CN112941458B - Chromium modified titanium and titanium alloy in-situ self-generated Ti-Al-Si gradient coating and preparation method thereof - Google Patents

Abstract

The invention discloses a chromium-modified titanium and titanium alloy in-situ self-generated Ti-Al-Si gradient coating and a preparation method thereof. The method comprises: 1. degreasing and cleaning the surface of titanium or titanium alloy; 2. configuring Al-Cr alloy hot-dip infiltration solution; 3. adopting a self-generated gradient hot-dipping method to form a chromium-modified Ti-Al-Si gradient coating with Ti(Al,Si) ₃ and Al-Si-Cr alloy layers on the surface of titanium or titanium alloy; Si) _3- layer, chromium-modified Ti-Al-Si gradient coating with dense α-Al-O _{3 -} layer containing SiO ₂ particles. _The present invention utilizes the chromium element to reduce the oxidation rate, so that _τ2 :Ti(Al, Si) ₂ phases change from block to island, reduce crack sources, and enhance the cohesiveness and compactness _{of the α-Al2O3 layer; the self-generated gradient hot infiltration method can prepare the Ti-Al-Si gradient coating with Ti(Al, Si)3 and Al-Si alloy layer; The principle and method of α-Al 2 O 3 layer containing SiO 2 particles to prepare titanium and} titanium alloy coatings with excellent mechanical properties and high temperature and hot corrosion resistance.

Description

A Chromium Modified Titanium and Titanium Alloy In Situ Self-Growing Ti-Al-Si Gradient Coating and Its Preparation method

technical field

The invention relates to the field of modification of titanium alloy surface coatings, which modifies traditional aluminum-based coatings and prepares an in-situ self-generated Ti-Al-Si gradient coating by adding chromium elements.

Background technique

The service temperature of high-temperature titanium alloy and titanium-aluminum intermetallic compound can reach 600~1000℃. However, due to the high oxygen solubility of titanium, dissolved oxygen embrittlement and surface oxidation are prone to occur under high temperature oxidation conditions, which seriously affect the thermal stability and service life of titanium alloys. Therefore, improving the high-temperature oxidation resistance of titanium alloys has become the key to expanding its application range.

Alloying can change the composition and structure of titanium alloys, thereby improving the morphology of the oxide film on its surface and improving its oxidation resistance at high temperatures. However, alloying can only improve the oxidation resistance of titanium alloys to a certain extent. On the one hand, with the increase of oxidation time and temperature, its protective ability will decrease significantly. Once a gap appears in the weak part of the oxide film, oxygen enters the titanium alloy substrate to form a titanium oxide film, which reduces the bonding strength with the substrate and causes the oxide film to peel off from the substrate. Second, ordered phases and brittle layers are formed on the surface of the substrate, causing lattice distortion and degrading the mechanical properties of the substrate. On the other hand, when a small amount of anti-oxidation alloy elements are added, the anti-oxidation effect is not obvious, and a large amount of addition will lead to a decrease in the mechanical properties of the alloy. Therefore, alloying is not an ideal method to improve the high temperature oxidation resistance of titanium alloys. In order to effectively protect titanium alloys from high temperature for a long time, applying a suitable high temperature protective coating is currently the only option.

Traditional high-temperature protective coatings on titanium surfaces are usually prepared by thermal diffusion aluminizing. High-temperature diffusion aluminizing of titanium alloys can form a coating rich in TiAl ₃ on the surface of titanium alloys. Among all Ti-Al intermetallic compounds, only TiAl ₃ can form Al ₂ O ₃ films during oxidation, which is the key component of its anti-oxidation. However, the traditional aluminum-based coating is brittle and prone to transverse cracks, and its actual performance is not high. Studies have shown that the addition of Si element can effectively reduce the number of cracks in the coating, and the Al-Si layer is less brittle, and it is more tightly combined with the substrate and is not easy to fall off.

In order to further improve the high temperature performance of the aluminized coating, binary co-infiltration can be carried out. According to the data, the Cr-modified aluminized coating can form a ternary Ti-Al-Cr phase with a plastic L1 ₂ crystal structure on the surface of the titanium alloy, avoiding the brittle Ti Al ₃ phase formed during the unit aluminizing process, thus showing excellent resistance to cyclic oxidation. Nishimoto and Narita used a two-step method to infiltrate Cr first and then Al on the surface of Ti-Al alloy. After high-temperature diffusion, a Ti-Al-Cr coating was formed. During the oxidation process, a protective α-Al ₂ O ₃ film was formed on the surface of the coating, which significantly improved the oxidation resistance of the base alloy.

