A method for preparing a graphite fiber-max ceramic reinforced martensitic steel composite

Abstract

The application discloses a preparation method of graphite fiber-MAX ceramic reinforced martensitic steel composite material, and belongs to the technical field of high-temperature wear-resistant composite material preparation technology. The application comprises the following steps: (1) vacuum drying of martensitic steel raw material powder, and surface energy modification treatment of graphite fibers and MAX ceramic particles; (2) vacuum ball milling of the modified MAX ceramic particles and the dried martensitic steel raw material powder to obtain mixed powder I, and then mechanical grinding of the mixed powder I and the modified graphite fibers to obtain mixed powder II; (3) cold pressing of the mixed powder II to obtain a preform; and (4) hot pressing sintering of the preform to obtain a graphite fiber-MAX ceramic dual-phase reinforced martensitic steel composite material. The composite material prepared by the application has excellent high-temperature wear resistance and stability, and can be applied to the manufacture of key parts under relatively severe and complex working conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature wear-resistant composite material preparation and relates to a preparation method of graphite fiber-MAX ceramic reinforced martensitic steel composite material. BACKGROUND

[0002] With the continuous progress of science and technology and the continuous improvement of production level, the demand for high-performance materials in the modern industrial field is increasingly urgent, especially for key parts working in high-temperature wear conditions, which puts extremely strict requirements on the comprehensive performance of the materials. Martensitic steel, as a common structural material, has been widely used in many fields such as mechanical manufacturing, aerospace, automobile industry, etc. due to its high strength and good toughness. However, the performance of traditional martensitic steel will decrease to some extent in high-temperature environment, which is difficult to meet the use requirements in severe working conditions. For example, the strength and hardness of martensitic steel will decrease with the increase of temperature in high-temperature environment, resulting in poor wear resistance, and the corrosion resistance also has certain limitations, which limits the service life of the martensitic steel in some complex working conditions of high temperature and high wear, affecting the stable operation of related equipment. Therefore, it is of great significance to improve the strength, hardness, wear resistance, corrosion resistance and other comprehensive performance of martensitic steel in complex working conditions of high temperature and high wear.

[0003] It is a relatively effective way to add reinforcing phases to improve the comprehensive performance of martensitic steel in complex working conditions to meet the use requirements. The performance of the reinforcing phase itself and the uniformity of its dispersion in the matrix and the interface bonding performance between the reinforcing phase and the matrix directly affect the reinforcing effect of the reinforcing phase. If the performance of the reinforcing phase itself is poor, it will lead to low performance improvement of the martensitic steel, which still cannot meet the use requirements. If the uniformity of the reinforcing phase distribution is poor, it will lead to local differences in the performance of the composite material, affecting its overall use performance. Especially in the case of multi-phase reinforcement, different reinforcing phases are prone to agglomeration in the mixing process, which seriously affects the dispersion uniformity of the reinforcing phase in the matrix and further affects the performance improvement effect of the composite material. The more firmly the interface between the reinforcing phase and the matrix is bonded, the more likely it is to form a stable synergistic effect between the reinforcing phase and the matrix, which can jointly bear external force, thereby promoting the strengthening effect of the reinforcing phase. On the contrary, the worse the interface bonding between the reinforcing phase and the matrix is, the more likely it is to cause interface debonding and other problems during the stress process, resulting in the loss of the strengthening effect of the composite material and further causing the performance decline of the composite material.

[0004] Therefore, it is necessary to provide a preparation method of graphite fiber-MAX ceramic reinforced martensitic steel composite material to effectively improve the uniformity of the reinforcing phase distribution and the interface bonding of the multi-phase reinforced composite material, thereby improving the reinforcing effect of the reinforcing phase and obtaining a martensitic steel composite material with excellent comprehensive performance in complex working conditions. SUMMARY

[0005] In order to overcome the problems in the background art, the present application effectively improves the uniformity of the distribution of the reinforcing phase and the interface bonding in the multiphase reinforced composite material by adopting graphite fibers and MAX ceramic particles with excellent performance as the reinforcing phase for dual-phase reinforcement of martensitic steel, and combining modification, preforming, hot-pressing sintering and other processes, thereby improving the strengthening effect of the reinforcing phase on the composite material, and further improving the comprehensive performance of the martensitic steel.

[0006] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0007] The present application provides a preparation method of graphite fiber-MAX ceramic reinforced martensitic steel composite material, which comprises the following steps:

[0008] (1) Raw material pretreatment: vacuum drying the martensitic steel raw material powder, and performing surface energy modification treatment on the graphite fibers and the MAX ceramic particles to obtain the dried martensitic steel raw material powder, the modified graphite fibers and the modified MAX ceramic particles.

