Method for manufacturing electroless nickel-plated component and electroless nickel-plated component manufactured thereby

Abstract

A method for manufacturing an electroless nickel-plated component is provided. According to this, an electroless nickel-plated layer formed on a component surface can prevent elements in the alloy of various components exposed to high-temperature environments of 600 °C or higher from becoming volatile, and due to the plated layer stably maintaining adhesiveness for a long period of time and having high hardness, abrasion resistance, and corrosion resistance, can also protect the component surface under various physical / chemical environments, and can therefore be widely applied to components in various devices, such as SOFCs, used in high-temperature conditions.

Description

[Technical Field]

[0001] The present invention relates to a method of manufacturing an electroless nickel-plated part, and more particularly, to a method of manufacturing an electroless nickel-plated part and an electroless nickel-plated part manufactured thereby.[Background Art]

[0002] Electroless plating is a method in which a metal plating layer is formed on a plating target through a redox reaction of metal, and it is used in various industrial fields because a plating layer can be formed regardless of the shape of the product.

[0003] Meanwhile, with growing concerns over the depletion of conventional energy resources such as petroleum and natural gas, and increasing demand for eco-friendly resources, research on fuel cells, as a new alternative energy source, has been actively conducted. Fuel cells, known as eco-friendly energy sources utilizing the reverse reaction of water electrolysis, include various types under development, such as phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells (hereinafter simply referred to as "SOFCs").

[0004] Among these, SOFCs use solid oxides permeable to oxygen or hydrogen ions as electrolytes and operate at the highest temperature (600 to 1000 °C) of any existing fuel cell. With all components being solid, SOFCs have a simpler structure than other fuel cells, with no issues of electrolyte loss, replenishment, or corrosion. Additionally, their high-temperature operation eliminates the need for precious metal catalysts, enables easy fuel supply through internal reforming, and allows combined heat and power generation by utilizing waste heat from high-temperature exhaust gas. Accordingly, research and development on SOFCs has been actively pursued, particularly in advanced countries such as the United States and Japan.

[0005] Due to the high operating temperature of SOFCs, fuel cell components are made of heat-resistant metal materials, and recent efforts increasingly adopt highly corrosion-resistant stainless steel for certain parts to counter corrosion from high-temperature water vapor generated during fuel cell operation.

[0006] Stainless steel contains alloying elements such as chromium to prevent surface corrosion. At high SOFC operating temperatures, chromium migrates to the component surface and forms a chromium oxide film, thereby protecting the stainless surface. However, within the high temperature range of SOFC operation, the chromium oxide film reacts with oxygen and water vapor to form volatile chromium gaseous species. These species migrate into the SOFC cathode due to partial pressure differences during operation, ultimately poisoning the cathode and severely degrading performance.

[0007] To mitigate this, research is underway on electroless nickel plating layers applied to stainless steel surfaces to prevent poisoning due to chromium volatilization. However, while the electroless nickel plating layers exhibit good adhesion and bonding to part surfaces at room temperature or moderately elevated temperatures, they suffer from a sharp decrease in adhesion and bonding at high operating temperatures at which SOFCs operate.

[0008] Thus, there is an urgent need for research on electroless nickel plating methods that prevent the volatilization of alloying elements in parts used in high-temperature devices such as SOFCs, while maintaining excellent long-term adhesion of the formed plating layer and providing high hardness to protect the part surfaces under various physical and chemical environments.[Technical Problem]

[0009] The present invention has been made in view of the above circumstances, and is directed to providing a method of manufacturing an electroless nickel-plated part and an electroless nickel-plated part manufactured thereby, wherein volatilization of alloying elements from alloys constituting parts in various devices operating under high-temperature conditions such as SOFCs is prevented, the formed plating layer maintains stable adhesion over a long time, and the part surface is protected under various physical and chemical environments due to its high hardness, corrosion resistance, and wear resistance.[Technical Solution]

[0010] To solve the above problems, the present invention provides a method of manufacturing an electroless nickel-plated part with improved high-temperature adhesion, including: (1) performing a pretreatment process including sandblasting and nickel strike plating on a part to be plated; (2) forming an electroless nickel plating layer on the part; and (3) performing high-temperature heat treatment on the electroless nickel-plated part at a temperature of 550 °C or higher.

