Preparation method of TiAl alloy matrix surface composite coating and TiAl alloy

Abstract

The invention discloses a preparation method of a TiAl alloy matrix surface composite coating and a TiAl alloy, and belongs to the technical field of TiAl alloy surface coatings. According to the method, the TiAl alloy matrix material is subjected to pre-plating treatment, so that the surface can be effectively cleaned and activated, the good binding force between the subsequent coating and the matrix is ensured, the binding strength is enhanced, and a multi-layer composite coating can be formed on the surface of the matrix by sequentially performing electroplating treatment in more than two electroplating solutions; therefore, wear resistance, corrosion resistance and hardness of the alloy surface are comprehensively improved, and key indexes such as wear resistance and service life of valve parts can be met. The method is clear in technological process and easy to implement, and the surface coating with the composite performance can be flexibly designed and prepared according to the specific application requirements of the TiAl alloy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of TiAl alloy surface coating preparation, and particularly relates to a TiAl alloy substrate surface composite coating preparation method and TiAl alloy. BACKGROUND

[0002] The gamma-TiAl intermetallic compound (hereinafter referred to as TiAl alloy) has the advantages of light weight, high specific strength, high specific modulus, good high-temperature fatigue resistance, fracture toughness and the like, and is a highly competitive strategic and cutting-edge structural material in the field of engines for aerospace, engineering vehicles, long-endurance unmanned aerial vehicles and advanced ships.

[0003] The TiAl alloy manufactured engine valve can not only significantly reduce the weight (the weight can be reduced by 40%-50%), improve the engine power output and working efficiency, but also reduce harmful gas emission and vibration and noise. However, the valve is subjected to the combined action of high temperature, oxidation and strong vibration load during service, and is prone to wear. In addition, the TiAl alloy has defects such as low hardness, poor wear resistance and insufficient high-temperature oxidation resistance, thereby limiting the use of the TiAl alloy under high-temperature friction conditions. Therefore, it is necessary to improve the wear resistance of the TiAl alloy. SUMMARY

[0004] The main purpose of the present application is to provide a TiAl alloy substrate surface composite coating preparation method and TiAl alloy, which solves the technical problems of low hardness and poor wear resistance of the TiAl alloy.

[0005] To achieve the above-mentioned purpose, the present application provides a TiAl alloy substrate surface composite coating preparation method, which comprises the following steps: The TiAl alloy substrate material is subjected to pre-plating treatment to obtain a pre-plating TiAl alloy substrate material; The pre-plating TiAl alloy substrate material is sequentially placed in two or more electroplating solutions for electroplating treatment to obtain a TiAl alloy with a surface containing a composite coating.

[0006] In some embodiments of the present application, the electroplating solution comprises a nickel plating electrolyte and a chromium plating electrolyte.

[0007] In some embodiments of the present application, the nickel plating electrolyte comprises nickel sulfamate, nickel chloride or sodium chloride, boric acid, sodium benzenesulfinate, 1,4-butynediol, sodium allylsulfonate and sodium dodecyl sulfate.

[0008] In some embodiments of the present invention, in the nickel plating electrolyte, the concentration of nickel aminosulfonate is 380 g / L to 500 g / L, the concentration of nickel chloride or sodium chloride is 2 g / L to 10 g / L, the concentration of boric acid is 35 g / L to 45 g / L, the concentration of sodium benzenesulfinate is 0.01 g / L to 0.10 g / L, the concentration of 1,4-butynediol is 0.1 g / L to 0.5 g / L, the concentration of sodium allyl sulfonate is 0.1 g / L to 1.0 g / L, and the concentration of sodium dodecyl sulfate is 0.01 g / L to 0.30 g / L.

[0009] In some embodiments of the present invention, the chromium plating electrolyte includes chromium trioxide, sulfuric acid, and trivalent chromium.

[0010] In some embodiments of the present invention, in the chromium plating electrolyte, the concentration of chromium trioxide is 200 g / L to 240 g / L, the concentration of sulfuric acid is 2.0 g / L to 2.4 g / L, and the concentration of trivalent chromium is 3 g / L to 8 g / L.

