Carbon-based material coating and preparation method thereof

Abstract

The invention discloses a carbon-based material coating and a preparation method thereof, and belongs to the technical field of coating protection. The coating comprises an Nb layer and an HfO2 layer, wherein the Nb layer is positioned between a carbon-based material and the HfO2 layer; the preparation method comprises the following steps: (1) carrying out surface treatment on a carbon-based material; (2) depositing an Nb coating on the surface of the carbon-based material through chemical vapor deposition under a vacuum negative pressure condition; (3) depositing an HfO2 coating on the surface of the Nb coating through chemical vapor deposition under a vacuum negative pressure condition; and (4) carrying out heat treatment on the carbon-based material under a vacuum negative pressure condition. The composite coating is deposited on the surface of the carbon-based material through a reasonable and convenient preparation method, atomic-scale diffusion strengthening is conducted on interfaces of a matrix and the coating, a metallurgical bonding interface is achieved through Nb, meanwhile, HfO2 is introduced to form a gradient passivation layer, the bonding strength of the coating is improved by 40% or above through pressure stress regulation and control and the mutual diffusion effect, and the bonding strength of the coating is improved by 30% or above. And the coating has a long-acting and stable protection effect in a high-temperature oxidation environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating protection, and relates to a carbon-based material coating and a preparation method thereof. Background Art

[0002] Carbon-based materials (such as graphite, C / C, C / SiC composites, etc.) have excellent comprehensive properties such as high specific strength, high-temperature stability, and thermal shock resistance, and play an important strategic role in the aerospace field. However, devices (such as nozzles, valve cores, etc.) made of carbon-based materials have difficulties in welding with other metal materials (such as nickel-based alloys, titanium alloys, niobium alloys, etc.), and are extremely prone to oxidation ablation in an oxygen-containing environment, which severely restricts the application of carbon-based materials.

[0003] Although carbon-based materials and metal materials can also be connected by bolts, bolt connection requires a graphite material as a sealing layer. After long-term placement, there is a hidden danger of air leakage. In addition, the bolt connection device is relatively heavy, which will offset the advantage of the light weight of carbon-based materials. Therefore, carbon-based materials inevitably need to be welded with other metal materials. However, carbon-based materials have a high porosity, and a large amount of gas will overflow during the brazing process, affecting the welding process and joint quality. When using diffusion welding, some metals need to be filled at the joint interface as intermediate materials. In order to meet the assembly requirements of the intermediate connection material and the carbon-based material, it is usually necessary to process the appearance size of the carbon-based material component, which will inevitably damage the woven structure of the carbon-based material.

[0004] Currently, usually by coating a coating on the surface of the carbon-based material, the performance disadvantages of the carbon-based material itself are improved by using the coating performance or the coating protection effect. The performance of the coating itself and the bonding effect between the coating and the carbon-based material directly affect the protection effect of the coating on the carbon-based material and the improvement effect of the coating on the performance of the carbon-based material itself. Therefore, the research on the performance of the coating itself and the bonding effect between the coating and the carbon-based material is of great significance.

[0005] Therefore, it is necessary to provide a carbon-based material coating and a preparation method thereof to strengthen the improvement effect of the coating on the performance of the carbon-based material and the long-term protection effect of the coating on the carbon-based material. Summary of the Invention

[0006] To overcome the problems in the background art, the present invention deposits a composite coating of an Nb layer and an HfO₂ layer on the surface of a carbon-based material. By virtue of the excellent welding performance of the metal Nb, the welding performance between the carbon-based material and other metal materials is improved through the Nb coating, the welding difficulty between the carbon-based material and other metal materials is reduced, and the high ductility of Nb is utilized to relieve the internal stress of the coating and inhibit crack propagation. By virtue of the oxidation resistance and ablation resistance of HfO₂, the carbon-based material is protected through the HfO₂ coating, thereby improving the oxidation resistance and ablation resistance of the carbon-based material. At the same time, through vacuum heat treatment, the interdiffusion between Nb, the carbon-based material, and HfO₂ is utilized to strengthen the bonding strength between the coating and the carbon-based material and between the coatings, generate intermediate phases such as carbides and oxides of Nb, strengthen the interface sealing effect of the coating, and enable the coating to exert long-term and relatively stable performance improvement and protection effects.

[0007] To achieve the above object, the present invention is realized through the following technical solutions:

[0008] On the one hand, the present invention provides a carbon-based material coating, the coating includes an Nb layer and an HfO₂ layer, and the Nb layer is located between the carbon-based material and the HfO₂ layer. The carbon-based material is a graphite, C / C, C / SiC and other composite materials, ceramic composite materials such as foam carbon materials.

