Titanium matrix surface super wear-resistant micro-arc oxidation coating and preparation method thereof, and titanium matrix composite material

Abstract

The application discloses a titanium base surface super wear-resistant micro-arc oxidation coating and a preparation method thereof, and a titanium base composite material, and belongs to the field of titanium coating preparation.The coating has a double-layer structure; the content of F elements in the inner layer of the coating is greater than that in the outer layer, the content of Zr elements in the inner layer is less than that in the outer layer, and the content of Zr elements in the outer layer is greater than 30 wt%. The fluorozirconate-based electrolyte is combined with micro-arc oxidation, the problem that a ZrO2-based micro-arc oxidation coating cannot be formed in situ on the surface of an alloy in a uniform distribution through exogenous incorporation in the prior art is solved, the prepared coating can have the characteristic of compactness when the thickness reaches 70 microns, and the wear resistance and service life of the coating are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of titanium coating preparation, and relates to an ultra-wear-resistant micro-arc oxidation coating on the surface of a titanium substrate and its preparation method, as well as a titanium-based composite material. Background Technology

[0002] Titanium and titanium alloys possess high specific strength, low density, and good electrical and thermal conductivity, making them widely used in critical industries such as aerospace, automotive, shipbuilding, and batteries. However, titanium alloys typically exhibit poor wear resistance, leading to component wear during service and severely limiting their application in frictional environments. Micro-arc oxidation (MAO) is an electrochemical surface modification technique capable of preparing oxide ceramic coatings on valve metal surfaces. To date, numerous studies have demonstrated that MAO is an effective surface modification technique for improving the wear resistance of titanium and titanium alloys. The wear resistance of MAO coatings on titanium and titanium alloy surfaces is closely related to their microstructure, which is influenced by the electrolyte composition and electrical parameters during the MAO process.

[0003] Micro-arc oxidation coatings consist of a base oxide and compounds containing electrolyte components. Conventional micro-arc oxidation coatings on titanium alloy surfaces are formed in alkaline base electrolytes such as phosphates, silicates, and aluminates, and their wear resistance typically follows this order: aluminate > silicate > phosphate. Conventional micro-arc oxidation components on titanium alloy surfaces consist of TiO2 and oxides containing phosphorus oxides / SiO2 / Al2O3. However, TiO2 and phosphorus oxides / SiO2 have poor mechanical properties and cannot significantly improve the wear resistance of the coating. Although Al2O3 has high hardness, its brittleness makes it prone to crack initiation and propagation due to stress concentration during friction, leading to coating failure. Compared to Al2O3, ZrO2 exhibits superior compressive strength, flexural strength, and fracture toughness. Furthermore, the phase transformation of metastable tetragonal zirconia (t-ZrO2) to monoclinic zirconia (m-ZrO2) under high stress is accompanied by volume expansion, generating compressive stress at the crack tip, which effectively prevents crack propagation. Therefore, forming a micro-arc oxidation coating based on ZrO2 is expected to significantly break through the wear resistance bottleneck of existing micro-arc oxidation coatings for titanium and titanium alloys, and achieve a significant improvement in wear resistance.

[0004] Most existing electrolyte systems are unsuitable for preparing ZrO2-based micro-arc oxidation coatings. This is primarily due to two reasons: Firstly, most studies involve adding insoluble ZrO2 particles to the electrolyte, incorporating these particles into the coating during its growth. Secondly, although many studies use soluble zirconium salts as precursors or additives, Zr in alkaline electrolytes tends to exist as suspended particles and readily combines with some anionic groups to form Zr salt precipitates. These particles decompose during micro-arc oxidation to form ZrO2, which is ultimately introduced into the coating. In most studies, the amount of ZrO2 incorporated is limited, preventing the preparation of ZrO2-rich micro-arc oxidation coatings and limiting the improvement in wear resistance. Furthermore, externally incorporated particles tend to be unevenly distributed and agglomerated within the coating, easily damaging its adhesion and density. These particles can also detach from the coating, becoming wear debris and further impairing its wear resistance.

[0005] Meanwhile, the ZrO2 micro-arc oxidation coatings prepared in existing studies still face the problem of thinness and difficulty in synergistic optimization of density, resulting in significant room for performance improvement; in addition, the evaluation and research on the long-term service life of the coatings are still relatively limited. Summary of the Invention

[0006] To address the problems in existing technologies, such as the inability to uniformly prepare ZrO2-based micro-arc oxidation coatings in situ through exogenous doping, as well as the thinness, poor density, and poor wear resistance of the coatings, the first objective of this invention is to provide an ultra-wear-resistant micro-arc oxidation coating for titanium substrates. The unique bilayer structure of this coating can work synergistically with the differential distribution of F and Zr elements in the inner and outer layers to significantly improve the coating's wear resistance and service life.

[0007] The second objective of this invention is to provide a method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface. The method of this invention has the advantages of simple process and low cost, and the coating obtained has excellent wear resistance.

