A fatigue-resistant discontinuous layered B4C / Al nanocomposite and its preparation method

Abstract

A fatigue-resistant discontinuous layered B4C / Al nanocomposite material and its preparation method. This invention belongs to the field of fatigue-resistant metal matrix composites, specifically relating to a fatigue-resistant discontinuous layered B4C / Al nanocomposite material and its preparation method. The purpose of this invention is to solve the problems of low fatigue strength, short fatigue life, and limited practical application of existing particle-reinforced metal matrix composites; and the complex preparation process, small particle size, and difficulty in controlling the microstructure of discontinuous layered metal matrix composites. Method: Spherical Al powder is ball-milled into flake Al powder, and then nano-B4C powder is added and ball-milled at high energy to obtain B4C-reinforced cold-welded Al particles. The cold-welded particles are cold-pressed to prepare a preform, and molten aluminum is impregnated into the voids of the cold-welded particles. A discontinuous layered structure with alternating distribution is formed by hot extrusion. This preparation method is simple and convenient, the microstructure is easily controlled, the production efficiency is high, the process is short, and it is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of fatigue-resistant metal matrix composites, specifically relating to a fatigue-resistant discontinuous layered B4C / Al nanocomposite material and its preparation method. Background Technology

[0002] B4C / Al nanocomposites possess advantages such as low density, high strength, and good wear resistance, making them suitable for applications in defense, military, transportation, and many other fields, and an ideal alternative to aluminum alloys. However, in practical use, these materials often bear cyclic loads, leading to failure under loads far below their tensile strength or even yield strength. Statistics show that over 90% of mechanical failures are caused by fatigue under cyclic loading. While B4C / Al nanocomposites achieve a significant increase in strength, their fatigue strength, especially low-cycle fatigue strength, decreases substantially, greatly limiting their practical applications. As the application of B4C / Al nanocomposites becomes more widespread, higher requirements are being placed on their fatigue performance.

[0003] Compared to traditional uniformly distributed B4C / Al nanocomposites, discontinuous layered B4C / Al nanocomposites can improve fatigue strength and extend fatigue life while maintaining essentially the same static strength. However, the current preparation process for discontinuous layered B4C / Al nanocomposites is complex, time-consuming, and produces materials with small dimensions. Furthermore, due to the complexity of the preparation process, achieving precise control over the microstructure of discontinuous layered B4C / Al nanocomposites is quite challenging. Therefore, a new preparation method is needed that simplifies the preparation process of discontinuous layered B4C / Al nanocomposites while simultaneously enabling microstructure control. Summary of the Invention

[0004] This invention aims to address the problems of low fatigue strength, short fatigue life, and limited practical application of existing particle-reinforced metal matrix composites; as well as the complex preparation process, small fabrication size, and difficulty in controlling the microstructure of discontinuous layered metal matrix composites. The invention provides a fatigue-resistant discontinuous layered B4C / Al nanocomposite material and its preparation method.

[0005] A fatigue-resistant discontinuous layered B4C / Al nanocomposite material has an internal structure in which hard and soft layers are arranged alternately, forming a discontinuous layered structure. The hard layer is reinforced with nano-B4C and the soft layer is reinforced with Al. The thickness of the hard layer is 5μm~40μm and the thickness of the soft layer is 1μm~10μm. The soft layer accounts for 20%~60% of the volume fraction of the composite material.

[0006] The preparation method of a fatigue-resistant discontinuous layered B4C / Al nanocomposite material is carried out according to the following steps:

[0007] I. Preparation of flake Al powder: Spherical Al powder with a micron size is ball-milled, and the ball-milled powder is heat-treated under an argon atmosphere to remove stearic acid, thereby obtaining flake Al powder;

[0008] II. Preparation of B4C / Al cold welding particles: Flake Al powder and nano-sized B4C powder are mixed and subjected to high-energy ball milling to obtain nano-B4C reinforced cold welding Al particles;

[0009] 3. Infiltration of B4C / Al cold-welded particles into molten aluminum: Cold-welded Al particles reinforced with nano B4C are loaded into a steel mold and pressed to obtain a preform. The preform is then heat-insulated. Molten aluminum is then poured into the steel mold containing the preform and pressure is applied for infiltration. The preform is then naturally cooled to room temperature and demolded to obtain a B4C / Al nanocomposite ingot with unevenly distributed nano B4C.

