CN1379000A - Process for preparing coated silicide layer on surface of silicon titanocarbide material - Google Patents

Abstract

The invention belongs to the surface engineering technology, specifically a method for preparing a silicide coating on the surface of a titanium silicon carbide (Ti ₃ SiC ₂ ) material. Composition of powder mixture, Ti ₃ SiC ₂ material is embedded with seepage material and then heat-diffused at 1000-1200°C for 2-8 hours. The obtained coating is composed of two phases of titanium disilicide (TiSi ₂ ) and silicon carbide (SiC), and the thickness is 10-60 microns. After the coating is oxidized in the air at 1000-1200°C, it mainly forms a SiO ₂ film, and the parabolic velocity constant of the constant temperature oxidation is 2-3 orders of magnitude lower than that of the Ti ₃ SiC ₂ material. The application of the present invention can make the Ti ₃ SiC ₂ material used in High temperature corrosive environment.

Description

A method for preparing silicide coating on the surface of titanium silicon carbide material

technical field

The invention belongs to surface engineering technology, in particular to a method for preparing a silicide coating on the surface of a titanium silicon carbide material.

Background technique

Titanium silicon carbide (Ti ₃ SiC ₂ ) is a structural/functional integrated material with excellent performance. It organically combines the plasticity, electrical conductivity, thermal conductivity, and ease of processing of metals with the high temperature resistance, thermal shock resistance, and high strength of ceramics. It has broad application prospects as high-temperature structural materials and electrodes for molten salt electrolysis, and is currently receiving great attention from researchers.

However, titanium silicon carbide (Ti ₃ SiC ₂ ) has poor high-temperature oxidation resistance above 1000°C. The reason is that although its material contains silicon, it cannot form a complete and continuous silicon dioxide film when oxidized. Constant temperature oxidation experiments at 900-1300°C and X-ray diffraction analysis show that a double-layer oxide film with an outer layer of titanium dioxide and an inner layer of a mixture of titanium dioxide and silicon dioxide is formed on the surface of titanium silicon carbide. Generally, only SiO ₂ and Al ₂ O ₃ have good oxidation protection performance above 1000°C. Therefore, as long as the silicon content on the surface of the material is increased, its oxidation resistance will be improved, and surface siliconization is a simple and effective way. Tamer El-Raghy and Michel W. Barsoum (Document: Tamer El-Raghy and Michel W.Barsoum, Diffusion kinetics of the carburization and silicidation of Ti ₃ SiC ₂ , J.Appl.Phys.83(1)(1998) 112-119 ) once sandwiched titanium silicon carbide material between two single crystal silicon wafers, applied a certain pressure to keep them in good contact, and then heat-treated it in vacuum at 1200-1350 ° C, and obtained silicide on the surface of titanium silicon carbide material coating. However, the above method can only deal with smooth surfaces, and needs to apply external force and be carried out in a vacuum, so the cost is high, the process is complicated, and the practicability is poor.

Contents of the invention

The object of the present invention is to provide a method for preparing a silicide coating on the surface of titanium silicon carbide (Ti ₃ SiC ₂ ) material, which has simple process, low cost, strong practicability and can effectively improve the high temperature oxidation resistance of titanium silicon carbide material .

In order to achieve the above object, the technical scheme of the present invention is: use the solid powder mixture formed by mixing silicon powder, aluminum oxide powder, potassium fluorosilicate and sodium fluoride as the infiltrating material, put the titanium silicon carbide material into the infiltrating material, Under the protection of an inert gas, at a heating rate of 20-40°C/min, at a temperature of 1000-1200°C, heat preservation for 2-8 hours, perform thermal diffusion treatment, and then cool to room temperature in the furnace, that is, 10-60 Micron-thick titanium disilicide and silicon carbide coatings;

The composition of the powder mixture in the present invention is calculated by weight percentage: silicon powder (Si) 25-80, alumina powder (Al ₂ O ₃ ) 15-70, potassium fluorosilicate (K ₂ SiF ₆ ) 0.5-3, fluorinated Sodium (NaF) 0.5-3; the silicon powder (Si) purity ≥ 99.00%, particle size ≤ 0.4 mm; alumina (Al ₂ O ₃ ) purity ≥ 99.00%, particle size ≤ 0.4 mm; potassium fluorosilicate (K ₂ SiF ₆ ) is analytically pure; sodium fluoride (NaF) is analytically pure; the inert gas is argon with a purity ≥ 99.99% or helium with a purity ≥ 99.99%.

The present invention has the following advantages:

1. The coating prepared by the present invention has excellent high-temperature oxidation resistance, and can significantly reduce the high-temperature oxidation rate of titanium silicon carbide. After constant temperature oxidation in air at 1200°C for 20 hours, the oxidation weight gain of Ti ₃ SiC ₂ reached 0.35kg/m ² , while the oxidation weight gain of the coating was only 0.022kg/m ² , which was reduced by 16 times. At 1100°C and 1200°C in air, the parabolic velocities of Ti ₃ SiC ₂ oxidation are 4.43×10 ^-7 and 1.81×10 ^-6 kg ² m ^-4 s ^-1 respectively, while the corresponding data of the coating are are 1.58×10 ^-9 and 5.15×10 ^-9 kg ² m ^-4 s ^-1 , which are reduced by 2 to 3 orders of magnitude. Cyclic oxidation experiments at 1100°C prove that the peeling resistance of the oxide film on the coating surface is also improved. The surface oxide film is mainly composed of SiO ₂ and contains a small amount of TiO ₂ .

