H-BN / Ti composite material with layered gradient structure and preparation method of h-BN / Ti composite material

Abstract

The invention discloses an h-BN / Ti composite material with a layered gradient structure and a preparation method of the h-BN / Ti composite material, and belongs to the field of metal-based composite materials. The composite material comprises a matrix and a reinforcing body, the base body is a pure titanium base body or a TC4 alloy base body; the reinforcing body is h-BN; and the layered gradient structure is realized by selecting pure titanium powder or TC4 alloy powder with different particle sizes for layer-by-layer gradient powder laying. By preparing h-BN modified titanium powder with different particle size units, the layered gradient structure of the composite material is regulated and controlled, the advantages of a gradient structure and a layered network structure titanium-based composite material are integrated, a structure with the size of a network structure changing in a gradient mode in the thickness direction is macroscopically formed, and microscopically, due to the pinning effect of TiB whiskers, the thickness of the titanium-based composite material is increased; grain growth is inhibited, the grain size of the formed titanium matrix changes in a gradient mode in the thickness direction, the problem of stress concentration in the deformation process of the material is effectively solved, and the room-temperature ductility and toughness of the material are greatly improved.

Description

Technical Field

[0001] This invention relates to a layered gradient structure h-BN / Ti composite material and its preparation method, belonging to the field of metal matrix composite technology. Background Technology

[0002] Titanium matrix composites (TMCs) possess advantages such as high specific strength and good fatigue resistance, and are widely used in aerospace, automotive, and other industries. Hexagonal boron nitride (h-BN), with its unique two-dimensional layered structure, excellent thermal conductivity, high-temperature stability, and low coefficient of friction, is considered an ideal reinforcing phase for improving the performance of titanium matrix composites. Traditional strategies for preparing h-BN-reinforced titanium matrix composites generally focus on achieving a uniform dispersion of h-BN nanosheets within the titanium matrix and optimizing sintering processes and interfacial reactions to obtain strong interfacial bonding. While this method significantly improves the strength and hardness of the composites, the uniformly dispersed reinforcing phase restricts the dimensional tolerance of the matrix's plastic deformation, resulting in poor room-temperature plasticity, which becomes an obstacle to the application of titanium matrix composites. For example, patent application CN116623108A uses hexagonal boron nitride nanosheets (h-BNNSs) as a single reinforcing phase. Through rapid hot-pressing sintering and subsequent heat treatment, a three-dimensional interface structure formed by h-BNNSs and nano-TiBw whiskers is constructed in a titanium matrix. However, this invention requires strict control of the temperature and holding time during hot-pressing sintering and heat treatment to prevent excessive reaction between h-BNNSs and the titanium matrix, which could destroy the intrinsic structure of h-BNNSs. Furthermore, improper control of the holding temperature or holding time can cause abnormal growth of TiBw, deteriorating the performance of the titanium-based composite material. Patent application CN116162871A combines graphene nanosheets and hexagonal boron nitride nanosheets as two reinforcing materials. Through ball milling, rapid hot-pressing sintering, and hot rolling deformation processes, a synergistic reinforcing interface of TiC-coated graphene and TiB whiskers pinning hexagonal boron nitride is formed in a TC4 titanium alloy matrix. While the aforementioned methods, through precise interface design, have improved the strength of composite materials to some extent and attempted to preserve plasticity, the distribution pattern of the reinforcing phase essentially remains within the scope of "uniform dispersion." According to classical theories of composite mechanics (such as the Hashin-Shtrikman model) and grain boundary strengthening theory, although uniformly dispersed hard reinforcing phases can effectively bear and improve the strength and hardness of materials, they also severely fragment the matrix, hindering long-range dislocation movement and limiting the dimensional tolerance of plastic deformation. This leads to a significant deterioration in the room-temperature plasticity and toughness of composite materials, creating a contradictory situation of high strength and low plasticity. This has become a core bottleneck restricting the application of such materials in fields requiring high reliability and high damage tolerance.

[0003] Therefore, going beyond the traditional uniform dispersion reinforcement mode, we innovate from the macroscopic distribution configuration of the reinforcing phase, design and prepare a titanium-based composite material with a quasi-continuous network distribution of the reinforcing phase. This will not only give full play to the strengthening effect of h-BN, but also provide a smoother path and a larger tolerance space for the plastic deformation of the matrix. This has become a key direction to overcome the defects of existing technologies and achieve the synergistic improvement of the strength and plasticity of materials.

[0004] Although existing research has made some progress in improving the plasticity (toughness) of materials through quasi-continuous network distribution of reinforcements, the incompatibility between the network structure and the matrix region under high strain rates, and the resulting localized stress concentration problems, remain prominent. Therefore, improving the strength and toughness of h-BN / Ti composites solely by improving the distribution or dispersion of h-BN is far from sufficient. In recent years, research on the application of biomimetic structures to the structural optimization of metallic materials has flourished, providing a good reference for the study of the integration of structure and function in metallic materials. For example, inspired by biomimetic structures such as seashells in nature, using silicon carbide as a nano-reinforcing phase and designing titanium-based composites with a "brick-like" layered heterostructure can reduce stress concentration during deformation. The layered structure exhibits good stress localization and crack propagation inhibition effects, giving titanium-based composites a good balance of strength and plasticity. This matrix configuration approach inspired by biomimetic structures such as seashells in nature provides a new way to solve the shortcomings of insufficient strength and toughness in h-BN / Ti composites. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a layered gradient structure h-BN / Ti composite material and its preparation method. In this method, h-BN is coated onto the surface of titanium powder using anionic and cation electrostatic adsorption. Then, h-BN / Ti powders of different particle sizes are layered and swept using a high-pressure gas spray gun. The composite material is obtained by cold pressing combined with sintering. During hot rolling, h-BN acts as a precursor to synthesize TiB whiskers in situ, coating the surface of Ti particles of different sizes. In the prepared titanium-based composite material, a layered gradient network structure of titanium powder unit particles is formed macroscopically, and a gradient structure with differentiated grain sizes is formed microscopically. Based on this gradient and layered configuration design, the problems of stress concentration and crack defects under tensile or compressive conditions are solved, and the strengthening effect of in-situ self-generated TiB whiskers is better utilized, thereby obtaining a titanium-based composite material with a good balance of strength and plasticity. To achieve the above objectives, this invention provides the following technical solution: A layered gradient structure h-BN / Ti composite material, comprising a matrix and a reinforcement; the matrix is ​​a pure titanium matrix or a TC4 alloy matrix; the reinforcement is h-BN; the layered gradient structure is achieved by layering pure titanium powder or TC4 alloy powder of different particle sizes; the reinforcement uniformly dispersed on the surface of the matrix generates TiB whiskers in situ, which are pinned to the surface of the matrix powder of different particle sizes, thereby forming a layered gradient network structure.

