Tantalum-tungsten alloy surface high-temperature anti-oxidation composite coating and preparation method thereof

Abstract

The invention relates to the field of high-temperature anti-oxidation coatings, in particular to a tantalum-tungsten alloy surface high-temperature anti-oxidation composite coating and a preparation method thereof.The coating is composed of two layers of coatings with different components, the thermal expansion coefficients of the coatings and a base body are matched, the thermal expansion coefficients of the coatings are matched, and residual stress and thermal stress are reduced. The coating is prepared by adopting an embedding boriding and slurry melting method, and the used material components comprise ZrB2, MoSi2, 8YSZ, B, La2O3, Al2O3, NaF, TaSi2 and the like. The preparation method specifically comprises the following steps: putting a substrate into embedding powder for boronizing treatment, then mixing a coating material with ethanol and a binder, putting the mixture into a ball mill for wet mixing to prepare coating slurry, spraying the coating slurry on the surface of the substrate, and putting the substrate into a vacuum tube furnace for sintering to prepare a coating, thereby obtaining the high-temperature anti-oxidation composite coating. The binding force between the developed coating and the tantalum-tungsten alloy matrix is strong, and the tantalum-tungsten alloy matrix can be protected from oxidation corrosion or the oxidation rate can be slowed down within 500-2500s at the high temperature (2000 DEG C or above).

Description

Technical Field

[0001] The present invention relates to the field of high-temperature anti-oxidation coatings, and in particular to a high-temperature anti-oxidation composite coating on the surface of a tantalum-tungsten alloy and a preparation method thereof. Background Art

[0002] Tantalum-tungsten alloy has a melting point of up to 3080°C and exhibits excellent high-temperature strength, wear resistance, and creep resistance under high-temperature conditions. For this reason, tantalum-tungsten alloy is highly sought after in the aerospace industry. It is not only an ideal material for missile warheads, but also suitable for many hot components in hypersonic wind tunnel systems, such as the stem, valve core, cylinder, and support plate of rapid-seal valves.

[0003] However, this alloy has an insurmountable flaw in an atmospheric environment at 500°C – it reacts with oxygen, resulting in a “pest” oxidation phenomenon. As the temperature continues to rise, the integrity of the alloy is completely destroyed, and it eventually completely pulverizes. This pulverization due to oxidation greatly limits the service life and application range of tantalum-tungsten alloys. Currently, there are two main methods to improve the oxidation resistance of tantalum-tungsten alloys: one is alloying protection, but this method will cause other properties of the alloy to be affected to a certain extent; the other is surface coating. In comparison, the advantage of the coating method is that it does not change the composition of the alloy matrix, thereby preserving the alloy's high-temperature mechanical properties to the greatest extent possible.

[0004] Judging from the current research status at home and abroad, research on high-temperature protective coatings on the surface of tantalum-tungsten alloys is mostly concentrated in application scenarios below 2000°C, while research on protective coatings above 2000°C is almost blank. In addition, some tantalum-based alloy components sometimes even need to operate for a short time in a high-temperature environment of 2300°C. At the same time, these components need to withstand higher allowable stresses at high temperatures to ensure that they can operate safely and reliably under high temperature and high pressure conditions. Therefore, improving the high-temperature oxidation resistance and thermal shock resistance of tantalum-based alloys in high-temperature environments above 2000°C is of vital importance to promoting their widespread application in high-temperature fields. Summary of the Invention

[0005] The present invention relates to a high-temperature anti-oxidation composite coating on the surface of a tantalum-tungsten alloy and a preparation method thereof. The coating comprises an inner diffusion barrier layer and an outer anti-oxidation layer. The presence of the diffusion barrier layer reduces the inward diffusion flux of silicon elements and reduces the occurrence of silicon-poor areas, thereby protecting the tantalum-tungsten alloy substrate from oxidative corrosion or slowing down the oxidation rate at high temperatures for a short period of time.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy, comprising the following raw materials: a first coating material and a second coating material stacked in sequence;

[0008] The composition of the first coating material is as follows: B powder is 25-35wt%, Al2O3 is 50-65wt%, NaF is 10-20wt%, and the balance is La2O3;

[0009] The composition of the second coating material is: ZrB2 40-50wt%, MoSi2 30-40wt%, TaSi2 7-14wt%, and the balance is 8YSZ;

[0010] The present invention provides a method for preparing a high-temperature anti-oxidation composite coating on the surface of a tantalum-tungsten alloy, comprising the following steps:

[0011] (1) placing the first coating material in a ball mill for ball milling, and then placing it in an oven for drying after the ball milling to prepare a first layer coating embedding powder;

[0012] (2) placing the substrate into a crucible, filling it with the first coating embedding powder prepared in step (1), and then placing it into a vacuum tube furnace for sintering at a sintering temperature of 1050°C to 1200°C for 1 to 3 hours. During the sintering process, high-purity argon gas is continuously introduced. The heating rate is 10°C / min before 1000°C, and the heating rate is reduced to 5°C / min after the temperature exceeds 1000°C. After the heating is completed, the substrate is cooled in the furnace, thereby obtaining the first diffusion barrier layer;

[0013] (3) mixing the second coating material with ethanol and a binder, and placing the mixture in a ball mill for wet mixing to prepare a second coating slurry;

[0014] (4) spraying the second coating slurry obtained in step (3) onto the surface of the substrate having the first diffusion barrier layer, placing the sprayed substrate in an oven for drying and then gently placing it on a corundum sheet, and then placing it in a vacuum tube furnace for sintering. When the temperature rises to 600-700°C, keep it warm for 2 hours. The final sintering temperature is 1300-1450°C, and keep it warm for 60-90 minutes. During the sintering process, when the temperature is below 1000°C, the vacuum gauge pressure in the vacuum tube furnace is less than 0.1 Pa. After the temperature exceeds 1000°C, high-purity argon gas is introduced. The heating rate before 1000°C is 10°C / min, and the heating rate after the temperature exceeds 1000°C is reduced to 5°C / min. After the heating is completed, the furnace is cooled to form the second layer of anti-oxidation coating;

[0015] More preferably, the particle size of the ZrB2 powder, MoSi2 powder, 8YSZ powder, B powder, La2O3 powder, Al2O3 powder, NaF powder, and TaSi2 powder is less than 50 μm, and the purity is greater than 99.9%.

[0016] More preferably, the binder added in step (3) is 0.8-1.2 wt% of polyvinyl butyral (PVB).

[0017] More preferably, the substrate in step (2) and step (4) is tantalum-tungsten alloy.

[0018] More preferably, the ball milling process parameters of step (1) and step (3) are 350 r / min and the milling time is 3 to 5 hours.

[0019] More preferably, the drying time in the oven in step (1) and step (4) is 30 to 60 minutes.

[0020] More preferably, the total thickness of the high-temperature anti-oxidation composite coating finally prepared on the surface of the substrate in step (4) is 160 μm to 200 μm.

[0021] More preferably, in step (4), a pneumatic spray gun is used as the coating spraying tool.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The coating prepared by the present invention is composed of two layers of coatings with different compositions, the inner and outer layers, which effectively alleviate the mismatch of thermal expansion coefficients between the coating and the alloy, reduce residual stress and thermal stress, and at the same time, there is a certain degree of mutual diffusion between the interlayer structure of the coating and between the coating and the alloy at high temperature, thereby enhancing the bonding strength and anti-shedding ability of the coating.

[0024] (2) The present invention optimizes the proportion of the composite coating spray slurry and the spraying process through a large number of experiments, so that the prepared coating has better oxidation resistance and thermal shock resistance.

[0025] (3) Tests show that the composite coating test piece prepared by the present invention has a static anti-oxidation life of not less than 0.5 h at 2000 ° C, and a thermal shock life of more than 50 times from 2000 ° C to room temperature (water cooling); a static anti-oxidation life of not less than 220 s at 2300 ° C, and a thermal shock life of more than 10 times from 2300 ° C to room temperature (water cooling).

[0026] (4) The coating prepared by the present invention generates SiO2 and B2O3 during the oxidation process and fills the skeleton of ZrO2 and ZrSiO4, which can effectively block the penetration of oxygen. The Ta atoms with smaller radius in TaSi2 can fill and occupy more tiny lattices, making the coating structure more compact. In addition, the presence of the inner diffusion barrier layer can effectively prevent the outer Si element from diffusing to the inner layer, resulting in the generation of Si depleted areas in the outer layer, so that the outer coating can provide sufficient Si source, so that the coating exhibits good oxidation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Scanning morphology of the coating surface of Example 1;

[0028] Figure 2 This is the surface scanning morphology of the coating in Example 1 after oxidation at 2000°C; DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to specific embodiments.

