thickness, composition, structure and coefficient of friction of the coated surfaces was investigated, and their role in protecting the titanium surfaces from wear was clarified. Dense coatings with the presence of newly formed wear-resistant phases and crystalline-amorphous structures were obtained, with roughness, thickness and microhardness that can be varied by the ESD modes in the range Ra = 2.5 ÷ 4.5 µm, δ = 8 ÷ 30 µm and HV 8.5 ÷ 14.0 GPa. The new coatings were found to reduce the abrasive and erosive wear of the coated surfaces by up to four times. The influence of the geometric characteristics, composition and structure of coatings on the wear intensity and wear resistance of coatings was studied.

Effect of boronizing on microstructure, high-temperature wear and corrosion behavior of additive manufactured Inconel 718

In this study, Ni-based Inconel 718 coatings were additively manufactured on the surface of AISI H13 work tool steel by electro-spark deposition (ESD). Some of the electro-spark deposited samples were boronized at 1000 °C for 5 h to evaluate the effects of boronizing on microstructure, high-temperature wear, and corrosion resistance. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), 2D profilometry, wear and electrochemical corrosion testing was used to characterize the surfaces, microstructures, microhardness, some mechanical properties, high-temperature wear, and corrosion resistance of the applied coatings. Wear tests were performed at room temperature and 650 °C, and corrosion tests were performed in 3.5% NaCl at room temperature, considering the applications of AISI H13 and Inconel 718 alloys. The characterization studies showed evidence of microcracking and oxidation in the as-deposited Inconel 178 coatings. In the boronized Inconel 718 coatings, the oxides and microcracks were slightly reduced. The hardness of the boronized Inconel 718 coating was increased to about four times the hardness of the as-deposited Inconel 718 coating, and this significantly improved its wear resistance. The highest wear resistance was achieved with the boronized coating, while the best corrosion resistance was obtained with the as-deposited coating. The improvements in wear resistance provided by boronizing have the potential for expanding the applications of Inconel 718 coatings in machine components. • AISI H13 tool-work steel exposed to combined electro-spark deposition and boronizing processes. • The microstructure, friction, wear and corrosion behaviors of different surfaces were compared and analyzed. • The irregularly shaped oxides and cracks in the ESD coatings were healed and the microstructure was refined by boronizing. • Electrospark deposition and boronizing improved corrosion and high-temperature wear resistance of AISI H13 steel. • Boronizing offers an alternative to laser surface modifications in improving the mechanical properties of ESD coatings.

Formation of coatings with technologies using concentrated energy stream

Abstract A number of modern surface processing methods use an energy flux. The examples include electro-spark deposition (ESD) and laser beam processing (LBP). The work concerns the study of Cu-Mo coatings deposited on C45 carbon steel, which were then eroded with a laser beam. The analysis included the analysis of the microstructure, measurements of macrogeometry and microhardness, corrosion resistance tests of selected areas after laser treatment. The coatings were applied with ELFA-541 and subjected to Nd:YAG laser treatment with variable laser parameters. The problem presented in the work can be used to extend the knowledge of the areas of application of ESD coatings, especially in sliding friction pairs.

Experimental study on aluminum bronze coating fabricated by electro-spark deposition with subsequent ultrasonic surface rolling

Aluminum bronze coatings were prepared on the as-cast substrate of the same material by electro-spark deposition (ESD), and the coatings were treated by ultrasonic surface rolling (USR). The effects of USR on the microstructural, mechanical, and tribological properties of the ESD coatings were investigated. The microstructure, phase composition, nanoindentation, microhardness, surface residual stress, and tribological properties of the coatings were experimentally determined and characterized in detail. The USR treatment with different static pressures (1.0 MPa, 2.5 MPa, 4.0 MPa) was employed to reveal the mechanism of microstructure evolution and surface modification. The results showed that the original columnar crystal structure of the coatings treated by USR was deflected, elongated, and even broken, resulting in the grain refinement of the coatings. The hole defects were healed after USR2.5 treatment. The phase composition of the coatings changed from β′ (Cu3Al) phase to α (Cu) and κ (Fe3Al) phase because of the heat released at USR. The nanohardness, static creep resistance, and microhardness of the ESD coatings were effectively promoted by USR. The nano-hardness of the ESD coating after USR4.0 treatment (4.4 GPa) was 1.38 times and 2.2 times that of the ESD coating and the as-cast alloy respectively, and the creep displacement (5.193 nm) was 27.2% and 18.5% that of the ESD coating and the as-cast alloy respectively. The residual tensile stress of the ESD coatings was eliminated after USR treatment and converted into the residual compressive stress. The surface residual stress of the ESD coating after USR2.5 was −337.16 MPa. After USR2.5 treatment, the wear loss of ESD coating reduced by about 1/2, which was attributed to the healing of hole defects, residual compressive stress, and the increase of the hardness.

