Preparation method of B4C / Al composite material with blended organization structure based on powder gradation

Abstract

The invention discloses a preparation method of a B4C / Al composite material with a blended organization structure based on powder grading. The invention relates to the field of preparation of particle reinforced metal matrix composite materials, in particular to a preparation method of a B4C / Al composite material with a blended organization structure based on powder gradation. The invention aims to solve the problems that the traditional B4C / Al composite material with a uniform structure is poor in plasticity, short in fatigue life and limited in practical application, the preparation method of the B4C / Al composite material with a harmonized organization structure is complicated, and the microstructure is difficult to accurately regulate and control. The method comprises the steps that coarse spherical Al powder, fine spherical Al powder and fine B4C powder are adopted for grading, then hot pressing sintering is conducted, and the B4C / Al composite material with the blended tissue structure that a hard B4C / Al'shell 'wraps a soft Al'core' can be obtained. The B4C / Al composite material prepared by the method has the advantages of low density, high toughness and fatigue resistance.

Description

Technical Field

[0001] The invention relates to the field of preparation of particle-reinforced metal-based composite materials, and in particular to a preparation method of a B4C / Al composite material with a blended organizational structure based on powder grading. Background Art

[0002] B4C / Al composite materials have low density, high strength, wear resistance, impact resistance, and large neutron absorption cross section. They are ideal materials for structural parts such as aircraft skins, helicopter propellers, car shells, train bodies, and spent fuel storage containers. They are of great significance to the safety of national defense, military, transportation, and other fields. However, the traditional uniform structure of B4C / Al composite materials has the classic problem of strength-plastic inversion, that is, while the tensile strength is greatly improved, the elongation drops sharply, causing the material to fracture brittlely, resulting in sudden failure of the material during service. In addition, the stress concentration near the B4C particles, especially at the sharp corners, is serious, which promotes the initiation of fatigue cracks and greatly reduces the fatigue life of the material. Therefore, the safe service of B4C / Al composite materials in practical applications is challenged. As B4C / Al composite materials receive more and more attention, higher requirements are placed on their strength-plastic coordination and fatigue strength.

[0003] Harmonic structure is a kind of heterogeneous structure, which refers to the structure of a hard fine grain "shell" encapsulating a soft coarse grain "core" in a metal material. Compared with nanocrystalline / ultrafine grain metals, the plasticity of the metal with a harmonic structure is significantly improved while maintaining high tensile strength, and the fatigue performance is significantly improved. Similar to the metal with a harmonic structure, by regulating the distribution of B4C particles, the hard B4C / Al "shell" encapsulating the soft Al "core" can be achieved, and the harmonic structure B4C / Al composite material can be obtained, overcoming the problems of strength-plasticity inversion and low fatigue life of the traditional uniform structure B4C / Al composite material. However, the preparation process of the harmonic structure B4C / Al composite material is complex, the preparation cycle is long, and the price is expensive. At the same time, the "core" of the harmonic structure B4C / Al composite material needs to have a suitable size to play the role of the harmonic structure. However, it is difficult to accurately control the microstructure of the harmonic structure B4C / Al composite material, which makes it difficult for the performance of the harmonic structure B4C / Al composite material currently prepared to meet expectations. Therefore, a new preparation method is needed to simplify the preparation process of B4C / Al composite materials with harmonious organizational structure while achieving precise control of their microstructure. Summary of the invention

[0004] The present invention aims to solve the problems that the conventional uniform structure B4C / Al composite material has poor plasticity, short fatigue life, limited practical application, and complex preparation method of the harmonic structure B4C / Al composite material, and the microstructure is difficult to accurately control. A preparation method of the harmonic structure B4C / Al composite material based on powder grading is provided.

[0005] A preparation method of a B4C / Al composite material with a blended structure based on powder grading is specifically carried out in the following steps:

[0006] 1. Powder gradation mixing: coarse spherical Al powder, fine spherical Al powder and fine B4C powder are ball-milled, stearic acid is used as a process control agent, and the protective atmosphere is argon gas; the ball-milled powder is heat-treated to remove stearic acid to obtain a B4C / Al mixed powder;

[0007] 2. Preparation of B4C / Al preform: B4C / Al mixed powder is loaded into a steel mold, and then a certain pressure is applied and the preform is obtained after holding the pressure for a certain period of time;

[0008] 3. Hot pressing sintering of B4C / Al composite material: The preform is kept at high temperature for a certain period of time, and then high pressure is applied and kept for a certain period of time, and naturally cooled to room temperature. After demolding, a B4C / Al composite material with a harmonious organizational structure is obtained.

