Electropolishing Parameters Research Articles

Electropolishing study of metastable austenitic steel AISI 347 for EBSD analyses

Abstract For the metastable austenitic steel AISI 347 (X6CrNiNb18-10), various electropolishing parameters were evaluated by means of hardness testing, electron backscatter diffraction (EBSD), and atomic force microscopy. Depending on the chosen parameters, different surface characteristics could be achieved simply by only varying voltage, flow rate, and polishing time, although EBSD indexing was always possible. Differences in hardness of up to 20 HV0.5 and in microscopic roughness could be detected on otherwise comparable samples. Finally, the microstructure distribution of a hot rolled bar material with a diameter of 153 mm made from AISI 347 was characterized over the cross section using the previously determined parameter set. Here, insights about recrystallization during forming were concluded and δ-ferrite was differentiated from α’-martensite by kernel average misorientation and morphology.

Electropolishing of complex-shaped bulk metallic glasses in NaCl-ethylene glycol electrolyte

Electropolishing (EP) has been widely used to obtain good surface roughness of metallic structures; however, precisely-shaped cathodes are still necessary for the EP of bulk metallic glass (BMG) devices and components. In this work, the EP behavior of a Zr-based BMG was investigated using a plain steel cathode in NaCl-ethylene glycol electrolyte. The recast layer of wire electrical discharge machined (WEDMed) BMG surfaces with crystallization was effectively removed through the EP process, restoring the surface properties of BMGs. The effects of processing parameters, such as voltage, temperature, time, and electrolyte concentration, on the EP performance were explored, and the optimal EP parameters were determined. The EP mechanisms were discussed, where pitting formation was found to consist of three stages. Finally, the EP of a curved BMG part was successfully achieved based on the optimized processing parameters, further validating the feasibility to electropolish complex-shaped BMG structures using direct current (DC) power and NaCl-ethylene glycol electrolyte.

Comparative study of surface roughness between electropolishing process and traditional sanding for low carbon steel

Steel is a versatile material utilized across various sectors, encompassing both industrial and decorative applications. AISI (American Iron and Steel Institute) 1005 steel, recognized for its low carbon content (approximately 0.05% carbon), is commonly referred to as mild steel and finds extensive use in society. This study aims to investigate the influence of electropolishing parameters, specifically current density, and time, on the surface roughness of steel. The methodology involved the preparation of samples for electropolishing tests, systematic variation of the parameters, and subsequent analysis of the resulting surface finish through roughness measurements. Samples subjected to higher current densities for shorter durations exhibited substantial reductions in roughness, while longer durations resulted in minimal or negligible changes in roughness regardless of the current density employed. This comparative analysis between electropolishing and tradi-tional sanding techniques provides valuable insights into optimizing surface finishing processes for low carbon steel applications.

Selective Surface Feature Electropolishing of Additively Manufactured 316L Using Pulse Electrochemistry

Electrochemical finishing of metallic surfaces is a scalable, relatively cost-effective technique that is also versatile. One of the main detractions is that the current distribution is uneven and unspecific, often leading to a lack of shape retention and, if it goes too far, inducing corrosion. Pulsing the electrical input creates an unsteady state during electropolishing, controlling the current distribution across the part. The pulse wave prevention of general non-uniform current distribution across the entire geometry instead produces local non-uniformities in the current distribution at given surface features. Many pulse electropolishing parameters can be varied to target individual surface features, including the electrolyte, pulse height, pulse width (equally and unequally distributed), time of polishing as well as the overall waveform.Additive manufacturing (AM) can produce unique, complex structures rapidly. The fast local melting of metal AM parts cool quickly due to the small area, causing unique microstructures, pores, and larger surface roughness compared to cast. AM microstructures change mechanical and chemical properties, such as strength and corrosion, compared to traditionally manufactured parts. Variations in build parameters and composition creates a complicated, feature dependent, corrosion response. By polishing the surface, some of the features, namely the corrosion resistance, wear, and aesthetics can be standardized and enhanced.In this work, we explore the underlying electrochemistry that governs pulse electropolishing. We show that controlling the electrolyte with environmentally benign chemicals ultimately influences the part dimensions that can be polished, the ability to polish, and the propensity to corrode. The pulse height, pulse width (Fig. 1), and total charge passed have an impact on different surface feature removal. We will demonstrate impact of the pulse parameters on the polishing of additively manufactured stainless steel. We go beyond simple planar geometry and apply our understanding to larger scale complex geometry parts, while maintaining near-net shape and minimizing mass loss. Figure 1

