Powder metallurgy method for improving strength and obtaining cohesion microstructure

Abstract

The invention relates to a powder metallurgy method for improving strength and obtaining a cohesion microstructure, which comprises the following steps of: firstly, enabling metal powder or metal liquid drops to generate plastic deformation under the action of mechanical stress and low-temperature cooling, and keeping the plastic deformation without restoring and recrystallizing; the device for achieving the mechanical stress and low-temperature cooling effects in the metallurgical method comprises a cooling disc (1), a cooling sleeve (2) and a hot pressing chamber (3), the cooling disc (1) can rotate around the central axis of the cooling disc (1), fan-shaped blades are installed on the edge of the cooling disc (1), a cooling sleeve (2) containing liquid nitrogen is arranged around the cooling disc (1), and a hot pressing chamber (3) is arranged below the cooling sleeve (2). According to the method, through the sequential design of powder laying layers, all components show anisotropy, and higher strength of materials is achieved in the specific direction.

Description

Technical Field

[0001] The invention discloses a powder metallurgy method for improving strength and obtaining a cohesive microstructure, and belongs to the technical field of heat dissipation component processing and manufacturing. Background Art

[0002] TiAl powder metallurgy bulk materials are widely used in the manufacture of components in the aerospace field due to their mechanical properties such as high strength. However, the material is brittle and easily damaged. Therefore, how to improve the toughness and improve the brittleness of TiAl powder metallurgy bulk materials is a hot topic for researchers. At present, a series of manufacturing methods are being explored at home and abroad, usually by adding other toughening phases to improve their brittleness. However, these methods often require the prefabrication of many alloy phases, and the adjustment method is not flexible. In addition, the study found that the alloy phase strengthening changes under stress and high temperature conditions. The reason for the failure of the alloy under long-term heating and loading conditions is that the strengthening elements in the alloy that resist dislocations are greatly reduced. Summary of the invention

[0003] The present invention is designed to address the above-mentioned existing technical situation and provides a powder metallurgy method for improving strength and obtaining a cohesive microstructure. This method makes each component exhibit anisotropy through the sequential design of powder layering, so that the material can achieve higher strength along a specific direction.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] This powder metallurgy method for improving strength and obtaining a cohesive microstructure first causes metal powder or metal droplets to undergo plastic deformation under the action of mechanical force and low-temperature cooling, after which the plastic deformation will not recover or recrystallize but will be retained. The product of the metal powder or metal droplets after the above treatment and cooling is layered and stacked, and then hot-pressed and sintered. After cooling, a cohesive microstructure material can be obtained.

[0006] During implementation, the device for realizing mechanical stress and low-temperature cooling in the metallurgical method includes a cooling plate 1, a cooling jacket 2 and a hot pressing chamber 3. The cooling plate 1 can rotate around its central axis and has fan-shaped blades installed on the edge. A cooling jacket 2 with liquid nitrogen inside is arranged around the cooling plate 1, and a hot pressing chamber 3 is arranged below the cooling jacket 2.

[0007] In addition, the fan-shaped blades are distributed along the radial direction of the rotation circumference of the cooling disk 1 .

[0008] In addition, the cooling jacket 2 and the hot pressing chamber 3 are made of stainless steel.

[0009] In implementation, the steps of preparing Mg-Al-Ti-Cu compound using the device are as follows:

[0010] Step 1, prepare Mg powder, Al powder, Ti powder and Cu powder with a powder particle size of -300 to -400 mesh, wherein the volume percentage of Mg powder and Cu powder is 20% and 10% respectively, and the volume percentage of Ti powder and Al powder is 35%;

[0011] Step 2: Start the cooling disk 1, rotate at a speed of 50-200 rad / s, sprinkle Ti powder from the top of the cooling disk 1, and let the Ti powder pass through the cooling disk 1 and the cooling chamber 2 into the hot pressing chamber 3 to form a layer. During this process, the Ti powder is hit by the fan-shaped blades of the cooling disk 1 and collides with the inner wall of the cooling chamber 2 to cause plastic deformation, but due to the cooling effect of the liquid nitrogen in the cooling jacket 2, no recovery and recrystallization occurs;

