An ultrahigh-strength gradient structure Ni-Ti-based composite material and a preparation method thereof

Abstract

The application relates to the technical field of metal matrix composite material preparation, in particular to a super-high-strength gradient structure Ni-Ti-based composite material and a preparation method thereof, the Ni-Ti-based composite material has a three-dimensional gradient structure; the preparation method comprises the following steps: S1, preparing Ni-Ti pre-alloyed powder; S2, mixing the Ni-Ti pre-alloyed powder with TiB2 ceramic particles; S3, hot-pressing sintering; and S4, performing thermal mechanical treatment on the Ni-Ti-based memory alloy composite material. The novel Ni-Ti-based shape memory alloy composite material is prepared by the method combining low-energy ball milling, hot-pressing sintering and thermal mechanical treatment, has super-high strength and excellent shape memory performance, does not need high-precision additive manufacturing equipment, has simple preparation process and relatively low cost; meanwhile, the method can be used for preparing large-size material, and hundreds of kilograms of Ni-Ti-based composite material filaments can be prepared at one time, and the manufacturing efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of metal matrix composite material preparation technology, and in particular to an ultra-high strength gradient structure Ni-Ti matrix composite material and its preparation method. Background Technology

[0002] Ni-Ti based shape memory alloys can recover their original shape after undergoing large-scale deformation under external forces. Devices developed based on their unique shape memory properties are now widely used in aerospace, marine, and biomedical fields. Recently, NASA and Goodyear Tire Company jointly developed a new type of metal chain tire woven from Ni-Ti based shape memory alloy wires. Shape memory alloy tires can withstand greater deformation than traditional tires, can cross obstacles such as rocks without damage, and achieve vibration reduction through their unique shape memory properties, enabling them to operate in complex ground environments and bringing technological innovation to Mars rovers, off-road vehicles, and other applications. However, although shape memory alloys currently possess excellent shape memory properties, their yield strength and compressive strength are relatively low. The compressive strength of existing commercial shape memory alloys is less than 1 GPa, resulting in low load-bearing capacity for shape memory alloy tires, making them unsuitable for transporting heavy goods and severely limiting their widespread application.

[0003] Introducing multi-scale gradient structures into Ni-Ti based shape memory alloys can enhance the mechanical properties of materials while preserving their original functional characteristics, potentially achieving structure-function integration. Publicly available patents CN202110084484.2 and CN202110424695.6 utilize additive manufacturing technology to prepare gradient Ni-Ti based shape memory alloys. The internal gradient structure of the alloy is controllable, and the compressive strength can be increased to approximately 2 GPa, but this still falls short of the required material performance. Furthermore, the aforementioned patents use powders with a particle size of less than 20 μm, and the alloy forming process requires high-precision additive manufacturing equipment, resulting in high raw material and processing costs, posing a technological bottleneck for large-scale engineering applications.

[0004] Publication number CN108893638B discloses an in-situ self-generated TiC method. x -Ni3(Al,Ti) / Ni-based gradient composite material and its hot-pressing preparation method: The preparation method involves placing mixed powders of Ti3AlC2 and Ni-based alloys with different volume ratios layer by layer into a hot-pressing mold, using a high-temperature consolidation method to allow them to fully react and densify, and then cooling to obtain TiC2. x -Ni3(Al,Ti) / Ni-based gradient composite materials. However, this method uses high-purity powders of various volume contents to be spherically mixed and pre-pressed into shape, resulting in a long production cycle and high cost.

[0005] Therefore, there is an urgent need to develop novel ultra-high strength structure-function integrated shape memory alloys to address the insufficient mechanical properties, such as compressive strength, of existing Ni-Ti based shape memory alloys. Furthermore, the aforementioned methods for preparing gradient Ni-Ti based shape memory alloys are costly and difficult to efficiently fabricate large-scale samples; therefore, it is still necessary to explore a new, low-cost, and high-efficiency method for preparing ultra-high strength gradient structure Ni-Ti based alloys. Summary of the Invention

[0006] In view of this, the present invention aims to propose an ultra-high strength gradient structure Ni-Ti based composite material and its preparation method, so as to solve the problems of insufficient mechanical properties such as compressive strength of existing Ni-Ti based shape memory alloys and high preparation costs.

