Metal elbow and manufacturing method therefor

Abstract

A metal elbow and a manufacturing method therefor. The manufacturing method comprise the following steps: preparing an interface layer (21): under a vacuum condition, providing a carbon source and a nitrogen source, and performing carbonitriding treatment on the surface of an elbow base body (1) by means of high-energy plasma, so as to form a carbonitrided layer as the interface layer (21); preparing a barrier layer (22): by means of chemical vapor deposition, depositing on the surface of the carbonitrided layer a metal oxide layer as the barrier layer (22); and preparing a corrosion-resistant layer (23): by means of chemical vapor deposition, depositing on the surface of the metal oxide layer a silicon carbide layer as the corrosion-resistant layer (23). The present method involves bonding to the surface of the elbow base body (1) a protective composite coating consisting of the interface layer (21) which is the carbonitrided layer, the barrier layer (22) which is the metal oxide layer and the corrosion-resistant layer (23), so as to enable metal elbows to have lower average erosion rates and average wear rates, thus significantly enhancing the safety and reliability of oil and gas field gathering and transportation systems.

Description

Metal elbow and preparation method thereof

[0001] Related applications

[0002] This application claims priority to the Chinese invention patent with patent application number 202311161148.9, application date September 8, 2023, and invention name “A metal elbow and its preparation method”. Technical Field

[0003] The present invention relates to the field of oil and gas technology, and in particular to a metal elbow and a preparation method thereof. Background Art

[0004] During the production operation of an oil field well or an oil and gas well, the fluid in the well is transported to a storage tank or a gathering station on the ground through the oil and gas field gathering and transportation system, thereby realizing oil and gas production.

[0005] Metal elbows are a critical structural component of oil and gas field gathering and transportation systems. These systems typically transport solid-liquid-gas multiphase media, including gravel, natural gas, crude oil, water, CO2 / H2S, and other materials. Metal elbows are highly susceptible to erosion and wear in the unsteady-state erosion and abrasion environments of these multiphase fluids. This can lead to rapid thinning and even perforation of the elbows, posing a serious safety hazard to oil and gas field production. Protecting metal elbows from erosion and wear in these erosive and abrasive environments has become a pressing issue for the safe operation of oil and gas field gathering and transportation systems.

[0006] At present, the main ways to improve the erosion and wear resistance of metal elbows are elbow flow stabilization structure design, elbow erosion position surfacing and adding ceramic lining, etc. However, the above methods still have obvious defects, such as the corrosion and wear resistance of the elbow flow stabilization structure is very small, the porosity of the surfacing layer is large, resulting in a short corrosion and wear life, and the ceramic lining interface fluid is easy to penetrate and accelerate corrosion, etc., resulting in the erosion and wear resistance of the metal elbow is still limited, affecting the production efficiency and use safety of the gathering and transportation system.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to provide a metal elbow and a preparation method thereof to solve the technical problem that the current metal elbow has serious insufficient erosion resistance and wear resistance in the solid-liquid-gas three-phase medium scouring environment of the oil and gas field gathering and transportation system, which affects the production efficiency and safety of the gathering and transportation system.

[0009] The above-mentioned purpose of the present invention can be achieved by adopting the following technical solutions:

[0010] The present invention provides a method for preparing a metal elbow, comprising the following steps: preparing an interface layer: under vacuum conditions, providing a carbon source and a nitrogen source, and performing carbon-nitrogen co-diffusion treatment on the surface of the elbow substrate by high-energy plasma to form a carbon-nitrogen co-diffusion layer as the interface layer; preparing a barrier layer: depositing a metal oxide layer on the surface of the carbon-nitrogen co-diffusion layer by chemical vapor deposition to form the barrier layer; preparing a corrosion-resistant layer: depositing a silicon carbide layer on the surface of the metal oxide layer by chemical vapor deposition to form the corrosion-resistant layer.

[0011] The present invention also provides a metal elbow, comprising an elbow substrate and a protective composite coating, wherein the protective composite coating comprises an interface layer bonded to the surface of the elbow substrate, a barrier layer bonded to the surface of the interface layer, and a corrosion-resistant layer bonded to the surface of the barrier layer; wherein the interface layer is a carbon-nitrogen co-diffusion layer; and the barrier layer is a metal oxide layer.

