A refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding and its preparation method

Abstract

This invention proposes a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding and its preparation method, belonging to the technical field of solid lubricating composite materials. By utilizing a chemical reduction reaction to modify the silver surface and control the interface, the modified silver powder is embedded as a lubricant into a refractory high-entropy alloy matrix using spark plasma sintering to synthesize the solid lubricating composite material. This method simultaneously improves the wear resistance and lubrication properties of the refractory high-entropy alloy-based solid lubricating composite material over a wide temperature range, showing broad application prospects in the field of wear-resistant lubrication materials.

Description

Technical Field

[0001] This invention belongs to the field of solid lubricating composite material technology, and particularly relates to a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding and its preparation method. Background Technology

[0002] As major national technological fields such as aerospace develop towards high temperature, high speed, high pressure, and heavy load, the requirements for the strong plastic bonding performance of moving parts and the lubrication and wear resistance at high temperatures are becoming more stringent. Current solid lubrication composite materials, such as nickel-based solid lubrication composite materials and ceramic-based solid lubrication composite materials, can no longer meet the service performance requirements under more severe conditions such as high temperature.

[0003] Refractory high-entropy alloys composed of high-melting-point elements exhibit significant strength at high temperatures due to inherent solid solution strengthening and slow diffusion, resulting in reduced thermal softening and grain coarsening. Compared to traditional alloys and ceramic materials, refractory high-entropy alloys demonstrate superior wear resistance or a strong-plasticity combination at high temperatures, making them promising candidates for reducing damage and energy loss caused by wear in high-temperature environments. Based on this, the development of refractory high-entropy alloy-based solid lubricant composite materials is imperative for improving their lubrication performance and meeting the comprehensive service performance requirements in ultra-high temperature environments.

[0004] However, due to the extremely high melting points of refractory high-entropy alloys, the significant melting point difference makes it difficult to combine them with existing high-efficiency solid lubricants such as Ag to prepare refractory high-entropy alloy-based solid lubricant composites. Therefore, this study aims to develop novel preparation methods by modifying the surface of solid lubricants and controlling the process to solve the preparation problem of refractory high-entropy alloy-based solid lubricant composites. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding and its preparation method. By utilizing a chemical reduction reaction to modify the silver surface and regulate the interface, the modified silver powder is embedded as a lubricant into the refractory high-entropy alloy-based solid lubricating composite material to improve the composite material's wear resistance and lubrication performance over a wide temperature range.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One of the technical solutions of the present invention:

[0008] A solid lubricating composite material based on a low-melting-point silver-intercalated refractory high-entropy alloy, comprising the following raw materials:

[0009] Modified Ag powder, as well as elemental Nb, Mo, W, Ta and Ti powders;

[0010] The atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder are 2.5-10%, 18-19.5%, 18-19.5%, 18-19.5%, 18-19.5%, and 18-19.5%, respectively; and the sum of the atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder is 100%.

[0011] The beneficial effects achieved by the above technical solution are as follows: the refractory high-entropy alloy-based solid lubricating composite material prepared by this invention consists of only two phases: the BCC matrix phase and the Ag lubricating phase, without the formation of other impurity phases, thus achieving high lubrication characteristics. As transition metal elements, Nb, Mo, W, Ta, and Ti have similar atomic characteristics and high solid solubility among themselves. Furthermore, according to the criteria for solid solution phase formation, when the atomic pair enthalpies between elements are all around 0, it is conducive to the formation of a single solid solution phase. The atomic pair enthalpies among Nb, Mo, W, Ta, and Ti range from -8 to 2, making it easy to form a single-phase solid solution when they are mixed and sintered. Conversely, the atomic pair enthalpies between Ag and Nb, Mo, W, and Ta range from a maximum of 43 to a minimum of 15, with extremely low solid solubility, thus they basically do not participate in the solid solution process of the BCC matrix phase. Therefore, it is possible to ensure the preparation of a solid lubricating composite material composed of both the BCC and Ag phases, avoiding the loss of lubrication performance due to the disappearance of the Ag phase. As a soft phase, during the friction process, the Ag phase, which is uniformly distributed in the composite material, will gradually move to the material surface and be sheared into a film, thereby playing a lubricating role.

