A NiTi / Al-based composite material with a dual heterostructure, its preparation method and application

Abstract

A NiTi / Al-based composite material with a dual heterogeneous structure, its preparation method, and its applications. This invention belongs to the field of NiTi / Al-based composite materials. The purpose of this invention is to solve the technical problem of existing NiTi / Al composite materials that cannot simultaneously achieve both strength and toughness. The method of this invention involves: firstly, mixing NiTi with pure aluminum powder through high-energy ball milling; then, mixing NiTi with aluminum alloy powder through high-energy ball milling; next, layering the two mixed powders and unmilled aluminum powder in a mold, and finally performing SPS sintering and low-temperature hot extrusion. The dual heterogeneous structure material prepared by this invention forms different crystalline regions with hard regions of high-density particles and tough regions without particles in the matrix, forming a brick-like layered structure heterogeneous structure through stacking. The method of this invention can also be used to prepare NiTi / reinforced composite materials of other metal matrices. The resulting composite material possesses both high strength and toughness, and can be applied in aerospace and automotive engineering fields.

Description

Technical Field

[0001] This invention belongs to the field of NiTi / Al-based composite materials, specifically relating to a NiTi / Al-based composite material with a dual heterostructure, its preparation method, and its application. Background Technology

[0002] Heterogeneous (HS) materials have emerged as a promising new type of material, possessing superior properties unattainable by traditional homogeneous materials. Generally, HS materials consist of tough and hard regions with significantly different flow stresses. This leads to strain distribution, with the tough regions carrying a larger proportion of strain than the hard regions. The strain gradient will develop near the regional interfaces to accommodate the strain distribution, requiring geometrically necessary dislocations (GNDs) to adapt, resulting in heterogeneous deformation-induced (HDI) work hardening and HDI stress enhancement. One feasible strategy is to adjust the grain shape to form a matrix heterogeneity based on traditional homogeneous equiaxed grains. Another feasible method is to establish a heterogeneous grain structure by improving ductility, but the improvement effect is not significant.

[0003] In recent years, a trimodal grain structure with grain sizes spanning from nanometers to micrometers has been shown to exhibit better strain hardening and strength-ductility synergy than bimodal grain structures. However, fabricating metals with trimodal grain structures remains a significant challenge. The most common method involves partial recrystallization through annealing following severe plastic deformation, but this method results in uneven grain size distribution and fails to achieve a toughening effect. Particularly for NiTip / Al composites, the uniform dispersion of NiTip, structural integrity, and NiTip / Al interfacial reactions must be considered. Therefore, developing a high-strength, high-toughness NiTip / Al composite is essential. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem that existing NiTi / Al composite materials cannot simultaneously achieve both strength and toughness, and to provide a NiTi / Al-based composite material with a dual heterostructure, its preparation method, and its application.

[0005] The technical solution of the present invention is as follows:

[0006] One objective of this invention is to provide a method for preparing a NiTi / Al-based composite material with a dual heterostructure, the method comprising the following steps:

[0007] S1: NiTip (NiTi micron-sized particles) and aluminum powder are mixed by high-energy ball milling to obtain NiTip-Al mixed powder;

[0008] S2: NiTip (NiTi micron particles) and aluminum alloy powder are mixed by high-energy ball milling to obtain NiTip-Al alloy mixed powder;

[0009] S3: NiTip-Al mixed powder, NiTip-Al alloy mixed powder and unmilled aluminum powder are layered and encapsulated in a mold, and then subjected to low-temperature discharge plasma sintering under vacuum conditions, followed by low-temperature hot extrusion to obtain a NiTi / Al-based composite material with a dual heterostructure.

[0010] Further specified, the amount of NiTip added in S1 is 11-50 wt.% of pure aluminum powder.

[0011] Further specified, the high-energy ball milling speed in S1 is 300-450 rpm, and the time is 8-15 h.

[0012] Further specifying, the particle size of the NiTi-Al mixed powder in S1 is <5μm.

