Electrical Discharge Coating Research Articles

Microstructure study on electro discharge deposited magnesium alloy with semi sintered and sintered electrode

In this research, electro discharge deposited ZE41A magnesium alloy with semi sintered and sintered electrode are studied. Parameters used in this study were compaction load, current and pulse on time and coating responses were material deposition rate (MDR), micro hardness (MH). For the electrical discharge coating (EDC), electrodes were prepared using tungsten carbide and copper powder by powder metallurgy method. It was observed that the MDR and MH increased when increased current and pulse on time in low compaction load for semi sintered and sintered electrode. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were analysed in the deposited surface to study the microstructure and presence of electrode materials respectively. Comparative microstructure study on electrical discharge coating of ZE41A magnesium alloy with powder metallurgy semi sintered and sintered electrode was carried. Among two conditioned electrode, semi sintered electrode has the higher material deposition rate and micro hardness. Further increased the sintering temperature the deposition is formed with the large cracks and craters.

Surface modification of nitinol by using electrical discharge coatings in deionized water

Nitinol, also known as nickel-titanium shape memory alloy, has a high potential in medical implantation due to its unique mechanical properties, shape memory effect, and low modulus of elasticity which close to bone’s modulus. However, high composition of nickel element in this alloy is harmful whenever the element is released into human body that can induce inflammation and allergic reactions. The objective of this study is to develop a deposition layer of titanium oxide on nitinol surface through the study of electrical discharge coatings (EDC) parameters effects. In particular, deionized water and pure titanium rod were as the dielectric fluids and electrodes, respectively, during the EDC process. Variation settings of polarity, gap voltage and erosion depth were employed in this study. Experimental results examined the coating thickness and surface roughness through full factorial design with ANOVA analysis. It was determined that the polarity gave the highest significant effect on the deposition thickness. Meanwhile, the interaction between polarity and gap voltage was exhibited significant effect to the surface roughness. In additional, reverse polarity and low gap voltage were preferred in EDC process to provide good surface roughness and higher uniformity of the material deposition.

Changes in Surface Roughness Caused by Electrical Discharge Coating

The effects of surface modification using an electrical discharge coating are investigated. The electrode used for the machining process is a Ti-type semi-sintered compact electrode. A thin and hard layer is formed on the machining surface. In this paper, the change in surface roughness during electrical discharge coating is described. The accretion layer surface became coarse after 10 min of machining. The peak height also increased. After 30 min of machining, the height of the accretion layer was lower than the original surface level, and the peak height decreased. Furthermore, the core roughness value increased. The surface roughness increased within several minutes from the start of electrical discharge coating using a Ti-type semi-sintered compact electrode. In this paper, we report on the temporal change of surface roughness during electrical discharge coating.

Optimization of Electrical Discharge Coating Process by Desirability Function approach

Optimization of Electrical Discharge Coating Process by Desirability Function approach

Preparation of MoS2+Cu coating through the EDC process and its analysis

ABSTRACTA solid-lubricant coating of molybdenum disulphide (MoS2) and copper (Cu) powder has been prepared on the mild steel substrate using electrical discharge coating (EDC) technique. The effect of machining parameters (peak current, duty factor, and powder mixing ratio) on surface integrity and tribological characteristics of the coated surface has been investigated. XRD result indicates the formation of different compounds such as Mo, Cu, MoS2, and FeS on the coated surface during the EDC process. The maximum coating thickness of 0.647 mm has been achieved. The coating exhibits lower hardness value (45.49 HV0.2–114 HV0.2) than that of a substrate (180HV0.2) which leads to the solid lubricating properties. Pin-on-disc tribometer has been used to observe the wear behaviour of the samples and found that average wear of the coated surface is 4.56 μm as compared to the mild steel substrate (95.61 μm).

Surface Modification of Ti-6Al-4V Alloy by Electrical Discharge Coating Process Using Partially Sintered Ti-Nb Electrode.