[0012] Preferably, the atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder are 2.5%, 19.5%, 19.5%, 19.5%, 19.5%, and 19.5%, respectively.

[0013] Preferably, the atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder are 5%, 19%, 19%, 19%, 19%, and 19%, respectively.

[0014] Preferably, the atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder are 10%, 18%, 18%, 18%, 18%, and 18%, respectively.

[0015] The second technical solution of the present invention:

[0016] The preparation method of the above-mentioned refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding includes the following steps:

[0017] The surface of Ag powder was modified by reduction reaction to obtain modified Ag powder with a particle size of 17-55 μm;

[0018] The modified Ag powder was mixed with elemental Nb, Mo, W, Ta and Ti powders according to the atomic percentages, ball-milled, and then a refractory high-entropy alloy-based solid lubricating composite material was prepared by spark plasma sintering. The purity of each elemental powder was ≥99.95%, and the particle size of each elemental powder was 15-53 μm.

[0019] Preferably, the reduction reaction process is as follows:

[0020] Ag powder was poured into an ammonium molybdate solution, heated and stirred until the water was completely evaporated, to obtain a precursor powder containing molybdenum compound coated with Ag.

[0021] Under 5% hydrogen and argon atmosphere, the precursor powder was heated to 900°C at a rate of 10°C / min, and then reduced at this temperature for 240 min to obtain Mo-coated Ag powder.

[0022] The beneficial effects achieved by the above technical solution are as follows: the reduction process specified in this application can ensure the preparation of uniformly coated Mo-coated Ag powder. If the hydrogen concentration is too low under hydrogen-argon gas conditions, it will lead to insufficient reduction, affecting the purity of the prepared powder; if the hydrogen concentration is too high, it increases the risk and wastes raw materials. Temperatures below 900℃ will result in insufficient reduction, affecting the purity of the prepared powder; times below 240 minutes will also lead to insufficient reduction, affecting the purity of the prepared powder. Excessive time will result in ineffective work and affect efficiency.

[0023] Preferably, the atomic ratio of Ag to Mo in the modified Ag powder is 1:(2-3).

[0024] The beneficial effects achieved by the above technical solution are as follows: the modified Ag powder with Ag and Mo atoms in a specific ratio as defined by this invention can achieve good coating of Ag particles. During the research, it was found that when the atomic ratio of Ag to Mo is higher than 1:2, insufficient Mo content may lead to incomplete coating, and Ag extrusion and volatilization can still be observed during sintering; while an atomic ratio lower than 1:3 will result in waste of raw materials. Within this range, a well-coated powder can be prepared.

[0025] Furthermore, the mass concentration of the ammonium molybdate solution is 10-12.5%, that is, the mass ratio of ammonium molybdate to ultrapure water is 1:10-1:8;

[0026] The heating and stirring conditions are as follows: heating temperature is 65-75℃, and stirring speed is 500-700 r / min.

[0027] The beneficial effects achieved by the above technical solution are as follows: the parameters and conditions in the reduction process specified above enable the prepared precursor powder to have good uniformity. If the mass concentration of ammonium molybdate is too low, it will lead to uneven coating in the precursor powder; if the mass concentration is too high, it will reduce the preparation efficiency. Excessive heating temperature and excessively fast stirring rate will cause solution splashing, resulting in inaccurate content and waste of raw materials; excessively low heating temperature will reduce the preparation efficiency, and excessively low stirring rate will cause Ag particles to precipitate and agglomerate, resulting in uneven coating of the precursor powder.

[0028] Furthermore, before the reduction reaction, the precursor powder is spread in a ceramic boat in an intermittent manner, with a spacing of 5-10 mm between each pile of powder.