Contents of the invention

The present invention adopts the method of in-situ self-generated component gradient thermal infiltration, and the purpose is to increase the thickness of the dense layer in the Ti-Al-Si gradient coating, so that the τ2 :Ti(Al, Si) ₂ phase changes from block to island, reducing the source of cracks; reducing its oxidation rate _, and improving the high-temperature oxidation resistance of the coating.

The invention provides a chromium-modified titanium and titanium alloy in-situ self-generated Ti-Al-Si gradient coating and a preparation method thereof, the preparation method comprising the following steps:

Step 1. Use a metal cleaning agent to degrease and clean the titanium or titanium alloy surface, and dry it;

Step 2, melting the Al-Cr master alloy into the high-purity aluminum liquid, and configuring the Al-Cr hot-dip infiltration solution;

Step 3. Prepare a chromium-modified Ti-Al-Si gradient coating by using the in-situ self-generated gradient hot-dipping method, pour the Al-Cr hot-dip infiltration solution in step 2 into a high-purity quartz vessel, and keep the high-temperature melt state, immerse the titanium or titanium alloy in the Al-Cr hot-dip infiltration solution, soak for a certain period of time, quickly extract it, and water quench to form a chromium-modified Ti-Al-Si gradient coating with Ti(Al,Si) ₃ and Al-Si-Cr alloy layers on the surface;

Step 4: Put the titanium or titanium alloy with the chromium-modified Ti-Al-Si gradient coating into a high-temperature furnace for pre-oxidation, and finally form a chromium-modified Ti-Al-Si gradient coating with a dense continuous TiAl alloy layer, a Ti(Al,Si) ₃ layer with high fracture toughness, and a dense α-Al ₂ O ₃ layer containing SiO ₂ particles.

Compared with the prior art, the present invention has the following advantages:

1. Using the in-situ self-generated component gradient hot infiltration method, the chromium-modified in-situ self-generated Ti-Al-Si gradient coating is obtained on the surface of the workpiece, so that the τ ₂ :Ti(Al,Si) ₂ phase is transformed from a block to an island shape, reducing the source of cracks, increasing the key component of Ti(Al,Si) ₃ , thereby improving the high-temperature oxidation resistance of the coating.

2. By controlling the in-situ self-generated component gradient thermal impregnation time, the required coating thickness can be obtained on the surface of the workpiece according to the actual situation. In actual use, the utility model has high flexibility and is easy to operate.

3. The steps of the present invention are simple, and the obtained coating has good oxidation resistance at high temperature and is tightly combined with the substrate, providing a new and effective protection method for titanium alloys in high-temperature working environments.

Description of drawings

Fig. 1 is a flow chart of the preparation of chromium-modified titanium and titanium alloy in-situ self-generated Ti-Al-Si gradient coating of the present invention.

Fig. 2 is the microstructure topography diagram of chromium-free Ti-Al-Si gradient coating.

Fig. 3 is the microstructure morphology diagram of the chromium-modified Ti-Al-Si gradient coating.

Detailed ways

It can be seen from Figure 1 that the chromium-modified in-situ self-generated Ti-Al-Si gradient coating was prepared on the surface of the titanium alloy by adding the modifying element Cr through the in-situ self-generated component gradient hot infiltration method.

Example one

Step 1. Use a metal cleaning agent to degrease and clean the titanium or titanium alloy surface, and dry it;

Step 2: Melting the Al-Cr master alloy into the high-purity aluminum liquid to configure the Al-Cr hot-dip infiltration solution; the weight percentage of the added chromium is 3wt.%.

Step 3: Prepare chromium-modified Ti-Al-Si gradient coating by self-generated gradient hot-dip infiltration method, pour the Al-Cr hot-dipping melt solution in step 2 into a high-purity quartz vessel, keep the high-temperature melt state, immerse titanium or titanium alloy in the Al-Cr hot-dipping melt solution, soak for a certain period of time, quickly extract it, and water quench to form a chromium-modified Ti-Al-Si gradient coating with Ti(Al,Si) ₃ and Al-Si-Cr alloy layer on the surface; The time is 20 minutes.

Step 4. Put the titanium or titanium alloy with the chromium-modified Ti-Al-Si gradient coating into a high-temperature furnace for pre-oxidation, and finally form a chromium-modified Ti-Al-Si gradient coating with a dense continuous TiAl alloy layer, a Ti(Al _, Si) ₃ layer with high fracture toughness, and a dense α-Al ₂ O ₃ layer containing SiO ₂ particles; the pre-oxidation temperature is 800 ° C, and the pre-oxidation time is 30 minutes. The average thickness of the layers _was 19.4 microns, and the average thickness of the α-Al ₂ O ₃ layer containing SiO ₂ particles was 22.5 microns.

