A steel-based composite material and a method for producing the same

Abstract

This invention relates to a steel-based composite material and its preparation method, belonging to the field of metal matrix composite technology. The main technical solution is as follows: the steel-based composite material comprises a continuous steel matrix phase and multiple reinforcing bundles; wherein the multiple reinforcing bundles are distributed within the continuous steel matrix phase; wherein each reinforcing bundle has a core-shell structure with Nb as the core and an NbC / Fe gradient multilayer structure as the shell; wherein the NbC / Fe gradient multilayer structure comprises multiple NbC layers and multiple α-Fe layers, with the NbC layers and α-Fe layers arranged alternately. A gradient heterogeneous interface exists between the reinforcing bundles and the continuous steel matrix phase; carbide particles with NbC as the core and solid-solution carbide (Nb,M)C as the shell are distributed within the gradient heterogeneous interface. Wherein, M is one or more elements selected from Ti, Ta, and Cr. This invention is mainly used to design and prepare a novel steel-based composite material to improve the performance of steel-based composite materials.

Description

Technical Field

[0001] This invention relates to the field of metal-based composite materials technology, and in particular to a steel-based composite material and its preparation method. Background Technology

[0002] Carbide-reinforced steel matrix composites are widely used in important sectors of the national economy, such as military, mining, and metallurgy, due to their combination of the superior toughness, hot and cold workability, and weldability of metallic materials with the high strength, high hardness, and wear resistance of carbides. With the rapid development of modern industry, increasingly harsh service environments place higher demands on the strength, toughness, and wear resistance of key components in related equipment. However, numerous studies on homogeneous steel matrix composites have shown that while the reinforcing phase strengthens the matrix, it also reduces the mean free path of dislocation motion, causing its mechanical properties to approach the lower limit of the theoretical strengthening model. Increased strength is accompanied by a significant decrease in toughness and damage tolerance, exhibiting an inverse relationship between strength and toughness. This greatly limits the widespread application of metal matrix composites.

[0003] In recent years, research on configurable steel-based composites has provided new solutions to the problem of the inverse relationship between strength and toughness. By constructing reinforcing phase-rich regions and large-area matrix plastic regions within the composite material, it strengthens the matrix while simultaneously utilizing the large-area matrix plastic deformation to suppress the propagation of unstable master cracks and plastic instability, thereby improving damage tolerance. For example, one related technology discloses a three-dimensional spherical metal / carbide core-shell reinforced steel-based composite material prepared using carbide-forming metal powder, iron powder, and graphite powder as raw materials via powder metallurgy. The high-toughness metal core improves the material's toughness, while the dense carbide shell enhances its strength. A second related technology uses a hot-pressing sintering process to prepare a steel-based morphological composite material composed of alternating NbC-Fe composite layers and T10 steel layers, with each component layer having a thickness of 1 mm. Compared to homogeneous composite materials, the steel-based morphological composite material achieves a better strength-toughness balance. In addition, other related studies have reported a bicontinuous ZTA / 40Cr composite material. First, a polylactide mold with a three-dimensional continuous porous structure was prepared using a die extrusion method. Then, a mixture of ZTA particles and water glass was injected into the mold, and the polylactide was removed by high-temperature sintering to obtain a regularly shaped porous ceramic skeleton preform. Finally, a bicontinuous ZTA / 40Cr composite material with a cylindrical structure was prepared using extrusion casting technology. Compared with the homogeneous ZTA / 40Cr composite material, the compressive strength and strain of the bicontinuous ZTA / 40Cr composite material were increased by 47% and 58%, respectively. Based on the above-mentioned techniques, it can be seen that shaped metal matrix composites achieve a synergistic improvement in strength and toughness through the rational distribution and coordinated coupling of the reinforcing phase and the matrix in space. However, for the aforementioned shaped metal composite materials, related studies have shown that under external loads, cracks preferentially initiate and propagate in the reinforcing phase-rich region. Meanwhile, due to the poor deformation coordination between the enriched region of the reinforcing phase and the plastic region of the matrix, strain localization is very likely to occur at the interface between the two, causing stress concentration and plastic instability. This makes the reinforcing phase and its interface with the matrix become crack sources, which is not conducive to the pinning and storage of dislocations, thereby weakening the strain hardening ability of the material.

[0004] In conclusion, designing and fabricating a high-strength and high-toughness steel-based composite material is a problem that urgently needs to be solved in the field of materials research. Summary of the Invention

[0005] In view of this, the present invention provides a steel-based composite material and a method for preparing the same, the main purpose of which is to improve the strength and toughness of the steel-based composite material.

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

[0007] On one hand, embodiments of the present invention provide a steel-based composite material, wherein the steel-based composite material comprises a continuous steel matrix phase and multiple reinforcing bundles; wherein the multiple reinforcing bundles are distributed in the continuous steel matrix phase; wherein,

[0008] Each of the reinforcements is a core-shell structure reinforcement with Nb as the core and an NbC / Fe gradient multilayer structure as the shell; wherein, the NbC / Fe gradient multilayer structure includes multiple NbC layers and multiple α-Fe layers, and the NbC layers and α-Fe layers are arranged alternately.

[0009] The superposition of the ...

[0010] Preferably, in the direction from the reinforcement to the steel matrix phase, the NbC content in the gradient heterogeneous interface exhibits a gradually decreasing gradient change, while the α-Fe phase content exhibits a gradually increasing gradient change.

[0011] Preferably, in the direction from the inside of the shell to the outside of the shell: the thickness of the NbC layer in the NbC / Fe gradient multilayer structure exhibits a gradually decreasing gradient change, the thickness of the α-Fe layer exhibits a gradually increasing gradient change; the size of NbC exhibits a gradually decreasing gradient change, the volume fraction of NbC exhibits a gradually decreasing gradient change, and the volume fraction of the α-Fe phase exhibits a gradually increasing gradient change.

[0012] Preferably, the diameter of the core-shell structure reinforcement is 0.4-1.5 mm.

[0013] Preferably, in each of the reinforcing phases, the metallic Nb is fibrous with a diameter of 0.2-1.0 mm.

[0014] Preferably, the microstructure of the continuous steel matrix phase is tempered martensite and retained austenite.

[0015] Preferably, the chemical composition of the steel-based composite material, by volume fraction, includes: 2-8% Nb fiber, 4-15% NbC particles, and 77-94% matrix; wherein the matrix is ​​a steel matrix or an iron matrix.

[0016] Preferably, the preparation method of the steel-based composite material includes the following steps:

[0017] The preparation steps for the green body are as follows: a deposition layer is prepared on a powder bed to obtain a first deposition layer; metal Nb fibers are laid on the first deposition layer to obtain a metal Nb fiber layer; then, a deposition layer is prepared on the metal Nb fiber layer and the deposition layer to obtain a second deposition layer; the steps of laying the metal Nb fiber layer and preparing the deposition layer on the metal Nb fiber layer and the deposition layer are repeated 0 times or at least once to obtain the green body; wherein, each deposition layer includes at least one matrix powder layer and a binder coated on each matrix powder layer; wherein, the matrix powder in the matrix powder layer includes a first powder and a second powder; wherein, the first powder is high-carbon steel powder and / or cast iron powder; the second powder is a metal powder, preferably one or more of Ti powder, Ta powder, and Cr powder.

[0018] Sintering process: The green body is first degreased and sintered to remove binder residues; then, the green body after degreased and sintered treatment is subjected to in-situ solid-phase diffusion sintering to form an NbC / Fe gradient multilayer structure in situ around the metal Nb fibers by utilizing the carbon concentration gradient diffusion and the molten mass transfer of iron, thus obtaining the composite material after in-situ solid-phase diffusion sintering.

[0019] Heat treatment: The composite material after in-situ solid-phase diffusion sintering is subjected to heat treatment to obtain a steel-based composite material.

[0020] Preferably, before the step of preparing the green body, a step of drying the matrix powder is further included, preferably, the drying temperature is 70-180°C, and the drying time is 2-6 hours; and / or

[0021] The diameter of the Nb metal fibers is 0.4-1.5 mm; and / or

[0022] The particle size of the first powder is 15-55 μm; and / or

[0023] The particle size of the second powder is 0.3-2 μm; and / or

[0024] The high-carbon steel powder has a carbon content of 0.6-1.7 wt%; and / or

[0025] The cast iron powder has a carbon content of 2.1-3.5 wt%; and / or

[0026] The adhesive comprises glycerin and water; wherein the volume ratio of glycerin to water is 1:2 to 1:5; and / or

[0027] In the matrix powder, the second powder accounts for 1-10% of the mass; and / or

[0028] The preparation steps of the matrix powder include: mixing the first powder and the second powder in a mixer; preferably, the speed of the mixer is 30-50 r / min and the mixing time is 6-10 h.