[0006] Furthermore, the h-BN size is 100 nm.

[0007] A method for preparing a layered gradient structure h-BN / Ti composite material includes the following steps: (1) H-BN and titanium powder are dried and surface treated. Then, the electrostatic adsorption method is used to allow H-BN to be adsorbed onto the surface of titanium powder with three different particle sizes to obtain three different particle sizes of H-BN / Ti composite powder. (2) Gradient powder spreading: Three different sizes of h-BN / Ti composite powder are spread in a cemented carbide mold in sequence using a spray gun. After all three sizes of composite powder are spread, pressure is applied for a short time. This process is repeated multiple times to obtain a cold-pressed h-BN / Ti-based composite material blank. (3) Transfer the cold-pressed compact to a graphite mold and sinter the compact using rapid hot pressing sintering technology to obtain a solidified sintered compact. (4) The solidified billet after sintering is subjected to hot deformation treatment by high temperature rolling hot deformation process to finally obtain h-BN / Ti composite material with layered gradient structure.

[0008] Furthermore, the specific steps for preparing the h-BN / Ti-based composite powder in step (1) are as follows: The h-BN / Ti composite powder was prepared using electrostatic adsorption to obtain a composite powder with good h-BN dispersion on the surface of titanium powder. First, Ti powder and h-BN powder of three different particle sizes were dried for several hours to remove surface-adsorbed moisture, thus avoiding interference with the charging effect. Then, the h-BN and Ti powders of different particle sizes were surface-treated and dried separately. This improved the wettability with the titanium powder and increased their surface resistance, making it easier to acquire and maintain electrostatic charge. Finally, the electrostatic adsorption process was carried out under an argon atmosphere to complete the preparation of the h-BN / Ti composite powder. Further, the titanium matrix powder in step (1) is pure titanium powder or TC4 powder, and the particle sizes of the three different sizes of titanium powder are 30-50 μm, 70-80 μm, and 100-150 μm, respectively. Furthermore, the drying of Ti and h-BN powder in step (1) is carried out in a vacuum drying oven at a temperature of 50-90 °C for 2-5 h; Furthermore, the drying temperature in step (1) is 60-80℃, and the drying time is 3-4 h. Furthermore, the surface treatment of Ti powder and h-BN in step (1) uses silane coupling agent (KH-500). On the one hand, it can form a monolayer on the surface of Ti powder with different particle sizes to passivate its surface and enhance charge retention. On the other hand, the silane coupling agent can enhance the dispersibility and negative electrophilicity of h-BN. Further, in step (1), the electrostatic adsorption process first requires placing three different particle sizes of Ti powder on the grounded aluminum plate of the electrostatic adsorption device, adjusting the distance between the electrode and the collecting plate to 70-80 mm (ensuring ±0.5 mm error), introducing argon gas into the electrostatic adsorption device, adjusting the electrode voltage to -20~-50 KV, injecting h-BN into the corona region at a rate of 0.2-0.4 g / min, monitoring the real-time current <10 μA, maintaining the voltage for 2 min after reaching the target amount of powder supply, and then slowly reducing the voltage to 0KV to obtain three different sizes of h-BN / Ti composite powder; Furthermore, the specific steps for gradient powder spreading in step (2) are as follows: h-BN / Ti composite powders of the same mass but different sizes are loaded into a spray gun. The amount of powder dispensed from the spray gun is controlled each time. Using cemented carbide as a mold, the powder is spread in layers of 100-150 μm, 70-80 μm, and 30-50 μm particle size according to the size of the powder. After all three particle sizes are spread, the cemented carbide mold containing the composite powder is placed in a hydraulic press and briefly pressurized. This process of spreading powder is repeated 4 to 6 times to complete the cold pressing of the powder mixture.

[0009] Furthermore, the mass of the h-BN / Ti composite powder of the same mass but different sizes in step (2) can be designed to be 0.5-100 g according to the requirements to control the layer thickness of each layer. According to the size of the powder, the powder is spread in a gradient by spraying gun in the order of large particle layer, medium particle layer and small particle layer to form a layered gradient structure composed of different powder sizes. Furthermore, the spray gun described in step (2) is a pneumatic powder spreading device, which means that a certain mass of powder is loaded into the powder storage chamber of the spray gun, and then the powder storage chamber is evacuated. After argon gas is filled into the gas filling chamber, the argon gas flow rate can be controlled by pressing the launch button to control the powder in the powder storage chamber to be evenly spread in the mold. By changing the powder storage chamber containing powder of different particle size, the powder spreading can be carried out quickly in sequence. Further, the cold pressing molding in step (2) is carried out using a hydraulic press. After the three different sizes of composite powder are laid once, the hydraulic press is used to pressurize briefly for 2 minutes. The pre-pressure of the hydraulic press is set to 400-500 MPa. The pressure is gradually increased to 400-500 MPa at a loading condition of 50-100 MPa / min. After all the powder is laid, the preset pressure is used to hold the pressure for 10-40 minutes. Then, the pressure is gradually reduced at a unloading condition of 100-200 MPa / min to complete the pressing molding of the powder mixture.

[0010] Further, the specific steps of sintering in step (3) are as follows: transfer the cylindrical compact to a graphite mold with carbon paper on it, then put the graphite mold into a rapid hot pressing sintering furnace, with an initial vacuum degree ≤5 Pa, a heating rate of 80-100℃ / min, and hold the temperature for 10-15 min when the temperature reaches 800-1000℃, and then cool it with the furnace to complete the rapid hot pressing sintering of the compact.

