Micro- and Nano-Synergistically Reinforced Heterogeneous Metal Matrix Composites and Hierarchical Assembly Preparation

Abstract

The present invention provides a micro- and nano-cooperatively enhanced heterogeneous metal matrix composite material and a hierarchical assembly preparation method. The material simultaneously includes micro and nano reinforcements and a metal matrix with a heterogeneous grain configuration. The preparation method is as follows: The nano reinforcements and metal powders are pre-dispersed by high-speed shearing and then subjected to low-speed ball milling to obtain a composite powder with uniform dispersion and a fragmented ultra-fine grain matrix. The composite powder is mixed with micro particles to achieve coating on the edges and corners of the particle surface. Then, powders with a coarse-grained original matrix are added for secondary mixing to complete the composite powder with uniform dispersion and hierarchical characteristics. After high-speed ball milling the hierarchical composite powder, it is formed and subjected to hot deformation processing to obtain the micro- and nano-enhanced heterogeneous aluminum matrix composite material. The hierarchical assembly preparation can achieve coating on the edges and corners of the micro particles, avoiding premature fracture of the composite material caused by poor contact interfaces. At the same time, it also makes the final composite structure exhibit hierarchical characteristics, realizing the synchronous improvement of strength and plasticity.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal matrix composites, and relates to a micro- and nano-synergistically reinforced heterogeneous metal matrix composite and hierarchical assembly preparation; in particular, it relates to a metal matrix (aluminum matrix) composite with micro- and nano-synergistically reinforced heterogeneous configuration characteristics and a hierarchical assembly preparation method. Background Art

[0002] Metal matrix composites have excellent properties such as high specific strength, specific stiffness, high thermal conductivity, low coefficient of thermal expansion, wear resistance and corrosion resistance, and can achieve a qualitative improvement in material properties based on a reasonable combination of the matrix and the reinforcement. They are widely used in national strategic pillar industries such as aerospace, national defense, and the automotive industry.

[0003] With the continuous development of the reinforcement, the reinforcement phase of metal matrix composites has gradually changed from the initial carbon fiber, boron fiber, etc. to discontinuous reinforcement, such as ceramic particles such as silicon carbide, boron carbide, and alumina; until now, high-performance nano-reinforcements such as carbon nanotubes and graphene, and the reinforcements with excellent intrinsic properties have further improved the properties of the composites. Due to the large differences in the microstructure, physical and chemical properties of micro- and nano-scale reinforcements, the composite strengthening effects and mechanical responses are also different; in order to further improve the comprehensive properties of materials and expand the application requirements, it is of important theoretical and practical significance to develop metal matrix composites with micro / nano synergistic strengthening and complementary advantages. However, it is found in actual research that composites with micro, nano, and hybrid reinforcements still face obvious strong-plasticity mismatch problems due to stress and strain concentration, etc., which greatly limits their applications.

[0004] In recent years, among metal structural materials, heterogeneous structure materials with non-uniform structure design have received extensive attention due to their good strength-plasticity matching, broad design space, and diverse preparation methods, and are considered to be the most effective means to solve the problem of the strength-plasticity inversion relationship of structural metal materials. Due to the elimination of interfacial stress concentration, stress-strain gradient distribution, unique dislocation activities, and significant back stress hardening effects brought about by this configuration effect, the materials can further achieve excellent anti-fatigue fracture, anti-impact damage, wear resistance, corrosion resistance, etc. on the basis of ensuring strength-plasticity synergy. However, due to the relatively low yield strength of heterogeneous metal materials themselves, the improvement in strength is limited, and the work hardening and other behaviors of metal materials themselves cannot be fully stimulated, and there is still a large room for improvement, and the potential can be exerted through the way of composites.

[0005] Through the search of existing technical research, it is found that there is currently a lack of relevant preparation research on the combination of micro- and nano-reinforcements and matrix heterogeneous materials. Summary of the Invention

[0006] Aiming at the defects in the prior art, the purpose of the present invention is to provide a micro- and nano-cooperatively enhanced heterogeneous metal matrix composite material and a hierarchical assembly preparation method.