[0029] Preferably, in the step of preparing the blank:

[0030] Each step of preparing the deposited layer includes: laying a substrate powder to obtain a substrate powder layer; then applying an adhesive to the substrate powder layer; and then repeating the steps of laying the substrate powder and applying the adhesive 0 times or at least once until the thickness of the deposited layer reaches the desired thickness; preferably, the substrate powder is laid using a powder spreading roller; more preferably, the rotation speed of the powder spreading roller is 1-2 rad / s and the translational speed of the roller is 15-30 mm / s; preferably, the adhesive is applied to the substrate powder layer using an inkjet printhead.

[0031] Preferably, in the step of preparing the blank:

[0032] In each prepared deposition layer: the thickness of each of the matrix powder layers is 100-150 μm; and / or

[0033] The thickness of the first deposition layer is 1-3 mm; and / or

[0034] The thickness of the second deposition layer is 1-3 mm; and / or

[0035] In each of the aforementioned metal Nb fiber layers, the spacing between the metal Nb fibers is 1-3 mm.

[0036] Preferably, in the sintering process step:

[0037] The preform is heated from room temperature to 350-400℃ and held for 60-150 minutes for debinding and sintering treatment; then the preform after debinding and sintering treatment is heated from 350-400℃ to 1100-1165℃ and held for 2-12 hours for in-situ solid-phase diffusion sintering treatment; after cooling, the composite material after in-situ solid-phase diffusion sintering treatment is obtained.

[0038] Preferably, during the in-situ solid-phase diffusion sintering process, an axial pressure of 25-30 MPa is applied to the billet.

[0039] Preferably, the heating rate of the billet from room temperature to 350-400°C is 3-6°C / min;

[0040] Preferably, the heating rate of the degreased and sintered green body from 350-400℃ to 1100-1165℃ is 30-50℃ / min.

[0041] Preferably, the heat treatment step includes:

[0042] Quenching treatment: The composite material after in-situ solid-phase diffusion sintering treatment is heated from room temperature to 800-900℃, held at that temperature for 20-40 minutes, and then quenched in water to room temperature to obtain the quenched composite material.

[0043] Tempering treatment: The quenched composite material is heated to 150-250℃, held for 2-4 hours, and then cooled to obtain a steel-based composite material.

[0044] Preferably, in the quenching process, the heating rate is 8-15℃ / min;

[0045] Preferably, in the tempering process, the heating rate is 8-15°C / min.

[0046] Compared with the prior art, the steel-based composite material and its preparation method of the present invention have at least the following beneficial effects:

[0047] On one hand, embodiments of the present invention provide a steel-based composite material, wherein the steel-based composite material includes a continuous steel matrix phase and multiple reinforcements; wherein the multiple reinforcements are distributed in the continuous steel matrix phase; wherein each reinforcement is a core-shell structure reinforcement with Nb as the core and an NbC / Fe gradient multilayer structure as the shell; wherein the NbC / Fe gradient multilayer structure includes multiple NbC layers and multiple α-Fe layers, and the NbC layers and α-Fe layers are arranged alternately. Here, the following explanation is given regarding the above-mentioned microstructure of the steel-based composite material: (1) The bundled metal Nb core with good plasticity and the steel matrix can simultaneously play the roles of delaying crack initiation, passivating cracks and reducing crack propagation rate, thereby improving the damage tolerance of the composite material; (2) The NbC / Fe gradient multilayer structure, due to the spacing between the NbC layer and the α-Fe layer, under the combined effect of geometric constraints and crack bridging and deflection, reduces the crack sensitivity of the reinforcing phase enrichment zone and achieves toughening; (3) A gradient heterogeneous interface structure is presented between the reinforcing body and the continuous steel matrix phase, in which carbide particles with NbC as the core and solid solution carbide (Nb,M)C as the shell are distributed; wherein, M is one or more elements among Ti, Ta and Cr. Here, by introducing Ti, Ta, and Cr elements to form a solid solution carbide (Nb,M)C, the interface achieves a lower interfacial energy, dissipating residual interfacial stress and significantly improving the heterogeneous deformation-induced hardening ability and crack passivation ability, thereby greatly enhancing the strength-toughness balance of the composite material. In summary, the steel-based composite material proposed in this embodiment of the invention can improve the strength and toughness of steel-based composite materials.

[0048] On the other hand, the method for preparing a steel-based composite material provided in this invention starts by optimizing the spatial distribution of the reinforcing phase and controlling the interface structure. Based on the principle of unsteady diffusion and the theory of strain gradient plasticity, it uses spray forming (i.e., the preform preparation step) + in-situ hot pressing sintering to prepare a gradient multilayer core-shell structure reinforced steel-based composite material with a gradient heterogeneous interface structure. On one hand, this invention utilizes spray forming (the preform preparation step) to directionally design the matrix composition and the distribution of niobium fibers, thereby achieving synergistic control of the multilayer core-shell structure reinforcement and the matrix microstructure. On the other hand, this invention, by controlling the in-situ reaction temperature, reaction time, and heat treatment method, can achieve control over the melting mass transfer of iron and the nucleation, growth, and coarsening processes of NbC, thereby optimizing the shell microstructure and the macro / micro interface structure. Furthermore, the preparation process of the steel-based composite material of this invention is simple, low-cost, and easily scalable for industrial production.

[0049] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the structure of a steel-based composite material provided in an embodiment of the present invention;

[0051] Figure 2 This is a schematic diagram of the surface morphology of a core-shell structure reinforcement provided in an embodiment of the present invention;

[0052] Figure 3 This is a cross-sectional schematic diagram of a core-shell structure reinforcement provided in an embodiment of the present invention;

[0053] Figure 4 This is a microstructure diagram of a steel-based composite material prepared according to an embodiment of the present invention;

[0054] Figure 5 This is a surface microstructure diagram of the core-shell structure reinforcement in the steel-based composite material prepared according to an embodiment of the present invention;

[0055] Figure 6 These are microstructure diagrams of the NbC / Fe gradient multilayer structure and gradient heterostructure interface in steel-based composite materials prepared according to embodiments of the present invention.

[0056] Figure 7 This is a microstructure of the matrix of a steel-based composite material prepared according to an embodiment of the present invention;

[0057] Figure 8This is the indentation morphology of the NbC / Fe gradient multilayer structure region in a steel-based composite material prepared according to an embodiment of the present invention.

[0058] Figure 9 This is a microstructure diagram of the composite material prepared in Comparative Example 1. Detailed Implementation

[0059] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0060] On the one hand, embodiments of the present invention provide a steel-based composite material, such as... Figure 1 , Figure 2 and Figure 3 As shown, the steel-based composite material of this embodiment includes a continuous steel matrix phase 2 and multiple reinforcement bundles 1; wherein, the multiple reinforcement bundles 1 are distributed in the continuous steel matrix phase 2; wherein, each reinforcement bundle 1 is a core-shell structure reinforcement with Nb fiber 4 as the core and NbC / Fe gradient multilayer structure 5 as the shell. The NbC / Fe gradient multilayer structure 5 includes multiple NbC layers 6 and multiple α-Fe layers 7, and the NbC layers 6 and α-Fe layers 7 are arranged alternately. A gradient heterogeneous interface 3 exists between the reinforcement bundles 1 and the continuous steel matrix phase 2. The NbC / Fe gradient multilayer structure 5 exhibits gradient variations in layer thickness, NbC size, and distribution. The diameter of the core-shell structure reinforcement is 0.4-1.5 mm. The structure includes a gradient heterogeneous interface between the reinforcing body and the continuous steel matrix phase. This interface contains carbide particles with NbC cores and solid-solution carbides (Nb,M)C shells. M is one or more elements selected from Ti, Ta, and Cr. The carbide particles at the gradient heterogeneous interface are dispersedly distributed.

[0061] Preferably, the microstructure of the continuous steel matrix phase 1 is tempered martensite and retained austenite.

[0062] Preferably, the chemical composition of the steel-based composite material, by volume fraction, includes: 2-8% Nb fibers, 4-15% NbC particles, and 77-94% matrix; wherein the matrix is ​​a steel matrix or an iron matrix.

