A composite powder with a core-shell structure, its preparation method and application

Abstract

This invention discloses a core-shell structured composite powder, its preparation method, and its applications. The composite powder comprises a solid metal core and an alumina coating layer on the surface of the solid metal core. The core-shell structured powder with a solid metal core and an alumina coating layer, prepared through selective oxidation, has advantages such as high sphericity, controllable particle size, simple processing, and low cost. Furthermore, the alumina coating layer on the outer layer of this composite powder has low interfacial strength with the metal matrix, such as Fe / Cu, making the composite powder particles prone to detachment during use. Simultaneously, the core-shell structured composite powder is a solid powder, making it less prone to breakage during cold pressing. Therefore, this core-shell structured composite powder is a pore-forming agent for superhard tools, offering advantages such as good pore-forming effect and high tool mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and more specifically, to a composite powder with a core-shell structure, its preparation method, and its application. Background Technology

[0002] With the development of science and technology and society, the requirements for the service performance, especially the machining efficiency, of superhard tools are becoming increasingly stringent. Therefore, introducing pores into the matrix of superhard tools helps to reduce heat and friction during contact with the workpiece, thereby reducing the load on the superhard tools and extending their service life.

[0003] For example, introducing porosity into the matrix of diamond tools increases chip space and cooling effect, thus maximizing the grinding function of diamond abrasive grains and becoming an important means of improving the service performance of diamond tools. However, as porosity increases, chip space and cooling effect also increase, but the mechanical properties of the tool decrease accordingly. When porosity increases to a certain extent, not only is the application range of the tool limited, but it also reduces the service performance of the tool. Therefore, it is necessary to minimize the damage to the mechanical properties of the tool while ensuring high porosity.

[0004] The main methods for introducing pores into the matrix are low-pressure sintering and pore-forming agent methods. The history of low-pressure sintering can be traced back to 1991. Takeshi Tanaka first used electroplating to coat the surface of diamond with a Ni-Cu-Sn metal layer, then cold-pressed and vacuum-sintered to prepare porous diamond tools. The metal coating melts during sintering and then solidifies between adjacent diamonds during cooling, forming bonding bridges that connect different diamond particles. Later, Tomino et al. prepared cast iron-based porous diamond grinding wheels with a porosity of 20%–35% by controlling the hot-pressing sintering temperature (640–800℃) at a relatively low hot-pressing pressure of 10 MPa. The pore-forming agent method utilizes pore-forming agents to generate pores within the matrix. Currently, pore-forming agents are mainly classified into three categories. The first category consists primarily of salts, which dissolve in solution to form pores. The second category mainly consists of organic compounds or metal hydrides, which decompose or volatilize at high temperatures, thus forming pores. The third category typically consists of high-temperature resistant, spacer-type pore-forming agents that do not change during high-temperature sintering but break or detach during use, forming spacer pores within the matrix. Compared to the pore-forming agent method, porous diamond tools prepared by low-pressure sintering not only have lower porosity but also a greater strength loss rate, approximately 2 to 24 times that of the pore-forming agent method. Therefore, the pore-forming agent method is more widely used.

[0005] Currently, among the third type of pore-forming agents with relatively small strength loss, commonly used hollow pore-forming agents such as SiO2 and Al2O3 hollow spheres are not only expensive and large in size (≥100μm), but are also prone to breakage during the cold pressing stage of superhard tool preparation, resulting in poor pore-forming effect.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a composite powder with a core-shell structure, its preparation method, and its application, so as to improve the above-mentioned technical problems.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides a composite powder having a core-shell structure, comprising a solid metal core and an alumina coating layer covering the surface of the solid metal core.

[0010] Secondly, the present invention also provides a method for preparing the above-mentioned composite powder with a core-shell structure, which includes: forming a core-shell structure powder having the solid metal core and the alumina coating layer by selective oxidation reaction.

[0011] Thirdly, the present invention also provides the application of the above-mentioned composite powder with a core-shell structure as a site-filling pore-forming agent.