[0007] The purpose of the present invention is achieved through the following solutions:

[0008] In a first aspect, the present invention provides a metal matrix composite material with micro- and nano-cooperatively enhanced heterogeneous configuration characteristics. The composite material simultaneously includes micro and nano reinforcements and a metal matrix. The characteristic of the metal matrix is that the grains of the metal matrix present a heterogeneous configuration and have a hierarchical structure characteristic. The heterogeneous structure of the matrix includes a coarse grain structure and an ultrafine grain structure. The hierarchical structure characteristic includes a transition from micro reinforcements to an ultrafine grain structure and finally to a coarse grain structure.

[0009] As an embodiment of the present invention, the size of the ultrafine grains is 100 - 500 nm, and the size of the coarse grains is 1 - 5 μm.

[0010] As an embodiment of the present invention, the volume fraction of the nano reinforcements in the composite material is 0.05 - 10%, and the size of the nano reinforcements in the composite material is 0.3 - 300 nm.

[0011] As an embodiment of the present invention, the volume fraction of the micro reinforcements in the composite material is 0.5 - 50%, and the size of the micro reinforcements in the composite material is 0.5 - 100 μm.

[0012] As an embodiment of the present invention, the metal powder is one or more of Al, Cu, Mg, Ti, Fe, and Ni.

[0013] As an embodiment of the present invention, the nano reinforcements are one or more of carbon nanotubes, graphene, graphene oxide, reduced graphene oxide, carbon nano-onion balls, carbon nanosheets, nano ceramic particles, and nano intermetallic compounds.

[0014] As an embodiment of the present invention, the micro reinforcements are one or more of boron carbide, silicon carbide, alumina, diamond, titanium diboride, and zirconium diboride.

[0015] In a second aspect, the present invention provides a hierarchical assembly preparation method for a metal matrix composite material with micro- and nano-cooperatively enhanced heterogeneous configuration characteristics. The method includes the following steps:

[0016] S1. After mixing the nano reinforcement powder with the original metal powder, perform high-speed shear predispersion treatment to obtain a composite powder in which the nano reinforcements are uniformly dispersed on the surface of the matrix;

[0017] S2. Perform low-speed ball milling treatment on the composite powder obtained in step S1 to obtain a fragmented composite powder with an ultrafine grain matrix;

[0018] S3. Perform primary mechanical mixing on the composite powder obtained in step S2 and the micron reinforcement to obtain a micron reinforcement with its surface edges and corners covered, and the micron reinforcement is evenly dispersed.

[0019] S4. Use the powder obtained in step S3 and the original metal powder as coarse grains for secondary mechanical mixing to obtain a uniformly dispersed multi-level composite powder.

[0020] S5. After high-energy ball milling the multi-level composite powder obtained in step S4, a metal matrix composite with the characteristics of micro-nano synergistic reinforcement and heterogeneous configuration is prepared through hot press sintering and hot deformation processing.

[0021] If only adding the reinforcement step by step can achieve good dispersion but does not solve the problem of poor bonding effect between the matrix itself and the reinforcement; the heterogeneous hierarchical structure formed by the method of the present invention can well realize the bonding of reinforcements and matrix at different scales.

[0022] As an embodiment of the present invention, in step S1, the proportion of the nano reinforcement in the original metal powder is 0.5 - 3 wt%.

[0023] As an embodiment of the present invention, in step S1, the rotational speed of high-speed shear pre-dispersion is 1200 - 2800 r / min, and the time is 5 - 30 min.

[0024] As an embodiment of the present invention, in step S1, the uniform dispersion condition is that the nano reinforcement is evenly dispersed on the surface of the metal matrix without agglomeration.

[0025] As an embodiment of the present invention, in step S2, the rotational speed of low-energy ball milling is 50 - 200 r / min, and the time is 2 - 20 h, including 5 - 20 h.

