Powder sintering preparation method of nickel-titanium-based composite material and nickel-titanium-based composite material

Abstract

The invention discloses a powder sintering preparation method of a nickel-titanium-based composite material and the nickel-titanium-based composite material, and belongs to the technical field of powder metallurgy and composite materials. The method comprises the following steps: taking metal nickel and titanium as raw materials, and carrying out induction melting and vacuum atomization to obtain nickel-titanium atomized powder; mixing the nickel-titanium particles with nanoscale reinforced phase powder, and performing low-energy ball milling to obtain composite powder with the reinforced phase coated on the surfaces of the nickel-titanium particles; and carrying out spark plasma sintering, and carrying out sintering molding under the conditions of high vacuum, specific pressure, specific temperature and pulse current to obtain the nickel-titanium-based composite material. According to the composite material, a reinforcing phase in network distribution is generated in situ at the grain boundary, the composite material has the R martensite phase transformation characteristic and linear hyperelasticity, the hyperelasticity curve is stable after ten thousands of loading and unloading cycles, the residual strain is zero, the compression breaking strength is higher than 2500 MPa, and the hardness is remarkably improved. The method is simple in process, high in controllability and suitable for large-scale preparation of the high-hardness and high-cycle-stability nickel-titanium-based composite material.

Description

Technical Field

[0001] This invention relates to the technical fields of powder sintering methods and composite materials, and more specifically, to a powder sintering preparation method for nickel-titanium-based composite materials and the nickel-titanium-based composite materials themselves. Background Technology

[0002] To improve mechanical and machinability, it is also necessary to increase the hardness of NiTi alloys. This is because NiTi alloys are subjected to dynamic loads or friction environments in medical applications such as vascular stents and orthopedic implants, and their performance may decline due to surface wear. Increasing hardness can reduce wear and extend device life. High hardness is usually accompanied by higher yield strength and resistance to plastic deformation, which is crucial for applications that need to withstand high loads, such as aerospace fasteners and robot actuators. NiTi alloys are prone to tool sticking and work hardening during machining. Increasing hardness can improve machinability and facilitate subsequent surface treatment. In recent years, researchers have further improved mechanical properties and hardness by adding reinforcing phases to NiTi alloys to form metal matrix composites. These reinforcing phases are usually ceramic materials with high elastic modulus, high strength, and high stiffness. Adding Al2O3 particles of different sizes to Ni-Ti powder, the Al2O3 particles are dispersed in the composite material. The finer the added Al2O3 particles, the higher the hardness of the composite material, which can reach up to 636 HV (Metals and Materials International, 30(4) (2024) 843-856). NiTi / SiC alloys were prepared by sintering mixed Ni, Ti, and SiC powders. SiC nanoparticles were dispersed in the substrate, forming multiple second-phase particles (Ni4Ti3, Ni2Ti, Ni3Ti). The dispersed SiC nanoparticles and the second-phase particles worked together to significantly strengthen the alloy matrix and improve the substrate strength (Materials Letters, 100 (2013) 74-77). NiTi-Ni3Ti / SiC nanocomposites were prepared by mechanical alloying and microwave-assisted sintering. The dispersed SiC particles increased the amount of Ni3Ti hard phase, improving the hardness of the composite material (Ceramics International, 49(14) (2023)23358-23366). The mechanism by which the NiTi composites prepared by the above methods improve hardness is that the ceramic material is dispersed in the substrate, promoting the formation of the second phase and refining the grains. However, the ceramic particles do not react with NiTi to form new compounds. At the same time, although the distribution of ceramic particles in the substrate effectively improves the hardness, the superelastic cycling stability is not considered.

[0003] The superelasticity of NiTi alloys has been utilized in robotics, aerospace, medical, and mechanical fields. However, NiTi requires mechanical cycling to stabilize its microstructure and exhibits limited fatigue life and cyclic stability. To accelerate the aging process and improve cyclic stability, researchers have explored several methods to strengthen NiTi alloys and reduce defect accumulation, including forming coherent or semi-coherent precipitates, increasing geometric compatibility by adding a third element, and refining grains to improve material strength. However, these methods struggle to achieve uniform stability and may even alter the properties of NiTi. For example, adding Cu to NiTi improves lattice compatibility, leading to the preparation of thin film materials with reduced hysteresis and cyclic stability (Science, 348 (2015) 1004-1007). However, thin film preparation techniques are difficult and costly. Prolonged low-temperature aging of NiTi alloys can lead to the formation of Ni4Ti3 semi-coherent precipitation. However, excessively long aging times can cause overgrowth of Ni4Ti3 precipitates, resulting in coarse grains and reduced functional stability of the NiTi alloy. Furthermore, a certain degree of metal oxidation is unavoidable during prolonged processing (Materials Characterization 172 (2021) 110832). Therefore, there is a need to find a simple and feasible nickel-titanium-based composite material that can achieve high hardness and high cycle stability to meet application requirements. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides a powder sintering preparation method for nickel-titanium based composite materials, the powder sintering preparation method specifically including the following steps: Step S1: Using metallic nickel and metallic titanium as raw materials, induction melting and vacuum atomization are carried out sequentially to obtain nickel-titanium atomized powder; Step S2: After mixing the nickel-titanium atomized powder and the reinforcing phase powder, the mixture is subjected to low-energy ball milling in an inert atmosphere to obtain the mixed powder; Step S3: Under high vacuum conditions, the mixed powder obtained in step S2 is sintered using a spark plasma sintering method to obtain a nickel-titanium-based composite material.