[0009] Preferably, there is no HfO₂ layer at the welding part of the carbon-based material. Since the Nb metal has relatively excellent welding performance, therefore, the deposition of the HfO₂ layer is not carried out at the welding part of the carbon-based material, so that the welding part of the carbon-based material is welded to other metal materials through the Nb layer, reducing the welding difficulty and improving the welding performance of the carbon-based material. Except for the welding part of the carbon-based material, the non-welding parts do not need to improve the welding performance. The key is that the coating forms a protection for the carbon-based material, improves the performance of the carbon-based material, and prolongs the service life of the carbon-based material. Therefore, the coating on the non-welding parts of the carbon-based material is two layers, namely the Nb layer and the HfO₂ layer, to provide more comprehensive performance improvement and protection for the carbon-based material.

[0010] On the other hand, the present invention provides a preparation method of the above coating, and the preparation method includes the following steps:

[0011] (1) Perform surface treatment on the carbon-based material.

[0012] (2) Under vacuum negative pressure conditions, deposit an Nb coating on the surface of the carbon-based material by chemical vapor deposition.

[0013] (3) Under vacuum negative pressure conditions, deposit an HfO₂ coating on the surface of the Nb coating by chemical vapor deposition.

[0014] (4) Under vacuum negative pressure conditions, perform heat treatment on the carbon-based material after depositing the HfO₂ coating.

[0015] Preferably, in the step (2), the specific steps of chemical vapor deposition are as follows:

[0016] Q1: Heat the Nb metal element and chlorinate the Nb metal element with Cl2 to generate NbCl5 gas.

[0017] Q2: Reduce the NbCl5 gas in the step Q1 with H2 to form Nb atoms. At the same time, inductively heat the carbon-based material, and the Nb atoms are deposited on the surface of the carbon matrix material to form a Nb layer.

[0018] Preferably, in the step Q1, the heating temperature is 200 - 400 °C, and the Cl2 flow rate is 100 - 300 ml / min.

[0019] Preferably, in the step Q2, the inductive heating temperature is 900 - 1300 °C, and the H2 flow rate is 300 - 900 ml / min.

[0020] Preferably, in the step (3), the specific steps of chemical vapor deposition are as follows:

[0021] S1: Heat the Hf metal element and chlorinate the Hf metal element with Cl2 to generate HfCl4 gas. Use a graphite sleeve to cover the welded part of the carbon-based material.

[0022] S2: Reduce the HfCl4 gas in the step S1 with H2 and CO2 to generate HfO2. At the same time, inductively heat the carbon-based material, and the HfO2 is deposited on the surface of the Nb layer to form a HfO2 layer.

[0023] Preferably, in the step S1, the heating temperature is 200 - 400 °C, and the Cl2 flow rate is 40 - 50 ml / min.

[0024] Preferably, in the step S2, the inductive heating temperature is 1100 - 1300 °C, the H2 flow rate is 350 - 450 ml / min, and the CO2 flow rate is 200 - 250 ml / min.

[0025] Preferably, in the steps (2) and (3), the vacuum degree ≥ 10 -2 Torr.

[0026] In the step (4), the vacuum degree ≥ 7.5 × 10 -8 Torr, the heat treatment temperature is 800 - 1000 °C, the heat preservation time is 2 - 8 h, and after the heat preservation is completed, it is naturally cooled.

[0027] Advantages of the present invention:

[0028] 1. The present invention deposits an Nb layer and an HfO2 layer on the surface of a carbon-based material, which can not only comprehensively improve the performance and provide protection for the carbon-based material, but also enhance the bonding strength between the coating and the carbon-based material and the interface sealing effect between the coating and the coating through the interdiffusion between Nb and the carbon-based material and HfO2 and the formation of intermediate phases, so that the coating can produce more excellent and long-lasting performance improvement and protection effects.

[0029] 2. The present invention prepares the coating by chemical vapor deposition, without special requirements for the external shape structure of the carbon-based material, and can deposit the coating on the carbon-based material with a relatively complex external shape structure. When the surface morphology of the carbon-based material is relatively complex (for example, there are step or groove structures on the surface of the carbon-based material), the mechanical bonding force generated by thermal expansion and contraction between the Nb layer and the carbon-based material can be further improved, which is beneficial to further improving the bonding strength between the coating and the carbon-based material.

[0030] 3. The density of the coating prepared by the present invention can reach more than 99.8% of the theoretical density. The critical load Lc between the Nb layer and the carbon-based material can reach 132 N, and the critical load Lc between the Nb layer and the HfO2 layer can reach 112 N. The coating prepared by the present invention has a good protection effect and a strong interface bonding strength, and can achieve long-term and stable protection.