Influence of Local Electropolishing Conditions on Ferritic–Pearlitic Steel on X-Ray Diffraction Residual Stress Profiling

Layer removal with electropolishing is a well-established method when measuring residual stress profiles with lab-XRD. This is done to measure the depth impact from processes such as shot peening, heat treatment, or machining. Electropolishing is used to minimize the influence on the inherent residual stresses of the material during layer removal, performed successively in incremental steps to specific depths followed by measurement. Great control of the material removal is critical for the measured stresses at each depth. Therefore, the selection of size of the measurement spot and electropolishing parameters is essential. The main objective in this work is to investigate how different electrolytes and electropolishing equipment affect the resulting surface roughness, geometry, microstructure, and consequently the measured residual stress. A second objective has been to establish a methodology of assessing the acquired electropolished depth. The aim has been to get a better understanding of the influence of the layer removal method on the accuracy of the acquired depth. Evaluation has been done by electropolishing one ground and one shot peened sample of a low-alloy carbon steel, grade 1.1730, with different methods. The results showed a difference in stresses depending on the electrolyte used where the perchloric acid had better ability to retain the stresses compared to the saturated salt. Electropolishing with saturated salt is fast and results in evenly distributed material removal but has high surface roughness, which is due to a difference in electropolishing of the two phases, ferrite, and pearlite. Perchloric acid electropolishing is slower but generates a smooth surface as both ferrite and pearlite have the same material removal rates but may cause an increased material removal for the center of the electropolished area. In this work, it is suggested to use perchloric acid electropolishing for the final layer removal step.

Rapid surface finishing of chemical vapour deposited tungsten carbide hard coatings by electropolishing

Tungsten/tungsten carbide (W/WC) coatings deposited through chemical vapour deposition (CVD) exhibit favourable mechanical properties and are widely used to extend the working life and performance of engineering parts which operate in high wear and corrosive environments. Following the coating deposition process, the coated parts must adhere to low surface roughness and geometrical tolerance specifications necessitating the need of a machining or surface finishing operation. Unlike monolithic materials, hard W/WC coatings have low machinability due to their high hardness and superior mechanical properties. In this study, electropolishing, which is independent of the material's hardness and capable of processing parts with complex geometries has been studied as a prospective noncontact machining and surface finishing technique for CVD W/WC coatings. Here we report the electropolishing behaviour of W/WC coatings with an average thickness of 50 ± 15 μm and 1300 ± 50 HV hardness. Optimal electropolishing parameters using 5 wt% sodium hydroxide (NaOH) electrolyte concentration at 21 °C allow a mirror-like surface finish with Ra of less than 50 nm and a change in coating thickness of up to 18 μm to be achieved within 5 min. The change in electrolyte temperature from 21 °C to 40 °C was found to have a significant effect on the electropolishing behaviour due to the formation of a thin and unstable viscous film. The electrolyte concertation of 5 wt% was more stable when compare to 3 wt%, giving an overall better surface finish. EBSD analysis revealed that grains with a {111} orientation were preferentially etched in NaOH.