[0007] The technical solution of this invention is implemented as follows:

[0008] One objective of this invention is to disclose an ultra-high strength gradient structure Ni-Ti based composite material. The microstructure of this gradient structure Ni-Ti based composite material is characterized by: a ceramic reinforcing phase composed of micron-scale in-situ self-generated TiB and Ti2Ni phases; fine-grained Ni-Ti grains and coarse-grained Ni-Ti grains forming a multi-level gradient structure; wherein: the ceramic reinforcing phase composed of micron-scale in-situ self-generated TiB and Ti2Ni phases forms a three-dimensional grid structure, with fine-grained Ni-Ti grains at the grid's inner edges and coarse-grained Ni-Ti grains at the grid's center; the multi-level gradient structure includes introducing a first-level ceramic reinforcing phase heterostructure composed of micron-scale in-situ self-generated TiB and Ti2Ni phases into the Ni-Ti based composite material; a second-level fine-grained structure and a third-level coarse-grained structure are constructed sequentially from near to far in the proximal and distal regions of the TiB and Ti2Ni phases; in addition to the microstructure gradient, the material also contains a stress gradient where the local stress gradually decreases with increasing distance from the TiB and Ti2Ni phases.

[0009] Another objective of this invention discloses a method for preparing ultra-high strength gradient structure Ni-Ti based composite materials, which includes the following specific steps:

[0010] S1: Prepare Ni-Ti alloy powder; determine the matrix composition of Ni-Ti based composite material according to the service temperature of the material, prepare Ni-Ti alloy rods using a vacuum arc melting furnace, and then prepare Ni-Ti pre-alloyed powder by rotating electrode atomization method, and screen to obtain Ni-Ti pre-alloyed powder with a particle size of D.

[0011] S2: Mix Ni-Ti pre-alloyed powder with TiB2 ceramic particles; mix Ni-Ti alloyed powder with particle size D with TiB2 ceramic particles with particle size d less than 10um by low-energy ball milling. After ball milling, TiB2 ceramic particles are uniformly attached to the surface of Ni-Ti alloy powder, and Ni-Ti alloy powder still maintains complete sphericity.

[0012] S3: Hot pressing sintering; The uniformly mixed powder is loaded into a mold and placed in a hot pressing sintering furnace for reactive hot pressing sintering;

[0013] S4: Ni-Ti based shape memory alloy composite material is subjected to thermomechanical treatment to prepare Ni-Ti based composite material with a three-dimensional gradient structure. The material forms a fine-grained to coarse-grained gradient structure from near to far from TiB, and at the same time forms a stress gradient with gradually decreasing local stress.

[0014] Furthermore, in step S1, when the material operates at room temperature according to its service temperature, the Ni-Ti alloy composition is Ni. x Ti 100-x (at.%) (x = 50-51).

[0015] Furthermore, in step S1, the particle size D of the Ni-Ti pre-alloyed powder ranges from 20 to 300 μm.

[0016] Furthermore, in step S2, the particle size d of the TiB2 ceramic particles ranges from 0.5 to 3 μm.

[0017] Furthermore, in step S2, the ball milling process parameters are a ball milling speed of 100 rpm to 350 rpm and a ball milling time of 200 min to 400 min.

[0018] Furthermore, in step S3, a graphite mold is used, which is placed in a vacuum hot-pressing sintering furnace for reactive hot-pressing sintering. During the sintering process, the vacuum degree does not exceed 8 × 10⁻⁶. -2 Pa, the sintering process parameters are sintering temperature 1000℃~1200℃, sintering time 80min~130min.

[0019] Furthermore, in step S4, the thermomechanical treatment process parameters are a hot working temperature of 950℃~1200℃ and a hot working deformation of 25%~75%.

[0020] Furthermore, in step S4, the Ni-Ti based composite material obtained after sintering is coated with an anti-oxidation coating and then placed in a heat treatment furnace for heating.

[0021] Compared with existing technologies, the ultra-high strength gradient structure Ni-Ti based composite material and its preparation method of the present invention have the following advantages:

[0022] 1. This invention constructs a three-dimensional structural gradient and stress gradient in a Ni-Ti-based shape memory alloy matrix by combining low-energy ball milling, hot pressing sintering and thermomechanical treatment. By utilizing second-phase strengthening and back stress strengthening, the strength of the alloy is significantly improved while retaining the excellent functional properties of the shape memory alloy matrix. The new Ni-Ti-based composite material has a yield strength higher than 1.3 GPa, a compressive strength higher than 3.0 GPa, and an elongation higher than 20%, exhibiting excellent mechanical properties.