[0026] As an embodiment of the present invention, in step S3, the rotational speed of primary mechanical mixing is 50 - 200 r / min, and the time is 0.5 - 5 h.

[0027] As an embodiment of the present invention, in step S3, the coating and dispersion condition is that the surface edges and corners of the micron reinforcement are well coated by fragmented powder, avoiding direct contact between the micron reinforcement and the coarse-grained matrix, and there is no agglomeration.

[0028] As an embodiment of the present invention, in step S4, the proportion of the original metal powder as coarse grains in the multi-level composite powder is 5 - 50 wt%.

[0029] As an embodiment of the present invention, in step S4, the uniform dispersion condition is that the coarse-grained metal powder is evenly dispersed in the powder of step S3 without agglomeration.

[0030] As an embodiment of the present invention, in step S4, the secondary mechanical mixing speed is 50 - 200 r / min, and the time is 5 - 20 h.

[0031] As an embodiment of the present invention, in step S5, the high-speed ball milling speed is 200 - 1000 r / min, and the time is 0.5 - 8 h.

[0032] As an embodiment of the present invention, in step S5, the pressing pressure is 400 - 700 MPa, the sintering temperature is 400 - 600 °C, the time is 1 - 5 h, the hot extrusion ratio is 15:1 - 40:1, and the hot extrusion temperature is 350 - 500 °C.

[0033] The present invention prepares a metal matrix composite material with micro- and nano-synergistic enhanced heterogeneous configuration characteristics, and through a hierarchical assembly preparation method, it obtains excellent yield strength, tensile strength and elongation, enabling the composite material to maintain high strength while simultaneously improving plasticity.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The metal matrix composite material with micro- and nano-synergistic enhanced heterogeneous configuration characteristics and the hierarchical assembly preparation method of the present invention can effectively coat the surface edges and corners of the micron reinforcement through fragmented ultrafine crystal composite powder, relieve the stress-strain concentration during the deformation process, ensure the de-strain localization of the composite material and avoid premature crack initiation;

[0036] (2) Through controllable hierarchical assembly, the hierarchical structure characteristics transition from micron reinforcement to ultrafine crystal structure and finally to coarse crystal structure characteristics to achieve a slow transition of the overall structure, realizing the improvement of strength by work hardening in the early stage of the material while avoiding plastic loss and breaking through the bottleneck of the existing strong-plasticity inversion relationship. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objectives and advantages of the present invention will become more obvious:

[0038] Figure 1 It is the hierarchical assembly preparation route map of the metal matrix composite material with micro- and nano-synergistic enhanced heterogeneous configuration characteristics of the present invention;

[0039] Figure 2 It is the scanning electron microscope photo of the micron particle surface coated with fragmented ultrafine crystal matrix powder provided by the present invention;

[0040] Figure 3It is a TEM micrograph showing the structural characteristics of the decomposition structure transitioning from micron reinforcements to ultrafine-grained structures and finally to coarse-grained structures;

[0041] Figure 4 It is a SEM micrograph of micron-sized particles of the composite material prepared without hierarchical assembly. Specific Embodiments

[0042] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all fall within the protection scope of the present invention.

[0043] Example 1

[0044] In this example, the B4C-CNT / ultrafine-grained Al-coarse-grained Al composite material was prepared by powder metallurgy. Among them, the mass fraction of carbon nanotubes CNT was 0.75%, the mass fraction of B4C was 15%, and the rest was 6061Al. The preparation route is as Figure 1 shown; including:

[0045] (1) 99.25 g of 6061Al powder with a medium particle size of 10 μm and 0.75 g of CNT (length 1 - 2 μm, diameter 20 nm) powder were mixed in a high-speed shear disperser at 1500 r / min for 20 min, and then ball-milled at 200 r / min for 8 h to obtain fragmented ultrafine-grained composite powder with a grain size of 400 nm;

[0046] (2) 15 g of B4C powder with a medium particle size of 7 μm and 76.5 g of the above-mentioned fragmented composite powder were mechanically mixed at 135 r / min for 5 h to obtain composite powder with the surface corners coated and evenly dispersed. The coating state is as Figure 2 shown;

