Mg-Li-Gd-Ni alloy based on lpso / matrix potential difference regulation degradation rate and preparation method and application thereof

Abstract

The application discloses a kind of Mg-Li-Gd-Ni alloy based on LPSO / matrix potential difference accurate regulation and control degradation rate and preparation method and application;Belong to metal material technical field.The present application solves the problem that the degradation rate of existing magnesium-lithium alloy is difficult to accurately control in degradable application.The alloy composition of the present application is as follows, by mass percentage:Li:8%, Gd:1-5%, Ni:0.25-1.25%, the balance is Mg.The stable electrochemical potential difference exists between the LPSO phase and the magnesium-lithium matrix of the present application, the potential difference is maintained in the range of 750-850 mV, and does not change with the change of LPSO content.The volume fraction and distribution of LPSO phase can be changed by controlling the content of Gd and Ni, and the degradation rate can be accurately controlled by increasing the area of cathode phase without changing the unit galvanic corrosion intensity.The degradation rate of the alloy of the present application can be continuously adjustable in the range of 0.09-0.23 mg / cm 2 ·min, and the degradation behavior has excellent temperature response characteristics, especially suitable for oil and gas well fracturing operation with accurate requirement for degradation time.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, specifically relating to a biodegradable magnesium-lithium alloy, particularly a Mg-Li-Gd-Ni alloy for use in oil and gas extraction biodegradable tools, which achieves precise control of degradation rate based on the potential difference between the LPSO phase and the matrix, as well as its preparation method and application. Background Technology

[0002] In oil and gas field fracturing operations, biodegradable fracturing balls and biodegradable bridge plugs are core components for implementing temporary plugging staged fracturing technology. These tools need to be effectively sealed in the high-pressure downhole environment and degrade automatically after the fracturing operation is completed, avoiding costly drilling and refining operations. Currently, commonly used biodegradable materials include ceramics, plastic composites, and magnesium alloys. Among them, magnesium alloys have become a research hotspot in this field due to their low density, high specific strength, and degradability in water-based fracturing fluids.

[0003] Magnesium-lithium alloys, as the lightest metallic structural materials, possess excellent specific strength and good processing properties. However, in degradable applications, the degradation rate is difficult to control precisely. Existing technologies mainly involve adding high-potential elements (such as Ni, Cu, and Fe) to form a second phase, utilizing the microcouple effect to accelerate degradation. However, current research focuses primarily on the influence of the amount of the second phase on the degradation rate, neglecting the fundamental laws governing the electrochemical interaction between the second phase and the matrix. Summary of the Invention

[0004] This invention addresses the problem of precise control over the degradation rate of existing magnesium-lithium alloys in biodegradable applications, and provides a Mg-Li-Gd-Ni alloy with degradation rate controlled by LPSO / matrix potential difference, its preparation method, and its application.

[0005] This invention introduces a long-period stacked ordered structure phase (LPSO phase) into the magnesium alloy. There is a stable electrochemical potential difference between the LPSO phase and the magnesium-lithium matrix, and this potential difference does not change with the change of LPSO phase content. This enables precise control of the degradation rate of the magnesium-lithium alloy and provides a brand-new technical approach: This invention achieves linear and predictable control of the degradation rate by controlling the area of ​​the cathode phase (LPSO) without changing the unit galvanic corrosion intensity.

[0006] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a Mg-Li-Gd-Ni alloy based on LPSO / matrix potential difference to regulate the degradation rate. The alloy composition, by mass percentage, is: Li: 8%, Gd: 1%-5%, Ni: 0.25%-1.25%, with the balance being Mg and unavoidable impurities, and the mass ratio of Gd to Ni is 4:1.

[0007] Furthermore, the alloy's microstructure forms a long-period stacked ordered phase (LPSO phase), and the electrochemical potential difference between the LPSO phase and the magnesium-lithium matrix is ​​stable within the range of 750-850 mV.

[0008] Further specifying, the LPSO phase is a 24R type long-period stacked ordered structure with an atomic layer period thickness of 2.07 nm.

[0009] Another objective of this invention is to provide a method for preparing the Mg-Li-Gd-Ni alloy based on the degradation rate regulation of LPSO / matrix potential difference.