[0023] 2. The preparation method of this invention does not require high-precision additive manufacturing equipment, the preparation process is simple, and the cost is relatively low. At the same time, this method can prepare materials of large size, and hundreds of kilograms of Ni-Ti based composite material filaments can be prepared in one go. It has high manufacturing efficiency and has the advantages of low cost and high efficiency.

[0024] 3. Using the ultra-high strength gradient structure Ni-Ti based composite material and its preparation method described in this invention, a novel Ni-Ti based shape memory alloy composite material with both ultra-high strength and excellent shape memory properties can be prepared by combining low-energy ball milling, hot pressing sintering and thermomechanical treatment. This material can be used to develop new high load-bearing capacity shape memory alloy chain tires, bringing technological innovation to fields such as space exploration and transportation. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of the gradient structure of Ni-Ti based composite materials;

[0027] Figure 2 SEM image of Ni-Ti powder and TiB2 powder after low-energy ball milling;

[0028] Figure 3 SEM images and stress gradient distribution results of the Ni-Ti based composite material provided in Example 1;

[0029] Figure 4 The compressive stress-strain curve of the Ni-Ti based composite material provided in Example 1;

[0030] Figure 5 SEM images and stress gradient distribution results of the Ni-Ti based composite material provided in Example 2;

[0031] Figure 6 The compressive stress-strain curve of the Ni-Ti based composite material provided in Example 2.

[0032] Figure label:

[0033] 1. Ni-Ti coarse grain; 2. Ni-Ti fine grain; 3. TiB+Ti2Ni. Detailed Implementation

[0034] To make the technical means and objectives and effects of the present invention easier to understand, the embodiments of the present invention will be described in detail below with reference to specific illustrations.

[0035] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "lateral," "longitudinal," and "center," are only used to explain the relative positional relationships and connections between components in a specific state. They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0036] In the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] One objective of this invention is to disclose an ultra-high strength gradient structure Ni-Ti based composite material. The microstructure of this gradient structure Ni-Ti based composite material is characterized by: a ceramic reinforcing phase composed of micron-scale in-situ self-generated TiB and Ti2Ni phases; a multi-level gradient structure consisting of fine-grained and coarse-grained Ni-Ti grains; and a three-dimensional mesh structure formed by the micron-scale in-situ self-generated TiB and Ti2Ni phases, with fine-grained Ni-Ti grains at the mesh's edges and coarse-grained Ni-Ti grains at the mesh's center. A schematic diagram of the microstructure is shown below. Figure 1 .

[0039] This unique three-dimensional gradient structure can fully utilize the second-phase strengthening effect of the in-situ self-generated ceramic phase, and also induce back stress strengthening. It introduces geometrically necessary dislocations with gradient distribution during deformation, enabling the material to exhibit ultra-high strength and excellent plasticity.

[0040] This method only requires controlling the thermomechanical processing to form fine-grained Ni-Ti grains at the proximal and distal ends of the in-situ ceramic reinforcement, respectively. Other materials with similar gradient structures require additive manufacturing methods such as 3D printing. In comparison, the manufacturing scheme described in this patent does not require high-precision additive manufacturing equipment, has a simple manufacturing process, and is relatively low in cost; moreover, this method can produce large-size materials, producing hundreds of kilograms of Ni-Ti based composite filaments in a single process, resulting in high manufacturing efficiency.

[0041] Specifically, the multi-level gradient structure includes introducing a first-level ceramic reinforcing phase heterostructure composed of micron-scale in-situ self-generated TiB and Ti2Ni phases in the Ni-Ti based composite material; constructing a second-level fine-grained structure and a third-level coarse-grained structure in the near and far regions of the TiB and Ti2Ni phases respectively; in addition to the microstructure gradient, the material also contains a stress gradient in which the local stress gradually decreases as the distance from the TiB and Ti2Ni phases increases.