[0011] In some embodiments of the present invention, when electroplating is performed using the nickel plating electrolyte, the electroplating power supply is a DC power supply with a current density of 1 A / dm³. 2 ~4A / dm 2 The electroplating temperature is 50℃~60℃, and the processing time is 10min~25min.

[0012] In some embodiments of the present invention, when electroplating is performed using a chromium plating solution, the electroplating power source is a DC power source with a current density of 30 A / dm². 2 ~40A / dm 2 The electroplating temperature is 25℃~35℃, and the processing time is 10min~20min.

[0013] In some embodiments of the present invention, the step of pre-plating treatment of the TiAl alloy substrate material includes: The surface of the TiAl alloy matrix material is subjected to grinding, first cleaning, degreasing, second cleaning, etching, third cleaning, brightening, fourth cleaning, and drying.

[0014] In some embodiments of the present invention, the thickness of the composite coating is 20 μm to 30 μm; and / or, the microhardness of the TiAl alloy with the composite coating on its surface is greater than or equal to 600 HV.

[0015] The present invention also provides a TiAl alloy, wherein the surface of the TiAl alloy contains a composite coating, and the composite coating is prepared by the method for preparing a composite coating on the surface of a TiAl alloy substrate as described above.

[0016] The beneficial effects that this invention can achieve are: This invention effectively cleans and activates the surface of TiAl alloy substrate material by pre-plating treatment, ensuring good adhesion between the subsequent coating and the substrate and enhancing the bonding strength. By electroplating in two or more electroplating solutions in sequence, a multi-layer composite coating can be formed on the substrate surface, thereby comprehensively improving the wear resistance, corrosion resistance and hardness of the alloy surface, which can meet the key indicators such as wear resistance and service life of valve parts.

[0017] The process flow of this invention is clear and easy to implement, and it can flexibly design and prepare surface coatings with composite properties to meet the specific application requirements of TiAl alloys. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of a method for preparing a composite coating on a TiAl alloy substrate according to the present invention. Figure 2 This is a cross-sectional elemental distribution diagram of the TiAl alloy containing a composite coating in Embodiment 1 of the present invention.

[0020] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] In this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention.

[0024] This invention provides a method for preparing a composite coating on a TiAl alloy substrate and a TiAl alloy, referring to... Figure 1 The preparation method includes the following steps: S10. Pre-plating treatment is performed on the TiAl alloy matrix material to obtain the TiAl alloy matrix material before plating. S20. The TiAl alloy substrate material before plating is sequentially placed in two or more electroplating solutions for electroplating treatment to obtain a TiAl alloy with a composite coating on the surface.

[0025] This invention effectively cleans and activates the surface of the TiAl alloy substrate through pre-plating treatment, ensuring good adhesion between the subsequent coating and the substrate and enhancing bonding strength. By sequentially electroplating in two or more electroplating solutions, a multi-layer composite coating can be formed on the substrate surface, thereby comprehensively improving the wear resistance, corrosion resistance, and hardness of the alloy surface, meeting key indicators such as wear resistance and service life of valve components. The process flow of this invention is clear and easy to implement, enabling the flexible design and preparation of surface coatings with composite properties to meet the specific application requirements of TiAl alloys.

[0026] In some embodiments, the TiAl alloy matrix material includes a manganese-containing β-solidified γ-TiAl alloy.

[0027] In some embodiments, the composition of the manganese-containing β-solidified γ-TiAl alloy, by atomic percentage, includes 41.0-45.0% Al, 0.5-5.0% Mn, the balance being Ti, and trace amounts of alloying elements such as W, Mo, and Nb. β-solidified γ-TiAl alloys do not undergo peritectic transformation, exhibit minimal main component segregation, and are hot-workable, possessing advantages such as low density, high specific strength, and high elastic modulus. Mn is a β-phase stabilizing element, exhibiting a strong β-phase stabilizing effect. W acts as a toughening agent for TiAl intermetallic compounds, Mo is a strong β-forming element, and Nb stabilizes the β-phase and improves the alloy's oxidation resistance. Adding small amounts of Mn, W, Mo, and Nb to TiAl alloys allows for compositional control, resulting in TiAl alloys with good microstructural stability and oxidation resistance.