[0031] 4. The preparation method of the present invention is reasonable, the process flow is simple, convenient, and the process is short, which has great advantages in large-scale applications and is suitable for industrial application and promotion. Specific Embodiments

[0032] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0033] In the embodiments and comparative examples of the present invention, chemical reagents not specifically stated are all used for experiments with commercially available analytical pure reagents.

[0034] Example 1

[0035] The carbon-based material containing an Nb layer and an HfO2 layer is prepared by the following method in this example:

[0036] (1) Using a square carbon-based material as the substrate, first use sandpaper to polish the surface of the substrate clean, then use alcohol to clean the polished substrate, and dry it in the air.

[0037] (2) Place the substrate in the deposition chamber of the chemical vapor deposition equipment, place the Nb metal single substance in the chlorination chamber of the chemical vapor deposition equipment, start the chemical vapor deposition equipment, heat the temperature of the chlorination chamber to 300 °C by resistance heating, and at the same time introduce Cl2 into the chlorination chamber at a flow rate of 200 ml / min. Nb reacts with Cl2 in the chlorination chamber to generate NbCl5.

[0038] (3) Evacuate the deposition chamber to a vacuum degree of ≥10 -2 Torr, then H2 is introduced at a flow rate of 600 ml / min, allowing gaseous NbCl5 to enter the deposition chamber along with the H2. Simultaneously, the substrate is heated to 1100°C using induction heating. Under the action of H2, NbCl5 is reduced to form Nb atoms, which are deposited on the substrate surface, forming a Nb layer. After the Nb layer is deposited, a graphite sleeve is used to cover the welding area of the substrate.

[0039] (4) After the Nb layer is deposited, the Nb metal element in the chlorination chamber is replaced with Hf metal element, and the temperature of the chlorination chamber is heated to 300°C by resistance heating. At the same time, Cl2 is introduced into the chlorination chamber at a flow rate of 45 ml / min. Hf reacts with Cl2 in the chlorination chamber to generate HfCl4.

[0040] (5) Evacuate the deposition chamber to a vacuum degree of ≥10 -2 Torr, then H2 and CO2 gases are introduced at flow rates of 400ml / min and 220ml / min, respectively, allowing gaseous HfCl4 to enter the deposition chamber along with the H2 and CO2. Simultaneously, the substrate is heated to 1200°C using induction heating. Under the action of H2 and CO2, HfCl4 transforms into HfO2, which is deposited on the substrate surface, forming an HfO2 layer. Because the substrate welding area is covered by a graphite sleeve, HfO2 cannot deposit on the surface of the Nb layer, thus preventing the Nb layer at the welding area from being covered by HfO2.

[0041] (6) Place the carbon-based material after coating deposition into a vacuum heat treatment device and heat it in a vacuum degree of ≥7.5×10 -8 Torr, the temperature is 800℃, and the heat treatment time is 8 hours.

[0042] The thickness of the Nb layer and HfO2 layer prepared in this embodiment is more than 4 mm, the deposition time of the Nb layer is 40 hours, and the deposition time of the HfO2 layer is more than 40 hours. The coating thickness is determined according to actual needs. After the coating thickness is determined, the deposition time is adjusted according to the coating thickness.

[0043] The samples prepared in this embodiment were tested, and the results showed that the density of the Nb layer and the HfO2 layer prepared in this embodiment reached more than 99.8% of the theoretical density. The scratch method was used to test the bonding strength between the coatings. The critical load Lc between the Nb layer and the carbon-based material can reach 132N, and the critical load Lc between the Nb layer and the HfO2 layer can reach 112N.

[0044] The sample of this example was placed in alcohol for an aeration test at a pressure of 2 MPa. No bubbles escaped from the interface, indicating good airtightness of the coating. No obvious cracks were generated on the surface of the HfO2 coating after 60 seconds of oxyacetylene flame ablation, indicating good ablation resistance of the coating.

[0045] Example 2

[0046] In this embodiment, a carbon-based material containing a Nb layer and a HfO2 layer is prepared by the following method:

[0047] (1) Using a square carbon-based material as the substrate, first use sandpaper to polish the substrate surface, then use alcohol to clean the polished substrate and air dry it;

[0048] (2) Place the substrate in the deposition chamber of the chemical vapor deposition equipment, place the Nb metal element in the chlorination chamber of the chemical vapor deposition equipment, start the chemical vapor deposition equipment, heat the chlorination chamber to 200°C using resistance heating, and at the same time, introduce Cl2 into the chlorination chamber at a flow rate of 100 ml / min. Nb and Cl2 react in the chlorination chamber to generate NbCl5.

