Mechanism of electrochemical discharge machining on film cooling holes with thermal barrier coatings

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By using NaOH as the working fluid and enhancing chip removal through electrode rotation, this study investigates the machining state transition laws, material removal mechanisms, and post-processing workpiece surface integrity in ECDM of film cooling holes with thermal barrier coatings. The results indicate that only the electrochemical discharge effect is active during the ECDM of the ceramic layer, with material removal primarily dependent on rapid thermal cycling and electrochemical discharge. In contrast, for metal substrates, both electrochemical and electrical discharge machining occur, involving electrochemical and thermal effects. This study provides valuable insights for the efficient and high-quality production of film cooling holes with thermal barrier coatings. Electrochemical discharge machining(ECDM) Film cooling holes with thermal barrier coatings Machining mechanism Electrical discharge machining Surface integrity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1 Introduction Hole structures with thermal barrier coatings are widely utilized in aerospace and other critical component fields, where their machining performance directly impacts the success of high-end equipment development [ 1 – 2 ]. These structures are characterized by an insulating ceramic layer on the surface, a bonding layer in the middle, and a difficult-to-machine metal layer underneath. Both the ceramic layer and the metal substrate are challenging to machine, making the machining of these parts particularly difficult [ 3 ]. When machined using conventional methods, these structures are more prone to issues such as coating breakage, extreme tool wear, cracks, and other problems that can impair functionality and even cause equipment failures[ 4 ]. Consequently, a key research focus in processing and manufacturing is developing effective and high-quality methods for machining film cooling hole structures with thermal barrier coatings. Non-traditional machining methods can bypass the hardness, strength, and toughness characteristics of materials, offering an effective approach for machining film cooling holes with thermal barrier coatings. Marimuthu et al. [ 5 ], Sun et al. [ 6 ], and Lu et al. [ 7 ] analyzed the processing of film cooling holes with thermal barrier coatings using millisecond, picosecond, and femtosecond lasers, respectively. They discovered that laser processing of thermal barrier-coated film cooling holes is efficient and free of swarf force, but the hole walls contained flaws such as microcracks and recast layers. Balaji et al. [ 8 ] processed Yttrium oxide stabilized zirconia (YSZ) coated nickel-based high-temperature alloy film cooling holes using garnet as a water jet abrasive grain. The study revealed several drawbacks to water jet machining, including impact, surface rupture of the holes, and burr formation at the exit. Antar et al. [ 9 ] and Kim et al. [ 10 ] suggested using microelectrical discharge machining and nanosecond pulsed laser in a composite process for high machining efficiency. However, this method results in thermal machining defects such as cracks and recast layers in the hole wall. Conversely, electrochemical discharge machining (ECDM) is a promising technique for machining film cooling holes with thermal barrier coatings due to its smooth surface, lack of mechanical stress, no material limitations, low cost, and minimal microcracks or recast layers [ 11 ]. Currently, Gao et al. [ 12 ] have investigated the machining of thermal barrier coating film cooling holes by presenting a composite approach of electric discharge machining and abrasive water jet. Geng et al. [ 13 ] proposed a backflush electrochemical discharge machining technique to address recast layers and fractures, resulting in high-quality film cooling holes. Geng et al. [ 14 ] investigated the recast layer and elemental distribution after film cooling hole machining using ECDM, while Liu et al. [ 15 ] examined gas film purity and consistent discharge energy distribution with ECDM. Vasudevan et al. [ 16 ] and Zhang et al. [ 17 ] addressed issues like thermal spalling, delamination, flaking, splattering, recast layers, and cracking on ceramic coatings, proposing that ECDM can mitigate these problems. Li et al. [ 18 ] analyzed delamination and recast layers in the machining of film cooling holes with thermal barrier coatings, finding that these issues can be eliminated by selecting low discharge energy and an appropriate duty cycle. Singh et al. [ 19 ] verified the feasibility of electrolyte flow and pressurized feed in ECDM and analyzed the zirconia removal mechanism under these conditions. According to the literature, current research focuses on process improvement; however, there is a lack of information on altering the process state and material removal mechanism, affecting the method's potential application. Based on this, this work investigates the material removal mechanism and discharge state of both the ceramic layer and metal substrate using ECDM, laying the groundwork for the production of high-quality thermal barrier coating film cooling holes. 2 Experimental details 2.1 Experimental setup In this study, a self-constructed three-axis ECDM experimental platform is utilized, as illustrated in Fig. 1 . Stepper motors control the X, Y, and Z axes. The tool electrode, a tungsten round rod, rotates via a spindle positioned on the Z-axis, which is motor-controlled. The workpiece, a nickel-based high-temperature alloy with a thermal barrier coating, is submerged in the solution by 3–4 mm. It consists of three layers: a 0.3 mm-thick zirconium oxide ceramic layer, a bonding layer of strong adhesive, and a 4 mm-thick nickel-based high-temperature alloy (GH4169) substrate. The electrolytic bath is positioned on the X-axis. The power supply is pulsed, with the positive terminal at the workpiece end and the negative terminal at the tool electrode. Voltage and current probes connected through an oscilloscope are used for data acquisition to obtain gap voltage and gap current. The data is then sent to a PC for storage. The ECDM principle diagram is shown in Fig. 2 . During ECDM, electrochemical dissolution and secondary discharge may occur, and under certain conditions, composite processing involving these three methods may coexist. 2.2 Experiment procedure A 200 MHz oscilloscope (TEK TBS1202C) was used to record the voltage and current signals of the treated metal and ceramic layers. Surface roughness was measured with a super depth-of-field microscope (VHX-6000_950F), surface morphology was analyzed using a scanning electron microscope (Zeiss Supra55 VP), and microhardness data was collected with a Vickers hardness tester (TMHV-1000Z). The precise machining parameters for the heat barrier-coated film cooling holes are shown in Table 1 . The process utilized electrode rotation and brief pulse on/off times. After analyzing the machined workpieces for roughness, electrical signals, micro-morphology, hole taper, and micro-hardness, the machining status and removal procedure were determined. The hole taper is calculated by the formula: $$C=\frac{D-d}{L}*100\%$$ 1 Where D denotes the hole inlet diameter; d denotes the hole outlet diameter; and L denotes the hole depth. Table 1 Thermal barrier coating film cooling hole processing parameters Parameters ECDM drilling Electrode Tungsten electrode Feed speed 1um/s Solution 30 wt % NaOH Electrode feed rate 1300 r/min Applied voltage 50 V Discharge frequency 27778 Hz Pulse on duration 24 us Pulse off duration 12 us 3 Results and discussion 3.1 Gap voltage current for electrochemical discharge machining Figure 3 (a) and (b) illustrate the voltage-current waveforms during the processing of the thermal barrier coating. In Fig. 3 (a), when a pulsed voltage is applied, a series of current changes occur, producing a constant change in hydrogen bubbles. In Fig. 3 (b), when numerous hydrogen bubbles form around the electrode, the pulse voltage rapidly increases in the a-b region, followed by a slight current reduction. The voltage from the b-c section then rises further to the peak; at this point, the voltage from