[0009] (2) Distribution of reinforcing body: mixing the modified MAX ceramic particles in the step (1) with the dried martensitic steel raw material powder to perform vacuum ball milling, to obtain a mixed powder I, and then mixing the mixed powder I with the modified graphite fibers in the step (1) to perform mechanical grinding, to obtain a mixed powder II. The vacuum ball milling makes the MAX ceramic particles uniformly distributed in the martensitic steel raw material powder, and the mechanical grinding makes the graphite fibers uniformly dispersed in the mixed powder I.

[0010] (3) Preparation of preform: cold-pressing the mixed powder II obtained in the step (2) to obtain a preform.

[0011] (4) Hot-pressing sintering: hot-pressing sintering the preform obtained in the step (3) to obtain a graphite fiber-MAX ceramic dual-phase reinforced martensitic steel composite material.

[0012] The cold-pressing preforming process is combined with the hot-pressing sintering technology, which effectively solves the problems related to the uniformity of the distribution of the reinforcing phase and the interface bonding.

[0013] Preferably, in the step (1), the composition of the martensitic steel includes, by mass fraction: Cr: 15-17%, Ni: 3-5%, C: 0.2-0.3%, Mo: 0.5-1.0%, and the balance is Fe. The particle size of the martensitic steel raw material powder is 5-12 μm, and the purity is ≥99.9%.

[0014] Preferably, the modification method of the graphite fibers in the step (1) comprises the following steps:

[0015] S1: adding graphite fiber into oxidant, oxidizing under heating condition, so that the surface of graphite fiber is fully oxidized to obtain oxidized graphite fiber. After the surface of graphite fiber is oxidized, a large number of oxygen-containing functional groups are generated.

[0016] S2: after the oxidized graphite fiber obtained in step S1 is washed to neutral, it is soaked in a KH-550 silane coupling agent aqueous solution, and after reaction under heating condition, the graphite fiber is washed and dried to obtain modified graphite fiber.

[0017] As preferred, in step S1, the oxidation temperature is 60℃, the oxidation time is 2-3h, and the oxidant is a mixed liquid of concentrated sulfuric acid and hydrogen peroxide, wherein the volume ratio of concentrated sulfuric acid to hydrogen peroxide is concentrated sulfuric acid: hydrogen peroxide = 3:1.

[0018] In step S2, the reaction temperature is 80℃, the reaction time is 3-4h, and in the KH-550 silane coupling agent aqueous solution, the mass percentage concentration of KH-550 silane coupling agent is 2%-3%.

[0019] As preferred, in step (1), the modification method of MAX ceramic particles specifically comprises the following steps:

[0020] Q1: heat treating MAX ceramic bulk under argon protective atmosphere, and after the MAX ceramic bulk is naturally cooled, crushing the MAX bulk into powder to obtain heat-treated MAX ceramic particles.

[0021] Q2: mixing and ball-milling the heat-treated MAX ceramic particles obtained in step Q1 with powder Ni under the wetting action of anhydrous ethanol, so that Ni coats the MAX ceramic particles, and then vacuum or inert atmosphere protective drying the Ni-coated MAX ceramic particles to obtain modified MAX ceramic particles.

[0022] As preferred, in step Q1, the heating rate of heat treatment is 1℃ / min, the heat treatment temperature is 1700℃, and the holding time is 5h.

[0023] In step Q2, the mass of Ni powder added is 15%-25% of the mass of MAX ceramic particles, the ball-to-material ratio of ball milling is 10-20:1, the ball milling balls use large balls with a diameter of 10mm and small balls with a diameter of 5mm mixed in a mass ratio of 1:1, the amount of anhydrous ethanol added is 1%-5% of the total mass of Ni powder and MAX ceramic particles, the ball milling speed is 300-400rpm, and the ball milling time is 4-8h.

[0024] After the MAX ceramic particles are modified, the crystal interlayer spacing of the MAX ceramic particles is increased by 10% to 15%, the surface of the MAX ceramic particles has an active layer with M-X bonds of 2 to 5 nm, the interface bonding force between the reinforcing phase and the martensitic steel matrix is enhanced, and the MAX ceramic particles have an irregular sheet layer overlapping shape, a specific surface area of about 5 to 8 m 2 / g, a surface roughness Ra of about 0.3 to 0.5 μm, and a unique concentration gradient from inside to outside, that is, the concentration of M elements gradually increases and the concentration of A elements gradually decreases, so that the MAX ceramic particles have excellent corrosion resistance and high-temperature stability.