[0063] On the other hand, embodiments of the present invention provide a method for preparing steel-based composite materials, which mainly includes the following steps:

[0064] Raw material preparation steps: Prepare niobium fibers (Nb, diameter D 0.4-1.5 mm), matrix powder, and binder. The matrix powder includes a first powder (high-carbon steel powder and / or cast iron powder) and a second powder (metal powder); wherein the high-carbon steel powder has a carbon content of 0.6-1.7 wt% and a particle size of 15-55 μm; the cast iron powder has a carbon content of 2.1-3.5 wt% and a particle size of 15-55 μm. The metal powder is one or more of Ti powder, Ta powder, and Cr powder. The binder is composed of glycerol and water (e.g., distilled water) in a volume ratio of 1:2 to 1:5. Furthermore, the mass fraction of the second powder in the matrix powder is 1-10%. The first and second powders are mixed in a V-type mixer; wherein the mixer speed is 30-50 r / min, and the mixing time is 6-10 h.

[0065] Drying process: To prevent the substrate powder from absorbing moisture and generating interaction forces that could lead to powder agglomeration and affect subsequent printing quality, the substrate powder is dried at 70-130℃ for 2-6 hours. Preferably, the drying process is carried out in a vacuum drying oven.

[0066] Inkjet setup procedure: Install the printhead on the mounting bracket and connect the adhesive supply line, ensuring a tight, leak-free connection. Open the device control software Action 3DSYS, click the "Pneumatic" function, and allow the adhesive to sequentially fill the ink cartridge, supply line, and printhead, repeating this process several times until no more air bubbles emerge from the bottom of the printhead, ensuring a continuous ink supply during printing.

[0067] Preparation of the preform (spraying compounding / spraying forming step): A deposition layer is prepared on a powder bed to obtain a first deposition layer; metal Nb fibers are laid on the first deposition layer to obtain a metal Nb fiber layer; then, a deposition layer is prepared on the metal Nb fiber layer and the deposition layer to obtain a second deposition layer; the steps of laying the metal Nb fiber layer and preparing the deposition layer on the metal Nb fiber layer and the deposition layer are repeated 0 times or at least once to obtain a preform; wherein, each deposition layer includes at least one matrix powder layer and a binder coated on each matrix powder layer; wherein, the matrix powder includes a first powder and a second powder; wherein, the first powder is high carbon steel powder and / or cast iron powder; the second powder is a metal powder, preferably one or more of Ti powder, Ta powder, and Cr powder.

[0068] Preferably, in this step: each step of preparing the deposited layer includes: laying substrate powder to obtain a substrate powder layer; then applying an adhesive to the substrate powder layer; then repeating the steps of laying substrate powder and applying adhesive 0 times or at least once until the thickness of the deposited layer reaches the desired thickness; preferably, the substrate powder is laid using a powder spreading roller; preferably, the rotation speed of the powder spreading roller is 1-2 rad / s, and the translational speed of the roller is 15-30 mm / s; preferably, the adhesive is applied to the substrate powder layer using an inkjet printhead.

[0069] Preferably, in this step: in each deposited layer: the thickness of each substrate powder layer is 100-150 μm; the thickness of the first deposited layer is 1 mm; the thickness of the second deposited layer is 1-3 mm; and in each metal Nb fiber layer, the spacing between the metal Nb fibers is 1-3 mm.

[0070] Specifically, the preform preparation steps are as follows: A layer of matrix powder with a thickness of 100-150 μm is evenly spread from the feed platform to the application platform (powder bed) using a powder spreading roller. The rotation speed of the spreading roller is 1-2 rad / s, and the translational speed of the roller is 15-30 mm / s. Subsequently, the inkjet printhead precisely applies the binder to the designated area. Then, the binder penetrates and forms capillary-mediated bridges between the powder particles. This process is repeated, with each subsequent layer laid on top of the previously deposited layer, and the binder is sprayed again.

[0071] When the thickness of the first deposited layer reaches 1-3 mm, niobium fibers are laid parallel to each other on the surface of the first deposited layer, with a spacing of 1-3 mm between the fibers. Then, a powder spreader is used to reciprocately spray matrix powder and binder onto the surface, with a layer thickness of 1-3 mm. This step is repeated until the entire 3D material is formed. After printing, the entire powder bed is carefully removed, and the preform is placed in a graphite mold and sintered in a rapid hot press furnace.

[0072] Sintering process: The green body is first degreased and sintered to remove binder residues; then, the degreased and sintered green body is subjected to in-situ solid-phase diffusion sintering to form an NbC / Fe gradient multilayer structure in situ around the metal Nb fibers by utilizing the carbon concentration gradient diffusion and the molten mass transfer of iron. The metal element M (M is one or more of Ti, Ta, and Cr) is diffused and segregated at the interface between the reinforcement and the continuous steel matrix phase to form a low interfacial energy solid solution carbide (Nb,M)C, thus obtaining the composite material after in-situ solid-phase diffusion sintering.

[0073] Specifically, the first stage of degreasing and sintering involves heating from room temperature to 350-400℃ (heating rate of 3-6℃ / min) and holding for 60-150 minutes to effectively remove adhesive residues.

[0074] The second stage involves in-situ solid-state diffusion sintering: the temperature is increased from 350-400℃ to 1100-1165℃ (heating rate of 30-50℃ / min), and the holding time is 2-12 hours. An axial pressure of 25-30 MPa is applied during sintering. During this period, a NbC / Fe gradient multilayer structure (Nb+C→NbC) is formed in situ around the Nb fibers using carbon concentration gradient diffusion and iron melt mass transfer. Simultaneously, the metallic element M (M being one or more of Ti, Ta, and Cr) diffuses and agglomerates at the interface between the reinforcement and the continuous steel matrix phase, forming low-interfacial-energy solid-solid carbides (Nb,M)C, thus controlling the micro-interface. After the holding time is completed, the mixture is cooled to room temperature by furnace cooling.

[0075] Heat treatment steps: The composite material after in-situ solid-state diffusion sintering is placed in an inert atmosphere quenching furnace for quenching. Specifically, the temperature is raised from room temperature to 800-900℃ (heating rate of 8-15℃ / min), held for 20-40 min, and then immediately water-quenched to room temperature. Tempering is then performed (heating rate of 8-15℃ / min) at a low temperature of 150-250℃ for 2-4 h. Finally, it is cooled to room temperature in the furnace to obtain a high-strength, high-toughness gradient multilayer core-shell structure reinforced steel matrix composite material. The matrix microstructure after heat treatment is tempered martensite + retained austenite (wherein, the microstructure before heat treatment is pearlite and ferrite).

[0076] It should be noted that heat treatment improves the matrix structure, promoting a good performance match between the matrix and the reinforcement. Without heat treatment (quenching and tempering), the matrix is ​​too soft to support the strength of the reinforcement. Quenching increases hardness but also increases internal stress, while tempering removes this internal stress.

[0077] In summary, the design of the core-shell structure reinforcement with Nb as the core and NbC / Fe gradient multilayer structure as the shell, and the preparation of its composite material, proposed in this invention, provide a new solution to overcome the problem of the inversion of strength and toughness in steel-based composite materials. This provides theoretical and technical support for the development of high-strength and high-toughness steel-based composite materials and products that meet the important application needs of related fields in my country.

[0078] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0079] Example 1

[0080] This embodiment prepares a steel-based composite material, mainly including the following steps:

[0081] Raw material preparation steps: The main raw materials are niobium fiber (Nb, diameter D 0.4 mm), cast iron powder (carbon content 3.2 wt%, particle size 15-55 μm), and metal powder (Ti powder, particle size 0.3-0.5 μm). The binder consists of glycerol and distilled water in a volume ratio of 1:2. The cast iron powder and metal powder are mixed to obtain the matrix powder. The metal powder accounts for 3% of the mass of the matrix powder.

[0082] Drying process: To prevent the powder from absorbing moisture and generating interaction forces that could lead to powder agglomeration and affect subsequent printing quality, the substrate powder needs to be dried in a vacuum drying oven. The drying temperature is 70℃, and the drying time is 6 hours.

[0083] Inkjet setup procedure: Install the printhead on the mounting bracket and connect the adhesive supply line, ensuring a tight, leak-free connection. Open the device control software Action 3DSYS, click the "Pneumatic" function, and allow the adhesive to sequentially fill the ink cartridge, supply line, and printhead, repeating this process several times until no more air bubbles emerge from the bottom of the printhead, ensuring a continuous ink supply during printing.

[0084] Preform preparation step (jet lamination / jet forming step): A 100μm thick layer of matrix powder is evenly spread from the feed platform to the application platform (powder bed) using a powder spreading roller. The spreading roller rotates at a speed of 1.5 rad / s, and the roller translation speed is 20 mm / s. Subsequently, the inkjet printhead precisely applies the binder to the designated area. Then, the binder penetrates and forms capillary-mediated bridges between the powder particles. The above powder spreading and binder application process is repeated until the thickness of the deposited layer reaches 1 mm, defined as the first deposited layer.

