Ceramic layer for in-situ sealing of pores and method for producing same

Abstract

The present application relates to the technical field of metal surface treatment, and in particular to a ceramic layer for in-situ sealing and a preparation method thereof. In a first aspect, the present application provides a preparation method of a ceramic layer for in-situ sealing, comprising the following steps: Step 1, providing a substrate, the substrate comprising oppositely arranged first and second surfaces, the first surface being provided with a Ni-W alloy layer; Step 2, taking the substrate as an anode and performing plasma electrolytic oxidation treatment in an electrolyte so as to form a ceramic layer on the Ni-W alloy layer. In the first aspect, the dynamic response and element migration of the Ni-W alloy layer in the PEO environment are utilized, so that the ceramic layer preparation and the pore sealing are performed synchronously, the in-situ growth and densification of the ceramic layer are realized, and the prepared ceramic layer has both wear resistance and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to an in-situ sealing ceramic layer and its preparation method. Background Technology

[0002] Lightweight alloys (such as aluminum, magnesium, and titanium alloys) have become indispensable key structural materials in high-end equipment fields such as aerospace, defense, and precision instruments due to their excellent specific strength. However, these materials generally suffer from inherent weaknesses such as low surface hardness, poor wear resistance, and insufficient corrosion resistance, which severely restrict their service life and reliability under harsh working conditions. Therefore, applying high-performance surface protective coatings to lightweight alloy components is a key technical approach to improve their overall performance and expand their application boundaries. Among many surface engineering technologies, plasma electrolytic oxidation (PEO) technology is favored because it can grow a ceramic layer with metallurgical bonding, high hardness, and excellent wear and heat resistance on a lightweight alloy substrate in situ. However, this technology has an inherent defect that has long remained unresolved: during the process, due to the inherent instability of instantaneous plasma discharge, molten material ejection, and gas escape, the resulting ceramic layer usually exhibits a typical porous structure. Numerous micropores are interconnected and often penetrate into the substrate, providing a rapid channel for the transport of corrosive media (such as chloride ions) to the interior, causing a sharp decline in the protective performance of the coating. This contradiction of "high wear resistance but poor corrosion resistance" greatly limits the application of PEO technology in scenarios with high corrosion resistance requirements.

[0003] To compensate for the porosity of PEO coatings, the industry currently widely employs post-treatment sealing techniques as a remedial measure, which can be mainly divided into two categories: Organic sealing: This involves impregnating and filling the pores with organic sealants such as epoxy resin, silane, or fluorocarbon resin. While this method can improve corrosion resistance in the short term, it introduces an organic phase, significantly deteriorating the coating's high-temperature resistance, thermal conductivity, and surface hardness. Furthermore, organic sealants suffer from aging and degradation, resulting in a limited protective lifespan. Inorganic sealing: This involves high-temperature hydration sealing or sealing with heavy metal salts (such as chromates). While this method avoids the disadvantages of organic materials, it typically faces problems such as cumbersome processes, high energy consumption, and potential environmental risks. In addition, the bonding between the sealing product and the ceramic substrate is mostly physical or mechanical, and the interface is prone to becoming a weak point under thermal shock or mechanical stress, leading to unreliable sealing results. Existing post-sealing technologies are all "passive remedial" solutions, and they share the following fundamental shortcomings: First, they are additional processes independent of the PEO process, leading to increased production costs and a longer process flow; second, the sealing agent has weak adhesion to the ceramic matrix and is prone to peeling off under thermal shock or mechanical stress; finally, the sealing layer, as a functional "outer membrane," will be the first to be damaged and fail under abrasive conditions, making its protective effect difficult to maintain and stabilize. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide an in-situ sealing ceramic layer and a method for preparing the same.

[0005] In a first aspect, the present invention provides a method for preparing an in-situ sealed ceramic layer, comprising the following steps:

[0006] Step 1: Provide a substrate, the substrate including a first surface and a second surface disposed opposite to each other, the first surface being provided with a Ni-W alloy layer;

[0007] Step 2: Using the substrate as the anode, perform plasma electrolytic oxidation treatment in the electrolyte to form a ceramic layer on the Ni-W alloy layer.

[0008] In the first aspect of the present invention, the dynamic response and element migration of the Ni-W alloy layer in the PEO environment are utilized to enable the simultaneous preparation of the ceramic layer and the sealing of the pores, thereby realizing the in-situ growth and densification of the ceramic layer. The prepared ceramic layer has both wear resistance and corrosion resistance.

[0009] In a second aspect of the invention, this application proposes an in-situ sealing ceramic layer, prepared according to the method of the second aspect of the invention. Thus, the ceramic layer possesses both superior wear resistance and corrosion resistance.

[0010] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0011] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0012] Figure 1 These are surface SEM images of samples from Examples 1-4 and Comparative Examples 1-2, wherein... Figure 1 Middle (a) to Figure 1 (d) represents the surface morphology of Examples 1, 2, 3, and 4, respectively. Figure 1 (e) Figure 1 (f) shows the surface morphology of Comparative Example 1 and Comparative Example 2, respectively;

[0013] Figure 2 These are cross-sectional SEM images of samples from Examples 1-4 and Comparative Examples 1-2, wherein... Figure 2 Middle (a) to Figure 2 (d) shows the cross-sectional morphology of Examples 1, 2, 3, and 4, respectively. Figure 2(e) Figure 2 (f) shows the cross-sectional morphology of Comparative Example 1 and Comparative Example 2, respectively;

[0014] Figure 3 Friction curves of samples from Examples 1-4 and Comparative Examples 1-2;

[0015] Figure 4 Electrochemical polarity curves of samples from Examples 1-4 and Comparative Examples 1-2;

[0016] Figure 5 The images show the morphology and elemental distribution of the Ni-W alloy layer in Example 1. Figure 5 In the diagram, a represents the morphology of the Ni-W alloy layer. Figure 5 b in the diagram represents the elemental distribution of the Ni-W alloy layer. Detailed Implementation

[0017] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0018] This application proposes an in-situ sealed ceramic layer and its preparation method, which can simultaneously seal the pores during the growth of the PEO ceramic layer, thereby obtaining an integrated composite coating with excellent wear resistance and corrosion resistance without any subsequent treatment.

