Metal elbow and preparation method thereof

Abstract

The preparation method comprises the following steps that an interface layer is prepared, specifically, under the vacuum condition, a carbon source and a nitrogen source are provided, and carbon-nitrogen co-permeation treatment is conducted on the surface of an elbow base body through high-energy plasma to form a carbon-nitrogen co-permeation layer serving as the interface layer; preparing a barrier layer: depositing on the surface of the carbonitriding layer through a chemical vapor deposition method to form a metal oxide layer as the barrier layer; and preparing a corrosion-resistant layer: depositing on the surface of the metal oxide layer through a chemical vapor deposition method to form a silicon carbide layer as the corrosion-resistant layer. The protective composite coating composed of the interface layer formed by the carbon-nitrogen co-permeation layer, the barrier layer formed by the metal oxide layer and the corrosion-resistant layer is combined to the surface of the elbow base body, so that the metal elbow has the low average erosion rate and average wear rate, and the safety and reliability of an oil and gas field gathering and transportation system can be remarkably improved.

Description

Technical Field

[0001] 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

[0002] When conducting production operations at oil field wells or oil and gas wells, the fluid in the well is transported to ground storage tanks or gathering stations through the oil and gas field gathering and transportation system, thereby achieving oil and gas production.

[0003] Metal elbows are one of the important structural components of the oil and gas field gathering and transportation system. The materials transported by the oil and gas gathering and transportation system are usually solid-liquid-gas multiphase media including gravel, natural gas, crude oil, water, CO2 / H2S, etc. Metal elbows are very prone to erosion and wear in the non-steady-state erosion and wear environment of multiphase fluid media, causing rapid thinning and even perforation of the elbows, posing serious safety hazards to oil and gas field production. How to carry out erosion and wear protection for metal elbows in the multiphase flow erosion and wear environment has become an urgent problem to be solved for the safe operation of oil and gas field gathering and transportation systems.

[0004] 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, 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 safety of the gathering and transportation system. Summary of the invention

[0005] The purpose of the present invention is to provide a metal elbow and a preparation method thereof, so as 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, thereby affecting the production efficiency and safety of the gathering and transportation system.

[0006] The above-mentioned purpose of the present invention can be achieved by adopting the following technical solutions:

[0007] The present invention provides a method for preparing a metal elbow, comprising the following steps: preparing an 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: a metal oxide layer is deposited on the surface of the carbon-nitrogen co-diffusion layer by chemical vapor deposition to form the barrier layer; preparing a corrosion-resistant layer: a silicon carbide layer is deposited on the surface of the metal oxide layer by chemical vapor deposition to form the corrosion-resistant layer.

[0008] In an embodiment of the present invention, the carbon source includes methane, ethane, propylene and / or acetylene; the nitrogen source includes high-purity nitrogen and / or ammonia.

[0009] In an embodiment of the present invention, in the step of preparing the interface layer, the temperature of the carbon-nitrogen co-diffusion treatment is 430° C. to 500° C.; and the time of the carbon-nitrogen co-diffusion treatment is 0.5 hour to 1.5 hours.

[0010] In an embodiment of the present invention, the step of preparing the barrier layer specifically includes: placing the elbow substrate combined with the carbon-nitrogen co-diffusion layer in a reaction chamber, and evacuating the reaction chamber; introducing a mixed gas of hydrogen and argon; heating the elbow substrate and the vacuum chamber to a deposition temperature; introducing a reaction precursor gas for a chemical reaction, thereby depositing a metal oxide layer on the surface of the carbon-nitrogen co-diffusion layer; wherein the deposition temperature is 850°C to 1050°C; and the deposition time is 2 hours to 6 hours.

[0011] In an embodiment of the present invention, the reaction precursor gas includes titanium tetrachloride, aluminum trichloride, trichloromethylsilane, argon, carbon monoxide, carbon dioxide, hydrogen sulfide, nitrogen and oxygen.

[0012] In an embodiment of the present invention, the step of preparing the corrosion-resistant layer specifically includes: cooling the elbow substrate combined with the metal oxide layer; introducing hydrogen and keeping it warm; reducing the flow rate of hydrogen and heating the reaction chamber to a deposition temperature; introducing reaction gas to deposit a silicon carbide layer on the surface of the metal oxide layer; wherein the deposition temperature is 1100°C to 1250°C; and the deposition time is 2 to 5 hours.

