Electrospark Deposition Research Articles

Fabrication, microstructural characterization and mechanical properties evaluation of Ti/TiB/TiB2 composite coatings deposited on Ti6Al4V alloy by electro-spark deposition method

In this study, briquettes of Ti–TiB–TiB2 composite were produced by mixing Ti and B powders, performing self-propagating high-temperature synthesis process and by applying hydrostatic pressure on the reaction products with a high-capacity press. Ti–TiB–TiB2 was then coated to Ti6Al4V substrate by Electro-Spark Deposition (ESD) technique under two atmospheres of air and argon, single and double-layer coatings and in two energy levels of 40 W and 110 W as input powers. Coatings microstructure were examined by Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS) analyzer. Comparison of the coatings microstructure with the electrode microstructure shows that the coatings have a much finer microstructure than that of the electrode due mainly to the high solidification rate in the ESD process. Microstructural observations also revealed that the main phases in the coatings are needle-shaped TiB and particle-shaped TiB2 in the Ti matrix. The coating microstructure was much finer due to an increase in solidification rate by reducing the input power from 110 to 40 W. In such a situation, two phases of TiB2 and TiB with nanometer sizes were scattered in the Ti matrix. Also, due to the trapping of the gases in low input power of 40 W, a limited number of very small gas pores was created in the microstructure. Interface examination of the coating and the substrate by the Line Scan and X-ray Image show a good coherence of the coating with the substrate. Adhesion results showed that the bond strength between the coating and the substrate was higher than 50 MPa in all coatings. No crack was observed in the coatings after bending tests which were performed, in accordance with the intended standard, on the samples around a mandrel. The hardness of all coatings was increased with decreasing the input energy from 110 to 40 W.

Synthesis of Ti-Al intermetallic coatings via electrospark deposition in a mixture of Ti and Al granules technique

In this paper, the results of studies of the formation of Ti-Al intermetallic coatings on a Ti6Al4V alloy by the electric spark deposition method in a mixture of titanium and aluminum granules are presented. Five mixtures of granules with an aluminum concentration of 24 to 88 at.% were prepared. As the concentration of aluminum in the mixture of granules increased, the phase composition of the corresponding coatings changed from αTi and titanium rich aluminides to aluminum aluminides rich and Al. According to EDS analysis, with an increase of the aluminum content in the mixture of granules from 24 to 88 at.% its concentration on the surface of the coatings increased from 19 to 68 at.%. The main mechanism of Ti-Al coatings formation at electrospark granule deposition is convective mixing of melted materials of granules and substrate. Potentiodynamic polarization tests in a 3.5% NaCl solution showed that coatings can improve the corrosion resistance of the Ti6Al4V alloy. A high-temperature corrosion test for 100 h at 900 °C showed that coated samples were oxidized 1.1–3.4 times less than initial Ti6Al4V substrate. The best oxidation resistance properties showed the coating with the highest aluminum content. Electric spark granule deposition increase microhardness of Ti6Al4V alloy up to 6.4–9.4 GPa. The wear resistance of the coatings at dry sliding with 10 and 25 N loads was 4–27 and 6–36 times higher, respectively, than wear resistance of the initial alloy. The wear rate of coatings decreased with increasing titanium concentration.

Production of Zinc Coatings by Electro-Spark Deposition

Abstract The paper describes the method of producing a zinc coating on steel by electro-spark deposition technology. The technology of applying electro-spark zinc to the surface was presented. Microscopic observations and corrosion resistance tests were made. The possibilities of practical application of this type of coatings in the process of repairing zinc coatings, either damaged or with manufacturing defects, were analyzed.

Effect of Shock Sintering Temperature and Carbon Content of the WC–Co Hardmetal Anode on the Mass Transfer in Electrospark Deposition

The paper examines how the shock sintering temperature and carbon content of the VK25 hardmetal and the process time and discharge energy in the electrospark deposition of the hardmetal onto steel 45 samples influence the mass transfer, thickness, and microhardness of the resultant surface layers. The experiments were performed employing an Elitron-24 unit providing a discharge energy of 0.34–1.1 J. The VK25 hardmetal was produced by shock sintering in the range 1150–1300°C using WC with different carbon contents. For the maximum mass transfer, the hardmetal sintering temperature should be 100–150°C lower than the temperature at which samples with the highest strength were produced. The maximum mass transfer was observed when the hardmetal was depleted of carbon (3.9 instead of estimated 4.59 wt.%). A protective layer 100–200 μm thick, with a hardness of 8.0–13.7 GPa, was produced on the steel samples.