[0019] In a first aspect of the invention, a method for preparing an in-situ sealed ceramic layer is provided.

[0020] In some embodiments, the method for preparing the in-situ sealed ceramic layer includes the following steps:

[0021] Step 1: Provide a substrate, which includes a first surface and a second surface disposed opposite to each other, and the first surface is provided with a Ni-W alloy layer;

[0022] Step 2: Using the substrate as the anode, perform plasma electrolytic oxidation treatment in the electrolyte to form a ceramic layer on the Ni-W alloy layer.

[0023] The first aspect of this invention utilizes the dynamic response and element migration of the Ni-W alloy layer in a PEO environment to combine the traditionally separate steps of ceramic layer preparation and pore sealing into one, achieving in-situ growth and densification of the ceramic layer, resulting in a ceramic layer with both wear resistance and corrosion resistance. This process is not a simple physical covering, but rather involves a series of precise physicochemical reactions to construct an inherently dense, bulk-sealed pore structure from the growth source. The specific sealing mechanism is as follows: Initial stage: Uniform nucleation and formation of a composite oxide film. In the early stages of PEO treatment, the Ni-W alloy layer, with its superior uniform conductivity compared to the aluminum alloy substrate, provides an ideal electron conduction path for current distribution, effectively avoiding localized ablation caused by uneven conductivity in the substrate. Simultaneously, the electrolyte penetrates through the microscopic defects of the Ni-W alloy layer, causing it to undergo initial oxidation together with the substrate, generating a composite oxide film containing components such as WO3 and Al2O3. This lays a solid foundation for the subsequent uniform and stable growth of the ceramic layer. Breakdown Stage: As the voltage increases, the breakdown discharge stage begins. Instantaneous high temperature and pressure are generated in the local micro-arc region, and element migration completes the initial filling of pores (molten glass effect). At this time, Ni and W elements in the Ni-W alloy layer are activated, with Ni acting as a flow carrier: NiO, formed by the oxidation of Ni during the PEO process, has a low melting point. It preferentially melts at the high temperature of the micro-arc, significantly reducing the overall viscosity and surface tension of the entire molten pool (composed of Al2O3, WO3, etc.). W acts as a filler: W is oxidized to WO3. Under the low viscosity and low surface tension environment created by NiO, WO3 and Al2O3 can rapidly form a WO3-Al2O3 composite transient eutectic with extremely low viscosity and excellent fluidity. This melt, like molten glass, is carried and guided by the NiO melt, rapidly and comprehensively migrating along the plasma discharge channel and filling the depths of the forming micropores and cracks. During the continuous breakdown-melting-solidification cycle of PEO, liquid phase sealing and structural densification occur. The WO3-Al2O3 composite melt that initially filled the pores remelts under the high temperature of subsequent discharges and eventually solidifies, forming a dense sealing structure. This process achieves in-situ sealing of the ceramic layer from the inside. The main structure of the Ni-W alloy layer, due to its high melting point and stability, is maintained and continues to serve as a stable conductive matrix, ensuring the continuation of the PEO process. The first aspect of this invention does not rely on simple physical covering, but rather on the local migration, ionization, and co-melting and resolidification with oxidation products of the Ni-W alloy layer during the PEO process. This active filling of pores from the source of ceramic layer growth forms an inherently dense bulk sealing structure, fundamentally different from traditional external sealing. This mechanism significantly reduces the porosity of the ceramic layer (down to below 5%), fundamentally cutting off the penetration channels of corrosive media and improving corrosion resistance several times over.This method combines preparation and sealing into one process, eliminating the need for a separate, cumbersome, and potentially environmentally unfriendly post-sealing process. This shortens the production cycle, reduces overall costs, and avoids the problems of weak adhesion and easy peeling of the outer sealing layer.

[0024] Step 1 of the first aspect of this application can be implemented through the following embodiments.

[0025] In some embodiments, the thickness of the Ni-W alloy layer is 10 μm to 15 μm. Therefore, the Ni-W alloy layer can serve as a tough transition layer, effectively mitigating thermal expansion mismatch and stress concentration between the ceramic layer and the metal substrate. For example, the thickness of the Ni-W alloy layer can be 10 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.

[0026] In the embodiments of this application, the thickness of the Ni-W alloy layer was measured using an eddy current thickness gauge.

[0027] In some preferred embodiments, the mass percentage of W in the Ni-W alloy layer is 18% to 50%. Therefore, if the W content exceeds the upper limit of this range, it will trigger a reversal of melt kinetics and failure of the sealing mechanism. Specifically, an excessively high W content means a relative scarcity of the low-melting-point flow aid NiO, leading to a rebound in viscosity and a sharp drop in fluidity in the transient eutectic system originally constructed from WO3-Al2O3. At this point, even with abundant W, it is difficult to effectively carry it to deep pores, and it can only remain on the surface after melt ejection, forming ineffective, isolated W-rich clusters. This surface-enriched, hollow structure not only fails to seal deep channels but also induces new microcracks within the ceramic layer due to increased shrinkage stress during solidification of the high-W melt, resulting in a decrease in corrosion resistance. For example, the mass percentage of W in the Ni-W alloy layer can be 18.0%, 18.6%, 20%, 25%, 30%, 35%, 37%, 48.7%, 50%, etc.

[0028] In the embodiments of this application, the mass percentage of W element in the Ni-W alloy layer was obtained by EDS testing.