[0047] (3) 8.5 g of 6061Al powder with a medium particle size of 10 μm was mechanically mixed with the above powder again at 135 r / min for 5 h. After that, it was high-speed ball-milled at a speed of 500 r / min for 30 min to obtain welded composite powder particles. Then, it was pressed under a pressure of 500 MPa, vacuum sintered at 570 °C for 2 h, and hot-extruded at 410 °C with an extrusion ratio of 20:1 to obtain the final dense B4C-CNT / ultrafine-grained Al-coarse-grained Al hierarchical composite material with micron and nano synergistic reinforcement and heterogeneous matrix configuration. The structural schematic diagram is as Figure 3 shown, and its mechanical properties are listed in Table 1.

[0048] Example 2

[0049] This example uses the same powder metallurgy method as Example 1, and the ultrafine grain size in this example increases slightly. Among them, the mass fraction of carbon nanotube CNT is 0.75%, the mass fraction of B4C is 15%, and the rest is 6061Al. The preparation route includes:

[0050] (1) Mix 99.25 g of 6061Al powder with a medium particle size of 10 μm and 0.75 g of CNT (length 1 - 2 μm, diameter 20 nm) powder in a high-speed shear disperser at 1500 r / min for 20 min, and then ball mill at 200 r / min for 6 h to obtain fragmented ultrafine grain composite powder with a grain size of 600 nm;

[0051] (2) Mechanically mix 15 g of B4C powder with a medium particle size of 7 μm and 76.5 g of the above-mentioned fragmented composite powder at 135 r / min for 5 h to obtain a composite powder with the surface edges and corners coated and evenly dispersed, and the particles are in the same coated state as above;

[0052] (3) Mechanically mix 8.5 g of 6061Al powder with a medium particle size of 10 μm and the above powder again at 135 r / min for 5 h, and then high-speed ball mill at a speed of 500 r / min for 30 min to obtain composite powder particles in a welded state. After that, press at a pressure of 500 MPa, vacuum sinter at 570 °C for 2 h, and perform hot extrusion at 410 °C with an extrusion ratio of 20:1 to obtain a finally dense B4C-CNT / ultrafine grain Al-coarse grain Al hierarchical composite material with micron and nano synergistic reinforcement and a heterogeneous matrix configuration. Its mechanical properties are listed in Table 1.

[0053] Example 3

[0054] This example uses the same powder metallurgy method as Example 1, and the proportion of coarse grains in this example increases slightly. Among them, the mass fraction of carbon nanotube CNT is 0.75%, the mass fraction of B4C is 15%, and the rest is 6061Al. The preparation route includes:

[0055] (1) Mix 99 g of 6061Al powder with a medium particle size of 10 μm and 1 g of CNT (length 1 - 2 μm, diameter 20 nm) powder in a high-speed shear disperser at 1500 r / min for 20 min, and then ball mill at 200 r / min for 8 h to obtain fragmented ultrafine grain composite powder with a grain size of 400 nm;

[0056] (2) Mechanically mix 15 g of B4C powder with a medium particle size of 7 μm and 63.75 g of the above-mentioned fragmented composite powder at 135 r / min for 5 h to obtain a composite powder with the surface edges and corners coated and evenly dispersed;

[0057] (3) 21.25 g of 6061 Al powder with a medium particle size of 10 μm was mechanically mixed with the above powder again at 135 r / min. After 5 h, it was ball-milled at a high speed of 500 r / min for 30 min to obtain composite powder particles in a welded state. Then, it was pressed under a pressure of 500 MPa, vacuum sintered at 570 °C for 2 h, and hot-extruded at an extrusion ratio of 20:1 at 410 °C to obtain a finally dense B4C-CNT / ultrafine-grained Al-coarse-grained Al hierarchical composite material with micron and nano synergistic reinforcement and a heterogeneous matrix configuration. Its mechanical properties are listed in Table 1.

