Nickel-titanium alloy surface high-temperature-resistant and corrosion-resistant surface coating suitable for carbon dioxide flooding oil well environment and preparation method thereof

Abstract

The invention discloses a nickel-titanium alloy surface high-temperature-resistant and corrosion-resistant surface coating suitable for a carbon dioxide flooding oil well environment and a preparation method thereof, and belongs to the field of metal material processing. The invention aims to solve the problems that the comprehensive effects in the aspects of high temperature resistance, corrosion resistance and reduction of nickel ion release are not ideal, and part of chemical plating solutions pollute the environment. According to the method, a transition layer is formed on the surface of the nickel-titanium alloy through two times of spraying of emulsions with different solid contents (15%-30% and 40%-60%) and different particle sizes (0.1-0.2 mu m and 0.2-0.5 mu m), the bonding strength of the coating and a matrix is effectively improved, and meanwhile a surface layer compact protection system is constructed through micron-sized polytetrafluoroethylene powder (2-10 mu m). The friction performance and the corrosion resistance of the nickel-titanium alloy are improved at the same time, and release of nickel ions is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing, and specifically relates to a high-temperature and corrosion-resistant surface coating for nickel-titanium alloys suitable for carbon dioxide-driven oil well environments, and its preparation method. Background Technology

[0002] In carbon dioxide flooding well environments, downhole temperatures are typically high and fluctuate significantly, and the environment also contains high concentrations of acidic ions, such as Cl. - Corrosive ions. Traditional rubber packers are prone to corrosion failure and creep deformation. Although nickel-titanium alloys possess shape memory effect and corrosion resistance, in high-temperature environments and acidic media, the selective dissolution and pitting tendency of nickel ions may induce stress corrosion cracking, limiting their long-term reliability in CO2-enhanced oil wells.

[0003] Polytetrafluoroethylene (PTFE) is a material with excellent chemical stability and a low coefficient of friction, widely used in various applications requiring corrosion resistance and friction reduction. Its unique molecular structure endows it with good high-temperature resistance, corrosion resistance, and aging resistance, while its extremely low coefficient of friction effectively reduces surface friction and wear. However, traditional PTFE coatings have some limitations when applied to nickel-titanium alloy surfaces. For example, the bonding strength between a single-layer PTFE coating and the nickel-titanium alloy substrate may be insufficient, leading to coating peeling under long-term use or complex operating conditions, thus affecting its protective effect and service life. Furthermore, simply using PTFE coatings cannot effectively control nickel ion release to a certain extent, failing to meet the comprehensive requirements of nickel-titanium alloys in terms of both high performance and environmental protection.

[0004] In existing technologies, there are various methods to improve the properties of nickel-titanium alloys, but most have certain shortcomings. Some methods modify nickel-titanium alloys by adding other elements, which can improve their performance to some extent, but may alter the original characteristics of the alloy. Furthermore, the type and content of the added elements need precise control, making the process complex and costly. Other methods employ traditional surface treatment techniques, such as electroless plating and electroplating. While these methods can improve the surface properties of nickel-titanium alloys to some extent, their overall effects on high-temperature resistance, corrosion resistance, and reduction of nickel ion release are not ideal, and some electroless plating solutions pose environmental pollution problems. Therefore, developing a surface coating preparation method that can simultaneously improve the frictional properties and corrosion resistance of nickel-titanium alloys while effectively reducing nickel ion release has become an important research direction in the field of metal processing. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a high-temperature resistant and corrosion-resistant nickel-titanium alloy and its surface coating, so as to simultaneously improve the friction performance and corrosion resistance of the nickel-titanium alloy and effectively reduce the release of nickel ions.

[0006] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a method for preparing a high-temperature and corrosion-resistant surface coating for nickel-titanium alloys suitable for carbon dioxide-driven oil well environments. This method involves first spraying two layers of liquid polytetrafluoroethylene (PTFE) onto the nickel-titanium alloy surface using high-temperature spraying technology, and then depositing a layer of PTFE micropowder through electrostatic spraying combined with a high-temperature curing process. The method includes the following steps: Step 1: First, remove any residual oil or dirt from the surface of the nickel-titanium alloy. Step 2: Polish the surface of the nickel-titanium alloy and then immerse it in an aqueous solution of sodium hydroxide and ethylenediamine. Step 3: Spray a layer of polytetrafluoroethylene emulsion with a solid content of 15%-30% onto the nickel-titanium alloy surface after step 2, and bake and cure it in a vacuum drying oven. Step 4: Then spray another layer of polytetrafluoroethylene emulsion with a solid content of 40%-60% and cure until it is surface dry. Step 5: Spray a layer of polytetrafluoroethylene micro powder onto the surface, bake and cure to obtain the coating on the nickel-titanium alloy surface.