[0009] Beneficial effects of the present invention:

[0010] The present invention provides a B4C / Al composite material with a harmonic structure based on powder grading, and obtains a B4C non-uniform distribution powder of fine B4C / Al mixed powder encapsulating coarse spherical Al powder by grading fine B4C powder and fine spherical Al powder and coarse spherical Al powder. Through hot pressing sintering, the fine B4C / Al mixed powder is sintered into a hard B4C / Al composite material, the coarse spherical Al powder is sintered into a soft Al matrix material, and the hard B4C / Al "shell" is interconnected to encapsulate the soft Al "core" to form a harmonic structure. During the tensile deformation process, the hard "shell" suppresses the plastic deformation of the soft "core", and the soft "core" bears the main plastic strain, so that the composite material has high strength and high plasticity. In addition, the hard "shell" and the soft "core" interact with each other, change the stress distribution of the matrix, relieve the stress concentration near the B4C in the hard "shell", and the soft "core" hinders the crack propagation, greatly improving the fatigue life of the composite material.

[0011] The harmonic structure B4C / Al composite material provided by the present invention is realized by powder grading, the raw materials are cheap and easy to obtain, the preparation process is few, the cycle is short, and it is easy to prepare on a large scale, which can meet the needs of industrial production. By changing the particle size of the coarse spherical Al powder, the size of the soft "core" can be regulated; by changing the volume fraction of the coarse spherical Al powder, the volume fraction of the soft "core" can be regulated; by changing the alloying elements of the fine spherical Al powder and the coarse spherical Al powder, the matrix alloy of the harmonic structure B4C / Al composite material can be regulated. The preparation method of the harmonic structure B4C / Al composite material based on powder grading provided by the present invention can realize the precise regulation of the microstructure parameters of the harmonic structure, thereby preparing a harmonic structure B4C / Al composite material with different mechanical properties to meet the application needs of various environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The microstructure photograph of the B4C / Al composite material with a harmonic structure obtained in Example 1;

[0013] Figure 2 The microstructure photograph of the B4C / Al composite material with a harmonic structure obtained in Example 2;

[0014] Figure 3 The tensile curve of the B4C / Al composite material with a harmonic structure obtained in Example 2;

[0015] Figure 4 This is the SN curve of the harmonic structure B4C / Al composite material obtained in Example 2. DETAILED DESCRIPTION

[0016] Specific implementation method 1: In this implementation method, a preparation method of a B4C / Al composite material with a blended structure based on powder grading is specifically carried out in the following steps:

[0017] 1. Powder gradation mixing: coarse spherical Al powder, fine spherical Al powder and fine B4C powder are ball-milled, stearic acid is used as a process control agent, and the protective atmosphere is argon gas; the ball-milled powder is heat-treated to remove stearic acid to obtain a B4C / Al mixed powder;

[0018] 2. Preparation of B4C / Al preform: B4C / Al mixed powder is loaded into a steel mold, and then a certain pressure is applied and the preform is obtained after holding the pressure for a certain period of time;

[0019] 3. Hot pressing sintering of B4C / Al composite material: The preform is kept at high temperature for a certain period of time, and then high pressure is applied and kept for a certain period of time, and naturally cooled to room temperature. After demolding, a B4C / Al composite material with a harmonious organizational structure is obtained.

[0020] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the particle size of the coarse spherical Al powder in step 1 is 20-100 μm, and the volume fraction of the coarse spherical Al powder is 20-60%. Others are the same as specific embodiment 1.

[0021] Specific embodiment 3: This embodiment is different from the specific embodiment 1 in that the particle size of the fine spherical Al powder in step 1 is 1-5 μm. The rest is the same as the specific embodiment 1.