[0012] Fourthly, the present invention also provides a superhard tool whose matrix contains the aforementioned composite powder with a core-shell structure.

[0013] The present invention has the following beneficial effects: the core-shell structured composite powder has an outer alumina coating layer with the same characteristics as existing hollow alumina spheres, namely, low interfacial strength with the metal matrix such as Fe / Cu, which makes it easy to detach during use and results in good pore-forming effect; at the same time, the core-shell structured composite powder is a solid powder, which is not easily broken or collapsed during cold pressing. Therefore, the pore structure formed by the later detachment is relatively regular, resulting in better pore-forming effect. In addition, the preparation of solid powder through selective oxidation reaction is not only simple and inexpensive, but also allows for better control of its sphericity and particle size (e.g., less than 100 μm). This allows superhard tools using the core-shell structured composite powder as a site-filling pore-forming agent to have both excellent pore structure and high mechanical properties. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 Here is a SEM image of the core-shell structured composite powder from Example 1;

[0016] Figure 2 Here is a SEM image of the core-shell structured composite powder from Example 2;

[0017] Figure 3 Here is a SEM image of the core-shell structured composite powder from Example 3;

[0018] Figure 4 SEM image of the composite powder in Comparative Example 1;

[0019] Figure 5 SEM image of the composite powder in Comparative Example 2;

[0020] Figure 6 SEM image of the composite powder in Comparative Example 3;

[0021] Figure 7 The image shows the SEM image of the composite powder in Comparative Example 4. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The following is a detailed description of a core-shell structured composite powder proposed in this invention, its preparation method, and its application.

[0024] The inventors discovered that existing hollow pore-forming agents, such as SiO2 and Al2O3 hollow spheres, have relatively large sizes (≥100μm) due to process limitations. Therefore, on the one hand, they are prone to breakage during cold pressing, preventing the full realization of the pore-forming effect; on the other hand, the addition of hollow pore-forming agents leads to a significant decrease in mechanical properties. Generally, the smaller the pore diameter, the higher the uniformity of pore size, and the higher the sphericity of the pores, the less damage the pores cause to the mechanical properties of superhard tools. Therefore, after extensive research and practice, the inventors proposed the following core-shell structured composite powder and its preparation method.

[0025] Some embodiments of the present invention provide a composite powder with a core-shell structure, comprising a solid metal core and an alumina coating layer covering the surface of the solid metal core.

[0026] This core-shell structured composite powder has a low interfacial strength between its outer alumina coating and the metal matrix, such as Fe / Cu, making it prone to detachment during use and resulting in good pore-forming properties. Furthermore, the composite powder is a solid powder, making it less prone to breakage during cold pressing. The particle size of this composite powder is primarily related to the particle size of the raw material (e.g., copper-aluminum alloy powder). Copper-aluminum alloy powder can be obtained through atomization, resulting in not only smaller particle sizes but also high particle size concentration through sieving. Therefore, superhard tools made from this composite powder exhibit a more regular pore structure, better pore-forming effect, and superior mechanical properties.

[0027] In some embodiments, the particle size of the core-shell structured composite powder is less than or equal to 150 μm; further, in some embodiments, the particle size of the core-shell structured composite powder is less than 100 μm. By controlling the particle size of the core-shell structured composite powder, it is beneficial to control its effect as a site-filling pore-forming agent on the pore size and mechanical properties of superhard tools.

[0028] To prevent the core-shell structured composite powder from bonding with the matrix and easily breaking and detaching during grinding to form pores, some embodiments use an alumina coating layer with a thickness of 3-10 μm. Excessive thickness is detrimental to grinding as the composite powder may break and detach, while insufficient thickness may lead to breakage during cold pressing, causing the metal core to bond with the matrix and affecting the formation of subsequent pore structures.