Wear Resistance of Electrospark-Deposited Coatings in Dry Sliding Friction Conditions

Wear Resistance of Electrospark-Deposited Coatings in Dry Sliding Friction Conditions

The Effect of Laser Beam Processing on the Properties of WC-Co Coatings Deposited on Steel.

The main objective of the present work is to determine the effects of laser processing on properties of WC-Co electro-spark deposited (ESD) coatings on steel substrates. Tungsten carbide coatings have been applied to steel substrates using a manual electrode feeder, model EIL-8A. The laser beam processing (LBP) of electro-spark coatings was performed using an Nd:YAG fiber laser. The microstructure and properties of laser treated/melted coatings were evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), surface geometric structure (SGS) and roughness measurements and adhesion, microhardness, residual stresses, corrosion resistance and application tests. The obtained experimental data were subjected to statistical analysis and multidimensional numerical and visual exploratory techniques. It has been shown conclusively that the laser-treated ESD WC-Co coatings are characterized by lower microhardness, higher resistance to corrosion, increased roughness and better adhesion to the substrate. LBP homogenizes the chemical composition, refines the microstructure and heals microcracks and pores of ESD coatings. The laser treated ESD WC-Co coatings can be used in frictional sliding nodes (e.g., on the front seal rings used in pumps) and as protective layers.

Effect of TaC particles on the microstructure and oxidation behavior of NiCoCrAlYTa coating prepared by electrospark deposition on single crystal superalloy

NiCoCrAlYTa/TaC metal matrix composite coatings were prepared on single crystal superalloy (SX) using electrospark deposition (ESD) to improve its high temperature performance. The effect of TaC addition on the coating microstructure, oxidation behavior, wear resistance and physical properties of electrode were investigated. The results showed that, with the addition of TaC particles, the density of electrode increased, while the thermal conductivity and thermal diffusivity decreased. In the electrode, TaC particles were distributed around or embedded into the NiCoCrAlYTa powders, while in ESD coatings, they were distributed homogeneously in both dendrite cores and interdendritic regions. The generation of β-NiAl phase in ESD coating was prevented by adding TaC particles. During 1000 °C/100 h oxidation, the mass gain of coating with TaC addition was lower than that without TaC addition during the first 40 h, and then became higher. The oxidative products were similar, except that θ-Al2O3 was relatively more in coating without TaC, while Y3Al5O12 was more in coating with TaC addition. The microhardness and wear resistance in both coatings decreased after oxidation, however, it was on the same level for NiCoCrAlYTa coating before oxidation and NiCoCrAlYTa/TaC coating after oxidation. Thus, the overall high temperature performance of the coatings was improved due to the addition of TaC particles.

EFFECT OF WC BASED COATINGS ON THE WEAR OF CK45 SHEET METAL FORMING DIES

DIN 1.2379 tool steel has a wide range of applications in die manufacturing industry owing to its high wear resistance. However, CK45 steel is cheaper but extensive wear occurs on CK45 die and sheet metal surfaces, which were attempted to be solved using a hard phase coating. An insert on a die was designed and manufactured for the area where the wear is expected the most. Electro-spark deposition (ESD) coating layer was formed with two separate layers of WC (tungsten carbide) and WC+SS (tungsten carbide and stainless steel) on die surfaces using optimum parameters to obtain wear resistant surfaces as a means of controlling the friction between sheet metal-die surfaces. After 500 pressings, insert surfaces were characterised by optical and scanning electron microscopy. The results showed that defects on sheet metals were reduced following the application of hard phase ESD coating. The microhardness values of ESD coatings were higher than that of CK45 base metal and similar to hardened DIN 1.2379 steel.

Structure and Wear Resistance of FeNiCrBSiC–MeB2 Electrospark Coatings

The structurization of coatings produced by electrospark deposition (ESD) from the commercial selffluxing FeNiCrBSiC alloy and FeNiCrBSiC-based composites, such as FTB20 (FeNiCrBSiC–20 wt.% TiB2) and FCB20 (FeNiCrBSiC–20 wt.% CrB2), on a steel 45 substrate was studied. The electrospark FeNiCrBSiC coating about 70 μm thick has a globular surface and the FTB20 and FCB20 coatings form a continuous layer up to 50 μm thick over the entire samples. The microhardness does not change across the deposited coating thickness and is 10–14 GPa. The chemical compositions of the ESD coatings and the electrodes are the same, which indicates that the electrode material does not mix with the steel substrate. The structure of the FeNiCrBSiC, FTB20, and FCB20 electrodes and coatings differs significantly because chromium boride and/or titanium boride inclusions refine from 20–25 μm to 1 μm in the ESD process. The heterophase structure of the ESD coatings represents a nickel–iron-base matrix reinforced with fine boride and carboboride particles. The effect of speeds and loads on the wear rate of ESD coatings in dry friction conditions was examined. Electrospark coatings produced from the WC–6% Co hardmetal were tested as wear resistance reference. The wear rate of the FeNiCrBSiC, FTB20, and FCB20 coatings decreases and that of the WC–6% Co coating increases when the speed rises from 4 to 12 m/sec. The wear rate of the ESD coatings becomes one order of magnitude higher when the load increases from 0.1 to 0.4 MPa. Analysis of the friction surfaces showed that wear of the FeNiCrBSiC coating was caused by failure of the globules and that of the FCB20 coating by brittle fracture of the deposited layer. The ESD FTB20 coating has two to three times higher wear resistance than the FeNiCrBSiС coating because of the oxidative wear mechanism whereby protective oxide films develop on the friction surfaces and act as a solid lubricant.