[0085] Niobium fibers are laid parallel to each other on the surface of the first deposition layer, with a spacing of 1 mm between the Nb fibers. Then, a powder-spreading roller is used to sequentially spray matrix powder and apply binder at least once until a thickness of 2 mm is achieved. This process (i.e., repeatedly laying niobium fibers, spreading matrix powder, and applying binder) is repeated until the entire 3D material is formed (20 layers of niobium fibers are laid). After printing, the entire powder bed is carefully removed, and the preform is placed in a graphite mold and sintered in a rapid hot press furnace.

[0086] Sintering process steps: The sintering process steps include the following two stages:

[0087] The first stage of debinding and sintering involves heating the green body from room temperature to 400°C and holding it at that temperature for 120 minutes to effectively remove adhesive residues; the heating rate is 5°C / min.

[0088] The second stage involves in-situ solid-state diffusion sintering: the billet is heated from 400℃ to 1100℃ at a rate of 50℃ / min, and held at 1000℃ for 4 hours, with an axial pressure of 30MPa applied during sintering. During this period, a NbC / Fe gradient multilayer structure (Nb+C→NbC) is formed in situ around the Nb fibers using carbon concentration gradient diffusion and iron melt mass transfer. Simultaneously, metallic element M diffuses and agglomerates at the interface between the reinforcement and the continuous steel matrix phase, forming low-interfacial-energy solid-solid carbides (Nb,M)C, thus controlling the micro-interface. After the holding period, the material is cooled to room temperature by furnace cooling, yielding the composite material after in-situ solid-state diffusion sintering.

[0089] Heat treatment steps: The composite material after in-situ solid-state diffusion sintering is placed in an inert atmosphere quenching furnace for quenching treatment. Specifically, the temperature is raised from room temperature to 800℃ (heating rate of 10℃ / min), held for 0.5h, and then immediately water-quenched to room temperature. Subsequently, tempering treatment is performed (heating rate of 10℃ / min), with a low-temperature tempering temperature of 225℃ and a holding time of 2h. Finally, it is cooled to room temperature in the furnace to obtain the steel-based composite material. After heat treatment, the matrix structure of the steel-based composite material is tempered martensite + retained austenite.

[0090] Example 2

[0091] This embodiment prepares a steel-based composite material, mainly including the following steps:

[0092] Raw material preparation steps: Prepare niobium fiber (Nb, diameter D 0.6 mm), cast iron powder (2.5 wt% carbon content, particle size 15-55 μm), and metal powder (Ta powder, particle size 0.3-0.5 μm) as the main raw materials. The binder consists of glycerol and distilled water in a volume ratio of 1:3. Mix the cast iron powder and metal powder to obtain the matrix powder. The metal powder accounts for 10% of the mass of the matrix powder.

[0093] Drying process: To prevent the powder from absorbing moisture and generating interaction forces that could lead to powder agglomeration and affect subsequent printing quality, the substrate powder needs to be dried in a vacuum drying oven. The drying temperature is 100℃, and the drying time is 3 hours.

[0094] Inkjet setup procedure: Install the printhead on the mounting bracket and connect the adhesive supply line, ensuring a tight, leak-free connection. Open the device control software Action 3DSYS, click the "Pneumatic" function, and allow the adhesive to sequentially fill the ink cartridge, supply line, and printhead, repeating this process several times until no more air bubbles emerge from the bottom of the printhead, ensuring a continuous ink supply during printing.

[0095] Preform preparation step (jet lamination / jet forming step): A 125μm thick layer of matrix powder is evenly spread from the feed platform to the application platform (powder bed) using a powder spreading roller. The spreading roller rotates at a speed of 1.2 rad / s, and the roller translation speed is 20 mm / s. Subsequently, the inkjet printhead precisely applies the binder to the designated area. Then, the binder penetrates and forms capillary-mediated bridges between the powder particles. The above powder spreading and binder application process is repeated until the thickness of the deposited layer reaches 1 mm, defined as the first deposited layer.

[0096] Niobium fibers are laid parallel to each other on the surface of the first deposition layer, with a spacing of 2 mm between the Nb fibers. Then, a powder-spreading roller is used to sequentially spray matrix powder and apply binder at least once until a thickness of 3 mm is achieved. This process (i.e., repeatedly laying niobium fibers, spreading matrix powder, and applying binder) is repeated until the entire 3D material is formed (15 layers of niobium fibers are laid). After printing, the entire powder bed is carefully removed, and the preform is placed in a graphite mold and sintered in a rapid hot press furnace.

[0097] Sintering process steps: The sintering process steps include the following two stages:

[0098] The first stage of debinding and sintering involves heating the green body from room temperature to 350°C and holding it at that temperature for 150 minutes to effectively remove adhesive residues; the heating rate is 5°C / min.

[0099] The second stage involves in-situ solid-state diffusion sintering: the billet is heated from 350℃ to 1135℃ at a rate of 45℃ / min, and held at 1135℃ for 8 hours, with an axial pressure of 30MPa applied during sintering. During this period, a NbC / Fe gradient multilayer structure (Nb+C→NbC) is formed in situ around the Nb fibers using carbon concentration gradient diffusion and iron melt mass transfer. Simultaneously, metallic element M diffuses and agglomerates at the interface between the reinforcement and the continuous steel matrix phase, forming low-interfacial-energy solid-solid carbides (Nb,M)C, thus controlling the micro-interface. After the holding period, the material is cooled to room temperature by furnace cooling, yielding the composite material after in-situ solid-state diffusion sintering.

[0100] Heat treatment steps: The composite material after in-situ solid-state diffusion sintering is placed in an inert atmosphere quenching furnace for quenching treatment. Specifically, the temperature is raised from room temperature to 850℃ (heating rate of 15℃ / min), held for 0.5h, and then immediately water-quenched to room temperature. Subsequently, tempering treatment is performed (heating rate of 10℃ / min), with a low-temperature tempering temperature of 200℃ and a holding time of 3h. Finally, it is cooled to room temperature in the furnace to obtain the steel-based composite material. After heat treatment, the matrix structure of the steel-based composite material is tempered martensite + retained austenite.

[0101] Example 3

[0102] This embodiment prepares a steel-based composite material, mainly including the following steps:

[0103] Raw material preparation steps: The main raw materials are niobium fiber (Nb, diameter D 0.6 mm), cast iron powder (2.5 wt% carbon content, particle size 15-55 μm), and metal powder (Cr powder, particle size 0.3-0.5 μm). The binder consists of glycerol and distilled water in a volume ratio of 1:3. The cast iron powder and metal powder are mixed to obtain the matrix powder. The metal powder accounts for 5% of the mass of the matrix powder.

[0104] Drying process: To prevent the powder from absorbing moisture and generating interaction forces that could lead to powder agglomeration and affect subsequent printing quality, the substrate powder needs to be dried in a vacuum drying oven. The drying temperature is 130℃, and the drying time is 2 hours.

[0105] Inkjet setup procedure: Install the printhead on the mounting bracket and connect the adhesive supply line, ensuring a tight, leak-free connection. Open the device control software Action 3DSYS, click the "Pneumatic" function, and allow the adhesive to sequentially fill the ink cartridge, supply line, and printhead, repeating this process several times until no more air bubbles emerge from the bottom of the printhead, ensuring a continuous ink supply during printing.

[0106] Preform preparation step (jet lamination / jet forming step): A 100μm thick layer of matrix powder is evenly spread from the feed platform to the application platform (powder bed) using a powder spreading roller. The spreading roller rotates at a speed of 1.5 rad / s, and the roller translation speed is 30 mm / s. Subsequently, the inkjet printhead precisely applies the binder to the designated area. Then, the binder penetrates and forms capillary-mediated bridges between the powder particles. The above powder spreading and binder application process is repeated until the thickness of the deposited layer reaches 1 mm, defined as the first deposited layer.

[0107] Niobium fibers are laid parallel to each other on the surface of the first deposition layer, with a spacing of 2 mm between the Nb fibers. Then, a powder-spreading roller is used to sequentially spray matrix powder and apply binder at least once until a thickness of 3 mm is achieved. This process (i.e., repeatedly laying niobium fibers, spreading matrix powder, and applying binder) is repeated until the entire 3D material is formed (15 layers of niobium fibers are laid). After printing, the entire powder bed is carefully removed, and the preform is placed in a graphite mold and sintered in a rapid hot press furnace.

[0108] Sintering process steps: The sintering process steps include the following two stages:

[0109] The first stage of debinding and sintering involves heating the green body from room temperature to 400°C and holding it at that temperature for 100 minutes to effectively remove adhesive residues; the heating rate is 6°C / min.