[0010] IV. Hot extrusion of B4C / Al nanocomposites: The B4C / Al nanocomposites ingot with unevenly distributed nano B4C is placed in a hot extrusion press for hot extrusion to obtain a discontinuous layered structure of B4C / Al nanocomposites.

[0011] The beneficial effects of this invention are:

[0012] The discontinuous layered B4C / Al nanocomposite material provided by this invention uses an Al-based composite material reinforced with nano-B4C as the hard layer and Al as the soft layer. The hard layer inhibits the deformation of the soft layer, giving the composite material high strength, while the soft layer alleviates stress concentration in the hard layer and hinders crack propagation. This results in a lightweight, high-strength composite material with excellent fatigue resistance. The discontinuous layered B4C / Al nanocomposite material provided by this invention is prepared by a combination of high-energy ball milling and pressure infiltration. The raw materials are inexpensive and readily available, the preparation process is simple and straightforward, and it is easy to mass-produce, meeting the needs of industrial production.

[0013] By changing the particle size of micron-sized Al powder, the size of B4C / Al cold-welded particles can be altered, thereby changing the thickness of the soft and hard layers in the discontinuous layered B4C / Al nanocomposite material. Similarly, by changing the packing density of the preform, the volume fraction of the Al impregnation solution can be changed, thus altering the volume fraction of the soft and hard layers in the discontinuous layered B4C / Al nanocomposite material. The method for preparing discontinuous layered B4C / Al nanocomposite materials provided by this invention allows for wide-ranging control of the thickness and volume fraction of the soft and hard layers, enabling the preparation of discontinuous layered B4C / Al nanocomposite materials with varying mechanical and fatigue properties to meet the application needs of different fields. Attached Figure Description

[0014] Figure 1 The image shows the microstructure of the discontinuous layered B4C / Al nanocomposite material obtained in Example 1.

[0015] Figure 2 The SN curve of the discontinuous layered B4C / Al nanocomposite obtained in Example 1;

[0016] Figure 3 The image shows the microstructure of the discontinuous layered B4C / Al nanocomposite material obtained in Example 2.

[0017] Figure 4 The SN curves are for the discontinuous layered B4C / Al nanocomposite material obtained in Example 2. Detailed Implementation

[0018] Specific Implementation Method 1: In this implementation method, a fatigue-resistant discontinuous layered B4C / Al nanocomposite material has an internal structure in which hard layers and soft layers are arranged alternately, forming a discontinuous layered structure; the Al-based composite material reinforced by nano B4C is the hard layer, and Al is the soft layer; the thickness of the hard layer is 5μm~40μm, and the thickness of the soft layer is 1μm~10μm; the soft layer accounts for 20%~60% of the volume fraction of the composite material.

[0019] Specific Implementation Method Two: The preparation method of the fatigue-resistant discontinuous layered B4C / Al nanocomposite material in this implementation method is carried out according to the following steps:

[0020] I. Preparation of flake Al powder: Spherical Al powder with a micron size is ball-milled, and the ball-milled powder is heat-treated under an argon atmosphere to remove stearic acid, thereby obtaining flake Al powder;

[0021] II. Preparation of B4C / Al cold welding particles: Flake Al powder and nano-sized B4C powder are mixed and subjected to high-energy ball milling to obtain nano-B4C reinforced cold welding Al particles;

[0022] 3. Infiltration of B4C / Al cold-welded particles into molten aluminum: Cold-welded Al particles reinforced with nano B4C are loaded into a steel mold and pressed to obtain a preform. The preform is then heat-insulated. Molten aluminum is then poured into the steel mold containing the preform and pressure is applied for infiltration. The preform is then naturally cooled to room temperature and demolded to obtain a B4C / Al nanocomposite ingot with unevenly distributed nano B4C.