[0025] The MAX ceramic is a hexagonal layered structure composed of metal elements (M), main group elements (A) and carbon / nitrogen elements (X), and has the characteristics of point thermal conductivity of metal and high strength, high temperature resistance and the like of ceramic. For example, Ti2AlC, V2AlC, Ti3SiC2, Ti2AlN, Ti3AlC2, Nb2AlC, Ti4SiC3, Cr2GeC and the like all belong to MAX ceramic, and the MAX ceramic used in the present application can be one kind of MAX ceramic or a mixture of multiple kinds of MAX ceramic in any proportion.

[0026] Preferably, in the step (2), the particle size of the modified MAX ceramic particles is 50 to 100 μm, the length of the modified graphite fiber is 2 to 5 mm, the diameter of the modified graphite fiber is 3 to 5 μm, the amount of the modified MAX ceramic particles is 6% to 10% of the mass of the martensitic steel raw material powder, the rotation speed of the vacuum ball mill is 380 to 420 rpm, the ball-to-material ratio is 10:1, and the ball milling time is 5 h, and the ball milling balls are large balls with a diameter of 10 mm and small balls with a diameter of 5 mm mixed in a mass ratio of 1:1.

[0027] The amount of the modified graphite fiber is 5% to 15% of the total mass of the mixed powder II, and anhydrous ethanol is used as a dispersant during the mechanical grinding, the amount of the anhydrous ethanol is 1% to 5% of the total mass of the mixed powder II, and the mechanical grinding time is 30 to 40 min.

[0028] Preferably, in the step (3), the cold pressing forming pressure is 70 to 100 MPa, and the pressure holding time is 30 to 40 min.

[0029] Preferably, in the step (4), the hot pressing sintering process is as follows: the preform is heated to 900 to 950 ℃ at a heating rate of 50 to 60 ℃ / min, and a pressure of 70 to 80 MPa is applied at the same time, then the preform is heated to 1030 to 1050 ℃ at a heating rate of 10 to 12 ℃ / min, and the pressure is maintained for 20 to 25 min.

[0030] The present application has the following advantages:

[0031] 1. The application solves the problem of poor wear resistance of traditional martensitic steel at high temperature by constructing a dual-phase reinforced system of graphite fibers and MAX ceramic and combining with advanced processes such as hot-pressing sintering, effectively prolonging the service life of the material under high-temperature wear conditions, especially suitable for manufacturing key components under high-temperature wear conditions.

[0032] 2. The application enhances the interfacial bonding force between the reinforcing phase and the martensitic steel matrix by surface modification treatment of graphite fibers and MAX ceramic particles, avoiding problems such as interfacial debonding during stress, ensuring that the reinforcing phase can form a synergistic effect with the matrix to bear external force together, thereby significantly improving the comprehensive performance of the composite material.

[0033] 3. The application uses a combination of vacuum ball milling and mechanical grinding to uniformly distribute MAX ceramic particles in the martensitic steel raw material powder, and then uniformly disperse graphite fibers in the mixed powder I, effectively solving the problem of easy aggregation and uneven distribution of the reinforcing phase, ensuring the stability and consistency of the performance of the composite material, and fully utilizing the advantages of the dual-phase reinforced system.

[0034] 4. The application uses graphite fibers and MAX ceramic particles as dual reinforcing phases, utilizes the high strength and high modulus of graphite fibers to provide good tensile and bending strength for the composite material, utilizes the unique crystal structure of MAX ceramic and good bonding with the matrix to disperse stress when the composite material is subjected to pressure and impact, improve the hardness and toughness of the composite material, and at the same time, utilize the toughness of graphite fibers to improve the toughness of the composite material, avoid the material cracking problem caused by the brittleness of MAX ceramic, so that the composite material has good strength, toughness and hardness at room temperature and high temperature, meeting the diversified demand for material performance under different working conditions.

[0035] 5. Graphene sheet structure is formed during the friction process of graphite fibers, and these sheets can slide on the friction surface to play a lubricating effect. The application utilizes the good lubricating performance of graphite fibers to reduce the friction coefficient during the friction process of the composite material, and the surface of MAX ceramic forms an oxide film under high temperature conditions and fills the gaps between graphite fibers, both of which synergistically construct a self-lubricating system of the composite material, significantly reducing the friction coefficient and improving the lubrication stability, reducing the wear of the composite material, improving the wear resistance of the composite material, thereby prolonging the service life of the composite material and reducing the wear and maintenance cost during equipment operation.