Precision Electropolishing on Fabricating SS 316L Microchannel – A Taguchi Approach

This paper presents the fabrication of a microchannel on stainless steel 316L (SS 316L) by electropolishing method. Machining parameters such as applied voltage, concentration of NaCl in the electrolyte solution and machining gap between tool and workpiece have been optimized in this electropolishing process. The Taguchi method is adopted to ascertain the optimum process parameters in order to increase maximum material removal rate using L9 orthogonal array. Pareto analysis of variance is employed in order to analyze the machining process parameters to the material removal rate. The result shows that the optimal parameters to achieve the maximum material removal rate is by using a combination of 10 V as applied voltage, NaCl concentration of 15 wt.%, and setting 1 cm as the machining gap. It has been also found out that in order to have relatively high material removal without sacrificing the surface quality and the geometrical accuracy of the microchannel produced, applied voltage at 7 V, NaCl concentration of 7 wt.% and machining gap of 3 cm is the best combination of the electropolishing parameters.

A multi-factorial mathematical model for the selection of electropolishing parameters with a view to reducing the environmental impact

Electrochemical metal processing is a process that generates harmful pollution. An important goal often disregarded by researchers is not only the achievement of the best possible quality of electropolished surface, but also minimising the load of metal ions in the wastewater generated in the process. The conducted experiments on the electropolishing of stainless steel in laboratory conditions, varied time, temperature and current density conditions, as well as process bath contamination (ranging from 0 to 6% Fe mass) allowed us to develop a multi-factorial mathematical model. This model offers the possibility of being able to select the process parameters recommended for achieving the desired effects. It takes into account such surface quality parameters as roughness and gloss, process duration and current density that determine power consumption, as well as the weight loss of the electropolished element that influence the rate of contamination in processing baths and wastewater. The study presents the composition of a passive film of stainless steel after the electropolishing process at the initial and final stages of the process bath’s exploitation. The results obtained from XPS tests were then correlated with the results of corrosion tests and resistance to pitting corrosion in the environment of 0.1 M NaCl.

Electrochemical-Based Surface Enhancement of Additively Manufactured Ti-6Al-4V Complex Structures

Poor surface quality has long been a significant challenge to the broad adoption of additive manufacturing (AM) in industry. This work deploys a customized electropolishing (EP) procedure to improve the surface finish of complex laser powder bed fusion Ti-6Al-4V parts with internal channels and various geometries using a substantially less hazardous, anhydrous, alcoholic solution, while maintaining the geometrical fidelity of the parts. A preliminary study on simple geometries was run to evaluate the effect of EP time on surface roughness and thickness loss of a part. By using a customized test setup and an artificial EP waveform to accurately control EP parameters, a high EP efficiency was achieved (maximum reduction of surface roughness up to 70% and a minimum thickness loss of 11%) with low treatment times. Subsequently, EP was conducted on the internal surfaces of various geometries in increasing order of complexity; the results showed the effectiveness of the proposed technique across different geometrical features, leading to maximum uniform surface roughness improvement of 77% with minimum thickness loss of only 7%. The proposed methodology from this work for a fast and cost-effective surface enhancement methodology in an environmentally safe solution may be used on real, complex AM parts to enhance both internal and external surface quality.

An apparatus for the continuous measurement of thickness during the electropolishing of superconducting cavities.

An apparatus allowing continuous acquisition of thickness measurements during electropolishing of superconducting cavities is described. The instrument is based on the ultrasound thickness measurement technique and allows the connection of up to six probes. The apparatus has been employed to monitor the surface treatment of PIP-II low beta single cell prototypes developed and manufactured by LASA-INFN and specifically to measure surface removal at different points of interest on the cavity surface. The apparatus facilitated the development and optimization of electropolishing parameters for incorporation into the cavity manufacturing process.