[0008] The third objective of this invention is to provide a titanium-based composite material containing an ultra-wear-resistant micro-arc oxidation coating, which can be used as a raw material in wear-resistant devices.

[0009] To achieve the above technical objectives, the present invention provides an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface, which has a double-layer structure; wherein, the F element content in the inner layer is greater than the F element content in the outer layer, the Zr element content in the inner layer is less than the Zr element content in the outer layer, and the ZrO2 content in the outer layer is greater than 30wt%.

[0010] Compared to existing single-layer Zr-containing coatings, the unique bilayer structure and elemental distribution of the coating in this invention are key to improving its wear resistance. The inner layer of this structure is rich in fluorine (F), forming a stable fluoride phase. This fluorine-rich inner layer not only significantly improves the interfacial bonding strength between the coating and the titanium alloy substrate by strengthening chemical bonding, but also effectively regulates the F content under the weakly acidic electrolyte environment. - Ion activity, thereby inhibiting F - The corrosion tendency of the titanium alloy substrate and the oxide phase inside the coating. Meanwhile, the F in the electrolyte... - The presence of [ZrF6] helps to soften the discharge sparks during the micro-arc oxidation process, promoting the formation of a denser microstructure in the coating and providing a robust and stable supporting substrate for the entire coating system. The outer layer is characterized by its high zirconium content, with [ZrF6] in the electrolyte. 2- The complex promotes the outward growth of the coating and ultimately transforms in situ into a uniformly distributed and firmly bonded ZrO2 phase, endowing the coating with excellent surface hardness and wear resistance. This coating exhibits excellent adhesion; the in-situ formed ZrO2 reinforcing phase is uniformly distributed and firmly bonded, achieving a significant toughening effect. It effectively alleviates internal stress concentration caused by external loads or thermal stress during service, significantly inhibits crack initiation and propagation, and ultimately greatly improves the overall wear resistance and service life of the coating.

[0011] As a preferred embodiment, the outer layer has a porous surface with a porosity of 5-30%. The porous morphology of the outer layer in this invention is obtained based on the characteristics of the micro-arc oxidation process. During the preparation process, this invention can control the porosity within a small range, thereby improving the overall material performance.

[0012] As a preferred embodiment, the thickness of the inner layer is 2~20μm, and the total coating thickness is 20~70μm. In this invention, the total coating thickness can be adjusted within a wide range to meet different scenario requirements. Furthermore, the maximum total coating thickness of this invention can reach 70 micrometers, which is significantly superior to existing coatings. Moreover, the thickness of the inner layer can be controlled to be less than the thickness of the outer layer, thus improving the overall wear resistance of the coating.

[0013] Furthermore, the ratio of F element content in the inner layer to F element content in the outer layer is (3~20):1, and the ratio of Zr element content in the inner layer to Zr element content in the outer layer is 1:(10~50). With the further preferred ratios of F to Zr in the inner and outer layers of this invention, a coating with superior wear resistance can be obtained.

[0014] The present invention also provides a method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface. The method uses a titanium substrate as an anode and stainless steel as a cathode, and places both the anode and cathode in an electrolyte for micro-arc oxidation, thereby obtaining a coating on the anode surface. The electrolyte should contain more than 5 g / L of fluorozirconate, have a pH of 4 to 7, and a conductivity of 5 to 30 ms / cm.

[0015] The electrolyte of this invention uses a high content of fluorozirconate under acidic conditions, which keeps Zr in the electrolyte in a stable state without precipitation. Combined with micro-arc oxidation, a bilayer structure can be formed, with the inner layer rich in F element and the outer layer forming a uniformly distributed ZrO2 phase in situ.

[0016] The formation mechanism of this double-layer structure is as follows: F - It has high electronegativity and reactivity, and in the micro-arc oxidation (MAO) process, F - It preferentially reacts with the substrate to form fluorides, and F has a strong affinity for Ti. Furthermore, F... - The smaller size and faster migration speed of the ions allow them to more easily penetrate the initially formed thin oxide layer or plasma channels to reach the titanium substrate interface, thus forming an inner layer enriched in F. [ZrF6] 2- It is a stable complex anion, which cannot be like F - It readily reacts with the substrate metal. Firstly, in the high-temperature, high-pressure plasma environment generated by MAO discharge, [ZrF6]... 2- It needs to be decomposed to release Zr. 4+ Ions. The released Zr-containing anions need to react with O in the electrolyte or air to form ZrO2, a process that requires energy (to overcome the activation barrier) and time. Meanwhile, [ZrF6]... 2- The ions in [ZrF6] are relatively large, resulting in a slower migration rate. Furthermore, the shift of the reaction site to the outermost layer and the easier access and participation of electrolyte components in the reaction make [ZrF6] more efficient. 2- The ZrO2 formed by decomposition tends to precipitate in the outer layer of the coating, resulting in a Zr-rich outer layer. The weakly acidic environment helps stabilize fluorozirconate in the solution, preventing its hydrolysis and precipitation in an alkaline environment, thus ensuring the in-situ formation of ZrO2 in the coating. The weakly acidic electrolyte also avoids high concentrations of H₂. + The rapid dissolution of the substrate makes it difficult for the coating to grow stably, and may even lead to localized peeling. More preferably, the electrolyte contains fluorozirconate at a concentration of ≥8.5 g / L, has a pH of 5.0–6.6, and a conductivity of 10–15 mS / cm.