[0022] Specific embodiment 4: This embodiment is different from specific embodiment 2 in that: the coarse spherical Al powder in step 1 is one of 1xxx, 2xxx, 5xxx, 6xxx or 7xxx. The rest is the same as specific embodiment 2.

[0023] Specific embodiment 5: This embodiment is different from specific embodiment 3 in that the fine spherical Al powder in step 1 is one of 1xxx, 2xxx, 5xxx, 6xxx or 7xxx. The rest is the same as specific embodiment 3.

[0024] Specific embodiment 6: This embodiment differs from specific embodiment 1 in that the heat treatment in step 1 is carried out in an argon atmosphere at a temperature of 400° C. for 0.5 h. The rest is the same as specific embodiment 1.

[0025] Specific implementation method 7: This implementation method is different from the specific implementation method 1 in that the particle size of the fine B4C powder in step 1 is 1-5 μm, and the volume fraction of the fine B4C powder is 5-20%. The rest is the same as the specific implementation method 1.

[0026] Specific embodiment eight: This embodiment differs from specific embodiment one in that: the ball milling process in step one is: the ball-to-material ratio is greater than 3:1, the ball milling speed is less than 300 rpm, the ball milling time is greater than 3 hours, and the amount of stearic acid added is 0.5-1 wt.%. The rest is the same as specific embodiment one.

[0027] Specific embodiment 9: This embodiment differs from specific embodiment 1 in that the pressure in step 2 is 150-200 MPa and the holding time is 5-10 min. The rest is the same as specific embodiment 1.

[0028] Specific embodiment 10: This embodiment differs from specific embodiment 1 in that: the high temperature in step 3 is 600-630°C, the holding time is 2-5h, the high pressure is 300-500MPa, and the holding time is 10-15min. The rest is the same as specific embodiment 1.

[0029] The effect of the present invention is verified by the following experiments:

[0030] Embodiment 1:

[0031] The preparation method of the B4C / Al composite material with a blended structure based on powder grading in this embodiment is carried out according to the following steps:

[0032] 1. Powder grading and mixing: 67.04g of 80μm spherical pure Al powder, 33.52g of 5μm spherical pure Al powder and 10.02g of 5μm B4C powder were ball-milled, and 0.55g of stearic acid was added as a process control agent. The protective atmosphere was argon. The ball-milling process was: ball-to-material ratio 3:1, ball-milling speed 250rpm, and ball-milling time 3h. The ball-milled powder was kept at 400℃ for 0.5h in an argon atmosphere to remove stearic acid;

[0033] 2. Preparation of B4C / Al preform: The B4C / Al mixed powder is placed in a steel mold, and then a pressure of 200 MPa is applied, and the preform is obtained after maintaining the pressure for 5 minutes;

[0034] 3. Hot pressing sintering of B4C / Al composite material: The B4C / Al preform was kept at 630°C for 2.5 hours, then a pressure of 500 MPa was applied and kept for 10 minutes, and naturally cooled to room temperature. After demolding, a B4C / Al composite material with a harmonic structure was obtained.

[0035] Figure 1 This is a microstructure photo of the B4C / Al composite material with a harmonic structure obtained in Example 1. It can be observed that the hard B4C / Al "shell" wraps the soft Al "core", the hard "shells" are interconnected, the soft "core" is independently distributed, and there are no obvious pores, inclusions, etc. The average diameter of the soft "core" is 82.5μm, which is very close to the diameter of the coarse spherical pure Al powder used (80μm).

[0036] Embodiment 2:

[0037] The preparation method of the B4C / Al composite material with a blended structure based on powder grading in this embodiment is carried out according to the following steps:

[0038] 1. Powder grading and mixing: 67.04g of 40μm spherical 7075Al powder, 33.52g of 5μm spherical 7075Al powder and 10.02g of 5μm B4C powder were ball-milled, and 0.55g of stearic acid was added as a process control agent. The protective atmosphere was argon. The ball-milling process was: ball-to-material ratio 3:1, ball-milling speed 250rpm, and ball-milling time 3h. The ball-milled powder was kept at 400℃ for 0.5h in an argon atmosphere to remove stearic acid;

[0039] 2. Preparation of B4C / 7075Al preform: The B4C / 7075Al mixed powder is placed in a steel mold, and then a pressure of 200 MPa is applied, and the preform is obtained after maintaining the pressure for 5 minutes;

[0040] 3. Hot pressing sintering of B4C / 7075Al composite material: The B4C / 7075Al preform was kept at 600°C for 2.5 hours, then a pressure of 500 MPa was applied and kept for 10 minutes, and naturally cooled to room temperature. After demolding, a B4C / 7075Al composite material with a harmonic structure was obtained.