[0110] The second stage involves in-situ solid-state diffusion sintering: the billet is heated from 400℃ to 1135℃ at a rate of 50℃ / min, and held at 1135℃ for 8 hours, with an axial pressure of 30MPa applied during sintering. During this period, a NbC / Fe gradient multilayer structure (Nb+C→NbC) is formed in situ around the Nb fibers using carbon concentration gradient diffusion and iron melt mass transfer. Simultaneously, metallic element M diffuses and agglomerates at the interface between the reinforcement and the continuous steel matrix phase, forming low-interfacial-energy solid-solid carbides (Nb,M)C, thus controlling the micro-interface. After the holding period, the material is cooled to room temperature by furnace cooling, yielding the composite material after in-situ solid-state diffusion sintering.

[0111] Heat treatment steps: The composite material after in-situ solid-state diffusion sintering is placed in an inert atmosphere quenching furnace for quenching treatment. Specifically, the temperature is raised from room temperature to 900℃ (heating rate of 12℃ / min), held for 0.5h, and then immediately water-quenched to room temperature. Subsequently, tempering treatment is performed (heating rate of 8℃ / min), with a low-temperature tempering temperature of 250℃ and a holding time of 2h. Finally, it is cooled to room temperature in the furnace to obtain the steel-based composite material. After heat treatment, the matrix structure of the steel-based composite material is tempered martensite + retained austenite.

[0112] Example 4

[0113] This embodiment prepares a steel-based composite material, mainly including the following steps:

[0114] Raw material preparation steps: The main raw materials are niobium fiber (Nb, diameter D = 1.0 mm), high-carbon steel powder (carbon content 1.0 wt%, particle size 15-55 μm), and metal powder (Ti powder, particle size 0.3-0.5 μm). The binder consists of glycerol and distilled water in a volume ratio of 1:5. The high-carbon steel powder and metal powder are mixed to obtain the matrix powder. The metal powder accounts for 3% of the mass of the matrix powder.

[0115] Drying process: To prevent the powder from absorbing moisture and generating interaction forces that could lead to powder agglomeration and affect subsequent printing quality, the substrate powder needs to be dried in a vacuum drying oven. The drying temperature is 80℃, and the drying time is 6 hours.

[0116] Inkjet setup procedure: Install the printhead on the mounting bracket and connect the adhesive supply line, ensuring a tight, leak-free connection. Open the device control software Action 3DSYS, click the "Pneumatic" function, and allow the adhesive to sequentially fill the ink cartridge, supply line, and printhead, repeating this process several times until no more air bubbles emerge from the bottom of the printhead, ensuring a continuous ink supply during printing.

[0117] Preform preparation step (jet lamination / jet forming step): A 150μm thick layer of matrix powder is evenly spread from the feed platform to the application platform (powder bed) using a powder spreading roller. The spreading roller rotates at a speed of 2 rad / s, and the roller translation speed is 30 mm / s. Subsequently, the inkjet printhead precisely applies the binder to the designated area. Then, the binder penetrates and forms capillary-mediated bridges between the powder particles. The above powder spreading and binder application process is repeated until the thickness of the deposited layer reaches 1 mm, defined as the first deposited layer.

[0118] Niobium fibers are laid parallel to each other on the surface of the first deposition layer, with a spacing of 1.5 mm between the fibers. Then, a powder-spreading roller is used to sequentially spray matrix powder and apply binder at least once until a thickness of 3 mm is achieved. This process (i.e., repeatedly laying niobium fibers, spreading matrix powder, and applying binder) is repeated until the entire 3D material is formed (10 layers of niobium fibers are laid). After printing, the entire powder bed is carefully removed, and the preform is placed in a graphite mold and sintered in a rapid hot press furnace.

[0119] Sintering process steps: The sintering process steps include the following two stages:

[0120] The first stage of debinding and sintering involves heating the green body from room temperature to 400°C and holding it at that temperature for 90 minutes to effectively remove adhesive residues; the heating rate is 6°C / min.

[0121] The second stage involves in-situ solid-state diffusion sintering: the billet is heated from 400℃ to 1150℃ at a rate of 45℃ / min, and held at 1150℃ for 6 hours, with an axial pressure of 30MPa applied during sintering. During this period, a NbC / Fe gradient multilayer structure (Nb+C→NbC) is formed in situ around the Nb fibers using carbon concentration gradient diffusion and iron melt mass transfer. Simultaneously, metallic element M diffuses and agglomerates at the interface between the reinforcement and the continuous steel matrix phase, forming low-interfacial-energy solid-solid carbides (Nb,M)C, thus controlling the micro-interface. After the holding period, the material is cooled to room temperature by furnace cooling, yielding the composite material after in-situ solid-state diffusion sintering.

[0122] Heat treatment steps: The composite material after in-situ solid-state diffusion sintering is placed in an inert atmosphere quenching furnace for quenching treatment. Specifically, the temperature is raised from room temperature to 850℃ (heating rate of 10℃ / min), held for 0.5h, and then immediately water-quenched to room temperature. Subsequently, tempering treatment is performed (heating rate of 10℃ / min), with a low-temperature tempering temperature of 200℃ and a holding time of 4h. Finally, it is cooled to room temperature in the furnace to obtain the steel-based composite material. After heat treatment, the matrix structure of the steel-based composite material is tempered martensite + retained austenite.

[0123] Example 5

[0124] This embodiment prepares a steel-based composite material, mainly including the following steps:

[0125] Raw material preparation steps: Prepare niobium fiber (Nb, diameter D 1.5 mm), high-carbon steel powder (carbon content 1.5 wt%, particle size 15-55 μm), and metal powder (Ti powder, particle size 0.3-0.5 μm) as the main raw materials. The binder consists of glycerol and distilled water in a volume ratio of 1:5. Mix the high-carbon steel powder and metal powder to obtain the matrix powder. The metal powder accounts for 3% of the mass of the matrix powder.

[0126] Drying process: To prevent the powder from absorbing moisture and generating interaction forces that could lead to powder agglomeration and affect subsequent printing quality, the substrate powder needs to be dried in a vacuum drying oven. The drying temperature is 100℃, and the drying time is 6 hours.

[0127] Inkjet setup procedure: Install the printhead on the mounting bracket and connect the adhesive supply line, ensuring a tight, leak-free connection. Open the device control software Action 3DSYS, click the "Pneumatic" function, and allow the adhesive to sequentially fill the ink cartridge, supply line, and printhead, repeating this process several times until no more air bubbles emerge from the bottom of the printhead, ensuring a continuous ink supply during printing.

[0128] Preform preparation steps: A 120μm thick layer of matrix powder is evenly spread from the feed platform to the application platform using a powder spreading roller. The roller rotates at 1.8 rad / s, and the translational speed is 25 mm / s. Subsequently, the inkjet printhead precisely applies the binder to the designated area. The binder then penetrates and forms capillary-mediated bridges between the powder particles. The powder spreading and binder application process is repeated until the thickness of the deposited layer reaches 1 mm, defined as the first deposited layer.

[0129] Niobium fibers are laid parallel to each other on the surface of the first deposition layer, with a spacing of 2 mm between the Nb fibers. Then, a powder spreader is used to sequentially spray matrix powder and apply binder at least once until a thickness of 3 mm is achieved. This process (i.e., repeatedly laying niobium fibers, spreading matrix powder, and applying binder) is repeated until the entire 3D material is formed (10 layers of niobium fibers are laid). After printing, the entire powder bed is carefully removed, and the preform is placed in a graphite mold and sintered in a rapid hot press furnace.

[0130] Sintering process steps: The sintering process steps include the following two stages:

[0131] The first stage of debinding and sintering involves heating the green body from room temperature to 400°C and holding it at that temperature for 100 minutes to effectively remove adhesive residues; the heating rate is 5°C / min.

[0132] The second stage involves in-situ solid-state diffusion sintering: the billet is heated from 400℃ to 1165℃ at a rate of 50℃ / min, and held at 1165℃ for 10 hours, with an axial pressure of 30MPa applied during sintering. During this period, a NbC / Fe gradient multilayer structure (Nb+C→NbC) is formed in situ around the Nb fibers using carbon concentration gradient diffusion and iron melt mass transfer. Simultaneously, the metal element M diffuses and agglomerates at the interface between the reinforcement and the continuous steel matrix phase, forming low-interfacial-energy solid-solid carbides (Nb,M)C, thus controlling the micro-interface. After the holding period, the material is cooled to room temperature by furnace cooling, yielding the composite material after in-situ solid-state diffusion sintering.