[0017] As a preferred embodiment, the electrolyte further includes at least one of a compounding agent and an additive.

[0018] As a preferred option, the compounding agent is at least one of carbonate, phosphate and fluoride.

[0019] As a preferred option, the additive is at least one of glycerol, ethylene glycol, polyethylene glycol, triethanolamine, sodium citrate, and disodium EDTA.

[0020] As a preferred embodiment, the carbonate is at least one of potassium bicarbonate, sodium bicarbonate, sodium carbonate, potassium carbonate, ammonium carbonate, and ammonium bicarbonate.

[0021] As a preferred embodiment, the phosphate is sodium hexametaphosphate.

[0022] As a preferred embodiment, the fluoride is at least one of potassium fluoride, sodium fluoride, and potassium fluorotitanate.

[0023] As a preferred embodiment, the fluorozirconate is at least one of potassium fluorozirconate and ammonium fluorozirconate.

[0024] As a preferred embodiment, the concentration of fluorozirconate in the electrolyte is 5-60 g / L, the concentration of the compounding agent is 0.5-50 g / L, and the amount of additive is 1-20 g / L of the solution mass, wherein the concentration of fluorozirconate is greater than the concentration of the compounding agent. In the electrolyte of this invention, fluorozirconate is the main component, which can form ZrO2 in situ in the coating, wherein [ZrF6] 2- The complex significantly promotes coating thickness, while F - Ions optimize the microstructure density by "softening" the plasma discharge spark. With increasing fluorozirconate concentration, the enrichment of Zr in the coating shows a positive correlation with the overall thickness, while F... - The spark softening effect is enhanced. However, the addition amount needs to be balanced: excessively high concentrations will cause a sharp increase in electrolyte conductivity, thereby aggravating the discharge intensity and potentially causing coating defects. To control this contradiction, the compounding agent precisely adjusts the electrolyte pH and conductivity to suppress excessive discharge and ensure uniform coating growth; the additives synergistically control the spark discharge intensity and electrolyte stability. The three work together to achieve optimized coating preparation with controllable microstructure. Further preferably, the concentration of fluorozirconate in the electrolyte is 7~10 g / L, the concentration of the compounding agent is 0.5~1.7 g / L, and the amount of additives is 1~2 g / L of the solution mass. When within the further preferred range, the best wear resistance performance can be achieved.

[0025] As a preferred embodiment, the temperature of the electrolyte is controlled below 30°C; the titanium matrix includes at least one of pure titanium and titanium alloys. Fluorozirates are prone to hydrolysis at higher temperatures, generating unstable zirconium hydroxide or zirconium oxide precipitates, which are detrimental to the in-situ formation of ZrO2.

[0026] As a preferred embodiment, the electrical process parameters for micro-arc oxidation are set as follows: constant voltage mode, positive voltage of 200~700V, negative voltage of 0~300V, pulse frequency of 200~1000Hz, duty cycle of 5~50%, and time of 5~180min. This invention, by controlling the micro-arc oxidation parameters within the above range, facilitates the formation of a thicker and denser coating, with a maximum thickness of approximately 70 micrometers and fewer micro-defects, thereby significantly improving the ultra-wear resistance of the titanium substrate. The constant voltage mode ensures the stability of the process; the positive voltage setting provides sufficient electric field strength to maintain continuous and stable micro-arc discharge, promoting the full participation of zirconium elements in the reaction and the formation of a stable zirconium oxide phase; while the control of the negative voltage effectively regulates plasma discharge behavior, reducing internal porosity and microcracks in the coating, improving density and bonding strength; and the adjustment of the pulse frequency and duty cycle avoids local overheating, resulting in more uniform coating growth while suppressing thermal stress accumulation. The flexible processing time allows for adjustments to the coating thickness based on actual needs, achieving a balance between abrasion resistance and substrate compatibility.

[0027] Finally, the present invention also provides a titanium-based composite material containing an ultra-wear-resistant micro-arc oxidation coating, comprising a titanium matrix and the above-mentioned ultra-wear-resistant micro-arc oxidation coating on the surface, which is particularly suitable for use in wear-resistant devices (such as aircraft engine parts and moving parts of electronic products).

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The electrolyte of this invention uses fluorozirconate as the main component. Compounding agents and additives can be added to adjust the pH and conductivity of the electrolyte, resulting in a stable acidic Zr salt electrolyte. The thickening effect of fluorozirconate ions and the softening effect of fluoride ions in the electrolyte, combined with compounding agents and additives, can regulate the ion concentration, conductivity, and spark discharge intensity during the micro-arc oxidation process. Furthermore, this electrolyte is easy to prepare, has low cost, and possesses significant potential for engineering applications.