[0013] In an embodiment of the present invention, 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.

[0014] 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.

[0015] In an embodiment of the present invention, the carbonitrided layer has a thickness of 0.5 μm to 30 μm.

[0016] In an embodiment of the present invention, the thickness of the metal oxide layer is 3 μm to 20 μm.

[0017] In an embodiment of the present invention, the material of the metal oxide layer includes TiO2, Al2O3 and / or SiO2.

[0018] In an embodiment of the present invention, the corrosion-resistant layer is a silicon carbide layer.

[0019] In an embodiment of the present invention, the thickness of the silicon carbide layer is 1 μm to 15 μm.

[0020] In an embodiment of the present invention, the silicon carbide layer is a silicon carbide layer including an amorphous phase.

[0021] In an embodiment of the present invention, the amorphous phase includes an amorphous carbon phase.

[0022] The characteristics and advantages of the present invention are:

[0023] 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, so that while utilizing the interface layer to enhance the hardness and strength of the surface of the elbow substrate, the chemical matching of the metal elbow and the metal oxide layer can also be improved and enhanced. 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, so that utilizing the barrier layer can enhance the barrier capacity for solid-liquid-gas three-phase media on the one hand, and enhance the wear resistance and corrosion resistance of the metal elbow on the other hand; further, 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; and 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

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. 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.

[0025] Figure 1 It is a cross-sectional schematic diagram of the metal elbow in the present invention.

[0026] Figure 2This is a cross-sectional SEM test image of the protective composite coating of the metal elbow prepared in the specific embodiment 1 of the present invention.

[0027] Figure 3 This is a bonding strength test diagram of the protective composite coating of the metal elbow prepared in the specific embodiment 1 of the present invention.

[0028] Figure 4 This is a test chart of the average friction coefficient of the protective composite coating of the metal elbow prepared in the specific embodiment 1 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0030] Implementation Method 1

[0031] like Figure 1 As shown, 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.

[0032] Specifically, the elbow base 1 is generally in the form of a curved pipe 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.

[0033] 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, so that while the interface layer 21 is used to enhance the hardness and strength of the surface of the elbow substrate 1, the chemical matching of the metal elbow and the metal oxide layer can be improved and enhanced. The carbon-nitrogen co-diffusion layer is used as a transition layer to 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. The barrier layer 22 can improve the barrier capacity for solid-liquid-gas three-phase media on the one hand, and can 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 substrate 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.

[0034] 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 elbow 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, etc.

[0035] In the embodiment of the present invention, the carbonitrided layer has a thickness of 0.5 μm to 30 μm, and preferably has a thickness of 10 μm to 30 μm.

[0036] 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.

[0037] Specifically, metal oxide particles are deposited on the surface of the interface layer 21 to form a barrier layer 22. The metal oxide particles are submicron-sized, which makes them have a high bonding force with the interface layer 21 and the corrosion-resistant layer 23. At the same time, the barrier layer 22 formed by the submicron-sized metal oxide particles can significantly block the penetration of the corrosive medium. Preferably, the particle size of the metal oxide particles in the barrier layer 22 is 100nm to 400nm.

[0038] In an embodiment of the present invention, the corrosion-resistant layer 23 is a silicon carbide layer. By using the silicon carbide layer as the corrosion-resistant layer 23, excellent erosion and wear resistance can be provided, and the bonding 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.

[0039] Specifically, silicon carbide particles are deposited on the surface of the barrier layer 22 to form the corrosion-resistant layer 23. The silicon carbide particles are nano-sized particles, which make them have a high bonding force with the barrier layer 22, and can significantly improve the corrosion resistance of the metal elbow. Preferably, the silicon carbide nanoparticle size in the corrosion-resistant layer 23 is 100nm to 400nm.

[0040] 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 within the above ranges is beneficial to further improve the erosion resistance and wear resistance of the metal elbow.

