CN107630184A - A kind of method for preparing niobium silicide coating in niobium or niobium alloy surface - Google Patents

Abstract

The invention relates to a method for preparing niobium silicide coating on the surface of niobium or niobium alloy. Using silicon powder as raw material, a silicon coating is prepared on the surface of niobium or niobium alloy substrate by using plasma spraying technology, and then placed in an inert atmosphere at 1000 Heat treatment at ~1500°C for 1-10 hours to form a niobium silicide coating on the surface of the substrate. The preparation method of the invention has the advantages of simple process, low cost, high efficiency, good repeatability, suitable for large-scale production, etc., and has broad application prospects.

Description

A method for preparing niobium silicide coating on the surface of niobium or niobium alloy

technical field

The invention relates to a method for preparing a silicide coating, in particular to a method for preparing a niobium silicide coating with a gradient structure on the surface of niobium or a niobium alloy, and belongs to the technical field of high-temperature coatings.

Background technique

Niobium (Nb) is a refractory metal with a high melting point (2468°C), moderate density, corrosion resistance, radiation resistance, high temperature strength and good high temperature mechanical properties. The excellent properties of niobium and niobium alloys make it one of the important candidate materials for high-temperature structural parts in the aviation, aerospace and nuclear industries, and can be used to manufacture key components such as rocket engines and nuclear reactors. However, its oxidation performance is poor. Pure niobium has a "pest" oxidation phenomenon at 600 °C, and as the temperature increases, the degree of oxidation intensifies, which eventually leads to the failure of its high-temperature performance. This shortcoming seriously restricts niobium and niobium. alloy application. In order to improve its high-temperature oxidation resistance, surface coating protection is an effective way to balance the high-temperature mechanical properties and oxidation resistance of niobium and niobium alloys.

When niobium disilicide (NbSi ₂ ) is oxidized, a SiO ₂ oxide film can be formed on the surface. The oxide film is dense and self-healing, and has good high-temperature oxidation resistance, making NbSi ₂ the best choice for high-temperature protective coatings of niobium and niobium alloys. main choice. Suzuki et al. used molten salt method to deposit a layer of NbSi ₂ coating on the surface of niobium substrate【1.R.Suzuki, M.Ishikawa, K.Ono, NbSi ₂ coating on niobium using molten salt, Journal of Alloys and Compounds 336(2002) 280–285], put the molten salt mixture 36.58NaCl-36.58KCl-21.95NaF-4.89Na ₂ SiF ₆ (mol%) and silicon powder into the Al ₂ O ₃ crucible, and at a high temperature of 900K, the surface of the Nb substrate formed silicide The niobium coating has the structural characteristics that the outer layer is NbSi ₂ , and the transition layer is pentaniobium trisilicide (Nb ₅ Si ₃ ). However, the molten salt system is complex, and the coating structure is greatly affected by the molten salt composition, and the thickness of the formed coating is uneven, which affects the oxidation resistance of the coating to a certain extent. Wang et al prepared a Ge-modified NbSi ₂ coating by wrapping niobium alloy in 16Si-8Ge-5NaF-71Al ₂ O ₃ (wt.%) mixed powder by embedding method [2.W.Wang, Formation and oxidation resistance of germanium modified silicide coating on Nb based in situ composites, Corrosion Science 80(2014) 164–168], but the thermal conductivity of the powder mixture in the embedding method is poor, and this method is affected by gravity, which will cause the coating thickness and structure to vary. uniform. The preparation method of _NbSi2 coating needs to be further improved.

Contents of the invention

At the problems referred to above, the object of the present invention is to provide a method for preparing niobium silicide coating on the surface of niobium or niobium alloy, using silicon powder as raw material, adopting plasma spraying technology to prepare silicon coating on the surface of niobium or niobium alloy substrate, and then placing Heat treatment at 1000-1500° C. for 1-10 hours in an inert atmosphere to form a niobium silicide coating on the surface of the substrate.