[0036] 6. The graphite fiber mainly occurs abrasive wear in a high-temperature environment, the high strength and high modulus characteristics of the graphite fiber can effectively resist shear force and impact force, reduce plastic deformation and micro-crack propagation of the material in the wear process, and the MAX ceramic mainly occurs oxidation wear, and a dense oxide film is formed on the surface of the MAX ceramic under high-temperature conditions, the oxide film can not only inhibit the further oxidation of the material, but also reduce the friction coefficient and the wear of the friction pair, so that the graphite fiber and the MAX ceramic in the composite material synergistically act, so that the material has good abrasive wear resistance and oxidation wear resistance under high-temperature wear working conditions, so that the composite material has excellent high-temperature wear resistance, and the composite material can maintain stable performance for a long time under high-temperature conditions, solves the problem that the performance of the traditional martensitic steel is sharply reduced under high temperature, and meets the requirement of material stability under high-temperature working conditions.

[0037] 7. The present application adopts the hot-pressing sintering technology and the cold-pressing preforming process, and through accurate control of the sintering temperature, the pressure and the holding time and other key parameters, the problems of the distribution of the reinforcing phase and the interface combination are effectively solved: in the hot-pressing sintering process, the application of the pressure promotes the close contact of the reinforcing phase and the matrix, and improves the interface bonding strength; the preforming process ensures the uniform distribution of the reinforcing phase in the preform and the shape stability, so that the controllability and stability of the preparation process are improved through the combined process, the quality problems caused by process fluctuation are reduced, the quality and performance of the composite material have good repeatability between different batches, reliable guarantee is provided for large-scale industrial production, the production cost is reduced, the production efficiency is improved, and the present application has remarkable innovation and practical application value.

[0038] 8. The present application provides a new idea and method for the research and development of high-performance composite materials by constructing the graphite fiber and MAX ceramic dual-phase reinforced martensitic steel composite material system and combining a series of innovative surface treatment and preparation processes, fills the gap of the technology in the field, and has high innovation value and broad development prospect. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The microstructure diagram of the modified MAX ceramic particle of the present application is shown in the figure;

[0040] Figure 2 The average Rockwell hardness comparison diagram of the composite material prepared by the embodiment and the comparative example of the present application is shown in the figure;

[0041] Figure 3 The schematic diagram of the composite material of the present application is shown in the figure.

[0042] Figure 4 The metallographic diagram of the composite material of the present application is shown in the figure. DETAILED DESCRIPTION

[0043] The application will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the application is not limited to the described content.

[0044] In the examples and comparative examples of the present application, the chemical reagents not specifically mentioned are commercially available analytical pure for experiments.

[0045] In the examples of the present application, the composition of the martensitic steel is shown in Table 1.

[0046] Table 1

[0047]

[0048] Example 1

[0049] (1) Raw material pretreatment: the martensitic steel raw material powder (all raw material powder particle sizes are 5 μm, purity≧99.9%) with the components in Table 1 was weighed and vacuum dried;

[0050] The graphite fibers with a length of 2 mm and a diameter of 3 μm were added to a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 3:1, soaked at 60℃ for 2 h, so that the surface of the graphite fibers was fully oxidized to generate a large number of oxygen-containing functional groups, then the graphite fibers were repeatedly washed with deionized water until neutral to remove the residual oxidizing agent and byproducts on the surface to prevent interference with the subsequent processing process; then the washed graphite fibers were soaked in a 2% KH-550 silane coupling agent aqueous solution and reacted at 80℃ for 3 h; finally, the graphite fibers modified by the silane coupling agent were taken out, washed with deionized water until neutral and dried at 100℃ to constant weight to obtain modified graphite fibers;

[0051] MAX ceramic selects Ti2AlC, heats the Ti2AlC block to 1700℃ at a heating rate of 1℃ / min in an argon protective atmosphere, keeps the temperature for 5 h, then breaks the Ti2AlC block into powder after natural cooling, the interlayer spacing of the Ti2AlC ceramic particle crystal is increased by 10%, the surface has a 2 nm M-X bond active layer, the powder is in irregular sheet layer overlapping shape, the specific surface area is 5 m 2 / g, the surface roughness Ra is 0.3 μm, the particle size is 50 μm, the purity is 99.9%, the Ti2AlC ceramic particles are mixed with powder Ni for ball milling (the mass of powder Ni is 15% of the mass of the ceramic particles, stainless steel balls are used as the ball milling medium, the ball-to-material ratio is 10:1, anhydrous ethanol is used as the wetting agent, the amount of anhydrous ethanol is 1% of the total mass of the powder Ni and the ceramic particles, the rotation speed of the ball mill is controlled at 300 rpm, and the ball milling time is 8 h), after ball milling, the powder is extracted from the wetting agent and dried in a vacuum atmosphere to obtain modified Ti2AlC ceramic particles.