b-b` indicates the start of the gas film formation stage. During the b-c stage, as the voltage increases, hydrogen bubbles become denser, eventually forming an insulating gas film, indicating an electrochemical reaction process. From c to d, the pulse voltage slowly declines from the peak value and tends to stabilize, as does the pulse current, indicating the electrochemical discharge stage. From d to e is the electrolysis stage, where voltage and current are nearly stable. From e to f, the voltage and current continuously decrease to zero. Therefore, the preparation of thermal barrier coatings involves only electrochemical discharge machining. The voltage-current electrical signals during the milling of the high-temperature alloy metal substrate are shown in Figs. 3 (c) and (d). The waveform in Fig. 3 (c) can be roughly classified into three processing states. The current waveform in Fig. 3 (c)a is similar to the thermal barrier coating processing current waveform due to analogous voltage and current trends. However, processing high-temperature alloy substrates, which are electrically conductive, results in a more intense electrochemical discharge reaction, raising the current value during this stage more than during coating processing. Figure 3 (c)b displays the current of the electrochemical process. An electrochemical reaction generates a complete insulating gas layer, starting when many hydrogen bubbles form following a series of electrochemical discharges. Figure 3 (c)c shows that after stage b, there is complete isolation between the electrodes and the electrolyte, resulting in an entirely insulating gas sheet and a discharge distinct from the electrochemical one. As shown in Fig. 3 (d), an electrochemical reaction current (a-b) and a distinct separate discharge (c-d) initially occur in one pulse width [ 20 ]. The discharge is identified as electrical when there is a significant voltage drop and current rise between c and d. During this period, both voltage and current waveforms show very high-frequency oscillations [ 21 ][ 22 ]. Consequently, high-temperature alloy metal substrates are machined using both electrical discharge machining (EDM) and ECDM. 3.2 Material removal mechanism 3.2.1 Mechanism of thermal barrier coating removal In this experiment, the ceramic layer is composed of zirconia ceramic. Figure 4 (a) shows that after 20 minutes of machining, some material has been removed, and the holes labeled a, b, and c exhibit three distinct levels of milling around them. In Part a, evident ceramic melting and re-solidification can be seen; Part b shows traces of melted ceramic with an altered material organization; Part c shows a shallow ring of machining marks. In Fig. 4 (d), the through-hole with thermal barrier coating is observed after machining using a super depth-of-field microscope. Around the hole, some ceramic traces resemble incomplete exfoliation, melting and re-solidification, and resin-like whiskers. These phenomena may result from machining with glue instead of the bonding layer. Figures 4 (b), (c), (e), and (f) show the shape of the ceramic layer after machining. The processed surface exhibits a melted morphology with remnants of partially and fully flaked ceramics, as shown in Fig. 4 (b). The morphology of the processed surface is significantly different from the unprocessed surface of the ceramic layer. As shown in Figs. 4 (c), (e), and (f), the machining morphology reveals numerous signs of layer flaking and material melting residue on the ceramic removal surface. During high-frequency electrochemical discharge machining, more heat is produced around the electrode, leading to more discharges. Consequently, the discharge produces significant heat, bursting force, and localized thermal stresses around the electrode during machining. Rapid heating and cooling cause the ceramic to fracture and flake off due to the rotating electrode, altering the flow field. A schematic diagram of the ECDM of the thermal barrier coating is shown in Fig. 5 , with the machining schematic in Fig. (e). As illustrated in Fig. 5 (a), hydrogen bubbles around the electrode grow as the voltage increases, and a heat source from the electrochemical process appears at the electrode's bottom; this phase corresponds to the waveform in Fig. 3 (b) as phase a-b. A complete gas film forms and an electrochemical discharge reaction occurs when the voltage and current reach their peak, as shown in Fig. 5 (b). This stage corresponds to stages b–c in Fig. 3 (b); the discharge produces significant heat and some bursting. As shown in Fig. 5 (c), the ceramic melts and ruptures under heat and pressure, then the electrochemical reaction's heat source is extinguished and the surrounding temperature rapidly drops. As illustrated in Fig. 5 (d), rapid heating and cooling produce thermal stresses, leading to ceramic spalling. Electrode rotation modifies the flow field, accelerating the rate of ceramic spalling. The ceramic removal process is cyclical: it begins as voltage and current rise again, causing hydrogen bubbles to form around the electrode, initiating the next cycle. Thus, the removal of the ceramic layer primarily depends on thermal stresses from rapid heating and cooling and the bursting force from electrochemical discharge machining, which causes ceramic spalling and melting. These findings are supported by analyses of electrical signals, machining phenomena, and microstructure. 3.2.2 High-temperature alloy removal mechanism Figure 6 shows the morphology of the film cooling holes in the processed metal substrate. Figure 3 (c) shows that after stage b, there is total isolation between the electrodes and the electrolyte, forming a fully insulating gas sheet and a discharge distinct from the electrochemical one. Combined with the phenomena in Fig. 3 (c) and (d), it is evident that metal processing primarily involves electrochemical discharge, electrochemical discharge machining, and electrical discharge machining. In Fig. 6 (a), craters etched by discharge are visible near the hole wall. In Fig. 6 (b) and (c), remnants of the material's recast layer, removed by electrochemical electrolysis and discharge, are visible. A schematic diagram of the ECDM of metal is shown in Fig. 7 . The waveform for this process is displayed in Fig. 4 (c)a. When numerous hydrogen bubbles form around the electrode, creating a complete gas film, the gas film isolates the electrode from the solution, forming an insulating space, as shown in Fig. 7 (a). As the electrochemical reaction proceeds, the solution's temperature rises, causing the gas film to expand due to vapor inflow, as seen in Fig. 7 (b). When the air film is large enough, it attaches to the workpiece, exposing the metal. At this point, using the electrode feed, an electrical discharge occurs when the discharge gap is reached and the voltage hits the breakdown voltage, as shown in Fig. 7 (c). The corresponding current is depicted in Fig. 4 (d). The high temperature from the discharge instantly removes the material, creating a crater in the workpiece, as shown in Fig. 7 (d). At the moment of discharge, the air film breaks, incorporating the electrolyte, and numerous bubbles form around the electrode to recreate the air film. This air film then enters the next cycle, repeating continuously to form the discharge process. Thus, two methods are used to machine the metal substrate: ECDM and EDM. The metal material is removed by combining these two techniques simultaneously. 3.3 Electrode surface processing morphology The electrodes before and after machining are shown in Fig. 8 (a). It is evident that some wear has occurred, primarily due to the high temperatures and corrosive nature of the electrochemical discharges during the machining process. Figure 8 (b) shows the partial elemental content of the working electrodes and those not involved in the work. Due to the migration of Fe and Ni elements from the metal substrate to the electrode surface during processing, reducing the W element, it can be inferred that the primary elements in the processed electrode are Fe and Ni. This indicates that electrode compensation occurs during the metal-machining process, helping to minimize electrode wear. 3.4 Coating surface morphology Figure 9 (a) shows a cross-section and three-dimensional image of the ECDM of a through-hole coated with a heat barrier. The figure shows no surface pits and no obvious delamination between the ceramic layer and the metal substrate, suggesting that the ECDM of the thermal barrier coating does not visibly harm the film cooling holes. The elemental maps of the ceramic layer pore wall and the ceramic layer after machining, shown in Fig. 9 (b), reveal a minor amount of Na element in the pore wall but no tungsten element in either. The absence of tungsten on the ceramic layer's surface is because the tungsten electrode isn't directly involved in the electrochemical reaction. Instead, the processed hole wall has Na due to the reaction between zirconia and Na ions in NaOH under an electric field. 