A Ce-modified Ti-Al-Si coating and preparation method thereof

Abstract

The present invention discloses a Ce-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 Ti3Al phase layer, a TiAl phase layer, a TiAl2 phase layer, and a Ce-rich Al2O3+Ti(Al,Si)3 mixed phase 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 a high-purity Al melt pool, and then hot-dip plating in an Al‑Si‑Ce alloy melt pool. Then, the excess hot-dip plating liquid on the surface of the workpiece is extracted and discarded, and the workpiece is dried after water quenching, and then subjected to high-temperature pre-oxidation treatment. The method has a simple process, low cost, and easy control of 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 Ce-modified Ti-Al-Si coating and a preparation method thereof. Background Art

[0002] Titanium and its alloys are widely recognized as ideal replacements for steel, stainless steel, copper, and their alloys due to their excellent resistance to high and low temperatures, corrosion, heat, strong acids, strong alkalis, high strength, and low density. They are also known as the "all-round metal" in the metals kingdom and are considered the "third metal," "strategic metal," and "space metal" with great development prospects after iron and aluminum. They are widely used in various fields. Aviation manufacturing is inseparable from titanium. Titanium and its alloys are primarily used in aircraft engine manufacturing. Aircraft manufactured with titanium alloys not only extend their service life but also reduce their weight and significantly improve their flight performance. However, titanium alloys readily react with oxygen at high temperatures, causing secondary oxidation that damages the matrix. This leads to a "thermal barrier temperature" of 600°C, making it difficult to fully demonstrate their excellent mechanical properties at high temperatures, significantly limiting their application. To enable titanium alloys to operate at high temperatures and fully demonstrate their excellent mechanical properties, scientists have proposed a method to increase the operating temperature of titanium alloys: adding a protective coating to the titanium alloy surface to prevent oxidation. Since Al oxidizes to form stable Al2O3 at high temperature, which has excellent protective effect on the matrix, it was initially chosen to plate a protective Al layer on the surface of the titanium alloy, hoping to obtain TiAl3, and eventually form a dense Al2O3 film in the air. However, at high temperatures above 800°C, Al plating cannot effectively protect the titanium alloy matrix because multiple Ti-Al phase layers are generated. The thermal expansion coefficient of the phase layer does not match that of the substrate, which will cause through-cracks. Adding Si can reduce the number of transverse cracks, but Si reacts with the Ti matrix earlier than Al, resulting in the inability to form TiAl3. Therefore, Ti is first reacted with Al to form TiAl 3, Then let TiAl3 react with Si to eventually form a Ti(Al,Si)3 phase layer on the surface of the titanium alloy.

[0003] Studies have shown that after adding Ce to the Ti-Al-Si coating, Ce will react with atomic hydrogen to form a compound with a high melting point and stable chemical properties, which can effectively avoid hydrogen embrittlement and hydrogen corrosion. The atomic radius of Ce element is larger than that of Ti, Al, and Si. After adding Ce element, it is not easy to move in the lattice, but tends to react with oxygen to form CeO2, which is concentrated at the grain boundary or crack, effectively purifying the oxygen element in the tissue, avoiding tissue oxidation, and reducing the residual stress inside the titanium or titanium alloy matrix to a certain extent. Adding Ce can also effectively inhibit the τ2:Ti(Al x Si 1-x)2 phase is generated to form a continuous and dense Al2O3 layer, which further improves the oxidation resistance of the coating. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a Ce-modified Ti-Al-Si coating and a preparation method thereof in view of the deficiencies of the existing technology. The method adopts a method of first hot-dip plating high-purity Al and then hot-dip plating Al-Si-Ce to ensure that a TiAl3 phase layer is formed first, and then Si atoms are introduced to form a Ti(Al,Si)3 phase layer with excellent high-temperature oxidation resistance and a solid solution of a certain amount of Si atoms; then a high-temperature pre-oxidation treatment is performed to finally form a Ce-modified Ti-Al-Si coating of a Ti3Al phase layer, a TiAl phase layer, a TiAl2 phase layer, and a Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer on the surface of titanium or titanium alloy. The Ce-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 Ce-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. Melt pool 1 contains high-purity Al liquid, and melt pool 2 contains Al-Si-Ce alloy liquid.

[0008] Step 3: Immerse the titanium or titanium alloy workpiece prepared in step 1 in a high-purity Al solution for a primary hot-dip coating. After holding the workpiece for a certain period of time, remove the workpiece from the high-purity Al solution and quickly immerse it in an Al-Si-Ce alloy solution for a secondary hot-dip coating. After holding the workpiece for a certain period of time, remove the workpiece from the Al-Si-Ce alloy solution, remove the excess hot-dip coating solution from the workpiece surface, and quench with water. This results in a Ce-modified Ti-Al-Si coating on the workpiece surface.

[0009] A Ce-modified Ti-Al-Si coating and preparation method are disclosed. High-purity Al is hot-dip plated on titanium or a titanium alloy to preferentially form a TiAl3 phase layer on the surface. Si atoms are then introduced to form a Ti(Al,Si)3 phase layer with a certain amount of Si atoms dissolved therein, exhibiting excellent high-temperature oxidation resistance. Ultimately, a Ti3Al phase layer, a TiAl phase layer, a TiAl2 phase layer, and a Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer are sequentially formed on the surface of the titanium or titanium alloy workpiece. The Ce-modified Ti-Al-Si coating and preparation method of the present invention combine the controllability of a two-step hot-dip coating preparation method. The thickness of the Ti(Al,Si)3 phase layer is primarily controlled by controlling the temperature and time of the two hot-dip plating steps. The surface of the first hot-dip coating is protected from excessive oxidation by controlling the time it takes for the hot-dip plated workpiece to be rapidly immersed in the Al-Si-Ce alloy solution after being withdrawn from the high-purity Al solution. The resulting coating exhibits advantages such as good thermal stability, a simple preparation process, and low cost, significantly extending the service life of titanium or titanium alloy workpieces in high-temperature environments.