[0011] Furthermore, the sintering temperature in step (3) is 850-950℃ and the time is 12-14 h.

[0012] Further, in step (4), a high-temperature rolling hot deformation process is used to heat deform the sintered billet. That is, the sintered billet is first heated to a high-temperature pre-deformation temperature, and then a hot rolling mill is used to heat deform the sintered billet so that the TiB whiskers are oriented along the rolling direction. In addition, the in-situ self-generated TiB whiskers are broken and refined during the high-temperature rolling hot deformation process, the network structure is elongated, and the grains in the network are further refined, finally obtaining an h-BN / Ti composite material with a layered gradient structure.

[0013] Further, the heating, sintering, and pressing of the billet is carried out according to the following steps: the temperature of the muffle furnace is set to 900-1000℃, and after the temperature of the muffle furnace rises to 900-1000℃, the cleaned sintered billet is placed in the muffle furnace and held for 10-15 minutes; Furthermore, the high-temperature rolling hot deformation is carried out according to the following steps: the initial rolling temperature is 900-1000 ℃, the circumferential speed of the upper and lower rolls of the rolling mill is adjusted to 60 mm / s, the deformation amount per pass is 5-10%, and the total deformation amount is 50-60%; the reflow temperature per pass is 900-1000 ℃, and the reflow time is 2-3 min. By controlling the hot rolling process, the TiB formed during the sintering process is further oriented along the grain boundaries, and the grains of the matrix are further refined, finally preparing a layered gradient structure h-BN / Ti composite material.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with other ceramic reinforcing phases (such as carbide ceramics), the h-BN material selected in this invention has the advantage of being lightweight. Furthermore, the B element in the h-BN material reacts in situ with the Ti matrix solid phase to generate TiB whiskers for reinforcement, while the N element plays a solid solution strengthening role, achieving a synergistic reinforcement effect. At the same time, by constructing a quasi-continuous network distribution of the reinforcing phase structure, the excessive segmentation of the matrix by the traditional uniform dispersion mode is broken. This biomimetic network structure can not only efficiently bear the load through the hard network skeleton, significantly improving the strength and hardness of the composite material, but also retain continuous or semi-continuous plastic deformation channels for the titanium matrix, greatly improving the room temperature ductility and toughness of the material. (2) In this invention, h-BN reacts in situ with titanium to form a TiB whisker network on the surface of titanium particles. The TiB whiskers form a network strengthening phase with continuous gradient characteristics along the interface of the titanium matrix particles, while inducing the matrix grains to exhibit a gradient size distribution, thereby obtaining a composite microstructure with both layered structure and gradient network characteristics. Therefore, macroscopically, a network structure with a gradient size along the thickness direction is formed, and microscopically, due to the pinning effect of TiB whiskers, grain growth is inhibited, resulting in a gradient change in the size of the titanium matrix grains along the thickness direction. This gradient layered structure effectively solves the stress concentration problem in the deformation process of the material, which is beneficial to the improvement of the material's strength and toughness. (3) This invention draws on the advantages of layered structures such as shells in nature for toughening. Based on the uniform dispersion reinforcement and quasi-continuous network reinforcement of traditional composite materials, it carries out layered gradient configuration design, which combines the advantages of gradient structure and layered network structure titanium-based composite materials. It effectively alleviates the stress localization problem of traditional composite materials and prepares titanium-based composite materials with good strength and plasticity matching. (4) The preparation method of the present invention is simple and can prepare large-sized titanium-based composite materials with light weight, high strength and high toughness. It successfully solves the problem of the inversion of strength and toughness in the prior art and has a wide range of applications, which broadens the path for the development of titanium-based composite materials. Attached Figure Description

[0015] Figure 1 The images show SEM images of pure titanium and composite powder with a median particle size of 30 μm in step (1) of Example 1.

[0016] Figure 2 The images show SEM images of pure titanium and composite powder with a median particle size of 80 μm in step (1) of Example 1.

[0017] Figure 3 The images show SEM images of pure titanium and composite powder with a median particle size of 150 μm in step (1) of Example 1.

[0018] Figure 4Metallographic image of the layered gradient structure h-BN / Ti composite material in Example 1.

[0019] Figure 5 This is a SEM image of TiB whiskers pinned to the surface of titanium powder in Example 1.

[0020] Figure 6 The figures show the room temperature tensile curves of the composite materials used in the examples and comparative examples. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Unless otherwise specified, the methods described are conventional methods, and the raw materials described are obtainable from publicly available commercial sources.

[0022] A specific embodiment of the present invention discloses a layered gradient structure h-BN / Ti composite material, which includes a matrix and a reinforcement; the matrix is ​​a pure titanium matrix or a TC4 alloy matrix; the reinforcement is h-BN; the layered gradient structure is achieved by layering pure titanium powder or TC4 alloy powder of different particle sizes; the reinforcement, uniformly dispersed on the surface of the matrix, generates TiB whiskers in situ, which are then anchored to the surface of the matrix powder of different particle sizes, thereby forming a layered gradient network structure. The h-BN has a size of 100 nm.

[0023] Compared with the prior art, the present invention provides a novel layered gradient network titanium-based composite material. The reinforcement uniformly dispersed on the matrix surface generates TiB whiskers in situ and pins them to the surface of matrix powders with different particle sizes. Due to the special structure, the composite material can achieve a significant improvement in room temperature plasticity and toughness, and a synergistic enhancement of strength and plasticity.

[0024] Another specific embodiment of the present invention discloses a method for preparing a layered gradient structure h-BN / Ti composite material, comprising the following steps: (1) H-BN and titanium powder are dried and surface treated. Then, the electrostatic adsorption method is used to allow H-BN to be adsorbed onto the surface of titanium powder with three different particle sizes to obtain three different particle sizes of H-BN / Ti composite powder. (2) Using a spray gun, three different sizes of h-BN / Ti composite powder are laid in a cemented carbide mold in a gradient. After all three sizes of composite powder are laid, pressure is applied for a short time. This process is repeated multiple times, and the h-BN / Ti-based composite material blank is obtained by cold pressing. (3) Transfer the cold-pressed compact to a graphite mold and sinter the compact using rapid hot pressing sintering technology to obtain a solidified sintered compact. (4) The solidified billet after sintering is subjected to hot deformation treatment by high temperature rolling hot deformation process to finally obtain h-BN / Ti composite material with layered gradient structure.