[0012] Step 3: The molten Al powder droplets are passed through the cooling plate 1 and the cooling chamber 2 into the hot pressing chamber 3 to form a layer. During this process, the aluminum powder droplets are hit by the fan-shaped blades of the cooling plate 1 and collide with the inner wall of the cooling chamber 2 to form a plate shape, but due to the cooling effect of the liquid nitrogen in the cooling jacket 2, recovery and recrystallization do not occur;

[0013] Step 4: hot press sintering the above two metal layers in the hot press chamber 3 at a sintering temperature of 600°C and a pressure of 800-1000 MPa for 30 minutes. During this process, the morphology of Ti and Al metals is restored, so that Al metal softens and wraps Ti metal.

[0014] Step 5: Repeat step 2 to lay the Ti powder in the hot pressing chamber 3;

[0015] Step 6: Repeat step 3 twice to lay Mg powder and Al powder in the hot pressing chamber 3 respectively;

[0016] Step 7: hot press sintering the whole layer in the hot press chamber 3, the sintering temperature is 600°C, the pressure is 800-1000MPa, and the temperature and pressure are kept for 30 minutes. During this process, the morphology of Ti, Mg, and Al metals is restored, so that Al metal and Mg metal are softened and wrap Ti metal;

[0017] Step 8: Repeat step 2 to lay Ti powder in the hot pressing chamber 3;

[0018] Step 9, repeat step 3 three times, and respectively lay Mg powder, Cu powder, and Al powder in the hot pressing chamber 3;

[0019] Step 10, repeat step 2 to lay the Ti powder in the hot pressing chamber 3;

[0020] Step 11: hot press sintering the entire layer in the hot press chamber 3 at a sintering temperature of 600°C and a pressure of 800-1000MPa for 30 minutes. Then, the temperature is increased to 1000-1100°C and the pressure is increased to 1500-1700MPa for 30 minutes. After cooling to room temperature, a powder block material with high strength and cohesive microstructure can be obtained.

[0021] In this embodiment, Ti and Al are used as matrix materials, Mg and Cu are used as reinforcing agents. During the low-temperature sintering stage, Al and Mg are softened and wrap around Ti, so that Ti always maintains a certain "boundary", while Cu does not melt during the sintering stage and always maintains a plate shape and is embedded in the microstructure. During the high-temperature sintering stage, Al and Mg melt on the one hand and fill the microstructure gaps like "mortar", while Cu is only slightly melted at this time, and the internal strength is improved by means of surface tension.

[0022] The prepared Mg-Al-Ti-Cu compound is a bulk material, which is mainly composed of Ti, Al, Mg and Cu, wherein the components in the microstructure have different shapes, Ti is nearly spherical, wrapped with Al and Mg on the outside, Cu is plate-like, small in size and embedded in Ti, Al and Mg, and dispersed in the microstructure. This microstructure is similar to the design of "bricks and mortar", which achieves high strength and high cohesion of the microstructure and can inhibit the expansion of cracks; in addition, before hot pressing and sintering of powder metallurgy materials, Ti, Al, Mg and Cu powders appear in the microstructure in the form of particles and plates, respectively, and the powders in the form of particles and plates before hot pressing and sintering are full of defects such as dislocations, which are more likely to make grains refined in the subsequent hot pressing and sintering process, thereby increasing the overall strength of the material by 30%;

[0023] In this implementation device, through the design of the cooling plate and the cooling chamber, the powder raw material can quickly change its shape while freezing the internal defects of the powder. By utilizing the heat-resistant properties of Ti, Al, Mg and Cu, a thin-sheet embedded microstructure phenomenon is formed during the subsequent heat treatment process, thereby blocking dislocation movement and improving the alloy's stress resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the device described in the technical solution of the present invention DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments:

[0026] See attached Figure 1As shown, the device for implementing the method of the present invention comprises a cooling plate 1, a cooling jacket 2 and a hot pressing chamber 3. The cooling plate 1 can rotate around its central axis and is provided with fan-shaped blades at its edge. The fan-shaped blades are distributed radially along the circumference of the rotation of the cooling plate 1. The cooling jacket 2 containing liquid nitrogen is provided around the cooling plate 1, and the hot pressing chamber 3 is provided below the cooling jacket 2. The cooling jacket 2 and the hot pressing chamber 3 are made of stainless steel.

