Titanium-aluminum alloy surface high-temperature protection composite coating and preparation method thereof

Abstract

The invention discloses a titanium-aluminum alloy surface high-temperature protection composite coating and a preparation method thereof, and belongs to the technical field of metal material surface modification. The thickness of the composite coating is uniform and controllable within the range of 2-6 microns, the composite coating is composed of three phases of TiSi2, Ti5Si3 and Al2O3, TiSi2 / Ti5Si3 is a continuous phase, and Al2O3 is a dispersed phase; the continuous phase TiSi2 / Ti5Si3 is in contact with and combined with a titanium-aluminum alloy matrix, and the dispersed phase Al2O3 is not in contact with the matrix. The preparation method comprises the steps that the titanium-aluminum alloy is subjected to pretreatment of cutting, polishing and cleaning; embedding into Si powder and SiO2 powder, and carrying out high-temperature diffusion in a vacuum environment. Compared with the prior art, the preparation process is simple and efficient, and the high-temperature protective composite coatings with different thicknesses can be prepared by adjusting the high-temperature treatment time.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material surface modification, and specifically relates to a titanium-aluminum alloy surface high-temperature protective composite coating and a preparation method thereof. Background Art

[0002] Titanium aluminum alloy is widely used in lightweight high-temperature structural parts such as aerospace engine blades and gas turbine hot end components due to its low density, high specific strength, high specific stiffness and excellent creep resistance. When titanium aluminum alloy is used as an aerospace engine material working in a marine atmosphere environment, it will not only be exposed to a high-temperature oxidizing atmosphere above 750°C for a long time, resulting in the formation of a non-protective mixed oxide layer on the surface, accelerating oxidation weight gain and matrix degradation, but also the sulfur oxides in the engine combustion gas react with seawater salt spray (NaCl) to form a low melting point mixed salt (Na 2 SO 4 / NaCl), the molten salt reacts with the matrix at high temperature to produce a porous corrosion layer, which aggravates the degradation and failure of the material and seriously restricts its service life as a high-temperature structural part. At present, there are two main methods to improve the high-temperature oxidation resistance and thermal corrosion resistance of titanium aluminum alloys: one is alloying, which enhances the performance by alloying with other elements. The second is surface coating technology, which improves the performance by adding a protective coating on the alloy surface. Compared with alloying, protective coatings are more effective because alloying may have a negative impact due to the addition of excessive elements. Studies have shown that silicide treatment is an effective surface treatment method, and the silicide layer has good adhesion and hardness, which can improve the oxidation resistance of titanium aluminum alloys. The present invention has developed a method for preparing an antioxidant diffusion coating on the surface of titanium aluminum alloy. This method has a simple process and high cost-effectiveness, and can form an antioxidant and thermal corrosion-resistant coating with strong metallurgical bonding on the titanium aluminum surface. Summary of the invention

[0003] The present invention aims at the deficiencies of the prior art and provides a titanium-aluminum alloy surface high-temperature protective composite coating and a preparation method thereof. The method is used to prepare the titanium-aluminum alloy surface high-temperature protective composite coating, which has a simple process, is easy to operate, has high cost-effectiveness, has a strong metallurgical bonding between the coating and the substrate, and has good high-temperature oxidation resistance and thermal corrosion resistance.

[0004] The technical solution of the present invention is as follows:

[0005] A high temperature protective composite coating on the surface of titanium aluminum alloy, with uniform thickness and controllable thickness within the range of 2 to 6 μm, composed of TiSi 2 、Ti 5 Si 3 and Al 2 O 3 Three phases, including TiSi 2 / Ti 5 Si3 As the continuous phase, Al 2 O 3 is the dispersed phase; the continuous phase is TiSi 2 / Ti 5 Si 3 Contact and combine with the titanium aluminum alloy matrix, the dispersed phase Al 2 O 3 No contact with the substrate.

[0006] A method for preparing a high temperature protective composite coating on the surface of a titanium aluminum alloy, specifically comprising the following steps:

[0007] (1) Pre-treating the titanium aluminum alloy: cutting, grinding, and cleaning;

[0008] (2) Si powder and SiO 2 After the powder is ball-milled and mixed, the titanium-aluminum alloy processed in step (1) is embedded therein;

[0009] (3) placing the embedded titanium-aluminum alloy described in step (2) in a vacuum environment for high-temperature diffusion treatment to obtain a high-temperature protective composite coating on the surface of the titanium-aluminum alloy.