[0005] Compared with the prior art, the present invention uses the above method to generate a grain boundary reinforcing phase in situ at the grain boundary, and the reinforcing phase has a network structure. The resulting composite material has high hardness, low hysteresis, R-martensitic phase transformation and high cycle stability. In particular, the mixed powder obtained in step S2 has the reinforcing phase powder uniformly coated around the nickel-titanium powder. This coating structure is the key to finally obtaining a uniform network reinforcing phase structure.

[0006] In one possible implementation, in step S1, the atomic ratio of metallic nickel to metallic titanium is (40-60):(60-40).

[0007] In one possible implementation, the mass percentage of nickel-titanium atomized powder with a particle size ≤15μm obtained in step S1 is ≥50%. Small-sized nickel-titanium powder is the raw powder required for composite materials, with a fast solidification rate and finer grains.

[0008] In one possible implementation, in step S2, the particle size of the nickel-titanium atomizing powder is ≤15 μm, and the particle size of the reinforcing phase powder is ≤50 nm.

[0009] Compared with the prior art, the present invention uses nickel-titanium powder with a small particle size of ≤15μm, which has a large specific surface area and is more likely to form a good interface with the reinforcing phase during ball milling. The reinforcing interface has a stronger ability to bond with the nickel-titanium powder. At the same time, the present invention uses nanoscale reinforcing phase powder of ≤50 nm, which is more likely to fully fill the gaps between nickel-titanium particles, resulting in more uniform mixing and helping to maintain the integrity of its structure and reinforcing function.

[0010] In one possible implementation, in step S2, the reinforcing phase powder is selected from one of silicon carbide, boron nitride, scandium oxide, zinc oxide, and carbon powder, and the reinforcing phase powder accounts for 0.1-10 vol of the nickel-titanium atomizing powder by volume percentage.

[0011] Compared with existing technologies, the reinforcing phase powder composition selected in this invention is more likely to form a hard alloy phase with nickel-titanium powder. When the reinforcing phase powder content is less than 0.1 vol%, the amount of reinforcing phase generated is small, and it is not easy to form a network structure. When the reinforcing phase powder content is higher than 10 vol%, non-reinforcing phases are easily generated at grain boundaries, which reduces performance.

[0012] In one possible implementation, in step S2, the nickel-titanium atomized powder and the reinforcing phase powder are mixed in a powder mixer and then subjected to low-energy ball milling in a nitrogen / argon atmosphere; wherein the mixing time is ≥2 h and the low-energy ball milling time is 5-12 h.

[0013] Compared with the prior art, the ball milling time used in this invention can fully disperse and closely contact the matrix powder and the reinforcing phase, while avoiding deformation of nickel-titanium particles, excessive accumulation of lattice defects and deep alloying. This is beneficial to maintaining the phase transformation characteristics of nickel-titanium powder and realizing a composite powder structure in which the reinforcing phase is coated on nickel-titanium particles.

[0014] In one possible implementation, the parameters of the spark plasma sintering method in step S3 are as follows: vacuum degree is 10. -4 -10 -3 Pa, sintering pressure is 40-60 MPa, heating rate is 50-100 ℃ / min, and sintering temperature is 1000-1200 ℃.

[0015] Compared with existing technologies, this invention employs optimized sintering pressure to effectively improve powder contact strength and diffusion rate, resulting in high density and fine-grained microstructure, improved interfacial bonding and mechanical properties, while reducing sintering conditions and improving processing quality, demonstrating significant energy-saving and engineering advantages. By optimizing the heating rate and the discharge plasma sintering temperature and time, high densification can be achieved rapidly while effectively suppressing grain coarsening and excessive reaction of the reinforcing phase, significantly improving the microstructure stability and overall performance of the composite material, while reducing energy consumption and production cycle.

[0016] In one possible implementation, the parameters for sintering in step S3 are as follows: pulse current of 2-80 ms and sintering time of 5-15 min.