[0010] A method for preparing a Mg-Li-Gd-Ni alloy based on LPSO / matrix potential difference to regulate degradation rate includes the following steps: melting the raw materials under inert gas protection, casting them into shape, and homogenizing them with heat treatment.

[0011] Further specifying, the raw materials are pure magnesium ingots, pure lithium, Mg-Gd master alloy, and Mg-Ni master alloy.

[0012] To further specify, the Mg-Gd master alloy is Mg-30wt%Gd.

[0013] To further specify, Mg-Ni master alloy Mg 30wt%Ni.

[0014] To further specify, the inert gas is argon.

[0015] Further specify the melting process: hold at 720℃ for 30 minutes.

[0016] Further, the homogenization heat treatment is defined as a hot pressing pretreatment at 70 MPa for 30 min.

[0017] Furthermore, the present invention also provides the application of the Mg-Li-Gd-Ni alloy based on LPSO / matrix potential difference to regulate degradation rate, specifically in the preparation of biodegradable tools for oil and gas wells.

[0018] Further specifying, the degradable tool is a degradable fracturing ball, a degradable bridge plug, or a degradable temporary plugging ball.

[0019] This invention achieves controllable degradation rate by controlling the Gd and Ni content to a Gd:Ni mass ratio of 4:1, resulting in long-period stacked ordered phase structures with different morphologies and distributions in the alloy's microstructure. The degradation rate of the alloy increases with increasing total Gd and Ni content. However, when the Gd and Ni content meets a specific ratio resulting in a discontinuous lamellar distribution of the LPSO phase, its degradation rate is higher than that of an alloy with a higher LPSO phase content but a concentrated blocky distribution. The degradation rate of the alloy at 93℃ is significantly higher than that at 25℃, and the degradation rate ranking trend among the alloys at different temperatures is consistent.

[0020] Existing technologies, by controlling the ratio of Mg, Gd, and Ni, form a large number of long-term stacked ordered phases (LPSO) with high potential. The significant electronegativity difference between the LPSO phase and the magnesium matrix creates numerous interfaces not only between the LPSO phase and the matrix but also between the lamellar structures within the LPSO, forming numerous micro-cells and greatly promoting the degradation of the alloy material. This approach only emphasizes a single high-speed degradation. In contrast, this invention precisely controls the mass ratio of Gd to Ni to 4:1, resulting in a discontinuous, lamellar, and disordered distribution of the LPSO phase in the alloy. At this point, the alloy's degradation rate is higher than that of alloys with a higher LPSO phase content but a concentrated, blocky distribution. This allows for a controllable design of the degradation rate from fast to slow, thus enabling the preparation of alloy materials suitable for different operating durations and achieving gradient control.

[0021] Compared with the prior art, the advantages of the present invention are as follows: 1. Precise and controllable degradation rate: This invention utilizes the stable electrochemical potential difference between the LPSO phase and the matrix, and controls the LPSO phase volume fraction within the range of 0.09-0.23 mg / cm³. 2 The degradation rate was linearly and predictably controlled within a certain range. This electrochemical mechanism-based control method, unlike traditional empirical methods, significantly improves both accuracy and reliability.

[0022] 2. Clear regulatory mechanism: The positive correlation between degradation rate and LPSO content is clearly revealed to stem from the increase in cathode area, rather than changes in potential difference. This mechanism provides clear theoretical guidance for alloy design.

[0023] 3. Excellent temperature response characteristics: The alloy degradation rate is highly sensitive to temperature and can automatically adapt to oil and gas reservoirs with different geothermal gradients, achieving "intelligent" degradation. The degradation rate at 93℃ can reach 27 times that at 25℃, making it particularly suitable for fracturing operations at different well depths.

[0024] 4. Excellent mechanical properties: The strengthening effect of the LPSO phase ensures that the alloy has sufficient strength. The tensile strength of the Mg-8Li-5Gd-1.25Ni alloy reaches 142.3 MPa, and the compressive strength reaches 379.0 MPa at a deformation of 40%, which fully meets the requirements of downhole high-pressure operations.

[0025] 5. Simple manufacturing process: Based on conventional casting and heat treatment processes, it is easy to achieve industrial production.