[0012] The characteristics and advantages of the present invention are:

[0013] The metal elbow and preparation method thereof of the present invention combine a carbon-nitrogen co-diffusion layer as an interface layer on the surface of the elbow substrate, and combine a metal oxide layer and the carbon-nitrogen co-diffusion layer as a barrier layer, thereby utilizing the interface layer to enhance the surface hardness and strength of the elbow substrate while also improving and enhancing the chemical matching of the metal elbow and the metal oxide layer. Utilizing the carbon-nitrogen co-diffusion layer as a transition layer can alleviate the thermal expansion coefficient mismatch problem between the elbow substrate and the metal oxide layer as a barrier layer, reduce the interface stress, and enhance the bonding strength of the barrier layer on the metal elbow. Utilizing the barrier layer can, on the one hand, enhance the barrier capacity for solid-liquid-gas three-phase media, and on the other hand, enhance the wear resistance and corrosion resistance of the metal elbow. Furthermore, by combining a corrosion-resistant layer on the surface of the metal oxide layer, the erosion resistance and wear resistance of the metal elbow are further enhanced. Furthermore, through measurement, the present invention combines a protective composite coating composed of an interface layer, a barrier layer and a corrosion-resistant layer on the surface of the elbow substrate, so that the metal elbow has a lower average erosion rate and average wear rate, which can significantly enhance the safety and reliability of the oil and gas field gathering and transportation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0015] FIG1 is a schematic cross-sectional view of a metal elbow according to the present invention.

[0016] FIG2 is a cross-sectional SEM test image of the protective composite coating of the metal elbow prepared in the first specific embodiment of the present invention.

[0017] FIG3 is a graph showing the bonding strength of the protective composite coating of the metal elbow prepared in the first embodiment of the present invention.

[0018] FIG4 is a test diagram of the average friction coefficient of the protective composite coating of the metal elbow prepared in the first specific embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] Implementation Method 1

[0021] As shown in Figure 1, the present invention provides a metal elbow, including an elbow substrate 1 and a protective composite coating 2, the protective composite coating 2 including an interface layer 21 bonded to the surface of the elbow substrate 1, a barrier layer 22 bonded to the surface of the interface layer 21, and a corrosion-resistant layer 23 bonded to the surface of the barrier layer 22; wherein the interface layer 21 is a carbon-nitrogen co-diffusion layer; and the barrier layer 22 is a metal oxide layer.

[0022] Specifically, the elbow base 1 is generally in the form of a bend structure. The material of the elbow base 1 includes carbon steel, stainless steel and / or corrosion-resistant alloy. The protective composite coating 2 can be provided only on the inner surface of the elbow base 1, or only on the outer surface of the elbow base 1. Of course, the protective composite coating 2 can also be provided on both the inner surface and the outer surface of the elbow base 1. The interface layer 21 is located between the elbow base 1 and the barrier layer 22, and the barrier layer 22 is located between the interface layer 21 and the corrosion-resistant layer 23. The surface of the interface layer 21 is the side of the interface layer 21 that is not combined with the elbow base 1, and the surface of the barrier layer 22 is the side of the barrier layer 22 that is not combined with the interface layer 21.

[0023] The metal elbow of the present invention combines a carbon-nitrogen co-diffusion layer as an interface layer 21 on the surface of the elbow substrate 1, and combines a metal oxide layer with the carbon-nitrogen co-diffusion layer as a barrier layer 22, thereby utilizing the interface layer 21 to enhance the hardness and strength of the surface of the elbow substrate 1 while also improving and enhancing the chemical matching of the metal elbow and the metal oxide layer. The use of the carbon-nitrogen co-diffusion layer as a transition layer can alleviate the thermal expansion coefficient mismatch problem between the elbow substrate 1 and the metal oxide layer as the barrier layer 22, reduce the interface stress, and improve the bonding strength of the barrier layer 22 on the metal elbow, thereby The barrier layer 22 can improve the barrier capacity to solid-liquid-gas three-phase media on the one hand, and improve the wear resistance and corrosion resistance of the metal elbow on the other hand; further, by combining the corrosion-resistant layer 23 on the surface of the metal oxide layer, the erosion resistance and wear resistance of the metal elbow are further improved; and through measurement, the present invention combines the protective composite coating 2 composed of the interface layer 21, the barrier layer 22 and the corrosion-resistant layer 23 on the surface of the elbow base 1, so that the metal elbow has a lower average erosion rate and average wear rate, which can significantly improve the safety and reliability of the oil and gas field gathering and transportation system.