[0133] Heat treatment steps: The composite material after in-situ solid-state diffusion sintering is placed in an inert atmosphere quenching furnace for quenching treatment. Specifically, the temperature is raised from room temperature to 800℃ (heating rate of 15℃ / min), held for 0.5h, and then immediately water-quenched to room temperature. Subsequently, tempering treatment is performed (heating rate of 10℃ / min), with a low-temperature tempering temperature of 250℃ and a holding time of 2h. Finally, it is cooled to room temperature in the furnace to obtain the steel-based composite material. After heat treatment, the matrix structure of the steel-based composite material is tempered martensite + retained austenite.

[0134] Figure 4 This is a microstructure diagram of the steel-based composite material prepared in Example 2; Figure 5 This is a surface microstructure diagram of a core-shell structure reinforcement in the steel-based composite material prepared in Example 3. From... Figure 4 and Figure 5 It can be seen that the steel-based composite material prepared in the embodiments of the present invention includes a continuous steel matrix phase and multiple reinforcing bundles; wherein, the multiple reinforcing bundles are distributed in the continuous steel matrix phase; wherein, each reinforcing bundle is a core-shell structured reinforcing bundle with Nb as the core and NbC / Fe gradient multilayer structure as the shell. Furthermore, a gradient heterogeneous interface exists between the reinforcing bundles and the continuous steel matrix phase; carbide particles with NbC as the core and solid solution carbide (Nb,M)C as the shell are distributed in the gradient heterogeneous interface.

[0135] Figure 6 This is a microstructure diagram of the NbC / Fe gradient multilayer structure and gradient heterostructure interface in the steel-based composite material prepared in Example 5; from Figure 6 It can be seen that the NbC / Fe gradient multilayer structure includes multiple NbC layers and multiple α-Fe layers, with the NbC layers and α-Fe layers arranged alternately; there is a gradient heterogeneous interface between the reinforcement and the continuous steel matrix phase, and carbide particles with NbC as the core and solid solution carbide (Nb,M)C as the shell are distributed in the gradient heterogeneous interface.

[0136] Figure 7 This is a microstructure image of the matrix of a steel-based composite material prepared in Example 4; from Figure 7 It can be seen that, after heat treatment, the matrix structure of the steel-based composite material obtained in this embodiment is tempered martensite + retained austenite.

[0137] Figure 8 This is the indentation morphology of the NbC / Fe gradient multilayer structure region in the steel-based composite material prepared in Example 4. Figure 8 It can be seen that the NbC / Fe gradient multilayer structure can effectively induce crack deflection and bridging, and the α-Fe layer can shield the crack tip and inhibit crack propagation, thereby improving the toughness of the composite material.

[0138] Comparative Example 1

[0139] Comparative Example 1 prepared a gradient multilayer core-shell structure reinforced steel matrix composite material, which differs from Example 1 in that:

[0140] The matrix powder in Comparative Example 1 contains only cast iron powder and no metal powder.

[0141] The other steps and parameters are the same as in Example 1.

[0142] It should be noted that: Example 1 and Comparative Example 1 are compared and analyzed as follows:

[0143] I. Differences in Interface Structure

[0144] 1. Lack of solid-solution carbide (Nb,M)C shell structure

[0145] In Example 1, Ti element diffuses and agglomerates at the interface to form a low-interface-energy solid solution carbide (Nb,Ti)C, which significantly reduces the interface energy, dissipates residual stress, and improves interfacial bonding strength and crack passivation capability. In Comparative Example 1, due to the lack of metallic elements such as Ti, such a solid solution carbide shell cannot be formed, and the interface is simply NbC in contact with the matrix, resulting in a higher interface energy, which easily becomes a stress concentration point and crack initiation source.

[0146] 2. Interface structure induces an increase in interfacial stress.

[0147] In Example 1, the gradient heterogeneous interface contains carbide particles with NbC cores and (Nb,M)C shells, achieving a gradient transition in composition and properties from the reinforcement to the matrix. In contrast, Comparative Example 1 lacks this gradient structure; the interface consists only of simple NbC particles, failing to achieve effective stress transfer and energy dissipation.

[0148] II. Performance Degradation

[0149] 1. Yield strength and maximum compressive strength are significantly reduced.

[0150] Due to weak interfacial bonding, lack of gradient transition, and solid solution strengthening effect, the yield strength and maximum compressive strength of Comparative Example 1 are lower than those of Example 1. Furthermore, in Comparative Example 1, the lack of a (Nb,M)C shell for crack passivation and deflection mechanisms leads to increased stress concentration and brittle fracture tendency at the interface, making the material more prone to early failure under stress.

[0151] 2. Insufficient wear resistance

[0152] In Example 1, the presence of a (Nb,M)C shell and gradient interface significantly improves wear resistance as particles are less likely to detach during wear. In contrast, in Comparative Example 1, the weak interfacial bonding makes particles prone to peeling off during wear, forming pit defects, which exacerbates abrasive wear and drastically reduces wear resistance.

[0153] Comparative Example 2

[0154] Comparative Example 2 prepared a gradient multilayer core-shell structure reinforced steel matrix composite material, which differs from Example 2 in that:

[0155] The process parameters for the second stage in-situ solid-state diffusion sintering of Comparative Example 2 are as follows: the temperature is raised from 350℃ to 1050℃ at a rate of 45℃ / min, the holding time is 8h, and the axial pressure applied during sintering is 30MPa.

[0156] The other steps and parameters are the same as in Example 2.

[0157] The core difference between Comparative Example 2 and Example 2 lies in the in-situ solid-state diffusion sintering temperature in the second stage. This parameter directly affects the formation process and final microstructure of the NbC / Fe gradient multilayer structure, leading to significant differences in material properties. The specific analysis is as follows:

[0158] I. Effect of sintering temperature on in-situ reaction and microstructure

[0159] 1. Insufficient formation of NbC phase and gradient multilayer structure

[0160] Thermodynamics and kinetics of the reaction are limited: The core reaction of in-situ solid-state diffusion sintering is Nb + C → NbC. This reaction requires sufficient temperature to drive carbon (C) to diffuse from cast iron powder to the surface of metallic niobium fiber (Nb) and form carbides.

[0161] The sintering temperature of Comparative Example 2 (1050℃) was lower than that of Example 2 (1135℃), resulting in a decrease in the atomic diffusion coefficient. According to the Arrhenius equation, the decrease in temperature significantly slowed down the diffusion rate of C atoms in the Fe matrix and the reactivity of the Nb surface. This reduced the nucleation and growth rate of the NbC phase, leading to a thinner, less continuous, and less multilayered NbC-Fe shell. Figure 9 As shown. Meanwhile, the excessively low sintering temperature resulted in insufficient mass transfer of iron during melting. In Example 2, the 1135℃ temperature was close to the eutectic temperature of the Fe-C alloy (approximately 1148℃), where part of the Fe matrix melted to form a liquid phase, accelerating the mass transfer of C and the in-situ growth of NbC. In contrast, at the 1050℃ temperature in Comparative Example 2, Fe was predominantly solid, with a very low proportion of liquid phase. The diffusion path of C was obstructed, and the NbC layer around the Nb fibers could not fully encapsulate the fibers, forming an incomplete core-shell structure.

[0162] 2. Reduced interfacial bonding strength

[0163] The weak interfacial bond between the unreacted Nb fibers and the Fe matrix is ​​mainly mechanical interlocking (e.g. Figure 9(As shown), instead of the metallurgical bond achieved through an NbC gradient transition layer as in Example 2. This weak interface is prone to becoming a crack initiation point under stress, leading to premature material failure.

[0164] II. The Influence of Microstructure Differences on Mechanical Properties

[0165] 1. Yield strength decreased significantly (2388MPa→1245MPa, a decrease of 48%).

[0166] In Example 2, during loading, the plastic Nb core absorbs plastic deformation energy through dislocation slip, while the NbC / Fe gradient multilayer structure hinders dislocation movement, achieving a synergistic effect of "work hardening + particle strengthening". Simultaneously, the interface gradient transition region induces heterogeneous deformation strengthening, with dislocations frequently multiplying and entangled at the NbC / Fe interface, thus increasing the yield strength.

[0167] In Comparative Example 1, the weak interfacial bonding makes it difficult for Nb fibers to effectively bear external loads, reducing load transfer efficiency. The load is mainly borne by the matrix, failing to effectively cooperate in load bearing. At the same time, the NbC-Fe shell contains dense NbC particle clusters, which are highly susceptible to brittle fracture, ultimately resulting in a significant reduction in yield strength.

[0168] 2. Fracture strain decreased (18.1% → 13.4%, a decrease of 26%).