[0058] Comparative Example 1

[0059] This comparative example used the same powder metallurgy method as Example 1. The same 6061 Al powder, CNT powder, and B4C powder as in Example 1 were taken and mechanically mixed together for 10 h, and then ball-milled at a high speed of 500 r / min for 30 min to obtain composite powder particles. After being pressed under a pressure of 500 MPa, vacuum sintered at 570 °C for 2 h, and hot-extruded at an extrusion ratio of 25:1 at 410 °C, a B4C-CNT / Al composite material with a coarse-grained matrix grain structure was finally obtained. Its mechanical properties are listed in Table 1.

[0060] Comparative Example 2

[0061] This comparative example used the same powder metallurgy method as Example 1. The same total amount of 6061 Al powder as in Example 1 and CNT powder were mixed in a high-speed shear disperser at 1500 r / min for 20 min, and then ball-milled at a low speed of 200 r / min for 8 h. The fragmented composite powder was then mechanically mixed with B4C powder at 135 r / min for 10 h. Then, it was ball-milled at a high speed of 500 r / min for 30 min to obtain composite powder particles. After being pressed under a pressure of 500 MPa, vacuum sintered at 570 °C for 2 h, and hot-extruded at an extrusion ratio of 25:1 at 410 °C, a B4C-CNT / Al composite material with an ultrafine-grained matrix grain structure was finally obtained. Its mechanical properties are listed in Table 1.

[0062] Comparative Example 3

[0063] In this comparative example, the same powder metallurgy method as in Example 1 was used. The same 6061Al powder as in Example 1 and CNT powder were taken and mixed in a high-speed shear disperser at 1500 r / min for 20 min, and then low-speed ball milled at a speed of 200 r / min for 8 h. The composite powder was mechanically mixed with B4C and 6061Al powder at 135 r / min for 10 h, and then high-speed ball milled at a speed of 500 r / min for 30 min to obtain composite powder particles. After pressing under a pressure of 500 MPa, vacuum sintering at 570 °C for 2 h, and hot extrusion at an extrusion ratio of 25:1 at 410 °C, a B4C-CNT / Al composite material with micron and nano synergistic enhancement and a matrix heterogeneous hierarchical configuration was finally obtained (since it was directly mixed instead of hierarchically mixed, the above hierarchical structure characteristics still existed in a small part of the area, but the overall distribution was random). Its mechanical properties are listed in Table 1.

[0064] Table 1 Microstructure, grain size and content of the composite material, and room temperature mechanical properties

[0065]

[0066]

[0067] It can be found from the data in Table 1 that in Comparative Example 1, the fragmented ultrafine-grained composite powder was not added, and the yield strength of the prepared composite material was relatively high but the elongation was extremely poor; in Comparative Example 2, it was not mechanically mixed with the powder of the original coarse-grained state, and the yield strength of the prepared composite material was relatively high but the elongation was extremely poor; in Comparative Example 3, the hierarchical mixing method was not adopted, and the surface of B4C obtained in the composite material was not in a coated state ( Figure 4 ), and both the strength and elongation were lower than those of the example.

[0068] To sum up, in the present invention, the nano-reinforcement and the metal powder are pre-dispersed by high-speed shear mixing and then low-speed ball milled for a certain period of time to obtain a composite powder with uniformly dispersed nano-reinforcement and an ultrafine-grained fragmented matrix; the composite powder is mixed with micron-reinforcement particles to achieve the coating of the edges and corners of the particle surface; then the powder with the original coarse-grained matrix is added for secondary mixing to complete the uniformly dispersed hierarchical powder, realizing the structural characteristics from micron-reinforcement to ultrafine-grained structure and finally to coarse-grained structure; finally, the two kinds of coarse and fine flaky composite powders are mixed according to the ratio, and after high-speed ball milling, cold pressing, sintering and deformation processing, a metal matrix composite material with micro and nano synergistic enhancement and heterogeneous configuration characteristics is prepared. Through hierarchical assembly preparation, good coating at the stress concentration points on the edges and corners of the micron particles surface is achieved, avoiding the premature fracture of the composite material caused by introducing poor contact interfaces; at the same time, the final composite structure can also show hierarchical characteristics, realizing the synchronous improvement of the strength and plasticity of the material.