[0024] Among them, through measurement, the metal elbow of the present invention, the bonding force between the protective coating and the metal substrate can be increased to 40N~54N; the average friction coefficient is 0.3-0.5; the average erosion rate of the metal elbow is 1.5×10 -10 ~4.5×10 -10 kg / m 2 ·s; the average wear rate of metal elbows is 1.2×10 -7 ~3.8×10 -7 mm 3 N -1 m -1 Therefore, compared with the existing metal elbow, the metal elbow of the present invention has the properties of high surface hardness, low erosion rate and wear rate.

[0025] In an embodiment of the present invention, the carbonitrided layer has a thickness of 0.5 μm to 30 μm, preferably 10 μm to 30 μm.

[0026] In an embodiment of the present invention, the thickness of the metal oxide layer is 3 μm to 20 μm, preferably 4 μm to 10 μm. The material of the metal oxide layer includes TiO2, Al2O3 and / or SiO2.

[0027] Specifically, metal oxide particles are deposited on the surface of the interface layer 21 to form the barrier layer 22. The metal oxide particles are submicron-sized, which provides a strong bond between the interface layer 21 and the corrosion-resistant layer 23. Furthermore, the barrier layer 22 formed by the submicron-sized metal oxide particles can significantly block the penetration of corrosive media. Preferably, the particle size of the metal oxide particles in the barrier layer 22 is 100 nm to 400 nm.

[0028] In an embodiment of the present invention, the corrosion-resistant layer 23 is a silicon carbide layer. Using a silicon carbide layer as the corrosion-resistant layer 23 provides excellent erosion and wear resistance, and the bond strength between the silicon carbide layer and the metal oxide layer is high. The thickness of the silicon carbide layer is 1 μm to 15 μm, preferably 1 μm to 4 μm.

[0029] Specifically, silicon carbide particles are deposited on the surface of barrier layer 22 to form corrosion-resistant layer 23. The silicon carbide particles are nanoscale, which provides a strong bond with barrier layer 22 and significantly improves the erosion resistance of the metal elbow. Preferably, the silicon carbide nanoparticles in corrosion-resistant layer 23 have a diameter of 100 nm to 400 nm.

[0030] It should be noted that the structures of the barrier layer 22 and the corrosion-resistant layer 23 include but are not limited to the above ranges. In some embodiments of the present invention, limiting them to the above ranges is beneficial to further improve the erosion resistance and wear resistance of the metal elbow.

[0031] In embodiments of the present invention, the silicon carbide layer comprises an amorphous phase, which acts as a drag-reducing and lubricating agent, further reducing the friction coefficient of the metal elbow. This also mitigates erosion damage from solid-liquid-gas three-phase media in oil and gas field gathering and transportation systems, further improving the metal elbow's erosion and wear resistance. Specifically, the amorphous phase comprises an amorphous carbon phase. The proportion of the amorphous carbon phase in the silicon carbide layer is preferably 1% to 5%.

[0032] The metal elbow of the present invention can be prepared using the preparation method in embodiment 2, and of course it can also be prepared using other preparation methods in the prior art, as long as the carbon-nitrogen co-diffusion layer can be combined with the surface of the elbow substrate 1 to form an interface layer 21, the metal oxide layer can be combined with the surface of the interface layer 21 to form a barrier layer 22, and then the corrosion-resistant layer 23 can be combined with the surface of the barrier layer 22 to form a protective composite coating 2.

[0033] Implementation Method 2

[0034] In order to further improve the bonding strength between the elbow base 1, the interface layer 21, the barrier layer 22 and the corrosion-resistant layer 23 in the metal elbow of the first embodiment, and to further improve the comprehensive performance of the metal elbow, such as erosion resistance and wear resistance, the present invention also provides a method for preparing the metal elbow.

[0035] The preparation method includes the following steps: preparing the interface layer 21: under vacuum conditions, providing a carbon source and a nitrogen source, and performing carbon-nitrogen co-diffusion treatment on the surface of the elbow substrate 1 by high-energy plasma to form a carbon-nitrogen co-diffusion layer as the interface layer 21; preparing the barrier layer 22: depositing a metal oxide layer on the surface of the carbon-nitrogen co-diffusion layer by chemical vapor deposition to form the barrier layer 22; preparing the corrosion-resistant layer 23: depositing a silicon carbide layer on the surface of the metal oxide layer by chemical vapor deposition to form the corrosion-resistant layer 23.