[0029] In some embodiments, the alumina coating layer is an alumina coating layer generated by a selective oxidation reaction. Generating the alumina coating layer through a selective reaction is beneficial for the tight bonding between the alumina coating layer and the solid metal core. Furthermore, by controlling the raw material ratio, reaction temperature, and reaction time of the selective oxidation reaction, the thickness, integrity, and formation location of the alumina coating layer can be controlled, thereby improving the performance of the composite powder as a site-filling pore-forming agent.

[0030] In some embodiments, when a copper-aluminum alloy is used as the core and aluminum oxide is generated on its surface to obtain a composite powder with a core-shell structure, the solid metal core of the composite powder is a copper alloy core with a small amount of residual aluminum, depending on the degree of aluminum reaction in the copper-aluminum alloy. The amount of residual aluminum has no effect on its occupancy and pore-forming effect.

[0031] Furthermore, some embodiments of the present invention also provide a method for preparing the above-mentioned composite powder with a core-shell structure, which includes: forming a core-shell structure powder having a solid metal core and the alumina coating layer through a selective oxidation reaction.

[0032] The preparation of core-shell structured composite powders by selective oxidation reaction is not only simple and inexpensive, but also allows for better control of sphericity and particle size (e.g., less than 100 μm). This enables superhard tools using the composite powder as a site-filling pore-forming agent to have both better pore structure and higher mechanical properties.

[0033] Specifically, in some embodiments, the preparation method of composite powder with a core-shell structure includes the following steps:

[0034] S1. Mixing to obtain a mixture of oxidant and copper-aluminum alloy powder.

[0035] In some embodiments, an oxidizing agent is added to the copper-aluminum alloy powder, and then the mixture is mixed in a mixer. The oxidizing agent includes, but is not limited to, cuprous oxide powder.

[0036] It should be noted that the aluminum content and the proportion of oxidant added in the copper-aluminum alloy powder have a significant impact on the subsequent alumina coating layer.

[0037] Therefore, in some embodiments, the aluminum content in the copper-aluminum alloy powder is 0.5wt% to 5.0wt%. Too low an aluminum content will lead to problems such as the inability to form an alumina coating layer on the surface, or the oxide layer being too thin, having poor integrity, or being too close to the powder core, thereby reducing the pore-forming effect; while too high an aluminum content will also easily lead to severe adhesion of the powder during high-temperature oxidation, increase the difficulty of powder breakage, and increase the degree of damage to the alumina layer during the breakage process.

[0038] In some embodiments, the amount of oxidant (e.g., cuprous oxide) added is measured using an oxygen source coefficient, which is 0.8 to 1.3. The oxygen source coefficient is the ratio of the actual amount of oxidant added to the theoretical amount added. The theoretical amount of oxidant added is the mass of oxidant required to completely oxidize the aluminum in a unit mass of copper-aluminum alloy powder. By controlling the oxygen source coefficient, it is possible to ensure that the aluminum in the copper-aluminum alloy is oxidized, forming a core-shell structure with aluminum oxide as the shell and copper alloy as the core.

[0039] Furthermore, in order to obtain composite powder with the desired particle size and form a core-shell structure with better morphology, the particle size of the copper-aluminum alloy powder is less than or equal to 150 μm.

[0040] To ensure that the oxidant and copper-aluminum alloy powder are mixed evenly and thus guarantee the best oxidation reaction effect, the mixing time should be at least 2 hours, for example, 2 to 4 hours.

[0041] S2. Selectively oxidize the copper-aluminum alloy powder with an oxidizing agent to transform the copper-aluminum alloy powder into a core-shell structure powder with an aluminum oxide coating on the surface.

[0042] Specifically, a homogeneous mixture containing copper-aluminum alloy powder and an oxidant is reacted at a temperature of 700℃ to 900℃. For example, the oxidation temperature can be selected as 700℃, 750℃, 800℃, 850℃, or 900℃.

[0043] In some implementations, the reaction time is 1 to 2 hours in order to ensure a more complete reaction.