[0023] IV. Hot extrusion of B4C / Al nanocomposites: The B4C / Al nanocomposites ingot with unevenly distributed nano B4C is placed in a hot extrusion press for hot extrusion to obtain a discontinuous layered structure of B4C / Al nanocomposites.

[0024] In this embodiment, after impregnation, the mixture is extruded, and the mixed powder forms a hard layer, while the impregnated molten aluminum forms a soft layer.

[0025] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method Two in that the particle size of the micron-sized spherical Al powder mentioned in step one is 1~100μm, and the material is 1xxx, 2xxx, 5xxx, 6xxx, 7xxx series aluminum alloys or pure aluminum. Everything else is the same as in Specific Implementation Method Two.

[0026] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Two in that: the ball milling process in step one is as follows: the ball-to-material ratio is greater than 5:1, the ball milling speed is greater than 200 rpm, and the ball milling time is greater than 5 hours; stearic acid is used as a process control agent, and the amount of stearic acid added is 0.5~2% by weight; the heat treatment process is as follows: holding at 400℃ for 0.5 hours. Everything else is the same as in Specific Implementation Method Two.

[0027] Specific Implementation Method 5: This implementation method differs from Specific Implementation Method 2 in that the particle size of the nano-sized B4C powder mentioned in step 2 is 50~300nm, and the volume fraction of nano-B4C in the nano-B4C-reinforced cold-welded Al particles is 1~8%. Everything else is the same as in Specific Implementation Method 2.

[0028] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Two in that the high-energy ball milling process described in step two is as follows: the ball-to-material ratio is greater than 20:1, the ball milling speed is greater than 250 rpm, and the ball milling time is greater than 5 hours. Everything else is the same as in Specific Implementation Method Two.

[0029] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Two in that: the pressing process in step three is: holding the pressure at 50~100MPa for 15~20 minutes; the bulk density of the preform is 40%~80%; and the heat preservation process is: heat preservation at 620~650℃ for 2~5 hours. Everything else is the same as in Specific Implementation Method Two.

[0030] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Two in that: the aluminum liquid material in step three is 1xxx, 2xxx, 5xxx, 6xxx, or 7xxx series aluminum alloys or pure aluminum; the aluminum liquid and the micron-sized spherical Al powder in step one are made of the same material. Everything else is the same as in Specific Implementation Method Two.

[0031] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the aluminum liquid impregnation pressure in step three is 150MPa~250MPa, and the pressure holding time is 5~10min. Everything else is the same as in Specific Implementation Method Eight.

[0032] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Two in that the hot extrusion process in step four is as follows: the extrusion ratio is 8:1, 10:1, or 13:1, the extrusion temperature is 350~550℃, and the extrusion rate is 0.2~0.5m / min. Everything else is the same as in Specific Implementation Method Two.

[0033] The effectiveness of the present invention was verified through the following experiments:

[0034] Example 1: A method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material, characterized in that the preparation method of the fatigue-resistant discontinuous layered B4C / Al nanocomposite material is carried out according to the following steps:

[0035] I. Preparation of flake Al powder: Weigh 42.6g of 10μm spherical pure Al powder, add 0.426g of stearic acid and ball mill. The ball milling process is as follows: ball-to-material ratio 10:1, ball milling speed 200rpm, ball milling time 10h. After ball milling, the powder is kept at 400℃ for 0.5h under argon atmosphere to remove stearic acid and obtain flake Al powder.

[0036] II. Preparation of B4C / Al cold welding particles: Flake Al powder and 2.1g of B4C powder with a particle size of 200nm were mixed and subjected to high-energy ball milling to obtain nano-B4C reinforced cold welding Al particles; The high-energy ball milling process was as follows: ball-to-material ratio 20:1, ball milling speed 300rpm, ball milling time 5h, and argon atmosphere.