[0052] (2) Distribution of reinforcement: The dry martensitic steel raw powder is mixed with modified Ti2AlC ceramic particles by vacuum ball milling (the mass of the modified Ti2AlC ceramic particles is 6% of the mass of the martensitic steel raw powder, stainless steel balls are used as the ball milling medium, the ball-to-powder ratio is 10:1, the ball milling speed is 380 rpm, and the ball milling time is 5 h), to obtain mixed powder I, which is then vacuum dried. Then, the modified graphite fibers are mixed with the mixed powder I by mechanical grinding in a glove box (the mass of the modified graphite fibers is 5% of the mass of the mixed powder I, and 1% of anhydrous ethanol is added as a dispersant during the mechanical grinding process, and the grinding time is 40 min), so that the fibers can be maximally retained in their original state and uniformly dispersed in the matrix.

[0053] (3) Preparation of the preform: The mixed powder II is placed into a circular block mold with a diameter of 100 mm and a height of 50 mm, and a pressure of 70 MPa is applied for 40 min for cold pressing.

[0054] (4) Hot-pressing sintering: The preform is heated to 900°C at a heating rate of 50°C / min, while a pressure of 70 MPa is applied, and then heated to 1030°C at a rate of 10°C / min, and the pressure is maintained for 25 min, to obtain the martensitic steel composite material.

[0055] The martensitic steel composite material prepared in this example has a dense internal structure and no obvious defects such as pores or cracks. The combination of the hot-pressing sintering process and the preforming process enables the graphite fibers and the Ti2AlC ceramic particles in this example to be uniformly distributed in the matrix, forming a good dual-phase reinforcement system. The Ti2AlC ceramic particles are in the form of irregular overlapping lamellae, uniformly dispersed in the martensitic steel matrix, and tightly combined with the matrix without obvious interface debonding. The graphite fibers are also uniformly dispersed in the matrix and maintain good integrity, and together with the Ti2AlC ceramic particles, they form a stable reinforcement network.

[0056] The average Rockwell hardness of the composite material in this example can reach HRC49, and during high-temperature friction, the friction coefficient is relatively stable, with an average friction coefficient of about 0.35, a low wear rate, and only 1 / 3~1 / 4 of that of traditional martensitic steel, showing excellent high-temperature wear resistance.

[0057] Example 2

[0058] (1) Raw material pretreatment: The martensitic steel raw powder (all raw powder particle sizes are 8 μm, and the purity is ≧99.9%) is vacuum dried according to the composition in Table 1.

[0059] The graphite fibers with a length of 3 mm and a diameter of 4 μm are added into a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 3:1, and soaked at 60°C for 2.5 h, so that the surface of the graphite fibers is fully oxidized to generate a large number of oxygen-containing functional groups, and then the graphite fibers are repeatedly washed with deionized water until neutral to remove the residual oxidizing agent and by-products on the surface, preventing interference with the subsequent processing process; then the washed graphite fibers are soaked in a 2.5% KH-550 silane coupling agent aqueous solution and reacted at 80°C for 3.5 h; finally, the graphite fibers modified by the silane coupling agent are taken out, washed with deionized water until neutral and dried at 100°C to constant weight to obtain modified graphite fibers;

[0060] MAX ceramic selects Ti3SiC2, Ti2AlC bulk is heated to 1700°C at a heating rate of 1°C / min in an argon protective atmosphere, and is kept for 5 h, then after the Ti3SiC2 bulk is naturally cooled, it is broken into powder, the interlayer spacing of Ti3SiC2 ceramic particles is increased by 12%, the surface has a 3 nm active layer rich in M-X bonds, the powder is in irregular sheet layer overlapping shape, the specific surface area is 6 m 2 / g, the surface roughness Ra is 0.4 μm, the particle size is 70 μm, and the purity is 99.9%, the Ti3SiC2 ceramic particles are mixed with powder Ni by ball milling (the mass of powder Ni is 20% of the mass of ceramic particles, stainless steel balls are used as ball milling medium, the ball-to-material ratio is 15:1, anhydrous ethanol is used as wetting agent, the amount of anhydrous ethanol is 2.5% of the total mass of Ni powder and ceramic particles, the rotation speed of the ball mill is controlled at 350 rpm, and the ball milling time is 6 h), after ball milling, the powder is extracted from the wetting agent and dried in a vacuum atmosphere to obtain modified Ti3SiC2 ceramic particles.

[0061] (2) Distribution of reinforcing bodies: dry martensitic steel raw powder is mixed with modified Ti3SiC2 ceramic particles by vacuum ball milling (the mass of modified Ti2AlC ceramic particles is 8% of the mass of martensitic steel raw powder, stainless steel balls are used as ball milling medium, the ball-to-material ratio is 10:1, the ball milling rotation speed is 400 rpm, and the ball milling time is 5 h), to obtain mixed powder I which is then vacuum dried, and then modified graphite fibers are mixed with mixed powder I in a glove box by mechanical grinding (the mass of modified graphite fibers is 10% of the mass of mixed powder I, during the mechanical grinding process, 2.5% anhydrous ethanol of the mass of mixed powder II is added as a dispersant, and the grinding time is 35 min), so that the fibers can be retained in the original state to the greatest extent and uniformly dispersed in the matrix.