[0044] To avoid the influence of the external environment on the oxidation process, such as oxygen in the air, the oxidation reaction is carried out in a vacuum environment or an inert atmosphere, for example, in a vacuum furnace. This involves placing the mixed powder into the vacuum furnace and then evacuating it to a vacuum level of 1×10⁻⁶. -1 Below Pa.

[0045] It should be noted that, in the embodiments of the present invention, during the reaction process, the oxidant preferentially reacts with the aluminum on the surface of the copper-aluminum alloy powder to generate alumina. After the reaction occurs, a concentration difference is formed between the aluminum inside the powder particles and the aluminum on the surface. Under high temperature conditions, the aluminum atoms inside continuously diffuse to the surface due to the concentration difference and continue to react with the oxidant to generate alumina, thereby forming an alumina coating layer on the powder surface. Therefore, it is important to emphasize that in the mixing step before the oxidation reaction in the embodiments of the present invention, methods with large plastic deformation characteristics such as ball milling should not be used to mix the oxidant and the copper-aluminum alloy powder. This is to avoid damaging the sphericity of the powder and to avoid forming too many defects inside the particles, which would allow oxygen in the oxidant to directly enter the interior of the copper-aluminum alloy particles and react to generate alumina. Ultimately, the alumina would not adhere to the particle surface in the form of a coating layer, but would be dispersed within the copper-aluminum alloy particles.

[0046] Furthermore, the selective oxidation reaction generates a core-shell structure with copper particles as the core and alumina as the coating layer. The key to this oxidation reaction lies in the selection of the aluminum content in the copper-aluminum alloy, the oxidation temperature, and the oxygen source coefficient. These three factors must work in tandem to form a complete and continuous alumina coating layer on the outer surface of the particles. Therefore, in some embodiments, when the aluminum content in the copper-aluminum alloy powder is 0.5wt% to 2wt%, the oxygen source coefficient of the oxidant is 0.8 to 1.0, and the oxidation temperature is 700℃ to 850℃. When the aluminum content in the copper-aluminum alloy powder is greater than 2wt% and less than or equal to 5wt%, the oxygen source coefficient of the oxidant is 0.8 to 1.3, and the oxidation temperature is 800℃ to 900℃.

[0047] S3. After oxidation, the reactants are sequentially broken down and reduced.

[0048] Specifically, after crushing, the material is passed through a 100-mesh sieve and then reduced using hydrogen. This reduction reaction ensures the reduction of any unreacted oxidant. In some embodiments, the reduction temperature is 500℃~600℃, and the reduction time is 1h~2h.

[0049] In some embodiments, in order to achieve efficient utilization of the composite powder, the following step S4 is also included.

[0050] S4. Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers, and below 44 micrometers are weighed separately, and then vacuum-sealed to obtain composite powders with different particle sizes.

[0051] Some embodiments of the present invention also provide the application of the core-shell structured composite powder of any of the above embodiments as a site-filling pore-forming agent. Because the composite powder of the embodiments of the present invention is a solid powder with high sphericity, small particle size, and high particle size concentration, it can impart a better pore structure to superhard tools and also give them higher mechanical properties.

[0052] In some embodiments of the present invention, a superhard tool has a matrix containing a composite powder with a core-shell structure as described in any of the above embodiments.

[0053] Specifically, superhard tools include, but are not limited to, diamond tools. In some implementations, superhard tools include, but are not limited to, any one of grinding and polishing tools, cutting tools, and drilling tools.

[0054] In some embodiments, the volume content of the composite powder in the matrix of the superhard tool is 10-70%.

[0055] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0056] Example 1

[0057] This embodiment provides a core-shell structured composite powder that can be used as a site-occupying pore-forming agent, which is prepared through the following steps:

[0058] (1) Mixing: Cu2O powder with an oxygen source coefficient of 0.8 is added to Cu-Al alloy powder with an Al mass content of 0.5%, and then mixed on a mixer for 2 hours.