[0017] Compared with existing technologies, this invention optimizes the pulse parameters of spark plasma sintering, enabling the composite powder particles to rapidly melt and react at the particle boundaries to generate a reinforcing phase under rapid heating and intermittent cooling modes. Indirect cooling also hinders the deep diffusion of the reinforcing phase, thereby obtaining a composite material with high density, uniform structure, strong interfacial bonding, and excellent performance, and also has significant energy-saving and consumption-reducing effects.

[0018] In one possible implementation, when the reinforcing phase powder in step S2 is silicon carbide, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ti. w Ni x Si y C z The atomic percentage ranges from 25%. w 31,34 x 40,11 y 13,11 z 13; When the reinforcing phase powder in step S2 is boron nitride, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ti. x N y B z The atomic percentage ranges are 50≤x≤52, 48≤y≤50, and 0≤z≤2. When the reinforcing phase powder in step S2 is scandium oxide, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ti. x Sc y O z The atomic percentage ranges from 21%. x 26,13 y 15,62 z 64; When the reinforcing phase powder in step S2 is zinc oxide, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ni. w Ti x Zn y O z The atomic percentage ranges from 0. w 9,0 x 29,14 y 20, 55 z 60; When the reinforcing phase powder in step S2 is carbon powder, the grain boundary reinforcing phase in the nickel-titanium based composite material obtained in step S3 is TiC.

[0019] Compared with existing technologies, this invention, by selecting specific reinforcing phase powders, can form grain boundary reinforcing phases with different characteristics in situ during sintering, thereby specifically improving the overall performance of the composite material. Specifically: when the reinforcing phase powder is silicon carbide, the generated reinforcing phase forms a semi-coherent interface with the substrate phase, which helps to reduce the hysteresis area of ​​the stress-strain curve and increase the material hardness; when the reinforcing phase powder is boron nitride, the in-situ generated Ti... x N y B z The compound possesses both high hardness and relatively high fracture toughness; when the reinforcing phase powder is scandium oxide, the resulting Ti... x Sc y O z The compound exhibits high hardness and excellent resistance to acid and alkali corrosion; when the reinforcing phase powder is zinc oxide, the obtained Ni... w Ti x Zn y O z The compound has a significantly higher hardness than the nickel-titanium matrix; when the reinforcing phase powder is carbon powder, the TiC phase can be directly generated at a relatively lower sintering temperature and a shorter sintering time.

[0020] A second objective of this invention is to provide a nickel-titanium-based composite material prepared by a powder sintering method, wherein a reinforcing phase is generated in situ at the grain boundaries, and the reinforcing phase exhibits a network structure. The uniform network structure provides abundant nucleation sites, promoting rapid dissipation of residual strain, which is a key structure for improving hardness, enhancing mechanical properties, and achieving superelastic cyclic stability.

[0021] More specifically, the nickel-titanium-based composite material exhibits an R-martensitic phase transformation, possesses linear superelasticity at room temperature, and maintains a stable stress-strain curve after more than ten thousand loading and unloading cycles, with a hysteresis area of ​​less than 1 MJ / m². 3 Its compressive strength is higher than 2500 MPa.

[0022] Compared with the prior art, the present invention has the following advantages: Firstly, this invention mixes nickel-titanium micron-sized atomized powder with reinforcing phase nanopowder and performs low-energy ball milling. The energy consumption of the low-energy ball milling process is significantly lower than that of traditional high-energy ball milling, which is less likely to cause excessive cold welding or structural breakage of the material, thus reducing processing energy consumption and conforming to the concept of green preparation. At the same time, while maintaining the spherical shape of the powder, the reinforcing phase powder is uniformly coated on the surface of the nickel-titanium particles to form a uniform composite powder, which effectively improves the performance stability of the composite material.

[0023] Secondly, the reinforcing phase powder consists of silicon carbide, boron nitride, scandium oxide, zinc oxide, and carbon powder. The selected reinforcing phase powder composition is more likely to form a hard alloy phase with nickel-titanium powder.

[0024] Thirdly, compared to traditional powder metallurgy (such as hot pressing and hot isostatic pressing), spark plasma sintering technology employs rapid heating and short-term holding, enabling high-density molding at lower temperatures, avoiding abnormal grain growth, and significantly improving the microstructure and porosity. The discharge pulse effect of spark plasma sintering promotes interfacial diffusion and in-situ reactions; depending on the type of reinforcing powder used, a reinforcing phase is generated in-situ, exhibiting high hardness and strength, with some reinforcing phases also possessing high toughness and corrosion resistance. Simultaneously, the strong interfacial bonding between the reinforcing phase and the substrate phase results in superior mechanical and functional properties; the high-speed densification process also effectively inhibits the decomposition, oxidation, or volatilization of heat-sensitive materials during sintering, maintaining the original phase composition of the substrate functional phase.