Effect of Laser Processing on the Qualitative Parameters of Protective Abrasion-Resistant Coatings

The wear of centrifuge screws, common components in industrial and municipal wastewater treatment plants, is studied. The TN-20 tungsten-free hardmetal serves for protecting screw flights against abrasive wear. The 12Kh18N10T steel is primarily used in the manufacture of centrifuge screws. A combined technique of depositing protective wear-resistant coatings is proposed. The technique includes electrospark deposition of a T15K6 hardmetal electrode, application of a metal polymer material (MPM), and final laser processing. To reinforce the MPM, small portions of a VK6 hardmetal mixture were added to a two-component epoxy system filled with ferrosilicon and thoroughly stirred. The reinforcement content was ~60%. This technique produces coatings up to 600 μm thick, with 7.3–10.0 GPa microhardness and 100% continuity. Abrasive water jet tests of the 12Kh18N10T steel samples with protective coatings show that their wear resistance is 7.5 times higher than that of the uncoated samples.

Effect of Cr-Ni coated Cu-Cr-Zr electrodes on the mechanical properties and failure modes of TRIP800 spot weldments

Resistance spot welding (RSW) is a highly preferred welding process in the automotive and other industries because of its faster and economical processes and also it has higher quality. However, during the joining process, the temperature at the electrode tip reaches the highest value and, in the meantime, electrode tips are deformed. For this reason, the electrode wears down with increasing weld numbers, which changes the thermal, electrical, and mechanical contact conditions at the electrode and sheet interfaces. The coating is generally applied onto the surface of Cu–Cr–Zr electrodes for extended electrode life during RSW process. In this study, the tip surfaces of the electrodes were coated with Cr–Ni filler metal by using electro-spark deposition (ESD) coating method under 40, 80, and 120 V. Consequently, the effects of the coating on electrode characteristics and properties of the TRIP800 resistance spot weldment are investigated. The mechanical behaviors of the joined samples under static load were investigated by applying a tensile shear test and cross tension test. Tensile-shear strength, cross-tension strength was determined, and the failure modes of the samples was investigated. The nugget size was measured by stereo microscope. Microstructure investigations have also been carried out by optic microscope and scanning electron microscopy (SEM).

Comparative investigation of single-layer and multilayer Nb-doped TiC coatings deposited by pulsed vacuum deposition techniques

Hard-yet-tough coatings are required to protect structural materials, cutting, stamping, and forging tools operating under harsh conditions that combine wear, corrosion, and elevated temperatures. To reveal the high potential of niobium (Nb) as an additive to binary Ti-based coatings, single-layer and multilayer Nb-doped TiC coatings were obtained by pulsed arc evaporation (PAE), electro-spark deposition (ESD) in vacuum, and combination of these methods. Structure, elemental, and phase compositions were studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The coatings were characterized in terms of their hardness, elastic modulus, tribological properties, and electrochemical behavior in 3.5% NaCl solution. Tribological tests were carried out under various conditions, such as applied load (5 and 10 N), medium (air and 3.5% NaCl solution), and counterpart material (Al2O3 and 440C steel). Thin PAE coating (1.8 μm thick) consisted of 2–5 × 50–100 nm (Ti,Nb)C crystallites, elongated in direction of the coating growth, embedded in an amorphous matrix (75% sp2 + 25% sp3-hybridized carbon). Thick ESD coating (20 μm) contained TiC grains uniformly distributed in an eutectic Fe(Co)-Fe2(Ti,Nb) matrix with a minor content of Ti-Ni and γ-Fe phases. The single-layer PAE coating demonstrated superior tribological performance both in air and 3.5% NaCl solution, as well as high oxidation resistance during tribocorrosion tests. As a top layer in the PAE/ESD coating, it provided wear protection of less wear-resistant ESD sublayer. It is assumed that the main benefit of the ESD sublayer in the PAE/ESD coating may be that it provides enhanced toughness and high thickness, which prevents a soft substrate from high stress-induced plastic deformation.

Structural and tribological properties of wear resistant coatings obtained by electrospark deposition

In the present work, a new type of wear-resistant coatings obtained on steels by non-contact Electrical Spark Deposition (ESD), using a rotating electrode has been studied. Multicomponent electrodes for ESD containing WC-Co, Ni-Cr-B-Si semi-self-fluxing alloys and additives of superhard and refractory compounds of B4C and TiB2 have been obtained by the methods of mechanochemistry and powder metallurgy. The phase composition, microhardness and structural peculiarities of the coatings have been studied using methods of XRD, optical microscopy and SEM. The influence of the electrode composition and parameters of the deposition process on the structure, roughness, thickness, and abrasion wear of coatings have been studied. Tribological properties and wear resistance characteristics of coatings have also been examined. Coatings obtained using examined electrodes show higher friction and abrasion wear resistance than that obtained by conventionally used materials.