[0030] Example 1

[0031] The present invention provides a high-temperature anti-oxidation composite coating on the surface of a tantalum-tungsten alloy, comprising the following raw materials: a first coating material and a second coating material stacked in sequence;

[0032] The composition of the first coating material is: B powder is 25wt%, Al2O3 is 55wt%, NaF is 15wt%, and the balance is La2O3;

[0033] The composition of the second coating material is: ZrB2 45wt%, MoSi2 35wt%, TaSi2 12wt%, and the balance 8YSZ;

[0034] The particle sizes of the above-mentioned ZrB2 powder, MoSi2 powder, 8YSZ powder, B powder, La2O3 powder, Al2O3 powder, NaF powder and TaSi2 powder are all less than 50 μm, and the purity is greater than 99.9%.

[0035] The present invention provides a method for preparing a high-temperature anti-oxidation composite coating on the surface of a tantalum-tungsten alloy, comprising the following steps:

[0036] (1) The first coating material was placed in a ball mill at a speed of 350 r / min and ball milled for 3.5 h. After the ball milling was completed, the powder was placed in an oven and dried for 30 min to prepare the first layer of coating embedding powder;

[0037] (2) placing the substrate into a crucible, filling it with the first coating embedding powder prepared in step (1), and then placing it into a vacuum tube furnace for sintering at a sintering temperature of 1100° C. for 3 hours. During the sintering process, high-purity argon gas is continuously introduced. The heating rate is 10° C. / min before 1000° C., and the heating rate is reduced to 5° C. / min after the temperature exceeds 1000° C. The substrate is cooled in the furnace after the heating is completed, thereby obtaining the first diffusion barrier layer;

[0038] (3) Mix the second coating material with ethanol and a binder, place the mixture in a ball mill and wet-mix at a speed of 350 r / min for 3 h to prepare a second coating slurry;

[0039] (4) using a pneumatic spray gun to spray the coating slurry obtained in step (3) onto the surface of the substrate having the first layer of anti-oxidation coating, placing the sprayed substrate in an oven to dry for 60 minutes, then gently placing it on a corundum sheet, and then placing it in a vacuum tube furnace for sintering. When the temperature rises to 600°C, keep it warm for 2 hours. The final sintering temperature is 1400°C, and keep it warm for 60 minutes. During the sintering process, when the temperature is below 1000°C, the vacuum gauge pressure in the vacuum tube furnace is less than 0.1Pa. After the temperature is greater than 1000°C, high-purity argon gas is introduced. The heating rate before 1000°C is 10°C / min, and the heating rate is reduced to 5°C / min after the temperature is greater than 1000°C. After the heating is completed, the furnace is cooled to form a second layer of anti-oxidation coating;

[0040] The first diffusion barrier layer and the second anti-oxidation coating constitute a high-temperature anti-oxidation composite coating with a total thickness of 180 μm.

[0041] The surface scanning morphology of the high temperature anti-oxidation composite coating prepared in this embodiment is as follows Figure 1 shown.

[0042] In the above-mentioned high-temperature anti-oxidation composite coating material on the surface of tantalum-tungsten alloy and its preparation method, the binder added in step (3) is 0.8-1.2 wt% of polyvinyl butyral (PVB).

[0043] The surface scanning morphology of the high temperature anti-oxidation composite coating prepared in this embodiment after oxidation at 2000℃ is as follows: Figure 2 As shown, the coating specimen has a life of 1850s in a static oxidation test at 2000℃ and a thermal shock life of 51 times; the coating specimen has a life of 240s in a static oxidation test at 2300℃ and a thermal shock life of 13 times.

[0044] Example 2

[0045] The present invention provides a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy, comprising the following raw materials: a first coating material and a second coating material stacked in sequence;

[0046] The composition of the first coating material is: B powder is 30wt%, Al2O3 is 60wt%, NaF is 13wt%, and the balance is La2O3;

[0047] The composition of the second coating material is: ZrB2 40wt%, MoSi2 40wt%, TaSi2 10wt%, and the balance 8YSZ;

[0048] The particle sizes of the above-mentioned ZrB2 powder, MoSi2 powder, 8YSZ powder, B powder, La2O3 powder, Al2O3 powder, NaF powder and TaSi2 powder are all less than 50 μm, and the purity is greater than 99.9%.