[0013] Further specified, the amount of NiTip added in S2 is 11-50 wt.% of the aluminum alloy powder.

[0014] Further specified, the high-energy ball milling speed in S2 is 300-450 rpm, and the time is 8-15 h.

[0015] Further specifying, the particle size of the NiTip-Al alloy mixed powder in S2 is 5–20 μm.

[0016] Further specifying, the mass ratio of NiTip-Al mixed powder, NiTip-Al alloy mixed powder and unmilled aluminum powder in S3 is (1.5~2.5):(1.5~2.5):1.

[0017] Further specifying, the particle size of the unmilled aluminum powder in S3 is 50–150 μm.

[0018] Further specified, the temperature of the low-temperature discharge plasma sintering in S3 is 500-530℃, the pressure is 40-60MPa, and the time is 5-15min.

[0019] Further specified, the hot extrusion temperature in S3 is 400-430℃, the extrusion ratio is (16-25):1, and the extrusion rate is 0.1-0.5mm / s.

[0020] The second objective of this invention is to provide a high-strength and high-toughness NiTi / Al-based composite material prepared by the above method, wherein the composite material has a tensile strength ≥360GPa and an elongation ≥6.7%.

[0021] The third objective of this invention is to provide an application of the high-strength and high-toughness NiTi / Al-based composite material prepared by the above method in the fields of aerospace and automotive engineering.

[0022] The fourth objective of this invention is to provide an application of the above-mentioned method in the preparation of NiTi / metal matrix composites.

[0023] Further specifying, the metal matrix is ​​one of Mg, Fe, Ti, Cu and their respective alloys.

[0024] The advantages of this invention compared to existing technologies are:

[0025] The dual-heterogeneous structure material prepared in this invention forms different crystalline heterogeneous regions in the matrix: a hard region composed of high-density particles and a tough region without particles. These heterogeneous regions are stacked to form a brick-like layered structure, resulting in unique structural effects in the composite material. First, NiTip is mixed with different aluminum matrices. Due to the significant differences in hardness of the aluminum matrices, mixing with NiTip using the same process results in mixed powders of different sizes. These mixed powders of different sizes are then layered and mixed in a reasonable proportion. Second, SPS sintering combined with low-temperature hot extrusion is used to control the process parameters to prepare a NiTip / Al composite material without an interface reaction layer, significantly improving the strength and toughness of the NiTip / Al-based composite material. NiTip combined with pure aluminum powder forms micron-sized grains <5μm (d1); NiTip combined with aluminum alloy powder forms micron-sized grains of 5–20μm (d2); and unmilled pure aluminum powder forms micron-sized grains >20μm (d3). This allows for the formation of a hard region composed of high-density reinforcing phase particles and a tough region without reinforcing phase particles with different grain sizes within the aluminum matrix. The hard regions will carry lower plastic strain, while the tough regions will bear higher plastic strain. However, due to the spatial difference in strength, a large strain incompatibility will occur between these soft and hard units during material deformation. Thus, geometrically necessary dislocations are generated to coordinate the interfacial strain gradient. Heterogeneous plastic deformation based on these geometrically necessary dislocations induces additional strain hardening and reinforcement, thereby improving the strength and toughness of the composite material. Attached Figure Description

[0026] Figure 1 This is a SEM image of the NiTip + pure Al composite powder obtained in step S1 of Example 1;

[0027] Figure 2 The image shows the SEM image of the NiTip+2024Al alloy composite powder obtained in step S2 of Example 1.

[0028] Figure 3 Here is a SEM image of the NiTip / Al-based composite material obtained in Example 1;

[0029] Figure 4 EDS image of the NiTip / Al-based composite material obtained in Example 1;

[0030] Figure 5 The image shows the EBSD pattern of the NiTip / Al-based composite material obtained in Example 1.

[0031] Figure 6 The grain size distribution of the NiTip / Al-based composite material obtained in Example 1 is shown in the diagram.