In the present research, a composite layer of TiO2-TiC-NbO-NbC was coated on the Ti-64 alloy using two different methods (i.e., the electric discharge coating (EDC) and electric discharge machining processes) while the Nb powder were mixed in dielectric fluid. The effect produced on the machined surfaces by both processes was reported. The influence of Nb-concentration along with the EDC key parameters (Ip and Ton) on the coated surface integrity such as surface topography, micro-cracks, coating layer thickness, coating deposition, micro-hardness has been evaluated as well. It has been noticed that in the EDC process the high peak current and high Nb-powder concentration allow improvement in the material migration, and a crack-free thick layer (215 μm) on the workpiece surface is deposited. The presence of various oxides and carbides on the coated surface further enhanced the mechanical properties, especially, the wear resistance, corrosion resistance and bioactivity. The surface hardness of the coated layer is increased from 365 HV to 1465 HV. Furthermore, the coated layer reveals a higher adhesion strength (~118 N), which permits to enhance the wear resistance of the Ti-64 alloy. This proposed technology allows modification of the mechanical properties and surface characteristics according to an orthopedic implant’s requirements.

A Study on Wear Behaviour of Electrical Discharge-Coated Magnesium Alloy

Wear behaviour of ZE41A magnesium alloy coated with WC/Cu using electrical discharge coating (EDC) has been investigated in this study. The wear test was conducted with pin-on-disc machine using different conditions such as normal load of 1.5 kg, 2.5 kg, 3.5 kg and sliding speed of 100 rpm, 200 rpm, 300 rpm and sliding time of 3 min, 5 min, 7 min through L9 Taguchi orthogonal array to study the effect of sliding parameters on the wear characteristics. A wear transition map was constructed to describe the different wear conditions such as mild wear, severe wear and ultra severe wear. The main wear mechanisms for each wear regime were identified and classified through wear mechanism map. The worn-out specimens were characterized using scanning electron microscope (SEM) to identify the various wear mechanisms.

Surface modification of ZE41A magnesium alloy using electrical discharge coating with semi sintered electrode

This present paper highlights the influence of WC/Cu composite powder metallurgy semi sintered electrode on the substrate of ZE41A magnesium alloy through electrical discharge coating (EDC). The effect of predominant process parameters such as compaction load, current and pulse on time during EDC on metal transfer rate (MTR) and surface roughness (Ra) have been studied. Experiments have been carried out through central composite design (CCD) by response surface methodology (RSM). The developed empirical model is used for analysing the machining parameters on EDC. The most significant EDC parameters were ascertained using analysis of variance (ANOVA). From the experiment results, it can be revealed that the MTR is higher at low compaction load, high current and pulse on time. Surface roughness diminished at high compaction load, low current and pulse on time. Surface morphology of coated surface has been evaluated using scanning electron microscope (SEM). Presents of elemental analysis has been carried out using energy dispersive spectroscopy (EDS).

Experimental analysis of electrical discharge coating characteristics of magnesium alloy using response surface methodology

Electrical discharge coating (EDC) process is one of the surface modification method to deposit electrode material (WC 50% Cu 50%) on the surface of the desired material. In the present study ZE41A magnesium alloy has been coated using this method to form hard layer on the surface to resist wear and corrosion. Compaction load, current and pulse on time were selected as input responses to study the coating characteristics in the form of metal transfer rate (MTR) and surface roughness (Ra). Response surface methodology (RSM) was used to design and analysis the experiment. The most significant EDC parameters were ascertained using analysis of variance (ANOVA). From the result, it can be found that the MTR increases with increase pulse on time and decreases with high compaction load, where as MTR increases with increase current, further increase in current MTR decreases. Surface roughness increases with increases in current, pulse on time and low compaction load and conversely it diminishes with low current, pulse on time and high compaction load. Layer thickness and morphology of coated surface was analyzed using scanning electron microscope (SEM) and elements presents on the surface were confirmed using energy dispersive spectroscope (EDS).