[0062] (3) Preparation of preform: mixed powder II is placed into a circular block mold with a diameter of 100 mm and a height of 50 mm, and a pressure of 85 MPa is applied for 35 min for cold pressing.

[0063] (4) Hot-pressing sintering: the preform was heated to 925℃ at a heating rate of 55℃ / min, while a pressure of 75MPa was applied, then heated to 1040℃ at a rate of 11℃ / min, and kept for 23min, to prepare the martensitic steel composite material.

[0064] The martensitic steel composite material prepared in this example has a compact internal structure, good integrity and uniformity, and no obvious defects. The distribution of the reinforcing phase is uniform, and the Ti3SiC2 ceramic and the graphite fiber cooperate with each other to enhance the performance of the matrix.

[0065] The average Rockwell hardness of the composite material of this example can reach HRC52, and the friction coefficient can be kept at a relatively low and stable level of about 0.30 in a high-temperature environment, the wear rate is further reduced, compared with traditional martensitic steel materials, the wear rate is reduced by about 70%~80%, showing more excellent wear resistance, which is due to the optimized preparation process parameters making the reinforcing phase play a more significant role.

[0066] Example 3

[0067] (1) Raw material pretreatment: the martensitic steel raw material powder (all raw material powders have a particle size of 8μm and a purity of ≧99.9%) was vacuum dried according to the composition in Table 1;

[0068] The graphite fiber with a length of 5mm and a diameter of 5μm was added to a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 3:1, and soaked at 60℃ for 3h, so that the surface of the graphite fiber was fully oxidized to generate a large number of oxygen-containing functional groups. Then the graphite fiber was washed repeatedly with deionized water until it was neutral, in order to remove the residual oxidizing agent and by-products on the surface and prevent interference with the subsequent treatment process. Then the washed graphite fiber was soaked in a 3% KH-550 silane coupling agent aqueous solution and reacted at 80℃ for 4h. Finally, the graphite fiber modified by the silane coupling agent was taken out, washed with deionized water until it was neutral, and dried at 100℃ to constant weight to obtain the modified graphite fiber.

[0069] MAX ceramic selected Ti2AlN, in an argon protective atmosphere, heated Ti2AlC block to 1700℃ at a rate of 1℃ / min, and kept for 5h, then the Ti2AlN block was naturally cooled, and then crushed into powder, the Ti2AlN ceramic particle crystal interlayer spacing increased by 15%, the surface had a 5nm M-X bond active layer, the powder was irregularly overlapped, the specific surface area was 8m 2 / g, the surface roughness Ra is 0.5 μm, the particle size is 100 μm, and the purity is 99.9%, the Ti2AlN ceramic particles are mixed with the powder Ni by ball milling (the mass of the powder Ni is 25% of the mass of the ceramic particles, stainless steel balls are used as the ball milling medium, the ball-to-material ratio is 20:1, anhydrous ethanol is used as the wetting agent, the amount of the anhydrous ethanol is 5% of the total mass of the powder Ni and the ceramic particles, the rotation speed of the ball mill is controlled at 400 rpm, and the ball milling time is 4 h), the powder is extracted from the wetting agent after the ball milling, and dried in a vacuum atmosphere to obtain modified Ti2AlN ceramic particles.

[0070] (2) Distribution of the reinforcing body: the dry martensitic steel raw material powder is mixed with the modified Ti2AlN ceramic particles by vacuum ball milling (the mass of the modified Ti2AlN ceramic particles is 10% of the mass of the martensitic steel raw material powder, stainless steel balls are used as the ball milling medium, the ball-to-material ratio is 10:1, the ball milling rotation speed is 420 rpm, and the ball milling time is 5 h), the mixed powder I is obtained and then vacuum dried, and then the modified graphite fibers are mixed with the mixed powder I by mechanical grinding in a glove box (the mass of the modified graphite fibers is 15% of the mass of the mixed powder I, 5% of the mass of the mixed powder II of anhydrous ethanol is added as a dispersant during the mechanical grinding, and the grinding time is 30 min), so that the fibers can be kept in the original state to the greatest extent and uniformly dispersed in the matrix.

[0071] (3) Preparation of the preform: the mixed powder II is placed into a circular block mold with a diameter of 100 mm and a height of 50 mm, and cold-pressed by applying a pressure of 100 MPa for 30 min.