[0032] Figure 7 The table shows the room temperature tensile stress-strain curves of the NiTip / Al-based composite materials obtained in Example 1 and Comparative Examples 1-2. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0035] Example 1: The preparation method of the NiTi / Al-based composite material with a dual isomeric structure in this example is carried out according to the following steps:

[0036] S1: 12.48g of NiTip (Ni:Ti atomic ratio = 50.82:49.18, average diameter ~16.10μm) and 47.52g of spherical aluminum powder (purity 99.9%, average diameter ~72.48μm) were added to a planetary ball mill and mixed at 350rpm for 10h with a ball-to-material ratio of 15:1 to obtain NiTip-Al mixed powder;

[0037] S2: 12.22g of NiTip (Ni:Ti atomic ratio = 50.82:49.18, average diameter ~16.10μm) and 47.78g of spherical 2024 aluminum alloy powder (purity 99.9%, average diameter ~72.48μm) were added to a planetary ball mill and mixed at 350rpm for 10h with a ball-to-material ratio of 15:1 to obtain NiTip-2024Al mixed powder;

[0038] S3: 24g of NiTip-Al mixed powder, 24g of NiTip-2024Al mixed powder, and 12g of unmilled aluminum powder (purity 99.9%, average diameter ~72.48μm) were layered and encapsulated in a mold. The mold was then placed in a discharge plasma sintering furnace and evacuated to avoid powder oxidation contamination from contact with air. Discharge plasma sintering was performed at a selected sintering temperature of 530℃, a uniaxial pressure of 50MPa, and a holding time of 10min. After sintering and furnace cooling, the mold was placed in a ring furnace. The mold contained, from top to bottom, an extrusion cup, a pure aluminum block, the sintered composite material, and a graphite gasket. Low-temperature hot extrusion was performed at a selected hot extrusion temperature of 430℃, a holding time of 1.5h, an extrusion ratio of 25:1, and an extrusion rate of 0.5mm / s to obtain a NiTi / Al-based composite material with a dual heterogeneous structure.

[0039] The NiTi / Al-based composite material with a dual heterostructure obtained in Example 1 was tested and found to have a tensile strength of 363 MPa and an elongation of 6.7%.

[0040] Comparative Example 1: The preparation method of the NiTi / Al-based composite material in this embodiment is carried out according to the following steps:

[0041] S1: 12.48g of NiTip (Ni:Ti atomic ratio = 50.82:49.18, average diameter ~16.10μm) and 47.52g of spherical aluminum powder (purity 99.9%, average diameter ~72.48μm) were added to a planetary ball mill and mixed at 350rpm for 10h with a ball-to-material ratio of 15:1 to obtain NiTip-Al mixed powder;

[0042] S2: 12.22g of NiTip (Ni:Ti atomic ratio = 50.82:49.18, average diameter ~16.10μm) and 47.78g of spherical 2024 aluminum alloy powder (purity 99.9%, average diameter ~72.48μm) were added to a planetary ball mill and mixed at 350rpm for 10h with a ball-to-material ratio of 15:1 to obtain NiTip-2024Al mixed powder;

[0043] S3: 21g of NiTip-Al mixed powder, 21g of NiTip-2024Al mixed powder, and 18g of unmilled aluminum powder (purity 99.9%, average diameter ~72.48μm) were layered and encapsulated in a mold. The mold was then placed in a discharge plasma sintering furnace and evacuated to avoid powder oxidation contamination from contact with air. Discharge plasma sintering was performed at a selected sintering temperature of 530℃, a uniaxial pressure of 50MPa, and a holding time of 10min. After sintering and furnace cooling, the mold was placed in a ring furnace. The mold contained, from top to bottom, an extrusion cup, a pure aluminum block, the sintered composite material, and a graphite gasket. Low-temperature hot extrusion was performed at a selected hot extrusion temperature of 430℃, a holding time of 1.5h, an extrusion ratio of 25:1, and an extrusion rate of 0.5mm / s to obtain the NiTi / Al-based composite material.