Defect-free TiC/Si multi-layer electrical discharge coatings

The process of electrical discharge coating (EDC) may be used to deposit hard materials on conformal substrate surfaces. Next generation EDM'd components may exploit attachment phenomena to enhance recast layer properties, to avoid the need for recast layer removal. Here, a ceramic based composite layer was developed without cracking and porosity for the first time, using sequential coating using sacrificial TiC and Si electrodes. Attenuation of the discharge process by gap widening using Si debris in the gap explained improved layer properties. Composite coatings combining WC and TiC were also demonstrated, with good elemental intermixing. Attachment level was correlated strongly with melting point, with high melting point materials resisting ejection due to more rapid solidification. Nanoindentation showed the TiC and WC/TiC layers possessed the highest mean hardness values, approximately double that of the Cu based machined layer which itself yielded a much higher hardness of 11.0 GPa compared to 1.9 GPa of the substrate.

Wear performance of TiC/Fe cermet electrical discharge coatings

The tribological behaviours of TiC-based cermet coatings, prepared by electrical discharge coating (EDC) using a semi-sintered TiC tool electrode, have been investigated. The as-deposited coatings exhibited complex microstructures, comprising TiC grains within an Fe matrix, on both high speed steel (HSS) and 304 stainless steel (304-SS) substrates. The wear resistance of TiC/Fe cermet coatings, on both substrate types, increased dramatically (one and two orders of magnitude improvement in specific wear rate), compared to as-polished substrates. Further, EDC cermet coatings on HSS were typically 2–4 times more wear resistant, depending on loading, than those deposited on 304-SS, with wear performance reflecting the composite nature of the coating coupled with the mechanical properties of the substrate. Laser surface treatments used to improve surface integrity of the as-deposited coatings, through elimination of cracks and porosity characteristic of ED coating, acted to increase wear rates for all samples, with the exception of coatings on HSS under conditions of high loading. The general increase of wear rate was attributed to a significant reduction in the proportion of TiC within the ED coatings, after laser treatment, combined with an increase in grain size; whilst improvements to the wear performance of laser treated, cermet coated HSS, under high loading, was attributed to the avoidance of an abrasive wear mechanism.

Modelling and Characterisation of Electrical Discharge TiC-Fe Cermet Coatings

The creation of coatings via Electrical Discharge (ED) methods can enhance the functionality of components which are subject to prior ED machining process steps. However, the industrial application of these methods has been limited due to poor understanding of the fundamental interaction between energy source and material. In this paper, for the case of a TiC sacrificial electrode deposited onto a stainless steel, 2D transient heat transfer is modelled and solved by a finite difference method to estimate the effective fraction of total energy transferred to the workpiece, as well as heat distribution and expected microstructure upon ED coating (EDC). The model was validated via comparison with experimental data, as well as data in literature. In addition, a TiC coating was tested under dry sliding wear conditions to evaluate its tribological properties against an Al2O3 counter face sphere using ball-on-flat geometry. The effective amount of energy transferred to the workpiece is predicted to vary between 17% and 23% for increasing current, from 2 to 19 A, at fixed pulse-on time of 8μs; and between 7% and 53% for increasing pulse-on time, from 2 to 64μs, at fixed current of 10 A. Backscattered electron (BSE) imaging showed that the coatings comprised a metal matrix composite, with a complex banded fine-grained microstructure and different cooling rate across the coating. A TiC-based ED coating on 304 stainless steel (304-SS) yielded a wear rate two orders of magnitude lower than that of the substrate only.