[0029] Preferably, the ball milling process is as follows: ball milling for 5-6 minutes, followed by a 2-minute pause to cool down, which constitutes one ball milling cycle;

[0030] The total ball milling time was 1600–1678 min.

[0031] The beneficial effects achieved by the above technical solution are as follows: the intermittent spreading method specified in this invention ensures the preparation of non-agglomerated coated powder; the ball milling process effectively suppresses overheating during ball milling, thereby preventing powder agglomeration and thermal welding to the ball mill jar wall, and achieving uniform and good mechanical alloying of the powder. If the spreading is not intermittent or the interval is too small, the powder will agglomerate due to the inability to expel water vapor during the reduction process, making it unusable for subsequent applications; if the interval is too large, it will significantly prolong the preparation time and reduce efficiency. A single ball milling time exceeding 5-6 minutes may cause powder agglomeration or welding to the ball mill jar wall, while a time less than 5-6 minutes may result in insufficient energy and failure to alloy. An excessively long pause time will severely affect the preparation efficiency, while an excessively short pause time may result in insufficient temperature drop and ineffective cooling. A total ball milling time that is too short will lead to poor alloying, while a total ball milling time that is too long may result in excessive ineffective ball milling, reducing efficiency.

[0032] Preferably, the discharge plasma sintering process is as follows:

[0033] First, the temperature was maintained at 2000℃ for 10 minutes under vacuum and inert gas conditions, with a pressure of 35kN, a power of 18-22kW, and a temperature of 2000℃.

[0034] Then, it was kept at 1600℃, 15kN, and 14-16kW for 30 minutes.

[0035] Finally, the temperature was lowered to room temperature to obtain a refractory high-entropy alloy-based solid lubricant composite material with low-melting-point silver inlay.

[0036] The beneficial effects achieved by the above technical solution are as follows: The spark plasma sintering process defined in this invention can ensure the successful preparation of a refractory high-entropy alloy-based solid lubricating composite material with uniform Ag embedding. Insufficient pressure will result in high porosity, leading to a decrease in the properties of the prepared material; excessive pressure may exceed the bearing threshold of the graphite mold, causing damage to the graphite mold and resulting in sintering failure. Temperatures above 2000℃ will introduce the risk of Mo coating layer failure, while temperatures below 2000℃ will result in insufficient alloying of the refractory high-entropy alloy matrix material. Holding at 1600℃ for 30 minutes provides sufficient time for metal atom diffusion, resulting in more complete alloying.

[0037] Furthermore, throughout the entire discharge plasma sintering process, the heating and cooling rates are both 100°C / min.

[0038] Preferably, a cold pressing process is required between the ball milling and spark plasma sintering processes, specifically with a cold pressing time of 8-10 minutes and a pressure of 50 MPa.

[0039] Furthermore, the vacuuming is performed with a vacuum degree of less than 5 × 10⁻⁶. -2 mbar.

[0040] Compared with the prior art, the present invention has the following advantages and technical effects:

[0041] 1. By using Ag particle surface modification and interface control, a refractory high-entropy alloy-based solid lubricant composite material with stable interface and uniform distribution of solid lubricant Ag particles was prepared by spark plasma sintering.

[0042] 2. The refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding provided by this invention has excellent wide-temperature-range wear resistance and lubrication properties, and has broad application prospects in the field of wear-resistant lubricating materials.

[0043] 3. The raw materials of this invention are easy to obtain, the preparation method is simple and easy to operate, highly controllable, and efficient, and has broad prospects for industrial application. Attached Figure Description

[0044] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0045] Figure 1 This is an XRD pattern of the Mo-coated Ag powder prepared in Example 1 of the present invention;

[0046] Figure 2 This is a cross-sectional microstructure SEM image of the Mo-coated Ag powder prepared in Example 1 of this invention;

[0047] Figure 3 These are XRD schematic diagrams of the refractory high-entropy alloy-based solid lubricating composite materials prepared according to Examples 1, 2, 3 and Comparative Example 1 provided by the present invention;

[0048] Figure 4 This is a comparison chart of the friction coefficients of the refractory high-entropy alloy-based solid lubricating composite materials prepared in Examples 1, 2, 3 and Comparative Example 1 of the present invention at test temperatures of room temperature, 300°C, 600°C and 800°C.