[0025] Fourth, the generated reinforcing phase exhibits a network structure. The uniform network structure provides abundant nucleation sites, promoting the rapid dissipation of residual strain, which is a key structure for improving hardness, mechanical properties, and achieving hyperelastic cyclic stability. Attached Figure Description

[0026] Figure 1 This is a microstructure diagram of the SiC / NiTi nickel-titanium-based composite powder prepared in Example 1 of the present invention; Figure 2 This is a microstructure diagram of the 3 vol%-10 vol% SiC / NiTi nickel-titanium composite material prepared in Example 1 of the present invention; Figure 3 The Vickers hardness diagram of the 3 vol%-10 vol% SiC / NiTi nickel-titanium composite material prepared in Example 1 of this invention; Figure 4This is a compression fracture curve of the 0 vol%-10 vol% SiC / NiTi nickel-titanium composite material prepared in Example 1 of the present invention. Figure 5 The 3 vol% SiC / NiTi nickel-titanium based composite material prepared in Example 1 of this invention is 10 4 Sub-hyperelastic cycle curve; Figure 6 The phase transition curves of the 0 vol%-10 vol% SiC / NiTi nickel-titanium composite material prepared in Example 1 of this invention are shown. Figure 7 This is a microstructure diagram of the BN / NiTi nickel-titanium-based composite powder prepared in Example 2 of the present invention; Figure 8 This is a microstructure diagram of the 1 vol%-5 vol% BN / NiTi nickel-titanium composite material prepared in Example 2 of the present invention; Figure 9 Vickers hardness diagram of the 1 vol%-5 vol% BN / NiTi nickel-titanium composite material prepared in Example 2 of the present invention; Figure 10 The image shows the compression fracture curve of the 0 vol%-5 vol% BN / NiTi nickel-titanium composite material prepared in Example 2 of this invention. Figure 11 The 1 vol% BN / NiTi nickel-titanium based composite material prepared in Example 2 of this invention is 10 4 Sub-hyperelastic cycle curve; Figure 12 The phase transition curve of the 0 vol%-5 vol% BN / NiTi nickel-titanium composite material prepared in Example 2 of this invention is shown. Figure 13 The image shows the microstructure analysis results of the 0.5 vol% C / NiTi nickel-titanium composite material prepared in Example 3 of this invention. Figure 14 The 0.5 vol% C / NiTi nickel-titanium based composite material prepared in Example 3 of this invention is 10 4 Sub-hyperelastic cycle curve; Figure 15 The tensile fracture strength diagram of the 0 vol%-1 vol% C / NiTi nickel-titanium matrix composite material prepared in Example 3 of the present invention is shown. Figure 16 This is a microstructure diagram of the Sc2O3 / NiTi nickel-titanium-based composite powder prepared in Example 4 of the present invention; Figure 17 The 0.5 vol% Sc2O3 / NiTi nickel-titanium based composite material prepared in Example 4 of this invention is 10 4 Sub-hyperelastic cycle curve; Figure 18 The 1 vol% ZnO / NiTi nickel-titanium based composite material prepared in Example 5 of this invention is 10 4 Hyperelastic cycle curve. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0028] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0030] Example 1 This embodiment provides a SiC / NiTi nickel-titanium based composite material, which is prepared by the following powder sintering method: S1. Using nickel and titanium, both with a purity of 99.99%, as raw materials, according to the atomic ratio Ni 50 Ti 50 Induction melting and vacuum atomization were performed to obtain nickel-titanium atomized powder, and powder with a particle size ≤15 μm was selected for use. S2. The nickel-titanium powder with a particle size ≤15 μm and silicon carbide powder with a particle size ≤50 nm were mixed at a volume ratio of 3 vol%, 5 vol%, and 10 vol%, respectively, and then mixed in a powder mixer for 5 h. Subsequently, the mixed powders were transferred to a stainless steel ball mill jar in a nitrogen atmosphere glove box, with a ball-to-powder ratio of 5:1. Large, medium, and small stainless steel balls were added at a mass ratio of 1:3:1, and alcohol equivalent to the total volume of powder and balls was added as a process control agent. The ball mill jar was placed in a planetary ball mill and ball milled at a speed of 200 r / min with a 5-minute interval every 30 min. The ball milling times for the mixed powders of 3 vol%, 5 vol%, and 10 vol% SiC were 5 h, 9 h, and 12 h, respectively. S3. The three different SiC volume ratio mixed powders obtained in step S2 are respectively loaded into graphite molds and placed in a spark plasma sintering furnace; vacuum is then applied to 10... -4 The SiC / NiTi nickel-titanium based composite material was obtained by discharge plasma sintering under the following conditions: sintering pressures of 40 MPa, 50 MPa and 60 MPa, sintering temperatures of 1000℃, 1100℃ and 1200℃, heating rate of 100℃ / min, sintering time of 5min, 10min and 15min, and pulse current width of 80 ms.