[0042] Due to the heterogeneous nucleation effect and stress concentration of TiB whiskers, the recrystallized grain size in the near-end region of TiB is small, forming a fine-grained region. As the distance from the TiB whiskers increases, the recrystallized grain size gradually increases, forming a coarse-grained region. In the gradient structure, the fine-grained region improves the strength and hardness of the material, while the coarse-grained region helps to improve the plasticity and toughness of the material. Furthermore, this gradient structure introduces geometrically required dislocations with a gradient distribution during deformation, generating a back stress strengthening effect. This combination makes the material exhibit superior mechanical properties and shape memory effect overall.

[0043] This gradient structure composite material has high mechanical properties, shape memory effect and thermal stability, and can be widely used in aerospace, biomedicine, mechanical engineering and other fields.

[0044] Another objective of this invention is to disclose a method for preparing ultra-high strength gradient structure Ni-Ti based composite materials, which is used to prepare any of the above-mentioned ultra-high strength gradient structure Ni-Ti based composite materials, comprising the following specific steps:

[0045] S1: Prepare Ni-Ti alloy powder; determine the matrix composition of Ni-Ti based composite material according to the service temperature of the material, prepare Ni-Ti alloy rods using a vacuum arc melting furnace, and then prepare Ni-Ti pre-alloyed powder by rotating electrode atomization method, and screen to obtain Ni-Ti pre-alloyed powder with a particle size of D.

[0046] S2: Mix Ni-Ti pre-alloyed powder with TiB2 ceramic particles; mix Ni-Ti alloyed powder with particle size D with TiB2 ceramic particles with particle size d less than 10um by low-energy ball milling. After ball milling, TiB2 ceramic particles are uniformly attached to the surface of Ni-Ti alloy powder, and Ni-Ti alloy powder still maintains complete sphericity.

[0047] S3: Hot pressing sintering; The uniformly mixed powder is loaded into a mold and placed in a hot pressing sintering furnace for reactive hot pressing sintering;

[0048] S4: Ni-Ti based shape memory alloy composite material is subjected to thermomechanical treatment to prepare Ni-Ti based composite material with a three-dimensional gradient structure. The material forms a fine-grained to coarse-grained gradient structure from near to far from TiB, and at the same time forms a stress gradient with gradually decreasing local stress.

[0049] S5: Material performance assessment and evaluation; The prepared gradient structure Ni-Ti based composite material has a yield strength higher than 1.3 GPa, a compressive strength higher than 3.0 GPa, and an elongation higher than 20%.

[0050] The matrix composition of the Ni-Ti based composite material was determined based on the material's service temperature. Pre-alloyed Ni-Ti powder with a set particle size was prepared using a vacuum arc melting furnace and rotating electrode physicochemical method, ensuring that the powder size, uniformity, and purity met the requirements. The Ni-Ti pre-alloyed powder was mixed with TiB2 ceramic particles using a low-energy grinding ball method. This ensured that the TiB2 ceramic particles were uniformly adhered to the surface of the Ni-Ti alloy powder during ball milling, while maintaining the complete sphericity of the Ni-Ti alloy powder, which is beneficial for densification during subsequent sintering. The uniformly mixed powder was then loaded into a mold and placed in a hot-pressing sintering furnace for reactive hot-pressing sintering. The high-temperature and high-pressure environment promoted the bonding between the powder particles. Densification: The Ni-Ti based shape memory alloy composite material undergoes thermomechanical treatment to regulate the three-dimensional spatial distribution of in-situ self-generated TiB whiskers within the alloy. Different recrystallization modes are activated in the near-end and far-end regions of TiB, resulting in a fine-grained to coarse-grained gradient structure from near to far from TiB. Simultaneously, a stress gradient is formed where the local stress gradually decreases with increasing distance from the TiB and Ti2Ni phases, ensuring the formation of the gradient structure and performance optimization. Ultimately, a Ni-Ti based composite material with a three-dimensional gradient structure is prepared. The material properties of the prepared gradient structure Ni-Ti based composite material are assessed and evaluated to ensure that the prepared material meets the process requirements and guarantees product quality.

[0051] This setup produces a novel Ni-Ti-based shape memory alloy composite material through a combination of low-energy ball milling, hot pressing sintering, and thermomechanical treatment. This material possesses ultra-high strength and excellent shape memory properties. It does not require high-precision additive manufacturing equipment, has a simple manufacturing process, and relatively low cost. Furthermore, this method can produce large-size materials, generating hundreds of kilograms of Ni-Ti-based composite filaments in a single process, resulting in high manufacturing efficiency.