[0010] Preferably, in step (2), Si powder and SiO 2 The powder purity is greater than 99.9%, all are irregular particles, the Si powder particle size range is 5-15μm, SiO 2 The powder particle size range is 2-10μm.

[0011] Preferably, in step (2), the Si powder and SiO 2 The mass ratio of the powder is 1:9 to 9:1, the speed of the powder mixing ball mill is 150-350r / min, and the mixing time is 0.5-2h.

[0012] Preferably, in step (3), the high temperature diffusion treatment is carried out at a temperature of 900-1100° C. for a treatment time of 0.5-5 h, and after the diffusion coating is formed, the coating is cooled to room temperature in the furnace.

[0013] The present invention has the following beneficial effects:

[0014] (1) Stable structure: The high-temperature protective composite coating prepared by the present invention has a strong metallurgical bonding force with the substrate, the coating is continuous and dense as a whole, and there are no defects such as cracks and holes inside.

[0015] (2) Strong resistance to high-temperature oxidation: Under the same high-temperature oxidation conditions, the diffusion coating prepared by the present invention has a significantly lower weight gain per unit area than the substrate sample.

[0016] (3) Strong resistance to thermal corrosion: Under the same thermal corrosion conditions, the diffusion coating prepared by the present invention has a significantly lower weight gain per unit area than the substrate sample.

[0017] (4) Simple process: Compared with the prior art, the preparation process of the present invention is simple and efficient, and high-temperature protective composite coatings of different thicknesses can be prepared by adjusting the high-temperature treatment time. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a cross-sectional scanning electron microscope photograph of a high-temperature protective composite coating on the surface of a titanium-aluminum alloy prepared in Example 1.

[0019] Figure 2 This is the XRD phase composition spectrum of a high-temperature protective composite coating on the surface of a titanium-aluminum alloy prepared in Example 1.

[0020] Figure 3 This is a cross-sectional scanning electron microscope photograph of a high-temperature protective composite coating on the surface of a titanium-aluminum alloy prepared in Example 2.

[0021] Figure 4 This is a cross-sectional scanning electron microscope photograph of a high-temperature protective composite coating on the surface of a titanium-aluminum alloy prepared in Example 3. DETAILED DESCRIPTION

[0022] Example 1

[0023] A high temperature protective composite coating on the surface of a titanium-aluminum alloy and a preparation method thereof, specifically comprising the following steps:

[0024] (1) Use an electric spark cutting machine to cut the titanium aluminum alloy into rectangular patterns, grind the alloy surface, and then use alcohol for ultrasonic cleaning to remove stains on the alloy surface.

[0025] (2) The sample was embedded in a Si and SiO 2 The mixed powders (mass ratio 5:5) were placed in a crucible and then placed in a vacuum furnace for high-temperature diffusion treatment.

[0026] (3) The vacuum furnace is heated to 1100°C and kept warm for 3 hours. During the warming process, the mixed powder will diffuse with the TiAl matrix and chemical reaction will occur at the interface. 2 The Si element contained in the matrix will preferentially combine with the Ti element in the matrix to form a continuously distributed TiSi 2 / Ti 5 Si 3 Composite layer, SiO 2 The O element in the powder will react with the Al element in the matrix to generate Al 2 O 3phase, and finally obtained by TiSi 2 / Ti 5 Si 3 and Al 2 O 3 The high temperature protective composite coating is then formed. The sample is then cooled to room temperature, and then taken out for alcohol ultrasonic cleaning to obtain a high temperature protective composite coating.

[0027] The thickness of the obtained high temperature protective composite coating is about 5.5 μm, and the outermost layer of the composite coating is TiSi 2 / Ti 5 Si 3 (Gray-bright structure), the middle layer is Al 2 O 3 (dark tissue), the innermost layer is TiSi 2 / Ti 5 Si 3 (Gray-bright structure), the scanning electron microscope photos of the coating sample cross section and the XRD patterns of the phase composition are shown in Figure 1 , Figure 2 shown.