[0030] (2) The method of the present invention solves the problem that the existing technology cannot form a ZrO2-based micro-arc oxidation coating on the alloy surface through exogenous doping. The present invention can significantly improve the wear resistance and service life of the coating. Moreover, it solves the problem of the limitation of the ZrO2 content introduced into the coating by the external particle doping method. The present invention can change the Zr content in the coating by adjusting the composition concentration of the electrolyte, which has better controllability.

[0031] (3) The unique double-layer structure of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface of the present invention can work together with the differential distribution of F and Zr elements in the inner and outer layers to achieve the wear resistance of the coating. The overall thickness of the coating is 20~70μm, and the thickness of the inner layer is 2~20μm. Under a load of 5N, it can withstand more than 2.66 million friction cycles without wear-through, and the volume wear rate is as low as 3.82×10 -6 mm 3 / (N·m), with a wear volume as low as 0.36 mm per million cycles. 3 This solves the problem that existing technologies for preparing ZrO2-containing micro-arc oxidation coatings on alloy surfaces cannot synergistically improve coating thickness and density, resulting in limited improvement in coating wear resistance.

[0032] (4) The ZrO2 in the coating of the present invention is formed in situ, and is ZrF6. - The coating is formed during the micro-arc oxidation process, has a uniform distribution, and bonds well with the coating; moreover, the coating of this invention can both utilize ZrF6 - The thickening effect can also play the role of F - By reducing the effect of micro-discharge during micro-arc oxidation, a coating thickness of up to 70 micrometers can be achieved while minimizing the number of micro-defects and maintaining density, thus providing a solid foundation for the coating's excellent performance. Attached Figure Description

[0033] Figure 1 The images shown are SEM images of the surface morphology of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate provided in Embodiment 1 of the present invention, and its surface energy spectrum. Among them, (a) is a low-magnification SEM image of the surface morphology, (b) is a high-magnification SEM image of the surface morphology, and (c) is a surface energy spectrum.

[0034] Figure 2 The image shows the cross-sectional morphology SEM image (a) and EDS elemental diagram of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface provided in Embodiment 1 of the present invention.

[0035] Figure 3 This is the XRD pattern of the ultra-wear-resistant micro-arc oxidation coating on the surface of the titanium substrate provided in Embodiment 1 of the present invention.

[0036] Figure 4 The image shows the SEM image (a) of the wear mark morphology of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface provided in Example 1 of the present invention, and the comparison image (b) of the friction coefficient-time curves of Example 1 and Comparative Example 4.

[0037] Figure 5 This is an optical three-dimensional profile diagram of Embodiment 1 of the present invention after a friction and wear test.

[0038] Figure 6The image shows the cross-sectional morphology SEM image (a) and EDS elemental diagram of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface provided in Embodiment 2 of the present invention.

[0039] Figure 7 The images shown are SEM images (a) and friction coefficient-time curves (b) of the wear track morphology of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface provided in Embodiment 2 of the present invention.

[0040] Figure 8 The image shows the cross-sectional morphology SEM image (a) and EDS elemental diagram of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface provided in Embodiment 3 of the present invention.

[0041] Figure 9 The images shown are SEM images (a) and friction coefficient-time curves (b) of the wear track morphology of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface provided in Embodiment 3 of the present invention.

[0042] Figure 10 The image shows the cross-sectional morphology SEM image (a) and EDS elemental diagram of the ultra-wear-resistant micro-arc oxidation coating on the titanium substrate surface provided in Embodiment 5 of the present invention.

[0043] Figure 11 The image shows the cross-sectional morphology SEM image (a) and EDS elemental image of the coating provided in Comparative Example 1 of this invention.

[0044] Figure 12 The images shown are SEM images (a) of the wear track morphology of the coating provided in Comparative Example 1 of this invention and friction coefficient-time curves (b).

[0045] Figure 13 The image shows the cross-sectional morphology SEM image (a) and EDS elemental image of the coating provided in Comparative Example 2 of this invention.

[0046] Figure 14 The images shown are SEM images (a) of the wear track morphology of the coating provided in Comparative Example 2 of this invention and friction coefficient-time curves (b).

[0047] Figure 15 The above are SEM images of the surface morphology of the coating provided in Comparative Example 3 of this invention and its surface energy spectrum. Among them, (a) is a low-magnification SEM image of the surface morphology, (b) is a high-magnification SEM image of the surface morphology, and (c) is a surface energy spectrum.

[0048] Figure 16 The image shows the cross-sectional morphology SEM image (a) and EDS elemental image of the coating provided in Comparative Example 3 of this invention.

[0049] Figure 17 The images shown are SEM images (a) of the wear track morphology of the coating provided in Comparative Example 3 of this invention and friction coefficient-time curves (b). Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0051] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0052] Test methods

[0053] Surface / section morphology and elemental composition analysis: The morphology of the sample surface and cross section was characterized using a scanning electron microscope (SEM, HeliosNanolab G3 UC, Czech Republic) equipped with EDS, in secondary electron and backscattered electron modes, 20 kV.