[0031] Example 2 This embodiment provides a BN / NiTi nickel-titanium based composite material, which is prepared by the following powder sintering method: S1. Using nickel and titanium, both with a purity of 99.99%, as raw materials, according to the atomic ratio Ni 50 Ti 50 Induction melting and vacuum atomization were performed to obtain nickel-titanium atomized powder, and powder with a particle size ≤15 μm was selected for use. S2. The nickel-titanium powder with a particle size ≤15 μm and boron nitride powder with a particle size ≤50 nm were mixed at a volume ratio of 1 vol%, 3 vol%, and 5 vol%, respectively, and placed in a powder mixer for 3 h. Then, the mixed powders were transferred to a stainless steel ball mill jar in a nitrogen atmosphere glove box, with a ball-to-powder ratio of 5:1. Large, medium, and small stainless steel balls were added at a mass ratio of 1:3:1, and alcohol equivalent to the total volume of powder and balls was added as a process control agent. The ball mill jar was placed in a planetary ball mill and ball milled at a speed of 200 r / min. After every 30 min of operation, there was a 5 min interval. The ball milling times for the mixed powders of 1 vol%, 3 vol%, and 5 vol% BN were 5 h, 7 h, and 9 h, respectively. S3. The three mixed powders with different BN volume ratios obtained in step S2 are respectively loaded into graphite molds and placed in a spark plasma sintering furnace; vacuum is then applied to 10... -4 The BN / NiTi nickel-titanium composite material was obtained by discharge plasma sintering under the following conditions: sintering pressures of 40 MPa, 50 MPa and 60 MPa, sintering temperatures of 1000℃, 1100℃ and 1200℃, heating rate of 100℃ / min, sintering time of 5min, 10min and 15min, and pulse current width of 2 ms.

[0032] Example 3 This embodiment provides a C / NiTi nickel-titanium based composite material, which is prepared by the following powder sintering method: S1. Using nickel and titanium, both with a purity of 99.99%, as raw materials, according to the atomic ratio Ni 50 Ti 50 Induction melting and vacuum atomization were performed to obtain nickel-titanium atomized powder, and powder with a particle size ≤15 μm was selected for use. S2. The nickel-titanium powder with a particle size ≤15 μm and carbon powder with a particle size ≤50 nm were mixed at a volume ratio of 0.5 vol% and 1 vol%, respectively, and placed in a powder mixer for 2 h. Then, the mixed powders were transferred to a stainless steel ball mill jar in a nitrogen atmosphere glove box. The ball-to-powder ratio was set to 5:1. Large, medium and small stainless steel balls were added at a mass ratio of 1:3:1. At the same time, alcohol equivalent to the total volume of powder and balls was added as a process control agent. The ball mill jar was placed in a planetary ball mill and ball milled at a speed of 200 r / min. The milling time was 5 h and 6 h for the mixed powders with a particle size ≤15 μm and a particle size ≤50 nm, respectively. S3. The mixed powders with two different carbon powder volume ratios obtained in step S2 are respectively loaded into graphite molds and placed in a spark plasma sintering furnace; vacuum is applied to 1.0 × 10⁻⁶. -4 C / NiTi nickel-titanium based composite material was obtained by discharge plasma sintering under the conditions of sintering pressure of 40 MPa and 50 MPa, sintering temperature of 1000℃, heating rate of 100 ℃ / min, sintering time of 15 min, and pulse current width of 80 ms.

[0033] Example 4 This embodiment provides a Sc2O3 / NiTi nickel-titanium based composite material, which is prepared by the following powder sintering method: S1. Using nickel and titanium, both with a purity of 99.99%, as raw materials, according to the atomic ratio Ni 50 Ti 50Induction melting and vacuum atomization were performed to obtain nickel-titanium atomized powder, and powder with a particle size ≤15 μm was selected for use. S2. The above-mentioned nickel-titanium powder with a particle size ≤15 μm and scandium oxide powder with a particle size ≤50 nm are mixed at a volume ratio of 0.5 vol% and placed in a powder mixer for 2 h. Then, the mixed powder is transferred to a stainless steel ball mill jar in an argon atmosphere glove box. The ball-to-powder ratio is set to 5:1. Large, medium and small stainless steel balls are added at a mass ratio of 1:3:1. At the same time, alcohol equivalent to the total volume of powder and balls is added as a process control agent. The ball mill jar is placed in a planetary ball mill and ball milled at a speed of 200 r / min. The milling is paused for 5 min every 30 min, and the total ball milling time is 5 h. S3. The mixed powder obtained in step S2 is loaded into a graphite mold and placed in a spark plasma sintering furnace; a vacuum of 1.0 × 10⁻⁶ is applied. -4 Scandium oxide-reinforced nickel-titanium composite material was obtained by discharge plasma sintering under the conditions of sintering pressure of 40 MPa, sintering temperature of 1100 ℃, heating rate of 100 ℃ / min, sintering time of 10 min, and pulse current width of 2 ms.