[0025] Specifically, the three different sizes of titanium powder mentioned in step (1) are pure titanium powder or TC4 powder with particle sizes of small particle size: 30-50μm (e.g., 30μm, 40μm, 50μm); medium particle size: 70-80μm (e.g., 70μm, 75μm, 80μm); and large particle size: 100-150μm (e.g., 100μm, 110μm, 120μm, 130μm, 140μm, 150μm).

[0026] Specifically, the drying and surface treatment operations in step (1) are as follows: h-BN and three different particle sizes of Ti powder are placed in a vacuum drying oven and dried at a temperature of 50-90 ℃, for example, 50℃, 60℃, 70℃, 80℃, and 90℃, for a drying time of 2-5 h, for example, 2 h, 3 h, 4 h, and 5 h. Then, the three different particle sizes of Ti powder and h-BN are surface treated with silane coupling agent and then vacuum dried again.

[0027] It is important to note that drying and surface treatment operations can, on the one hand, form a monolayer on the surface of Ti powder with different particle sizes to passivate its surface and enhance charge retention, and on the other hand, enhance the dispersibility and negative electrophilic affinity of h-BN.

[0028] Specifically, in step (1), the electrostatic adsorption method is as follows: three Ti powders of different particle sizes are placed on the grounded aluminum plate of the electrostatic adsorption device, and the distance between the electrode and the collecting plate is adjusted to 70-80 mm, for example, 70 mm, 75 mm, and 80 mm. After argon gas is introduced into the electrostatic adsorption device, the electrode voltage is adjusted to -20~-50KV, for example, -20 KV, -30 KV, -40 KV, and -50KV. h-BN is injected into the corona region at a rate of 0.2-0.4 g / min (for example, 0.2 g / min, 0.3 g / min, and 0.4 g / min). The real-time current is monitored to be <10 μA. After the target amount of powder is reached, the voltage is maintained for 2 min and then slowly reduced to 0 KV to obtain three h-BN / Ti composite powders of different sizes.

[0029] It is important to note that this invention enables the reinforcement to be uniformly dispersed on the matrix surface through electrostatic adsorption. Compared to the traditional ball milling method, this not only improves the dispersion effect of the reinforcement but also avoids the influence of internal stress caused by the pre-deformation of the matrix powder before hot pressing and sintering on the composite material properties. Furthermore, the uniformly dispersed h-BN in situ generates TiB whiskers that are pinned to the surface of matrix powders of different particle sizes, thereby forming a layered gradient network structure.

[0030] Specifically, the specific operation steps of gradient powder spreading in step (2) are as follows: h-BN / Ti composite powders of the same mass but different sizes are loaded into the spray gun, the powder output of the spray gun is controlled each time, and a hard alloy is used as the mold. Based on the powder size, the spray gun is used to spread the powder into layers with a large particle size of 100-150 μm (e.g., 100μm, 110μm, 120μm, 130μm, 140μm, 150μm), a medium particle size of 70-80 μm (e.g., 70μm, 75μm, 80μm), and a medium particle size of 30-50 μm. Powder is sequentially spread in layers of small particle sizes (e.g., 30μm, 40μm, 50μm). After all three particle sizes are spread, the cemented carbide mold containing the composite powder is placed in a hydraulic press and briefly pressurized. This process is repeated 4-6 times (e.g., 4, 5, 6 times). The hydraulic press is preset to a pressure of 400-500 MPa (e.g., 400 MPa, 450 MPa, 500 MPa), and the pressure is gradually increased to 400-500 MPa (e.g., 400 MPa, 450 MPa, 500 MPa) at a loading rate of 50-100 MPa / min (e.g., 50 MPa / min, 75 MPa / min, 100 MPa / min). After all the powder is spread, the preset pressure is maintained for 10-40 minutes (e.g., 10 min, 20 min, 30 min, 40 min), and then the pressure is increased to 100-200 MPa / min (e.g., 100 MPa, 450 MPa, 500 MPa). The unloading conditions (MPa / min, 150 MPa / min, 200 MPa / min) are gradually reduced to reduce pressure, thus completing the compression molding of the powder mixture.

[0031] It should be noted that the present invention achieves cold pressing of a powder mixture with a size gradient by sequentially spreading powder in three particle sizes (large, medium, and small) and repeating this process 4 to 6 times, in conjunction with hydraulic pressure.

[0032] Specifically, the rapid hot pressing sintering operation in step (3) is as follows: the cold-pressed compact is transferred to a graphite mold with carbon paper on it, and then the graphite mold is placed in a rapid hot pressing sintering furnace with an initial vacuum degree ≤5 Pa and a heating rate of 80-100 ℃ / min (e.g., 80 ℃ / min, 90 ℃ / min, 100 ℃ / min). When the temperature rises to 800-1000 ℃, for example, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, the temperature is held for 10-15 min, for example, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min. After that, the compact is cooled with the furnace to complete the rapid hot pressing sintering.

[0033] Specifically, the specific steps of the high-temperature rolling hot deformation in step (4) are as follows: the sintered composite material blank is placed in a muffle furnace at 900-1000 ℃ and kept at 900-1000 ℃ for 10-15 min, and then rolled. The circumferential speed of the upper and lower rolls of the hot rolling mill is set to 60 mm / s. The rolling process is carried out in 6 passes, with a deformation of 5-10% per pass. The initial rolling temperature is 900-1000 ℃. After each pass, the material is returned to the furnace for 2-3 min. Finally, the layered gradient structure h-BN / Ti composite material is prepared.

[0034] The technical solution of the present invention will be further explained below with reference to specific embodiments.