Surface Performance and Optimization of Nickel Titanium Alloy Electropolishing Parameters

Surface Performance and Optimization of Nickel Titanium Alloy Electropolishing Parameters

Electropolishing of Inside Surfaces of Stainless-Steel Tubing

Electropolishing has proved to be an affordable and flexible method for improving the surface quality of metal parts. It improves surface roughness and eliminates the minor scratches and deformed layer present on the surface from previous manufacturing processes. Therefore, the final metal finish is smooth, bright and shiny. In addition to enhancement of the visual appearance of the piece, during electropolishing, a thin but dense and compact passive layer is formed on the surface that makes it hydrophobic and prevents moisture accumulation. Also, by removing rust, debris and nonmetallic inclusions that can act as potential sites for surface contamination, electropolishing yields ultra-clean metal parts with greatly improved corrosion resistance.[1–4]Many industries can benefit from the merits of electropolishing. The mirror-like surface finish can be quite appealing for numerous decorative purposes such as appliances and automotive. Meanwhile, the cleanliness of electropolished parts has always been a reason for many industries to incorporate electropolishing. For example, the semiconductor industry demands ultra-clean distribution equipment that supplies highly pure gases and chemicals. Therefore electropolishing is commonly used for obtaining ultra-clean metal parts and preventing process contamination.Also, nowadays, to comply with regulations for contamination control such as FDA, pharmaceuticals and food and beverage industries utilize electropolishing treatment to ensure that the inside surfaces of their piping systems, mixers, vessels, etc. are ultra-clean.Many studies are published on the effect of different electropolishing parameters such as potential, polishing time, temperature and bath composition, on surface roughness of the workpiece. [5–9] However, only a few studies have thoroughly investigated the effect of operating conditions on the brightness of the surface. Considering the broad range of decorative applications of electropolishing, more research on this topic is justified.Results from several studies indicate that to achieve a uniform electropolishing effect, a proper cathode to anode distance should be maintained.[10,11] This can make uniform electropolishing of internal spaces practically challenging. While many industrial equipments have internal surfaces to be electropolished, there seems to be a gap in our knowledge in this area that calls for further investigation.In the present study, the inside walls of stainless-steel tubing were electropolished in sulfuric and phosphoric acid electrolyte using internal cylindrical copper electrodes. Effect of various parameters including the outer diameter and position of the cathodes as well as the length of the tubing, on the final quality of the surface, were systematically investigated.It was observed that under the proper combination of electropolishing voltage and duration, irrespective of the initial surface condition of stainless-steel samples, they were all significantly brightened, and their surface roughness was decreased to almost similar final values. Refrences: [1] S.H. Kim, S.G. Choi, W.K. Choi, E.S. Lee, Int. J. Adv. Manuf. Technol. 85 (2016) 2313–2324.[2] G. Yang, B. Wang, K. Tawfiq, H. Wei, S. Zhou, G. Chen, Surf. Eng. 33 (2017) 149–166.[3] A.M.A. Abouelata, ARPN J. Eng. Appl. Sci. 13 (2018) 2422–2428.[4] L.S. Andrade, S.C. Xavier, R.C. Rocha-Filho, N. Bocchi, S.R. Biaggio, Electrochim. Acta 50 (2005) 2623–2627.[5] F. Nazneen, P. Galvin, D.W.M. Arrigan, M. Thompson, P. Benvenuto, G. Herzog, J. Solid State Electrochem. 16 (2012) 1389–1397.[6] A.K. Singh, M.A. Quraishi, Corrosion 7 (2012) 3222–3241.[7] Z. ur Rahman, K.M. Deen, L. Cano, W. Haider, Appl. Surf. Sci. 410 (2017) 432–444.[8] E.-S. Lee, Int. J. Adv. Manuf. Technol. 16 (2000) 591–599.[9] H. Hocheng, P.S. Kao, Y.F. Chen, J. Mater. Eng. Perform. 10 (2001) 414–418.[10] V. Chouhan, S. Kato, K. Nii, T. Yamaguchi, M. Sawabe, H. Hayano, Y. Ida, Phys. Rev. Accel. Beams 20 (2017) 83502.[11] S. Jin, A.T. Wu, X.Y. Lu, R.A. Rimmer, L. Lin, K. Zhao, J. Mammosser, J. Gao, Appl. Surf. Sci. 280 (2013) 93–103.