Machining of Molybdenum by EDM-EP and EDC Processes

Molybdenum metal (Mo) can be machined with conventional tools and equipment, however, its refractory propertytends to chip when being machined. In this study, the nonconventional processes of electrical discharge machining (EDM) and electro-polishing (EP) have been conducted to investigate the machining of Mo metal and fabrication of Mo grid. Satisfactory surface quality was obtained using appropriate EDM parameters of Ip ≦ 3A and Ton < 80μs at a constant pulse interval of 100μs. The finished Mometal has accomplished by selecting appropriate EP parameters such as electrolyte flow rate of 0.42m/s under EP voltage of 50V and flush time of 20 sec to remove the recast layer and craters on the surface of Mo metal. The surface roughness of machined Mo metal can be improved from Ra of 0.93μm (Rmax = 8.51μm) to 0.23μm (Rmax = 1.48μm). Machined Mo metal surface, when used as grid component in electron gun, needs to be modified by coating materials with high work function, such as silicon carbide (SiC). The main purpose of this study is to explore the electrical discharge coating (EDC) process for coating the SiC layer on EDMed Mo metal. Experimental results proved that the appropriate parameters of Ip = 5A and Ton = 50μs at Toff = 10μs can obtain the deposit with about 60μm thickness. The major phase of deposit on machined Mo surface was SiC ceramic, while the minor phases included MoSi2 and/or SiO2 with the presence of free Si due to improper discharging parameters and the use of silicone oil as the dielectric fluid.

Modelling of single spark interactions during electrical discharge coating

Electrical discharge coating (EDC) methods may be used to enhance the surface functionality of electrical discharge machined components. However, industrial uptake of EDC has been restricted due to limited understanding of the fundamental interactions between energy source and workpiece material. The fraction of energy transferred to the workpiece, Fv, as a consequence of sparking, is an important parameter which affects directly crater geometry and the microstructural development of the near surface modified layer. In this paper, a 2D transient heat transfer model is presented using finite difference methods, validated against experimental observations, to estimate effective values for Fv as a function of processing conditions. Through this method we can predict coating layer thicknesses and microstructures through appropriate consideration of heat flow into the system. Estimates for crater depths compared well with experimentally determined values for coating layer thicknesses, which increased with the increasing fraction of energy transfer to the workpiece. Predictions for heat transfer and cooling of melt pools, arising from single spark events, compared well with experimental observations for the developed cermet microstructures. In particular, intermediate processing conditions were associated with the development of complex, banded, fine-grained microstructures, reflecting differences in localised cooling rates and the competing pathways for heat conduction into the substrate and convection within the dielectric fluid. Increased pulse-on times were associated with a propensity towards increasing grain size and columnar growth, reflecting the higher energies imparted into the coatings and slower cooling rates.

Formation mechanism of electrical discharge TiC-Fe composite coatings

Comparison of electric discharge (ED) processed single deposit and continuum TiC-Fe cermet coatings, formed from a sacrificial powder metallurgy TiC tool electrode at negative polarity, on 304 stainless steel, provided insight into the ED coating (EDC) formation mechanism. A deposit from a single spark event was dominated by TiC, phase separated from a ∼2wt% Fe matrix, with strongly aligned grains and banded microstructure, indicative of solidification from the coating/substrate interface. Conversely, a continuum coating, subjected to ∼200 spark events per location, exhibited a more complex, banded microstructure, with a mixture of equiaxed and columnar TiC grains within a ∼30wt% Fe-based matrix, along with some concentrations of carbon from the oil dielectric. It is considered that each sparking event remelts previously solidified coating material, with or without further TiC particle incorporation, leading to gradual TiC dilution and the development of a TiC-Fe composite coating with increasing levels of substrate material forming the matrix.

Electrical discharge coating of nanostructured TiC-Fe cermets on 304 stainless steel

The electrical discharge coating (EDC) process, as used for the development of TiC-Fe cermet coatings on 304 stainless steel, has been investigated as a function of increasing current (2–19 A) and pulse-on time (2–64 μs). Coating morphologies, comprising of a mixture of TiC, γ-Fe, ά-Fe and amorphous carbon, were characterised using the combined techniques of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and cross-sectional transmission electron microscopy (TEM). The developed coatings exhibited variable hardness values, up to an order of magnitude higher than that of the substrate, depending on the content and dispersion of nanostructured TiC particles within the Fe matrix. Coating hardness was found to increase with increasing current, but decrease under conditions of high pulse-on times, reflecting differences in the amount of TiC incorporated into the coatings. Optimised coatings were achieved using conditions of low processing energy which minimised the development of pores and cracks.