[0007] Further specifying, in step 1, the nickel content in the nickel-titanium alloy is 30at%-50at.

[0008] To further specify, in step 1, the nickel-titanium alloy is cleaned in acetone for 10 minutes to remove surface oil and impurities.

[0009] Further specifying, in step 2, the nickel-titanium alloy surface is subjected to cross-polishing treatment.

[0010] To further specify, the cross-polishing process is performed as follows: use 400# sandpaper to polish the nickel-titanium alloy surface in a fixed direction (from bottom to top); then switch to 800# sandpaper, rotate the nickel-titanium alloy 90° so that the new polishing direction is perpendicular to the previous unidirectional texture, and the round trip distance and polishing time are the same as the initial polishing; then use 1200# sandpaper, rotate the nickel-titanium alloy 45° so that the polishing direction forms a certain angle with the previous two directions.

[0011] Further specifying, in step 2, the sodium hydroxide content is 1wt%-5wt%, the ethylenediamine mass concentration is 25%, and the aqueous solution of sodium hydroxide and ethylenediamine is prepared by completely dissolving ethylenediamine in deionized water, then adding sodium hydroxide, and stirring until completely dissolved.

[0012] Further specifying, in step 2, soaking is performed at room temperature for 1-5 hours.

[0013] Further specifying, in step 3, the average particle size of polytetrafluoroethylene is 0.1μm-0.2μm, and the coating thickness is 5μm-10μm.

[0014] Further specifying, in step 4, the average particle size of polytetrafluoroethylene is 0.2μm-0.5μm, and the coating thickness is 10μm-20μm.

[0015] Further specifying, in step 5, the average particle size of the polytetrafluoroethylene micro powder is 2μm-10μm, and the coating thickness is 20μm-50μm.

[0016] Further specifying, in steps 3 and 4, curing is performed at 100℃-200℃.

[0017] Further specifying, in step 5, the temperature is increased to 300℃-400℃ at a rate of 5℃ / min-20℃ / min, and then kept at that temperature for 10min-30min to cure.

[0018] Another object of the present invention is to provide a coating prepared by any of the methods described above.

[0019] In this invention, the polytetrafluoroethylene (PTFE) emulsion used in the first application has a solid content of 15%-30%, an average particle size of 0.1μm-0.2μm, and a spray thickness of 5μm-10μm. Its main effects are to wet the substrate, strengthen the interfacial bonding with the nickel-titanium alloy, and fill surface defects. The first baking and curing temperature is 100℃-200℃, and the time is 10min-60min. The second sprayed PTFE emulsion has a solid content of 40%-60%, an average particle size of 0.2μm-0.5μm, and a spray thickness of 10μm-20μm. Its main effects are to improve the density and wear resistance of the coating, reduce the number of spraying times, avoid excessive sagging, and improve coating continuity. The second curing time is reduced by 10 minutes compared to the first time, ensuring the high-solids-content layer is surface-dry and improving the adhesion rate of the PTFE micropowder. The average particle size of polytetrafluoroethylene micro powder is 2μm-10μm. The baking temperature is increased to 300℃-400℃, the heating rate is 5℃ / min-20℃ / min, the time is 10 minutes-30 minutes, and the thickness is 20μm-50μm. Compared with the prior art, the present invention has the following beneficial effects: This invention employs a composite design of "double-layer polytetrafluoroethylene emulsion + micro powder layer". By spraying emulsions with different solid contents (15%-30% and 40%-60%) and particle sizes (0.1μm-0.2μm and 0.2μm-0.5μm) twice, a transition layer is formed, which effectively improves the bonding strength between the coating and the substrate. At the same time, a dense protective system is constructed using micron-sized polytetrafluoroethylene powder (2μm-10μm). Compared with the traditional single-layer spraying process, it has better corrosion resistance.