[0037] III. Infiltration of B4C / Al cold-welded particles into molten aluminum: Nano-B4C reinforced cold-welded Al particles are loaded into a steel mold and subjected to a pressure of 70MPa for 15 minutes to form a preform. The preform is then held at 640℃ for 3 hours. Pure aluminum liquid is then poured into the steel mold containing the preform and subjected to a pressure of 250MPa for infiltration. The pressure is held for 10 minutes and then allowed to cool naturally to room temperature. After demolding, a B4C / Al nanocomposite ingot with unevenly distributed nano-B4C is obtained.

[0038] IV. Hot Extrusion of B4C / Al Nanocomposites: The B4C / Al nanocomposite ingot with unevenly distributed nano-B4C is placed in a hot extrusion press for hot extrusion to obtain a discontinuous layered B4C / Al nanocomposite. The hot extrusion process is as follows: extrusion ratio is 10:1, extrusion temperature is 500℃, and extrusion rate is 0.25m / min.

[0039] Figure 1The image shows the microstructure of the discontinuous layered B4C / Al nanocomposite obtained in Example 1. It clearly shows a hard layer and a soft layer, which are distributed in an overlapping layered manner with good interfacial bonding and no delamination or other defects. The boron carbide nanoparticles in the hard layer are uniformly distributed and well bonded to the matrix. The average thickness of the hard layer is 8.62 μm, and the average thickness of the soft layer is 2.31 μm.

[0040] Figure 2 The SN curve of the discontinuous layered B4C / Al nanocomposite obtained in Example 1 shows that under a cyclic load of 146.7 MPa, the fatigue life is 208330, which is about 100 times that of the uniformly distributed B4C / Al nanocomposite. The fatigue limit is 73.4 MPa, which is 17.5 MPa higher than that of the uniformly distributed B4C / Al nanocomposite.

[0041] Example 2: A method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material, characterized in that the preparation method of the fatigue-resistant discontinuous layered B4C / Al nanocomposite material is carried out according to the following steps:

[0042] I. Preparation of flake Al powder: Weigh 42.6g of 40μm spherical pure Al powder, add 0.426g of stearic acid and ball mill. The ball milling process is as follows: ball-to-material ratio 10:1, ball milling speed 200rpm, ball milling time 10h. After ball milling, the powder is kept at 400℃ for 0.5h under argon atmosphere to remove stearic acid and obtain flake Al powder.

[0043] II. Preparation of B4C / Al cold welding particles: Flake Al powder and 2.1g of B4C powder with a particle size of 200nm were mixed and subjected to high-energy ball milling to obtain nano-B4C reinforced cold welding Al particles; The high-energy ball milling process was as follows: ball-to-material ratio 20:1, ball milling speed 300rpm, ball milling time 5h, and argon atmosphere.

[0044] III. Infiltration of B4C / Al cold-welded particles into molten aluminum: Nano-B4C reinforced cold-welded Al particles are loaded into a steel mold and subjected to a pressure of 50MPa for 15 minutes to form a preform. The preform is then held at 640℃ for 3 hours. Pure aluminum liquid is then poured into the steel mold containing the preform and subjected to a pressure of 250MPa for infiltration. The pressure is held for 10 minutes and then allowed to cool naturally to room temperature. After demolding, a B4C / Al nanocomposite ingot with unevenly distributed nano-B4C is obtained.

[0045] IV. Hot Extrusion of B4C / Al Nanocomposites: The B4C / Al nanocomposite ingot with unevenly distributed nano-B4C is placed in a hot extrusion press for hot extrusion to obtain a discontinuous layered B4C / Al nanocomposite. The hot extrusion process is as follows: extrusion ratio is 10:1, extrusion temperature is 500℃, and extrusion rate is 0.25m / min.

[0046] Figure 3 The image shows the microstructure of the discontinuous layered B4C / Al nanocomposite obtained in Example 2. It clearly shows a hard layer and a soft layer, which are distributed in an overlapping layered manner with good interfacial bonding and no delamination or other defects. The boron carbide nanoparticles in the hard layer are uniformly distributed and well bonded to the matrix. The average thickness of the hard layer is 38.5 μm, and the average thickness of the soft layer is 44.6 μm.