Structural and Tribological Properties of Multicomponent Coatings on 45 and 210Cr12 Steels Obtained by Electrospark Deposition with WC-B4C-TiB2-Ni-Cr-Co-B-Si Electrodes

In the present work, a new type of wear-resistant coatings obtained on steels by contactless electro-spark deposition using a rotating electrode and by electrical discharge deposition with a vibrating electrode has been studied. Electrodes have been obtained by pressing and sintering multi-component powder mixtures of hard metal WC-Co with additives of super-hard and refractory compounds of B4C and TiB2 and semi-self-fluxing alloys Ni-Cr-B-Si. High density coatings, with a thickness up to 80 μm and micro hardness up to 17.0 GPa, have been obtained. The roughness, thickness, composition, and structure of the coatings thus obtained have been studied by X-ray diffraction, scanning electron microscopy, and electro-spark deposition. The influence of micro-geometric parameters, composition and structure of coatings on their tribological properties and wear resistance were studied by comparative tests of friction and abrasion wear. The friction tests showed that the wear of the coated steel surfaces is up to 5 times lower compared to the uncoated those. On the base of the experimental data, a comparative analysis of the coatings obtained by the two methods have been made. Appropriate regimes and conditions for deposition of coatings with optimal properties have been defined.

Investigation of Wear and Corrosion Behaviour of AISI 316 L Stainless Steel Coated By ESD Surface Modification

AISI 316 L austenitic stainless steel is widely used in various sectors of the industry (chemical, petro-chemical industry, paper industry, nuclear engineering, dairy equipment and medical field) because of its good corrosion resistance and biocompatibility. In contrast to these superior properties, it has a low hardness and poor wear performance, thus, limiting its use in some areas of industry. As a result of progress in science and technology, the expectation of superior properties from materials has increased and the surface modification has become an important part of this development. Amongst many coating processes, Electro-spark Deposition (ESD) is a micro-bonding process that is used to deposit a stronger, more robust and durable coating layer on a metallic substrate. This method can also be used to repair damaged parts, tools or equipment or to extend the tool and equipment life. In this study, the surface of AISI 316 L stainless steel was coated with WC and Ti6Al4V by ESD method. Morphology and microstructure of the deposited layers were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Surface hardness distributions were determined with a micro hardness tester. XRD analysis revealed that Fe–α, Fe–γ, W2C, Cr–Ti, Al–Fe–Ti phases exist on the deposited layers. The wear behavior of the coated surfaces was carried out by ball-on-disc wear method using WC-Co ball bearing with a diameter of 8 mm for a sliding distance of 250 meters at a sliding rate of 0.3 m/s under a dry condition using a load of 5 N. Corrosion behavior of coated surfaces i.e. Tafel extrapolation and linear polarization methods were investigated for the duration of 1 h in the SBF (Simule Body Fluid) solution. Morphology of layers formed on steel surface was examined by SEM microscope. Wear tests showed that AISI 316 L stainless steel has a low surface hardness but wear resistant coatings improved this property. The wear rate of coated AISI 316 L stainless steel decreased by 3–10 times with respect to the type of coating. The electrochemical experiments showed that the expected improvement was not achieved due to the high corrosion resistance of AISI 316 L stainless steel. However, the weakness of the surface hardness was partly replaced by an acceptable compromise from corrosion resistance.

Electro spark deposition of WC–TiC–Co–Ni cermet coatings on St52 steel

The electro spark deposition (ESD) technique has been successfully applied to deposit a cermet layer of WC/TiC/Co/Ni at room temperature on a St52 carbon steel substrate and the electrochemical properties of the bare and coated samples were evaluated. Influence of ESD process parameters on electrochemical properties of coatings were examined by using of potentiodynamic polarization and impedance spectroscopy (EIS) techniques. It has been possible to obtain a dense coating with adjusting the ESD process as the current limit of 15 A, frequency of 11 KHz, duty cycle of 50%, rotating speed of 200 rpm and spark energy of 1.46 mJ. The results confirmed that the sample with these fabrication parameters had higher ESD efficiency with the value of 64% and the dense coating without holes and micro cracks could be fabricated through the process. The electrochemical tests also confirm the good quality of the optimized coated sample. According to the results, the largest corrosion resistance with maximum Rcoat 76.16 Ω cm2 was observed in optimized coating condition.