[0028] In some embodiments, the electroplating solution includes a nickel plating electrolyte and a chromium plating electrolyte. This embodiment, by sequentially treating with both nickel and chromium plating solutions, can form a nickel / chromium composite coating. This fully utilizes the good adhesion and toughness of the nickel layer and the excellent hardness and corrosion resistance of the chromium layer. The resulting composite coating can significantly improve the overall performance of the TiAl alloy surface, such as wear resistance, corrosion resistance, and high-temperature oxidation resistance.

[0029] In some embodiments, the TiAl alloy substrate material is first electroplated with a nickel plating electrolyte to obtain a nickel plating layer, and then electroplated with a chromium plating electrolyte to form a chromium plating layer on the surface of the nickel plating layer. The nickel plating layer, as an intermediate plating layer, not only provides protection and decoration, but also significantly improves the corrosion resistance of the overall plating layer through an electrochemical protection mechanism. The chromium plating layer, as a surface layer, has excellent hardness and corrosion resistance. The resulting composite coating can significantly improve the comprehensive performance of the TiAl alloy surface, such as wear resistance, corrosion resistance and high-temperature oxidation resistance.

[0030] In some embodiments, the nickel plating electrolyte includes nickel sulfamate, nickel chloride or sodium chloride, boric acid, sodium benzenesulfonate, 1,4-butynediol, sodium allyl sulfonate, and sodium dodecyl sulfate.

[0031] Nickel aminosulfonate, as the main salt in nickel plating electrolyte, primarily functions to provide Ni. 2+ Boric acid acts as a buffer in nickel plating electrolytes, maintaining pH stability during electroplating and ensuring smooth plating. Nickel chloride or sodium chloride acts as an anode activator; its chloride ions adsorb onto the anode surface, lowering the anode potential and significantly depolarizing the anode, thus effectively preventing passivation. Insufficient chloride ion content in the electrolyte can easily lead to anode passivation, which is extremely detrimental to electroplating production. Adding chloride in this case prevents divalent nickel ions from oxidizing to trivalent nickel ions, avoiding the formation of a passivation film. Sodium dodecyl sulfate acts as a wetting agent (also known as a pinhole preventer), improving the wettability of the electrolyte on the electrode surface and reducing hydrogen adsorption and retention on the cathode surface, thus preventing pinhole problems caused by hydrogen bubble shielding. Sodium benzenesulfinate is a primary brightener that significantly refines the grain size of the nickel plating layer, imparting a certain degree of brightness. These additives can induce compressive stress in the coating. When used in conjunction with secondary brighteners (such as 1,4-butynediol), they can counteract the tensile stress caused by the secondary brighteners, thereby improving the ductility of the coating. Sodium allyl sulfonate, as an auxiliary brightener, has limited effect on improving the brightness of the coating when used alone. Its main functions are to accelerate the brightening and leveling process, help prevent pinholes, reduce the consumption of secondary brighteners, and improve the corrosion resistance of the plated product.

[0032] In some embodiments, the concentration of nickel sulfamate in the nickel plating electrolyte is 380 g / L to 500 g / L, the concentration of nickel chloride or sodium chloride is 2 g / L to 10 g / L, the concentration of boric acid is 35 g / L to 45 g / L, the concentration of sodium benzenesulfinate is 0.01 g / L to 0.10 g / L (or 0.05 g / L), the concentration of 1,4-butynediol is 0.1 g / L to 0.5 g / L (or 0.2 g / L), the concentration of sodium allyl sulfonate is 0.1 g / L to 1.0 g / L (or 0.5 g / L), and the concentration of sodium dodecyl sulfate is 0.01 g / L to 0.30 g / L (or 0.1 g / L).

[0033] In some embodiments, the electroplating electrolyte for chromium plating includes chromium trioxide, sulfuric acid, and trivalent chromium.