[0041] Figure 2 This is a microstructure photo of the B4C / 7075Al composite material with a harmonic structure obtained in Example 2. It can be observed that the hard B4C / 7075Al "shell" wraps the soft 7075Al "core", the hard "shells" are interconnected, and the soft "cores" are independently distributed, without obvious pores, inclusions, etc. The average diameter of the soft "core" is 39.2μm, which is very close to the diameter of the coarse spherical 7075Al powder (40μm) used.

[0042] Figure 3 The tensile curve of the harmonic structure B4C / 7075Al composite material obtained in Example 2 shows a yield strength of 453.5 MPa, a tensile strength of 612.6 MPa, and an elongation of 11.5%. Compared with the traditional uniform structure B4C / 7075Al composite material, the strength is almost not reduced, but the elongation is increased by 76.9%.

[0043] Figure 4 The SN curve of the harmonic structure B4C / 7075Al composite material obtained in Example 2 shows that under a cyclic load of 300 MPa, the fatigue life is 15627, which is about twice that of the traditional uniform structure B4C / 7075Al composite material. The fatigue limit is 200 MPa, which is 25 MPa higher than that of the traditional uniform structure B4C / 7075Al composite material.

Claims

1. A method for preparing a B4C / Al composite material with a blended structure based on powder grading, characterized in that The preparation method of the B4C / Al composite material with a blended structure based on powder grading is specifically carried out in the following steps:

1. Powder gradation mixing: coarse spherical Al powder, fine spherical Al powder and fine B4C powder are ball-milled, stearic acid is used as a process control agent, and the protective atmosphere is argon gas; the ball-milled powder is heat-treated to remove stearic acid to obtain a B4C / Al mixed powder; 2. Preparation of B4C / Al preform: B4C / Al mixed powder is loaded into a steel mold, and then a certain pressure is applied and the preform is obtained after holding the pressure for a certain period of time; 3. Hot pressing sintering of B4C / Al composite material: The preform is kept at high temperature for a certain period of time, and then high pressure is applied and kept for a certain period of time, and naturally cooled to room temperature. After demolding, a B4C / Al composite material with a harmonious organizational structure is obtained.

2. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 1, characterized in that In step 1, the particle size of the coarse spherical Al powder is 20-100 μm, and the volume fraction of the coarse spherical Al powder is 20-60%.

3. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 1, characterized in that The particle size of the fine spherical Al powder in step 1 is 1 to 5 μm.

4. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 2, characterized in that The coarse spherical Al powder in step 1 is one of 1xxx, 2xxx, 5xxx, 6xxx or 7xxx.

5. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 3, characterized in that The fine spherical Al powder in step 1 is one of 1xxx, 2xxx, 5xxx, 6xxx or 7xxx.

6. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 1, characterized in that The heat treatment in step 1 is carried out in an argon atmosphere at a temperature of 400° C. for 0.5 h.

7. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 1, characterized in that In step 1, the particle size of the fine B4C powder is 1 to 5 μm, and the volume fraction of the fine B4C powder is 5 to 20%.

8. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 1, characterized in that The ball milling process in step 1 is as follows: the ball-to-material ratio is greater than 3:1, the ball milling speed is less than 300 rpm, the ball milling time is greater than 3 hours, and the amount of stearic acid added is 0.5-1 wt.%.

9. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 1, characterized in that The pressure in step 2 is 150-200 MPa, and the holding time is 5-10 min.

10. The method for preparing a B4C / Al composite material with a blended structure based on powder grading according to claim 1, characterized in that In step 3, the high temperature is 600-630° C., the holding time is 2-5 hours, the high pressure is 300-500 MPa, and the holding time is 10-15 minutes.

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