[0049] (3) Evacuate the deposition chamber to a vacuum degree of ≥10 -2 Torr, then H2 is introduced at a flow rate of 300 ml / min, allowing gaseous NbCl5 to enter the deposition chamber along with the H2. Simultaneously, the substrate is heated to 900°C using induction heating. Under the action of H2, NbCl5 is reduced to form Nb atoms, which are deposited on the substrate surface, forming a Nb layer. After the Nb layer is deposited, a graphite sleeve is used to cover the welding area of the substrate.

[0050] (4) After the Nb layer is deposited, the Nb metal element in the chlorination chamber is replaced with Hf metal element, and the temperature of the chlorination chamber is heated to 200°C by resistance heating. At the same time, Cl2 is introduced into the chlorination chamber at a flow rate of 40 ml / min. Hf reacts with Cl2 in the chlorination chamber to generate HfCl4.

[0051] (5) Evacuate the deposition chamber to a vacuum degree of ≥10 -2 Torr, then H2 and CO2 gases are introduced at flow rates of 350ml / min and 200ml / min, respectively, allowing gaseous HfCl4 to enter the deposition chamber along with the H2 and CO2. Simultaneously, the substrate is heated to 1100°C using induction heating. Under the action of H2 and CO2, HfCl4 transforms into HfO2, which is deposited on the substrate surface, forming an HfO2 layer. Because the substrate welding area is covered by a graphite sleeve, HfO2 cannot deposit on the surface of the Nb layer, thus preventing the Nb layer at the welding area from being covered by HfO2.

[0052] (6) Put the prepared coating material into a vacuum heat treatment equipment, with a vacuum degree ≥ 7.5×10-8 Torr, a heat treatment temperature of 1000 °C, and a heat treatment time of 2 hours.

[0053] In this example, the thicknesses of the Nb layer and the HfO2 layer prepared are above 4 mm, the deposition time of the Nb layer is 40 h, the deposition time of the HfO2 layer is above 40 h, the coating thickness is determined according to actual requirements, and after the coating thickness is determined, the deposition time is adjusted according to the coating thickness.

[0054] The performance of the sample prepared in this example is similar to that of the sample in Example 1.

[0055] Example 3

[0056] In this example, a carbon-based material containing an Nb layer and an HfO2 layer is prepared by the following method:

[0057] (1) Using a square carbon-based material as the substrate, first use sandpaper to polish the surface of the substrate clean, then use alcohol to clean the polished substrate, and air dry it until it is dry;

[0058] (2) Place the substrate into the deposition chamber of a chemical vapor deposition equipment, place elemental Nb metal into the chlorination chamber of the chemical vapor deposition equipment, start the chemical vapor deposition equipment, heat the temperature of the chlorination chamber to 400 °C by means of resistance heating, and at the same time introduce Cl2 into the chlorination chamber at a flow rate of 300 ml / min. Nb reacts with Cl2 in the chlorination chamber to generate NbCl5.

[0059] (3) Evacuate the deposition chamber to make the vacuum degree in the deposition chamber ≥ 10 -2 Torr, then introduce H2 at a flow rate of 900 ml / min, so that gaseous NbCl5 enters the deposition chamber along with H2. At the same time, heat the substrate to 1300 °C by means of induction heating. NbCl5 is reduced under the action of H2 to form Nb atoms, which are deposited on the surface of the substrate to form an Nb layer. After the deposition of the Nb layer is completed, use a graphite sleeve to cover the welded part of the substrate.

[0060] (4) After the deposition of the Nb layer is completed, replace the elemental Nb metal in the chlorination chamber with elemental Hf metal, heat the temperature of the chlorination chamber to 400 °C by means of resistance heating, and at the same time introduce Cl2 into the chlorination chamber at a flow rate of 50 ml / min. Hf reacts with Cl2 in the chlorination chamber to generate HfCl4.

[0061] (5) Evacuate the deposition chamber to make the vacuum degree in the deposition chamber ≥ 10 -2Torr, and then introduce H2 and CO2 gases into the deposition chamber at the flow rates of 450 ml / min and 250 ml / min respectively, so that gaseous HfCl4 enters the deposition chamber along with H2 and CO2. At the same time, heat the substrate to 1300 °C by induction heating. HfCl4 forms HfO2 under the action of H2 and CO2 and deposits on the surface of the substrate to form an HfO2 layer. Since the welded part of the substrate is covered by a graphite sleeve, HfO2 cannot be deposited on the surface of the Nb layer, and the Nb layer at the welded part can be kept from being covered by HfO2.