The Morphology and Mechanical Properties of ESD Coatings before and after Laser Beam Machining.

Electro-spark deposition (ESD) and laser beam machining (LBM) are the technologies using the concentrated energy flux. This paper deals with the issue of the impact of laser modification on the morphology and mechanical properties of carbide/copper coatings produced by electro-spark treatment. The coatings were applied to C45 carbon steel samples using the EIL-8A device. The following three types of electrodes made using the powder metallurgy (PM) hot pressing technique, from copper and tungsten carbide powders of different percentage compositions, were used for the coatings: 25% WC and 75% Cu; 50% WC and 50% Cu; and 75% WC and 25% Cu. Laser modification of the surface layers was performed with an Nd:YAG laser. The research focused on the analysis of the morphology of coatings applied by electro-spark technology before and after laser processing. The analysis of the morphology of electro-spark coatings revealed that the coatings had microcracks and pores. The laser beam machining of ESD coatings led to the homogenization of chemical composition, fragmentation of the structure, and elimination of microcracks. In addition, measurements of porosity, microhardness, adhesion, and analysis of XRD phase composition of the electro-spark coatings were performed. Laser processing proved to have a positive effect on improving the adhesion of coatings and reducing their porosity. This paper also presents a simulation model of heat transfer processes for the case of laser radiation impact on a WC-Cu coating. The developed numerical model, describing the influence of laser treatment on the distribution of temperature fields in the heated material (at a given depth) is of significant importance in the development of treatment technologies. Laser-modified ESD coatings perform anti-wear and protective functions, which enable their potential application in means of transport such as rolling stock.

Modeling Technological Parameters for Producing Combined Electrospark Deposition Coatings

The paper represents a formalized methodology for solving the problem of creating fundamentally new materials, such as "base - coating" ones, which have increased surface wear resistance and relatively high strength and viscosity. Electrospark alloying (ESA) method is proposed as a process for depositing protective coatings on metal surfaces. There are considered the issues of improving the quality of the coatings formed by the ESA method. There is specified a feature of processing the surfaces having been treated with the use of the ESA method, which feature being associated with a relatively small thickness of the layers formed (tens of micrometers). Since to reduce the roughness of the surface, the process of grinding is difficult or even unacceptable to perform, it has been suggested to use the method of surface plastic deformation (SPD). One of the effective SPD methods for finishing the parts is a diamond smoothing process, which, in contrast to running-in with a ball or roller, allows processing the parts of very high hardness values. As a reserve to improve the quality of coatings formed by the ESA method, there is considered a process for producing combined electrospark deposition coatings (CEC) with hard wear-resistant and soft anti-friction metals integrated therein. There are represented the results of mass transfer process investigation performed at forming the CEC on the specimens of steel 45 with indium, tin and copper being used as soft antifriction metals, and tungsten and hard alloy of VK8 grade applied as wear-resistant materials. There is represented a mathematical model for calculating the main ESA technological parameters being necessary for forming the CEC and allowing to predict the weight gain (increase in weight) and size gain (increase in size) at the cathode (the part). It allows predicting the CEC main technological parameters for any electrode pair materials (substrate material and electrode materials making up the CEC).

Considerations regarding WC-cermets depositions by HVOF and ESD techniques used for reinforced steel components for geothermal turbines

The cumulative effect of erosion-corrosion process in geothermal turbines results in significant damages, especially for rotors and turbine blades; the degree in which they are affected depends on steam temperature, mechanical impact and the geothermal composition of the substances dissolved in steam. Layer composite materials are a feasible option to improve the erosion-corrosion resistance and the durability of turbine components. There cermet powders containing tungsten carbide are used for High Velocity Oxy-Fuel (HVOF) spaying and for Electro Spark Deposition (ESD) to obtain graduate microstructure and to form local hard structures. Both techniques by WC-cermet depositions were found to be most suitable to improve wear resistance, to repair rotors and blades and to provide possible life extension of geothermal turbines. The paper presents a comparative assessment of tungsten carbide and the technological parameters used for HVOF and ESD cermets layers depositions. Also, the work presents the analysis of the micro chemical composition of the microstructure, the micromechanical characterization and erosion-oxidation resistance of HVOF and ESD coatings using WC-cermets on steel substrates. The experimental procedure involved X-ray diffraction of the samples, micro mechanical tests and SEM investigations to provide specifically information about micro-morphological modifications and grade of adhesion of protective layers.