[0054] Friction and wear test: A ball-and-disc high-temperature friction and wear tester (Zhongke Kaihua HT-1000) was used for the friction test. The applied load was 5N, and the rotation speed was 400r / min. The grinding material used was Si3N4 ceramic balls with a radius of 3mm. After friction, the wear tracks and the amount of wear were analyzed using SEM and an optical profilometer (Veeco Metrology Inc WYKO NT9100, USA).

[0055] Phase analysis of the coating: The general phase composition of the coating was characterized using X-ray diffraction (XRD, PANalytic Empyrean, Netherlands). The XRD test parameters were: 40 mA current interruption, 45 kV voltage, 2θ angle range of 20~100°, and scan rate of 5° / min.

[0056] Example 1

[0057] Step 1: Matrix Pretreatment

[0058] Using TC18 as the titanium matrix, the titanium matrix was ultrasonically cleaned in acetone and anhydrous ethanol, then polished stepwise with 80#, 320#, 800# and 1200# sandpaper, and then ultrasonically cleaned in anhydrous ethanol and air-dried to obtain the pretreated titanium matrix.

[0059] Step 2: Prepare the electrolyte

[0060] Add 8.5 g / L potassium fluorozirconate and 1.7 g / L potassium fluoride (a compounding agent) to deionized water, and bring the electrolyte to a final volume of 2 L. The electrolyte should be clear, with a pH of 6.56, a conductivity of 10.18 mS / cm, and a temperature of 25 °C.

[0061] Step 3: Micro-arc oxidation

[0062] Using a titanium substrate as the anode and stainless steel as the cathode, both the anode and cathode were placed in an electrolyte for micro-arc oxidation. The micro-arc oxidation process parameters were set as follows: constant voltage mode, positive voltage 550V, negative voltage 0V, duty cycle 20%, frequency 500Hz, and processing time 30min.

[0063] Step 4: After the voltage drops to 0V, the sample after micro-arc oxidation is ultrasonically cleaned with deionized water and anhydrous ethanol in sequence, and finally air-dried. The anode is then removed to obtain the titanium-based composite material (composed of a titanium matrix and an ultra-wear-resistant micro-arc oxidation coating on the surface of the titanium matrix).

[0064] The micro-arc oxidation coating prepared by the above steps has the following surface morphology and elemental content: Figure 1 The coating surface exhibits a porous morphology with a porosity of 7.5%, and is rich in Zr. The cross-sectional morphology and EDS spectrum of the coating are shown in [reference needed]. Figure 2 The coating exhibits a double-layer structure with excellent density, an overall thickness of 50-70 μm, and an inner layer thickness of 15-20 μm. The outer layer is rich in Zr, while the inner layer is rich in F. Specifically, the F content in the inner layer is greater than that in the outer layer, while the Zr content in the inner layer is less than that in the outer layer. The ratio of F content in the inner layer to F content in the outer layer is approximately 5:1, and the ratio of Zr content in the inner layer to Zr content in the outer layer is approximately 1:10. Based on XRD analysis (… Figure 3 The outer layer is rich in ZrO2 phase, and its content can be obtained by semi-quantitative calculation as 37.2 wt%.

[0065] The friction curve and friction surface morphology of the sample in Example 1 after 111.2 hours of friction and wear test are shown in the figure below. Figure 4 As shown, it can be observed that the sample of Example 1 did not wear through after more than 2.66 million friction cycles, and a friction transfer film had formed on the coating surface. Combined with the three-dimensional profile of the sample's friction surface ( Figure 5 The volumetric wear rate of the sample in Example 1 was found to be 3.82 × 10⁻⁶. -6 mm 3 / (N·m), with a wear volume as low as 0.36 mm per million cycles. 3 The sample in Example 1 exhibits excellent coating abrasion resistance and service life.

[0066] Example 2

[0067] Step 1: Matrix Pretreatment

[0068] Using TC18 as the titanium matrix, the titanium matrix was ultrasonically cleaned in acetone and anhydrous ethanol, then polished stepwise with 80#, 320#, 800# and 1200# sandpaper, and then ultrasonically cleaned in anhydrous ethanol and air-dried to obtain the pretreated titanium matrix.

[0069] Step 2: Prepare the electrolyte

[0070] Add 8.5 g / L potassium fluorozirconate and 18.4 g / L sodium hexametaphosphate (a compounding agent) to deionized water, and bring the electrolyte to a final volume of 2 L. The electrolyte should be clear, with a pH of 4.72, a conductivity of 13.03 mS / cm, and a temperature of 25 °C.

[0071] Step 3: Micro-arc oxidation

[0072] Using a titanium substrate as the anode and stainless steel as the cathode, both the anode and cathode were placed in an electrolyte for micro-arc oxidation. The micro-arc oxidation process parameters were set as follows: constant voltage mode, positive voltage 550V, negative voltage 0V, duty cycle 20%, frequency 500Hz, and processing time 30min.