[0011] According to an embodiment, the pretreatment process may further include, between the sandblasting process and the nickel strike plating process: a degreasing process of immersing the part in a 10 to 15 wt% degreasing solution at 40 to 60 °C for 1 to 10 minutes, followed by electrolytic degreasing at a current density of 1 to 2 A / dm 2< for 1 to 5 minutes; an acid etching process of immersing the part for 1 to 10 minutes in an etching solution prepared by mixing a 1 to 7 wt% aqueous nitric acid solution, a 1 to 6 wt% aqueous hydrofluoric acid solution, and a 1 to 15 wt% aqueous hydrochloric acid solution; and an activation process of immersing the part in a 15 to 25 wt% aqueous hydrochloric acid solution for 2 to 15 minutes.

[0012] The sandblasting process may be performed such that a plating region of the part has a center-line average roughness (Ra) of 0.8 µm or more, and the nickel strike plating process may be performed by immersing the surface-activated part in a nickel strike plating solution and then applying a current density of 1.5 to 5.0 A / dm 2< for 5 to 10 minutes.

[0013] The center-line surface roughness may be 0.8 to 5.0 µm.

[0014] Step (2) may be performed by immersing the part in an electroless nickel plating solution having a pH of 4 to 5 at a temperature of 80 to 90 °C for 20 to 120 minutes.

[0015] Step (3) may include performing low-temperature heat treatment at 190 to 410 °C for 1 to 9 hours, followed by high-temperature heat treatment at 550 °C or higher for 3 to 7 hours on the part, which has been cooled after the low-temperature heat treatment, and more preferably, the high-temperature heat treatment may be performed at 600 to 700 °C for 4 to 5 hours under vacuum.

[0016] The present invention provides an electroless nickel-plated part manufactured according to the present invention.[Advantageous Effects]

[0017] The method of manufacturing an electroless nickel-plated part according to the present invention forms an electroless nickel plating layer on the part surface that prevents volatilization of alloying elements from alloys constituting various parts exposed to high-temperature environments of 600 °C or higher, while maintaining stable adhesion for a long time. The layer also exhibits high hardness, wear resistance, and corrosion resistance, thereby protecting the part surface under various physical and chemical environments. Accordingly, the method is widely applicable to parts in various high-temperature devices such as SOFCs.[Description of Drawings]

[0018] FIGS. 1 and 2 are a surface photograph of a part to be plated after completion of the sandblasting process as the pretreatment step (1) in the method of manufacturing an electroless nickel-plated part according to an embodiment of the present invention, and a graph showing the measured surface roughness thereof, respectively. FIGS. 3A to 3C are photographs of a part manufactured according to the method of manufacturing an electroless nickel-plated part according to an embodiment of the present invention, wherein FIG. 3A is a surface photograph of the electroless nickel-plated part, FIG. 3B is a photograph after cross-cut evaluation of the surface of the electroless nickel-plated part, and FIG. 3C is a series of photographs after 90° and 180° mandrel bending tests. FIG. 4 is a surface photograph of an electroless nickel-plated part according to Comparative Example 1 of the method of manufacturing an electroless nickel-plated part of the present invention. FIG. 5 is a surface photograph of an electroless nickel-plated part according to Comparative Example 2 of the method of manufacturing an electroless nickel-plated part of the present invention. FIGS. 6A and 6B are cross-sectional H / X SEM-EDS photographs of an electroless nickel-plated part manufactured by the method of manufacturing an electroless nickel-plated part according to an embodiment of the present invention, wherein FIG. 6A is a 5000× cross-sectional SEM image, and FIG. 6B is an EDS mapping photograph for each element and the analysis results thereof. FIGS. 7A and 7B are cross-sectional H / X SEM-EDS photographs of an electroless nickel-plated part according to Comparative Example 3 of the method of manufacturing an electroless nickel-plated part, wherein FIG. 7A is a 5000× cross-sectional SEM image, and FIG. 7B is an EDS mapping photograph for each element and the analysis results thereof. FIGS. 8A and 8B are cross-sectional H / X SEM-EDS photographs of an electroless nickel-plated part according to Comparative Example 5 of the method of manufacturing an electroless nickel-plated part, wherein FIG. 8A is a 5000× cross-sectional SEM image, and FIG. 8B is an EDS mapping photograph for each element and the analysis results thereof. [Best Mode]