[0035] Among them, hexagonal boron nitride (h-BN, 99.3%) was produced by Hubei Xinmao High-Tech Materials Co., Ltd. The Ti-based powder is in flake or near-spherical form, with a purity of 98.5 wt.%, produced by Ganzhou Jingke Technology Co., Ltd. Example 1 A method for preparing a layered gradient structure h-BN / Ti composite material, the specific steps of which are as follows: (1) Preparation of h-BN / Ti-based composite powder 1.1) Pure Ti powder and h-BN powder with median particle sizes of 150 μm, 80 μm and 30 μm were dried in a vacuum drying oven at 80 °C for 5 h to remove surface-adsorbed moisture; 1.2) Three different particle sizes of pure Ti powder and h-BN were surface-treated with silane coupling agent (KH-500) and then vacuum-dried. 1.3) Pure Ti powder of three different particle sizes was placed on the grounded aluminum plate of the electrostatic adsorption device. The distance between the electrode and the collecting plate was adjusted to 80 mm (to ensure an error of ±0.5 mm). After argon gas was introduced into the electrostatic adsorption device, the electrode voltage was adjusted to -20 kV. h-BN was injected into the corona region at a rate of 0.2 g / min. The real-time current was monitored to be <10 μA. After the target amount of powder was reached, the voltage was maintained for 2 min and then slowly reduced to 0 kV to obtain h-BN / Ti composite powder. (2) Gradient powder spreading with spray gun 2.1) Control the amount of powder dispensed from the spray gun each time, and control the amount of powder dispensed per layer to about 0.6 g; 2.2) Hard alloy was selected as the mold for spreading the powder. The powder was spread in sequence with a spray gun according to the size of 150 μm composite powder, 80 μm composite powder and 30 μm composite powder. The powder was spread in this way 5 times. Each layer of each size of composite powder was 0.6 g. After the powder of the three sizes was spread once, the hydraulic press was used to pressurize for 2 min for a short time. The pre pressure of the hydraulic press was set to 400 MPa. The pressure was gradually increased to 400 MPa at a loading condition of 50 MPa / min. After all the powder was spread, the pressure was held at the preset pressure for 10 min. Then the pressure was gradually reduced at a unloading condition of 200 MPa / min to complete the pressing and molding of the powder mixture. (3) Rapid hot pressing sintering The cylindrical compact is transferred to a graphite mold lined with carbon paper, and then the graphite mold is placed in a rapid hot pressing sintering furnace with an initial vacuum of ≤5 Pa and a heating rate of 100 ℃ / min. When the temperature reaches 1000 ℃, it is held for 10 min, and then cooled with the furnace to complete the rapid hot pressing sintering of the compact. (4) High-temperature rolling hot deformation 4.1) Set the temperature of the muffle furnace to 900 ℃. After the temperature of the muffle furnace reaches 900 ℃, place the cleaned sintered billet into the muffle furnace and hold it for 10 min. 4.2) Before rolling, the circumferential speed of both the upper and lower rolls of the hot rolling mill was adjusted to 60 mm / s, the initial rolling temperature was 900 ℃, the deformation per pass was 10%, and the total deformation was 60%. The reflow temperature per pass was 900 ℃, and the reflow time was 3 min. By controlling the hot rolling process, the TiB whiskers formed during sintering were further oriented along the rolling direction, and the grains of the matrix were further refined, ultimately producing a titanium-based composite material with a layered gradient network structure. The metallographic structure of the layered gradient network along the thickness direction of the material after high-temperature rolling hot deformation is shown in the figure. Figure 4 As shown; Depend on Figure 1 , Figure 2 , Figure 3 It can be seen that after electrostatic adsorption, h-BN is uniformly attached to the surface of titanium powder without obvious agglomeration, showing good dispersibility. This lays the foundation for the uniform distribution of in-situ self-generated TiB whiskers during the subsequent sintering process.

[0036] Depend on Figure 4 It can be seen that the composite material in Example 1 exhibits a good layered gradient network structure, which lays a structural foundation for the transmission and redistribution of stress during the deformation process.

[0037] Depend on Figure 5 It can be seen that TiB whiskers are pinned to the surface of titanium powder, and TiB whiskers are distributed in a quasi-continuous network at the boundaries of titanium powder particles.

[0038] Depend on Figure 6 It can be seen that this h-BN reinforced titanium matrix composite material with a layered gradient structure achieves a good match between high strength and plasticity, and obtains excellent room temperature mechanical properties.

[0039] Example 2 A method for preparing a layered gradient structure h-BN / Ti composite material, the specific steps of which are as follows: (1) Preparation of h-BN / Ti-based composite powder 1.1) TC4 powder and h-BN powder with median particle sizes of 110 μm, 70 μm and 40 μm were dried in a vacuum drying oven at 60 °C for 4 h to remove surface-adsorbed moisture; 1.2) Three different particle sizes of TC4 powder and h-BN were surface-treated with silane coupling agent (KH-500) and then vacuum-dried. 1.3) Three types of TC4 powder with different particle sizes were placed on the grounded aluminum plate of the electrostatic adsorption device. The distance between the electrode and the collecting plate was adjusted to 70 mm (to ensure an error of ±0.5 mm). After argon gas was introduced into the electrostatic adsorption device, the electrode voltage was adjusted to -30 KV. h-BN was injected into the corona region at a rate of 0.3 g / min. The real-time current was monitored to be <10 μA. After the target amount of powder was reached, the voltage was maintained for 2 min and then slowly reduced to 0 KV to obtain h-BN / Ti composite powder. (2) Gradient powder spreading with spray gun 2.1) Control the amount of powder dispensed from the spray gun each time, and control the amount of powder dispensed per layer to about 0.6 g; 2.2) Hard alloy was selected as the mold for spreading the powder. The 110 μm composite powder, 70 μm composite powder and 40 μm composite powder were spread in sequence by spray gun. The powder was spread in this way 4 times. Each layer of each size of composite powder was 0.6 g. After the powder of each size was spread once, the hydraulic press was used to pressurize for 2 min for a short time. The pre-pressure of the hydraulic press was set to 400 MPa. The pressure was gradually increased to 400 MPa at a loading condition of 50 MPa / min. After all the powder was spread, the pressure was held at the preset pressure for 10 min. Then the pressure was gradually reduced at a unloading condition of 200 MPa / min to complete the pressing and molding of the powder mixture. (3) Rapid hot pressing sintering The cylindrical compact is transferred to a graphite mold lined with carbon paper. The graphite mold is then placed in a rapid hot pressing sintering furnace with an initial vacuum of ≤5 Pa and a heating rate of 100 ℃ / min. The compact is held at 1000 ℃ for 10 min and then cooled in the furnace to complete the rapid hot pressing sintering. (4) High-temperature rolling hot deformation 4.1) Set the temperature of the muffle furnace to 950 ℃. After the temperature of the muffle furnace reaches 950 ℃, place the cleaned sintered billet into the muffle furnace and hold it for 10 min. 4.2) Before rolling, the circumferential speed of the upper and lower rolls of the hot rolling mill is adjusted to 60 mm / s, the initial rolling temperature is 950 ℃, the deformation per pass is 5%, and the total deformation is 50%; the reflow temperature per pass is 950 ℃, and the reflow time is 2 min. By controlling the hot rolling process, the TiB whiskers formed during sintering are further oriented along the grain boundaries, and the grains of the matrix are further refined, finally preparing a layered gradient structure h-BN / Ti composite material.