[0010] The Ce-modified Ti-Al-Si coating and preparation method are characterized in that, in step 3, the hot-dip plating temperature in a high-purity Al solution is 750-800°C for 5-15 minutes; and the hot-dip plating temperature in an Al-Si-Ce alloy solution is 750-800°C for 5-20 minutes. This hot-dip plating temperature range ensures that the target product after hot-dip plating is a Ti(Al,Si)3 phase, and the hot-dip plating time range controls the thickness of the Ti(Al,Si)3 phase layer, resulting in a Ti(Al,Si)3 phase layer thickness of 30-140 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 Ce-modified Ti-Al-Si coating and its preparation method.

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

[0014] The Ce-modified Ti-Al-Si coating can be designed according to actual usage requirements, and the thickness of the generated Ti(Al,Si)3 phase layer can be adjusted by controlling the temperature and time of the two hot-dip plating processes. By controlling the time it takes for the hot-dip plated workpiece to be quickly immersed in the Al-Si-Ce alloy solution after being withdrawn from the high-purity Al solution, the surface of the first hot-dip coating is ensured to be protected from excessive oxidation. Therefore, the Ce-modified Ti-Al-Si coating on the titanium or titanium alloy surface has good controllability.

[0015] like Figure 1 As shown in the figure, after completing the coating phase structure design, the Ce-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 chamber. High-purity Al liquid is added to melt pool 1. Ce is added to melt pool 2, which contains an Al-Si master alloy, to prepare an Al-Si-Ce alloy solution with Si content of 5 wt.% to 15 wt.% and Ce content of 0.5 wt.% to 3 wt.%.

[0018] Step 3: Set the temperature of melt pool 1 to 750-800°C, and set the temperature of melt pool 2 to 750-800°C. Immerse the workpiece in step 1 into high-purity Al liquid and keep it warm for 5-15 minutes. Then, under argon protection, extract the workpiece from the high-purity Al liquid and quickly transfer it to Al-Si-Ce alloy liquid for hot dip plating. After keeping it warm for 5-20 minutes, extract the sample from the Al-Si-Ce alloy liquid, remove the excess plating liquid on the surface of the sample, quench it with water, and dry it. Then, pre-oxidize it at 500°C for 1 hour and 850°C for 2 hours. Finally, a Ti3Al phase layer, a TiAl phase layer, a TiAl2 phase layer, and a Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer are formed on the surface of the titanium or titanium alloy workpiece in sequence. The total thickness of the Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer required above is 30-140 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 chamber. High-purity Al liquid is added to melt pool 1. Ce is added to melt pool 2 containing an Al-Si master alloy to prepare an Al-Si-Ce alloy solution with 10 wt.% Si and 1 wt.% Ce.

[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 in a 750°C high-purity Al solution for 15 minutes. Then, under argon protection, remove the Ti65 alloy sample from the high-purity Al solution and quickly transfer it to an Al-Si-Ce alloy solution for a second hot-dip plating. After 15 minutes of holding, remove the sample from the Al-Si-Ce alloy solution, remove excess plating solution from the surface of the sample, quench with water, and dry. Pre-oxidize the sample at 500°C for 1 hour and 850°C for 2 hours. Finally, a Ti3Al phase layer, a TiAl phase layer, a TiAl2 phase layer, and a Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer are formed on the surface of the Ti65 alloy sample in this order. The total thickness of the Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer is 106 microns.

Claims

1. A method for preparing a Ce-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 placed in a hot-dip plating box filled with argon gas. Melt pool 1 contains high-purity Al liquid, and melt pool 2 contains Al-Si-Ce alloy liquid. Step 3: Immerse the titanium or titanium alloy workpiece in step 1 in a high-purity Al solution for hot dip plating. After keeping the workpiece warm for a certain period of time, remove the workpiece from the high-purity Al solution and then quickly immerse it in an Al-Si-Ce alloy solution for hot dip plating. After keeping the workpiece warm for a certain period of time, remove the workpiece from the Al-Si-Ce 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 Ce-modified Ti-Al-Si coating on the surface of the workpiece.

2. The method for preparing a Ce-modified Ti-Al-Si coating according to claim 1, characterized in that: The mass percentage of Si in the Al-Si-Ce alloy liquid in step 2 is 5wt.%-15wt.%, and the mass percentage of Ce is 0.5wt.%-3wt.%. The Al-Si-Ce alloy liquid is obtained by directly adding Ce into the Al-Si master alloy.

3. The method for preparing a Ce-modified Ti-Al-Si coating according to claim 1, wherein: The temperature for hot-dip plating in the high-purity Al solution described in step 3 is 750-800°C, and the time for hot-dip plating is 5-15 minutes; the temperature for hot-dip plating in the Al-Si-Ce alloy solution is 750-800°C, and the time for hot-dip plating is 5-20 minutes.

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

5. The method for preparing a Ce-modified Ti-Al-Si coating according to claim 1, characterized in that: The process parameters of the high-temperature pre-oxidation treatment in step 3 are 500°C for 1-2 hours + 850°C for 2-3 hours.

6. The method for preparing a Ce-modified Ti-Al-Si coating according to claim 1, characterized in that: The Ce-modified Ti-Al-Si coating described in step three is characterized in that a Ti3Al phase layer, a TiAl phase layer, a TiAl2 phase layer, and a Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer are formed in sequence from the substrate to the outside, wherein the total thickness of the Ce-rich Al2O3+Ti(Al,Si)3 mixed phase layer is 30-140 microns.

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