[0041] In an embodiment of the present invention, the silicon carbide layer is a silicon carbide layer including an amorphous phase, which can play a drag reduction and lubrication role, further reduce the friction coefficient of the metal elbow, and reduce the erosion damage of the solid-liquid-gas three-phase medium of the oil and gas field gathering and transportation system, and further improve the erosion resistance and wear resistance of the metal elbow. Specifically, the amorphous phase includes an amorphous carbon phase. The proportion of the amorphous carbon phase in the silicon carbide layer is preferably 1%-5%.

[0042] The metal elbow of the present invention can be prepared by the preparation method in the second embodiment, and of course, it can also be prepared by 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.

[0043] Implementation Method 2

[0044] 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 in the first embodiment, and 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.

[0045] The preparation method includes the following steps: preparing the interface layer 21: under vacuum conditions, providing a carbon source and a nitrogen source, and subjecting the surface of the elbow substrate 1 to carbon-nitrogen co-diffusion treatment 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.

[0046] Before the step of preparing the interface layer 21, cleaning is also included: the surface of the metal elbow is cleaned by high-energy plasma under vacuum conditions. Specifically, the high-energy plasma is argon plasma. The high-energy plasma cleaning time is 15 minutes to 45 minutes. In addition, before high-energy plasma cleaning, the elbow base 1 can also be surface polished to remove impurities, and the surface is sandblasted with brown corundum sand, and then the surface is polished, and then the surface of the elbow base 1 is ultrasonically cleaned with alcohol, and then the cleaned metal elbow base 1 is placed in an oven and dried at 100°C for 5 hours.

[0047] 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; the nitrogen source includes high-purity nitrogen and / or ammonia.

[0048] In some embodiments of the present invention, in the step of preparing the interface layer 21, the temperature of the carbon-nitrogen co-diffusion treatment is 430°C to 500°C; and the time of the carbon-nitrogen co-diffusion treatment is 0.5 hour to 2 hours.

[0049] 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 it within the above range is beneficial to further increase the carburizing-silicon-nitrogen depth, thereby further improving the hardness and strength of the metal elbow.

[0050] 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 mixed gas of hydrogen and argon; heating the elbow substrate 1 and the reaction chamber to a deposition temperature; introducing a reaction precursor gas for 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;

[0051] 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.

[0052] 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.

[0053] In an embodiment of the present invention, the step of preparing the corrosion-resistant layer 23 specifically includes: cooling the elbow substrate 1 combined with the metal oxide layer; introducing hydrogen and keeping it warm; adjusting the flow rate of hydrogen, and heating the vacuum chamber to the deposition temperature; introducing the reaction gas to deposit and form a silicon carbide layer on the surface of the metal oxide layer. Specifically, the temperature is reduced to 200°C to 400°C. The insulation time is 1 hour to 3 hours. The flow rate of hydrogen during the insulation process is 500sccm to 800sccm. During the heating process, the flow rate of hydrogen is reduced to 50sccm to 200sccm. The reaction gas includes hydrogen, trichloromethylsilane, argon and methane; wherein the flow rate of hydrogen is 300sccm to 800sccm; the flow rate of trichloromethylsilane is 300sccm to 800sccm; the flow rate of argon is 100sccm to 500sccm; the flow rate of methane is 300sccm to 600sccm.

[0054] 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.

[0055] 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 range, and limiting it within the above 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.

[0056] Some specific embodiments are provided below to facilitate better understanding and implementation of the preparation method of the present invention for preparing a metal elbow, but are not to be construed as limiting the scope of protection claimed by the present invention. Specific embodiment 1

[0058] The preparation of the metal elbow comprises the following steps:

[0059] 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, put the cleaned metal elbow base 1 into an oven, dry it at 100°C for 5 hours, and then place it in a vacuum chamber.

[0060] 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 for 30 minutes.

[0061] 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.

[0062] 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 introduce hydrogen and nitrogen at the same time, with a hydrogen flow rate of 200 sccm and a nitrogen flow rate of 200 sccm; start the furnace heating program, set the heating rate to 5°C / min, and the deposition temperature to 950°C.