Surface Treatment Effects on the Corrosion Characteristics of Additively-Manufactured Metals

Metal Additive Manufacturing (MAM) powder-bed technology has recently become a widespread manufacturing option for, medical, aerospace, and auto industries. While this clearly demonstrates the impact of this new production path for manufacturing, MAM products must still meet many traditional requirements to interface with other components for maximum performance and reliability. These requirements include surface specifications, such as finish (roughness), coatings, and corrosion resistance. However, initial studies indicate that these requirements may not directly transfer to MAM materials, with complications including degraded corrosion resistance, rougher finishes in hidden surfaces, and inability to achieve specified plated surface requirements. Currently, there is a knowledge gap with respect to how MAM components will perform to these specifications, and testing cycles can exceed several years.The focus of our work was to identify and understand the effects of production surface treatments and how they affect the corrosive properties on MAM materials in corrosive environments. This includes understanding the effects of heat treatments applied to MAM components in post-processing, a step which can significantly affect results. This work will help identify appropriate post-processing treatments to ensure MAM components meet the expected requirements for surface finish and corrosion resistance.Surface treatments that are typically used in manufacturing include chemical cleaning, polishing processes, and heat treatments. While these processes have been optimized for wrought type materials the unique surface finish and grain structure will require more tailored approaches. Heat-treatments applied to additive manufactured (AM) stainless steel have been shown to improve the corrosion properties of stainless steel that could be linked to chromium segregation in the grain boundaries, leading to intergranular corrosion and intergranular stress corrosion cracking, due to the elevated temperatures used during manufacturing. While most heat-treatments have been optimized for wrought material, augmented heat-treatments could result in an improvement on the corrosion properties of MAM materials.Furthermore, polishing treatments such a mechanical, machining, or electropolishing can be used to improve the surface finish of MAM materials. Changes in the surface finish, such as roughness, will affect the corrosion properties of metals in corrosive environments. Electropolishing is attractive treatment since it is a non-contact surface processes method. Unlike physical methods, such as mechanical polishing or machining, it can more evenly polish difficult to reach surfaces. It has also been shown to modify the protective passivation layer that is found on the surface of AM stainless steels, which can improve the corrosion resistance of the materials. We have explored the effects of tradition DC electropolishing in strong acids, but also pulse electropolishing which can be performed in less toxic solutions. We present how various electropolishing parameters effect the corrosion performance of MAM materials

Electropolishing of niobium coatings on spherical shape samples

Selection of electropolishing parameters on rolled niobium samples (10 × 20 mm) in the mixed solution H2SO4 – HF was performed. The range of potentials and the duration of electropolishing were chosen. A special anode construction for the electropolishing of spherical shape samples from carbopyroceram coated niobium was used. Due to the small niobium coating thickness on the rotor, electropolishing was carried out in several stages. The duration of each stage was 2 minutes and totally five electropolishings were performed. It was found that the electropolishing of spherical shape samples should be carried out at a potential of 6.0 V relatively to the cathode from glassy carbon.

An Investigation of the Electropolishing of Metal Parts Fabricated By Powder Bed Fusion Additive Manufacturing

In this work the use of non-aqueous electropolishing for the surface treatment of the as-received Ti6Al4V and IN718 parts fabricated by laser and electron beam powder bed fusion additive manufacturing (PBF-AM) was investigated. Using the non-aqueous electrolyte, the characteristics of the voltage-current curve of the electropolishing exhibit a general absence of the plateau stage for both materials. Experimental design was carried out to quantify the significance of individual electropolishing parameters on the surface qualities of the samples. The electrolyte flow rate, the temperature and the electropolishing voltage appear to be the most significant input variables, and strong coupling effects among various electropolishing parameters were observed. The surface roughness of the electroplished samples exhibits significant improvement to less than 1μm, although the macroscopic surface texture was not effectively eliminated. In addition, the high-cycle fatigue performance of the electropolished samples exhibit significant improvement, which demonstrated the effectiveness of the surface treatment.