[0072] (4) Hot-pressing sintering: the preform is heated to 950 ℃ at a heating rate of 60 ℃ / min, and at the same time, a pressure of 80 MPa is applied, and then heated to 1050 ℃ at a rate of 12 ℃ / min, and the pressure is maintained for 20 min, to prepare the martensitic steel composite material.

[0073] The composite material prepared in this example has a complete internal structure, no macroscopic defects, and good compactness. The distribution of the graphite fibers and the Ti2AlN ceramic in the matrix is good in uniformity, and an effective reinforcing phase synergistic mechanism is formed.

[0074] The composite material prepared in this example has a high average Rockwell hardness, which can reach HRC 54. Under high-temperature friction conditions, the friction coefficient is stable at 0.30-0.32, the wear rate is extremely low, which is less than 1 / 5 of that of traditional martensitic steel, and has excellent high-temperature wear resistance, which is mainly due to the high Ti2AlN ceramic content and the strong comprehensive performance improvement brought by the optimized preparation process.

[0075] Comparative Example 1

[0076] The comparative example is prepared by the same method as example 1, and the martensitic steel composition is the same, the difference is that the comparative example is not modified by ceramic particles.

[0077] The composite material prepared in the comparative example has a certain degree of porosity and local loose defects inside.

[0078] Because the ceramic particles are not modified, the ceramic particles are not tightly combined with the matrix, and interface separation phenomenon easily occurs during preparation, and the distribution is not uniform, and there is aggregation phenomenon in some areas, resulting in local difference in material performance.

[0079] The average Rockwell hardness of the composite material prepared in the comparative example is only HRC43, the friction coefficient fluctuates greatly at high temperature, and the average is about 0.45, the wear rate is relatively high, about 1 / 2 of the traditional martensitic steel, and the wear resistance is significantly lower than the composite material prepared in the example.

[0080] Comparative example 2

[0081] The comparative example is prepared by the same method as example 2, and the martensitic steel composition is the same, the difference is that the comparative example does not add ceramic particles as reinforcing phase.

[0082] The comparative example only adds graphite fibers as reinforcing phase, although the composite material is relatively dense inside, but lacks the synergistic effect of MAX ceramic, the overall structure stability is slightly poor. The distribution of graphite fibers in the matrix is acceptable, but in the high temperature friction process, due to the lack of the high temperature resistance of MAX ceramic, the friction coefficient first decreases and then increases, and the average reaches about 0.40, and the wear rate is also high, about 2 / 5 of the traditional martensitic steel.

[0083] The average Rockwell hardness of the composite material prepared in the comparative example is HRC46, and the comprehensive performance is not as good as the dual-phase reinforced composite material in the example.

[0084] Comparative example 3

[0085] The comparative example is prepared by the same method as example 3, and the martensitic steel composition is the same, the difference is that the comparative example does not add graphite fibers as reinforcing phase.

[0086] The composite material of the comparative example has a certain density inside, but lacks the synergistic effect of graphite fibers, resulting in insufficient self-lubricating performance in high temperature friction; the MAX ceramic is distributed relatively uniformly, but the interface combination with the matrix will appear partial weakening phenomenon under long-term high temperature action.

[0087] The average Rockwell hardness of the composite material of the present comparative example is HRC47, the friction coefficient is about 0.42, the wear rate is about 1 / 3 of the traditional martensitic steel, and the overall performance is worse than that of the composite material in the example, and the advantage of double-phase reinforcement is not fully utilized.

[0088] By Figure 1 It can be seen that the modified MAX ceramic particles prepared by the present application successfully coat the surface of the MAX ceramic particles with Ni powder.

[0089] By Figure 4 It can be seen that the graphite fibers in the composite material prepared by the present application are well dispersed and uniformly distributed.

[0090] In summary, by using graphite fibers and MAX ceramic particles as reinforcing phases for double-phase reinforcement of martensitic steel, the advantages of graphite fibers and MAX ceramic particles and their synergistic effect are utilized, and the processes of modification, preforming, hot pressing and sintering are combined, the comprehensive performance of the martensitic steel is effectively improved, the composite material with high temperature wear resistance and high hardness is obtained, and the use performance of the martensitic steel composite material is effectively improved, so that the martensitic steel composite material has more excellent use performance under complex working conditions such as high temperature and high wear, thereby expanding the application scenarios of the martensitic steel composite material.

[0091] Finally, it should be pointed out that the above preferred embodiments are only used to illustrate the technical solutions of the present application and are not limiting, although the present application has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and content without departing from the scope defined by the claims of the present application.