[0020] This invention utilizes a two-stage emulsion spraying process with particle size differences to enhance interfacial bonding using a high specific surface area nanoscale emulsion (0.1μm-0.2μm). This reduces the number of spraying layers and lowers costs, while also providing ideal anchoring points for subsequent micro-powder layers. To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0021] Figure 1 This is an optical image of a nickel-titanium alloy that has undergone grinding, polishing, soaking treatment, and polytetrafluoroethylene coating in Embodiment 1 of the method of the present invention; Figure 2 This is an SEM image of the thickness of the polytetrafluoroethylene coating in Example 1 of the method of the present invention; Figure 3 These are optical images of the nickel-titanium alloy and the nickel-titanium alloy coated with polytetrafluoroethylene after being etched by the etching solution in Embodiment 1 of the method of the present invention. Figure 4 This is a SEM image of the nickel-titanium alloy after being etched by the etching solution in Example 1 of the method of the present invention; Figure 5 This is an optical image of a nickel-titanium alloy with a polytetrafluoroethylene coating after being etched by an etching solution in Embodiment 1 of the method of the present invention; Figure 6 It is the apparent uniform corrosion rate after corrosion in the corrosive solution in Example 1 of the method of the present invention; Figure 7 This is a comparison diagram of the Tafel polarization curves of nickel-titanium alloy measured in the corrosive solution in Example 1 of the method of the present invention; Figure 8 This is a comparison chart of the Tafel polarization curves of the polytetrafluoroethylene-coated nickel-titanium alloy measured in the etching solution in Example 1 of the method of the present invention. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, while not limiting the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0023] Example 1: The preparation method of the high-temperature and corrosion-resistant surface coating of nickel-titanium alloy suitable for carbon dioxide flooding oil well environments in this example is carried out according to the following steps: Step 1: Clean the nickel-titanium alloy in acetone for 10 minutes to remove surface oil and impurities.

[0024] Step 2: Perform cross-polishing on the cleaned nickel-titanium alloy: First, use 400# sandpaper for initial polishing for 3 minutes. Then, switch to 800# sandpaper and rotate the nickel-titanium alloy 90° so that the new polishing direction is perpendicular to the previous unidirectional texture, polishing for another 3 minutes. Next, use 1200# sandpaper and rotate the nickel-titanium alloy 45° for polishing for another 3 minutes. Afterward, ultrasonically treat the polished nickel-titanium alloy in anhydrous ethanol for 30 minutes. Then, immerse the nickel-titanium alloy in an aqueous solution of sodium hydroxide and ethylenediamine to promote the formation of amino groups on the surface. The sodium hydroxide content in the aqueous solution is 2 wt%, and the ethylenediamine concentration is 25%. The aqueous solution is prepared by completely dissolving ethylenediamine in deionized water, then adding sodium hydroxide and stirring until completely dissolved. Step 3: Spray a layer of polytetrafluoroethylene emulsion onto the nickel-titanium alloy surface treated in Step 2, using 20% ​​solid content, an average particle size of 0.1 μm, and a spray thickness of 5 μm. Bake and cure in a vacuum drying oven at 150°C for 20 minutes. Step 4: Next, spray a layer of polytetrafluoroethylene emulsion with an average particle size of 0.3 μm and a solid content of 50%, with a thickness of 15 μm, and cure it at 150°C until it is surface dry. Step 5: While it is not completely cured, spray a layer of polytetrafluoroethylene micro powder with an average particle size of 5μm and a thickness of 30μm on the surface. Finally, raise the temperature to 380℃ in a muffle furnace at a heating rate of 10℃ / min and bake for 20 minutes to obtain a nickel-titanium alloy with a polytetrafluoroethylene coating.

[0025] Example 2: The preparation method of the high-temperature and corrosion-resistant surface coating of nickel-titanium alloy suitable for carbon dioxide flooding oil well environments in this example is carried out according to the following steps: Step 1: Clean the nickel-titanium alloy in acetone for 10 minutes to remove surface oil and impurities.