3.5 Machining quality of high-temperature alloy substrates 3.5.1 Two types of discharge in a metal matrix The two different discharges in the metal matrix are shown in Fig. 10 . In Fig. 10 (a), an air film forms around the hole wall, isolating the electrode from the solution. When the breakdown voltage is reached, an electric spark discharge is generated. In Fig. 10 (b), the electric spark discharge creates a rapid, high temperature that melts and evaporates the material, leaving a crater. Following an electric spark discharge, as shown in Fig. 10 (c), the solution enters the pit created by the discharge and creates an air film again. At this point, the space between the air film and the pit fills with solution, leading to electrochemical discharge and processes. The heat and corrosion from the electrochemical discharge and reaction trim the crater surface, as shown in Fig. 10 (d). The primary mechanism for material removal is electrical discharge between the electrode and the workpiece. The main contributor to secondary material removal is electrochemical discharge between the electrode and the solution. 3.5.2 Effects of electrochemical discharge machining Figure 11 (a), (b), (c), and (d) show the cross sections of the metal matrix under a scanning electron microscope. Figure 11 (a) shows very little recast layer in either side wall of the hole. For the microstructure study, three sections of the hole's side walls were examined: the top, middle, and bottom. Figure 11 (b) shows no recast layer and only a small heat-affected area. Figure 11 (c) shows the middle end of the hole wall, revealing a small recast layer and a heat-affected area. Figure 11 (d) illustrates the bottom end of the hole wall, where a recast layer is visible. The organization of the three sections has changed dramatically, as shown in Fig. 11 (e), (f), and (g), which display the microstructure morphology of the metal matrix, the heat-affected region, and the recast layer, respectively. As seen in Fig. 11 (j), the microhardness measured in the middle and bottom holes, from the recast layer to the substrate, is 306HV. The average microhardness of the metal substrate is approximately 443HV, indicating that the recast layer influences the substrate's microhardness. As illustrated in Fig. 11 (e), (f), and (g), the instantaneous high temperature generated by the discharge exceeds the melting point of the metal matrix, resulting in refined but less hardened metal grains. This high temperature causes the material to melt and then cool, forming the recast layer. The sudden high temperatures cause the metal's surface layer to torsionally deform and undergo a phase transition [ 23 ], damaging the surface microstructure and destroying the grain boundary reinforcement phase [ 24 ]. This results in the recast layer's hardness being lower than the metal matrix's normal microhardness. The overall roughness of the metal hole wall, as well as the roughness of its upper, middle, and bottom portions, were measured independently, as shown in Fig. 11 (h). The surface roughness values of the machined hole's inner wall at the top, middle, and bottom were measured, with corresponding Ra values of 1.92µm, 3.56µm, and 6.04µm, respectively. The top end of the processed hole wall has the lowest surface roughness, while the bottom end has the highest. The sequential increase in Ra values from top to bottom indicates the inner wall's surface roughness increases after processing. These observations are supported by the measured Ra values. Additionally, the entire hole wall's Ra value is lower than the bottom end's, proving that electrochemical machining remains consistent throughout the process. As shown in Fig. 11 (i), the inlet and outlet diameters of the film cooling hole suggest that secondary electrochemical processing may enlarge the hole size. The elemental contents of the recast layer and the metal matrix are shown in Fig. 11 (k), with tungsten included in the recast layer elements. During electrochemical reactions and electrical discharge machining, tungsten electrodes are exposed to intense current densities in specific areas. This sharp temperature rise causes thermal expansion and stresses, releasing tungsten onto the machined surface. Consequently, roughness, microhardness, hole diameter, and the recast layer are all directly impacted by secondary machining in ECDM. 3.5.3 Variation of hole taper and recast layer Figure 12 (a) shows the variation of taper at different locations at the top, middle, and bottom of the hole. The taper at the top end of the hole is the least at 0.6%, while the taper at the bottom end is the greatest at 1.4%. This is primarily because the bottom end taper is larger than the top end taper due to the longer electrochemical secondary machining time at the top end and the shorter time at the bottom end. Figure 12 (b) shows the thickness of the recast layer at different locations, with measurements taken at four points at the top, middle, and bottom of the hole. Due to the electrochemical secondary process, there is no recast layer at the top end and a thicker recast layer at the bottom end. 4 Conclusions This study successfully used ECDM to manufacture film cooling holes with thermal barrier coatings. The voltage and current signals generated during machining were used to categorize the machining states of the metal substrate and ceramic layer, revealing their removal techniques. A surface quality examination of the processed workpieces was conducted to understand the phenomenon and mechanism of electrochemical secondary processing. The following conclusions can be drawn. (1) The viability of ECDM for film cooling holes in thermal barrier coatings was investigated. It was found that, for ceramic layers, only ECDM occurs in each discharge pulse, while for metal substrates, both ECDM and EDM occur. (2) The removal of the metal substrate relies on electrical spark discharge followed by ECDM. The ceramic layer primarily relies on ECDM, which produces bursting force and instantaneous high temperature, causing thermal stress and spalling. The thermal effect melts and removes the ceramic layer. (3) During ECDM of metal substrates, a small amount of secondary discharge is removed from the hole wall, primarily due to the discharge between the electrode and the solution. (4) The elemental content, hole taper, and microhardness of the treated metal matrix were examined. It was found that the recast layer has lower microhardness than the metal matrix, the hole's overall taper is 1.39%, and Fe and Ni elements migrate to the tungsten electrode's surface, minimizing electrode loss. Declarations Funding information The Natural Science Foundation of Xinjiang Uygur Autonomous Region (2023D01C189), the Xinjiang Uygur Autonomous Region Tianchi Young Doctoral Programme of Excellence (51052300550) and the National Natural Science Foundation of China (52265061) served as the sources for this study. Compliance with ethical standards Conflict of interest The authors declare no conflict of interest in this study. Authors' contributions Ajian Zhang was responsible for the planning and implementation of the experimental protocol and authored the manuscript. Xiaokang Chen undertook the revision and conducted the final review of the experimental protocol and the manuscript. Tongyi Ma and Qianlong Zhu were responsible for data processing and analysis. 