[0040] Example 3 A method for preparing a layered gradient structure h-BN / Ti composite material, the specific steps of which are as follows: (1) Preparation of h-BN / Ti-based composite powder 1.1) Pure Ti powder with median particle sizes of 100 μm, 70 μm, and 30 μm was packaged and placed together with h-BN powder in a vacuum drying oven at 90 °C for 3 h to remove surface-adsorbed moisture. 1.2) Three different particle sizes of pure Ti powder and h-BN were surface-treated with silane coupling agent (KH-500) and then vacuum-dried. 1.3) Pure Ti powder of three different particle sizes was placed on the grounded aluminum plate of the electrostatic adsorption device. The distance between the electrode and the collecting plate was adjusted to 75 mm (to ensure an error of ±0.5 mm). After argon gas was introduced into the electrostatic adsorption device, the electrode voltage was adjusted to -40 kV. h-BN was injected into the corona region at a rate of 0.4 g / min. The real-time current was monitored to be <10 μA. After the target amount of powder was reached, the voltage was maintained for 1 min and then slowly reduced to 0 kV to obtain h-BN / Ti composite powder. (2) Gradient powder spreading with spray gun 2.1) Control the amount of powder dispensed from the spray gun each time, and control the amount of powder dispensed per layer to about 0.6 g; 2.2) Hard alloy was selected as the mold for spreading the powder. The powder was spread in sequence according to 100 μm composite powder, 70 μm composite powder and 30 μm composite powder. The powder was spread in this way 5 times. Each layer of each size of composite powder was 0.6 g. After the powder of each size was spread once, the hydraulic press was used to pressurize for 2 min for a short time. The pre-pressure of the hydraulic press was set to 400 MPa. The pressure was gradually increased to 400 MPa at a loading condition of 50 MPa / min. After all the powder was spread, the pressure was held at the preset pressure for 10 min. Then the pressure was gradually reduced at a unloading condition of 200 MPa / min to complete the pressing and molding of the powder mixture. (3) Rapid hot pressing sintering The cylindrical compact is transferred to a graphite mold lined with carbon paper, and then the graphite mold is placed in a rapid hot pressing sintering furnace with an initial vacuum of ≤5 Pa and a heating rate of 80 ℃ / min. When the temperature reaches 800 ℃, it is held for 15 min, and then cooled with the furnace to complete the rapid hot pressing sintering of the compact. (4) High-temperature rolling hot deformation 4.1) Set the temperature of the muffle furnace to 1000 ℃. After the temperature of the muffle furnace rises to 1000 ℃, put the cleaned sintered billet into the muffle furnace and keep it warm for 15 min. 4.2) Before rolling, the circumferential speed of the upper and lower rolls of the hot rolling mill is adjusted to 60 mm / s, the initial rolling temperature is 1000 ℃, the deformation per pass is 5%, and the total deformation is 60%; the reflow temperature per pass is 1000 ℃, and the reflow time is 3 min. By controlling the hot rolling process, the TiB whiskers formed during sintering are further oriented along the grain boundaries, and the grains of the matrix are further refined, finally preparing a titanium-based composite material with a layered gradient network structure.

[0041] Comparative Example 1 (1) Weigh 0.15 g of hexagonal boron nitride (h-BN) and pour it into a beaker. Add 30 ml of ethanol solution and sonicate for 10 min to obtain a white suspension of h-BN. (2) Pour the white suspension of h-BN into a stainless steel ball mill jar containing pure titanium powder with a median particle size of 80 μm. The mass of the titanium powder in the ball mill jar is 30 g. Then, after evacuating the ball mill jar, fill it with argon gas and ball mill for 3 h using a planetary ball mill with a rotation speed of 250 rpm and a ball-to-material ratio of 15:1. (3) After separating the small balls from the composite powder in the ball mill jar, the composite powder and ethanol mixture were poured into a round-bottom flask and dried using a vacuum rotary evaporator. The rotary evaporator was placed in a constant temperature water bath at 60 °C for 30 min, and the rotation speed of the flask was set to 50 r / min. Finally, h-BN / Ti-based composite powder was obtained. (4) Pour the BN / Ti-based composite powder into a cemented carbide mold and cold press it into a blank using a hydraulic press. The pre-pressure of the hydraulic press is set to 400 MPa. The pressure is gradually increased to 400 MPa at a loading condition of 100 MPa / min and held for 20 min. Then, the pressure is gradually reduced at a unloading condition of 100 MPa / min to complete the pressing and molding of the powder mixture. (5) Transfer the cylindrical compact to a graphite mold with carbon paper on it, and then put the graphite mold into a rapid hot pressing sintering furnace. The initial vacuum degree is ≤5 Pa, the heating rate is set to 100 ℃ / min, and the temperature is held for 10 min when it reaches 1000 ℃. Then the compact is cooled with the furnace to complete the rapid hot pressing sintering. (6) Set the temperature of the muffle furnace to 900 ℃. After the temperature of the muffle furnace reaches 900 ℃, put the cleaned sintered billet into the muffle furnace and hold it for 10 min. Before rolling, adjust the circumferential speed of the upper and lower rolls of the hot rolling mill to 60 mm / s, the initial rolling temperature to 900 ℃, the deformation amount per pass to 10%, and the total deformation amount to 60%. The reflow temperature per pass is 900 ℃, and the reflow time is 3 min. Finally, TiB whisker-reinforced titanium-based composite material is prepared.