[0026] Step 2: Perform cross-polishing treatment on the cleaned nickel-titanium alloy: First, use 400# sandpaper for initial polishing for 3 minutes. Then, switch to 800# sandpaper and rotate the nickel-titanium alloy 90° so that the new polishing direction is perpendicular to the previous unidirectional texture. Polish for another 3 minutes. Next, use 1200# sandpaper and rotate the nickel-titanium alloy 45° for 3 minutes. After polishing, place the nickel-titanium alloy in anhydrous ethanol for ultrasonic treatment for 30 minutes. Then, immerse the nickel-titanium alloy in a mixed solution of sodium hydroxide and ethylenediamine to promote the formation of amino groups on the surface. The sodium hydroxide and ethylenediamine aqueous solution contains 2 wt% sodium hydroxide and 25% ethylenediamine. The sodium hydroxide and ethylenediamine aqueous solution is prepared by completely dissolving ethylenediamine in deionized water, then adding sodium hydroxide and stirring until completely dissolved.

[0027] Step 3: Spray a layer of polytetrafluoroethylene emulsion onto the nickel-titanium alloy surface, using 30% solid content, an average particle size of 0.2μm, and a spray thickness of 5μm. Bake and cure in a vacuum drying oven at 200℃ for 20 minutes. Step 4: Next, spray a layer of polytetrafluoroethylene emulsion with an average particle size of 0.4μm and a solid content of 40%, with a thickness of 10μm, and cure it at 200℃ until it is surface dry. Step 5: While it is not completely cured, spray a layer of polytetrafluoroethylene micro powder with an average particle size of 5μm and a thickness of 20μm on the surface. Finally, raise the temperature to 380℃ in a muffle furnace at a heating rate of 10℃ / min and bake for 20 minutes to cure, and finally obtain a nickel-titanium alloy with a polytetrafluoroethylene coating.

[0028] The optical image of the nickel-titanium alloy after grinding, polishing, and soaking treatment in Example 1 is as follows: Figure 1 As shown. From Figure 1 The images show that the nickel-titanium alloy surface still retains a metallic luster. Furthermore, the optical image of the PTFE-coated nickel-titanium alloy shows a uniform black surface that is relatively smooth. It is also evident that the coating is tightly bonded to the substrate, with no obvious peeling or flaking, indicating good adhesion between the coating and the substrate.

[0029] SEM images of the polytetrafluoroethylene coating thickness in Example 1 are shown below. Figure 2 As shown. The polytetrafluoroethylene coating has a thickness of approximately 50 μm.

[0030] The optical image of the nickel-titanium alloy after etching with the etchant in Example 1 is as follows: Figure 3As shown. Due to the complex internal environment of the oil well, this embodiment simulated an internal acidic environment to conduct an acid corrosion resistance test. The acid mixture consisted of 15% hydrochloric acid, 2% formaldehyde, 2% acetic acid, and 81% deionized water. The nickel-titanium alloy was placed in the acid mixture and heated from room temperature (25°C) to 120°C, and its surface morphology was observed. It can be seen that the surface of the corroded nickel-titanium alloy is very rough and severely corroded. In contrast, the polytetrafluoroethylene-coated nickel-titanium alloy did not have obvious cracks, pores, or other defects and still maintained a good luster.

[0031] The SEM image of the nickel-titanium alloy after etching with the etchant in Example 1 is shown below. Figure 4 As shown. From Figure 4 It can be seen that the surface of the corroded nickel-titanium alloy is obviously uneven, and there are also obvious local corrosion pits.

[0032] The optical image of the polytetrafluoroethylene-coated nickel-titanium alloy after etching with the etchant in Example 1 is shown below. Figure 5 As shown, polytetrafluoroethylene (PTFE) can be seen adhering to the nickel-titanium alloy surface in a scale-like arrangement. Despite high-temperature corrosion, no cracks were formed on the surface, indicating that PTFE not only bonds firmly to the substrate but also effectively prevents corrosion from the corrosive liquid.

[0033] In Example 1, the apparent uniform corrosion rates of nickel-titanium alloy and polytetrafluoroethylene-coated nickel-titanium alloy after corrosion in the corrosive solution are as follows: Figure 6 As shown in the figure, by calculating the apparent uniform corrosion rate, it can be seen that the corrosion rate of the nickel-titanium alloy increases significantly with temperature from 25℃ to 120℃ (1.3715→42.7006 mm / a), and the weight loss increases (0.0848→1.1319 g). The corrosion rate of the PTFE-coated nickel-titanium alloy also increases with temperature (0.0046→0.0516 mm / a), but the rate of increase is much lower than that of the uncoated sample.