[0073] Step 4: After the voltage drops to 0V, the sample after micro-arc oxidation is ultrasonically cleaned with deionized water and anhydrous ethanol in sequence, and finally air-dried. The anode is then removed to obtain the titanium-based composite material (composed of a titanium matrix and an ultra-wear-resistant micro-arc oxidation coating on the surface of the titanium matrix).

[0074] The cross section and energy spectrum of the sample obtained in Example 2 are shown below. Figure 6 The coating cross-section exhibits a double-layer structure with an overall thickness of 20~25μm and an inner layer thickness of 2~5μm. The outer layer of the coating is rich in Zr, while the inner layer is rich in F. That is, the F content in the inner layer is greater than that in the outer layer, and the Zr content in the inner layer is less than that in the outer layer.

[0075] The friction curve and wear track morphology of the sample in Example 2 after 52.4 hours of friction and wear test are as follows. Figure 7 As shown, the sample of Example 2 did not wear through after more than 1.25 million friction cycles. The volumetric wear rate of the sample of Example 2 was 6.09 × 10⁻⁶. -6 mm 3 / (N·m), with a wear volume as low as 0.57 mm per million cycles. 3 The sample in Example 2 exhibited excellent wear resistance and service life. Comparing Example 2 with Example 1, it can be observed that when the content of the compounding agent sodium hexametaphosphate exceeds that of potassium fluorozirconate, the conductivity of the electrolyte increases, the pH value of the electrolyte decreases, and F... - The lower concentration of F leads to more intense spark discharge, resulting in larger pore defects within the coating. - and H+ The faster dissolution rate of the substrate and coating creates an imbalance with the coating growth rate, resulting in a relatively thinner coating. Furthermore, the addition of sodium hexametaphosphate leads to the formation of a weaker phosphorus-containing phase within the coating. These synergistic effects reduce the coating's wear resistance, thus decreasing its wear rate.

[0076] Example 3

[0077] Step 1: Matrix Pretreatment

[0078] Using TC18 as the titanium matrix, the titanium matrix was ultrasonically cleaned in acetone and anhydrous ethanol, then polished stepwise with 80#, 320#, 800# and 1200# sandpaper, and then ultrasonically cleaned in anhydrous ethanol and air-dried to obtain the pretreated titanium matrix.

[0079] Step 2: Prepare the electrolyte. Add 8.5 g / L potassium fluorozirconate, 6.2 g / L sodium hexametaphosphate (a compounding agent), and 2 g / L glycerol (an additive) to deionized water. Make up the electrolyte to 2 L. The electrolyte should be clear, with a pH of 5.32, a conductivity of 8.29 mS / cm, and a temperature of 25 °C.

[0080] Step 3: Micro-arc oxidation

[0081] Using a titanium substrate as the anode and stainless steel as the cathode, both the anode and cathode were placed in an electrolyte for micro-arc oxidation. The micro-arc oxidation process parameters were set as follows: constant voltage mode, positive voltage 550V, negative voltage 0V, duty cycle 20%, frequency 500Hz, and processing time 30min.

[0082] Step 4: After the voltage drops to 0V, the sample after micro-arc oxidation is ultrasonically cleaned with deionized water and anhydrous ethanol in sequence, and finally air-dried. The anode is then removed to obtain the titanium-based composite material (composed of a titanium matrix and an ultra-wear-resistant micro-arc oxidation coating on the surface of the titanium matrix).

[0083] The cross section and energy spectrum of the sample obtained in Example 3 are shown below. Figure 8 The coating cross-section exhibits a double-layer structure with good density and an overall thickness of 25~30μm. The inner layer has a thickness of 3~5μm. The outer layer of the coating is rich in Zr, while the inner layer is rich in F. That is, the F content in the inner layer is greater than that in the outer layer, and the Zr content in the inner layer is less than that in the outer layer.

[0084] The friction curve and wear track morphology of the sample in Example 3 after a 24-hour friction and wear test are as follows: Figure 9 As shown, the sample of Example 3 did not wear through after more than 570,000 friction cycles. The volumetric wear rate of the sample of Example 3 was 4.81 × 10⁻⁶. -6 mm 3 / (N·m), with a wear volume as low as 0.45mm per million cycles. 3 The sample in Example 3 exhibited excellent wear resistance and service life. Compared to Example 2, the amount of sodium hexametaphosphate added in Example 3 was significantly reduced. In this case, the electrolyte was mainly composed of potassium fluorozirconate, resulting in an increased pH value, decreased conductivity, increased coating thickness, and significantly improved density, thus enhancing the coating's wear resistance. Furthermore, the addition of glycerol also optimized the spark discharge behavior, contributing to the improved coating density.