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Int J Adv Manuf Technol 120(3): 2363-2372. https://doi.org/10.21203/rs.3.rs-706030/v1 Ren X, Liu ZQ (2016) Influence of cutting parameters on work hardening behavior of surface layer during turning superalloy Inconel 718. Int J Adv Manuf Technol 86: 2319-2327. https://doi.org/10.1007/s00170-016-8350-9 Cite Share Download PDF Status: Published Journal Publication published 17 Feb, 2025 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted Editorial decision: Major Revisions Needed 15 Aug, 2024 Reviewers agreed at journal 16 Jun, 2024 Reviewers invited by journal 16 Jun, 2024 Editor assigned by journal 13 Jun, 2024 First submitted to journal 11 Jun, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4552706","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":314991481,"identity":"81b3e125-9ce0-4bac-8881-89c7bff9f776","order_by":0,"name":"Ajian Zhang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Ajian","middleName":"","lastName":"Zhang","suffix":""},{"id":314991482,"identity":"c5563bcc-301d-46f7-a3a4-180fb12465b5","order_by":1,"name":"Xiaokang Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAz0lEQVRIiWNgGAWjYBAC/hkg8gADMwN7Y+PDD8RokbgB08JzuNlYghgtBhEQLUDN6W0CPERpkW4+9pjnzGF2g5sP2xgkGOzkdBsIaZE5lm4440Yas8HtxLYHBQzJxmYHCGmRyDGT+PDBBqSl3UCC4UDiNsJa8r9JJHyQYDa4ebBNgocoLRE5bBIfbgBtucFIpBaJG2lmkjPOpDFLnkkEBrIBEX7hn5H8TJrn2OFkvuPHHz78UGEnR1ALDCRD3UmkchCwI0HtKBgFo2AUjDQAAPXZQ7gVI/QsAAAAAElFTkSuQmCC","orcid":"","institution":"Xinjiang University","correspondingAuthor":true,"prefix":"","firstName":"Xiaokang","middleName":"","lastName":"Chen","suffix":""},{"id":314991483,"identity":"2dde09fd-b951-4b89-82a5-a732656f7a3a","order_by":2,"name":"Tongyi Ma","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Tongyi","middleName":"","lastName":"Ma","suffix":""},{"id":314991484,"identity":"064cd537-8811-4099-8883-48aeb3e6aea4","order_by":3,"name":"Qianlong Zhu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Qianlong","middleName":"","lastName":"Zhu","suffix":""},{"id":314991485,"identity":"4d909fd0-5760-411e-a9f4-e01e29796e67","order_by":4,"name":"Jianping Zhou","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jianping","middleName":"","lastName":"Zhou","suffix":""},{"id":314991486,"identity":"374249b0-a421-4c82-94b4-6864051ede6e","order_by":5,"name":"Bingbing Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Bingbing","middleName":"","lastName":"Wang","suffix":""},{"id":314991487,"identity":"86484fb7-7d0d-433a-90d4-74f582740b47","order_by":6,"name":"Ning Ma","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Ning","middleName":"","lastName":"Ma","suffix":""},{"id":314991488,"identity":"f2f4516a-fd35-4b60-9a09-db66d31f16c9","order_by":7,"name":"Hai Liu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Hai","middleName":"","lastName":"Liu","suffix":""},{"id":314991489,"identity":"82b6be3e-fbbc-4a66-b9d4-7c30d004f18f","order_by":8,"name":"Yulong Chen","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yulong","middleName":"","lastName":"Chen","suffix":""}],"badges":[],"createdAt":"2024-06-09 06:53:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4552706/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4552706/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00170-025-15243-1","type":"published","date":"2025-02-17T15:56:59+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":59493053,"identity":"2c769995-bb7f-4f50-baa7-33bd7c146d1e","added_by":"auto","created_at":"2024-07-02 12:34:47","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":541440,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental equipment\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/a6709b7a7f40afab0beb841b.png"},{"id":59493054,"identity":"e43951c5-d969-46bb-b926-fa336325f000","added_by":"auto","created_at":"2024-07-02 12:34:47","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":552699,"visible":true,"origin":"","legend":"\u003cp\u003eMachining principle diagram\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/96a0f5b1cbf3550b199185db.png"},{"id":59492584,"identity":"7ec4b40e-2f4a-4f98-b8db-fb014411796a","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1781632,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage-current waveform. (a) The voltage-current waveform of the thermal barrier coating; (b) Partial enlarged drawing;(b) Metal substrate voltage-current waveforms;(d) Electrical Discharge Voltage and Current Waveforms.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/90a9834af58fa8d9a78391fa.png"},{"id":59493056,"identity":"e231800a-6889-4ace-8ab3-1da54d9d05c5","added_by":"auto","created_at":"2024-07-02 12:34:47","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2567540,"visible":true,"origin":"","legend":"\u003cp\u003eCeramic layer removal mechanism. (a) Ceramic layer after 20 min of the processing; (d) Hole ceramic layer under the super depth-of-field microscope; (b)(c)(e)(f) Ceramic layer under SEM.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/493115426754437d5e64c204.png"},{"id":59492592,"identity":"5a5c50ad-5324-444e-9cd9-429ca29a012e","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":847861,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of ceramic layer processing\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/fb8016d9dd80ecffe9f66e36.png"},{"id":59492588,"identity":"b6e8ed48-2dfd-4977-a7d3-b8ab6fdc233d","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1154291,"visible":true,"origin":"","legend":"\u003cp\u003eMorphology of metal matrix after machining\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/e5d7d44b4ac6fb8648cb1d4d.png"},{"id":59492586,"identity":"dff51440-5632-44b4-9649-76295296e0e2","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":837981,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of metal matrix machining\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/d579152419d7250b4f730384.png"},{"id":59492595,"identity":"fc097162-1328-443a-971d-dac34e2a00cb","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1375690,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Morphology of the electrode before and after machining; (b) Electrode working and non-working element content\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/475d3ffaf39ac4759c37516a.png"},{"id":59492590,"identity":"4c2f9aaf-1320-44a1-8f05-4a2c2d0eabf4","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1431628,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Cross-section of a thermal barrier coating film cooling hole; (b) Elemental map of the area where the ceramic layer is processed and the unprocessed area\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/b0e0cfd44b90c5430c4adc9c.png"},{"id":59492593,"identity":"260fc114-a05e-4b56-832a-421b7f0ba8c8","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":689738,"visible":true,"origin":"","legend":"\u003cp\u003eTwo types of discharges in a metallic matrix. (a) Discharge; (b) Discharge pits; (c) Electrochemical discharge; (d) Craters formed after both discharges\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/00c09901eab825e3ddffa51f.png"},{"id":59492596,"identity":"2f4afe58-cc0f-4b46-8ee5-0e5ef04413d3","added_by":"auto","created_at":"2024-07-02 12:26:47","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":4168162,"visible":true,"origin":"","legend":"\u003cp\u003e(a)~(d) Microscopic morphology of the metal matrix under SEM; (e)~(g) Metals, heat affected regions and recast layers under SEM; (h) Roughness of the inner wall of the hole; (i) Borehole inlet and outlet diameters; (j) Microhardness of the metal matrix; (k) Elemental content of metal matrix and recast layer.\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/d97d9a0e77e7feb795713a55.png"},{"id":59493055,"identity":"7c2b3f0a-dbbc-474c-bfbf-258fcd31992a","added_by":"auto","created_at":"2024-07-02 12:34:47","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":305580,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Bore taper at different positions; (b) Thickness of recast layer at different positions.