2. The present invention adopts the mixture of solid silicon powder and other additives to embed the sample of titanium silicon carbide material, and obtain the silicide coating through high temperature thermal diffusion. The preparation process does not need to apply external force and is not carried out in a vacuum, so the method is simple and the cost is low.

3. The invention can be used to process smooth surfaces and actual workpieces with complex surfaces, and has a wide range of applications. The application of the invention can make Ti ₃ SiC ₂ materials used in high-temperature corrosive environments.

Description of drawings

Fig. 1 is the X-ray diffraction spectrum of the surface of Ti ₃ SiC ₂ of the present invention after siliconizing treatment.

Fig. 2 is a scanning electron micrograph of the silicide coating formed on the surface of Ti ₃ SiC ₂ of the present invention after siliconizing treatment.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1

The composition of the solid powder mixture of the present invention: silicon powder (Si) purity ≥ 99.00%, particle size ≤ 0.4 mm; aluminum oxide (Al ₂ O ₃ ) purity ≥ 99.00%, particle size ≤ 0.4 mm; potassium fluorosilicate (K ₂ SiF ₆ ) is analytically pure; sodium fluoride (NaF) is analytically pure;

The solid powder mixture is composed by weight percentage: 25-80% of silicon powder, 15-70% of aluminum oxide, 0.5-3% of potassium fluorosilicate, and 0.5-3% of sodium fluoride.

Embed the sample of titanium silicon carbide material in the material tank with seepage material, and then place the material tank in a system that can be vacuumed and filled with argon. %Ar), heated to 1000-1200°C at a heating rate of 20-40°C/min, kept for 2-8 hours and then naturally cooled to room temperature to complete the entire process of siliconizing, and obtain titanium disilicide (TiSi ₂ ) and The coating is composed of two phases of silicon carbide (SiC), and the thickness is 10-60 microns.

The specific data of this embodiment are: the size of the titanium silicon carbide sample is 10×5×2 mm, and the composition of the powder mixture is by weight percentage: 66% silicon, 33% aluminum oxide, 0.5% potassium fluorosilicate, 0.5% sodium fluoride, The total weight is 175g; the system is evacuated to 10Pa, and then filled with argon (99.99% Ar); heating temperature: 1100°C; heating rate: 35°C/min; holding time: 6 hours. The samples were taken out after the furnace was cooled to room temperature.

X-ray diffraction analysis shows that a coating composed of titanium disilicide (TiSi ₂ ) and silicon carbide (SiC) is formed on the surface of the titanium silicon carbide material after the above process, and the X-ray diffraction spectrum is shown in Figure 1. Observing the surface and cross-section with a scanning electron microscope confirmed that the surface of the infiltrated sample was smooth and black-gray; a complete, continuous and well-bonded coating was formed with a thickness of 50 microns, see Figure 2. By measuring the mass change of the sample after infiltration, the amount of infiltration was 21 mg/cm ² .

After applying the silicide coating, the parabolic velocity constant of the constant temperature oxidation of titanium silicon carbide in the air at 1100-1200 ° C is reduced by 2 to 3 orders of magnitude, reaching a complete anti-oxidation level. The cyclic oxidation experiment at 1100°C (oxidation for 1 hour followed by air cooling for 15 minutes is a cycle) proves that the peeling resistance of the oxide film on the coating surface is also improved.

Example 2

The difference from Example 1 is that the titanium silicon carbide material sample is 10 × 5 × 2 mm, and the composition of the powder mixture is by weight percentage: 35% silicon, 63% aluminum oxide, 1% potassium fluorosilicate, 1% sodium fluoride , with a total weight of 125g; heating temperature: 1050°C; holding time: 6 hours. The samples were taken out after the furnace was cooled to room temperature.

After testing, a 22-micron-thick coating composed of a mixture of titanium disilicide (TiSi ₂ ) and silicon carbide (SiC) was formed on the surface of the titanium silicon carbide material sample. The surface of the infiltrated oxygen product is smooth and dark gray. The cross-section observation shows that the coating is continuous and complete, and is well combined with the substrate.

The inert gas in the present invention is also helium with a purity ≥ 99.99%.

Claims (4)

1. method for preparing silicide coating at the silicon titanium-carbide material surface; it is characterized in that: the solid powder mixture that mixes with silica flour, aluminum oxide powder, potassium silicofluoride, Sodium Fluoride is a bleed; the silicon titanium-carbide material is embedded in the bleed; under protection of inert gas; with the heat-up rate of 20～40 ℃/min, under 1000～1200 ℃ of conditions, the insulation 2～8 hours; carry out heat diffusion treatment, stove is chilled to room temperature then, promptly forms titanium disilicide and coat of silicon carbide at sample surfaces.

2. in accordance with the method for claim 1, it is characterized in that: percentage meter by weight, described powdered mixture is formed by weight percentage: silica flour 25～80, aluminum oxide powder 15～70, potassium silicofluoride 0.5～3, Sodium Fluoride 0.5～3.

3. it is characterized in that in accordance with the method for claim 1: described silica flour purity 〉=99.00%, granularity≤0.4 millimeter; Aluminum oxide purity 〉=99.00%, granularity≤0.4 millimeter; Potassium silicofluoride is an analytical pure; Sodium Fluoride is an analytical pure.

4. it is characterized in that in accordance with the method for claim 1: described rare gas element is the argon gas of purity 〉=99.99% or the helium of purity 〉=99.99%.