The invention adopts the method of combining plasma spraying and heat treatment to prepare the niobium silicide coating. Specifically, using metal niobium or niobium alloy as the substrate and silicon powder as the raw material for spraying, a silicon coating with a certain thickness is prepared by plasma spraying technology, and then undergoes heat treatment in an inert atmosphere (heat treatment at 1000-1500°C for 1-10 hours) , that is, element diffusion reaction), so that the Nb element in the substrate and the Si element in the silicon coating undergo interdiffusion to form a niobium silicide coating, which has a gradient structure of NbSi ₂ outer layer and Nb ₅ Si ₃ transition layer. The niobium silicide coating obtained by the preparation method has a compact structure and uniform thickness, and at the same time forms a firm chemical metallurgical bond with the substrate. In addition, plasma spraying technology is a commonly used method for preparing coatings. It has the characteristics of high deposition efficiency, controllable coating composition and thickness, quick repair of failed coatings, and easy realization of industrial production, making it more commercial in coating preparation. potential. The invention also has the advantages of simple process, low cost, high efficiency, good repeatability, controllable coating thickness, suitable for large-scale production and the like.

Preferably, the silicon powder has a particle size of 10-120 μm and a purity greater than 98wt.%.

Preferably, the surface of the niobium or niobium alloy substrate is pre-treated by sand blasting, and the pressure of the sand blast pre-treatment is 0.1-0.5 MPa.

Preferably, the process parameters of the plasma spraying technology include: plasma gas Ar: 30-50 slpm; plasma gas H ₂ : 6-15 slpm; powder carrier gas Ar: 2-7 slpm; spraying distance: 100-200 mm; Spraying power: 30~50kW; powder feeding rate: 10~30rpm.

Preferably, the silicon coating has a thickness of 30-300 μm.

Preferably, the inert atmosphere is argon.

In another aspect, the present invention provides a niobium silicide coating prepared on the surface of a substrate according to the above method, comprising an outer layer of NbSi ₂ and a transition layer of Nb ₅ Si ₃ between the substrate and the outer layer of NbSi ₂ . Preferably, the thickness of the Nb ₅ Si ₃ transition layer is 5-30 μm. Preferably, the thickness of the outer layer of NbSi ₂ is 20-100 μm.

Beneficial effects of the present invention:

(1) The niobium silicide coating obtained in this invention has a gradient structure of NbSi ₂ outer layer and Nb ₅ Si ₃ transition layer, forming a firm chemical metallurgical bond with the substrate, reducing the thermal expansion coefficient of the surface coating and the Nb substrate mismatch problem;

(2) Since the thickness of the silicon coating can be precisely controlled, that is, the amount of the silicon source can be precisely controlled, so it is easier to control the thickness of the niobium silicide coating, there is no residual silicon, the surface is difficult to clean, etc., and the surface of the component can be realized Preparation of niobium silicide coatings in localized areas;

(3) The preparation method has the advantages of simple process, low cost, high efficiency, good repeatability, suitable for large-scale production, etc., and has broad application prospects.

Description of drawings

Fig. 1 is the XRD spectrum of plasma sprayed silicon coating in embodiment 1, shows that plasma sprayed silicon coating is mainly made up of Si of cubic phase;

Figure 2 is the XRD spectrum of the silicon coating on the surface of the Nb substrate in Example 1 after argon-protected heat treatment, the heat treatment temperature is 1300 ° C, and the time is 3 hours, indicating that the silicon coating and the Nb substrate have a diffusion reaction to form a hexagonal phase NbSi ₂ and hexagonal phase Nb ₅ Si ₃ , in which NbSi ₂ is the main one;

Fig. 3 is the cross-sectional morphology and element surface scanning pattern of the silicon coating on the surface of the Nb substrate in Example 1 after argon protection heat treatment. The heat treatment temperature is 1300 ° C and the time is 3 hours; Elements undergo interdiffusion reaction to form niobium silicide coating. The outer layer is NbSi ₂ , and the transition layer is Nb ₅ Si ₃ . The coating has a dense structure and forms a good metallurgical bond with the substrate.