[0044] The NiTi / Al-based composite material obtained in Comparative Example 1 was tested and found to have a tensile strength of 342 MPa and an elongation of 12.4%.

[0045] Comparative Example 2: The preparation method of the NiTi / Al-based composite material in this embodiment is carried out according to the following steps:

[0046] S1: 12.48g of NiTip (Ni:Ti atomic ratio = 50.82:49.18, average diameter ~16.10μm) and 47.52g of spherical aluminum powder (purity 99.9%, average diameter ~72.48μm) were added to a planetary ball mill and mixed at 350rpm for 10h with a ball-to-material ratio of 15:1 to obtain NiTip-Al mixed powder;

[0047] S2: 12.22g of NiTip (Ni:Ti atomic ratio = 50.82:49.18, average diameter ~16.10μm) and 47.78g of spherical 2024 aluminum alloy powder (purity 99.9%, average diameter ~72.48μm) were added to a planetary ball mill and mixed at 350rpm for 10h with a ball-to-material ratio of 15:1 to obtain NiTip-2024Al mixed powder;

[0048] S3: 27g of NiTip-Al mixed powder, 27g of NiTip-2024Al mixed powder, and 6g of unmilled aluminum powder (purity 99.9%, average diameter ~72.48μm) were layered and encapsulated in a mold. The mold was then placed in a discharge plasma sintering furnace and evacuated to avoid powder oxidation contamination from contact with air. Discharge plasma sintering was performed at a selected sintering temperature of 530℃, a uniaxial pressure of 50MPa, and a holding time of 10min. After sintering and furnace cooling, the mold was placed in a ring furnace. The mold contained, from top to bottom, an extrusion cup, a pure aluminum block, the sintered composite material, and a graphite gasket. Low-temperature hot extrusion was performed at a selected hot extrusion temperature of 430℃, a holding time of 1.5h, an extrusion ratio of 25:1, and an extrusion rate of 0.5mm / s to obtain the NiTi / Al-based composite material.

[0049] The NiTi / Al-based composite material obtained in Comparative Example 2 was tested and found to have a tensile strength of 384 MPa and an elongation of 5.4%.

[0050] Figure 1 The morphology of the NiTip-Al mixed powder obtained in step S1 of Example 1 is shown below. Figure 1 As can be seen, consistent with the typical morphological changes of metal powders during ball milling, pure aluminum exhibits better deformability than NiTip. Near-spherical pure aluminum is pressed into thin aluminum sheets, uniformly dispersed without significant stacking. In contrast, NiTip changes from a spherical shape to an oblate spheroid, and under this ball milling energy, the NiTip distribution is uniform. This achieves a uniform and ideal mixing effect during the ball milling process.

[0051] Figure 2 The morphology of the NiTip-2024Al mixed powder obtained in step S2 of Example 1 is shown below. Figure 2 As can be seen, because 2024Al powder is harder than pure aluminum, NiTi powder deforms significantly and forms a flattened spherical shape when using the same ball milling process. With increasing ball milling speed and time, the 2024Al powder gradually transforms from a spherical shape to an ellipsoidal shape. Compared to NiTip-Al mixed powder, the 2024Al powder flakes are thicker and have a smaller radial length, while the NiTip exhibits greater deformation.

[0052] Figure 3 The morphology of the NiTi / Al-based composite material with a dual isomorphic structure obtained in Example 1 is shown below. Figure 3 As can be seen, firstly, the preparation method of SPS low-temperature sintering + low-temperature hot extrusion achieved uniform distribution of NiTip in the two layers (Al-NiTip, 2024Al-NiTip). Figure 4Secondly, due to the low sintering and hot extrusion temperatures, no intermetallic compounds were found at the NiTip / Al and NiTip / 2024Al interfaces in the composite material, resulting in a good metallurgical bond between NiTip and the Al matrix in the composite material. Finally, because the particle deformation of NiTip differs when ball-milled with different matrices, it can be clearly seen in the composite material.