[0034] Example 5 This embodiment provides a ZnO / NiTi nickel-titanium based composite material, which is prepared by the following powder sintering method: S1. Mix metallic nickel (99.99% purity) and metallic titanium (99.99% purity) according to the atomic ratio Ni 50 Ti 50 The proportions were induction melted and vacuum atomized to obtain nickel-titanium atomized powder, and powder with a particle size of 0-15μm was screened out. S2. Nickel-titanium powder with a particle size of 0-15μm and 1vol% ZnO with a particle size of 0-50nm were mixed in a powder mixer for 2 hours. The mixed powder was then placed in a stainless steel ball mill jar in an argon-atmosphere glove box with a ball-to-powder ratio of 5:1. Three different sizes of stainless steel balls were selected, with a mass ratio of large, medium and small balls of 1:3:1. Alcohol was added, with the amount of alcohol being equal to that of the powder and stainless steel balls. The ball mill jar was then placed in a planetary ball mill at a speed of 200r / min, with a 5-min pause after every 30 minutes of rotation. The ball milling time for the mixed powder was 6 hours. S3. Place the ZnO / NiTi nickel-titanium composite material obtained in step S2 into a graphite mold, and evacuate the spark plasma sintering furnace to 10°C. -4 Pa was subjected to discharge plasma sintering at a sintering pressure of 40 MPa, a sintering temperature of 1000 °C, a heating rate of 100 °C / min, a sintering time of 15 min, and pulse parameters of 80 ms and 2 ms.

[0035] The inventors conducted performance tests on the nickel-titanium-based composite materials obtained in Examples 1-5, and the test results are as follows: Figures 1-18 As shown, where Figure 1 This is a microstructure diagram of the SiC / NiTi nickel-titanium-based composite powder prepared in Example 1 of the present invention. The nickel-titanium powder maintains a spherical shape, and the SiC particles are uniformly coated on the surface of the NiTi particles. Figure 2 This is a microstructure diagram of the 3 vol%-10 vol% SiC / NiTi nickel-titanium matrix composite material prepared in Example 1 of this invention. Ti and Si elements are enriched at grain boundaries to form a second phase, producing a mesh-like structure coating the surface of the NiTi matrix. The second phase is Ti. w Ni x Si y C z The atomic percentage ranges from 25%. w 31,34 x 40,11 y 13,11 z 13; Figure 3 The image shows the Vickers hardness diagram of the 3vol%-10vol% SiC / NiTi nickel-titanium composite material prepared in Example 1 of this invention. As the SiC content increases, the hardness increases from 250 HV1 to 730 HV1. Figure 4 The image shows the compression fracture curve of the 0 vol%-10 vol% SiC / NiTi nickel-titanium composite material prepared in Example 1 of this invention. As the SiC content increases, the fracture strength increases from 2510 MPa to 2873 MPa. Figure 5 The 3 vol% SiC / NiTi nickel-titanium based composite material prepared in Example 1 of this invention is 10 4 The hyperelastic cyclic curve shows that as the number of cycles increases, the residual strain decreases to zero, and the hysteresis area decreases to 0.6 MJ / m. 3 ; Figure 6 The phase transformation curve of the 0 vol%-10 vol% SiC / NiTi nickel-titanium composite material prepared in Example 1 of the present invention shows that the heating and cooling hysteresis in the ρ-T curve is very small or almost non-existent, indicating that the B2→R phase transformation has occurred. Figure 7 This is a microstructure diagram of the BN / NiTi nickel-titanium-based composite powder prepared in Example 2 of the present invention. The nickel-titanium powder maintains a spherical shape, and the BN particles are uniformly distributed on the surface of the NiTi particles. Figure 8This is a microstructure diagram of the 1 vol%-5 vol% BN / NiTi nickel-titanium based composite material prepared in Example 2 of the present invention. Hard phases TiN and Ti are formed at the grain boundaries. x N y B z The atomic percentage range of the phase is 50≤x≤52, 48≤y≤50, 0≤z≤2. The hard phase uniformly coats the nickel-titanium phase to form a network structure.