Wire electropolishing of microgroove structures on a cobalt-based alloy

The surface quality of microstructures greatly affects their performance. Electropolishing has many advantages as a technique for eliminating surface defects of microstructures and components. This paper presents a new electropolishing method to improve the surface quality of microgrooves. A wire with a diameter in the micrometer range is employed as the cathode. The whole of the microgroove is polished by moving this wire electrode along the outline of the microgroove. The anodic dissolution behaviors of a cobalt-based alloy in phosphoric acid solutions with various concentrations are investigated using polarization curves. The effects of the wire electropolishing parameters, namely, the wire electrode diameter, feed rate, polishing gap, applied voltage, pulse period, and duty cycle are also studied both theoretically and experimentally. Using optimized values of these parameters, the surface roughness of the microgroove is reduced from Ra = 0.3 to 0.036 μm. A mirror-like surface is obtained after polishing.

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.

Investigation of roughness and specular quality of commercial aluminum (6061 alloy) for fabrication of nanoporous anodic alumina films

Nanoporous anodic alumina (NAA), obtained via aluminum anodization, have been used as template for fabrication of nanostructure materials and photonic devices. In order to promote the formation of regular porous and to control the desired properties, high-purity aluminum and pretreatment of Al surfaces are mandatory. This procedure consists in electrochemically removing the external irregular layer of the metal promoting a flat, bright and smooth metallic surface. In this study, the effect of electropolishing parameters on commercial aluminum samples (6061 alloy, 97%) was investigated. This procedure was performed at constant potential in a mixture of perchloric acid and ethyl alcohol solution in different experimental conditions. A factorial design was used to investigate the effect of applied potential, electropolishing time and electrolyte temperature on roughness and specularity of Al substrates. These samples were characterized by Atomic Force Microscopy (AFM) and Diffuse Reflectance Spectroscopy (DRS). All variables presented significant effects on roughness of Al substrates, although electropolishing time presented the most important effect on specularity of these samples. After galvanostatic anodization in oxalic acid solution, the results showed the influence of Al surface roughness on morphology of NAA films. Since all Al samples were anodized under same conditions, the differences observed in micrographs of NAA films were related to roughness of Al substrates, which was affected by electropolishing parameters, mainly the applied potential and electropolishing time.

Electropolishing parameters optimization for enhanced performance of nickel coating electroplated on mild steel

Abstract The purpose of this work is to investigate the influence of electropolishing process on performance parameters of nickel coating electroplating on Q235A mild steel as substrate, including the surface roughness, thickness, elastic modulus and hardness. The contribution of magnetic stirring was first studied. On the basis of this, we explored the effect rules of electropolishing parameters on nickel coating using orthogonal test. The result showed that nickel coating became smoother and thicker by magnetic stirring in electropolishing process. The current density in electropolishing process significantly influenced the thickness, elastic modulus and hardness of Ni coating, while it showed little influence on the coating surface roughness. The above three parameters were also affected by polishing time and the temperature of polishing slurry. With the other condition remaining the same, elastic modulus and hardness of nickel coating reached their peaks after electropolishing with a current density of 30 A/dm 2 in electrolyte at 65 °C for 15 min.

Depth Profiling of Residual Stress for Shot-Peened “U”-Bend Alloy-800 Tubes for the PHWR Steam Generator

AbstractResidual tensile stresses influence the mechanical behavior in terms of fatigue and fracture resistance, stress corrosion behavior, and dimensional stability of critical components of nuclear reactors. Glass-bead shot-peened “U”-bend Alloy-800 tubes are used as steam generators in pressurized heavy water reactors (PHWRs), where stress corrosion cracking is the common cause of its premature failure. Therefore, compressive residual stresses are induced by glass-bead shot peening to overcome the tensile stresses generated more along the bend region. The variation of these compressive residual stresses as a function of depth from the surface has been estimated by successive material removal followed by stress measurement. Optimization of electropolishing parameters for removal of a fixed amount of material is carried out. Stepwise removal of material by electropolishing is proved to be better for stress analysis instead of removal “at-a-time.” Effect of shot-peening pressure is also studied as a function of stress pattern developed along the depth from the surface of the straight tube and bent tube.