[0026] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0027] Figure 1 Mg-8Li-4xGd-xNi ( x Morphology images, surface potential maps, and potential distribution maps of alloys with weights of 0.25, 0.5, 1, and 1.25 wt.%). Figure 1 (a1) Morphology image of Mg-8Li-1Gd-0.25Ni alloy; (a2) Surface potential diagram of Mg-8Li-1Gd-0.25Ni alloy; (a3) ​​Potential distribution diagram of Mg-8Li-1Gd-0.25Ni alloy; (b1) Morphology image of Mg-8Li-2Gd-0.5Ni alloy; (b2) Surface potential diagram of Mg-8Li-1Gd-0.25Ni alloy; (b3) Potential distribution diagram of Mg-8Li-1Gd-0.25Ni alloy. Distribution diagrams, (c1) morphology image of Mg-8Li-4Gd-1Ni alloy, (c2) surface potential diagram of Mg-8Li-4Gd-1Ni alloy, (c3) potential distribution diagram of Mg-8Li-4Gd-1Ni alloy, (d1) morphology image of Mg-8Li-5Gd-1.25Ni alloy, (d2) surface potential diagram of Mg-8Li-5Gd-1.25Ni alloy, (d3) potential distribution diagram of Mg-8Li-5Gd-1.25Ni alloy; Figure 2 High-resolution TEM images and SAED diffraction patterns of the 24R type LPSO phase. Figure 2 (a) TEM image of LPSO in Mg-8Li-2Gd-0.5Ni alloy, (b) TEM image and diffraction pattern of LPSO in Mg-8Li-5Gd-1.25Ni alloy, (c) high-resolution image of LPSO in Mg-8Li-5Gd-1.25Ni alloy, (d) EDS surface scan result of LPSO in Mg-8Li-2Gd-0.5Ni alloy, (e) EDS result of LPSO in Mg-8Li-5Gd-1.25Ni alloy; Figure 3 Statistical chart of LPSO phase volume fraction of Mg-8Li-4xGd-xNi alloys with different compositions; Figure 4 This is a comparison of the weight loss rates of alloys with different compositions at 25℃ and 93℃. Figure 4 (a) Rate of weight loss at different temperatures, (b) Rate of weight loss after maintaining different pressures; Figure 5 (a) is the potentiodynamic polarization curve of Mg-8Li-4xGd-xNi (x = 0.25, 0.5, 1 and 1.25 wt.%) alloy in 3.0 wt.% KCl solution; Figure 5 (b) shows the fitting results of Mg-8Li-4xGd-xNi (x = 0.25, 0.5, 1 and 1.25 wt.%) alloys in 3.0 wt.% KCl solution; Figure 6 Nyquist electrochemical impedance spectroscopy curves of alloys with different compositions. Figure 6 (a) Nyquist curve, (b) and (c) Bode curve, (d) equivalent circuit of EIS spectrum; Figure 7 Tensile stress-strain curves for alloys with different compositions. Figure 7 (a) Tensile curves of Mg-8Li-4xGd-xNi (x=0.25,0.5,1,1.25) alloy, and (b) Compression curves of Mg-8Li-4xGd-xNi (x=0.25,0.5,1,1.25) alloy. Detailed Implementation

[0028] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0029] Examples 1-4: Preparation of alloys with different compositions Four different Mg-Li-Gd-Ni alloys were prepared according to the proportions shown in Table 1.

[0030] Table 1. Composition (mass percentage) of the Mg-Li-Gd-Ni alloy in the examples.

[0031] The preparation method of Mg-Li-Gd-Ni alloy is as follows: (1) Weigh out industrial pure magnesium ingots, pure lithium, Mg-Gd master alloy and Mg-Ni master alloy according to the proportions. Select Mg-30wt%Gd for Mg-Gd master alloy and Mg-30wt%Ni for Mg-Ni master alloy. (2) Melting was carried out in a vacuum induction melting furnace under an argon protective atmosphere at a melting temperature of 720°C for 30 minutes. (3) The melt is poured into a preheated steel mold to obtain an ingot; (4) The ingot is subjected to homogenization heat treatment at 300℃ for 12 hours.