[0019] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily implement the present invention. The present invention can be embodied in various forms and is not limited to the embodiments described herein.

[0020] According to an embodiment of the present invention, an electroless nickel-plated part may be manufactured through steps including: (1) pretreating a part to be plated; (2) forming an electroless nickel plating layer on the part; and (3) performing high-temperature heat treatment on the electroless nickel-plated part at a temperature of 550 °C or higher.

[0021] First, as step (1) according to the present invention, a step of pretreating the part is performed.

[0022] The part may be a known device component requiring electroless nickel plating, and the present invention is not particularly limited thereto. For example, the part may be various components such as pipes, fins, plates, and covers. In addition, the device in which the part is mounted may be a device exposed to or operating in a high-temperature environment, for example, 600 °C or higher. Specifically, the device may be a solid oxide fuel cell, and the part may be various components constituting a heat exchanger or the like provided in the solid oxide fuel cell, without limitations on size, type, shape, and the like.

[0023] In addition, the material of the part may be a known material suitable for electroless nickel plating, for example, a stainless steel alloy, and the present invention is not particularly limited to the detailed composition thereof. For example, there is no limitation on SS310, SS304, and the like.

[0024] The pretreatment process for the part includes sandblasting and nickel strike plating, and may further include known pretreatment sub-processes performed before electroless nickel plating, such as a degreasing process, an acid etching process, and an activation process between the sandblasting process and the nickel strike plating process.

[0025] The sandblasting process and the nickel strike plating process, performed as the pretreatment process, may be combined with the high-temperature heat treatment of step (3) described below to allow the electroless nickel plating layer to maintain excellent adhesion at high temperatures. The electroless nickel plating layer formed in step (2) described below may generally experience a decrease in hardness when heat-treated at temperatures exceeding 400 °C, so heat treatment is conventionally not performed at high temperatures of 500 to 600 °C or higher. Although a decrease in hardness does not directly cause a decrease in adhesion, the reduced hardness may increase the probability of adhesion degradation, which is thus undesirable. However, according to the present invention, by performing electroless nickel plating on the surface of the part that has undergone the sandblasting process and the nickel strike plating process as the pretreatment process, even when the high-temperature heat treatment of step (3) is performed, the electroless nickel plating layer may maintain excellent adhesion for a long time under high-temperature use conditions. If either the sandblasting process or the nickel strike plating process is omitted during the pretreatment process, or even if both the sandblasting process and the nickel strike plating process are performed but step (3) described below is not performed or the heat treatment is performed at less than 550 °C, partial delamination may occur after the high-temperature heat treatment of step (3), or even if no appearance defects are observed after the high-temperature heat treatment, there is a concern that the time for maintaining adhesion under high-temperature environments during use may be shortened.

[0026] The sandblasting process may be performed using conventional equipment, methods, and conditions known in the art. Preferably, the surface of the part that has undergone the sandblasting process may have a center-line average roughness (Ra) of 0.8 µm or more, more preferably 0.8 to 5.0 µm, and even more preferably 0.8 to 2.2 µm. If the center-line average roughness is less than 0.8 µm, it may be difficult to achieve the desired level of high-temperature adhesion. In addition, if the center-line average roughness exceeds 5.0 µm, uniform treatment over the entire surface may not be achieved during the nickel strike plating pretreatment, which may lead to decreased adhesion after the high-temperature heat treatment of step (3) or a shortened period of stable adhesion maintenance during use at high temperatures.