[0085] Example 4

[0086] The only difference between this embodiment and Embodiment 1 is that the parameters of the micro-arc oxidation are replaced as follows: constant voltage mode, positive voltage of 500V, negative voltage of -50V, duty cycle of 20%, frequency of 500Hz, and processing time of 60min are adopted; the remaining steps and conditions are the same, and a titanium-based composite material (composed of a titanium matrix and an ultra-wear-resistant micro-arc oxidation coating on the surface of the titanium matrix) is obtained. The coating cross-section shows an inner and outer double-layer structure, the coating has good density, the overall thickness is 55~62μm, and the inner layer thickness is 10~15μm.

[0087] The sample in Example 4 did not wear through after more than 520,000 friction cycles. The volumetric wear rate of the sample in Example 4 was 7.98 × 10⁻⁶. -6 mm 3 / (N·m), with a wear volume as low as 0.75 mm per million cycles. 3 .

[0088] Example 5

[0089] The difference between this embodiment and Example 1 is only that the electrolyte composition is replaced with: 2L of electrolyte containing 7.2 g / L ammonium fluorozirconate and 1.7 g / L potassium fluoride (a compounding agent). The electrolyte is clear, with a pH of 6.20, a conductivity of 9.24 mS / cm, and a temperature of 25°C. All other steps and conditions are the same, resulting in a titanium-based composite material (composed of a titanium matrix and an ultra-wear-resistant micro-arc oxidation coating on the surface of the titanium matrix). The cross-section and energy spectrum of the sample obtained in Example 5 are shown in [reference needed]. Figure 10 The coating cross-section exhibits a double-layer structure with good density, an overall thickness of 30~55μm, and an inner layer thickness of 3~15μm.

[0090] The sample in Example 5 did not wear through after more than 570,000 friction cycles. The volumetric wear rate of the sample in Example 5 was 6.12 × 10⁻⁶. -6 mm 3 / (N·m), with a wear volume as low as 0.57 mm per million cycles. 3 The sample in Example 5 exhibited excellent wear resistance and service life.

[0091] Comparative Example 1

[0092] The only difference between this comparative example and Example 1 is that the electrolyte is replaced by adding 8.5 g / L potassium fluorozirconate and 4.3 g / L sodium monohydrogen phosphate to deionized water, bringing the electrolyte volume to 2 L. The electrolyte is in suspension state, with a pH of 5.86, a conductivity of 10.33 mS / cm, and a temperature of 25 °C. All other steps and conditions are the same.

[0093] The cross section and energy spectrum of the sample obtained in Comparative Example 1 are shown below. Figure 11 The coating exhibits a double-layer structure, but it contains numerous cracks and begins to break, showing poor density. The overall thickness is 25–35 μm, with the inner layer measuring 4–6 μm. Despite being rich in Zr, the coating on Comparative Example 1 sample was damaged after 8 minutes of friction and wear testing. Its friction curve and wear track morphology are shown below. Figure 12 As shown. The volumetric wear rate of the sample in Comparative Example 1 was 1.68 × 10⁻⁶. -3 mm 3 The wear resistance and service life of the sample in Comparative Example 1 were very poor (N·m). Although the electrolyte was weakly acidic, hydrogen phosphate ions readily combined with Zr-containing ions to form insoluble zirconium hydrogen phosphate. However, the suspension electrolyte was not conducive to the formation of a dense coating, and the precipitation reaction solution containing zirconium ions was not conducive to the in-situ formation of ZrO2. Therefore, a stable fluorozirconate electrolyte system is a prerequisite for preparing an ultra-wear-resistant maintenance oxide coating.

[0094] Comparative Example 2

[0095] The only difference between this comparative example and Example 1 is the replacement of the electrolyte: 8.5 g / L potassium fluorozirconate and 4.9 g / L sodium phosphate were added to deionized water, and the electrolyte was brought to a final volume of 2 L. The electrolyte was in suspension state, with a pH of 7.03, a conductivity of 12.20 ms / cm, and a temperature of 25°C. All other steps and conditions were the same.

[0096] The cross section and energy spectrum of the sample obtained in Comparative Example 2 are shown below. Figure 13 The cross-sectional morphology shows that the double-layer structure of the coating is no longer discernible, and most of the coating is broken, exhibiting very poor density. The overall thickness is 170–200 μm. Although the coating is rich in Zr, the coating of Comparative Example 2 sample was found to be damaged within ~16 s after friction and wear testing. Its friction curve and wear track morphology are as follows. Figure 14 As shown. The volumetric wear rate of the sample in Comparative Example 2 was 4.40 × 10⁻⁶. -2 mm 3 / (N·m), the wear resistance and service life of the sample in Comparative Example 2 were very poor. This result is attributed to the addition of sodium phosphate, which made the electrolyte alkaline, causing hydrolysis of the electrolyte and the formation of many particulate precipitates. Furthermore, phosphate ions combine with Zr to form precipitates, and these particles damage the coating adhesion and density during the micro-arc oxidation process.

[0097] Comparative Example 3

[0098] The only difference between this comparative example and Example 1 is that the electrolyte is replaced by adding 8.5 g / L potassium fluorozirconate and 3.7 g / L sodium silicate to deionized water, bringing the electrolyte volume to 2 L. The electrolyte is in suspension state, with a pH of 7.56, a conductivity of 13.12 ms / cm, and a temperature of 25°C. All other steps and conditions are the same.