[0049] Figure 5 This is a comparison chart of the wear rates of the refractory high-entropy alloy-based solid lubricating composite materials prepared in Examples 1, 2, 3 and Comparative Example 1 provided by the present invention at test temperatures of room temperature, 300°C, 600°C and 800°C.

[0050] Figure 6 This is an XRD pattern of the refractory high-entropy alloy-based solid lubricating composite material prepared in Comparative Example 2 provided by the present invention (the right image is an enlarged view of the left image). Detailed Implementation

[0051] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0052] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0053] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0054] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0055] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0056] This invention discloses a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding, the preparation method of which includes the following steps:

[0057] S1. Dissolve ammonium molybdate powder in a beaker containing ultrapure water to prepare an ammonium molybdate solution;

[0058] S2. Pour the Ag powder into a beaker containing an ammonium molybdate solution, and then heat while stirring until all the water in the beaker evaporates, to obtain the precursor powders of ammonium molybdate and molybdenum oxide-coated Ag.

[0059] S3. The precursor powder is loaded into ceramic boats in batches. The ceramic boats containing the precursor powder are placed in a tube furnace and a reduction reaction is carried out at 900℃ and 5% hydrogen argon atmosphere for 240 minutes to obtain Mo-coated Ag powder.

[0060] S4. In a glove box protected by inert gas, Nb, Mo, W, Ta, Ti and Mo are coated with Ag according to the atomic percentages (the atomic percentages of Ag and elemental Nb, Mo, W, Ta and Ti in the modified Ag powder are 2.5-10%, 18-19.5%, 18-19.5%, 18-19.5%, 18-19.5%, 18-19.5%, 18-19.5%), and the six powders are uniformly mixed in a ball mill jar.

[0061] S5. Load the ball mill jar containing the mixed powder into the high-energy ball mill for high-energy ball milling;

[0062] S6. Take out the ball-milled powder from the glove box under inert gas protection and put it into the graphite mold;

[0063] S7. Remove the graphite mold containing the ball milled powder from the glove box and transfer it to the spark plasma sintering furnace for cold pressing;

[0064] S8. Discharge plasma sintering is performed in an inert gas environment at 2000℃. After the sintering process is completed, a refractory high-entropy alloy-based solid lubricating composite material with low melting point silver inlay is obtained.

[0065] In some preferred embodiments, the mass ratio of ammonium molybdate to ultrapure water in S1 is between 1:10 and 1:8.

[0066] In some preferred embodiments, the atomic ratio of Ag powder poured into the beaker in S2 to molybdenum in the ammonium molybdate solution is between 1:3 and 1:2.

[0067] In some preferred embodiments, the heating temperature in S2 is 65-75°C, and the stirring rate is 500-700 r / min.

[0068] In some preferred embodiments, the precursor powder in S3 is spread in the ceramic boat in an intermittent manner, with a spacing of 5-10 mm between each pile of powder.

[0069] In some preferred embodiments, the heating rate of the tube furnace in S3 is 10°C / min, and the holding time at 900°C is 240min.

[0070] In some preferred embodiments, the purity of each elemental powder in S4 is ≥99.95%, and the particle size of each elemental powder is 15-53 μm.

[0071] In some preferred embodiments, the ball milling process in S5 is 5-6 minutes per milling cycle, followed by a 2-minute pause for cooling, with a total milling time of 1600-1678 minutes.

[0072] In some preferred embodiments, the cold pressing time in S7 is 8 to 10 minutes and the pressure is 50 MPa.