[0036] Figure 9 The Vickers hardness diagram of the 1 vol%-5 vol% BN / NiTi nickel-titanium composite material prepared in Example 2 of the present invention shows that the hardness increases from 250 HV1 to 580 HV1 as the BN content increases. Figure 10 The compression fracture curve of the 0 vol%-5 vol% BN / NiTi nickel-titanium composite material prepared in Example 2 of the present invention has a fracture strength higher than 2500 MPa; Figure 11 The 1 vol% BN / NiTi nickel-titanium based composite material prepared in Example 2 of this invention is 10 4 The sub-hyperelastic cycle curve shows stable linear hyperelasticity with a hysteresis area of ​​0.8 MJ / m². 3 ; Figure 12 The phase transformation curve of the 0 vol%-5 vol% BN / NiTi nickel-titanium composite material prepared in Example 2 of the present invention shows that the heating and cooling hysteresis in the ρ-T curve is very small or almost non-existent, indicating that the B2→R phase transformation has occurred. Figure 13 The image shows the microstructure of the 0.5 vol% C / NiTi nickel-titanium composite material prepared in Example 3 of this invention. The TiC phase is generated in situ at the grain boundaries and has a network structure.

[0037] Figure 14 The 0.5 vol% C / NiTi nickel-titanium based composite material prepared in Example 3 of this invention is 10 4 The sub-hyperelastic cyclic curve shows stable linear hyperelasticity with a hysteresis area of ​​0.7 MJ / m². 3 ; Figure 15 The tensile fracture strength diagram of the 0 vol%-1 vol% C / NiTi nickel-titanium composite material prepared in Example 3 of the present invention is shown, with a fracture strength of 2556-3149 MPa. Figure 16 This is a microstructure diagram of the Sc2O3 / NiTi nickel-titanium-based composite powder prepared in Example 4 of the present invention. The nickel-titanium powder maintains a spherical shape, and scandium oxide uniformly coats the nickel-titanium powder. Figure 17The 0.5 vol% Sc2O3 / NiTi nickel-titanium based composite material prepared in Example 4 of this invention is 10 4 The sub-hyperelastic cycle curve shows stable linear hyperelasticity with a hysteresis area of ​​0.2 MJ / m². 3 ; Figure 18 The 1 vol% ZnO / NiTi nickel-titanium based composite material prepared in Example 5 of this invention is 10 4 The sub-hyperelastic cyclic curve shows stable linear hyperelasticity with a hysteresis area of ​​0.4 MJ / m². 3 .

[0038] Comparative Example 1 The Al2O3 / NiTi composite material method provided in this comparative example is from the literature Metals and Materials International, 30(4)(2024) 843-856. The reinforcing powder is Al2O3 with a particle size greater than 80 nm, the ball-to-particle ratio is 10:1, the ball milling rate is 300 rpm, the ball milling time is 3 h, and the sintering pressure used for spark plasma sintering is 30 MPa. Compared with this patent, the reinforcing powder used is different, the particle size is different, and the preparation parameters are different. Comparative Example 1 did not form coated ball-milled particles, nor a composite material with a network structure of new grain boundary phases.

[0039] Comparative Example 2 The SiC / NiTi composite material method provided in this comparative example is derived from the literature Materials Letters, 100(2013) 74-77. A NiTi / SiC composite material was prepared by mixing 61μm Ni powder, 51μm Ti powder, and 80nm SiC powder (3% and 5% by mass), cold-pressing, and then sintering at high temperature. The SiC nanoparticles were dispersed throughout the substrate. Compared to this patent, the preparation method and powder particle size are different, resulting in different phases and microstructures.

[0040] Comparative Example 3 The SiC / NiTi composite material method provided in this comparative example is derived from the literature Ceramics International, 49(14) (2023) 23358-23366. By mixing Ni powder, Ti powder, and SiC powder, mechanical alloying is performed using ball milling at a ball-to-powder ratio of 10:1. Further, NiTi-Ni3Ti / SiC nanocomposite materials are prepared by microwave-assisted sintering. Compared to this patent, the preparation method and powder particle size are different, resulting in different phases and microstructures.

[0041] The results above demonstrate that this invention, through the selection of specific reinforcing phase powders, optimized powder particle size matching, and spark plasma sintering process, successfully achieved in-situ generation of a network-structured reinforcing phase at the grain boundaries of nickel-titanium composite materials. As shown in Examples 1-5, the composite materials prepared by this method exhibit excellent performance in terms of hardness, compressive strength, superelastic cyclic stability, and hysteresis properties: the hardness is approximately twice that of pure nickel-titanium alloys, the compressive strength is higher than 2500 MPa, the stress-strain curve remains stable after tens of thousands of loading-unloading cycles, the residual strain is zero, and the hysteresis area is less than 1 MJ / m². 3 It exhibits obvious R-martensite phase transformation characteristics.