[0027] In addition, the nickel strike plating process, as a pretreatment process, serves to improve adhesion of the electroless nickel plating layer formed on the surface of the part thereafter and, in combination with the previously performed sandblasting process, enables the electroless nickel plating layer to have excellent adhesion to the surface of the part even at high temperatures. The nickel strike plating step may be performed by methods and conditions known in the art. Preferably, however, it may be performed by immersing the part in a nickel strike plating solution for 10 to 20 minutes and then applying a current density of 1.5 to 5.0 A / dm 2< for 5 to 10 minutes, which is advantageous for achieving the objectives of the present invention. If the current density and / or the plating time during nickel strike plating deviates from these ranges, it may be difficult to ensure high-temperature adhesion. The nickel strike solution may be used without limitation as long as it is known to be suitable for the material of the part, for example, stainless steel, and specifically may be a mixed solution of 120 to 240 g / L aqueous nickel chloride and 65 to 125 g / L aqueous hydrochloric acid, or a mixed solution of 110 to 120 g / L nickel sulfate, 110 to 120 g / L nickel chloride, 10 to 20 g / L boric acid, and 10% hydrochloric acid, but is not limited thereto.

[0028] Meanwhile, the above-described nickel strike plating process is more preferably performed on the surface-activated part, and for this purpose, an activation process may be further performed between the sandblasting process and the nickel strike plating process described above. In addition, prior to performing the activation process, a degreasing process and an acid etching process may be further performed to remove contaminants such as surface contamination and rust from the surface of the part that has undergone the sandblasting process.

[0029] The degreasing process is for removing foreign substances and oily components present on the surface of the alloy part, and may be performed by conventional methods. The degreasing process may be performed, for example, by immersing the part in a degreasing solution or by an electrolytic degreasing method in which voltage is applied after immersion. At this time, the degreasing solution used for immersion degreasing or electrolytic degreasing preferably contains one or more selected from sodium carbonate, sodium hydroxide (NaOH), and surfactants. Preferably, the degreasing solution contains anionic surfactants such as ethoxylated nonylphenol. Anionic surfactants are effective for removing oily components. For example, the degreasing solution may be composed of an aqueous solution containing 80 to 150 g / L of sodium carbonate (Na 2 CO 3 ), 80 to 150 g / L of sulfuric acid (H 2 SO 4 ), and 2 to 7 mL / L of an anionic surfactant, based on 1 L of the total degreasing solution.

[0030] During electrolytic degreasing, the part may be immersed in a 10 to 15 wt% degreasing solution at 40 to 60 °C for 1 to 10 minutes, followed by electrolytic degreasing at a current density of 1 to 2 A / dm 2< for 1 to 5 minutes, or more preferably, the part may be immersed in a 12 to 15 wt% degreasing solution at 50 to 55 °C for 3 to 5 minutes, followed by electrolytic degreasing at a current density of 1 to 2 A / dm 2< for 1 to 3 minutes. Washing may additionally be performed after electrolytic degreasing.

[0031] Next, the acid etching process is for removing oxide films or smut, which is a reducing metal, formed on the surface of the part, and may be performed by a conventional acid etching method. For example, the acid etching process may be performed by cleaning with an etching solution, which is an acidic solution. Specifically, the etching solution may be prepared by mixing a 1 to 7 wt% aqueous nitric acid solution, a 1 to 6 wt% aqueous hydrofluoric acid solution, and a 1 to 15 wt% aqueous hydrochloric acid solution, and more preferably, a 3 to 7 wt% aqueous nitric acid solution, a 3 to 6 wt% aqueous hydrofluoric acid solution, and a 10 to 15 wt% aqueous hydrochloric acid solution in a volume ratio of 1: 0.1 to 3: 0.1 to 3.

[0032] The acid etching process may be performed by immersing the part in such an etching solution for 1 to 10 minutes, more preferably 5 to 10 minutes, and may further include a washing process after immersion if necessary.