[0029] In some embodiments, the substrate is a lightweight metal substrate. This enhances the wear resistance and corrosion resistance of the lightweight metal substrate.

[0030] Optionally, the light metal can be aluminum, aluminum alloy, magnesium, magnesium alloy, titanium, or titanium alloy.

[0031] Preferably, the light metal can be aluminum or an aluminum alloy. Thus, when the matrix is ​​aluminum or an aluminum alloy, the oxides used in PEO are mainly Al2O3 (γ-Al2O3 and α-Al2O3). Al2O3 melt has low viscosity, good fluidity, and extremely strong reflow ability after melt ejection, which is beneficial for filling pores.

[0032] In some embodiments, pulse electrodeposition can be used to form the Ni-W alloy layer. The pulse electrodeposition uses the substrate as the cathode and the nickel sheet as the consumable anode. This allows for the formation of a well-bonded Ni-W alloy layer on the substrate. At the same time, the formed Ni-W alloy layer has a uniform composition and thickness, and will not cause compositional segregation due to unstable current. This ensures that the Ni-W alloy layer melts uniformly throughout during PEO discharge, without local melting or detachment, and provides a continuous and stable current carrier for the W phase, allowing the WO3-Al2O3 composite melt to fill rapidly along the entire discharge channel.

[0033] Optionally, the substrate can be pretreated by grinding, cleaning, alkaline washing, acid washing for brightening and zinc immersion treatment in sequence to thoroughly clean the surface and form a uniform and activated zinc immersion transition layer to ensure the quality of subsequent electroplating.

[0034] In some embodiments, a Ni-W alloy layer is formed by pulse electrodeposition in a plating bath comprising the following components: 30 g / L–50 g / L nickel sulfate hexahydrate, 60 g / L–80 g / L sodium tungstate dihydrate, 30 g / L–40 g / L ammonium chloride, 160 g / L–180 g / L sodium citrate dihydrate, 20 g / L–40 g / L sodium bromide, 10 g / L–20 g / L sodium saccharin, and 5 g / L–10 g / L sodium dodecyl sulfate. This plating bath optimizes the Ni... 2+ With WO4 2- The proportion of W is conducive to the formation of a Ni-W alloy layer with a mass percentage of W of 18% to 50%; and the sodium citrate dihydrate as a complexing agent, sodium saccharin as a stress reliever, and sodium dodecyl sulfate as a wetting agent can make the formed Ni-W alloy layer dense, uniform and with low internal stress. For example, in this plating solution, the concentration of nickel sulfate hexahydrate can be 30 g / L, 35 g / L, 40 g / L, 50 g / L, etc.; the concentration of sodium tungstate dihydrate can be 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, etc.; the concentration of ammonium chloride can be 30 g / L, 35 g / L, 40 g / L, etc.; the concentration of sodium citrate dihydrate can be 160 g / L, 170 g / L, 175 g / L, 180 g / L, etc.; the concentration of sodium bromide can be 20 g / L, 30 g / L, 35 g / L, 40 g / L, etc.; the concentration of sodium saccharin can be 10 g / L, 15 g / L, 20 g / L, etc.; and the concentration of sodium dodecyl sulfate can be 5 g / L, 6 g / L, 9 g / L, 10 g / L, etc.

[0035] In some embodiments, a Ni-W alloy layer is formed by pulse electrodeposition, and the pH of the plating bath for pulse electrodeposition is 5-6.

[0036] Optionally, boric acid can be used to adjust the pH of the plating solution to 5-6.

[0037] In some embodiments, the Ni-W alloy layer is formed by pulse electrodeposition, with a pulse electrodeposition current density of 20 A / dm³. 2 ~40 A / dm 2 For example, the current density can be 20 A / dm³. 2 30 A / dm 2 35 A / dm 2 40 A / dm 2 wait.

[0038] In some embodiments, a Ni-W alloy layer is formed by pulse electrodeposition at a temperature of 40 °C to 60 °C. For example, the electrodeposition temperature can be 40 °C, 45 °C, 50 °C, 60 °C, etc.

[0039] In some embodiments, a Ni-W alloy layer is formed by pulsed electrodeposition for a time of 30 min to 60 min. For example, the electrodeposition time can be 30 min, 40 min, 45 min, 55 min, 60 min, etc.

[0040] Step 2 of the first aspect of this application can be implemented through the following embodiments.

[0041] In some embodiments, stainless steel may be used as the cathode.

[0042] In some embodiments, plasma electrolytic oxidation is performed in a silicate system electrolyte. This allows for PEO treatment in the silicate system electrolyte, leveraging the synergistic reaction of the Ni-W alloy layer during high-voltage discharge to achieve simultaneous ceramic layer growth and in-situ pore sealing.

[0043] Optionally, the silicate system electrolyte includes tungstate. Thus, sodium tungstate is added to the silicate system, increasing the WO4 content in the electrolyte. 2- It can react in situ with the Ni-W molten phase in the discharge micro-region to generate low-melting WO3-Al2O3, which increases the total amount and stability of the filler phase and avoids incomplete sealing due to insufficient W coating alone.

[0044] As examples, silicate system electrolytes may include the following components and concentrations: 10 g / L to 20 g / L sodium hexametaphosphate, 20 g / L to 30 g / L sodium tungstate, 2 g / L to 10 g / L ammonium metavanadate, 5 g / L to 10 g / L sodium silicate, 10 g / L to 20 g / L potassium carbonate, and 10 g / L to 20 g / L sodium carbonate. For example, in silicate electrolyte systems, the concentration of sodium hexametaphosphate can be 10 g / L, 15 g / L, 20 g / L, etc.; the concentration of sodium tungstate can be 20 g / L, 25 g / L, 30 g / L, etc.; the concentration of ammonium metavanadate can be 2 g / L, 5 g / L, 7 g / L, 10 g / L, etc.; the concentration of sodium silicate can be 5 g / L, 8 g / L, 10 g / L, etc.; the concentration of potassium carbonate can be 10 g / L, 15 g / L, 20 g / L, etc.; and the concentration of sodium carbonate can be 10 g / L, 15 g / L, 20 g / L, etc.