detailed description

The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

The invention adopts the method of combining plasma spraying technology and heat treatment to prepare niobium silicide coating on the surface of niobium or niobium alloy, thereby improving the high-temperature oxidation resistance of niobium or niobium alloy. The niobium silicide coating includes an outer layer of NbSi ₂ and a transition layer of Nb ₅ Si ₃ between the substrate and the outer layer of NbSi ₂ . The thickness of the Nb ₅ Si ₃ transition layer may be 5-30 μm. The thickness of the NbSi ₂ outer layer may be 20-100 μm. The invention has the advantages of simple process, low cost, high efficiency, good repeatability, controllable coating thickness, suitable for large-scale production and the like.

The present invention selects silicon powder with a certain particle size distribution and purity, uses plasma spraying technology to prepare a certain thickness of silicon coating on the surface of metal niobium or niobium alloy, and then puts the sample with silicon coating into a high-temperature atmosphere furnace for heat treatment , to obtain a niobium silicide coating that is metallurgically bonded to the substrate. The method for preparing a niobium silicide coating on the surface of niobium or niobium alloy provided by the present invention is exemplarily described below.

Grit blasting pretreatment of the substrate. The substrate can be metal niobium or niobium alloy, and has been pretreated by surface sandblasting and the like. As an example, after blasting metal niobium or niobium alloy (blasting pressure is 0.1-0.5MPa), ultrasonically 1-2 times in alcohol solution, 3-5 minutes each time, and dry at 100-120°C 1 to 2 hours, set aside.

Preparation of silicon coating. Specifically, silicon powder with a certain particle size distribution is selected, and the silicon powder is sprayed onto the surface of sandblasted niobium or niobium alloy by plasma spraying technology to form a silicon coating. The selected powder for spraying is silicon powder with a particle size of 10-120 μm, and the purity of the powder is greater than 98wt.%. Dry at 100-120°C for 1-3 hours and set aside. Among them, the process parameters of plasma spraying technology can include: plasma gas Ar: 30~50slpm; plasma gas _H2 : 6~15slpm; powder carrier gas Ar: 2~7slpm; spraying distance: 100~200mm; spraying power: 30 ~50kW; powder feeding rate: 10~30rpm. In the invention, by controlling the process parameters of the plasma spraying technology, the silicon powder is sprayed on the surface of the niobium or niobium alloy substrate to form a silicon coating with a thickness of 30-300 μm.

The substrate sprayed with the silicon coating is placed in an inert protective atmosphere furnace for heat treatment to form a niobium silicide coating metallurgically combined with the substrate. Wherein, the heat treatment temperature may be 1000-1500° C., and the heat treatment time may be 1-10 hours. The inert atmosphere may be argon.

As an example of a method for preparing a niobium silicide coating on the surface of niobium or niobium alloy, the specific process is as follows: 1) The substrate is niobium or niobium alloy, and the surface of the substrate is treated by sandblasting (sandblasting pressure is 0.1-0.5MPa) , Ultrasound 1-2 times in alcohol solution, 3-5 minutes each time, dry at 100-120°C for 1-2 hours, and set aside. 2) The selected powder is silicon powder with a particle size of 10-120 μm, and the purity of the powder is greater than 98wt.%. Dry at 100-120°C for 1-3 hours and set aside. 3) Spraying silicon powder on the surface of niobium or niobium alloy by plasma spraying technology to prepare a silicon coating, the thickness of the silicon coating is 30-300 μm. The spraying process parameters are shown in Table 1. 4) Place the sprayed silicon coating in an argon protective atmosphere furnace for heat treatment. The heat treatment temperature is 1000-1500 °C, and the heat treatment time is 1-10 hours;

Table 1 is the vacuum plasma spraying Si coating process parameters:

Plasma gas Ar 30～50slpm Powder carrier gas Ar 2～7slpm Plasma gas H ₂ 6～15slpm Spray distance 100～200mm Spraying power 30～50kW Powder feeding rate 10～30rpm

*slpm: standard liter/minute; rpm: revolution/minute.