[0073] In some preferred embodiments, the discharge plasma sintering furnace in S8 is evacuated to a vacuum level of less than 5 × 10⁻⁶. - 2 After repeated purging 2-3 times, ensure that the furnace cavity is filled with an argon protective atmosphere with a mass concentration of 99.9% or higher.

[0074] In some preferred embodiments, the sintering process in S8 is first held at 2000℃ for 10 minutes at a pressure of 35kN and a power of 18-22kW, and then held at 1600℃, 15kN, and 14-16kW for 30 minutes. The heating rate and cooling rate of the entire process are both 100℃ / min.

[0075] All raw materials used in the embodiments of this invention were obtained through commercial purchase.

[0076] The technical solution of the present invention will be further illustrated by the following embodiments.

[0077] In the following examples, "5% hydrogen-argon gas atmosphere" refers to a hydrogen-argon gas mixture with a hydrogen volume ratio of 5%.

[0078] In the following examples, room temperature refers to 25°C.

[0079] Example 1

[0080] A method for preparing a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding includes the following steps:

[0081] S1. An ammonium molybdate solution is prepared by dissolving ammonium molybdate powder in a beaker containing ultrapure water, wherein the mass ratio of ammonium molybdate to ultrapure water is 1:8.

[0082] S2. Pour Ag powder into a beaker containing ammonium molybdate solution, and then heat while stirring (heating temperature is 65℃; stirring speed is 700r / min) until the water in the beaker is completely evaporated, to obtain the precursor powder of ammonium molybdate and molybdenum oxide coated Ag; wherein, the atomic ratio of Ag powder to molybdenum in ammonium molybdate solution is 1:2.

[0083] S3. The precursor powder is loaded into the ceramic boat in batches (spread in the ceramic boat in an intermittent manner, with a 10mm gap between each pile of powder, and the gas atmosphere is 5% hydrogen and argon). The ceramic boat containing the precursor powder is placed in a tube furnace and heated to 900℃ at a heating rate of 10℃ / min. Then, a reduction reaction is carried out at 900℃ and in a 5% hydrogen and argon atmosphere for 240min to obtain Mo-coated Ag powder.

[0084] Figure 1 XRD characterization of the Mo-coated Ag powder prepared in this embodiment was performed from... Figure 1 As can be seen, the powder before coating is pure Ag powder, while the powder after coating consists of two phases: Mo phase and Ag phase.

[0085] Figure 2 This is a cross-sectional SEM image of the Mo-coated Ag powder prepared in this embodiment. As can be seen from the image, the powder exhibits Mo elements uniformly coating uniformly dispersed Ag particles. Therefore, this indicates that the Mo-coated Ag powder was successfully prepared in this embodiment.

[0086] S4. In an inert gas-protected glove box, Nb, Mo, W, Ta, and Ti powders, as well as Mo-coated Ag powder, are uniformly mixed in a ball mill jar according to atomic percentages. The purity of each elemental powder is ≥99.95%, and the particle size of each elemental powder is 15–53 μm. The atomic percentages are: Nb 19.5%, Mo 19.5% (including only elemental Mo powder, excluding molybdenum in molybdenum-coated silver powder, the same below), W 19.5%, Ta 19.5%, Ti 19.5%, and Ag 2.5% in the modified Ag powder.

[0087] S5. Place the ball mill jar containing the mixed powder into a high-energy ball mill for high-energy ball milling. The ball milling process is 5-6 minutes per milling, followed by a 2-minute pause to cool down. This cycle is repeated, and the total ball milling time is 1678 minutes.

[0088] S6. Take out the ball-milled powder from the glove box under inert gas protection and put it into the graphite mold;

[0089] S7. Remove the graphite mold containing the ball milled powder from the glove box and transfer it to the spark plasma sintering furnace, where it is cold-pressed for 10 minutes at a pressure of 50 MPa.