[0033] The acid etching process may be performed at room temperature, for example, 20 to 25 °C, but is not limited thereto.

[0034] Next, the activation process activates the part surface to ensure smooth subsequent plating processes including the electroless nickel plating described below, using activation methods known to be suitable for the specific part and the plating type. For example, the activation process may be performed by immersing the part in a 15 to 30 wt% aqueous hydrochloric acid solution for 2 to 15 minutes, more preferably in a 15 to 25 wt% aqueous hydrochloric acid solution for 2 to 15 minutes, which is advantageous for achieving the objectives of the present invention. A washing process may be further performed after surface activation if necessary. The activation process may be performed at room temperature, for example, 20 to 25 °C.

[0035] Next, as step (2) according to the present invention, a step of forming an electroless nickel plating layer is performed. The electroless nickel plating layer may prevent volatilization of components susceptible to volatilization at high temperatures among the elements constituting the part, and improve corrosion resistance, wear resistance, and the like of the part.

[0036] The electroless nickel plating of step (2) may be performed by immersing the part in a nickel-phosphorus-containing plating solution having a pH of 4 to 5 at a temperature of 80 to 90 °C for 20 to 120 minutes, which is advantageous for forming an electroless nickel plating layer of desired thickness with uniformity and excellent surface quality.

[0037] The electroless nickel plating solution may be a conventional plating solution used in electroless nickel plating including a nickel precursor, and the present invention is not particularly limited thereto. For example, the electroless nickel plating solution includes a solvent, a nickel metal salt as a nickel precursor, and a reducing agent, and may further include known complexing agents, stabilizers, metal stabilizers, and pH adjusters.

[0038] The solvent may be a conventional solvent used in electroless nickel plating solutions, for example, water.

[0039] The nickel metal salt, as a nickel precursor, may include, for example, a nickel salt hydrate, and may specifically include at least one of nickel sulfamate, nickel sulfate, nickel chloride, nickel nitrate, nickel oxide, and nickel carbonate. The nickel metal salt may be included in an amount of 4 g to 7 g per 1 L of the electroless nickel plating solution.

[0040] The reducing agent may reduce nickel ions dissociated from the nickel metal salt. The reducing agent may include, for example, at least one of hypophosphite, boron hydride, dimethylamine borane, and hydrazine, preferably hypophosphite such as at least one of sodium hypophosphite, potassium hypophosphite, and ammonium hypophosphite. Due to these phosphorus-based reducing agents, the formed electroless nickel plating layer may contain phosphorus.

[0041] The reducing agent may be included in an amount of 20 g to 50 g per 1 L of the electroless nickel plating solution, but is not limited thereto.

[0042] Furthermore, as for various additives contained in the electroless nickel plating solution, known additives may be used, so a detailed description thereof is omitted in the present invention.

[0043] The thickness of the electroless nickel plating layer formed through step (2) may be 6.5 to 20 µm, which is more advantageous for preventing the volatilization of alloying elements constituting the part, as well as improving the corrosion resistance and wear resistance of the part. If the thickness of the electroless nickel plating layer is less than 6.5 µm, it may be difficult to prevent the volatilization of alloying elements or maintain the long-term stability thereof. If the thickness exceeds 20 µm, the density of the electroless nickel plating layer may decrease, leading to poor long-term durability such as adhesion degradation under high-temperature conditions, and may also be economically disadvantageous.

[0044] Next, as step (3) according to the present invention, high-temperature heat treatment is performed on the electroless nickel-plated part at a temperature of 550 °C or higher.

[0045] The high-temperature heat treatment of step (3) is performed to prevent adhesion degradation of the electroless nickel plating layer when the part with the electroless nickel plating layer is exposed to a high-temperature environment. The high-temperature heat treatment may be performed at a temperature of 550 °C or higher for 3 to 7 hours, preferably at 600 to 700 °C for 3 to 5 hours. If the high-temperature heat treatment is performed at a temperature lower than 550 °C, delamination of the electroless nickel plating layer may occur on the surface of the electroless nickel-plated part during high-temperature use, despite the heat treatment. Conversely, if the heat treatment is performed at a temperature exceeding 700 °C, the improvement in high-temperature adhesion may be insignificant, and there is a risk of the electroless nickel plating layer melting.