[0052] Specifically, in step S1, when the material is operating at room temperature according to its service temperature, the Ni-Ti alloy composition is NixTi100-x (at.%) (x = 50~51).

[0053] Preferably, the Ni-Ti alloy composition is Ni 50 Ti 50 .

[0054] The NiTi alloy, which operates at room temperature, has a relatively stable microstructure, which is beneficial for maintaining the long-term performance and stability of the material. At the same time, when the atomic ratio is close to equiatomic, the NiTi alloy exhibits excellent shape memory effect and superelasticity. By precisely controlling the Ni and Ti content in the range of 50-51%, the mechanical properties of the alloy, such as strength, hardness and toughness, can be optimized to meet specific engineering needs.

[0055] This configuration makes nickel-titanium alloys easy to process into various shapes and sizes to meet different design and manufacturing needs. It also has excellent shape memory effect, superelasticity and stability, which can ensure the reliability of the material during long-term use. At the same time, the material has the advantages of wide application range, good biocompatibility and low cost.

[0056] Specifically, in step S1, the particle size D of the Ni-Ti pre-alloyed powder ranges from 20 to 300 μm.

[0057] By selecting the particle size D range of Ni-Ti pre-alloyed powder, the uniformity and flowability of mixing can be improved, making mixing easier and more effective. This helps to obtain a uniform and fine microstructure after sintering, thereby improving the mechanical properties of the material and enhancing the shape memory effect.

[0058] This setup can optimize key properties of Ni-Ti based composites, such as mechanical properties, thermal stability, and shape memory effect.

[0059] Preferably, the particle size D of the Ni-Ti pre-alloyed powder ranges from 50 to 200 μm.

[0060] By selecting the appropriate powder particle size range, this setting can achieve higher density and better performance, while reducing raw material waste and processing costs.

[0061] Specifically, in step S2, the particle size d of the TiB2 ceramic particles ranges from 0.5 to 3 μm.

[0062] Smaller-sized TiB2 ceramic particles can be more uniformly dispersed on the surface of Ni-Ti pre-alloyed powder. During hot pressing, the TiB2 particles undergo a thermodynamic reaction with the Ni-Ti pre-alloyed powder to form TiB. During thermomechanical processing, TiB provides localized stress that gradually decreases with increasing distance from the TiB, inducing more Ni-Ti grain nucleation sites in the vicinity of TiB and promoting the formation of fine-sized Ni-Ti recrystallized grains. In the region further away from TiB, there are relatively fewer Ni-Ti grain nucleation sites, allowing them to grow into larger Ni-Ti grains.

[0063] This design can effectively improve the mechanical properties of Ni-Ti based composites, such as yield strength, tensile strength, and hardness, and optimize the microstructure. It can prepare ultra-high strength gradient structure Ni-Ti based composites containing in-situ self-generated TiB phase and TiB2 phase, fine Ni-Ti grains, and coarse Ni-Ti grains in a low-cost and high-efficiency manner. This material can simultaneously exhibit excellent mechanical properties and shape memory properties, making it more suitable for applications requiring precise shape control and rapid effects.

[0064] Preferably, the particle size d of TiB2 ceramic particles is in the range of 1 to 2 μm.

[0065] Preferably, the TiB2 ceramic particles have a particle size d of 1.5 μm.

[0066] Setting the TiB2 ceramic particle size d helps it to be more uniformly dispersed in the Ni-Ti matrix, improving the strength and hardness of the composite material and helping to form finer recrystallized grains.

[0067] Specifically, in step S2, the ball milling process parameters are a ball milling speed of 100 rpm to 350 rpm and a ball milling time of 200 min to 400 min.

[0068] By setting reasonable milling speed and time, the ball milling process can avoid uneven powder mixing caused by excessively low milling speed or short milling time, and also avoid "cold welding" phenomenon, where powder clumps adhere to the milling balls and jar, caused by excessively high milling speed or long milling time. The appropriate milling speed and time can generate suitable impact force, thereby more effectively promoting the uniform adhesion of small-sized TiB2 ceramic particles to the surface of Ni-Ti alloy powder, while maintaining the ideal sphericity of the Ni-Ti alloy powder. The frequent collisions and friction between the milling media and powder particles promote the mixing between different components, which helps the TiB2 ceramic particles to be more uniformly dispersed in the matrix.