[0090] S8. Evacuate the spark plasma sintering furnace until the vacuum level inside the furnace cavity is less than 5×10⁻⁶. -2 After repeated purging 2-3 times to ensure an argon protective atmosphere with a mass concentration of over 99.9% in the furnace cavity, spark plasma sintering is performed at 2000℃ under this atmosphere. The specific spark plasma sintering process is as follows: first, holding at 2000℃ for 10 minutes at a pressure of 35kN, a power of 18-22kW, and a temperature of 25kN; then holding at 1600℃, 15kN, and a power of 14-16kW for 30 minutes; finally, cooling to room temperature to end the sintering process, resulting in a low-melting-point silver-embedded refractory high-entropy alloy-based solid lubricating composite material. The heating and cooling rates throughout the entire process are both 100℃ / min.

[0091] The refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding obtained in this embodiment was characterized by XRD, such as... Figure 3 As shown, the results indicate that Example 1 consists of two phases: a BCC phase and an Ag phase. No other impurity phases precipitate. These results demonstrate the successful preparation of a low-melting-point silver-embedded refractory high-entropy alloy-based solid lubricant composite material.

[0092] The refractory high-entropy alloy-based solid lubricant composite material based on low-melting-point silver embedding obtained in this embodiment was machined into long strip-shaped friction samples, which were then polished using metallographic sandpaper of 200 to 2000 grit, from smallest to largest. The tribological properties of the samples were tested using a high-temperature tribological testing machine, and the tests were repeated at least three times. Figure 4 As shown, the results indicate that the coefficient of friction of the solid lubricated composite material in this embodiment is below 0.45 at all temperatures, and is between 0.35 and 0.45. Figure 5 As shown, the results indicate that the wear rates of the solid lubricated composite material in this embodiment at room temperature, 300℃, 600℃, and 800℃ are 1.47 × 10⁻⁶ and 1.47 × 10⁻⁶, respectively. -4 mm 3 / Nm, 4×10 -4 mm 3 / Nm, 2×10 -6 mm3 / Nm and 3.22×10 -5 mm 3 / Nm. The above results indicate that the solid lubricating composite material prepared in this invention exhibits excellent tribological properties over a wide temperature range.

[0093] Example 2

[0094] The difference from Example 1 is that the mass ratio of ammonium molybdate to ultrapure water in S1 is 1:9, the heating temperature in S2 is 70°C, the stirring rate is 650 r / min, and the atomic percentage of the elements in step S4 is: Nb 19%, Mo 19%, W 19%, Ta 19%, Ti 19%, Ag 5% in the modified silver powder, and other conditions are the same as in Example 1.

[0095] The solid lubricating composite material obtained in this embodiment was machined into long strip-shaped friction samples, which were then polished using metallographic sandpaper of grits ranging from 200 to 2000 grit, from smallest to largest. The tribological properties of the samples were tested using a high-temperature tribological testing machine, and the tests were repeated at least three times. Figure 4 As shown, the results indicate that the coefficient of friction of the solid lubricated composite material in this embodiment is also below 0.45 at all temperatures, ranging from 0.35 to 0.45. Figure 5 As shown, the results indicate that the wear rates of the solid lubricated composite material in this embodiment at room temperature, 300℃, 600℃, and 800℃ are 1.37 × 10⁻⁶ and 1.37 × 10⁻⁶, respectively. -4 mm 3 / Nm, 3.3×10 -4 mm 3 / Nm, 1.67×10 -5 mm 3 / Nm and 4.67×10 -5 mm 3 / Nm. The above results indicate that the solid lubricating composite material prepared in this embodiment exhibits excellent tribological properties over a wide temperature range.

[0096] Example 3

[0097] The difference from Example 1 is that the mass ratio of ammonium molybdate to ultrapure water in S1 is 1:10, the heating temperature in S2 is 75°C, the stirring rate is 600 r / min, and the atomic percentage of the elements in step S4 is: Nb 18%, Mo 18%, W 18%, Ta 18%, Ti 18%, Ag in the modified silver powder is 10%, and other conditions are the same as in Example 1.