[0099] The surface morphology and elemental content of the sample obtained in Comparative Example 3 are shown in the figure. Figure 15 The coating surface exhibits a highly irregular morphology, and the coating has peeled off, resulting in large pits. Compared to Example 1, the Zr content is significantly reduced. Its cross-section and energy spectrum are shown below. Figure 16 The double-layer structure was no longer discernible in the cross-section of the coating, but the coating exhibited large-area breakage and very poor density, with an overall thickness of 170–240 μm. Although the coating still contained a certain amount of Zr, the coating of Comparative Example 3 was found to be damaged within ~10.5 min after friction and wear testing. Its friction curve and wear track morphology are as follows. Figure 17 As shown. The volumetric wear rate of the sample in Comparative Example 3 was 3.09 × 10⁻⁶. -3 mm 3 The wear resistance and service life of the Comparative Example 3 sample were very poor, with a viscosity of / (N·m). This result was also attributed to the unstable suspension formed by the alkaline electrolyte. Furthermore, when silicate ions mixed with acidic fluorozirconate ions, silica colloids were formed.

[0100] Comparative Example 4

[0101] Traditional wear-resistant micro-arc oxidation coatings on titanium alloy surfaces are prepared using aluminate electrolytes. This comparative example uses an aluminate electrolyte system to prepare a micro-arc oxidation coating and compares it with Example 1. The electrolyte is a 2L solution containing 8.2g / L sodium aluminate, in a clear state, with a pH of 11.97, a conductivity of 9.85ms / cm, and a temperature of 25°C. All other steps and conditions are the same.

[0102] The coating thickness of Comparative Example 4 is 30~35μm, and its friction curve is as follows. Figure 4As shown, the sample fractured after approximately 1.15 million friction cycles. In contrast, the sample in Example 1 did not fracture after over 2.66 million friction cycles, with a volumetric wear rate of 3.82 × 10⁻⁶. -6 mm 3 / (N·m), with a wear volume as low as 0.36mm per million cycles. 3 Therefore, the coating proposed in this invention has superior wear resistance and service life compared to traditional aluminate micro-arc oxidation coatings.

Claims

1. A wear-resistant micro-arc oxidation coating for a titanium substrate surface, characterized in that: The coating has a double-layer structure; wherein the F element content in the inner layer is greater than the F element content in the outer layer, the Zr element content in the inner layer is less than the Zr element content in the outer layer, and the ZrO2 content in the outer layer is greater than 30wt%.

2. The ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface according to claim 1, characterized in that: The outer layer has a porous morphology with a porosity of 5-30%.

3. The ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface according to claim 1 or 2, characterized in that: The thickness of the inner layer is 2~20μm, and the total thickness of the coating is 20~70μm.

4. A method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface as described in any one of claims 1 to 3, characterized in that: Using a titanium substrate as the anode and stainless steel as the cathode, and placing both the anode and cathode in a clear electrolyte for micro-arc oxidation, a coating is obtained on the anode surface. The electrolyte should contain more than 5 g / L of fluorozirconate, have a pH of 4-7, and a conductivity of 5-30 mS / cm.

5. The method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface according to claim 4, characterized in that: The electrolyte also includes at least one of a compounding agent and an additive; The compounding agent is at least one of carbonate, phosphate and fluoride; The additive is at least one of glycerin, ethylene glycol, polyethylene glycol, triethanolamine, sodium citrate, and disodium EDTA; The fluorozirconate is at least one of potassium fluorozirconate and ammonium fluorozirconate.

6. The method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface according to claim 5, characterized in that: The carbonate is at least one of potassium bicarbonate, sodium bicarbonate, sodium carbonate, potassium carbonate, ammonium carbonate, and ammonium bicarbonate. The phosphate is sodium hexametaphosphate; The fluoride is at least one of potassium fluoride, sodium fluoride, and potassium fluorotitanate.

7. The method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface according to claim 6, characterized in that: The concentration of fluorozirconate in the electrolyte is 5~60 g / L, the concentration of the compounding agent is 0.5~50 g / L, the amount of additive is 1~20 g / L of the solution mass, and the concentration of fluorozirconate is greater than the concentration of the compounding agent.

8. The method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface according to claim 4, characterized in that: The temperature of the electrolyte is controlled below 30°C; the titanium matrix includes at least one of pure titanium and titanium alloy.

9. The method for preparing an ultra-wear-resistant micro-arc oxidation coating on a titanium substrate surface according to claim 4, characterized in that: The electrical process parameters for the micro-arc oxidation are set as follows: constant voltage mode, positive voltage 200~700 V, negative voltage 0~300 V, pulse frequency 200~1000 Hz, duty cycle 5~50%, and time 5~180 min.

10. A titanium-based composite material, characterized in that: It comprises the coating and titanium substrate as described in any one of claims 1 to 3.

Images