[0045] In some embodiments, a substrate with a Ni-W alloy layer is used as the anode and a stainless steel plate as the cathode, and plasma electrolytic oxidation is performed in an electrolyte. This provides a basis for continuous and uniform plasma discharge between the anode and cathode, thereby ensuring the continuous and controllable migration and reaction of functional elements (W, Ni) in the Ni-W alloy layer into the pores of the ceramic layer, enabling efficient in-situ pore sealing.

[0046] In some embodiments, plasma electrolytic oxidation treatment includes: employing a bipolar pulsed power supply mode, controlling the termination voltage to be 450V~500V, the pulse duty cycle to be 10%~15%, the treatment time to be 30 min~60 min, the electrolyte temperature to be 20℃~25℃, and the PEO process to be in constant current mode; thus, the combination of the bipolar pulsed power supply and the low duty cycle of 10%~15% creates a high-density but short-pulse-width intermittent discharge mode. This mode can provide high instantaneous energy sufficient to break through the oxide film and induce local melting of the Ni-W alloy layer, while avoiding the destructive ablation of the coating by continuous arc due to its long intermittent period. This provides ample time for the sealing material migrating from the Ni-W alloy layer to transport, diffuse, and co-melt and re-solidify in the pores, which is crucial for achieving uniform, tight pore sealing rather than forming large melt spots. The termination voltage is controlled at 450 V~500 V, a voltage window sufficient to excite a uniform and intense micro-arc discharge across the entire workpiece surface, ensuring the Ni-W alloy layer is effectively activated and participates in the reaction. Simultaneously, this upper voltage limit avoids excessive energy density leading to over-sintering of the ceramic layer surface, the formation of new macroscopic cracks, or breakdown of the underlying Ni-W alloy layer, thus achieving an optimal balance between deep pore sealing and maintaining the integrity of the coating structure. Controlling the electrolyte temperature at 20℃~25℃ and setting a treatment time of 30 min~60 min together constitutes a stable external reaction environment. Low-temperature control effectively suppresses the thermal decomposition and side reactions of the electrolyte components, ensuring stable solution conductivity and thus maintaining consistent discharge characteristics. Sufficient processing time ensures that the ceramic layer can grow to the ideal thickness, and the sealing effect of the Ni-W alloy layer has a sufficient working period to fully and thoroughly fill the micropores from the surface to the inside, ultimately obtaining a high-quality composite coating with extremely low porosity, uniform performance and high reproducibility.

[0047] For example, the process conditions for PEO include a termination voltage of 450V, 460V, 480V, 500V, etc.; a pulse duty cycle of 10%, 12%, 14%, 15%, etc.; a processing time of 30 min, 40 min, 50 min, 60 min, etc.; and an electrolyte temperature of 20℃, 22℃, 24℃, 25℃, etc.

[0048] A second aspect of the present invention provides an in-situ sealed ceramic layer, prepared according to the preparation method of the first aspect of the present invention. Thus, the triple-gradient composite structure of metal matrix-Ni-W toughening transition layer-in-situ sealed ceramic layer, inevitably formed by this specific method, is the physical basis for the breakthrough performance of this ceramic layer, and brings the following significant beneficial effects: Dense structure and orders-of-magnitude improvement in corrosion resistance: Thanks to the in-situ sealing mechanism, the porosity of this ceramic layer can be significantly reduced to below 5%, far exceeding the typical porosity of 20%-30% for traditional plasma electrolytic oxidation coatings. This inherent densification fundamentally cuts off the rapid penetration channels of corrosive media (such as chloride ions) into the interior. Tests show that the composite coating prepared in this way has corrosion resistance several times higher than that of traditional coatings, providing long-term and stable protection for light alloy substrates. This ceramic layer not only inherits the inherent high hardness of micro-arc oxidation ceramic layers, but also generates a dispersion strengthening effect due to the introduction of hard phases such as tungsten oxide into the entire ceramic layer by the Ni-W transition layer during film formation. This makes the composite coating significantly more wear-resistant than a single micro-arc oxidation coating, effectively resisting abrasive wear under harsh operating conditions. In this gradient structure, the Ni-W alloy layer has a strong metallurgical bond with the metal substrate, while it forms a three-dimensional interlocked interface with the surface ceramic layer through element interdiffusion. This strong interfacial bonding effectively alleviates stress concentration caused by the mismatch in thermal expansion coefficients between the ceramic layer and the metal substrate, making the entire coating system less prone to cracking, blistering, or peeling under mechanical impact or thermal shock, exhibiting extremely high service reliability. In addition, this product successfully combines high wear resistance and excellent corrosion resistance, which are traditionally difficult to achieve simultaneously, solving the industry dilemma of "high wear resistance but not corrosion resistance, and corrosion resistance but not wear resistance" in light alloy surface protection. It has a long protective life and slow performance degradation, making it particularly suitable for key components of high-end equipment with extremely high requirements for reliability and durability.

[0049] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0050]

Example 1

[0051] This embodiment provides a method for preparing a highly corrosion-resistant and wear-resistant composite coating on an aluminum alloy surface, the specific steps of which are as follows:

[0052] (1) Matrix pretreatment

[0053] The surface of the 6061 aluminum alloy sample was pretreated to ensure good adhesion and density of the subsequent coating. The process is as follows:

[0054] Grinding: Use #400, #600, #800, and #1000 grit sandpaper for progressive mechanical grinding;

[0055] Cleaning: The polished sample is ultrasonically cleaned to remove residual abrasive and oil from the surface;

[0056] Alkali washing: Immerse in a 5 g / L NaOH aqueous solution and treat at room temperature for 10 minutes. Then rinse with distilled water.