[0098] The solid lubricating composite material obtained in this embodiment was machined into long strip-shaped friction samples, which were then polished using metallographic sandpaper of grits ranging from 200 to 2000 grit, from smallest to largest. The tribological properties of the samples were tested using a high-temperature tribological testing machine, and the tests were repeated at least three times. Figure 4 As shown, the results indicate that the coefficient of friction of the solid lubricated composite material in this embodiment is also below 0.45 at temperatures ranging from 25 to 600°C, and is between 0.35 and 0.45. Figure 5 As shown, the results indicate that the wear rates of the solid lubricated composite material in this embodiment at room temperature, 300℃, 600℃, and 800℃ are 9.89 × 10⁻⁶. -5 mm 3 / Nm, 2.22×10 -4 mm 3 / Nm, 1.99×10 -5 mm 3 / Nm and 4.67×10 -5 mm 3 / Nm. The above results indicate that the solid lubricating composite material prepared in this embodiment exhibits excellent tribological properties over a wide temperature range.

[0099] Comparative Example 1

[0100] This comparative example prepares a refractory high-entropy alloy-based solid lubricant composite material, Nb, without low-melting-point silver embedding. 20 Mo 20 W 20 Ta 20 Ti 20 The difference from Example 1 is that Ag is not added, i.e., steps S1-S3 are not performed. In addition, the percentages of each atom are: Nb 20%, Mo 20%, W 20%, Ta 20%, Ti 20%. Other conditions are the same as in Example 1.

[0101] The obtained Nb 20 Mo 20 W 20 Ta 20 Ti 20 Refractory high-entropy alloys were characterized by XRD, such as... Figure 3 As shown, Comparative Example 1 consists of a single BCC phase. No other impurity phases were precipitated.

[0102] The obtained Nb 20 Mo 20 W 20 Ta 20 Ti 20Refractory high-entropy alloys were machined into elongated friction samples, which were then polished using metallographic sandpaper of grits ranging from 200 to 2000 grit, from smallest to largest. The tribological properties of the samples were tested using a high-temperature tribological testing machine, with the tests repeated at least three times. Figure 4 As shown, the results indicate that Nb 20 Mo 20 W 20 Ta 20 Ti 20 Refractory high-entropy alloys exhibit high coefficients of friction at all temperatures, ranging from 0.49 to 0.6. For example... Figure 5 As shown, the results indicate that Nb 20 Mo 20 W 20 Ta 20 Ti 20 The wear rates of the refractory high-entropy alloy at room temperature, 300℃, 600℃, and 800℃ were 1.68×10⁻⁶. -4 mm 3 / Nm, 6.22×10 -4 mm 3 / Nm, 7.69×10 -7 mm 3 / Nm and 3.11×10 -5 mm 3 / Nm.

[0103] Comparative Example 2

[0104] This comparative example demonstrates the preparation method of an Ag-embedded refractory high-entropy alloy-based solid lubricant composite material without any modification treatment. The difference from Example 1 is that the added Ag was not surface-modified, i.e., steps S1-S3 were not performed. The atomic percentages in S4 were consistent with those in Example 1. Other conditions were the same as in Example 1.

[0105] When unmodified silver powder is added, it melts and is squeezed out during the sintering process when the temperature exceeds 1600℃, and volatilization also occurs. Therefore, it cannot reach 2000℃ and has to be stopped.

[0106] Figure 6 For the XRD characterization of this comparative example, from Figure 6 As can be seen, although a small amount of elemental Ag was present, the NbMoWTaTi powder was not fully alloyed due to insufficient sintering temperature, failing to form a single-phase structure. Therefore, a refractory high-entropy alloy-based solid lubricant material was not successfully prepared. Consequently, without the ability to prepare a uniform sample, subsequent tribological tests were not possible. This comparative example also reflects the current limitation of combining refractory high-entropy alloys with excellent solid lubricants to prepare refractory high-entropy alloy-based solid lubricants.