[0169] In Example 2, the gradient core-shell structure dissipates energy through mechanisms such as crack passivation, crack bridging, and crack deflection. In contrast, in Comparative Example 1, due to interface defects and the non-gradient multilayer structure of the shell, the cracks propagate rapidly along the reinforcement / matrix interface and within the shell, resulting in a significant decrease in fracture strain.

[0170] III. Mechanism Analysis of the Difference in Abrasion Resistance (Relative Abrasion Resistance 216→153, a decrease of 29%)

[0171] In Example 2, the reinforcement and matrix are firmly bonded, and particles are not easily detached during wear; the wear mechanism is mainly slight abrasive wear. In contrast, in Comparative Example 1, the interface between the reinforcement and matrix is ​​weak, and particles are prone to peeling off during wear, forming pit defects and exacerbating abrasive wear.

[0172] Table 1 Mechanical properties of cast iron matrix and gradient multilayer core-shell structure reinforced steel matrix composites prepared in Examples 1-5

[0173]

[0174] Comparative Example 3

[0175] See patent application number 202310469909.0, entitled "Multidimensional and Multiscale NbC Reinforcement and Its Preparation and Application Method".

[0176] The multidimensional, multiscale NbC reinforced material prepared by this patent has the following shortcomings, see the patent for details. Figures 1-3 .

[0177] 1. Functional limitations of the reinforcement structure: In Comparative Example 3, the core of the reinforcement is a dense NbC ceramic region, and the outer layer is a network of nano / micro NbC particles. The overall structure is dominated by brittle ceramic phases, which easily leads to rapid crack propagation due to the concentration of brittle phases under high stress, resulting in limited toughness improvement. In the embodiments of this invention, the bundled metal core and the NbC / Fe gradient multilayer structure synergistically delay crack initiation, passivate cracks, and reduce crack propagation rate, which can significantly improve damage tolerance.

[0178] 2. The process path depends on the intermediate matrix, resulting in a complex flow: Comparative Example 3 requires first preparing niobium wire-gray cast iron preforms through lost foam casting, then removing the iron matrix through corrosion to finally obtain independent NbC reinforcements. This process is cumbersome and introduces an intermediate matrix (gray cast iron), which may contain residual impurities (such as incompletely corroded Fe / Nb), affecting subsequent bonding with the target matrix (such as aluminum). The embodiments of this invention employ spray molding + in-situ hot pressing sintering, directly using high-carbon steel powder / cast iron powder and metallic niobium fibers as raw materials. A core-shell structure is formed in one step through directional layup and in-situ reaction, avoiding interference from the intermediate matrix, resulting in a simpler process and more precise composition control.

[0179] 3. Narrow window for key parameters, limiting yield: In Comparative Example 3, the casting temperature of molten gray cast iron needs to be strictly controlled between 1680℃ and 1760℃. Excessive temperature can lead to an excessively thick NbC dense layer (>60μm) and a 45% increase in crack rate, while insufficient temperature results in incomplete casting and porosity defects (7%). The secondary holding temperature and time also require precise control, resulting in a low process tolerance. This invention, through spray molding, allows for flexible design of niobium fiber distribution (spacing 1-3mm) and matrix composition. The in-situ sintering temperature (1100℃-1165℃) and time (2-12h) control range is wider, and interlayer bonding can be precisely controlled through binders, resulting in better yield and structural uniformity.

[0180] 4. Indirectness and Limitations of Cross-Matrix Application: The prior art claims that the reinforcement can be used in "different metal matrices," but its preparation process relies on gray cast iron to provide a carbon source (NbC is generated through the reaction of niobium wire with C in cast iron), followed by corrosion to remove the iron matrix before composite with an aluminum matrix. This indirect method limits the NbC formation process of the reinforcement to the carbon content of the cast iron, and the corrosion step may damage the reinforcement structure, making it difficult to directly apply to other carbon-free metal matrices (such as pure aluminum, magnesium, etc.). This invention patent directly uses steel matrix (high carbon steel / cast iron) as the matrix, generating an Nb-NbC / Fe core-shell structure through carbon concentration gradient diffusion and in-situ reaction. The bonding between the matrix and the reinforcement relies on natural carbon sources and metallurgical reactions, eliminating intermediate steps and making it suitable for the direct preparation of steel matrix composites with greater specificity.

[0181] 5. Interfacial bonding relies on externally added elements, resulting in insufficient endogenous bonding: Comparative studies show that in the preparation of aluminum-based composite materials, an additional 1-5% wt. Cr and Nb are required to improve the fluidity and wettability of the molten metal. While this reduces the crack rate by 94%, it increases the cost of composition control and relies on external elements to regulate the interface. This invention, however, utilizes an in-situ solid-state diffusion reaction (Nb fibers react with the matrix carbon to generate NbC). The interfacial bonding is based on an endogenous metallurgical reaction, requiring no additional alloying elements. The interfacial bonding strength originates from the chemical metallurgical bonding of the gradient structure, resulting in higher stability.

[0182] 6. The problem of strength-toughness inversion remains unresolved: While the prior art achieves improved strength and wear resistance through "multi-scale particle reinforcement," it is still essentially a particle-reinforced composite material. When the volume fraction of the reinforcement is high (e.g., 20 wt% in the example), micron-sized NbC particles (2-8 μm) may become obstacles to dislocation movement, limiting the matrix's deformation capacity and leading to decreased toughness. This invention, through a multi-layered core-shell structure and gradient heterogeneous interface, utilizes the plastic deformation of the metal core, crack bridging of the NbC layer, and strain gradient hardening of the matrix to achieve a synergistic improvement in strength and toughness, breaking through the bottleneck of the "strength-toughness inversion" in traditional particle reinforcement.

[0183] 7. Cost and Efficiency Disadvantages of Industrialized Preparation: The prior art uses polyethylene / polystyrene white molds, requiring steps such as applying refractory coatings, dry sand compaction, and negative pressure extraction. This necessitates high-end equipment (e.g., casting furnaces above 1700℃), and the corrosion process uses HCl and hydrofluoric acid, posing environmental and safety hazards and resulting in high production costs. This invention patent employs spray molding + hot-pressing sintering, using powder and fiber as raw materials. The process is highly automated, allowing for complex structural designs through 3D printing, making it suitable for large-scale production. It also avoids the use of toxic reagents, making it more environmentally friendly and efficient. Furthermore, the prior art requires multiple steps in preparing the reinforcement: casting → heat preservation → corrosion → cleaning → drying. Errors in any step (such as incomplete corrosion) will affect the final performance. In contrast, this invention patent reduces intermediate processing steps and improves production efficiency through in-situ reaction and one-time sintering.

[0184] Comparative Example 4

[0185] See patent application number 202110475399.9, entitled: A wear-resistant carbide composite material and its preparation method.

[0186] See the patent. Figure 1 The wear-resistant carbide composite material prepared by this patent has the following shortcomings:

[0187] 1. In Comparative Example 4, the reinforcing phase NbC particles are distributed in bundles, which leads to a sharp increase in local crack sensitivity and reduces the toughness of the composite material.

[0188] Unlike Comparative Example 4, the reinforcing structure in this invention exhibits a gradient multilayer core-shell structure. The Nb core and steel matrix macroscopically suppress crack initiation and deflection, while the NbC / Fe multilayer structure induces crack deflection and bridging. The synergistic coupling of the two improves the high crack sensitivity of the reinforcing phase enrichment region, thereby significantly improving the strength and toughness of the steel matrix composite material.

[0189] 2. Comparative Example 4 employs the lost foam casting process, which requires multiple steps including "mold making, wire insertion, coating application, pouring, graphite coating, and heat preservation." The array / random distribution of the inserted niobium wires relies on manual operation, resulting in poor controllability of the three-dimensional spatial distribution and making it difficult to achieve precise design of complex components. Furthermore, when the volume fraction of niobium wire is high, cold shuts are highly likely to occur during casting, making it difficult to prepare a high volume fraction of reinforcing phase. In addition, defects such as shrinkage cavities and porosity have already appeared during the casting process. Finally, the high-temperature smelting of molten steel not only causes environmental pollution but also poses certain safety risks.

[0190] Unlike Comparative Example 4, this invention employs spray molding technology with digital control over powder deposition and binder spraying, enabling not only localized and / or overall reinforcement but also controllable preparation of high-volume reinforcing phases. Furthermore, the preparation process is green and pollution-free, and intelligent spray molding reduces the need for manual labor.