[0046] The high-temperature heat treatment is preferably performed under vacuum, which alleviates concerns about hardness reduction from the high-temperature heat treatment while further enhancing high-temperature adhesion.

[0047] The high-temperature heat treatment may involve heating at a rate of 10 to 16 °C / min until the target temperature is reached, which is advantageous for achieving the objectives of the present invention. If the heating rate is less than 10 °C / min, the process time may be undesirably prolonged, whereas if it exceeds 16 °C / min, it may be difficult to maintain sustained adhesion under high-temperature use conditions.

[0048] Meanwhile, in a preferred embodiment of the present invention, step (3) may further include performing low-temperature heat treatment at 190 to 410 °C for 1 to 9 hours prior to the high-temperature heat treatment, which is more advantageous for improving the adhesion and hardness of the electroless nickel plating layer under high-temperature conditions. The low-temperature heat treatment may additionally remove hydrogen embrittlement generated in the acid etching and activation progresses performed before step (2).

[0049] Preferably, the high-temperature heat treatment after the low-temperature heat treatment may be performed through separate heat treatment processes, particularly with a cooling step interposed therebetween. This is more advantageous for maintaining adhesion and improving the hardness of the electroless nickel plating layer under high-temperature environments. If the high-temperature heat treatment is performed continuously without cooling after the low-temperature heat treatment, the high-temperature adhesion of the electroless nickel plating layer may instead be reduced.

[0050] The present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the scope of the present invention, and should be construed as merely illustrating the present invention.<Example 1>

[0051] A stainless steel (STS310) part having a thickness of 0.5 mm was prepared as a part to be plated, and then pretreatment was performed. First, sandblasting was performed on the surface, and the center-line average roughness of the surface after sandblasting was 0.839 µm. The part was then immersed in a 12.5 wt% degreasing solution (Clean-L20) at 55 °C for 5 minutes, followed by electrolytic degreasing at a current density of 2 A / dm 2< for 2 minutes. Subsequently, etching was performed at 23 °C for 5 minutes in an etching solution prepared by mixing 5 wt% aqueous nitric acid, 4 wt% aqueous hydrofluoric acid, and 12.5 wt% aqueous hydrochloric acid. For surface activation, the part was immersed in a 22 wt% aqueous hydrochloric acid solution at 23 °C for 2 minutes, followed by washing with water. The part was then immersed at 23 °C for 15 minutes in a nickel strike solution composed of 250 g / L nickel chloride and 100 mL / L aqueous hydrochloric acid, followed by nickel strike plating at a current density of 2 A / dm 2< for 10 minutes, and water washing.

[0052] The stainless steel part that had undergone the pretreatment process was immersed in an electroless nickel plating solution (Nichem ®< MP 1189) having a pH of 4.7 at 83 °C for 30 minutes to form an electroless nickel plating layer.

[0053] The part with the electroless nickel plating layer was placed in a furnace, heated at a rate of 15 °C / min under an air atmosphere, low-temperature heat-treated at 350 °C for 1.5 hours, and naturally cooled. The low-temperature heat-treated part was then placed again in the furnace, heated at a rate of 15 °C / min under vacuum, high-temperature heat-treated at 620 °C for 4 hours, and naturally cooled to obtain a part with an electroless nickel plating layer.<Examples 2 to 4>

[0054] Parts with electroless nickel plating layers as shown in Table 1 below were manufactured in the same manner as in Example 1, except that the surface roughness after sandblasting or the high-temperature heat treatment temperature was changed as shown in Table 1.<Comparative Examples 1 to 5>