[0107] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A solid lubricating composite material based on a refractory high-entropy alloy with low-melting-point silver embedding, characterized in that, Raw materials include: Modified Ag powder, as well as elemental Nb, Mo, W, Ta and Ti powders; The atomic percentages of Ag in the modified Ag powder and of elemental Nb, Mo, W, Ta, and Ti are 2.5-10%, 18-19.5%, 18-19.5%, 18-19.5%, 18-19.5%, and 18-19.5%, respectively; and the sum of the atomic percentages of Ag in the modified Ag powder and of elemental Nb, Mo, W, Ta, and Ti is 100%. The preparation method of the refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding includes the following steps: Surface modification of Ag powder was carried out by reduction reaction to obtain modified Ag powder; The modified Ag powder was mixed with elemental Nb, Mo, W, Ta and Ti powders according to the atomic percentages, ball-milled, and then a refractory high-entropy alloy-based solid lubricating composite material was prepared by spark plasma sintering. The reduction reaction process is as follows: Ag powder was poured into an ammonium molybdate solution, heated and stirred until the water was completely evaporated, to obtain a precursor powder containing molybdenum compound coated with Ag. Under 5% hydrogen and argon atmosphere, the precursor powder was heated to 900°C at a rate of 10°C / min, and then reduced at this temperature for 240 min to obtain Mo-coated Ag powder.

2. The refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 1, characterized in that, The atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder are 2.5%, 19.5%, 19.5%, 19.5%, 19.5%, and 19.5%, respectively.

3. The refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 1, characterized in that, The atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder are 5%, 19%, 19%, 19%, 19%, and 19%, respectively.

4. The refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 1, characterized in that, The atomic percentages of Ag and elemental Nb, Mo, W, Ta, and Ti in the modified Ag powder are 10%, 18%, 18%, 18%, 18%, and 18%, respectively.

5. The method for preparing a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to any one of claims 1-4, characterized in that, The steps are as follows: Surface modification of Ag powder was carried out by reduction reaction to obtain modified Ag powder; The modified Ag powder was mixed with elemental Nb, Mo, W, Ta and Ti powders according to the stated atomic percentages, ball-milled, and then prepared into a refractory high-entropy alloy-based solid lubricating composite material by spark plasma sintering.

6. The method for preparing a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 5, characterized in that, The reduction reaction process is as follows: Ag powder was poured into an ammonium molybdate solution, heated and stirred until the water was completely evaporated, to obtain a precursor powder containing molybdenum compound coated with Ag. The precursor powder was reduced at 900°C under 5% hydrogen and argon atmosphere for 240 min to obtain Mo-coated Ag powder, i.e., modified Ag powder.

7. The method for preparing a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 6, characterized in that, The modified Ag powder has an Ag to Mo atomic ratio of 1:(2-3).

8. The method for preparing a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 6, characterized in that, The mass concentration of the ammonium molybdate solution is 10–12.5%. The heating and stirring conditions are as follows: heating temperature is 65-75℃, and stirring speed is 500-700 r / min.

9. The method for preparing a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 5, characterized in that, The ball milling process is as follows: mill for 5-6 minutes, pause for 2 minutes to cool down, and this is one ball milling cycle; The total ball milling time was 1600–1678 min.

10. The method for preparing a refractory high-entropy alloy-based solid lubricating composite material based on low-melting-point silver embedding according to claim 5, characterized in that, The discharge plasma sintering process is as follows: First, hold the temperature at 35kN, 18-22kW, and 2000℃ for 10 minutes. Then, it was kept at 1600℃, 15kN, and 14-16kW for 30 minutes. Finally, the temperature was lowered to room temperature to obtain a refractory high-entropy alloy-based solid lubricant composite material with low-melting-point silver inlay.

Images