[0059] (2) Oxidation: The mixed powder is placed in a vacuum furnace and evacuated to a vacuum level of 1×10⁻⁶. -1 The temperature is below Pa, then raised to 700℃ and held for 1 hour;

[0060] (3) Crushing and reduction: Crush the powder, pass it through a 100-mesh sieve, and then reduce it at 500℃ under hydrogen for 1 hour;

[0061] (4) Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers and below 44 micrometers are weighed respectively. Then, they are vacuum packaged to obtain composite powders with different particle sizes.

[0062] Example 2

[0063] This embodiment provides a core-shell structured composite powder that can be used as a site-occupying pore-forming agent, which is prepared through the following steps:

[0064] (1) Mixing: Cu2O powder with an oxygen source coefficient of 1.0 is added to Cu-Al alloy powder with an Al mass content of 2.0%, and then mixed on a mixer for 3 hours.

[0065] (2) Oxidation: The mixed powder is placed in a vacuum furnace and evacuated to a vacuum level of 1×10⁻⁶. -1 The temperature is below Pa, then raised to 800℃ and held for 2 hours.

[0066] (3) Crushing and reduction: Crush the powder, pass it through a 100-mesh sieve, and then reduce it at 600℃ under hydrogen for 2 hours;

[0067] (4) Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers and below 44 micrometers are weighed respectively. Then, they are vacuum packaged to obtain composite powders with different particle sizes.

[0068] Example 3

[0069] This embodiment provides a core-shell structured composite powder that can be used as a site-occupying pore-forming agent, which is prepared through the following steps:

[0070] (1) Mixing: Cu2O powder with an oxygen source coefficient of 1.3 is added to Cu-Al alloy powder with an Al mass content of 5.0%, and then mixed on a mixer for 4 hours.

[0071] (2) Oxidation: The mixed powder is placed in a vacuum furnace and evacuated to a vacuum level of 1×10⁻⁶. -1 The temperature is below Pa, then raised to 900℃ and held for 2 hours.

[0072] (3) Crushing and reduction: Crush the powder, pass it through a 100-mesh sieve, and then reduce it at 600℃ under hydrogen for 2 hours;

[0073] (4) Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers and below 44 micrometers are weighed respectively. Then, they are vacuum packaged to obtain composite powders with different particle sizes.

[0074] Example 4

[0075] This embodiment provides a diamond saw blade prepared by using a core-shell structured composite powder as a site-filling pore-forming agent, which is obtained through the following steps:

[0076] (1) Mixing: The composite powder below 44 micrometers, the Fe-30Cu-10Sn powder below 44 micrometers and the diamond powder of 300-500 micrometers obtained in step 2 are mixed in a volume fraction of 10%:80%:10% and then mixed in a mixer for 4 hours.

[0077] (2) Cold pressing: The mixed powder is automatically pressed into a green body on an automatic cold pressing machine, wherein the cold pressing pressure is 15MPa and the pressure is held for 3 seconds;

[0078] (3) Molding: The green blank is placed into the graphite mold;

[0079] (4) Hot pressing: The assembled graphite mold is placed into a hot pressing sintering machine for hot pressing sintering, wherein the sintering temperature is 850℃, the pressure is 35MPa, and the sintering holding time is 4min.

[0080] (5) Demolding: After sintering, the mold is cooled to room temperature and the diamond tool head is demolded.

[0081] (6) Welding: Weld the diamond cutting head to the 45# steel body to obtain a diamond saw blade.

[0082] Compared to diamond saw blades without added composite powder, diamond saw blades with added composite powder increased the linear speed of cutting rock slabs from 2.5 m / min to 5.8 m / min, resulting in a 132% increase in cutting efficiency.

[0083] Comparative Example 1

[0084] This comparative example was prepared through the following steps:

[0085] (1) Mixing: Cu2O powder with an oxygen source coefficient of 1.3 is added to Cu-Al alloy powder with an Al mass content of 10.0%, and then mixed on a mixer for 4 hours.