[0028] The coating sample prepared in this example was subjected to a high temperature oxidation test: after oxidation at 900°C in air for 600 min, the oxidation weight gain per unit area was 0.55 mg / cm 2 The oxidation weight gain of the untreated titanium aluminum alloy under the same conditions was reduced by about 48.5%. The prepared coating samples were subjected to hot corrosion tests: in 700℃ molten salt (3:1 (wt.%) Na 2 SO 4 After 600 min of corrosion in a NaCl environment, the corrosion weight gain per unit area was only 0.09 mg / cm 2 , which is significantly lower than the 4.23 mg / cm2 per unit area oxidation weight gain of untreated titanium-aluminum alloy under the same hot corrosion environment. 2 .

[0029] Example 2

[0030] A high temperature protective composite coating on the surface of a titanium-aluminum alloy and a preparation method thereof, specifically comprising the following steps:

[0031] Steps (1) and (2) are the same as in Example (1), except that

[0032] (3) The vacuum furnace is heated to 1000°C and kept warm for 3 h, then cooled to room temperature with the furnace, and the sample is taken out and ultrasonically cleaned with alcohol to obtain a high-temperature protective composite coating.

[0033] The thickness of the obtained high temperature protective composite coating is about 1.8 μm, and the outermost layer of the composite coating is TiSi 2 / Ti5 Si 3 (Gray-bright structure), the middle layer is Al 2 O 3 (dark tissue), the innermost layer is TiSi 2 / Ti 5 Si 3 (Gray-bright structure), scanning electron microscope photo of the coating sample cross section Figure 3 shown.

[0034] The coating sample prepared in this example was subjected to a high temperature oxidation test: after oxidation at 900°C in air for 600 min, the oxidation weight gain per unit area was 0.62 mg / cm 2 The oxidation weight gain of the untreated titanium aluminum alloy under the same conditions was reduced by about 41.2%. The prepared coating samples were subjected to hot corrosion tests: in 700℃ molten salt (3:1 (wt.%) Na 2 SO 4 After 600 min of corrosion in a NaCl environment, the corrosion weight gain per unit area was only 0.11 mg / cm 2 , which is significantly lower than the 4.23 mg / cm2 per unit area oxidation weight gain of untreated titanium-aluminum alloy under the same hot corrosion environment. 2 .

[0035] Example 3

[0036] A high temperature protective composite coating on the surface of a titanium-aluminum alloy and a preparation method thereof, specifically comprising the following steps:

[0037] Steps (1) and (2) are the same as in Example (1), except that

[0038] (3) The vacuum furnace is heated to 900°C and kept warm for 4 hours, then cooled to room temperature with the furnace, and the sample is taken out and ultrasonically cleaned with alcohol to obtain a high-temperature protective composite coating.

[0039] The thickness of the obtained high temperature protective composite coating is about 1.1 μm, and the outermost layer of the composite coating is TiSi 2 / Ti 5 Si 3 (Gray-bright structure), the middle layer is Al 2 O 3 (dark tissue), the innermost layer is TiSi 2 / Ti 5 Si 3 (Gray-bright structure), scanning electron microscope photo of the coating sample cross section Figure 4 shown.

[0040] The coating sample prepared in this example was subjected to a high temperature oxidation test: after oxidation at 900°C in air for 600 min, the oxidation weight gain per unit area was 0.68 mg / cm 2 The oxidation weight gain of the untreated titanium aluminum alloy under the same conditions was reduced by about 36.2%. The prepared coating samples were subjected to hot corrosion tests: in 700℃ molten salt (3:1 (wt.%) Na 2 SO 4 After 600 min of corrosion in a NaCl environment, the corrosion weight gain per unit area was only 0.19 mg / cm 2 , which is significantly lower than the 4.23 mg / cm2 per unit area oxidation weight gain of untreated titanium-aluminum alloy under the same hot corrosion environment. 2 .

[0041] Comparative Example 1

[0042] Steps (1) and (2) are the same as in Example (1), except that

[0043] (3) The vacuum furnace was heated to 800°C and kept at this temperature for 5 h. The sample was then cooled to room temperature. The sample was taken out and ultrasonically cleaned with alcohol. No obvious coating appeared on the surface of the prepared sample.