[0036] Before the step of preparing the interface layer 21, the process also includes cleaning: cleaning the surface of the metal elbow by high-energy plasma under vacuum conditions. Specifically, the high-energy plasma is argon plasma. The high-energy plasma cleaning time is 15 to 45 minutes. In addition, before the high-energy plasma cleaning, the surface of the elbow base 1 can be polished to remove impurities, sandblasted with brown corundum sand, and then polished. The surface of the elbow base 1 is then ultrasonically cleaned with alcohol. The cleaned metal elbow base 1 is then placed in an oven and dried at 100°C for 5 hours.

[0037] In an embodiment of the present invention, in the step of preparing the interface layer 21 , the carbon source includes methane, ethane, propylene and / or acetylene; and the nitrogen source includes high-purity nitrogen and / or ammonia.

[0038] In some embodiments of the present invention, in the step of preparing the interface layer 21 , the temperature of the carbonitriding treatment is 430° C. to 500° C.; and the time of the carbonitriding treatment is 0.5 hour to 2 hours.

[0039] It should be noted that the temperature and time of the carbon-nitrogen co-diffusion treatment include but are not limited to the above ranges, and limiting them within the above ranges is beneficial to further increase the carburizing-silicon-nitrogen depth, thereby further improving the hardness and strength of the metal elbow.

[0040] In an embodiment of the present invention, the step of preparing the barrier layer 22 specifically includes: placing the elbow substrate 1 combined with the carbon-nitrogen co-diffusion layer in a reaction chamber and evacuating the reaction chamber; introducing a mixture of hydrogen and argon; heating the elbow substrate 1 and the reaction chamber to a deposition temperature; introducing a reaction precursor gas to carry out a chemical reaction, thereby depositing a metal oxide layer on the surface of the carbon-nitrogen co-diffusion layer. Specifically, the reaction precursor gas includes titanium tetrachloride, aluminum trichloride, trichloromethylsilane, argon, carbon monoxide, carbon dioxide, hydrogen sulfide, nitrogen, and oxygen. The vacuum degree of the reaction chamber is 1×10 2 Pa~3×10 4 Pa;

[0041] In some embodiments of the present invention, in the step of preparing the barrier layer 22, the deposition temperature is 850° C. to 1050° C.; the deposition time is 2 hours to 6 hours; and the deposition pressure is 1×10 2 Pa~2×10 4 Pa.

[0042] It should be noted that the temperature, time and pressure of deposition in the step of preparing the barrier layer 22 include but are not limited to the above ranges, and limiting them within the above ranges is beneficial to further improve the bonding force between the barrier layer 22 formed by the metal oxide layer and the interface layer 21 formed by the carbon-nitrogen co-diffusion layer, thereby helping to further improve the comprehensive performance of the metal elbow, such as erosion resistance and wear resistance.

[0043] In an embodiment of the present invention, the step of preparing the corrosion-resistant layer 23 specifically includes: cooling the elbow substrate 1 with the metal oxide layer; introducing hydrogen gas and maintaining the temperature; adjusting the hydrogen flow rate and heating the vacuum chamber to the deposition temperature; and introducing a reaction gas to deposit a silicon carbide layer on the surface of the metal oxide layer. Specifically, the temperature is lowered to 200°C to 400°C. The holding time is 1 to 3 hours. During the holding process, the hydrogen flow rate is 500 sccm to 800 sccm. During the heating process, the hydrogen flow rate is reduced to 50 sccm to 200 sccm. The reaction gases include hydrogen, trichloromethylsilane, argon, and methane. The hydrogen flow rate is 300 sccm to 800 sccm; the trichloromethylsilane flow rate is 300 sccm to 800 sccm; the argon flow rate is 100 sccm to 500 sccm; and the methane flow rate is 300 sccm to 600 sccm.

[0044] In some embodiments of the present invention, in the step of preparing the corrosion-resistant layer 23 , the deposition temperature is 1100° C. to 1250° C., and the deposition time is 2 hours to 5 hours.