[0057] Acid pickling and activation: Immerse in a 5% (w / w) dilute nitric acid solution to remove the surface oxide film and achieve activation, then rinse with distilled water;

[0058] Zinc immersion treatment: Immerse the activated substrate in zinc immersion solution (composition: 10 g / L NaOH and 10 g / L ZnO) for 2 minutes, then briefly rinse with dilute nitric acid solution to remove the displaced zinc layer; repeat this zinc immersion-pickling step 2 to 5 times until a uniform and dense zinc immersion transition layer is formed on the substrate surface.

[0059] (2) Plating solution preparation

[0060] The composition of the plating solution used for pulse electrodeposition is as follows:

[0061] Nickel sulfate hexahydrate: 30 g / L; sodium tungstate dihydrate: 60 g / L; ammonium chloride: 30 g / L; sodium citrate dihydrate: 160 g / L; sodium bromide: 30 g / L; sodium saccharin: 14 g / L; sodium dodecyl sulfate: 5 g / L; the pH of the plating solution was adjusted to 5-6 using boric acid solution; the solvent was distilled water.

[0062] (3) Preparation of Ni-W alloy layer

[0063] A Ni-W alloy layer was prepared on the pretreated aluminum alloy surface using a pulse electrodeposition process:

[0064] A pretreated aluminum alloy sample was used as the cathode, and a high-purity nickel plate was used as the consumable anode.

[0065] Place the cathode and anode in the plating solution prepared in step (2);

[0066] Electrodeposition was performed under the following process parameters: pulse duty cycle 95%, frequency 48 Hz, mechanical stirring speed 300 rpm, plating bath temperature maintained at 55℃, and cathode current density controlled at 20 A / dm³. 2 ;

[0067] After electrodeposition for 30 minutes, the sample was removed and rinsed with deionized water, resulting in a dense Ni-W alloy layer on the aluminum alloy surface. The Ni-W alloy layer had a thickness of 10 μm and a W content of 20% by mass.

[0068] (4) In-situ formation of ceramic layer by plasma electrolytic oxidation

[0069] Plasma electrolytic oxidation treatment was performed on the Ni-W prefabricated layer to achieve ceramic layer growth and in-situ pore sealing.

[0070] An aluminum alloy workpiece with a Ni-W prepreg layer was used as the anode, and a 316L stainless steel plate was used as the cathode.

[0071] The anode and cathode are placed in a silicate electrolyte system. The silicate electrolyte system consists of 10 g / L sodium hexametaphosphate, 20 g / L sodium tungstate, 5 g / L ammonium metavanadate, 8 g / L sodium silicate, 15 g / L potassium carbonate, and 1 g / L sodium carbonate, with distilled water as the solvent.

[0072] The oxidation process was carried out using a bipolar pulse power supply with the following specific parameters: constant current of 2A, termination voltage of 450V, pulse duty cycle of 15%, and processing time of 30 minutes.

[0073] Throughout the entire process, the electrolyte temperature is maintained at a constant 20°C through a circulating cooling system.

[0074]

Example 2

[0075] The other steps are the same as in Example 1, except for steps 2 and 3, which are different as follows:

[0076] (2) Plating solution preparation

[0077] The composition of the plating solution used for pulse electrodeposition is as follows:

[0078] Nickel sulfate hexahydrate: 30 g / L; sodium tungstate dihydrate: 70 g / L; ammonium chloride: 30 g / L; sodium citrate dihydrate: 160 g / L; sodium bromide: 30 g / L; sodium saccharin: 14 g / L; sodium dodecyl sulfate: 5 g / L; the pH of the plating solution was adjusted to 5-6 using boric acid solution; the solvent was distilled water, and the pH of the plating solution was 5.

[0079] (3) Preparation of Ni-W alloy layer

[0080] A Ni-W alloy layer was prepared on the pretreated aluminum alloy surface using a pulse electrodeposition process:

[0081] A pretreated aluminum alloy sample was used as the cathode, and a high-purity nickel plate was used as the consumable anode.

[0082] Place the cathode and anode in the plating solution prepared in step (2);

[0083] Electrodeposition was performed under the following process parameters: pulse duty cycle 95%, frequency 48 Hz, mechanical stirring speed 300 rpm, plating bath temperature maintained at 55℃, and cathode current density controlled at 20 A / dm³. 2 ;

[0084] After electrodeposition for 30 minutes, the sample was removed and rinsed with deionized water, resulting in a dense Ni-W alloy layer on the aluminum alloy surface. The Ni-W alloy layer had a thickness of 10 μm and a W content of 37% by mass.

[0085]

Example 3

[0086] The other steps are the same as in Example 1, except for steps 2 and 3, which are different as follows:

[0087] (2) Plating solution preparation

[0088] The composition of the plating solution used for pulse electrodeposition is as follows:

[0089] Nickel sulfate hexahydrate: 30 g / L; sodium tungstate dihydrate: 80 g / L; ammonium chloride: 30 g / L; sodium citrate dihydrate: 160 g / L; sodium bromide: 30 g / L; sodium saccharin: 14 g / L; sodium dodecyl sulfate: 5 g / L; the pH of the plating solution was adjusted to 5-6 using boric acid solution; the solvent was distilled water, and the pH of the plating solution was 5.

[0090] (3) Preparation of Ni-W alloy layer

[0091] A Ni-W alloy layer was prepared on the pretreated aluminum alloy surface using a pulse electrodeposition process:

[0092] A pretreated aluminum alloy sample was used as the cathode, and a high-purity nickel plate was used as the consumable anode.