[0055] Parts with electroless nickel plating layers as shown in Table 1 below were manufactured in the same manner as in Example 1, except that, for the pretreatment, the sandblasting process or the nickel strike plating process was omitted, or the high-temperature heat treatment, or both low- and high-temperature heat treatments, were omitted as shown in Table 1.<Experimental Example 1>

[0056] For the parts with electroless nickel plating layers manufactured in Examples and Comparative Examples, the following physical properties were evaluated, and the results are shown in Table 1 below.1. Surface Roughness Measurement

[0057] The surface roughness of the parts after the sandblasting process in Examples 1 and 2 was measured using a confocal microscope, and the corresponding photographs are shown in FIGS. 1 and 2, respectively.2. Appearance Defect Evaluation of Electroless Nickel Plating Layer

[0058] For 10 specimens from each Example and Comparative Example, appearance defect evaluation was performed by counting the number of specimens exhibiting delamination. The rating was × for 0 delaminated specimens, Δ for delamination in 1 to 3 specimens, and ∘ for delamination in 4 or more specimens.3. Adhesion Evaluation of Electroless Nickel Plating Layer after High-Temperature Exposure

[0059] Parts without appearance defects were exposed to 650 °C for 50 hours.

[0060] Thereafter, mandrel bending tests were performed at 90° and 180°, and plating adhesion defects were visually evaluated. Results were rated o for lifting or delamination, Δ for cracking, and × for no abnormalities.

[0061] In addition, after performing a 10×10 cross-cut evaluation at 1 cm intervals, the number of squares, among a total of 100 squares, exhibiting even slight delamination was counted. The cross-cut evaluation was conducted according to ASTM D3359 Standard Test Method for Rating Adhesion by Tape Test. [Table 1]Exam ple 1Exam ple 2Exam ple 3Exam ple 4Comp arative Exam ple 1Comp arative Exam ple 2Comp arative Exam ple 3Comp arative Exam ple 4Comp arative Exam ple 5Pretreatment ProcessSandblasting / S urface Roughness (Ra, µm)○ / 0.83 9○ / 0.77 5○ / 0.83 9○ / 0.83 9Not perfor med○ / 0.83 9○ / 0.83 9○ / 0.83 9○ / 0.83 9Nickel Strike Plating○○○○○Not perfor med○○○Low-Temperature Heat TreatmentTemperature (°C) / Time / Atm osphere350 / 1. 5 h / air350 / 1. 5 h / airNot perfor med350 / 1. 5 h / air350 / 1. 5 h / air350 / 1. 5 h / air400 / 1 h / air350 / 1. 5 h / airNot perfor medHigh-Temperature Heat TreatmentTemperature (°C) / Time / Atm osphere620 / 4 h / vac uum620 / 4 h / vac uum620 / 4 h / vac uum560 / 6 h / vac uum620 / 4 h / vacu um620 / 4 h / vacu umNot perfor med500 / 8 h / vacu umNot perfor medAppearance of Electroless Nickel Plating Layer××××○Δ×××Adhesion after High-Temperature Exposure90° Bending / 180° Bending / Numb er of Delaminated Squares after Cross-Cut Evaluation× / × / 0× / ○ / 2 0○ / ○ / 1 5× / × / 1 0Not evalua ted○ / ○ / 41○ / ○ / 10 0○ / ○ / 54○ / ○ / 10 0

[0062] As shown in Table 1, Comparative Examples 1 and 2, in which either sandblasting or nickel strike plating was not performed as the pretreatment process, exhibited higher frequencies of appearance defects after high-temperature heat treatment compared to Examples.

[0063] Comparative Examples 3 and 5, in which no high-temperature heat treatment was performed, and Comparative Example 4, in which the high-temperature heat treatment temperature was outside the range of the present invention, showed significantly reduced or lost adhesion of the electroless nickel plating layer after prolonged high-temperature exposure, compared to Examples.<Experimental Example 2>

[0064] Cross-sectional H / X SEM-EDS analyses were performed on the parts according to Example 1, Comparative Example 3, and Comparative Example 5, and the results are shown in FIGS. 6A and 6B for Example 1, FIGS. 7A and 7B for Comparative Example 3, and FIGS. 8A and 8B for Comparative Example 5.