[0045] It should be noted that the temperature and time of deposition in the step of preparing the corrosion-resistant layer 23 include but are not limited to the above-mentioned range, and limiting it within the above-mentioned range is beneficial to further improve the bonding force between the corrosion-resistant layer 23 formed by the silicon carbide layer and the barrier layer 22 formed by the metal oxide layer, thereby helping to further improve the comprehensive performance of the metal elbow, such as erosion resistance and wear resistance.

[0046] Some specific embodiments are provided below to facilitate a better understanding and implementation of the preparation method of the present invention for preparing a metal elbow, and are not to be construed as limiting the scope of protection claimed in the present invention.

[0047] Specific embodiment 1

[0048] The preparation of the metal elbow includes the following steps:

[0049] Step 101: Grind and remove impurities from the surface of the elbow base 1, use brown corundum sand for surface sandblasting, then polish the surface, and then use alcohol to ultrasonically clean the substrate. Then, place the cleaned metal elbow base 1 in an oven, dry it at 100°C for 5 hours, and then place it in a vacuum chamber.

[0050] Step 102: Use a vacuum pump to evacuate the vacuum chamber to a vacuum degree of 2×10 -4 Pa; then a certain amount of argon is introduced, and a high-frequency pulse voltage is applied to form a high-energy argon plasma to clean the surface of the elbow substrate 1. The cleaning time is 30 minutes.

[0051] Step 103, formation of carbon-nitrogen co-diffusion layer: After cleaning, a certain amount of NH3 and C2H2 are introduced, and the surface of the elbow substrate 1 is carbon-nitrogen co-diffusion treated by high-energy plasma; wherein, the temperature of the carbon-nitrogen co-diffusion treatment is 430°C, and the time of the carbon-nitrogen co-diffusion treatment is 40 minutes.

[0052] Step 104: Place the elbow substrate 1 containing the carbon-nitrogen co-diffusion layer into a CVD (Chemical Vapor Deposition) device, and use a two-stage vacuum pump group to evacuate the CVD device to a vacuum of 1×10 -2 Pa, and then hydrogen and nitrogen are introduced at the same time, with a hydrogen flow rate of 200 sccm and a nitrogen flow rate of 200 sccm; the furnace heating program is started, the heating rate is set to 5°C / min, and the deposition temperature is 950°C.

[0053] Step 105: an aluminum oxide layer is formed on the surface of the carbonitrided layer by chemical vapor deposition as a barrier layer 22, comprising the following steps: heating the CVD apparatus to 500°C at a heating rate of 5°C / min and holding the temperature for 1 hour, then heating to 950°C at a heating rate of 8°C / min, then entering a coating deposition process, introducing reaction precursor gases such as aluminum chloride, carbon monoxide, carbon dioxide, hydrogen, and hydrogen sulfide, wherein the flow rate of aluminum chloride is 800 sccm, the flow rate of carbon monoxide and carbon dioxide is 600 sccm, the flow rate of hydrogen is 1200 sccm, and the flow rate of hydrogen sulfide is 50 sccm. The deposition time is 5 hours, and the deposition pressure is 7×10 4 Pa.

[0054] Step 106: After the aluminum oxide layer is prepared, the CVD device enters a controllable cooling mode, stops introducing all gases, and cools down to 200°C at a cooling rate of 8°C / min.

[0055] Step 107: The temperature in the reaction chamber is lowered to 200° C., and hydrogen is introduced at a flow rate of 600 sccm, and the temperature is maintained for 3 hours.

[0056] Step 108: After the insulation process is completed, the flow rate of hydrogen is adjusted to 200 sccm, and the heating program is started to heat the reaction chamber to 1100°C.

[0057] Step 109: When the temperature is raised to 1100°C, a silicon carbide layer is formed on the surface of the aluminum oxide layer by chemical vapor deposition as a corrosion-resistant layer 23: hydrogen, trichloromethylsilane, argon, and methane are introduced in sequence; the flow rate of hydrogen is 800 sccm, the flow rate of trichloromethylsilane is 500 sccm, the flow rate of argon is 200 sccm, and the flow rate of methane is 500 sccm; the deposition time is 5 h, and the deposition pressure is 5×10 4 Pa.

[0058] Step 1010: After the silicon carbide layer is prepared, the flow rate of argon gas is maintained at 200 sccm, and the introduction of other gases is stopped. The temperature is naturally lowered to room temperature, thereby obtaining a corrosion-resistant and wear-resistant metal elbow.

