A Cr-modified Ti-Al-Si coating and its preparation method

Abstract

The present invention discloses a Cr-modified Ti-Al-Si coating and a preparation method thereof, wherein the coating is prepared on the surface of a titanium or titanium alloy workpiece to improve the high-temperature oxidation resistance of the workpiece. The coating is characterized in that a Ti-Al binary alloy phase layer, a Ti-Al / Ti-Si mixed phase layer, a Ti(Al, Si, Cr)3 phase layer, and an Al2O3 layer are formed in sequence from the substrate to the outside. The preparation method of the coating is to place the titanium or titanium alloy workpiece after surface pretreatment in a hot-dip plating box filled with argon protection, first hot-dip plating in an Al-Cr alloy melt pool, then hot-dip plating in an Al-Si alloy melt pool, and then extracting and discarding the excess hot-dip plating liquid on the surface of the workpiece, drying after water quenching, and finally performing high-temperature pre-oxidation treatment. The method is simple in process, low in cost, and easy to control the coating thickness.

Description

Technical Field

[0001] The invention relates to the technical field of titanium or titanium alloy surface treatment, and in particular to a Cr-modified Ti-Al-Si coating and a preparation method thereof. Background Art

[0002] Titanium and its alloys, characterized by high specific strength, low density, and excellent corrosion resistance, are widely used in key fields such as aerospace, military, and chemical engineering. Titanium alloys, particularly in aircraft engines, play a crucial role. With the development of high thrust-to-weight ratio engines, the demand for titanium alloys' high-temperature oxidation resistance is increasing. However, this resistance decreases sharply when the service temperature exceeds 600°C, limiting their further application. To improve the high-temperature oxidation resistance of titanium alloys, various surface modification methods have been employed. Initially, aluminizing the surface of titanium alloys was employed, aiming to create a dense TiAl3 phase layer and an alumina protective layer. However, due to thermal expansion coefficient mismatches between the coatings and between the coating and the substrate, stresses develop at high temperatures, causing cracks in the coating and exposing the substrate to the atmosphere. Ultimately, the coating cracks and fails. Therefore, the introduction of Si mitigates this thermal expansion coefficient mismatch and improves the high-temperature oxidation resistance of titanium alloys. In addition, since Si will combine with Ti before Al to form a Ti-Si compound, thus preventing the formation of a TiAl3 phase layer, we adopted a two-step hot-dip plating method, first allowing Ti to combine with Al to generate TiAl3, then introducing Si atoms, and finally forming a Ti(Al,Si)3 phase layer on the titanium alloy surface.

[0003] Studies have shown that adding a certain amount of Cr can reduce the activity of Ti. As the temperature rises, the activity of Al increases rapidly. At higher temperatures, Al2O3 films are more likely to form. However, once the Al2O3 film forms, the growth of TiO2 is inhibited, which reduces the minimum Al content required for Al2O3 film formation based on thermodynamics and promotes the formation of Al2O3. Therefore, we introduced Cr into the secondary hot-dip plating process to obtain a Cr-modified Ti-Al-Si coating. The results show that the addition of Cr significantly improves the coating's resistance to high-temperature oxidation and extends the service life of the titanium alloy at high temperatures. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a Cr-modified Ti-Al-Si coating and a preparation method thereof in view of the deficiencies of the existing technology. The method adopts the method of first hot-dip plating Al-Cr and then hot-dip plating Al-Si to ensure that a TiAl3 phase layer with excellent high-temperature oxidation resistance and a certain amount of Cr atoms dissolved therein is formed first, and then Si atoms are introduced to form a Ti(Al, Si, Cr)3 phase layer; finally, a high-temperature pre-oxidation treatment is performed to eventually form a Cr-modified Ti-Al-Si coating having a Ti-Al binary alloy phase layer, a Ti-Al / Ti-Si mixed phase layer, a Ti(Al, Si, Cr)3 phase layer, and an Al2O3 layer on the surface of titanium or titanium alloy. The Cr-modified Ti-Al-Si coating of the present invention can significantly improve the high-temperature oxidation resistance of the coating, the coating has good thermal stability, is well bonded to the substrate, and the preparation method is simple, the cost is low, and it is easy to implement.

[0005] Another object of the present invention is to provide a Cr-modified Ti-Al-Si coating and a preparation method thereof, wherein the preparation method comprises the following steps:

[0006] Step 1: Use a metal cleaning agent to clean and degrease the surface of the pre-treated titanium or titanium alloy workpiece, and then place it in a drying oven for drying;

[0007] Step 2: Two melt pools with independently controllable temperatures are arranged in a hot dip plating box filled with argon protection, wherein melt pool 1 contains Al-Cr alloy liquid and melt pool 2 contains Al-Si alloy liquid.