[0063] Step 105, preparing an aluminum oxide layer as a barrier layer 22 on the surface of the carbon-nitrogen co-diffusion layer by chemical vapor deposition, comprising the steps of: heating the CVD device to 500°C at a heating rate of 5°C / min and keeping the temperature for 1 hour, then heating to 950°C at a heating rate of 8°C / min, then entering the coating deposition program, introducing reaction precursor gases such as aluminum chloride, carbon monoxide, carbon dioxide, hydrogen, and hydrogen sulfide, wherein the flow rate of aluminum chloride is 800sccm, the flow rate of carbon monoxide and carbon dioxide is 600sccm, the flow rate of hydrogen is 1200sccm, the flow rate of hydrogen sulfide is 50sccm, the deposition time is 5 hours, and the deposition pressure is 7×10 4 Pa.

[0064] 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.

[0065] Step 107, the temperature in the reaction chamber is lowered to 200°C, hydrogen is introduced at a flow rate of 600 sccm, and the temperature is maintained for 3 hours.

[0066] Step 108, after the heat preservation process is completed, the flow rate of hydrogen is adjusted to 200 sccm, and the heating program is started at the same time to heat the reaction chamber to 1100°C.

[0067] Step 109, when the temperature is raised to 1100°C, a silicon carbide layer is prepared on the surface of the aluminum oxide layer as a corrosion-resistant layer 23 by chemical vapor deposition: 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.

[0068] Step 1010: After the silicon carbide layer is prepared, the flow rate of argon gas is maintained at 200 sccm, and other gases are stopped, and the temperature is naturally lowered to room temperature, thereby obtaining a corrosion-resistant and wear-resistant metal elbow.

[0069] Determination of metal elbows

[0070] Figure 2 This is a cross-sectional morphology test diagram of the metal elbow obtained in the specific embodiment 1 of the present invention. Figure 2 It can be seen that in the metal elbow prepared in specific embodiment 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 density is high, wherein the thickness of the interface layer 21 is about 1 μm, the thickness of the barrier layer 22 is about 15 μm, and the thickness of the corrosion-resistant layer 23 is about 8 μm.

[0071] Figure 3 The figure is a test result of the bonding strength of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 1 of the present invention. Figure 3 It can be seen that the bonding force of the protective composite coating 2 in the metal elbow prepared in the specific embodiment 1 is 54N.

[0072] Figure 4 The figure is a test result of the average friction coefficient of the metal elbow made in the specific embodiment 1 of the present invention. Figure 4 It can be seen that the average friction coefficient of the metal elbow prepared in the specific embodiment 1 is 0.30.

[0073] In addition, the average erosion rate test shows that the average erosion rate of the metal elbow prepared in the specific embodiment 1 is 1.5×10 -10 kg / m 2 ·s.

[0074] 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 . Specific embodiment 2

[0076] The only difference from the first specific embodiment is that in step 103, the temperature of the carbonitriding treatment is 500°C.

[0077] 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, the average wear rate is 2.3×10 -7 mm 3 N -1 m -1 . Specific embodiment three

[0079] The only difference from the preparation method in the first specific embodiment is that in step 105, the deposition temperature is 850°C.

[0080] 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 . Specific embodiment 4

[0082] The only difference from the preparation method in the first specific embodiment is that in step 105, the deposition temperature is 1050°C.

[0083] 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, the average wear rate is 2.9×10 -7 mm 3 N -1 m -1 . Specific embodiment five

[0085] The only difference from the preparation method in the first specific embodiment is that in step 106, the temperature is lowered to 400°C.

[0086] 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, the average wear rate is 2.1×10 -7 mm 3 N -1 m -1 . Specific embodiment six

[0088] The only difference from the preparation method in the first specific embodiment is that in step 109, the deposition temperature is 1250°C.

[0089] 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, the average wear rate is 3.5×10 -7 mm 3 N -1 m -1 . Specific embodiment seven

[0091] The only difference from the preparation method in the first specific embodiment is that in step 109, the flow rate of methane is 300 sccm and the deposition temperature is 1250°C.

[0092] 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, the average wear rate is 3.8×10 -7 mm 3 N -1 m -1 . Specific embodiment eight

[0094] The only difference from the preparation method in the first specific embodiment is that in step 109, the flow rate of trichloromethylsilane is 300 sccm.

[0095] 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, the average wear rate is 1.8×10 -7 mm 3 N -1 m-1 .

[0096] The above 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: The thickness of the carbon-nitrogen co-diffusion layer is 0.5 μm to 30 μm.

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

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

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

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

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

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

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