[0049] The present invention provides a method for preparing a high-temperature anti-oxidation composite coating on the surface of a tantalum-tungsten alloy, comprising the following steps:

[0050] (1) The first coating material was placed in a ball mill at a speed of 350 r / min for 4 h. After the ball milling was completed, the powder was placed in an oven and dried for 30 min to prepare the first layer of coating embedding powder;

[0051] (2) placing the substrate into a crucible, filling it with the first coating embedding powder prepared in step (1), and then placing it into a vacuum tube furnace for sintering at a sintering temperature of 1150°C for 2 hours. During the sintering process, high-purity argon gas is continuously introduced. The heating rate is 10°C / min before 1000°C, and the heating rate is reduced to 5°C / min after the temperature exceeds 1000°C. After the heating is completed, the substrate is cooled in the furnace, thereby obtaining the first diffusion barrier layer;

[0052] (3) Mix the second coating material with ethanol and a binder, place the mixture in a ball mill and wet-mix at a speed of 350 r / min for 4 h to prepare a second coating slurry;

[0053] (4) using a pneumatic spray gun to spray the coating slurry obtained in step (3) onto the surface of the substrate having the first layer of anti-oxidation coating, placing the sprayed substrate in an oven to dry for 60 minutes, then gently placing it on a corundum sheet, and then placing it in a vacuum tube furnace for sintering. When the temperature rises to 650°C, keep it warm for 2 hours. The final sintering temperature is 1350°C, and keep it warm for 75 minutes. During the sintering process, when the temperature is below 1000°C, the vacuum gauge pressure in the vacuum tube furnace is less than 0.1Pa. After the temperature is greater than 1000°C, high-purity argon gas is introduced. The heating rate before 1000°C is 10°C / min, and the heating rate is reduced to 5°C / min after the temperature is greater than 1000°C. After the heating is completed, the furnace is cooled to form a second layer of anti-oxidation coating;

[0054] The first diffusion barrier layer and the second anti-oxidation coating constitute a high-temperature anti-oxidation composite coating with a total thickness of 170 μm.

[0055] In the above-mentioned high-temperature anti-oxidation composite coating material on the surface of tantalum-tungsten alloy and its preparation method, the binder added in step (3) is 0.8-1.2 wt% of polyvinyl butyral (PVB).

[0056] The coating specimen has a lifespan of 1780s in a static oxidation test at 2000℃ and a thermal shock test of 49 times; the coating specimen has a lifespan of 260s in a static oxidation test at 2300℃ and a thermal shock test of 14 times.

[0057] Example 3

[0058] The present invention provides a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy, comprising the following raw materials: a first coating material and a second coating material stacked in sequence;

[0059] The composition of the first coating material is: B powder is 35wt%, Al2O3 is 50wt%, NaF is 12%, and the balance is La2O3;

[0060] The composition of the second coating material is: ZrB2 48wt%, MoSi2 32wt%, TaSi2 8wt%, and the balance 8YSZ;

[0061] The particle sizes of the above-mentioned ZrB2 powder, MoSi2 powder, 8YSZ powder, B powder, La2O3 powder, Al2O3 powder, NaF powder and TaSi2 powder are all less than 50 μm, and the purity is greater than 99.9%.

[0062] The present invention provides a method for preparing a high-temperature anti-oxidation composite coating on the surface of a tantalum-tungsten alloy, comprising the following steps:

[0063] (1) The first coating material was placed in a ball mill at a speed of 350 r / min for 5 h. After the ball milling was completed, the powder was placed in an oven and dried for 30 min to prepare the first layer of coating embedding powder;

[0064] (2) placing the substrate into a crucible, filling it with the first coating embedding powder prepared in step (1), and then placing it into a vacuum tube furnace for sintering at a sintering temperature of 1200°C for 1.5 hours. During the sintering process, high-purity argon gas is continuously introduced. The heating rate is 10°C / min before 1000°C, and the heating rate is reduced to 5°C / min after the temperature exceeds 1000°C. After the heating is completed, the crucible is cooled in the furnace, thereby obtaining the first diffusion barrier layer;

[0065] (3) Mix the second coating material with ethanol and a binder, place the mixture in a ball mill and wet-mix at a speed of 350 r / min for 4.5 h to prepare a second coating slurry;

[0066] (4) using a pneumatic spray gun to spray the coating slurry obtained in step (3) onto the surface of the substrate having the first layer of anti-oxidation coating, placing the sprayed substrate in an oven to dry for 60 minutes, then gently placing it on a corundum sheet, and then placing it in a vacuum tube furnace for sintering. When the temperature rises to 700°C, keep it warm for 2 hours. The final sintering temperature is 1350°C, and keep it warm for 90 minutes. During the sintering process, when the temperature is below 1000°C, the vacuum gauge pressure in the vacuum tube furnace is less than 0.1Pa. After the temperature is greater than 1000°C, high-purity argon gas is introduced. The heating rate before 1000°C is 10°C / min, and the heating rate is reduced to 5°C / min after the temperature is greater than 1000°C. After the heating is completed, the furnace is cooled to form a second layer of anti-oxidation coating;

[0067] The first diffusion barrier layer and the second anti-oxidation coating constitute a high-temperature anti-oxidation composite coating with a total thickness of 190 μm.