[0008] Step 3: Immerse the titanium or titanium alloy workpiece in step 1 in an Al-Cr alloy solution for hot dip plating. After keeping the workpiece warm for a certain period of time, remove the workpiece from the Al-Cr alloy solution and then quickly immerse it in an Al-Si alloy solution for hot dip plating. After keeping the workpiece warm for a certain period of time, remove the workpiece from the Al-Si alloy solution, remove the excess hot dip plating solution on the surface of the workpiece, quench with water and dry it, and then perform high-temperature pre-oxidation treatment to obtain a Cr-modified Ti-Al-Si coating on the surface of the workpiece.

[0009] A Cr-modified Ti-Al-Si coating and preparation method thereof comprises first hot-dip plating Al-Cr on titanium or titanium alloy to preferentially form a TiAl3 phase layer having a certain amount of Cr atoms dissolved therein and having excellent high-temperature oxidation resistance on its surface, then introducing Si atoms to form a Ti(Al,Si,Cr)3 phase layer, and finally performing a high-temperature pre-oxidation treatment to ultimately form a Cr-modified Ti-Al-Si coating on the surface of the titanium or titanium alloy workpiece in sequence, including a Ti-Al binary alloy phase layer, a Ti-Al / Ti-Si mixed phase layer, a Ti(Al,Si,Cr)3 phase layer, and an Al2O3 layer. The Cr-modified Ti-Al-Si coating and preparation method of the present invention combine the controllability of coating preparation by a double hot-dip plating method, primarily controlling the thickness of the Ti(Al,Si,Cr)3 phase layer by controlling the temperature and time of the two hot-dip plating processes, and ensuring that the surface of the first hot-dip plating layer is not excessively oxidized by controlling the time it takes for the hot-dip plating workpiece to be quickly immersed in the Al-Si alloy liquid after being withdrawn from the Al-Cr alloy liquid. The obtained coating has the advantages of good thermal stability, simple preparation process, low cost, etc., and can significantly improve the service life of titanium or titanium alloy workpieces in high temperature environments.

[0010] The Cr-modified Ti-Al-Si coating and preparation method are characterized in that, in step 3, the first hot-dip coating in the Al-Cr alloy solution is performed at a temperature of 750-850°C for 5-20 minutes; and the second hot-dip coating in the Al-Si alloy solution is performed at a temperature of 750-800°C for 5-20 minutes. The above hot-dip coating temperature range ensures that the target product after the two hot-dip coatings is a Ti(Al,Si,Cr)3 phase. The above hot-dip coating time range can control the thickness of the Ti(Al,Si,Cr)3 phase layer, resulting in a Ti(Al,Si,Cr)3 phase layer thickness of 40-150 microns.

[0011] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The present invention is a flow chart of the Cr-modified Ti-Al-Si coating and its preparation method.

[0013] Figure 2 3 is a microstructural morphology of the Cr-modified Ti-Al-Si coating obtained in the embodiment. DETAILED DESCRIPTION

[0014] The Cr-modified Ti-Al-Si coating can be designed based on actual usage requirements. The thickness of the resulting Ti(Al, Si, Cr) three-phase layer can be adjusted by controlling the temperature and duration of the two hot-dip coatings. The time between the hot-dip plated workpiece being withdrawn from the Al-Cr alloy solution and quickly immersed in the Al-Si alloy solution can be controlled to ensure that the hot-dip plated coating surface is not excessively oxidized. Therefore, the Cr-modified Ti-Al-Si coating on the surface of the titanium or titanium alloy workpiece has good controllability.

[0015] like Figure 1 As shown, after completing the coating phase structure design, the Cr-modified Ti-Al-Si coating is prepared according to the following steps:

[0016] Step 1: Use a metal cleaning agent to clean and degrease the surface of the pre-treated titanium or titanium alloy workpiece, and then place it in a drying oven for drying;

[0017] Step 2: Two independently temperature-controlled melt pools are placed in an argon-filled hot-dip plating tank. Al-Cr master alloy is added to melt pool 1 containing high-purity aluminum liquid to prepare an Al-Cr alloy liquid with a Cr content of 1wt.%-5wt.%; Al-Si master alloy is added to melt pool 2 containing high-purity aluminum liquid to prepare an Al-Si alloy liquid with a Si content of 5wt.%-15wt.%;

[0018] Step 3. Set the temperature of melt pool 1 to 750-850°C, set the temperature of melt pool 2 to 750-800°C, immerse the workpiece in step 1 into the molten Al-Cr alloy liquid, keep it warm for 5-20 minutes, and then, under argon protection, extract the workpiece from the Al-Cr alloy liquid, and then quickly immerse it in the molten Al-Si alloy liquid. After keeping warm for 5-20 minutes, extract the workpiece from the Al-Si alloy liquid, remove excess immersion liquid on the surface of the workpiece, water quench and dry it, and then pre-oxidize it at 800-850°C for 2-4 hours. Finally, form a Ti-Al binary alloy phase layer, a Ti-Al / Ti-Si mixed phase layer, a Ti(Al,Si,Cr)3 phase layer, and an Al2O3 layer on the surface of the titanium or titanium alloy workpiece in sequence; the total thickness of the Ti(Al,Si,Cr)3 phase layer required above is 40-150 microns.