[0191] 3. The heat treatment process in Comparative Example 4 is unreasonable. First, for steel materials, it is impossible to obtain martensite structure through heat treatment below 220℃. Based on the carbon content in the steel matrix and the TTT curve, for hypoeutectoid steel, the heat treatment temperature is generally 30-50℃ higher than the Ac3 line, while for eutectoid and hypereutectoid steel, the heat treatment temperature is generally 30-50℃ higher than the Ac1 line. Only when quenching is performed can martensite structure be obtained. Moreover, after quenching, a large internal stress is generated in the matrix, which can easily lead to material shrinkage. Therefore, tempering is required to relieve the internal stress.

[0192] Unlike Comparative Example 4, no tempering treatment was performed in this invention. Secondly, when the matrix structure is bainitic, the interface structure still cannot achieve a good match due to the significant difference in mechanical properties between it and the reinforcement. Therefore, based on the reinforcement structure design, this invention employs a quenching + low-temperature tempering process to improve the strength of the matrix material, thereby improving the interface match between the matrix and the reinforcement, maximizing the strengthening and toughening effect between the matrix and the reinforcement, and obtaining a high-strength, high-toughness steel-based composite material.

[0193] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A steel-based composite material, characterized in that, The steel-based composite material comprises a continuous steel matrix phase and multiple reinforcing bundles; wherein the multiple reinforcing bundles are distributed within the continuous steel matrix phase; wherein... Each of the reinforcements is a core-shell structure reinforcement with Nb as the core and an NbC / Fe gradient multilayer structure as the shell; wherein, the NbC / Fe gradient multilayer structure includes multiple NbC layers and multiple α-Fe layers, and the NbC layers and α-Fe layers are arranged alternately; in each of the reinforcements, the Nb is fibrous; The reinforced body and the continuous steel matrix phase have a gradient heterogeneous interface; the gradient heterogeneous interface contains carbide particles with NbC core and solid solution carbide (Nb, M)C shell; wherein M is one or more elements selected from Ti, Ta, and Cr. In the direction from the reinforcement to the steel matrix phase, the NbC content in the gradient heterogeneous interface exhibits a gradually decreasing gradient change, while the α-Fe phase content exhibits a gradually increasing gradient change. In the direction from the inside of the shell to the outside: the thickness of the NbC layer in the NbC / Fe gradient multilayer structure shows a gradually decreasing gradient change, the thickness of the α-Fe layer shows a gradually increasing gradient change; the size of NbC shows a gradually decreasing gradient change, the volume fraction of NbC shows a gradually decreasing gradient change, and the volume fraction of the α-Fe phase shows a gradually increasing gradient change. The chemical composition of the steel-based composite material, by volume fraction, includes: 2-8% Nb fiber, 4-15% NbC particles, and 77-94% matrix; wherein the matrix is ​​a steel matrix or an iron matrix.

2. The steel-based composite material according to claim 1, characterized in that, The diameter of the core-shell structure reinforcement is 0.4-1.5 mm.

3. The steel-based composite material according to claim 1, characterized in that, The diameter of the metal Nb fiber is 0.2-1.0 mm.

4. The steel-based composite material according to any one of claims 1-3, characterized in that, The microstructure of the continuous steel matrix phase consists of tempered martensite and retained austenite.

5. The method for preparing the steel-based composite material according to any one of claims 1-4, characterized in that, The preparation method of the steel-based composite material includes the following steps: The preparation steps for the green body are as follows: a deposition layer is prepared on a powder bed to obtain a first deposition layer; metal Nb fibers are laid on the first deposition layer to obtain a metal Nb fiber layer; then, a deposition layer is prepared on the metal Nb fiber layer and the deposition layer to obtain a second deposition layer; the steps of laying the metal Nb fiber layer and preparing the deposition layer on the metal Nb fiber layer and the deposition layer are repeated 0 times or at least once to obtain the green body; wherein, each deposition layer includes at least one matrix powder layer and a binder coated on each matrix powder layer; wherein, the matrix powder in the matrix powder layer includes a first powder and a second powder; wherein, the first powder is high-carbon steel powder and / or cast iron powder; the second powder is a metal powder, which is one or more of Ti powder, Ta powder, and Cr powder. Sintering process: The green body is first degreased and sintered to remove binder residues; then, the green body after degreased and sintered treatment is subjected to in-situ solid-phase diffusion sintering to form an NbC / Fe gradient multilayer structure in situ around the metal Nb fibers by utilizing the carbon concentration gradient diffusion and the molten mass transfer of iron, thus obtaining the composite material after in-situ solid-phase diffusion sintering. Heat treatment: The composite material after in-situ solid-phase diffusion sintering is subjected to heat treatment to obtain a steel-based composite material.

6. The method for preparing steel-based composite materials according to claim 5, characterized in that, Prior to the step of preparing the preform, the method further includes a step of drying the matrix powder; and / or The particle size of the first powder is 15-55 μm; and / or The particle size of the second powder is 0.3-2 μm; and / or The high-carbon steel powder has a carbon content of 0.6-1.7 wt%; and / or The cast iron powder has a carbon content of 2.1-3.5 wt%; and / or The adhesive comprises glycerin and water; wherein the volume ratio of glycerin to water is 1:2 to 1:5; and / or In the matrix powder, the second powder accounts for 1-10% by mass; and / or The preparation steps of the matrix powder include: mixing the first powder and the second powder in a mixer.

7. The method for preparing the steel-based composite material according to claim 5 or 6, characterized in that, In the step of drying the matrix powder, the drying temperature is 70-180℃ and the drying time is 2-6 hours.

8. The method for preparing steel-based composite materials according to claim 5 or 6, characterized in that, When mixing the first powder and the second powder in the mixer, the mixer speed is 30-50 r / min and the mixing time is 6-10 h.

9. The method for preparing the steel-based composite material according to claim 5 or 6, characterized in that, In the step of preparing the preform: Each step of preparing the deposited layer includes: laying a substrate powder to obtain a substrate powder layer; then applying a binder onto the substrate powder layer; and then repeating the steps of laying the substrate powder and applying the binder 0 times or at least once until the thickness of the deposited layer reaches the desired thickness.

10. The method for preparing the steel-based composite material according to claim 9, characterized in that, The base powder is laid using a powder spreading roller.

11. The method for preparing the steel-based composite material according to claim 10, characterized in that, The rotational speed of the powder spreading roller is 1-2 rad / s, and the translational speed of the roller is 15-30 mm / s.

12. The method for preparing steel-based composite materials according to claim 9, characterized in that, The adhesive is applied to the substrate powder layer using an inkjet printhead.

13. The method for preparing the steel-based composite material according to any one of claims 5, 6, and 10-12, characterized in that, In the step of preparing the preform: In each prepared deposition layer: the thickness of each of the matrix powder layers is 100-150 μm; and / or The thickness of the first deposition layer is 1-3 mm; and / or The thickness of the second deposition layer is 1-3 mm; and / or In each of the aforementioned metal Nb fiber layers, the spacing between the metal Nb fibers is 1-3 mm.

14. The method for preparing the steel-based composite material according to any one of claims 5, 6, and 10-12, characterized in that, In the sintering process step: The preform is heated from room temperature to 350-400℃ and held for 60-150 minutes for debinding and sintering treatment; then the preform after debinding and sintering treatment is heated from 350-400℃ to 1100-1165℃ and held for 2-12 hours for in-situ solid-phase diffusion sintering treatment; after cooling, the composite material after in-situ solid-phase diffusion sintering treatment is obtained.

15. The method for preparing the steel-based composite material according to claim 14, characterized in that, During the in-situ solid-phase diffusion sintering process, an axial pressure of 25-30 MPa is applied to the green body.

16. The method for preparing the steel-based composite material according to claim 14, characterized in that, The heating rate of the blank from room temperature to 350-400℃ is 3-6℃ / min.

17. The method for preparing steel-based composite materials according to claim 14, characterized in that, The heating rate of the degreased and sintered green body from 350-400℃ to 1100-1165℃ is 30-50℃ / min.

18. The method for preparing steel-based composite materials according to any one of claims 5, 6, 10-12, and 15-17, characterized in that, The heat treatment step includes: Quenching treatment: The composite material after in-situ solid-phase diffusion sintering treatment is heated from room temperature to 800-900℃, held at that temperature for 20-40 minutes, and then quenched in water to room temperature to obtain the quenched composite material. Tempering treatment: The quenched composite material is heated to 150-250℃, held for 2-4 hours, and then cooled to obtain a steel-based composite material.

19. The method for preparing steel-based composite materials according to claim 18, characterized in that, In the quenching process, the heating rate is 8-15℃ / min.

20. The method for preparing steel-based composite materials according to claim 18, characterized in that, In the tempering process, the heating rate is 8-15℃ / min.

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