[0059] Determination of metal elbows

[0060] Figure 2 is a cross-sectional morphology test diagram of the metal elbow produced in Specific Example 1 of the present invention. As shown in Figure 2, in the metal elbow produced in Specific Example 1, the interface layer 21 and the elbow substrate 1, the interface layer 21 and the barrier layer 22, and the barrier layer 22 and the corrosion-resistant layer 23 are all tightly bonded, and the coating has a high density. Specifically, the thickness of the interface layer 21 is approximately 1 μm, the thickness of the barrier layer 22 is approximately 15 μm, and the thickness of the corrosion-resistant layer 23 is approximately 8 μm.

[0061] Figure 3 is a graph showing the bonding strength test results of the protective composite coating 2 in the metal elbow prepared in Example 1 of the present invention. As shown in Figure 3, the bonding strength of the protective composite coating 2 in the metal elbow prepared in Example 1 is 54N.

[0062] Figure 4 is a graph showing the average friction coefficient test results of the metal elbow prepared in Example 1 of the present invention. As shown in Figure 4, the average friction coefficient of the metal elbow prepared in Example 1 is 0.30.

[0063] In addition, the average erosion rate test shows that the average erosion rate of the metal elbow prepared in the first embodiment is 1.5×10 -10 kg / m 2 ·s.

[0064] In addition, the average wear rate test shows that the average wear rate of the metal elbow prepared in the first embodiment is 1.2×10 -7 mm 3 N -1 m -1 .

[0065] Specific embodiment 2

[0066] The only difference from the first embodiment is that in step 103 , the temperature of the carbonitriding treatment is 500° C.

[0067] The test results show that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 2 is 48N; the average friction coefficient is 0.40, and the average erosion rate is 2.5×10 -10 kg / m 2 ·s, and the average wear rate is 2.3×10 -7 mm 3 N -1 m -1 .

[0068] Specific embodiment three

[0069] The only difference from the preparation method in the first embodiment is that in step 105 , the deposition temperature is 850° C.

[0070] The test results show that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 3 is 42N, the average friction coefficient is 0.44, and the average erosion rate is 3.7×10 -10 kg / m 2 ·s, the average wear rate is 3.0×10 -7 mm 3 N -1 m -1 .

[0071] Specific embodiment 4

[0072] The only difference from the preparation method in the first embodiment is that in step 105 , the deposition temperature is 1050° C.

[0073] The test results show that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 4 is 44N, the friction coefficient is 0.46, and the average erosion rate is 3.6×10 -10 kg / m 2 ·s, and the average wear rate is 2.9×10 -7 mm 3 N -1 m -1 .

[0074] Specific embodiment five

[0075] The only difference from the preparation method in the first embodiment is that in step 106 , the temperature is lowered to 400° C.

[0076] The test results show that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 5 is 48N, the friction coefficient is 0.45, and the average erosion rate is 2.8×10 -10 kg / m 2 ·s, and the average wear rate is 2.1×10 -7 mm 3 N -1 m -1 .

[0077] Specific embodiment six

[0078] The only difference from the preparation method in the first embodiment is that in step 109 , the deposition temperature is 1250° C.

[0079] The test results show that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 6 is 43N, the friction coefficient is 0.48, and the average erosion rate is 3.7×10 -10 kg / m 2 ·s, and the average wear rate is 3.5×10 -7 mm 3 N -1 m -1 .

[0080] Specific embodiment seven

[0081] The only difference from the preparation method in the first embodiment is that in step 109 , the flow rate of methane is 300 sccm and the deposition temperature is 1250° C.

[0082] The test results show that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 7 is 40N, the friction coefficient is 0.5, and the average erosion rate is 4.5×10 -10 kg / m 2 ·s, and the average wear rate is 3.8×10 -7 mm 3 N -1 m -1 .

[0083] Specific embodiment eight

[0084] The only difference from the preparation method in the first embodiment is that in step 109 , the flow rate of trichloromethylsilane is 300 sccm.

[0085] The test results show that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 8 is 49N, the friction coefficient is 0.38, and the average erosion rate is 1.6×10 -10 kg / m 2 ·s, and the average wear rate is 1.8×10 -7 mm3 N -1 m -1 .