[0069] This configuration allows for the uniform distribution of TiB2 ceramic particles, which more effectively strengthens the Ni-Ti matrix, improves the strength, hardness, and wear resistance of the sintered composite material, optimizes the microstructure, and enhances overall performance.

[0070] Preferably, the ball milling process parameters are a ball milling speed of 150 rpm to 300 rpm and a ball milling time of 240 min to 360 min.

[0071] Setting the ball milling process parameters in this way can better promote the mixing of TiB2 ceramic particles and Ni-Ti alloy powder, while adhering the TiB2 ceramic particles to the surface of Ni-Ti alloy powder, such as... Figure 2 As shown, this lays the foundation for subsequent sintering and ensures the mechanical properties of the composite material.

[0072] Specifically, in step S3, a graphite mold is used, which is placed in a vacuum hot-pressing sintering furnace for reactive hot-pressing sintering. During the sintering process, the vacuum degree does not exceed 8 × 10⁻⁶. -2 Pa, the sintering process parameters are sintering temperature 1000℃~1200℃, sintering time 80min~130min.

[0073] Graphite molds have excellent high-temperature resistance, ensuring the smooth progress of the sintering process. They do not chemically react with the sintering material at high temperatures, maintaining the integrity and stability of the mold; they also shorten sintering time and improve sintering efficiency.

[0074] The vacuum degree during sintering should not exceed 8×10. -2 The Pa sintering environment can effectively prevent the material from oxidizing or undergoing other adverse chemical reactions at high temperatures, thereby ensuring the purity and quality of the sintered product. At the same time, it reduces the porosity and defects inside the material, promotes the densification process of the material, and further improves the density and mechanical properties of the sintered body. The phase transformation and chemical reaction rate inside the material can be controlled by sintering temperature and time, thereby obtaining sintered products with specific microstructures and properties.

[0075] This setup not only improves the quality and performance of sintered products, but also optimizes the microstructure, increases production efficiency, and reduces costs.

[0076] Preferably, the sintering process parameters are a sintering temperature of 1050℃~1150℃ and a sintering time of 90min~120min.

[0077] Setting the sintering process parameters in this way can produce sintered products with fine grains, uniform structure and good phase interface. These microstructural features help to improve the mechanical properties, thermal stability and corrosion resistance of the material.

[0078] Specifically, in step S4, the thermomechanical treatment process parameters are a hot working temperature of 950℃~1200℃ and a hot working deformation of 25%~75%.

[0079] Preferably, the thermomechanical treatment adopts a hot drawing process with process parameters of hot working temperature of 1000℃~1100℃ and hot working deformation of 30%~70%.

[0080] Hot drawing can control the three-dimensional spatial distribution and orientation of in-situ self-grown TiB whiskers in Ni-Ti based composites. Appropriately increasing the hot drawing deformation can adjust the orientation of TiB whiskers to be aligned along the hot drawing direction, resulting in a better mechanical property strengthening effect. However, the hot drawing deformation should not be too high to avoid material fracture and damage during the drawing process. In addition, the hot drawing process takes place in a high-temperature environment, which induces dynamic recrystallization of Ni-Ti grains. This patent designs the hot drawing temperature and combines it with the different local stresses in the near-end and far-end regions of TiB to make the Ni-Ti grains in the near-end and far-end regions of TiB recrystallize in different ways during the hot drawing process, thus preparing a gradient structure Ni-Ti based composite material with fine-sized Ni-Ti grains at the near end and coarse-sized Ni-Ti grains at the far end.

[0081] This hot-drawing process for nickel-titanium composites can significantly improve the mechanical properties of Ni-Ti based composites, reduce stress concentration and deformation resistance during the hot-drawing process, making it smoother and more efficient. While ensuring material performance, it reduces energy consumption during processing, increases the yield of materials in a single pass, and thus reduces production costs.

[0082] Specifically, in step S4, the Ni-Ti based composite material obtained after sintering is coated with an anti-oxidation coating and then placed in a heat treatment furnace for heating.