[0053] Figure 5 and Figure 6 The EDSD image and grain statistics of the NiTi / Al-based composite material with a dual heterogeneous structure obtained in Example 1 clearly show a distinct three-peak grain distribution and a layered structure. The Al-NiTip region, the 2024Al-NiTip region, and the Al region are streamlined along the extrusion direction. The NiTip in the 2024Al-NiTip region is more deformed than that in the Al-NiTip region, exhibiting a long strip-like distribution. The Al-NiTip region shows significant grain refinement, with an average grain size of 2.61 μm. Figure 6 ); 2024Al-NiTip forms larger micron-sized grains with an average grain size of 11.62μm; unmilled Al powder forms large micron-sized grains with an average grain size of 22.82μm.

[0054] Figure 7 The room temperature tensile test results of the NiTi / Al-based composite material with a dual heterostructure obtained in Example 1 are shown below. Figure 7 As can be seen, the yield strength of the dual-heterogeneous NiTi / Al-based composite material in Example 1 is 178.9 MPa, the tensile strength is 363 MPa, and the elongation is 6.7%. The dual-structure exhibits better strain hardening and strength-ductility synergy. The layered structure improves the mechanical properties of the composite material in the direction parallel to the laminations, providing additional back stress reinforcement. This demonstrates the great potential of dual-heterogeneous composite materials in achieving the goal of strengthening and toughening aluminum-based composites.

[0055] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a NiTi / Al-based composite material with a dual heterostructure, characterized in that, The method described: S1: NiTip and pure aluminum powder are mixed by high-energy ball milling to obtain NiTip-Al mixed powder; the particle size of NiTip-Al mixed powder is <5μm; S2: NiTip and aluminum alloy powder are mixed by high-energy ball milling to obtain NiTip-Al alloy mixed powder; the particle size of NiTip-Al alloy mixed powder is 5~20μm; S3: NiTip-Al mixed powder, NiTip-Al alloy mixed powder and unmilled aluminum powder are layered and encapsulated in a mold, and then subjected to low-temperature discharge plasma sintering under vacuum conditions, followed by low-temperature hot extrusion to obtain a NiTi / Al-based composite material with a dual heterostructure; the mass ratio of NiTip-Al mixed powder, NiTip-Al alloy mixed powder and unmilled aluminum powder is (1.5~2.5):(1.5~2.5):1, and the particle size of unmilled aluminum powder is 50~150μm.

2. The method according to claim 1, characterized in that, In S1, the amount of NiTip added is 11~50wt.% of pure aluminum powder, the high-energy ball milling speed is 300~450rpm, and the time is 8~15h.

3. The method according to claim 1, characterized in that, In S2, the amount of NiTip added is 11~50wt.% of the aluminum alloy powder, the high-energy ball milling speed is 300~450rpm, and the time is 8~15h.

4. The method according to claim 1, characterized in that, The temperature for S3 low-temperature discharge plasma sintering is 500~530℃, the pressure is 40~60MPa, and the time is 5~15min.

5. The method according to claim 1, characterized in that, The hot extrusion temperature of S3 is 400~430℃, the extrusion ratio is (16~25):1, and the extrusion speed is 0.1~0.5mm / s.

6. The high-strength and high-toughness NiTi / Al-based composite material prepared by the method according to any one of claims 1-5, characterized in that, The composite material has a tensile strength ≥360GPa and an elongation ≥6.7%.

7. The application of the high-strength and high-toughness NiTi / Al-based composite material according to claim 6 in the fields of aerospace and automotive engineering.

8. The application of the method according to any one of claims 1-5 in the preparation of NiTi / metal matrix composites.

9. The application according to claim 8, characterized in that, The metallic matrix is ​​one of Mg, Fe, Ti, Cu, and their respective alloys.

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