[0062] (6) Put the prepared coating material into a vacuum heat treatment equipment, with the vacuum degree ≥ 7.5×10-8 Torr, the heat treatment temperature of 900 °C, and the heat treatment time of 5 hours.

[0063] The thicknesses of the Nb layer and the HfO2 layer prepared in this embodiment are more than 2 mm. The deposition time of the Nb layer is 20 h, and the deposition time of the HfO2 layer is 20 h. The coating thickness is determined according to actual requirements. After the coating thickness is determined, the deposition time is adjusted according to the coating thickness.

[0064] The performance of the sample prepared in this embodiment is similar to that of the sample in Example 1.

[0065] Comparative Example 1

[0066] This comparative example prepares a coating by the same preparation method as in Example 1, with the difference that: only an HfO2 layer is deposited on the substrate.

[0067] [[ID=1⑧]]Use the scratch method to test the bonding strength between the coating in this comparative example and the carbon substrate. The critical load Lc is 89 N.

[0068] It can be seen from the comparison between Example 1 and Comparative Example 1 that the bonding strength between the Nb layer and the HfO2 and the bonding strength between the Nb layer and the carbon substrate are both higher than the bonding strength between the HfO2 and the substrate, which fully demonstrates that the mutual diffusion between Nb and the substrate and HfO2 in the present invention effectively strengthens the bonding strength between the coating and the carbon-based material and between the coatings, enabling the coating to function stably for a long time.

[0069] In summary, the present invention deposits a coating on the surface of the carbon-based material through a reasonable, simple and convenient preparation method. On the basis of having a relatively comprehensive effect on the carbon-based material, the coating can strengthen the bonding strength between the coating and the carbon-based material, between the coatings and the coating interface sealing effect, enabling the coating to function fully, long-term and stably.

[0070] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A carbon-based material coating, characterized in that: The coating includes an Nb layer and an HfO2 layer, and the Nb layer is located between the carbon-based material and the HfO2 layer.

2. The coating according to claim 1, wherein: There is no HfO2 layer at the welded part of the carbon-based material.

3. The method for preparing the coating according to claim 1 or 2, characterized in that: The preparation method includes the following steps: (1) Perform surface treatment on the carbon-based material; (2) Deposit an Nb coating on the surface of the carbon-based material by chemical vapor deposition under a vacuum negative pressure condition; (3) Deposit an HfO2 coating on the surface of the Nb coating by chemical vapor deposition under a vacuum negative pressure condition; (4) Heat-treat the carbon-based material after depositing the HfO2 coating under a vacuum negative pressure condition.

4. The preparation method according to claim 3, characterized in that: In the step (2), the specific steps of chemical vapor deposition are as follows: Q1: Heat the Nb metal single substance and use Cl2 to chlorinate the Nb metal single substance to generate NbCl5 gas; Q2: Use H2 to reduce the NbCl5 gas in the step Q1 into Nb atoms, and at the same time perform induction heating on the carbon-based material, and the Nb atoms are deposited on the surface of the carbon matrix material to form an Nb layer.

5. The preparation method according to claim 4, characterized in that: In the step Q1, the heating temperature is 200-400 °C, and the Cl2 flow rate is 100-300 ml / min.

6. The preparation method according to claim 4, characterized in that: In the step Q2, the induction heating temperature is 900-1300 °C, and the H2 flow rate is 300-900 ml / min.

7. The preparation method according to claim 3, characterized in that: In the step (3), the specific steps of chemical vapor deposition are as follows: S1: Heat the Hf metal single substance and use Cl2 to chlorinate the Hf metal single substance to generate HfCl4 gas, and use a graphite sleeve to cover the welded part of the carbon-based material; S2: Use H2 and CO2 to reduce the HfCl4 gas in the step S1 to generate HfO2, and at the same time perform induction heating on the carbon-based material, and the HfO2 is deposited on the surface of the Nb layer to form an HfO2 layer.

8. The preparation method according to claim 7, characterized in that: In the step S1, the heating temperature is 200-400 °C, and the Cl2 flow rate is 40-50 ml / min.

9. The preparation method according to claim 7, characterized in that: In the step S2, the induction heating temperature is 1100-1300 °C, the H2 flow rate is 350-450 ml / min, and the CO2 flow rate is 200-250 ml / min.

10. The preparation method according to claim 3, characterized in that: In the said steps (2) and (3), the vacuum degree ≥ 10 - 2 Torr; In the step (4), the vacuum degree ≥ 7.5×10 -8 Torr, the heat treatment temperature is 800 - 1000 °C, the heat preservation time is 2 - 8 h, and after the heat preservation is completed, it is naturally cooled.