The niobium silicide coating provided by the invention has the structural feature that the outer layer is NbSi ₂ and the transition layer is Nb ₅ Si ₃ , and forms a strong chemical metallurgical bond with the substrate.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Example 1:

A niobium silicide coating on a niobium metal surface, the preparation of which comprises the steps of:

1) Sandblasting the surface of the Nb substrate with a sandblasting pressure of 0.4 MPa, ultrasonicating twice in absolute ethanol solution for 5 minutes each time, drying at 100°C for 2 hours, and set aside;

2) Use silicon powder with a median particle size of about 30 μm and a purity greater than 98wt.% as the raw material for spraying, dry at 100°C for 3 hours, and set aside;

3) Using a plasma spraying system (A-2000, Sulzer Metco AG, Switzerland), select the process parameters in Table 2, spray silicon powder onto the surface of the Nb substrate to form a silicon coating, the thickness of the silicon coating is about 110 μm, as shown in Figure 1 XRD results show that the silicon coating is a cubic phase;

Table 2 is the plasma spraying Si coating process parameters:

4) Vacuum-atmosphere sintering furnace (ZT-50-22, Shanghai Chenhua Electric Furnace Co., Ltd.) protected by argon gas, through heat treatment, the diffusion reaction between the silicon coating and the Nb substrate forms a niobium silicide coating, and the heat treatment temperature is 1300°C, heat treatment time is 3h.

After argon protection heat treatment, a coating system with a certain gradient is formed between the silicon coating and the Nb substrate, from outside to inside, NbSi ₂ (thickness is about 50 μm), Nb ₅ Si ₃ (thickness is about 5 μm) and Nb matrix. A good metallurgical bond is formed between the coating and the substrate due to diffusion, without cracks and pores, as shown in the XRD spectrum of Figure 2 and the cross-sectional morphology and element surface scanning spectrum of Figure 3 (a in Figure 3 is shown in the box in the cross-sectional view Enlarged view, b is the surface scan spectrum of Nb element, c is the surface scan spectrum of Si element).

Claims (9)

1. A kind of 1. method for preparing niobium silicide coating in niobium or niobium alloy surface, it is characterised in that using silica flour as raw material, using etc. Ionomer spray technology prepares silicon coating in niobium or niobium alloy matrix surface, is subsequently placed in inert atmosphere at 1000~1500 DEG C Lower heat treatment 1~10 hour, so as to form niobium silicide coating in matrix surface.
2. 2. according to the method for claim 1, it is characterised in that the particle diameter of the silica flour is 10~120 μm, and purity is more than 98 wt.%。
3. 3. method according to claim 1 or 2, it is characterised in that described matrix pre-processes by surface sand-blasting, the spray The pressure of sand pretreatment is 0.1~0.5 MPa.
4. 4. according to the method any one of claim 1-3, it is characterised in that the technique of the plasma spray technology Parameter includes：Plasma gas Ar：30~50 slpm；Plasma gas H₂：6~15 slpm；Powder carrier gas Ar：2~7 slpm；Spray distance：100~200 mm；Spray power：30~50 kW；Powder feeding rate：10~30 rpm.
5. 5. according to the method any one of claim 1-4, it is characterised in that the thickness of the silicon coating is 30~300 μm。
6. 6. according to the method any one of claim 1-5, it is characterised in that the inert atmosphere is argon gas.
7. 7. the niobium silicide coating that a kind of method according to any one of claim 1-6 is prepared in matrix surface, including NbSi₂ Outer layer and positioned at described matrix and NbSi₂Nb between outer layer₅Si₃Transition zone.
8. 8. niobium silicide coating according to claim 7, it is characterised in that the Nb₅Si₃The thickness of transition zone is 5~30 μ m。
9. 9. the niobium silicide coating according to claim 7 or 8, it is characterised in that the NbSi₂The thickness of outer layer is 20~100 μm。