Example two

Step 1. Use a metal cleaning agent to degrease and clean the titanium or titanium alloy surface, and dry it;

Step 2: Melting the Al-Cr master alloy into the high-purity aluminum liquid to configure the Al-Cr hot-dip infiltration solution; the weight percentage of the added chromium is 3wt.%.

Step 3: Prepare chromium-modified Ti-Al-Si gradient coating by self-generated gradient hot-dip infiltration method, pour the Al-Cr hot-dipping melt solution in step 2 into a high-purity quartz vessel, keep the high-temperature melt state, immerse titanium or titanium alloy in the Al-Cr hot-dipping melt solution, soak for a certain period of time, quickly extract it, and water quench to form a chromium-modified Ti-Al-Si gradient coating with Ti(Al,Si) ₃ and Al-Si-Cr alloy layer on the surface; The time is 30 minutes.

Step 4. Put the titanium or titanium alloy with chromium-modified Ti-Al-Si gradient coating into a high-temperature furnace for pre-oxidation, and finally form a chromium-modified Ti-Al-Si gradient coating with dense continuous TiAl alloy layer, high fracture toughness Ti(Al,Si) ₃ layers, and dense α-Al ₂ O ₃ layers containing SiO ₂ particles; the pre-oxidation temperature _is 800 ° C, and the pre-oxidation time is 40 minutes. The thickness is 19.9 μm, and the average thickness of the α-Al ₂ O ₃ layer containing SiO ₂ particles is 28.5 μm.

Example three

Step 1. Use a metal cleaning agent to degrease and clean the titanium or titanium alloy surface, and dry it;

Step 2: Melting the Al-Cr master alloy into the high-purity aluminum liquid to configure the Al-Cr hot-dip infiltration solution; the weight percentage of the added chromium is 3wt.%.

Step 3: Prepare chromium-modified Ti-Al-Si gradient coating by self-generated gradient hot-dip infiltration method, pour the Al-Cr hot-dipping melt solution in step 2 into a high-purity quartz vessel, keep the high-temperature melt state, immerse titanium or titanium alloy in the Al-Cr hot-dipping melt solution, soak for a certain period of time, quickly extract it, and water quench to form a chromium-modified Ti-Al-Si gradient coating with Ti(Al,Si) ₃ and Al-Si-Cr alloy layer on the surface; The time is 40 minutes.

Step 4. Put the titanium or titanium alloy with chromium-modified Ti-Al-Si gradient coating into a high-temperature furnace for pre-oxidation, and finally form a chromium-modified Ti-Al-Si gradient coating with a dense continuous TiAl alloy layer, a _high fracture toughness Ti(Al,Si) ₃ layer, and a dense α-Al ₂ O ₃ layer containing SiO ₂ particles; the pre-oxidation temperature is 800 ° C, and the pre-oxidation time is 40 minutes. The thickness is 16.5 μm, and the average thickness of the α-Al ₂ O ₃ layer containing SiO ₂ particles is 21.3 μm.

Claims (2)

1. a kind of preparation method of chromium-modified titanium and titanium alloy in situ self-generated Ti-Al-Si gradient coating, it is characterized in that, the method comprises the following steps: Step 1. Use a metal cleaning agent to degrease and clean the titanium or titanium alloy surface, and dry it; Step 2, melting the Al-Cr master alloy into the high-purity aluminum liquid, adding 3 wt.% of chromium, and configuring the Al-Cr hot dip infiltration solution; Step 3. Prepare chromium-modified Ti-Al-Si gradient coating by in-situ self-generated gradient hot-dip infiltration method. Pour the Al-Cr hot-dip infiltration solution in step 2 into a high-purity quartz vessel to keep the high-temperature melt state. Immerse titanium or titanium alloy in the Al-Cr hot-dip infiltration solution. The hot-dip infiltration temperature is 900°C-950°C, and the hot-dip infiltration time is 20-40 minutes. Pull out quickly and quench in water to form a layer of Ti(Al,Si) ₃ and Al-Si-Cr alloy on the surface. Chromium modified Ti-Al-Si gradient coating; Step 4: Put the titanium or titanium alloy with the chromium-modified Ti-Al-Si gradient coating into a high-temperature furnace for pre-oxidation, and finally form a chromium-modified Ti-Al-Si gradient coating with a dense continuous TiAl alloy layer, a Ti(Al,Si) ₃ layer with high fracture toughness, and a dense α-Al ₂ O ₃ layer containing SiO ₂ particles. 2. A method for preparing a chromium-modified titanium and titanium alloy in-situ self-generated Ti-Al-Si gradient coating according to claim 1, characterized in that: in step 4, the pre-oxidation temperature is 800-850° C., and the pre-oxidation time is 30-60 minutes.