Comparative study of coatings obtained by ESD method using TiC–NiCr and TiC–NiCr–Eu2O3 electrodes

The study covers coatings obtained on 40Kh steel substrates by electro-spark deposition (ESD) using TiC–NiCr and TiC–NiCr– Eu2O3 electrodes. Coatings were deposited by the Alier-Metal 303 unit in argon environment under the normal pressure using direct and opposite polarity. The structure, elemental and phase composition of electrodes and coatings were studied using X-ray phase analysis, scanning electron microscopy, energy dispersive spectroscopy, glow discharge optical emission spectroscopy, and optical profilometry. Mechanical and tribological properties of coatings were determined by nanoindentation and testing according to the «pin-disk» scheme including high-temperature conditions in the range of 20–500 °C. The tests conducted include abrasive wear tests using the Calowear tester, impact resistance tests using the CemeCon impact tester, and tests for gas and electrochemical corrosion resistance. Test results showed that electrodes contain titanium carbide, nickel-chromium solid solution, and europium oxide in case of a doped sample. Coatings exhibit the same phase composition but solid solution is formed on the iron base. Coatings with the Eu2O3 additive do not differ significantly in structural characteristics, hardness, friction coefficient, and exceed the base coatings in terms of their abrasive resistance, repeated impact resistance, heat and corrosion resistance. There was an increase in impact resistance by 1.2–2.0 times, a decrease in corrosion current by more than 20 times, and an oxidation index by almost 2 times during the transition to doped coatings.

Effect of ElectroSpark Process Parameters on the WE43 Magnesium Alloy Deposition Quality

This research aims to investigate the effects of process parameters on the quality of WE43 coatings deposited on homologue substrate by ElectroSpark Deposition (ESD) technology. ESD is new technology used to apply coatings or for the restoration and refurbishment of worn or damaged high valued parts. The depositions were processed using five different levels of Energy input (Es, Spark Energy). The microstructure of both the base material and deposits cross-section were characterized by optical and scanning electron microscopies. Also, X-ray diffraction technique was used. In addition, stereological studies of the through-thickness heterogeneities of the deposits (e.g., voids) were performed. The mechanical properties were evaluated by Vickers micro-hardness. The results show that the deposits exhibited a fine grained microstructure due to the rapid solidification. The average micro-hardness values of the deposits are lower than that of the substrate and distributed in a small range (49–60 HV). The lower hardness of the deposits respect to the base material is due to the presence of defectiveness such as spherical, laminar and random shaped voids. The defects area percentage inside the deposits remains well below than 11%. All the deposits were mainly affected by laminar morphology defects. The results indicate that the deposits defectiveness decreases as the energy input increases.

Magnetic-aided electrospark deposition

A new electrospark deposition (ESD) method and related system are provided in the present invention based on the use of a magnetized electrode, namely magnetic-aided ESD (M-ESD). In particular, the present invention uses a magnetized electrode (either magnetized by an electro-magnet or being a permanent magnet) to attract fine coating powders at the tip thereof which acts as a soft brush to coat on intricate surface profiles. Accordingly, the method of the present invention is able to provide a soft contact between the magnetized anode and the workpiece to be coated or manipulated. The present invention is useful in various surface engineering applications in the fields of aeronautical (e.g. restoration and repair of damaged aircraft turbine blades), nuclear reactors, military engineering, and in medical industries. As compared to conventional ESD, the present invention can address complicated surface geometries and internal surfaces while the cost can be significantly lowered by using inexpensive components and simplified method steps.

Control of Metal Surface Mechanical and Tribological Characteristics Using Cost Effective Electro-Spark Deposition

Electro-spark deposition (ESD) has been already recognized as an economically effective surface coating method. It requires a simple and low-cost equipment to run a process. Furthermore, mechanical and tribological properties of the coatings deposited using ESD are very promising, being, in many cases, improved compared to those of a substrate. When coatings are secondary treated via laser beam, they get a smoother surface and an amorphous structure. This paper reviews the investigations conducted on different substrates using different deposition materials via ESD as well as those of mechanical and tribological properties obtained. In particular, the review specifies: the role of ESD in enhancing the metal surface mechanical and tribological characteristics. It seems reasonable to apply ESD wider in order to improve mechanical and tribological properties of metal surfaces.