[0042] Comparative Example 2 (1) Pure Ti powder and h-BN powder with a median particle size of 70 μm were dried in a vacuum drying oven at 70 °C for 4 h to remove surface adsorbed moisture; (2) The pure Ti powder and h-BN were surface-treated with silane coupling agent (KH-500) and then vacuum dried again; (3) Place pure Ti powder on the grounded aluminum plate of the electrostatic adsorption device, adjust the distance between the electrode and the collection plate to 75 mm (ensure ±0.5 mm error), introduce argon gas into the electrostatic adsorption device, adjust the electrode voltage to -20 KV, inject h-BN into the corona region at a rate of 0.2 g / min, monitor the real-time current <10 μA, maintain the voltage for 2 min after reaching the target amount of powder supply, and then slowly reduce the voltage to 0 KV to obtain h-BN / Ti composite powder; (4) Weigh 8 parts of pure titanium powder (with a particle size of 70 μm) with a mass of 0.6 g and 8 parts of h-BN / Ti-based composite powder with a mass of 0.6 g. Use a carbide mold as the mold for spreading the powder to spread the pure titanium powder and h-BN / Ti-based composite powder alternately. Press lightly with a carbide press head after each type of powder is spread. Press the two types of powder twice with a hydraulic press for a short time. After all the powder is spread, press the mixture with a hydraulic press for a long time to complete the cold pressing of the mixed powder. (5) Transfer the cylindrical compact to a graphite mold with carbon paper on it, and then put the graphite mold into a rapid hot pressing sintering furnace. The initial vacuum degree is ≤5 Pa, the heating rate is set to 100 ℃ / min, and the temperature is held for 10 min when it reaches 1000 ℃. Then the compact is cooled with the furnace to complete the rapid hot pressing sintering. (6) Set the temperature of the muffle furnace to 900 ℃. After the temperature of the muffle furnace reaches 900 ℃, put the cleaned sintered billet into the muffle furnace and hold it for 10 min. Before rolling, adjust the circumferential speed of the upper and lower rolls of the hot rolling mill to 60 mm / s, the initial rolling temperature to 900 ℃, the deformation amount per pass to 10%, and the total deformation amount to 60%. The reflow temperature per pass is 900 ℃, and the reflow time is 3 min. Finally, TiB whisker-reinforced layered titanium matrix composite material is prepared.

[0043] Comparative Example 3 (1) Weigh two portions of 0.15 g hexagonal boron nitride (h-BN) and pour them into two beakers respectively. Add 30 ml of ethanol solution and sonicate for 10 min to obtain a white suspension of h-BN. (2) Pour the white h-BN suspension in the two beakers into two stainless steel ball milling jars containing pure titanium powder with median particle size of 30 μm and 80 μm, respectively. The mass of pure titanium powder in each ball milling jar is 30 g. Then, after evacuating the ball milling jars, fill them with argon gas and ball mill for 3 h using a planetary ball mill. The speed is set to 250 rpm and the ball-to-material ratio is 15:1. (3) After separating the small balls and composite powder from the two ball milling jars, the composite powder from the two ball milling jars was poured into two round-bottom flasks and dried using a vacuum rotary evaporator. The rotary evaporator was placed in a constant temperature water bath at 60 °C for 30 min and the rotation speed of the flask was set to 50 r / min. Finally, h-BN / Ti-based composite powder with two sizes of pure titanium powder coated with h-BN was obtained. (4) Weigh 0.6 g of each composite powder of each size in 5 portions using an electronic balance; select Φ20 hard alloy as the mold for spreading the powder, spread the powder in sequence according to 80 μm composite powder and 30 μm composite powder, and repeat this process 8 times. Spread 0.6 g of each size of composite powder in each layer. Press each layer of composite powder lightly with a hard alloy press head. After spreading the powder of both sizes once, press the hydraulic press for 2 min for a short time. Set the pre-pressure of the hydraulic press to 400 MPa. Press the pressure up to 400 MPa step by step with a loading condition of 50 MPa / min. After all the powder is spread, hold the pressure for 10 min with the preset pressure, and then depressurize step by step with an unloading condition of 200 MPa / min to complete the pressing and molding of the powder mixture. (5) Transfer the cylindrical compact to a graphite mold with carbon paper on it, and then put the graphite mold into a rapid hot pressing sintering furnace. The initial vacuum degree is ≤5 Pa, the heating rate is set to 100 ℃ / min, and the temperature is held for 10 min when it reaches 1000 ℃. Then the compact is cooled with the furnace to complete the rapid hot pressing sintering. (6) Set the temperature of the muffle furnace to 900 ℃. After the temperature of the muffle furnace rises to 900 ℃, put the cleaned sintered billet into the muffle furnace and keep it warm for 10 min. Before rolling, adjust the circumferential speed of the upper and lower rolls of the hot rolling mill to 60 mm / s, the initial rolling temperature to 900 ℃, the deformation amount per pass to 10%, and the total deformation amount to 60%. The return temperature per pass is 900 ℃, and the return time is 3 min. By controlling the hot rolling process, the TiB whiskers formed during the sintering process are further oriented along the grain boundaries, and the grains of the matrix are further refined. Finally, a titanium-based composite material with a layered gradient network structure is prepared.