\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/46454ee65a38fed2387c062e.png"},{"id":77052584,"identity":"a1bee7ae-85d7-4139-bbda-a73ac3967947","added_by":"auto","created_at":"2025-02-24 16:15:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":20271560,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4552706/v1/7caee3e3-c46c-4cad-a778-d90c3a713e78.pdf"}],"financialInterests":"","formattedTitle":"Mechanism of electrochemical discharge machining on film cooling holes with thermal barrier coatings","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eHole structures with thermal barrier coatings are widely utilized in aerospace and other critical component fields, where their machining performance directly impacts the success of high-end equipment development [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. These structures are characterized by an insulating ceramic layer on the surface, a bonding layer in the middle, and a difficult-to-machine metal layer underneath. Both the ceramic layer and the metal substrate are challenging to machine, making the machining of these parts particularly difficult [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. When machined using conventional methods, these structures are more prone to issues such as coating breakage, extreme tool wear, cracks, and other problems that can impair functionality and even cause equipment failures[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Consequently, a key research focus in processing and manufacturing is developing effective and high-quality methods for machining film cooling hole structures with thermal barrier coatings.\u003c/p\u003e \u003cp\u003eNon-traditional machining methods can bypass the hardness, strength, and toughness characteristics of materials, offering an effective approach for machining film cooling holes with thermal barrier coatings. Marimuthu et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], Sun et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], and Lu et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] analyzed the processing of film cooling holes with thermal barrier coatings using millisecond, picosecond, and femtosecond lasers, respectively. They discovered that laser processing of thermal barrier-coated film cooling holes is efficient and free of swarf force, but the hole walls contained flaws such as microcracks and recast layers. Balaji et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] processed Yttrium oxide stabilized zirconia (YSZ) coated nickel-based high-temperature alloy film cooling holes using garnet as a water jet abrasive grain. The study revealed several drawbacks to water jet machining, including impact, surface rupture of the holes, and burr formation at the exit. Antar et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] and Kim et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] suggested using microelectrical discharge machining and nanosecond pulsed laser in a composite process for high machining efficiency. However, this method results in thermal machining defects such as cracks and recast layers in the hole wall. Conversely, electrochemical discharge machining (ECDM) is a promising technique for machining film cooling holes with thermal barrier coatings due to its smooth surface, lack of mechanical stress, no material limitations, low cost, and minimal microcracks or recast layers [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCurrently, Gao et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] have investigated the machining of thermal barrier coating film cooling holes by presenting a composite approach of electric discharge machining and abrasive water jet. Geng et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] proposed a backflush electrochemical discharge machining technique to address recast layers and fractures, resulting in high-quality film cooling holes. Geng et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] investigated the recast layer and elemental distribution after film cooling hole machining using ECDM, while Liu et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] examined gas film purity and consistent discharge energy distribution with ECDM. Vasudevan et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and Zhang et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] addressed issues like thermal spalling, delamination, flaking, splattering, recast layers, and cracking on ceramic coatings, proposing that ECDM can mitigate these problems. Li et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] analyzed delamination and recast layers in the machining of film cooling holes with thermal barrier coatings, finding that these issues can be eliminated by selecting low discharge energy and an appropriate duty cycle. Singh et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] verified the feasibility of electrolyte flow and pressurized feed in ECDM and analyzed the zirconia removal mechanism under these conditions. According to the literature, current research focuses on process improvement; however, there is a lack of information on altering the process state and material removal mechanism, affecting the method's potential application. Based on this, this work investigates the material removal mechanism and discharge state of both the ceramic layer and metal substrate using ECDM, laying the groundwork for the production of high-quality thermal barrier coating film cooling holes.\u003c/p\u003e"},{"header":"2 Experimental details","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Experimental setup\u003c/h2\u003e \u003cp\u003eIn this study, a self-constructed three-axis ECDM experimental platform is utilized, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Stepper motors control the X, Y, and Z axes. The tool electrode, a tungsten round rod, rotates via a spindle positioned on the Z-axis, which is motor-controlled. The workpiece, a nickel-based high-temperature alloy with a thermal barrier coating, is submerged in the solution by 3\u0026ndash;4 mm. It consists of three layers: a 0.3 mm-thick zirconium oxide ceramic layer, a bonding layer of strong adhesive, and a 4 mm-thick nickel-based high-temperature alloy (GH4169) substrate. The electrolytic bath is positioned on the X-axis. The power supply is pulsed, with the positive terminal at the workpiece end and the negative terminal at the tool electrode. Voltage and current probes connected through an oscilloscope are used for data acquisition to obtain gap voltage and gap current. The data is then sent to a PC for storage. The ECDM principle diagram is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. During ECDM, electrochemical dissolution and secondary discharge may occur, and under certain conditions, composite processing involving these three methods may coexist.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Experiment procedure\u003c/h2\u003e \u003cp\u003eA 200 MHz oscilloscope (TEK TBS1202C) was used to record the voltage and current signals of the treated metal and ceramic layers. Surface roughness was measured with a super depth-of-field microscope (VHX-6000_950F), surface morphology was analyzed using a scanning electron microscope (Zeiss Supra55 VP), and microhardness data was collected with a Vickers hardness tester (TMHV-1000Z). The precise machining parameters for the heat barrier-coated film cooling holes are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The process utilized electrode rotation and brief pulse on/off times. After analyzing the machined workpieces for roughness, electrical signals, micro-morphology, hole taper, and micro-hardness, the machining status and removal procedure were determined.\u003c/p\u003e \u003cp\u003eThe hole taper is calculated by the formula:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$C=\\frac{D-d}{L}*100\\%$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eD\u003c/em\u003e denotes the hole inlet diameter; \u003cem\u003ed\u003c/em\u003e denotes the hole outlet diameter; and \u003cem\u003eL\u003c/em\u003e denotes the hole depth.