[0044] After the sample of this comparative example was oxidized at 900°C in air atmosphere for 600 min, the oxidation weight gain per unit area was 1.01 mg / cm 2 Compared with the titanium aluminum alloy without any treatment under the same oxidation conditions, the unit area oxidation weight increase is 1.06 mg / cm 2 The oxidation resistance under this condition is basically not improved. The sample was subjected to a hot corrosion test in a molten salt (3:1 (wt.%) Na 2 SO 4 After 600 min of corrosion in NaCl environment, the corrosion weight gain per unit area is 3.83 mg / cm 2 , which is closer to the unit area oxidation weight gain of untreated titanium aluminum alloy under the same hot corrosion environment, which is 4.23 mg / cm 2 .

[0045] Comparative Example 2

[0046] Steps (1) and (2) are the same as in Example (1), except that

[0047] (3) The sample was heated to 1200°C in a vacuum furnace for 0.5 h, then cooled to room temperature in the furnace, and the sample was taken out for alcohol ultrasonic cleaning to obtain a high-temperature protective composite coating.

[0048] The thickness of the obtained high temperature protective composite coating is about 2.5 μm. The outer and inner layers of the composite coating are TiSi 2 / Ti5 Si 3 , the middle layer is Al 2 O 3 After the sample was oxidized at 900℃ in air for 300min, the oxidation weight gain per unit area was 0.65mg / cm 2 Compared with the oxidation weight gain of untreated titanium aluminum alloy under the same conditions, it is 0.80 mg / cm 2 The sample was subjected to a hot corrosion test in a molten salt (3:1 (wt.%) Na 2 SO 4 After 600 min of corrosion in a NaCl environment, the corrosion weight gain per unit area was 1.36 mg / cm 2 Although it is much lower than the unit area oxidation weight gain of untreated titanium aluminum alloy in the same hot corrosion environment (4.23 mg / cm 2 However, compared with Examples 1, 2, and 3, the high-temperature oxidation resistance and thermal corrosion resistance of the composite coating samples obtained are greatly reduced, and excessively high-temperature treatment temperatures can easily lead to deterioration of the mechanical properties of the substrate.

Claims

1. A high-temperature protective composite coating on the surface of a titanium-aluminum alloy, with a uniform thickness and controllable thickness within the range of 2 to 6 μm, composed of three phases of TiSi2, Ti5Si3 and Al2O3, wherein TiSi2 / Ti5Si3 is a continuous phase and Al2O3 is a dispersed phase; the continuous phase TiSi2 / Ti5Si3 is in contact with and combined with a titanium-aluminum alloy substrate, and the dispersed phase Al2O3 is not in contact with the substrate.

2. A method for preparing a high temperature protective composite coating on a titanium aluminum alloy surface according to claim 1, comprising the following steps: (1) Pre-treating the titanium aluminum alloy: cutting, grinding, and cleaning; (2) mixing Si powder and SiO2 powder by ball milling and embedding the titanium aluminum alloy processed in step (1); (3) placing the embedded titanium-aluminum alloy described in step (2) in a vacuum environment for high-temperature diffusion treatment to obtain a high-temperature protective composite coating on the surface of the titanium-aluminum alloy.

3. The method for preparing a high temperature protective composite coating on the surface of a titanium aluminum alloy according to claim 2, characterized in that: In step (2), the purity of Si powder and SiO2 powder is greater than 99.9%, both are irregular particles, the particle size range of Si powder is 5-15μm, and the particle size range of SiO2 powder is 2-10μm.

4. The method for preparing a high temperature protective composite coating on the surface of a titanium aluminum alloy according to claim 2, characterized in that: In step (2), the mass ratio of Si powder to SiO2 powder in the mixed powder is 1:9 to 9:1, the speed of the mixed powder ball mill is 150-350 r / min, and the mixing time is 0.5-2 h.

5. The method for preparing a high temperature protective composite coating on the surface of a titanium aluminum alloy according to claim 2, characterized in that: In step (3), the high temperature diffusion treatment is carried out at a temperature of 900-1100° C. for a treatment time of 0.5-5 h. After the diffusion coating is formed, the coating is cooled to room temperature in the furnace.

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