[0065] As can be seen from the results in Table 1 and from FIGS. 6A and 6B, 7A and 7B, and 8A and 8B, all of Example 1, Comparative Example 3, and Comparative Example 5 formed electroless nickel plating layers of predetermined thickness on the part surfaces.

[0066] However, as can be seen from FIG. 8A, in Comparative Example 5, in which no heat treatment process was performed, the electroless nickel plating layer showed no adhesion issues with the part surface, but the results in Table 1 indicate that adhesion could not be maintained upon high-temperature exposure.

[0067] In addition, as can be seen from Table 1 and FIG. 7A, in Comparative Example 3 subjected only to low-temperature heat treatment, although no abnormalities were observed in the visual appearance inspection, minute and continuous lifting occurred between the electroless nickel plating layer and the part surface. Also, despite the low-temperature heat treatment, due to the absence of high-temperature heat treatment, the results in Table 1 confirm that plating layer adhesion could not be maintained under high-temperature environments.

[0068] In contrast, as can be seen from Table 1 and FIG. 6A, Example 1 showed no lifting between the electroless nickel plating layer and the part surface due to the high-temperature heat treatment, compared to Comparative Example 3, demonstrating that it ensures excellent adhesion of the plating layer even under high-temperature environments.

[0069] Although an embodiment of the present invention has been described above, the spirit of the present invention is not limited to the embodiment presented in this specification. Those skilled in the art who understand the spirit of the present invention can easily propose other embodiments by adding, modifying, deleting, or substituting components within the scope of the same spirit, and such embodiments should also fall within the scope of the spirit of the present invention.

Claims

1. A method of manufacturing an electroless nickel-plated part with improved high-temperature adhesion, comprising: (1) performing a pretreatment process including sandblasting and nickel strike plating on a part to be plated; (2) forming an electroless nickel plating layer on the part; and (3) performing high-temperature heat treatment on the electroless nickel-plated part at a temperature of 550 °C or higher.

2. The method of claim 1, wherein the pretreatment process further includes, between the sandblasting process and the nickel strike plating process: a degreasing process of immersing the part in a 10 to 15 wt% degreasing solution at 40 to 60 °C for 1 to 10 minutes, followed by electrolytic degreasing at a current density of 1 to 2 A / dm2 for 1 to 5 minutes; an acid etching process of immersing the part for 1 to 10 minutes in an etching solution prepared by mixing a 1 to 7 wt% aqueous nitric acid solution, a 1 to 6 wt% aqueous hydrofluoric acid solution, and a 1 to 15 wt% aqueous hydrochloric acid solution; and an activation process of immersing the part in a 15 to 25 wt% aqueous hydrochloric acid solution for 2 to 15 minutes.

3. The method of claim 1, wherein the sandblasting process is performed such that a plating region of the part has a center-line average roughness (Ra) of 0.8 µm or more.

4. The method of claim 1, wherein the nickel strike plating process is performed by immersing the surface-activated part in a nickel strike plating solution and then applying a current density of 1.5 to 5.0 A / dm2 for 5 to 10 minutes.

5. The method of claim 3, wherein the center-line surface roughness is 0.8 to 5 µm.

6. The method of claim 1, wherein step (2) is performed by immersing the part in an electroless nickel plating solution having a pH of 4 to 5 at a temperature of 80 to 90 °C for 20 to 120 minutes.

7. The method of claim 1, wherein step (3) includes performing low-temperature heat treatment at 190 to 410 °C for 1 to 9 hours, and then performing high-temperature heat treatment at 550 °C or higher for 3 to 7 hours on the part, which has been cooled after the low-temperature heat treatment.

8. The method of claim 7, wherein the high-temperature heat treatment is performed at a temperature of 600 to 700 °C for 4 to 5 hours under vacuum.

9. An electroless nickel-plated part manufactured according to any one of claims 1 to 8.

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