[0068] In the above-mentioned high-temperature anti-oxidation composite coating material on the surface of tantalum-tungsten alloy and its preparation method, the binder added in step (3) is 0.8-1.2 wt% of polyvinyl butyral (PVB).

[0069] The coating specimen has a static oxidation test life of 1830s at 2000℃ and a thermal shock test life of 47 times; the static oxidation test life of 2300℃ is 235s and a thermal shock test life of 12 times.

[0070] The above description merely represents the preferred embodiments of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications, improvements, and substitutions without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy, characterized by: The high-temperature anti-oxidation composite coating is composed of a first coating material and a second coating material stacked in sequence; The composition of the first coating material is: B powder is 25-35wt%, Al2O3 is 50-65wt%, NaF is 10-20wt%, and the balance is La2O3; The components of the second coating material are: ZrB2 is 40-50wt%, MoSi2 is 30-40wt%, TaSi2 is 5-11wt%, and the balance is 8YSZ.

2. The high-temperature oxidation-resistant composite coating on the surface of tantalum-tungsten alloy according to claim 1, characterized in that: The particle sizes of the ZrB2 powder, MoSi2 powder, 8YSZ powder, B powder, La2O3 powder, Al2O3 powder, NaF powder and TaSi2 powder are all less than 50 μm, and the purity is greater than 99.9%.

3. The method for preparing a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy according to claim 1 or 2, characterized in that: The steps include: (1) placing the first coating material in a ball mill for ball milling, and then placing it in an oven for drying after the ball milling to prepare a first layer coating embedding powder; (2) placing the substrate into a crucible, filling it with the first coating embedding powder prepared in step (1), and then placing it into a vacuum tube furnace for sintering at a sintering temperature of 1050°C to 1200°C for 1 to 3 hours. During the sintering process, high-purity argon gas is continuously introduced. The heating rate is 10°C / min before 1000°C, and the heating rate is reduced to 5°C / min after the temperature exceeds 1000°C. After the heating is completed, the substrate is cooled in the furnace, thereby obtaining the first diffusion barrier layer; (3) mixing the second coating material with ethanol and a binder, and placing the mixture in a ball mill for wet mixing to prepare a second coating slurry; (4) spraying the second coating slurry obtained in step (3) onto the surface of the substrate having the first diffusion barrier layer, placing the sprayed substrate in an oven for drying and then gently placing it on a corundum sheet, and then placing it in a vacuum tube furnace for sintering. When the temperature rises to 600-700°C, keep it warm for 2 hours. The final sintering temperature is 1300-1450°C, and keep it warm for 60-90 minutes. During the sintering process, when the temperature is below 1000°C, the vacuum gauge pressure in the vacuum tube furnace is less than 0.1 Pa. After the temperature exceeds 1000°C, high-purity argon gas is introduced. The heating rate before 1000°C is 10°C / min, and the heating rate after the temperature exceeds 1000°C is reduced to 5°C / min. After the heating is completed, the furnace is cooled to form the second layer of anti-oxidation coating; The first diffusion barrier layer and the second anti-oxidation coating layer connected in sequence constitute a high-temperature anti-oxidation composite coating.

4. The method for preparing a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy according to claim 3, characterized in that: The binder added in step (3) is 0.8-1.2 wt% of polyvinyl butyral (PVB).

5. The method for preparing a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy according to claim 3, characterized in that: The substrate in step (2) and step (4) is tantalum-tungsten alloy.

6. The method for preparing a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy according to claim 3, characterized in that: The ball milling process parameters of step (1) and step (3) are 350 r / min and grinding for 3 to 5 hours.

7. The method for preparing a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy according to claim 3, characterized in that: The drying time in the oven of step (1) and step (4) is 30 to 60 minutes.

8. The method for preparing a high-temperature oxidation-resistant composite coating material on the surface of a tantalum-tungsten alloy according to claim 3, characterized in that: The total thickness of the high-temperature anti-oxidation composite coating finally prepared on the surface of the substrate in step (4) is 160 μm to 200 μm.

9. The method for preparing a high-temperature oxidation-resistant composite coating on the surface of a tantalum-tungsten alloy according to claim 3, characterized in that: In the step (4), a pneumatic spray gun is used as the coating spraying tool.

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