Claims

1. A method of making a graphite fiber-MAX ceramic reinforced martensitic steel composite, characterized by: The preparation method comprises the following steps: (1) raw material pretreatment: vacuum drying the martensitic steel raw material powder, and surface energy modification treatment of the graphite fiber and the MAX ceramic particles, to obtain the dry martensitic steel raw material powder, modified graphite fiber and modified MAX ceramic particles; (2) distribution of reinforcing bodies: mixing the modified MAX ceramic particles in step (1) with the dry martensitic steel raw material powder for vacuum ball milling to obtain mixed powder I, and then mixing the mixed powder I with the modified graphite fiber in step (1) for mechanical grinding to obtain mixed powder II; (3) preparation of a preform: cold pressing the mixed powder II obtained in step (2) to obtain a preform; (4) hot-pressing sintering: hot-pressing sintering the preform obtained in step (3) to obtain a graphite fiber-MAX ceramic dual-phase reinforced martensitic steel composite material; In step (1), the composition of the martensitic steel comprises, by mass fraction: Cr: 15-17%, Ni: 3-5%, C: 0.2-0.3%, Mo: 0.5-1.0%, and the balance being Fe; The modification method of the graphite fiber in step (1) comprises the following steps: S1: adding the graphite fiber into an oxidizing agent, and oxidizing under heating conditions to fully oxidize the surface of the graphite fiber to obtain oxidized graphite fiber; S2: after washing the oxidized graphite fiber obtained in step S1 to neutral, soaking in a KH-550 silane coupling agent aqueous solution, and reacting under heating conditions, the graphite fiber is washed and dried to obtain modified graphite fiber; In step (1), the modification method of the MAX ceramic particles comprises the following steps: Q1: under an argon protective atmosphere, heat treating the MAX ceramic bulk body, and after the MAX ceramic bulk body is naturally cooled, crushing the MAX bulk body into powder to obtain heat-treated MAX ceramic particles; Q2: mixing the heat-treated MAX ceramic particles obtained in step Q1 with powder Ni under the wetting action of anhydrous ethanol for ball milling to coat the MAX ceramic particles with Ni, and then vacuum or inert atmosphere protection drying the Ni-coated MAX ceramic particles to obtain modified MAX ceramic particles.

2. The method of claim 1, wherein: In step S1, the oxidation temperature is 60°C, the oxidation time is 2-3h, and the oxidizing agent is a mixed liquid of concentrated sulfuric acid and hydrogen peroxide, wherein the volume ratio of concentrated sulfuric acid to hydrogen peroxide is concentrated sulfuric acid: hydrogen peroxide = 3:1; In step S2, the reaction temperature is 80°C, the reaction time is 3-4h, and in the KH-550 silane coupling agent aqueous solution, the mass percentage concentration of KH-550 silane coupling agent is 2%-3%.

3. The method of claim 1, wherein: In step Q1, the heat treatment heating rate is 1°C / min, the heat treatment temperature is 1700°C, and the holding time is 5h; In the step Q2, the mass of the Ni powder is 15%~25% of the mass of the MAX ceramic particles, the ball-to-material ratio is 10~20:1, the ball mill uses large balls with a diameter of 10 mm and small balls with a diameter of 5 mm mixed in a mass ratio of 1:1, the amount of anhydrous ethanol added is 1%~5% of the total mass of the Ni powder and the MAX ceramic particles, the ball mill rotation speed is 300~400 rpm, and the ball milling time is 4~8 h.

4. The method of claim 1, wherein: In the step (2), the modified MAX ceramic particles have a particle size of 50~100 μm, the modified graphite fibers have a length of 2~5 mm and a diameter of 3~5 μm, the amount of the modified MAX ceramic particles is 6%~10% of the mass of the martensitic steel raw material powder, the vacuum ball mill rotation speed is 380~420 rpm, the ball-to-material ratio is 10:1, the ball milling time is 5 h, and the ball mill uses large balls with a diameter of 10 mm and small balls with a diameter of 5 mm mixed in a mass ratio of 1:1; The amount of the modified graphite fibers is 5%~15% of the total mass of the mixed powder II, and anhydrous ethanol is used as a dispersant during the mechanical grinding process, the amount of the anhydrous ethanol is 1%~5% of the total mass of the mixed powder II, and the mechanical grinding time is 30~40 min.

5. The method of claim 1, wherein: In the step (3), the cold pressing forming pressure is 70~100 MPa, and the pressure holding time is 30~40 min.

6. The method of claim 1, wherein: In the step (4), the hot pressing sintering process is as follows: the preform is heated to 900~950 ℃ at a heating rate of 50~60 ℃ / min, while a pressure of 70~80 MPa is applied, the preform is then heated to 1030~1050 ℃ at a heating rate of 10~12 ℃ / min, and the pressure holding time is 20~25 min.

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