Application of Electrospark Deposition and Modified SHS Electrode Materials to Improve the Endurance of Hot Mill Rolls. Part 2. Structure and Properties of the Formed Coatings

The electrospark deposition of coatings onto SPKhN–60 white cast iron samples has been undertaken in two stages. A barrier sublayer has been deposited at the first stage, using chromium and nickel electrodes, and a multifunctional protective coating was deposited at the second stage. The effect of the sublayer on coating properties upon application of STIM–40NAOKn (TiC–NiAl + $${\text{ZrO}}_{2}^{{{\text{nano}}}}$$ ) and STIM-11OKn (TiB2–NiAl + $${\text{ZrO}}_{2}^{{{\text{nano}}}}$$ ) electrodes is studied. The coating structures are investigated. The grain size of the refractory phase is found to be smaller than 100 nm. The application of double-layer coatings increased the wear and heat resistances of white cast iron samples. Pre-deposition of a nickel sublayer enhanced the heat resistance of STIM-11OKn coating over eightfold. The full-scale tests of the rolls strengthened using SHS electrodes were carried out and positive results were obtained.

Mathematical Modeling of Roughness Changing of Hard Metal Coatings Obtained by Contactless Electrospark Deposition

Results of the roughness studies of multicomponent hard metal layers on X12 tool steel (210Cr12/1.8–2.2% C, 12%Cr) obtained by contactless local electrospark deposition using two types hard metal electrodes (WC–TaC–Co–Al2O3 and WC–(Ti, Ta, Nb)C–Co–Al2O3) are presented here. Dense, smooth, and uniform coatings with a good repeatability of properties have been obtained. The minimal and maximal values of thickness δ, of the roughness parameter Ra, and of micro hardness HV of obtained coatings are changed by altering the stratification regimes in borders: δ = 3–12 μm, Ra = 0.8–2.2 μm and HV = 8.5–18 GPa, respectively. The influence of the process parameters and the electrode composition on the roughness of the layers obtained have been studied. Mathematical-statistical models and equations describing the roughness of the coatings have been created and worked out. They enable obtaining of coatings with a predetermined roughness by controlling regime parameters. Specific ways of obtaining coatings with reduced roughness at the maximum possible thickness, as well as recommendations for their appropriate application, have also been proposed and justified. Based on the obtained regression equations and graphical dependencies, it is possible to optimize properties of the coatings and the conditions of their deposition in order to obtain maximum tribo-effect and increased performance properties of the coated surfaces for different cases of exploitation.

Modification of the surface layer of magnesium with 1050A aluminum alloy using electrospark deposition

This paper discusses the results of the preliminary investigations into the use of electrospark deposition (ESD) for the surface enrichment of magnesium with 1050A aluminum alloy. The experiments focused on the effects of the capacitor’s value on the surface layer microstructure. Four capacitances were considered. The modified material was analyzed at the macro and micro scales, using optical and electron scanning microscopy. The microhardness of the modified layer was also determined.

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).

A novel method to fabricate composite coatings via ultrasonic-assisted electro-spark powder deposition

To improve traditional electro-spark deposition (ESD) technology and meet the requirements for special applications, a novel ultrasonic-assisted electro-spark powder deposition (UEPD) process is developed in this study. The unique electrode tool in this new method consists of a NiCrBSi alloy powder as a deposition material and a Cu electrode core as a support component, which are bonded to each other by means of a silver-containing conductive adhesive. By using this UEPD process, a metal matrix composite (MMC) coating is successfully fabricated on ASTM 1045 steel. The coating has an average thickness of approximately 52.3 μm and exhibits efficient metallurgical bonding with the substrate as well as good continuity. The microstructure in the coating mainly presents submicron-columnar dendrites that epitaxially grow perpendicular to the substrate surface, which mainly contain a Ni-rich γ-(Ni, Fe) solid solution, intermetallic FeNi3 and Cr-rich carbide and boride precipitates. These refined grains and hard reinforcements significantly increase the hardness and tribological properties of the coating. Combining the discharge morphology, microstructure and chemical composition of the UEPD electrode and coating, the formation process of the UEPD coating is analysed and discussed in detail. The adhesive NiCrSiB powder layer was melted and transferred to the surface of the substrate during the UEPD process. The separation of the powder tends to start from the interface of the powder layer and electrode core due to weak connectivity. This behaviour is considered beneficial to the quantitative control of powder deposition. In addition, the introduction of ultrasonication can promote dispersion of the metal droplets to obtain a better quality coating.