[0069] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A metal matrix composite material with micro- and nano-synergistic enhanced heterogeneous configuration characteristics, characterized in that, The material simultaneously contains micron reinforcements, nano reinforcements, and a metal matrix. The grains of the metal matrix exhibit a heterogeneous configuration, and the overall material has a hierarchical structure feature. The matrix heterogeneous structure includes a coarse-grained structure and an ultrafine-grained structure. The hierarchical structure feature includes a transition from micron reinforcements to an ultrafine-grained structure and finally to a coarse-grained structure. The size of the ultrafine grains is 100 - 500 nm, and the size of the coarse grains is 1 - 5 μm. The method for the hierarchical assembly preparation of the metal matrix composite material includes the following steps: S1. After mixing the nano reinforcement powder with the raw metal powder, perform high-speed shear predispersion treatment to obtain a composite powder with the nano reinforcements uniformly dispersed on the surface of the matrix. S2. Perform low-speed ball milling treatment on the composite powder obtained in step S1 to obtain a fragmented composite powder with an ultrafine-grained matrix. S3. Perform primary mechanical mixing on the composite powder obtained in step S2 with the micron reinforcements to obtain micron reinforcements with surface edges and corners achieving a coating effect and the micron reinforcements being uniformly dispersed. S4. Perform secondary mechanical mixing on the powder obtained in step S3 with the raw metal powder serving as the coarse grains to obtain a uniformly dispersed multi-level composite powder. S5. After high-speed ball milling the multi-level composite powder obtained in step S4, prepare a metal matrix composite material with micro- and nano-synergistic reinforcement heterogeneous configuration characteristics through hot press sintering and hot deformation processing.

2. The metal matrix composite material with micro- and nano-synergistically enhanced heterogeneous configuration features according to claim 1, wherein In the composite material, the volume fraction of the nano reinforcements is 0.05 - 10%, and the size of the nano reinforcements is 0.3 - 300 nm. In the composite material, the volume fraction of the micron reinforcements is 0.5 - 50%, and the size of the micron reinforcements is 0.5 - 100 μm.

3. The metal matrix composite material with micro-nano synergistic enhanced heterogeneous configuration characteristics according to claim 1, characterized in that, In step S1, the high-speed shear predispersion rotation speed is 1200 - 2800 r / min, and the time is 5 - 30 min.

4. The metal matrix composite material with the characteristics of micro-nano synergistic enhancement and heterogeneous configuration according to claim 1, wherein In step S2, the low-speed ball milling rotation speed is 50 - 200 r / min, and the time is 5 - 20 h.

5. The metal matrix composite material with micro- and nano-synergistic enhanced heterogeneous configuration features according to claim 1, wherein, In step S3, the primary mechanical mixing rotation speed is 50 - 200 r / min, and the time is 0.5 - 5 h.

6. The metal matrix composite material with micro-nano synergistic enhanced heterogeneous configuration features according to claim 1, characterized in that, In step S4, the secondary mechanical mixing rotation speed is 50 - 200 r / min, and the time is 5 - 20 h.

7. The metal matrix composite material with micro-nano synergistic enhanced heterogeneous configuration characteristics according to claim 1, wherein, In step S5, the high-speed ball milling rotation speed is 200 - 1000 r / min, and the time is 0.5 - 8 h.

8. The metal matrix composite material with the characteristics of micro-nano synergistic enhanced heterogeneous configuration according to claim 1, characterized in that, In step S5, the pressing pressure for hot press sintering is 400 - 700 MPa, the sintering temperature is 400 - 600 °C, and the time is 1 - 5 h. The hot extrusion ratio is 15:1 - 40:1, and the hot extrusion temperature is 350 - 500 °C.

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