[0034] Chromium trioxide is the main salt in chromium plating electrolyte, serving to supply Cr... 6+ The role of sulfuric acid in chromium electroplating: Sulfuric acid acts as a catalyst, playing a crucial role in the chromium electroplating process and coating quality through various functions, including forming complexes, adjusting the conductivity and pH of the plating solution, influencing cathode current efficiency and coating quality, promoting the diffusion and deposition of metal ions, and cleaning the metal surface. Cr 3+ It also acts as a catalyst in chromium electroplating. It has a significant impact on the chromium electroplating process and coating quality by forming colloidal films, affecting current efficiency, promoting chromium deposition, improving plating solution performance, and synergistic catalytic effects with other compounds.

[0035] In some embodiments, the concentration of chromium trioxide in the chromium plating electrolyte is 200 g / L to 240 g / L, the concentration of sulfuric acid is 2.0 g / L to 2.4 g / L, and the concentration of trivalent chromium is 3 g / L to 8 g / L.

[0036] In some embodiments, when electroplating is performed using a nickel plating electrolyte, the electroplating power source is a DC power source with a current density of 1 A / dm³. 2 ~4A / dm 2 The electroplating temperature is 50℃~60℃, and the processing time is 10min~25min.

[0037] In some embodiments, chromium plating solution is used for electroplating, and the electroplating power source is a DC power source with a current density of 30 A / dm³. 2 ~40A / dm 2 It can be 35 A / dm 2 The electroplating temperature is 25℃~35℃, and the processing time is 10min~20min.

[0038] In some embodiments, the pre-plating treatment steps for the TiAl alloy substrate material include: grinding the surface of the TiAl alloy substrate material, primary cleaning, degreasing, secondary cleaning, etching, tertiary cleaning, brightening, quaternary cleaning, and drying.

[0039] In some embodiments, during the polishing step, the surface of the TiAl alloy matrix material is polished to 2000 grit using SiC sandpaper.

[0040] In some embodiments, during a cleaning step, the polished TiAl alloy matrix material is ultrasonically cleaned in distilled water for 10 minutes.

[0041] In some embodiments, during the degreasing step, the ultrasonically cleaned TiAl alloy matrix material is placed in a weak alkaline solution for chemical degreasing at a temperature of 72°C for 50 seconds.

[0042] In some embodiments, the weak alkaline solution includes sodium hydroxide, sodium carbonate, and trisodium phosphate, wherein the concentration of sodium hydroxide in the weak alkaline solution is 17.5 g / L, the concentration of sodium carbonate is 45 g / L, the concentration of trisodium phosphate is 27.5 g / L, and the remainder is distilled water.

[0043] In some embodiments, during the secondary cleaning step, the chemically degreased TiAl alloy matrix material is placed in distilled water for cleaning.

[0044] In some embodiments, during the etching step, the TiAl alloy matrix material after secondary cleaning is placed in an acidic solution for etching treatment at a temperature of 72°C for 65 seconds.

[0045] In some embodiments, the acidic solution used for etching includes concentrated sulfuric acid and chromium trioxide. In the acidic solution, the concentration of concentrated sulfuric acid (98% by mass) is 100 ml / L, the concentration of chromium trioxide is 35 g / L, and the remainder is distilled water.

[0046] In some embodiments, during the three-step cleaning process, the etched TiAl alloy substrate material is placed in distilled water for cleaning.

[0047] In some embodiments, during the brightening step, the TiAl alloy matrix material after three cleanings is placed in an acidic solution for brightening treatment at a temperature of 25°C for 5 seconds.

[0048] In some embodiments, the acidic solution for the light extraction process includes nitric acid and hydrofluoric acid, wherein the concentration of nitric acid in the acidic solution is 400 ml / L, the concentration of hydrofluoric acid is 80 ml / L, and the remainder is distilled water. In some embodiments, during the four-cleaning step, the TiAl alloy matrix material after brightening treatment is placed in distilled water for cleaning and then dried.

[0049] In some embodiments, the thickness of the composite coating on the TiAl alloy substrate surface is 20μm to 30μm. Controlling the coating thickness within this range can protect the substrate material and improve its wear resistance, while preventing the coating from peeling off easily due to excessive thickness, thus affecting the use of the material. In some embodiments, the microhardness of the composite coating on the TiAl alloy substrate surface is above 600 HV, which effectively improves the wear resistance of the surface coating.

[0050] The present invention also provides a TiAl alloy, the surface of which contains a composite coating, the composite coating being prepared by the above-described composite coating method on the surface of the TiAl alloy substrate.