[0019] Implementation Examples

[0020] Step 1: Use a metal cleaning agent to clean and degrease the surface of the pretreated Ti65 alloy sample, and then place it in a drying oven for drying;

[0021] Step 2: Two independently temperature-controlled melt pools are placed in an argon-filled hot-dip plating tank. Al-Cr master alloy is added to melt pool 1 containing high-purity aluminum liquid to prepare an Al-Cr alloy liquid with a Cr content of 3 wt.%. Al-Si master alloy is added to melt pool 2 containing high-purity aluminum liquid to prepare an Al-Si alloy liquid with a Si content of 10 wt.%.

[0022] Step 3: Set the temperature of melt pool 1 to 750°C and the temperature of melt pool 2 to 750°C. Immerse the Ti65 alloy sample prepared in step 1 into the molten Al-Cr alloy solution and keep it warm for 5 minutes. Then, under argon protection, withdraw the Ti65 alloy sample from the Al-Cr alloy solution and quickly immerse it in the molten Al-Si alloy solution. After keeping it warm for 15 minutes, withdraw the sample from the Al-Si alloy solution, remove the excess immersion solution from the surface of the sample, quench it with water, dry it, and then pre-oxidize it at 850°C for 2 hours. Finally, a Ti-Al binary alloy phase layer, a Ti-Al / Ti-Si mixed phase layer, a Ti(Al,Si,Cr)3 phase layer, and an Al2O3 layer are formed on the surface of the Ti65 alloy sample in sequence. The total thickness of the Ti(Al,Si,Cr)3 phase layer required above is 55 microns.

Claims

1. A method for preparing a Cr-modified Ti-Al-Si coating, characterized in that: The following steps are involved: Step 1: Use a metal cleaning agent to clean and degrease the surface of the pre-treated titanium or titanium alloy workpiece, and then place it in a drying oven for drying; Step 2: two independently temperature-controlled melt pools are arranged in a hot-dip plating box filled with argon gas, wherein melt pool 1 contains Al-Cr alloy liquid and melt pool 2 contains Al-Si alloy liquid; Step 3: Immerse the titanium or titanium alloy workpiece in step 1 in an Al-Cr alloy solution for hot dip plating. After holding the workpiece for a certain period of time, remove the workpiece from the Al-Cr alloy solution and then quickly immerse it in an Al-Si alloy solution for hot dip plating. After holding the workpiece for a certain period of time, remove the workpiece from the Al-Si alloy solution, remove the excess hot dip plating solution on the surface of the workpiece, quench with water, dry it, and then perform high-temperature pre-oxidation treatment; thereby obtaining a Cr-modified Ti-Al-Si coating on the surface of the workpiece.

2. The method for preparing a Cr-modified Ti-Al-Si coating according to claim 1, characterized in that: The mass percentage of Cr in the Al-Cr alloy liquid in step 2 is 1wt.%-5wt.%; it is obtained by directly adding Al-Cr master alloy into high-purity aluminum liquid.

3. The method for preparing a Cr-modified Ti-Al-Si coating according to claim 1, characterized in that: The mass percentage of Si in the Al-Si alloy liquid in step 2 is 5wt.%-15wt.%; it is obtained by directly adding Al-Si master alloy into high-purity aluminum liquid.

4. The method for preparing a Cr-modified Ti-Al-Si coating according to claim 1, characterized in that: The first immersion in the Al-Cr alloy solution for hot dip plating in step 3 is at a temperature of 750-850°C and a hot dip plating time of 5-20 minutes; then the immersion in the Al-Si alloy solution for hot dip plating is at a temperature of 750-800°C and a secondary hot dip plating time of 5-20 minutes.

5. The method for preparing a Cr-modified Ti-Al-Si coating according to claim 1, characterized in that: In step 3, the workpiece is extracted from the Al-Cr alloy liquid and then quickly immersed in the Al-Si alloy liquid, and the process time is 3-5 seconds.

6. The method for preparing a Cr-modified Ti-Al-Si coating according to claim 1, characterized in that: In step 3, the temperature of the high-temperature pre-oxidation treatment is 800-850° C. and the time is 2-4 hours.

7. The method for preparing a Cr-modified Ti-Al-Si coating according to claim 1, characterized in that: The Cr-modified Ti-Al-Si coating described in step three is characterized in that a Ti-Al binary alloy phase layer, a Ti-Al / Ti-Si mixed phase layer, a Ti(Al,Si,Cr)3 phase layer, and an Al2O3 layer are formed in sequence from the substrate to the outside, and the total thickness of the Ti(Al,Si,Cr)3 phase layer is 40-150 microns.

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