[0042] Comparative Examples 1-3 show that, due to differences in the type of reinforcing phase, powder particle size, and process parameters compared to the present invention, the prior art failed to form a uniformly coated composite powder structure and grain boundary network reinforcing phase. Therefore, its overall performance, especially its cycle stability and hardness improvement effect, is significantly lower than that of the present invention.

[0043] In summary, the method provided by this invention is simple and highly controllable, and can significantly improve the hardness, strength and cycle stability of the material while maintaining the superelasticity and phase transformation properties of the nickel-titanium matrix, thus having significant engineering application value.

[0044] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for preparing nickel-titanium-based composite materials by powder sintering, characterized in that, The powder sintering preparation method specifically includes the following steps: Step S1: Using metallic nickel and metallic titanium as raw materials, induction melting and vacuum atomization are carried out sequentially to obtain nickel-titanium atomized powder; Step S2: After mixing the nickel-titanium atomized powder and the reinforcing phase powder, the mixture is subjected to low-energy ball milling in an inert atmosphere to obtain the mixed powder; Step S3: Under high vacuum conditions, the mixed powder obtained in step S2 is sintered using a spark plasma sintering method to obtain a nickel-titanium-based composite material.

2. The powder sintering preparation method according to claim 1, characterized in that, In step S1, the atomic ratio of nickel to titanium is (40-60):(60-40).

3. The powder sintering preparation method according to claim 1, characterized in that, In the nickel-titanium atomized powder obtained in step S1, the mass percentage of particles with a diameter ≤15μm is ≥50%; and / or, In step S2, the particle size of the nickel-titanium atomizing powder is ≤15 μm, and the particle size of the reinforcing phase powder is ≤50 nm.

4. The powder sintering preparation method according to claim 1, characterized in that, In step S2, the reinforcing phase powder is selected from one of silicon carbide, boron nitride, scandium oxide, zinc oxide, and carbon powder, and the reinforcing phase powder accounts for 0.1-10 vol of the nickel-titanium atomizing powder by volume percentage.

5. The powder sintering preparation method according to claim 1, characterized in that, In step S2, the nickel-titanium atomized powder and the reinforcing phase powder are mixed in a powder mixer, and then subjected to low-energy ball milling in a nitrogen / argon atmosphere; wherein the mixing time is ≥2 h, and the low-energy ball milling time is 5-12 h.

6. The powder sintering preparation method according to claim 1, characterized in that, In step S3, the parameters of the spark plasma sintering method are as follows: vacuum degree is 10. -4 -10 -3 Pa, sintering pressure is 40-60 MPa, heating rate is 50-100 ℃ / min, and sintering temperature is 1000-1200 ℃.

7. The powder sintering preparation method according to claim 1, characterized in that, In step S3, the sintering parameters are as follows: pulse current is 2-80 ms, and sintering time is 5-15 min.

8. The powder sintering preparation method according to claim 1, characterized in that, When the reinforcing phase powder in step S2 is silicon carbide, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ti. w Ni x Si y C z The atomic percentage ranges from 25%. w 31,34 x 40,11 y 13,11 z 13; When the reinforcing phase powder in step S2 is boron nitride, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ti. x N y B z The atomic percentage ranges are 50≤x≤52, 48≤y≤50, and 0≤z≤2. When the reinforcing phase powder in step S2 is scandium oxide, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ti. x Sc y O z The atomic percentage ranges from 21%. x 26,13 y 15,62 z 64; When the reinforcing phase powder in step S2 is zinc oxide, the grain boundary reinforcing phase in the nickel-titanium-based composite material obtained in step S3 is Ni. w Ti x Zn y O z The atomic percentage ranges from 0. w 9,0 x 29,14 y 20, 55 z 60; When the reinforcing phase powder in step S2 is carbon powder, the grain boundary reinforcing phase in the nickel-titanium based composite material obtained in step S3 is TiC.

9. The nickel-titanium based composite material prepared by the powder sintering method according to any one of claims 1-8, characterized in that, The nickel-titanium-based composite material generates an in-situ reinforcing phase at the grain boundaries, and the reinforcing phase has a network structure.

10. The nickel-titanium based composite material according to claim 9, characterized in that, The nickel-titanium-based composite material undergoes an R-martensitic phase transformation and exhibits linear superelasticity at room temperature. Its stress-strain curve remains stable after tens of thousands of loading and unloading cycles, with a hysteresis area of ​​less than 1 MJ / m². 3 Its compressive strength is higher than 2500 MPa.

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