[0093] Place the cathode and anode in the plating solution prepared in step (2);

[0094] Electrodeposition was performed under the following process parameters: pulse duty cycle 95%, frequency 48 Hz, mechanical stirring speed 300 rpm, plating bath temperature maintained at 55℃, and cathode current density controlled at 20 A / dm³. 2 ;

[0095] After electrodeposition for 30 minutes, the sample was removed and rinsed with deionized water, resulting in a dense Ni-W alloy layer on the aluminum alloy surface. The Ni-W alloy layer had a thickness of 10 μm and a W content of 50% by mass.

[0096]

Example 4

[0097] The other steps are the same as in Example 1, except for steps 2 and 3, which are different as follows:

[0098] (2) Plating solution preparation

[0099] The composition of the plating solution used for pulse electrodeposition is as follows:

[0100] Nickel sulfate hexahydrate: 30 g / L; sodium tungstate dihydrate: 87 g / L; ammonium chloride: 30 g / L; sodium citrate dihydrate: 160 g / L; sodium bromide: 30 g / L; sodium saccharin: 14 g / L; sodium dodecyl sulfate: 5 g / L; the pH of the plating solution was adjusted to 5-6 using boric acid solution; the solvent was distilled water, and the pH of the plating solution was 5.

[0101] (3) Preparation of Ni-W alloy layer

[0102] A Ni-W alloy layer was prepared on the pretreated aluminum alloy surface using a pulse electrodeposition process:

[0103] A pretreated aluminum alloy sample was used as the cathode, and a high-purity nickel plate was used as the consumable anode.

[0104] Place the cathode and anode in the plating solution prepared in step (2);

[0105] Electrodeposition was performed under the following process parameters: pulse duty cycle 95%, frequency 48 Hz, mechanical stirring speed 300 rpm, plating bath temperature maintained at 55℃, and cathode current density controlled at 20 A / dm³. 2 ;

[0106] After electrodeposition for 30 minutes, the sample was removed and rinsed with deionized water, resulting in a dense Ni-W alloy layer on the aluminum alloy surface. The Ni-W alloy layer had a thickness of 10 μm and a W content of 56% by mass.

[0107] Comparative Example 1

[0108] The other steps are the same as in Example 1, except that steps (2) and (3) are not present. Specifically:

[0109] (1) Matrix pretreatment

[0110] The surface of the 6061 aluminum alloy sample was pretreated to ensure good adhesion and density of the subsequent coating. The process is as follows:

[0111] Grinding: Use #400, #600, #800, and #1000 grit sandpaper for progressive mechanical grinding;

[0112] Cleaning: The polished sample is ultrasonically cleaned to remove residual abrasive and oil from the surface;

[0113] Alkali washing: Immerse in a 5 g / L NaOH aqueous solution and treat at room temperature for 10 minutes. Then rinse with distilled water.

[0114] Acid pickling and activation: Immerse in a 5% (w / w) dilute nitric acid solution to remove the surface oxide film and achieve activation, then rinse with distilled water;

[0115] Zinc immersion treatment: Immerse the activated substrate in zinc immersion solution (composition: 10 g / L NaOH and 10 g / L ZnO) for 2 minutes, then briefly rinse with dilute nitric acid solution to remove the displaced zinc layer; repeat this zinc immersion-pickling step 2 to 5 times until a uniform and dense zinc immersion transition layer is formed on the substrate surface.

[0116] (2) In-situ formation of ceramic layer by plasma electrolytic oxidation

[0117] The pretreated aluminum alloy is subjected to plasma electrolytic oxidation treatment to achieve the growth of a ceramic layer:

[0118] The aluminum alloy workpiece is the anode, and the 316L stainless steel plate is the cathode.

[0119] The anode and cathode are placed in a silicate electrolyte system. The components of the silicate electrolyte system are: 10 g / L sodium hexametaphosphate, 20 g / L sodium tungstate, 5 g / L ammonium metavanadate, 8 g / L sodium silicate, 15 g / L potassium carbonate and 1 g / L sodium carbonate, and the solvent is distilled water.

[0120] Oxidation treatment was performed using a bipolar pulse power supply. The specific process parameters were: termination voltage 450 V, pulse duty cycle 15%, and treatment time 30 minutes.

[0121] Throughout the entire process, the electrolyte temperature is maintained at a constant 20°C through a circulating cooling system.

[0122] Comparative Example 2

[0123] The other steps are the same as in Example 1, except that step (2) is modified as follows:

[0124] (1) Matrix pretreatment

[0125] The surface of the 6061 aluminum alloy sample was pretreated to ensure good adhesion and density of the subsequent coating. The process is as follows:

[0126] Grinding: Use #400, #600, #800, and #1000 grit sandpaper for progressive mechanical grinding;

[0127] Cleaning: The polished sample is ultrasonically cleaned to remove residual abrasive and oil from the surface;

[0128] Alkali washing: Immerse in a 5 g / L NaOH aqueous solution and treat at room temperature for 10 minutes. Then rinse with distilled water.

[0129] Acid pickling and activation: Immerse in a 5% (w / w) dilute nitric acid solution to remove the surface oxide film and achieve activation, then rinse with distilled water;

[0130] Zinc immersion treatment: Immerse the activated substrate in zinc immersion solution (composition: 10 g / L NaOH and 10 g / L ZnO) for 2 minutes, then briefly rinse with dilute nitric acid solution to remove the displaced zinc layer; repeat this zinc immersion-pickling step 2 to 5 times until a uniform and dense zinc immersion transition layer is formed on the substrate surface.