[0047] Figure 4 The SN curve of the discontinuous layered B4C / Al nanocomposite obtained in Example 2 shows that under a cyclic load of 146.7 MPa, the fatigue life is 57632, which is about 28 times that of the uniformly distributed B4C / Al nanocomposite. The fatigue limit is 73.4 MPa, which is 17.5 MPa higher than that of the uniformly distributed B4C / Al nanocomposite.

Claims

1. A fatigue-resistant discontinuous layered B4C / Al nanocomposite material, characterized in that... The fatigue-resistant discontinuous layered B4C / Al nanocomposite material has an alternating arrangement of hard and soft layers, exhibiting a discontinuous layered structure. The Al-based composite material reinforced with nano-B4C consists of hard layers and Al layers consists of soft layers. The thickness of the hard layers is 5μm~40μm, and the thickness of the soft layers is 1μm~10μm. The soft layers account for 20%~60% of the volume fraction of the composite material.

2. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material as described in claim 1, characterized in that... The preparation method of fatigue-resistant discontinuous layered B4C / Al nanocomposite material is carried out according to the following steps: I. Preparation of flake Al powder: Spherical Al powder with a micron size is ball-milled, and the ball-milled powder is heat-treated under an argon atmosphere to remove stearic acid, thereby obtaining flake Al powder; II. Preparation of B4C / Al cold welding particles: Flake Al powder and nano-sized B4C powder are mixed and subjected to high-energy ball milling to obtain nano-B4C reinforced cold welding Al particles; 3. Infiltration of B4C / Al cold-welded particles into molten aluminum: Cold-welded Al particles reinforced with nano B4C are loaded into a steel mold and pressed to obtain a preform. The preform is then heat-insulated. Molten aluminum is then poured into the steel mold containing the preform and pressure is applied for infiltration. The preform is then naturally cooled to room temperature and demolded to obtain a B4C / Al nanocomposite ingot with unevenly distributed nano B4C. IV. Hot extrusion of B4C / Al nanocomposites: The B4C / Al nanocomposites ingot with unevenly distributed nano B4C is placed in a hot extrusion press for hot extrusion to obtain a discontinuous layered structure of B4C / Al nanocomposites.

3. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 2, characterized in that... The micron-sized spherical Al powder mentioned in step one has a particle size of 1~100μm and is made of 1xxx, 2xxx, 5xxx, 6xxx, 7xxx series aluminum alloys or pure aluminum.

4. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 2, characterized in that... The ball milling process described in step one is as follows: the ball-to-material ratio is greater than 5:1, the ball milling speed is greater than 200 rpm, the ball milling time is greater than 5 hours, and stearic acid is used as a process control agent, with the amount of stearic acid added being 0.5~2% by weight; the heat treatment process is as follows: holding at 400℃ for 0.5 hours.

5. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 2, characterized in that... The particle size of the nano-sized B4C powder in step two is 50~300nm, and the volume fraction of nano-B4C in the nano-B4C-reinforced cold-welded Al particles is 1~8%.

6. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 2, characterized in that... The high-energy ball milling process described in step two is as follows: ball-to-material ratio greater than 20:1, ball milling speed greater than 250 rpm, and ball milling time greater than 5 hours.

7. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 2, characterized in that... The pressing process in step three is as follows: holding the pressure at 50~100MPa for 15~20min; the bulk density of the preform is 40%~80%; the heat preservation process is as follows: heat preservation at 620~650℃ for 2~5h.

8. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 2, characterized in that... The aluminum liquid in step three is made of 1xxx, 2xxx, 5xxx, 6xxx, or 7xxx series aluminum alloys or pure aluminum; the aluminum liquid and the micron-sized spherical Al powder in step one are made of the same material.

9. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 8, characterized in that... The aluminum molten metal impregnation pressure in step three is 150MPa~250MPa, and the pressure holding time is 5~10min.

10. The method for preparing a fatigue-resistant discontinuous layered B4C / Al nanocomposite material according to claim 2, characterized in that... The hot extrusion process described in step four is as follows: the extrusion ratio is 8:1, 10:1 or 13:1, the extrusion temperature is 350~550℃, and the extrusion rate is 0.2~0.5m / min.

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