[0086] (2) Oxidation: The mixed powder is placed in a vacuum furnace and evacuated to a vacuum level of 1×10⁻⁶. -1 The temperature is below Pa, then raised to 900℃ and held for 2 hours.

[0087] (3) Crushing and reduction: Crush the powder, pass it through a 100-mesh sieve, and then reduce it at 600℃ under hydrogen for 2 hours;

[0088] (4) Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers and below 44 micrometers are weighed respectively. Then, they are vacuum packaged to obtain composite powders with different particle sizes.

[0089] Comparative Example 2

[0090] This comparative example was prepared through the following steps:

[0091] (1) Mixing: Cu2O powder with an oxygen source coefficient of 1.3 is added to Cu-Al alloy powder with an Al mass content of 0.5%, and then mixed on a mixer for 4 hours.

[0092] (2) Oxidation: The mixed powder is placed in a vacuum furnace and evacuated to a vacuum level of 1×10⁻⁶. -1 The temperature is below Pa, then raised to 900℃ and held for 2 hours.

[0093] (3) Crushing and reduction: Crush the powder, pass it through a 100-mesh sieve, and then reduce it at 600℃ under hydrogen for 2 hours;

[0094] (4) Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers and below 44 micrometers are weighed respectively. Then, they are vacuum packaged to obtain composite powders with different particle sizes.

[0095] Comparative Example 3

[0096] This comparative example was prepared through the following steps:

[0097] (1) Mixing: Cu2O powder with an oxygen source coefficient of 1.1 is added to Cu-Al alloy powder with an Al mass content of 0.5%, and then mixed on a mixer for 4 hours.

[0098] (2) Oxidation: The mixed powder is placed in a vacuum furnace and evacuated to a vacuum level of 1×10⁻⁶. -1 The temperature is below Pa, then raised to 800℃ and held for 2 hours.

[0099] (3) Crushing and reduction: Crush the powder, pass it through a 100-mesh sieve, and then reduce it at 600℃ under hydrogen for 2 hours;

[0100] (4) Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers and below 44 micrometers are weighed respectively. Then, they are vacuum packaged to obtain composite powders with different particle sizes.

[0101] Comparative Example 4

[0102] This comparative example was prepared through the following steps:

[0103] (1) Mixing: Cu2O powder with an oxygen source coefficient of 1.3 is added to Cu-Al alloy powder with an Al mass content of 2.0%, and then mixed on a mixer for 3 hours.

[0104] (2) Oxidation: The mixed powder is placed in a vacuum furnace and evacuated to a vacuum level of 1×10⁻⁶. -1 The temperature is below Pa, then raised to 900℃ and held for 2 hours.

[0105] (3) Crushing and reduction: Crush the powder, pass it through a 100-mesh sieve, and then reduce it at 600℃ under hydrogen for 2 hours;

[0106] (4) Sieving and vacuum packaging. The reduced powder is sieved, and the powders with particle sizes of 150-74 micrometers, 74-44 micrometers and below 44 micrometers are weighed respectively. Then, they are vacuum packaged to obtain composite powders with different particle sizes.

[0107] The composite powders prepared in Examples 1-3 and Comparative Examples 1-4 were observed using scanning electron microscopy, and the results are as follows: Figures 1 to 7 As shown. SEM images corresponding to Examples 1-3 ( Figures 1-3 As can be seen, both formed a core-shell structure coated with alumina; through comparative example 1... Figure 4 It can be seen that when the aluminum content in the copper-aluminum alloy is too high, the adhesion between powder particles is more severe during high-temperature oxidation, and the powder cannot maintain its original sphericity, which has an adverse effect on the pore-forming effect; through comparative example 2... Figure 5 It can be seen that when the aluminum content in the copper-aluminum alloy is low, if the oxidation temperature and oxygen source coefficient are not properly matched, the formed alumina will be uniformly distributed in the copper matrix and will not form an alumina shell. This can be observed through Comparative Example 3. Figure 6 It can be seen that when the aluminum content in the copper-aluminum alloy is low, if the oxidation temperature and oxygen source coefficient are not properly matched, the resulting alumina shell is thin and too close to the powder core, failing to achieve the desired pore-forming effect; this is demonstrated by comparing Example 4. Figure 7 It can be seen that when the aluminum content in the copper-aluminum alloy is high, if the oxidation temperature and oxygen source coefficient are not properly matched, a continuous and complete alumina shell cannot be formed, making it difficult to obtain the ideal pore-forming effect.