[0131] (2) The plating solution used for pulse electrodeposition is prepared as follows:

[0132] Nickel sulfate hexahydrate: 30 g / L; ammonium chloride: 30 g / L; sodium bromide: 30 g / L; sodium saccharin: 14 g / L; sodium dodecyl sulfate: 5 g / L; the pH of the plating solution was adjusted to 5-6 using boric acid solution; the solvent was distilled water.

[0133] (3) Preparation of Ni alloy layer

[0134] A Ni alloy layer was prepared on the pretreated aluminum alloy surface using a pulse electrodeposition process:

[0135] A pretreated aluminum alloy sample was used as the cathode, and a high-purity nickel plate was used as the consumable anode.

[0136] Place the cathode and anode in the plating solution prepared in step (2);

[0137] Electrodeposition was performed under the following process parameters: pulse duty cycle 95%, frequency 48 Hz, mechanical stirring speed 300 rpm, plating bath temperature maintained at 55℃, and cathode current density controlled at 20 A / dm³. 2 ;

[0138] After electrodeposition for 30 minutes, the sample was removed and rinsed with deionized water, thus obtaining a dense Ni alloy layer on the aluminum alloy surface.

[0139] (4) In-situ formation of ceramic layer by plasma electrolytic oxidation

[0140] Plasma electrolytic oxidation treatment is performed on the Ni prefabricated layer to achieve the growth of the ceramic layer:

[0141] An aluminum alloy workpiece with a Ni prepreg layer was used as the anode, and a 316L stainless steel plate was used as the cathode.

[0142] The anode and cathode are placed in a silicate electrolyte system. The components of the silicate electrolyte system are: 10 g / L sodium hexametaphosphate, 20 g / L sodium tungstate, 5 g / L ammonium metavanadate, 8 g / L sodium silicate, 15 g / L potassium carbonate and 1 g / L sodium carbonate, and the solvent is distilled water.

[0143] Oxidation treatment was performed using a bipolar pulse power supply. The specific process parameters were: termination voltage 450 V, pulse duty cycle 15%, and treatment time 30 minutes.

[0144] Throughout the entire process, the electrolyte temperature is maintained at a constant 20°C through a circulating cooling system.

[0145] [Test Example]

[0146] I. Morphological characteristics:

[0147] SEM tests were performed on the surfaces of samples from Examples 1-4 and Comparative Examples 1-2. The results are shown in the figure. Figure 1 , Figure 1 Middle (a) ~ Figure 1 (d) represents the surface morphology of Examples 1, 2, 3, and 4, respectively. Figure 1 (e) Figure 1 (f) shows the surface morphology of Comparative Example 1 and Comparative Example 2, respectively; Figure 1 It can be seen that Examples 1, 2, and 3 sealed the ceramic layer while forming it.

[0148] SEM tests were performed on the cross-sections of samples from Examples 1-4 and Comparative Examples 1-2. The results are shown in [Figure number missing]. Figure 2 The results are shown Figure 2 , Figure 2 Middle (a) ~ Figure 2 (d) shows the cross-sectional morphology of Examples 1, 2, 3, and 4, respectively. Figure 2 (e) Figure 2 (f) shows the cross-sectional morphology of Comparative Example 1 and Comparative Example 2, respectively; Figure 2 It can be seen that, compared with Comparative Examples 1 and 2, Examples 1, 2, and 3 show reduced pore density and smaller pore size in the depth direction, indicating that Examples 1, 2, and 3 not only formed the ceramic layer but also sealed the pores in the ceramic layer. Comparative Example 2 shows that simply electrodepositing a pure Ni layer did not achieve a sealing effect on micro-arc oxidation. This is because, although the pure Ni layer can temporarily reduce the viscosity and improve the fluidity of the Al2O3 melt during plasma micro-region melting, the high vapor pressure of Ni-NiO and its tendency to volatilize at high temperatures prevent it from forming a stable, low-melting-point, glassy sealing phase with the Al2O3 melt.

[0149] II. Porosity Testing:

[0150] The surface SEM images of Examples 1-4 and Comparative Examples 1-2 were imported into image analysis software. First, the images were converted to grayscale and their contrast enhanced to clearly display the pore boundaries. Then, a suitable grayscale threshold was set using the threshold segmentation function, marking the pore areas (above 1 μm) as black and the film substrate areas as white. Finally, the proportion of the total pixel area occupied by the black pixel area was calculated using the particle analysis function, which is the surface porosity (%) of the film. At least five different fields of view were randomly selected for measurement of each sample, and the average value was taken as the final result to evaluate the influence of different process parameters on the film compactness. The results are shown in Table 1.

[0151] III. Friction Coefficient Test:

[0152] The coefficient of friction of the coated samples prepared in Examples 1-4 and Comparative Examples 1-2 was tested using a ball-disc friction and wear tester. Before testing, the sample surfaces were cleaned with anhydrous ethanol and dried. The test conditions were: normal load 4 N, grinding balls were 6 mm diameter GCr15 steel balls (hardness HRC 60±2), rotation radius 5 mm, rotation speed 200 r / min, and wear time 1200 s. The tests were conducted at room temperature (25±2℃) and relative humidity 40%~60%, and the coefficient of friction was automatically recorded in real time by a computer. Each group of samples was tested three times, and representative curves were taken. The test results are as follows: Figure 3 As shown in the figure, the ceramic layers prepared in Examples 1-4 exhibited lower and less fluctuating friction coefficients throughout the wear process, with significantly lower average friction coefficients compared to the ceramic layers in Comparative Examples 1-2. This indicates that the sealing ceramic layer of this application possesses excellent wear resistance. In tribological testing (such as ball-disc wear tests), the average friction coefficient refers to the arithmetic mean of the friction coefficient from 0 s to 1200 s throughout the entire test process, as shown in Table 1.