[0051] In some embodiments, using TiAl alloy with a composite coating on valve parts, such as valve stems, can reduce wear between the valve stem and the guide.

[0052] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0053] Example 1 Preparation of nickel plating electrolyte and chromium plating electrolyte: The composition of the nickel plating electrolyte is as follows: 400 g / L nickel sulfamate, 6 g / L nickel chloride, and 40 g / L boric acid. Additives include 0.05 g / L sodium benzenesulfinate, 0.2 g / L 1,4-butynediol, 0.5 g / L sodium allyl sulfonate, and 0.1 g / L sodium dodecyl sulfate.

[0054] The composition of the chromium plating electrolyte is as follows: 220 g / L chromium trioxide, 2.2 g / L sulfuric acid, 4 g / L Cr 3+ .

[0055] Preparation of matrix material: The matrix material used is a manganese-containing β-solidified γ-TiAl alloy. By atomic percentage, its composition includes 42.0% Al, 5.0% Mn, and the balance Ti. The alloy was cut into samples with dimensions of 40 mm × 10 mm × 3 mm by wire cutting.

[0056] Substrate material treatment: Before electroplating, the surface of the TiAl alloy substrate material is polished to 2000 grit with SiC sandpaper. The polished TiAl alloy substrate material is then ultrasonically cleaned in distilled water for 10 minutes. After ultrasonic cleaning, the TiAl alloy substrate material is chemically degreased in a weak alkaline solution at 72°C for 50 seconds. The chemically degreased TiAl alloy substrate material is then rinsed with distilled water. To remove surface contaminants and oxide film, the cleaned TiAl alloy substrate material is etched in an acidic solution at 72°C for 65 seconds. The etched TiAl alloy substrate material is then rinsed with distilled water. At this point, some residue remains on the surface of the TiAl alloy substrate material after etching. The cleaned TiAl alloy substrate material is then brightened in an acidic solution at room temperature for 5 seconds. After brightening, it is dried to obtain the pre-plating TiAl alloy substrate material. The purpose of the above process is to remove surface contaminants and oxide film.

[0057] The preparation method of the composite coating is as follows: The TiAl alloy substrate material before plating was immersed in the nickel plating electrolyte under a stable DC power supply with a current density of 3.0 A / dm³. 2 Electroplating was performed at a temperature of 55℃ for 20 minutes to form a nickel plating layer on the surface of the TiAl alloy substrate before plating. Then, the TiAl alloy substrate containing the nickel plating layer was immersed in a chromium plating electrolyte under a stable DC power supply with a current density of 35 A / dm³. 2 TiAl alloys with a composite coating on the surface were obtained by electroplating at a temperature of 30℃ and a processing time of 10 min.

[0058] Example 2 Example 2 describes the preparation of a coating on the surface of a TiAl alloy using the same method as in Example 1, but with the following difference: the composition of the chromium plating electrolyte is as follows: 230 g / L chromium trioxide, 2.1 g / L sulfuric acid, and 3 g / L chromium iodide. 3+ .

[0059] Example 3 Example 3 describes the preparation of a coating on the surface of a TiAl alloy using the same method as in Example 1. However, the difference is that a chromium plating solution was used for electroplating, and the electroplating power source was a stable DC power supply with a current density of 35 A / dm³. 2 The electroplating temperature was 34℃ and the processing time was 15 minutes.

[0060] Comparative Example 1 Comparative Example 1 prepared a coating on the surface of a TiAl alloy using the same method as in Example 1, but the difference was that only a nickel coating was prepared on the surface of the TiAl alloy.

[0061] Performance testing (1) Coating hardness test: The Vickers hardness of the sample was tested using an HVS-1000Z Vickers hardness tester. Before the hardness test, the sample was first leveled to prevent excessive data error caused by the test surface not being level. The experimental load was 3N and the loading time was 10s. To prevent errors caused by factors such as uneven sample composition, 10 points on the sample were tested, and the average hardness was calculated. The test results are shown in Table 1.