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThermal barrier coating film cooling hole processing parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eECDM drilling\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrode\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTungsten electrode\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFeed speed\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1um/s\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSolution\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30 wt % NaOH\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrode feed rate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1300 r/min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApplied voltage\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50 V\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDischarge frequency\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27778 Hz\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePulse on duration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24 us\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePulse off duration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12 us\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Gap voltage current for electrochemical discharge machining\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (a) and (b) illustrate the voltage-current waveforms during the processing of the thermal barrier coating. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a), when a pulsed voltage is applied, a series of current changes occur, producing a constant change in hydrogen bubbles. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b), when numerous hydrogen bubbles form around the electrode, the pulse voltage rapidly increases in the a-b region, followed by a slight current reduction. The voltage from the b-c section then rises further to the peak; at this point, the voltage from b-b` indicates the start of the gas film formation stage. During the b-c stage, as the voltage increases, hydrogen bubbles become denser, eventually forming an insulating gas film, indicating an electrochemical reaction process. From c to d, the pulse voltage slowly declines from the peak value and tends to stabilize, as does the pulse current, indicating the electrochemical discharge stage. From d to e is the electrolysis stage, where voltage and current are nearly stable. From e to f, the voltage and current continuously decrease to zero. Therefore, the preparation of thermal barrier coatings involves only electrochemical discharge machining.\u003c/p\u003e \u003cp\u003eThe voltage-current electrical signals during the milling of the high-temperature alloy metal substrate are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) and (d). The waveform in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) can be roughly classified into three processing states. The current waveform in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c)a is similar to the thermal barrier coating processing current waveform due to analogous voltage and current trends. However, processing high-temperature alloy substrates, which are electrically conductive, results in a more intense electrochemical discharge reaction, raising the current value during this stage more than during coating processing. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c)b displays the current of the electrochemical process. An electrochemical reaction generates a complete insulating gas layer, starting when many hydrogen bubbles form following a series of electrochemical discharges. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c)c shows that after stage b, there is complete isolation between the electrodes and the electrolyte, resulting in an entirely insulating gas sheet and a discharge distinct from the electrochemical one. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d), an electrochemical reaction current (a-b) and a distinct separate discharge (c-d) initially occur in one pulse width [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The discharge is identified as electrical when there is a significant voltage drop and current rise between c and d. During this period, both voltage and current waveforms show very high-frequency oscillations [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e][\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Consequently, high-temperature alloy metal substrates are machined using both electrical discharge machining (EDM) and ECDM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Material removal mechanism\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1 Mechanism of thermal barrier coating removal\u003c/h2\u003e \u003cp\u003eIn this experiment, the ceramic layer is composed of zirconia ceramic. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a) shows that after 20 minutes of machining, some material has been removed, and the holes labeled a, b, and c exhibit three distinct levels of milling around them. In Part a, evident ceramic melting and re-solidification can be seen; Part b shows traces of melted ceramic with an altered material organization; Part c shows a shallow ring of machining marks. In Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d), the through-hole with thermal barrier coating is observed after machining using a super depth-of-field microscope. Around the hole, some ceramic traces resemble incomplete exfoliation, melting and re-solidification, and resin-like whiskers. These phenomena may result from machining with glue instead of the bonding layer.\u003c/p\u003e \u003cp\u003eFigures\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b), (c), (e), and (f) show the shape of the ceramic layer after machining. The processed surface exhibits a melted morphology with remnants of partially and fully flaked ceramics, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b). The morphology of the processed surface is significantly different from the unprocessed surface of the ceramic layer. As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c), (e), and (f), the machining morphology reveals numerous signs of layer flaking and material melting residue on the ceramic removal surface. During high-frequency electrochemical discharge machining, more heat is produced around the electrode, leading to more discharges. Consequently, the discharge produces significant heat, bursting force, and localized thermal stresses around the electrode during machining. Rapid heating and cooling cause the ceramic to fracture and flake off due to the rotating electrode, altering the flow field.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA schematic diagram of the ECDM of the thermal barrier coating is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, with the machining schematic in Fig. (e). As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a), hydrogen bubbles around the electrode grow as the voltage increases, and a heat source from the electrochemical process appears at the electrode's bottom; this phase corresponds to the waveform in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) as phase a-b. A complete gas film forms and an electrochemical discharge reaction occurs when the voltage and current reach their peak, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b). This stage corresponds to stages b\u0026ndash;c in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b); the discharge produces significant heat and some bursting. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c), the ceramic melts and ruptures under heat and pressure, then the electrochemical reaction's heat source is extinguished and the surrounding temperature rapidly drops. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d), rapid heating and cooling produce thermal stresses, leading to ceramic spalling. Electrode rotation modifies the flow field, accelerating the rate of ceramic spalling. The ceramic removal process is cyclical: it begins as voltage and current rise again, causing hydrogen bubbles to form around the electrode, initiating the next cycle.\u003c/p\u003e \u003cp\u003eThus, the removal of the ceramic layer primarily depends on thermal stresses from rapid heating and cooling and the bursting force from electrochemical discharge machining, which causes ceramic spalling and melting. These findings are supported by analyses of electrical signals, machining phenomena, and microstructure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2 High-temperature alloy removal mechanism\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the morphology of the film cooling holes in the processed metal substrate. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) shows that after stage b, there is total isolation between the electrodes and the electrolyte, forming a fully insulating gas sheet and a discharge distinct from the electrochemical one. Combined with the phenomena in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c) and (d), it is evident that metal processing primarily involves electrochemical discharge, electrochemical discharge machining, and electrical discharge machining. In Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a), craters etched by discharge are visible near the hole wall. In Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b) and (c), remnants of the material's recast layer, removed by electrochemical electrolysis and discharge, are visible.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA schematic diagram of the ECDM of metal is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The waveform for this process is displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c)a. When numerous hydrogen bubbles form around the electrode, creating a complete gas film, the gas film isolates the electrode from the solution, forming an insulating space, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a). As the electrochemical reaction proceeds, the solution's temperature rises, causing the gas film to expand due to vapor inflow, as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b). When the air film is large enough, it attaches to the workpiece, exposing the metal. At this point, using the electrode feed, an electrical discharge occurs when the discharge gap is reached and the voltage hits the breakdown voltage, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c). The corresponding current is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d). The high temperature from the discharge instantly removes the material, creating a crater in the workpiece, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(d). At the moment of discharge, the air film breaks, incorporating the electrolyte, and numerous bubbles form around the electrode to recreate the air film. This air film then enters the next cycle, repeating continuously to form the discharge process. Thus, two methods are used to machine the metal substrate: ECDM and EDM. The metal material is removed by combining these two techniques simultaneously.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Electrode surface processing morphology\u003c/h2\u003e \u003cp\u003eThe electrodes before and after machining are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a). It is evident that some wear has occurred, primarily due to the high temperatures and corrosive nature of the electrochemical discharges during the machining process. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(b) shows the partial elemental content of the working electrodes and those not involved in the work. Due to the migration of Fe and Ni elements from the metal substrate to the electrode surface during processing, reducing the W element, it can be inferred that the primary elements in the processed electrode are Fe and Ni. This indicates that electrode compensation occurs during the metal-machining process, helping to minimize electrode wear.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Coating surface morphology\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a) shows a cross-section and three-dimensional image of the ECDM of a through-hole coated with a heat barrier. The figure shows no surface pits and no obvious delamination between the ceramic layer and the metal substrate, suggesting that the ECDM of the thermal barrier coating does not visibly harm the film cooling holes. The elemental maps of the ceramic layer pore wall and the ceramic layer after machining, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b), reveal a minor amount of Na element in the pore wall but no tungsten element in either. The absence of tungsten on the ceramic layer's surface is because the tungsten electrode isn't directly involved in the electrochemical reaction. Instead, the processed hole wall has Na due to the reaction between zirconia and Na ions in NaOH under an electric field.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Machining quality of high-temperature alloy substrates\u003c/h2\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e3.5.1 Two types of discharge in a metal matrix\u003c/h2\u003e \u003cp\u003eThe two different discharges in the metal matrix are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. In Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a), an air film forms around the hole wall, isolating the electrode from the solution. When the breakdown voltage is reached, an electric spark discharge is generated. In Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(b), the electric spark discharge creates a rapid, high temperature that melts and evaporates the material, leaving a crater. Following an electric spark discharge, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(c), the solution enters the pit created by the discharge and creates an air film again. At this point, the space between the air film and the pit fills with solution, leading to electrochemical discharge and processes. The heat and corrosion from the electrochemical discharge and reaction trim the crater surface, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(d). The primary mechanism for material removal is electrical discharge between the electrode and the workpiece. The main contributor to secondary material removal is electrochemical discharge between the electrode and the solution.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e3.5.2 Effects of electrochemical discharge machining\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(a), (b), (c), and (d) show the cross sections of the metal matrix under a scanning electron microscope. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(a) shows very little recast layer in either side wall of the hole. For the microstructure study, three sections of the hole's side walls were examined: the top, middle, and bottom. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(b) shows no recast layer and only a small heat-affected area. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(c) shows the middle end of the hole wall, revealing a small recast layer and a heat-affected area. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(d) illustrates the bottom end of the hole wall, where a recast layer is visible. The organization of the three sections has changed dramatically, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(e), (f), and (g), which display the microstructure morphology of the metal matrix, the heat-affected region, and the recast layer, respectively.\u003c/p\u003e \u003cp\u003eAs seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(j), the microhardness measured in the middle and bottom holes, from the recast layer to the substrate, is 306HV. The average microhardness of the metal substrate is approximately 443HV, indicating that the recast layer influences the substrate's microhardness. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(e), (f), and (g), the instantaneous high temperature generated by the discharge exceeds the melting point of the metal matrix, resulting in refined but less hardened metal grains. This high temperature causes the material to melt and then cool, forming the recast layer. The sudden high temperatures cause the metal's surface layer to torsionally deform and undergo a phase transition [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], damaging the surface microstructure and destroying the grain boundary reinforcement phase [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. This results in the recast layer's hardness being lower than the metal matrix's normal microhardness.\u003c/p\u003e \u003cp\u003eThe overall roughness of the metal hole wall, as well as the roughness of its upper, middle, and bottom portions, were measured independently, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(h). The surface roughness values of the machined hole's inner wall at the top, middle, and bottom were measured, with corresponding Ra values of 1.92\u0026micro;m, 3.56\u0026micro;m, and 6.04\u0026micro;m, respectively. The top end of the processed hole wall has the lowest surface roughness, while the bottom end has the highest. The sequential increase in Ra values from top to bottom indicates the inner wall's surface roughness increases after processing. These observations are supported by the measured Ra values. Additionally, the entire hole wall's Ra value is lower than the bottom end's, proving that electrochemical machining remains consistent throughout the process. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(i), the inlet and outlet diameters of the film cooling hole suggest that secondary electrochemical processing may enlarge the hole size. The elemental contents of the recast layer and the metal matrix are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(k), with tungsten included in the recast layer elements. During electrochemical reactions and electrical discharge machining, tungsten electrodes are exposed to intense current densities in specific areas. This sharp temperature rise causes thermal expansion and stresses, releasing tungsten onto the machined surface.\u003c/p\u003e \u003cp\u003eConsequently, roughness, microhardness, hole diameter, and the recast layer are all directly impacted by secondary machining in ECDM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.5.3 Variation of hole taper and recast layer\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(a) shows the variation of taper at different locations at the top, middle, and bottom of the hole. The taper at the top end of the hole is the least at 0.6%, while the taper at the bottom end is the greatest at 1.4%. This is primarily because the bottom end taper is larger than the top end taper due to the longer electrochemical secondary machining time at the top end and the shorter time at the bottom end. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(b) shows the thickness of the recast layer at different locations, with measurements taken at four points at the top, middle, and bottom of the hole. Due to the electrochemical secondary process, there is no recast layer at the top end and a thicker recast layer at the bottom end.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThis study successfully used ECDM to manufacture film cooling holes with thermal barrier coatings. The voltage and current signals generated during machining were used to categorize the machining states of the metal substrate and ceramic layer, revealing their removal techniques. A surface quality examination of the processed workpieces was conducted to understand the phenomenon and mechanism of electrochemical secondary processing. The following conclusions can be drawn.\u003c/p\u003e \u003cp\u003e(1) The viability of ECDM for film cooling holes in thermal barrier coatings was investigated. It was found that, for ceramic layers, only ECDM occurs in each discharge pulse, while for metal substrates, both ECDM and EDM occur.\u003c/p\u003e \u003cp\u003e(2) The removal of the metal substrate relies on electrical spark discharge followed by ECDM. The ceramic layer primarily relies on ECDM, which produces bursting force and instantaneous high temperature, causing thermal stress and spalling. The thermal effect melts and removes the ceramic layer.\u003c/p\u003e \u003cp\u003e(3) During ECDM of metal substrates, a small amount of secondary discharge is removed from the hole wall, primarily due to the discharge between the electrode and the solution.\u003c/p\u003e \u003cp\u003e(4) The elemental content, hole taper, and microhardness of the treated metal matrix were examined. It was found that the recast layer has lower microhardness than the metal matrix, the hole's overall taper is 1.39%, and Fe and Ni elements migrate to the tungsten electrode's surface, minimizing electrode loss.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Natural Science Foundation of Xinjiang Uygur Autonomous Region (2023D01C189), the Xinjiang Uygur Autonomous Region Tianchi Young Doctoral Programme of Excellence (51052300550) and the National Natural Science Foundation of China (52265061) served as the sources for this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompliance with ethical standards\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e The authors declare no conflict of interest in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAjian Zhang was responsible for the planning and implementation of the experimental protocol and authored the manuscript. Xiaokang Chen undertook the revision and conducted the final review of the experimental protocol and the manuscript. Tongyi Ma and Qianlong Zhu were responsible for data processing and analysis. Jianping Zhou and Bingbing Wang provided experimental guidance. Ning Ma, Hai Liu, and Yulong Chen conducted auxiliary experiments and collected data. All authors reviewed and approved the final version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKrishna Anand VG, Parammasivam KM (2021) Thermal barrier coated surface modifications for gas turbine film cooling: a review. J Therm Anal Calorim 146(2): 545-580. https://doi.org/10.1007/s10973-020-10032-2\u003c/li\u003e\n\u003cli\u003eOgiriki EA, Li YG, Nikolaidis T, Isaiah TE, Sule G (2015) Effect of fouling, thermal barrier coating degradation and film cooling holes blockage on gas turbine engine creep life. 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Int J Adv Manuf Technol 86: 2319-2327. https://doi.org/10.1007/s00170-016-8350-9\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Electrochemical discharge machining(ECDM), Film cooling holes with thermal barrier coatings, Machining mechanism, Electrical discharge machining, Surface integrity","lastPublishedDoi":"10.21203/rs.3.rs-4552706/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4552706/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis paper investigates the electrochemical discharge machining (ECDM) mechanism to address the susceptibility of coatings to cracking, delamination, microcracks, and recast layers during the machining of film cooling holes with thermal barrier coatings. By using NaOH as the working fluid and enhancing chip removal through electrode rotation, this study investigates the machining state transition laws, material removal mechanisms, and post-processing workpiece surface integrity in ECDM of film cooling holes with thermal barrier coatings. The results indicate that only the electrochemical discharge effect is active during the ECDM of the ceramic layer, with material removal primarily dependent on rapid thermal cycling and electrochemical discharge. In contrast, for metal substrates, both electrochemical and electrical discharge machining occur, involving electrochemical and thermal effects. This study provides valuable insights for the efficient and high-quality production of film cooling holes with thermal barrier coatings.\u003c/p\u003e","manuscriptTitle":"Mechanism of electrochemical discharge machining on film cooling holes with thermal barrier coatings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-02 12:26:42","doi":"10.21203/rs.3.rs-4552706/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revisions Needed","date":"2024-08-15T06:35:50+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-06-16T12:13:21+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-16T10:41:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-13T08:01:34+00:00","index":"","fulltext":""},{"type":"submitted","content":"The International Journal of Advanced Manufacturing Technology","date":"2024-06-11T07:55:45+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ebb70c21-c554-4e2b-9199-6c53149072f4","owner":[],"postedDate":"July 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-02-24T16:01:25+00:00","versionOfRecord":{"articleIdentity":"rs-4552706","link":"https://doi.org/10.1007/s00170-025-15243-1","journal":{"identity":"the-international-journal-of-advanced-manufacturing-technology","isVorOnly":false,"title":"The International Journal of Advanced Manufacturing Technology"},"publishedOn":"2025-02-17 15:56:59","publishedOnDateReadable":"February 17th, 2025"},"versionCreatedAt":"2024-07-02 12:26:42","video":"","vorDoi":"10.1007/s00170-025-15243-1","vorDoiUrl":"https://doi.org/10.1007/s00170-025-15243-1","workflowStages":[]},"version":"v1","identity":"rs-4552706","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4552706","identity":"rs-4552706","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}