[0153] IV. Electrochemical performance testing:

[0154] Potentiodynamic polarization was tested using a three-electrode system in 3.5% NaCl solution. The working electrode consisted of the test samples from Examples 1-4 and Comparative Examples 1-2. The auxiliary electrode was a platinum sheet electrode, and the reference electrode was a saturated calomel electrode (SCE). Before testing, the sample surface was successively sanded to 2000# with sandpaper, rinsed with deionized water, ultrasonically cleaned with anhydrous ethanol, and then dried, with an exposed area of ​​1 cm². 2 The sample was immersed in 3.5% NaCl solution at room temperature (25±2℃) and allowed to stand for 30 min until the open circuit potential stabilized. Then, potentiodynamic polarization was tested at a scan rate of 1 mV / s, with a scan range of ±0.8 V relative to the open circuit potential. The potential-current density curve was recorded, and the test results are shown below. Figure 4 .from Figure 4It can be seen that, compared with Comparative Examples 1 and 2, the self-corrosion potential of Examples 1 to 4 shifted significantly to the positive direction, the corrosion current density decreased significantly, and the current density in the anodic polarization region increased more gradually. This indicates that the micro-arc oxidation coating for sealing the pores effectively improved the corrosion resistance of the substrate. Among them, Example 1 had the best corrosion resistance, while the corrosion performance of Example 4 decreased.

[0155] In addition, the self-corrosion potential and self-corrosion current density were tested using this three-electrode system, and the results are shown in Table 1.

[0156] V. Element Distribution Test:

[0157] The cross-section of the sample taken in step 3 of Example 1 was subjected to SEM testing and EDS line scanning. The results are shown in the figure below. Figure 5 a and Figure 5 b, Figure 5 In the diagram, AlKa1 represents the characteristic X-ray emitted by the electron transition of Al in the K layer, which is used in EDS testing to identify and calibrate the presence of aluminum. WMA1 represents the characteristic X-ray emitted by the electron transition of tungsten atoms in the M layer, which is used in EDS testing to identify and calibrate the presence of tungsten. NiKa1 represents the characteristic X-ray emitted by the electron transition of Ni in the K layer, which is used in EDS testing to identify and calibrate the presence of nickel. It can be seen that the Ni-W alloy layer deposited by pulse electrodeposition has good bonding and uniform element distribution.

[0158] Table 1

[0159]

[0160] As shown in Table 1, the average friction coefficient and porosity of the ceramic layers in Examples 1-4 are lower than those in Comparative Examples 1-2. The self-corrosion potentials of Examples 1, 2, 3, and 4 are approximately -0.2 to -0.61 V, indicating good corrosion resistance. In contrast, the self-corrosion potentials of Comparative Examples 1 and 2 are approximately -0.80 to -0.85 V, indicating poorer corrosion resistance. This is because the ceramic layers in Examples 1-4 underwent self-sealing during formation, thus possessing both wear resistance and corrosion resistance.

[0161] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0162] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing an in-situ sealed ceramic layer, characterized in that, Includes the following steps: Step 1: Provide a substrate, the substrate including a first surface and a second surface disposed opposite to each other, the first surface being provided with a Ni-W alloy layer; The mass percentage of W in the Ni-W alloy layer is 18% to 50%. The substrate is a light metal substrate; the light metal includes at least one of aluminum, aluminum alloy, magnesium, magnesium alloy, titanium, and titanium alloy. Step 2: Using the substrate as the anode, perform plasma electrolytic oxidation treatment in the electrolyte to form a ceramic layer on the Ni-W alloy layer; The electrolyte includes a silicate-based electrolyte. The electrolyte in the silicate system includes tungstate.

2. The method for preparing the in-situ sealed ceramic layer according to claim 1, characterized in that, In step 1, the thickness of the Ni-W alloy layer is 10 μm to 15 μm.

3. The method for preparing an in-situ sealed ceramic layer according to claim 1, characterized in that, The silicate electrolyte system comprises the following components: 10 g / L to 20 g / L sodium hexametaphosphate, 20 g / L to 30 g / L sodium tungstate, 2 g / L to 10 g / L ammonium metavanadate, 5 g / L to 10 g / L sodium silicate, 10 g / L to 20 g / L potassium carbonate, and 10 g / L to 20 g / L sodium carbonate.

4. The method for preparing the in-situ sealed ceramic layer according to claim 1, characterized in that, In step 2, the plasma electrolytic oxidation treatment includes: The system employs a bipolar pulse power supply mode to maintain a constant current, controls the termination voltage to be 450 V~500 V, the pulse duty cycle to be 10%~15%, the processing time to be 30 min~60 min, and the temperature of the electrolyte to be 20 ℃~25 ℃.

5. The method for preparing an in-situ sealed ceramic layer according to claim 1, characterized in that, In step 1, the Ni-W alloy layer is formed by pulsed electrodeposition, and the pulsed electrodeposition satisfies at least one of the following conditions: (a) Using the substrate as the cathode and a nickel sheet as the consumable anode; (b) The pulse electrodeposition is carried out in a plating solution comprising the following components: 30 g / L to 50 g / L nickel sulfate hexahydrate, 60 g / L to 80 g / L sodium tungstate dihydrate, 30 g / L to 40 g / L ammonium chloride, 160 g / L to 180 g / L sodium citrate dihydrate, 20 g / L to 40 g / L sodium bromide, 10 g / L to 20 g / L sodium saccharin, and 5 g / L to 10 g / L sodium dodecyl sulfate; (c) The pulse electrodeposition is carried out in a plating solution with a pH of 5 to 6; (d) The current density of the pulse electrodeposition is 20 A / dm. 2 ~40 A / dm 2 ; (e) The temperature of the plating solution is 40 ℃~60 ℃; (f) The pulse electrodeposition time is 30 min to 60 min.

6. A ceramic layer for in-situ sealing, characterized in that, It is prepared according to the preparation method of any one of claims 1 to 5.

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