Influence of Workpiece Materials on the Characteristics of the Layers by Electrical Discharge Coating

We investigated the influence of iron-based workpiece materials on the characteristics of the Si layers by electrical discharge coating. It was found that the chemical elements of the precipitations were uniformly dispersed in the layers on the workpieces containing precipitations a few micrometers in diameter. By contrast, voids occurred in the layer on the workpiece containing bigger precipitations because the precipitations that had not totally melted in the coating process were the starting points of the voids. In addition, the surface of the Si layer on FC250 was extremely rough, and the distribution of the chemical elements of the layer was inhomogeneous. However, the layer was amorphous, and the friction coefficient of the layer was lower than that of the workpiece.

Fabrication of a hydroxyapatite-containing coating on Ti–Ta alloy by electrical discharge coating and hydrothermal treatment

Abstract This study presented a method to surface-modify titanium alloy by electrical discharge coating (EDC). A hydroxyapatite (HA)-containing coating was formed on a 70Ti–30Ta alloy using EDC followed by hydrothermal treatment. Distilled water with HA powder was used as a dielectric medium in the EDC process. The microstructure, chemical composition, surface roughness, and wettability of the coating were characterized. The surface of the coating comprised Ti and Ta oxides and contained Ca and P. The thickness of the coating was approximately 7 μm. After hydrothermal treatment at 150 °C, the incorporated Ca and P precipitated to form petal-like HA crystals on the coating surface. The HA-containing coating exhibited hydrophilic tendencies.

Mechanism of Defect Generation in the TiC Layer and Si Layer by Electrical Discharge Coating

Defects such as cracks and voids are generated in the layer by electrical discharge coating. An effective method for suppressing the defects is not established because the mechanism of the defect generation has not been clarified. In this study, we investigated the characteristics of the TiC layer and Si layer on S50C by electrical discharge coating, and compared the generation state of the defects in the layers. In addition, we investigated the generation process of the defects in the layers. As a result, it was found that cracks and voids were generated in the TiC layer, and voids were generated and cracks were not generated in the Si layer. The number of voids in the TiC layer was greater than that in the Si layer. Compared with the whole surface of the TiC layer, the concentration of Fe at the voids of the layer was high and that of Ti and C was low. Compared with the whole surface of the Si layer, the concentration of Fe at the voids of the layer was high and that of Si and C was low. It became clear that neither crack nor void was generated in the first single discharge craters on the workpiece in the TiC layer and Si layer. Several voids and cracks were generated in the TiC layer and a few voids were generated in the Si layer when two or more of the discharge craters were deposited by progress of the coating.

Morphology and Wear Behaviour of Single and Multi-layer Electrical Discharge Coatings

Electrical discharge coating (EDC) is a version of electrical discharge machining (EDM) which can produce a coating of material from a tool or from a powder suspended in the oil, onto a workpiece. Since spark temperatures are high, a large range of materials, such as hard ceramics, can be melted and deposited in the coating. These material properties, combined with the rapid quenching of the EDC layer, result in coatings which are typically very hard. Since EDC is an adaptation of EDM, coatings can be produced on components with conformal surfaces. In this study, hard ceramic materials tungsten carbide and powder-sintered titanium carbide are used as negative polarity tool electrodes, from which material is donated to produce hard coatings. The workpiece material is 304 stainless steel. Mechanical properties of the single and multi-layer coatings are assessed by dry sliding wear testing using the ball-on-flat method. Morphology and composition both on the surface and in cross-section are also analysed using SEM and EDX. The TiC single layer coating produced the best wear results for the conditions of the experiment, with the lowest and most constant coefficient of friction of approximately 0.2-0.3 despite cracking remaining in this layer. The TiC + Si double coating, despite better morphology including eliminated surface cracks, produced worse friction characteristics compared to TiC.