[0032] The following experiments were used to verify the effectiveness of the invention: Experiment 1: Measurement of LPSO / Matrix Potential Difference The surface potential distribution of the alloy samples from Examples 1-4 was measured using Kelvin probe force microscopy mode of an atomic force microscope. Prior to measurement, the sample surfaces underwent mechanical polishing and ion etching. The results are as follows: Figure 1 As shown, a long-period stacked ordered structure phase, namely the LPSO phase, is formed in the alloy.

[0033] The measurement results show that the potential difference between the LPSO phase and the surrounding magnesium-lithium matrix in each alloy example is stable within the range of 750-850 mV. Specifically, the potential difference between the LPSO phase and the matrix in Example 2 (Mg-8Li-2Gd-0.5Ni) is approximately 800 mV, which is comparable to the potential difference measured in Example 4 (Mg-8Li-5Gd-1.25Ni). This indicates that the electrochemical behavior of the LPSO phase is highly stable under different content conditions, and the electrochemical potential difference between the LPSO phase and the matrix remains at a high and stable level.

[0034] The LPSO phase is a 24R type long-period stacked ordered structure. For example... Figure 2 As shown in (c), the high-resolution TEM image revealed that the LPSO atomic layers were periodically arranged, with a complete cycle thickness of approximately 2.07 nm, consistent with the structural parameters of the 24R type LPSO reported in the literature. SAED diffraction pattern ( Figure 2 (b) shows that there are seven darker diffraction spots between the two main spots in the (0002) direction, dividing the spacing into eight equal parts, which is a typical diffraction feature of the 24R type LPSO phase.

[0035] Experiment 2: Degradation Rate Determination like Figure 3 and Figure 4 As shown, as the Gd and Ni contents increased from x=0.25 to x=1.25, the volume fraction of the LPSO phase increased from approximately 5% to approximately 25%, and the degradation rate of the alloy at 25°C increased from 0.09 mg / cm³.2 The degradation rate increased linearly to 0.23 mg / cm²·min. This linear relationship stems from the stability of the potential difference—the galvanic corrosion intensity contributed by a unit LPSO area remains constant, and the total degradation rate is proportional to the cathode area.

[0036] The alloys from Examples 1-4 were machined into 10mm × 10mm × 3mm samples and subjected to weight loss tests in a 3% KCl solution. The test temperatures were 25℃ and 93℃, and the immersion time was 2 hours. After the tests, corrosion products were removed, and the weight loss rate was calculated. The results are as follows: Figure 4 As shown in (a), when the temperature increases from 25℃ to 93℃, the degradation rate of each alloy increases by 10-27 times, and the degradation rate ranking trend among different alloys is consistent. This indicates that the degradation behavior of this alloy system is temperature-sensitive and can adapt to oil and gas wells with different geothermal gradients.

[0037] Test results show that: At 25°C, the degradation rates of the alloys in each example were as follows: Example 1 (0.09 mg / cm³). 2 •min) < Example 3 (0.16 mg / cm 2 •min) < Example 2 (0.20 mg / cm 2 •min) < Example 4 (0.23 mg / cm 2 ·min) At 93℃, the degradation rates of the alloys in each example were as follows: Example 1 (0.49 mg / cm²·min) < Example 3 (1.18 mg / cm²·min). 2 •min) < Example 2 (1.39 mg / cm 2 •min) < Example 4 (2.43 mg / cm 2 ·min) The degradation rate increased by the following factors when the temperature increased from 25°C to 93°C: Example 1 (5.4 times), Example 2 (6.95 times), Example 3 (7.38 times), Example 4 (10.6 times). It is worth noting that the degradation rate of Example 2 was higher than that of Example 3, which had a higher LPSO content, which is related to the distribution morphology of its LPSO phase. However, overall, Example 4, with the highest LPSO content, exhibited the fastest degradation rate, which is consistent with the mechanism of maximizing cathode area.

[0038] Experiment 3: Electrochemical Performance Testing Potentiodynamic polarization tests were performed on the alloys of Examples 1-4 using a 3% KCl solution and a scan rate of 1 mV / s. The results are as follows: Figure 5 As shown.