[0108] In summary, the core-shell structured composite powder in this invention exhibits good pore-forming effect due to the low interfacial strength between its outer alumina coating layer and the metal matrix (e.g., Fe / Cu), which is prone to detachment during use. Furthermore, its solid nature makes it less prone to breakage during cold pressing, resulting in a more regular pore structure and superior pore-forming effect. Moreover, this invention offers a simple and low-cost process, and allows for better control over the sphericity, particle size (e.g., less than 100 μm), and particle size distribution of the composite powder. This enables superhard tools using this composite powder as a site-filling pore-forming agent to possess both superior pore structure and excellent mechanical properties, thus significantly improving service performance.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite powder with a core-shell structure, characterized in that, It includes a solid metal core and an aluminum oxide coating layer covering the surface of the solid metal core; The particle size of the composite powder is less than or equal to 150 μm; And / or, the thickness of the alumina coating is 3-10 μm; And / or, the alumina coating is an alumina coating generated by a selective oxidation reaction; The solid metal core is a copper alloy core; The selective oxidation reaction includes: reacting a homogeneous mixture containing copper-aluminum alloy powder and a powdered oxidant at a temperature of 700°C to 900°C. The reaction time is 1 to 2 hours. The oxidant is Cu2O; The particle size of the copper-aluminum alloy powder is less than or equal to 150 μm; The reaction is carried out in a vacuum or inert atmosphere; The aluminum content in the copper-aluminum alloy powder is 0.5wt%~5.0wt%; The oxygen source coefficient of the oxidant is 0.8~1.3, wherein the oxygen source coefficient is the ratio of the actual amount of oxidant added to the theoretical amount of oxidant added, and the theoretical amount of oxidant added is the mass of oxidant required to completely oxidize the aluminum in a unit mass of copper-aluminum alloy powder. After oxidation, the reactants are also subjected to sequential crushing and reduction, and / or crushing and passing through a 100-mesh sieve, followed by reduction with hydrogen. The reduction temperature is 500℃~600℃, and the reduction time is 1h~2h; When the aluminum content in the copper-aluminum alloy powder is 0.5wt%~2wt%, the oxygen source coefficient of the oxidant is 0.8, and the oxidation temperature is 700℃~850℃; when the aluminum content in the copper-aluminum alloy powder is greater than 2wt%, the oxygen source coefficient of the oxidant is 0.8~1.3, and the oxidation temperature is 800℃~900℃.

2. The method for preparing a core-shell structured composite powder as described in claim 1, characterized in that, It includes: A core-shell structure powder with the solid metal core and the alumina coating is formed by selective oxidation reaction.

3. The method for preparing a core-shell structured composite powder according to claim 2, characterized in that, It includes: The copper-aluminum alloy powder is oxidized by an oxidant, which causes the solute Al atoms in the copper-aluminum alloy powder to aggregate to the surface of the powder particles and preferentially react with the oxidant to transform it into a core-shell structure powder with an aluminum oxide coating on the surface.

4. The application of the composite powder with a core-shell structure as described in claim 1 as a site-filling pore-forming agent.

5. An ultrahard tool, characterized in that, Its matrix contains the composite powder with a core-shell structure as described in claim 1.

6. The superhard tool according to claim 5, characterized in that, The superhard tool is a diamond tool or a CBN tool; And / or, the superhard tool is any one of a polishing tool, a cutting tool, and a drilling tool; And / or, in the fetal body, the volume fraction of the composite powder with a core-shell structure is 10-70%.

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