[0034] The Tafel polarization curves of the nickel-titanium alloy measured in corrosive solutions at different temperatures in Example 1 are as follows: Figure 7 As shown. From Figure 7 As can be seen, the self-corrosion potential of nickel-titanium alloy decreases with increasing temperature, indicating an increase in its corrosion driving force. The rightward shift of the polarization curve also shows a rapid increase in the self-corrosion current. Calculations show that the corrosion rate (R) of nickel-titanium alloy at room temperature is 1.3543 mm / a, increasing 30-fold when the temperature rises to 120℃. Therefore, unprotected nickel-titanium alloy cannot withstand high-temperature corrosive environments.

[0035] The Tafel polarization curves of the polytetrafluoroethylene-coated nickel-titanium alloy in Example 1, measured in etching solutions at different temperatures, are as follows: Figure 8 As shown. From Figure 8As can be seen, the self-corrosion potential of the PTFE-coated nickel-titanium alloy increases with increasing temperature, from -0.4142V to -0.3812V. This indicates that in a high-temperature environment, the PTFE coating and the nickel-titanium alloy substrate bond more firmly, thus reducing the corrosion driving force. The corrosion current also shows that the PTFE-coated nickel-titanium alloy exhibits a lower corrosion rate. The corrosion rate is 0.0034 mm / a at room temperature, and even at 120℃, the corrosion rate is only 0.0539 mm / a. Therefore, this example demonstrates that the PTFE coating can significantly improve the corrosion resistance of nickel-titanium alloys at high temperatures.

[0036] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a high-temperature and corrosion-resistant surface coating on a nickel-titanium alloy surface suitable for carbon dioxide-driven oil well environments, characterized in that, Includes the following steps: Step 1: First, remove any residual oil or dirt from the surface of the nickel-titanium alloy. Step 2: Polish the surface of the nickel-titanium alloy and then immerse it in an aqueous solution of sodium hydroxide and ethylenediamine. Step 3: Spray a layer of polytetrafluoroethylene emulsion with a solid content of 15%-30% onto the nickel-titanium alloy surface after step 2, and bake and cure it in a vacuum drying oven. Step 4: Then spray another layer of polytetrafluoroethylene emulsion with a solid content of 40%-60% and cure until it is surface dry. Step 5: Spray a layer of polytetrafluoroethylene micro powder onto the surface, bake and cure to obtain the coating on the nickel-titanium alloy surface.

2. The method according to claim 1, characterized in that, The nickel content in nickel-titanium alloys is 30 at% to 50 at%.

3. The method according to claim 1, characterized in that, The surface of the nickel-titanium alloy is subjected to cross-grinding. The cross-grinding process is carried out in the following steps: use 400# sandpaper to grind the surface of the nickel-titanium alloy in a fixed direction (from bottom to top); then switch to 800# sandpaper, rotate the nickel-titanium alloy 90° so that the new grinding direction is perpendicular to the previous unidirectional texture, and the round trip distance and grinding time are the same as the initial grinding; then use 1200# sandpaper to rotate the nickel-titanium alloy 45° so that the grinding direction forms a certain angle with the previous two directions.

4. The method according to claim 3, characterized in that, In step 2, the sodium hydroxide content is 1wt%-5wt%, the ethylenediamine mass concentration is 25%, and the soaking time is 1h-5h at room temperature.

5. The method according to claim 1, characterized in that, In step 3, the average particle size of polytetrafluoroethylene is 0.1μm-0.2μm, and the coating thickness is 5μm-10μm.

6. The method according to claim 1, characterized in that, In step 4, the average particle size of polytetrafluoroethylene is 0.2μm-0.5μm, and the coating thickness is 10μm-20μm.

7. The method according to claim 1, characterized in that, In step 5, the average particle size of the polytetrafluoroethylene micro powder is 2μm-10μm, and the coating thickness is 20μm-50μm.

8. The method according to claim 1, characterized in that, In steps 3 and 4, curing is carried out at 100℃-200℃.

9. The method according to claim 1, characterized in that, In step 5, the temperature is increased to 300℃-400℃ at a rate of 5℃ / min-20℃ / min, and then kept at that temperature for 10min-30min to cure.

10. A coating prepared by the method according to any one of claims 1-9.

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