[0086] The above descriptions are only several embodiments of the present invention. Those skilled in the art may make various changes or modifications to the embodiments of the present invention based on the contents disclosed in the application documents without departing from the spirit and scope of the present invention.

Claims

1. A method for preparing a metal elbow, wherein: The following steps are involved: Preparation of the interface layer: Under vacuum conditions, a carbon source and a nitrogen source are provided, and the surface of the elbow substrate is subjected to carbon-nitrogen co-diffusion treatment by high-energy plasma to form a carbon-nitrogen co-diffusion layer as the interface layer; Preparing a barrier layer: depositing a metal oxide layer as the barrier layer on the surface of the carbon-nitrogen co-diffusion layer by chemical vapor deposition; Preparation of the corrosion-resistant layer: A silicon carbide layer is deposited on the surface of the metal oxide layer by chemical vapor deposition to serve as the corrosion-resistant layer.

2. The method for preparing a metal elbow according to claim 1, wherein: The carbon source includes methane, ethane, propylene and / or acetylene; the nitrogen source includes high-purity nitrogen and / or ammonia.

3. The method for preparing a metal elbow according to claim 1, wherein: In the step of preparing the interface layer, the temperature of the carbon-nitrogen co-diffusion treatment is 430° C. to 500° C.; the time of the carbon-nitrogen co-diffusion treatment is 0.5 hour to 1.5 hours.

4. The method for preparing a metal elbow according to claim 1, wherein: The step of preparing the barrier layer specifically comprises: Placing the elbow substrate combined with the carbon-nitrogen co-diffusion layer in a reaction chamber, and evacuating the reaction chamber; A mixed gas of hydrogen and argon is introduced; Heating the elbow substrate and the reaction chamber to a deposition temperature; Passing a reaction precursor gas to carry out a chemical reaction, thereby depositing a metal oxide layer on the surface of the carbon-nitrogen co-diffusion layer; The deposition temperature is 850° C. to 1050° C., and the deposition time is 2 hours to 6 hours.

5. The method for preparing a metal elbow according to claim 4, wherein: The reaction precursor gas includes titanium tetrachloride, aluminum trichloride, trichloromethylsilane, argon, carbon monoxide, carbon dioxide, hydrogen sulfide, nitrogen and oxygen.

6. The method for preparing a metal elbow according to claim 4, wherein: The step of preparing the corrosion-resistant layer specifically comprises: Cooling the elbow substrate combined with the metal oxide layer; Pass hydrogen and keep warm; reducing the flow rate of hydrogen gas and heating the reaction chamber to a deposition temperature; Passing a reaction gas to deposit a silicon carbide layer on the surface of the metal oxide layer; The deposition temperature is 1100° C. to 1250° C., and the deposition time is 2 hours to 5 hours.

7. The method for preparing a metal elbow according to claim 6, wherein: The reaction gas includes hydrogen, trichloromethylsilane, argon and methane; wherein the flow rate of hydrogen is 300 sccm to 800 sccm; the flow rate of trichloromethylsilane is 300 sccm to 800 sccm; the flow rate of argon is 100 sccm to 500 sccm; and the flow rate of methane is 300 sccm to 600 sccm.

8. A metal elbow, wherein: It includes an elbow substrate and a protective composite coating, wherein the protective composite coating includes an interface layer bonded to the surface of the elbow substrate, a barrier layer bonded to the surface of the interface layer, and a corrosion-resistant layer bonded to the surface of the barrier layer; wherein the interface layer is a carbon-nitrogen co-diffusion layer; and the barrier layer is a metal oxide layer.

9. The metal elbow according to claim 8, wherein: The thickness of the carbon-nitrogen co-diffusion layer is 0.5 μm to 30 μm.

10. The metal elbow according to claim 8, wherein: The thickness of the metal oxide layer is 3 μm to 20 μm.

11. The metal elbow according to claim 8, wherein: The material of the metal oxide layer includes TiO2, Al2O3 and / or SiO2.

12. The metal elbow according to claim 8, wherein: The corrosion-resistant layer is a silicon carbide layer.

13. The metal elbow according to claim 12, wherein: The thickness of the silicon carbide layer is 1 μm to 15 μm.

14. The metal elbow according to claim 12, wherein: The silicon carbide layer is a silicon carbide layer including an amorphous phase.

15. The metal elbow according to claim 14, wherein: The amorphous phase includes an amorphous carbon phase.

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