[0062] (2) Surface distribution of different elements in the coating section: The TiAl alloy of Example 1 was observed and analyzed using an electron probe microanalyzer (EPMA) to observe the surface distribution of elements in the coating section. The distribution of each element in the sample and the chemical composition of the specified area were analyzed using a wavelength dispersive spectroscopy (WDS) instrument equipped with the EPMA.

[0063] The distribution of cross-sectional elements is shown in the figure. Figure 2 . Figure 2 As can be seen from the observation under a magnified 2000x angle, the coating has good density and no inclusions are present in the coating; there are no defects such as pores or microcracks at the junction of the Cr coating and the Ni coating.

[0064] Table 1

[0065] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a composite coating on the surface of a TiAl alloy substrate, characterized in that, Includes the following steps: The TiAl alloy matrix material is pre-plated by undergoing pre-plating treatment to obtain the TiAl alloy matrix material before plating. The TiAl alloy substrate material before plating is sequentially placed in two or more electroplating solutions for electroplating treatment to obtain a TiAl alloy with a composite coating on the surface.

2. The method for preparing the composite coating on the surface of the TiAl alloy substrate according to claim 1, characterized in that, The electroplating solution includes nickel plating electrolyte and chromium plating electrolyte.

3. The method for preparing the composite coating on the surface of the TiAl alloy substrate according to claim 2, characterized in that, The nickel plating electrolyte includes nickel aminosulfonate, nickel chloride or sodium chloride, boric acid, sodium benzenesulfonate, 1,4-butynediol, sodium allyl sulfonate, and sodium dodecyl sulfate.

4. The method for preparing the composite coating on the surface of the TiAl alloy substrate according to claim 3, characterized in that, In the nickel plating electrolyte, the concentration of nickel aminosulfonate is 380 g / L to 500 g / L, the concentration of nickel chloride or sodium chloride is 2 g / L to 10 g / L, the concentration of boric acid is 35 g / L to 45 g / L, the concentration of sodium benzenesulfinate is 0.01 g / L to 0.10 g / L, the concentration of 1,4-butynediol is 0.1 g / L to 0.5 g / L, the concentration of sodium allyl sulfonate is 0.1 g / L to 1.0 g / L, and the concentration of sodium dodecyl sulfate is 0.01 g / L to 0.30 g / L.

5. The method for preparing the composite coating on the surface of the TiAl alloy substrate according to claim 2, characterized in that, The chromium plating electrolyte includes chromium trioxide, sulfuric acid, and trivalent chromium.

6. The method for preparing the composite coating on the surface of the TiAl alloy substrate according to claim 5, characterized in that, In the chromium plating electrolyte, the concentration of chromium trioxide is 200 g / L to 240 g / L, the concentration of sulfuric acid is 2.0 g / L to 2.4 g / L, and the concentration of trivalent chromium is 3 g / L to 8 g / L.

7. The method for preparing the composite coating on the surface of the TiAl alloy substrate according to claim 2, characterized in that, When electroplating with the aforementioned nickel plating electrolyte, the electroplating power supply is a DC power supply with a current density of 1 A / dm³. 2 ~4A / dm 2 The electroplating temperature is 50℃~60℃, and the processing time is 10min~25min; And / or, when using a chromium plating solution for electroplating, the electroplating power source is a DC power source with a current density of 30 A / dm³. 2 ~40A / dm 2 The electroplating temperature is 25℃~35℃, and the processing time is 10min~20min.

8. The method for preparing the composite coating on the surface of the TiAl alloy substrate according to claim 1, characterized in that, The steps for pre-plating treatment of the TiAl alloy substrate material include: The surface of the TiAl alloy matrix material is subjected to grinding, first cleaning, degreasing, second cleaning, etching, third cleaning, brightening, fourth cleaning, and drying.

9. The method for preparing a composite coating on the surface of a TiAl alloy substrate according to any one of claims 1 to 8, characterized in that, The thickness of the composite coating is 20μm to 30μm; and / or the microhardness of the TiAl alloy with the composite coating on its surface is greater than or equal to 600HV.

10. A TiAl alloy, characterized in that, The surface of the TiAl alloy contains a composite coating, which is prepared by any one of the methods for preparing a composite coating on the surface of a TiAl alloy substrate as described in claims 1 to 9.

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