[0044] Table 1 Comparison of room temperature performance between the examples and comparative examples sample Ultimate tensile strength at room temperature room temperature elongation Example 1 1205MPa 20.2% Example 2 1296MPa 17% Example 3 1142MPa 19.1% Comparative Example 1 1003MPa 3.2% Comparative Example 2 894MPa 12% Comparative Example 3 1083MPa 15% The mechanical properties of the composite materials prepared in Examples 1-3 and Comparative Examples 1-3 were tested. The statistical results in the table show that this titanium-based composite material with a three-layered gradient network alternating structure achieved the optimal strength-plasticity match at room temperature. Macroscopically, the composite material exhibits a gradient network, and microscopically, its grain size exhibits a gradient. This gradient layered structure reduces the differences in physical properties between layers, not only alleviating stress concentration at the layer interfaces and preventing premature material failure, but also, due to the differences in mechanical properties between layers, mechanical incompatibility under stress will generate a plastic strain gradient at the regional interfaces, activating geometrically necessary dislocations for regulation, thereby generating back stress to strengthen the soft regions. Furthermore, the alternating structure delays crack propagation during tensile testing through the interaction of different layers, and the network-distributed TiB whiskers strengthen the material through load transfer and crack deflection mechanisms. The construction of the gradient structure ensures good interfacial bonding, guaranteeing effective transfer of interlayer loads and preventing interlayer delamination, thus achieving a good strength-plasticity match.

[0045] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A layered gradient structure h-BN / Ti composite material, characterized in that: The composite material includes a matrix and a reinforcement; The substrate is a pure titanium substrate or a TC4 alloy substrate; The reinforcing agent is h-BN; The layered gradient structure is achieved by layering pure titanium powder or TC4 alloy powder of different particle sizes.

2. The layered gradient structure h-BN / Ti composite material according to claim 1, characterized in that: The reinforcement h-BN has a size of 100 nm. The reinforcement is uniformly dispersed on the surface of the matrix and generates TiB whiskers in situ, which are pinned to the surface of matrix powders of different particle sizes, thereby forming a layered gradient network structure.

3. A method for preparing the layered gradient structure h-BN / Ti composite material as described in claim 1 or 2, characterized in that, The method steps are as follows: (1) H-BN and titanium powder are dried and surface treated. Then, the electrostatic adsorption method is used to allow H-BN to be adsorbed onto the surface of titanium powder with three different particle sizes to obtain three different particle sizes of H-BN / Ti composite powder. (2) Using a spray gun, three different sizes of h-BN / Ti composite powder are laid in a cemented carbide mold in a gradient. After all three sizes of composite powder are laid, pressure is applied for a short time. This process is repeated multiple times, and the h-BN / Ti-based composite material blank is obtained by cold pressing. (3) Transfer the cold-pressed compact to a graphite mold and sinter the compact using rapid hot pressing sintering technology to obtain a solidified sintered compact. (4) The solidified blank after sintering is subjected to hot deformation treatment by high temperature rolling hot deformation process to finally obtain h-BN / Ti composite material with layered gradient structure.

4. The method for preparing a layered gradient structure h-BN / Ti composite material according to claim 3, characterized in that: The three different sizes of titanium powder mentioned in step (1) are pure titanium powder or TC4 powder with particle sizes of 30-50μm, 70-80μm and 100-150μm respectively.

5. The method for preparing a layered gradient structure h-BN / Ti composite material according to claim 3, characterized in that: The specific operations for drying and surface treatment in step (1) are as follows: h-BN and Ti powders of three different particle sizes were placed in a vacuum drying oven and dried at 50-90 ℃ for 2-5 h. Then, Ti powder and h-BN with three different particle sizes were surface-treated with silane coupling agents and then vacuum-dried again.

6. The method for preparing a layered gradient structure h-BN / Ti composite material according to claim 3, characterized in that: In step (1), the electrostatic adsorption method is as follows: Ti powder of three different particle sizes was placed on the grounded aluminum plate of the electrostatic adsorption device. The distance between the electrode and the collecting plate was adjusted to 70-80 mm. After argon gas was introduced into the electrostatic adsorption device, the electrode voltage was adjusted to -20~-50KV. h-BN was injected into the corona region at a rate of 0.2-0.4 g / min. The real-time current was monitored to be <10 μA. After the target amount of powder was reached, the voltage was maintained for 2 min and then slowly reduced to 0KV to obtain three h-BN / Ti composite powders of different sizes.

7. The method for preparing a layered gradient structure h-BN / Ti composite material according to claim 3, characterized in that: The specific steps for gradient powder spreading in step (2) are as follows: h-BN / Ti composite powders of the same mass but different sizes are loaded into a spray gun. The amount of powder dispensed from the spray gun is controlled each time. Using cemented carbide as a mold, the powder is spread in layers of 100-150μm, 70-80μm, and 30-50μm particle size according to the size of the powder. After all three particle sizes of powder are spread, the cemented carbide mold containing the composite powder is placed in a hydraulic press and briefly pressurized. This process of spreading powder is repeated 4-6 times. The preset pressure of the hydraulic press is 400-500MPa. The pressure is gradually increased to 400-500MPa at a loading condition of 50-100 MPa / min. After all the powder is spread, the preset pressure is maintained for 10-40 minutes. Then, the pressure is gradually reduced at a unloading condition of 100-200 MPa / min to complete the pressing and molding of the powder mixture.

8. The method for preparing a layered gradient structure h-BN / Ti composite material according to claim 3, characterized in that: The specific operation of rapid hot pressing sintering in step (3) is as follows: The cold-pressed compact is transferred to a graphite mold lined with carbon paper. The graphite mold is then placed in a rapid hot pressing sintering furnace with an initial vacuum of ≤5 Pa and a heating rate of 80-100 ℃ / min. When the temperature reaches 800-1000 ℃, it is held for 10-15 min. After that, the compact is cooled in the furnace to complete the rapid hot pressing sintering.

9. The method for preparing a layered gradient structure h-BN / Ti composite material according to claim 3, characterized in that: The specific steps of high-temperature rolling hot deformation described in step (4) are as follows: The sintered composite material preform was placed in a muffle furnace at 900-1000 ℃ and held for 10-15 min, followed by rolling. The circumferential speed of the upper and lower rolls of the hot rolling mill was set to 60 mm / s. The rolling process was carried out in 6 passes, with a deformation of 5-10% per pass. The initial rolling temperature was 900-1000 ℃. After each pass, the preform was returned to the furnace for 2-3 min, and finally, the layered gradient structure h-BN / Ti composite material was obtained.

10. The method for preparing a layered gradient structure h-BN / Ti composite material according to claim 3, characterized in that: The drying temperature in step (1) is 60-80℃ and the time is 3-4 h; the sintering temperature in step (3) is 850-950℃ and the time is 12-14 h.

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