[0039] The corrosion current density (i) obtained by fitting using the Tafel extrapolation method corr ) as follows: The corrosion current density in Example 1 was 0.85 mA / cm². 2 The corrosion current density in Example 2 was 1.68 mA / cm². 2 The corrosion current density in Example 3 was 1.92 mA / cm². 2 The corrosion current density in Example 4 was 2.77 mA / cm². 2 The corrosion current density generally increased with increasing Gd and Ni content, consistent with the results of the weight loss test. Example 4 exhibited the highest corrosion current density, indicating that its electrochemical reaction was the most vigorous and its degradation rate was the fastest.

[0040] Electrochemical impedance spectroscopy test results ( Figure 6 (a) shows that Example 4 has the smallest capacitive arc in the high-frequency region, and the corresponding charge transfer resistance (R) is... ct Minimum (25.12 Ω·cm) 2 This further confirms its fastest degradation kinetics.

[0041] Experiment 4: Mechanical Property Testing Room temperature tensile tests were performed on the alloys of Examples 1-4, and the results are as follows: Figure 7 As shown.

[0042] The tensile strength is as follows: The tensile strength of Example 1 was 112 MPa; the tensile strength of Example 2 was 125 MPa; the tensile strength of Example 3 was 118 MPa; and the tensile strength of Example 4 was 142.3 MPa.

[0043] Example 4 (Mg-8Li-5Gd-1.25Ni) exhibited the highest tensile strength, reaching 142.3 MPa, with a deformation of 37.5%. This is due to the distribution of the LPSO phase at the grain boundaries, which effectively hinders dislocation slip and enhances the alloy strength.

[0044] Compression tests showed that Example 2 had the highest compressive strength of 379.0 MPa at a deformation of 40%, indicating that the alloy has good plastic deformation capacity.

[0045] Experiment 5: Effect of hot-pressing pretreatment on degradation rate The as-cast alloy of Example 4 (Mg-8Li-5Gd-1.25Ni) was subjected to a hot-pressing pretreatment at 70 MPa for 30 min, and then its degradation rate was compared with that of the untreated alloy. The test conditions were 25°C and 3% KCl solution. The results are as follows. Figure 4 As shown in (b)).

[0046] After hot-pressing pretreatment, the degradation rate in Example 4 decreased from 0.23 mg / cm³. 2 •min increased to 0.25 mg / cm 2 The degradation rate is approximately 1.5 min. This is because pressure treatment increases the dislocation density in the alloy, thereby enhancing its corrosion susceptibility. This method provides a simple and effective means to further fine-tune the degradation rate.

[0047] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A Mg-Li-Gd-Ni alloy with degradation rate regulated by LPSO / matrix potential difference, characterized in that, Its composition by mass percentage is: Li: 8%, Gd: 1%-5%, Ni: 0.25%-1.25%, with the balance being Mg and unavoidable impurities; the mass ratio of Gd to Ni is 4:

1.

2. The alloy according to claim 1, characterized in that, Its composition by mass percentage is: Li: 8%, Gd: 5%, Ni: 1.25%, with the balance consisting of magnesium and unavoidable impurities.

3. The alloy according to claim 1, characterized in that, The alloy forms a long-period stacked ordered phase (LPSO phase) in its microstructure, and the electrochemical potential difference between the LPSO phase and the magnesium-lithium matrix is ​​stable in the range of 750-850 mV.

4. The alloy according to claim 3, characterized in that, The LPSO phase is a 24R type long-period stacked ordered structure with an atomic layer period thickness of 2.07 nm.

5. The method for preparing the alloy according to any one of claims 1-4, characterized in that, Includes the following steps: The raw materials are melted under inert gas protection, cast into shape, and then homogenized by heat treatment.

6. The method according to claim 5, characterized in that, The raw materials are industrial pure magnesium ingots, pure lithium, Mg-Gd master alloy, and Mg-Ni master alloy.

7. The method according to claim 5, characterized in that, The inert gas is argon; the melting process is: heat treatment at 720℃ for 30 minutes.

8. The method according to claim 5, characterized in that, The homogenization heat treatment was a hot pressing pretreatment at 70 MPa for 30 min.

9. The use of the alloy according to any one of claims 1-4 in the preparation of biodegradable tools for oil and gas wells.

10. The application according to claim 9, characterized in that, The biodegradable tool is a biodegradable fracturing ball, a biodegradable bridge plug, or a biodegradable temporary plugging ball.

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