[0083] Anti-oxidation coatings can form a dense protective film at high temperatures, isolating oxygen in the air from direct contact with Ni-Ti based composite materials. This effectively prevents oxidation and burn-off of the material at high temperatures, maintains the performance stability of the material at high temperatures, and avoids performance degradation and shortened lifespan due to oxidation. To a certain extent, it also improves the surface quality of the material, making it smoother and more uniform, which is beneficial for subsequent processing and use.

[0084] This setup can significantly reduce the performance degradation and shortened lifespan of materials caused by high-temperature oxidation, thereby improving material lifespan and reliability, reducing material usage and maintenance costs, and enhancing the overall quality and competitiveness of the product.

[0085] Example 1:

[0086] (1) Using vacuum melting equipment, according to the alloy composition Ni 50 Ti 50 Ni-Ti rods with diameters of φ300–320 mm were prepared by (at.%). Ni was also prepared using a rotating electrode atomization method. 50 Ti 50 Pre-alloyed powder with a particle size range of 100–150 μm.

[0087] (2) Ni 50 Ti 50 Pre-alloyed powder and TiB2 ceramic particles with an average particle size of 2 μm were placed in a ball mill jar for low-energy ball milling at a speed of 150 rpm to 200 rpm for 240 min to 300 min. The resulting Ni... 50 Ti 50 Pre-alloyed powder and TiB2 ceramic particles, such as Figure 2 .

[0088] (3) Place the uniformly mixed powder into a graphite mold and transfer it to a vacuum sintering furnace for vacuum reaction hot pressing sintering. The sintering temperature is 1050℃~1100℃ and the sintering time is 90min~100min.

[0089] (4) After sintering, the Ni-Ti based composite material is coated with an anti-oxidation coating and placed in a heat treatment furnace. It is heated to 1000℃~1050℃ and held for 120min~180min before hot drawing. The hot drawing deformation is 50%.

[0090] (5) The Ni-Ti based composite material prepared in Example 1 was characterized by microstructure, and the SEM images are shown below. Figure 3 As shown in (a), three-dimensional in-situ self-generated TiB whiskers and Ti2Ni are distributed around the Ni-Ti alloy matrix. The Ni-Ti grains are finer and coarser in appearance, respectively, from the closest to the TiB. The stress distribution of the Ni-Ti based composite material is shown in Figure [image missing]. Figure 3 As shown in (b), the local stress gradually decreases from near to far from TiB, forming a three-dimensional stress gradient. The room temperature compressive stress-strain curve of the Ni-Ti based composite material prepared in Example 1 is shown below. Figure 4 As shown, the material has a yield strength (critical dislocation slip stress) of 1.33 GPa, a compressive strength of 3.18 GPa, and a fracture elongation of 23.7%.

[0091] Example 2:

[0092] (1) Using vacuum melting equipment, according to the alloy composition Ni 50 Ti 50 Ni-Ti rods with diameters of φ300–320 mm were prepared by (at.%). Ni was also prepared using a rotating electrode atomization method. 50 Ti 50 Pre-alloyed powder with a particle size range of 50–100 μm.

[0093] (2) Ni 50 Ti 50 The pre-alloyed powder and TiB2 ceramic particles with an average particle size of 1 μm were placed in a ball mill jar for low-energy ball milling at a speed of 200 rpm to 250 rpm for a time of 300 min to 360 min.

[0094] (3) Place the uniformly mixed powder into a graphite mold and transfer it to a vacuum sintering furnace for vacuum reaction hot pressing sintering. The sintering temperature is 1050℃~1100℃ and the sintering time is 110min~120min.

[0095] (4) After sintering, the Ni-Ti based composite material is coated with an anti-oxidation coating and placed in a heat treatment furnace. It is heated to 1000℃~1050℃ and held for 120min~180min before hot drawing. The hot drawing deformation is 30%.

[0096] (5) The Ni-Ti based composite material prepared in Example 2 was characterized by microstructure, and the SEM images are shown below. Figure 5 As shown in (a), three-dimensional in-situ self-generated TiB whiskers and Ti2Ni are distributed around the Ni-Ti alloy matrix. The Ni-Ti grains are finer and coarser in appearance, respectively, from the closest to the TiB. The stress distribution of the Ni-Ti based composite material is shown in Figure [image missing]. Figure 5 As shown in (b), the local stress gradually decreases from near to far from TiB, forming a three-dimensional stress gradient. The room temperature compressive stress-strain curve of the Ni-Ti based composite material prepared in Example 2 is shown below. Figure 6 As shown, the material has a yield strength (critical dislocation slip stress) of 1.34 GPa, a compressive strength of 3.23 GPa, and an elongation at break of 21.6%.

[0097] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Ni-Ti based composite material with an ultra-high strength gradient structure, characterized in that, Microstructural characteristics of gradient structure Ni-Ti based composites: The ceramic reinforcing phase consists of micron-scale in-situ self-generated TiB and Ti2Ni phases, with fine-grained Ni-Ti grains and coarse-grained Ni-Ti grains forming a multi-level gradient structure. Among them, the ceramic reinforcing phase composed of micron-scale in-situ self-generated TiB phase and Ti2Ni phase forms a three-dimensional grid structure, with fine-grained Ni-Ti grains at the inner edge of the grid and coarse-grained Ni-Ti grains at the center of the grid; The multi-level gradient structure includes the introduction of a first-level ceramic reinforcing phase heterostructure composed of micron-scale in-situ self-generated TiB and Ti2Ni phases into Ni-Ti based composite materials. The second-level fine-grained structure and the third-level coarse-grained structure are constructed sequentially from near to far in the near and far regions of the TiB and Ti2Ni phases. In addition to the microstructure gradient, the material also contains a stress gradient in which the local stress gradually decreases as the distance from the TiB and Ti2Ni phases increases. A method for preparing ultra-high strength gradient structure Ni-Ti based composite material, comprising the following specific steps: S1: Prepare Ni-Ti alloy powder; determine the matrix composition of the Ni-Ti based composite material based on the material's service temperature; the Ni-Ti alloy composition is Ni. x Ti 100-x Ni-Ti alloy rods were prepared using a vacuum arc melting furnace at.%, x=50~51, and then Ni-Ti pre-alloyed powder was prepared by rotating electrode atomization method. Ni-Ti pre-alloyed powder with a particle size of D was obtained by screening. S2: Mix Ni-Ti pre-alloyed powder with TiB2 ceramic particles; mix Ni-Ti alloyed powder with particle size D with TiB2 ceramic particles with particle size d less than 10μm by low-energy ball milling. After ball milling, TiB2 ceramic particles are uniformly attached to the surface of Ni-Ti alloy powder, and Ni-Ti alloy powder still maintains complete sphericity. S3: Hot pressing sintering; The uniformly mixed powder is loaded into a graphite mold and placed in a vacuum hot pressing sintering furnace for reactive hot pressing sintering. The vacuum degree during sintering is no greater than 8 × 10⁻⁶. -2 Pa, the sintering process parameters are sintering temperature 1000℃~1200℃, sintering time 80min~130min; S4: The Ni-Ti based shape memory alloy composite material is subjected to thermomechanical treatment. The thermomechanical treatment process parameters are hot working temperature of 950℃~1200℃ and hot working deformation of 25%~75%, to prepare Ni-Ti based composite material with a three-dimensional gradient structure. The material forms a fine-grained to coarse-grained gradient structure from near to far from TiB, and at the same time forms a stress gradient with gradually decreasing local stress.

2. The method for preparing ultra-high strength gradient structure Ni-Ti based composite material according to claim 1, characterized in that, In step S1, the particle size D of the Ni-Ti pre-alloyed powder ranges from 20 to 300 μm.

3. The method for preparing ultra-high strength gradient structure Ni-Ti based composite material according to claim 1, characterized in that, In step S2, the particle size d of the TiB2 ceramic particles ranges from 0.5 to 3 μm.

4. The method for preparing ultra-high strength gradient structure Ni-Ti based composite material according to claim 3, characterized in that, In step S2, the ball milling process parameters are a ball milling speed of 100 rpm to 350 rpm and a ball milling time of 200 min to 400 min.

5. The method for preparing ultra-high strength gradient structure Ni-Ti based composite material according to claim 1, characterized in that, In step S4, the Ni-Ti based composite material obtained after sintering is coated with an anti-oxidation coating and then placed in a heat treatment furnace for heating.

Images