[0027] In this embodiment, the Mg-Al-Ti-Cu compound is prepared using the above device, and the steps are as follows:

[0028] Step 1, prepare Mg powder, Al powder, Ti powder and Cu powder with a powder particle size of -300 to -400 mesh, wherein the volume percentage of Mg powder and Cu powder is 20% and 10% respectively, and the volume percentage of Ti powder and Al powder is 35%;

[0029] Step 2: Start the cooling disk 1, rotate at a speed of 50-200 rad / s, sprinkle Ti powder from the top of the cooling disk 1, and let the Ti powder pass through the cooling disk 1 and the cooling chamber 2 into the hot pressing chamber 3 to form a layer. During this process, the Ti powder is hit by the fan-shaped blades of the cooling disk 1 and collides with the inner wall of the cooling chamber 2 to cause plastic deformation, but due to the cooling effect of the liquid nitrogen in the cooling jacket 2, no recovery and recrystallization occurs;

[0030] Step 3: The molten Al powder droplets are passed through the cooling plate 1 and the cooling chamber 2 into the hot pressing chamber 3 to form a layer. During this process, the aluminum powder droplets are hit by the fan-shaped blades of the cooling plate 1 and collide with the inner wall of the cooling chamber 2 to form a plate shape, but due to the cooling effect of the liquid nitrogen in the cooling jacket 2, recovery and recrystallization do not occur;

[0031] Step 4: hot press sintering the above two metal layers in the hot press chamber 3 at a sintering temperature of 600°C and a pressure of 800-1000 MPa for 30 minutes. During this process, the morphology of Ti and Al metals is restored, so that Al metal softens and wraps Ti metal.

[0032] Step 5: Repeat step 2 to lay the Ti powder in the hot pressing chamber 3;

[0033] Step 6: Repeat step 3 twice to lay Mg powder and Al powder in the hot pressing chamber 3 respectively;

[0034] Step 7: hot press sintering the whole layer in the hot press chamber 3, the sintering temperature is 600°C, the pressure is 800-1000MPa, and the temperature and pressure are kept for 30 minutes. During this process, the morphology of Ti, Mg, and Al metals is restored, so that Al metal and Mg metal are softened and wrap Ti metal;

[0035] Step 8: Repeat step 2 to lay Ti powder in the hot pressing chamber 3;

[0036] Step 9, repeat step 3 three times, and respectively lay Mg powder, Cu powder, and Al powder in the hot pressing chamber 3;

[0037] Step 10, repeat step 2 to lay the Ti powder in the hot pressing chamber 3;

[0038] Step 11: hot press sintering the entire layer in the hot press chamber 3 at a sintering temperature of 600°C and a pressure of 800-1000MPa for 30 minutes. Then, the temperature is increased to 1000-1100°C and the pressure is increased to 1500-1700MPa for 30 minutes. After cooling to room temperature, a powder block material with high strength and cohesive microstructure can be obtained.

Claims

1. A powder metallurgy method for improving strength and obtaining a cohesive microstructure, characterized in that: The metallurgical method first causes metal powder or metal droplets to undergo plastic deformation under the action of mechanical force and low-temperature cooling, and then the plastic deformation will not recover or recrystallize but will be retained. The products of the metal powder or metal droplets after the above treatment and cooling are layered and stacked, and then hot-pressed and sintered. After cooling, a cohesive microstructure material can be obtained.

2. The powder metallurgy method for improving strength and obtaining a cohesive microstructure according to claim 1, characterized in that: The device for realizing mechanical stress and low-temperature cooling in the metallurgical method comprises a cooling plate (1), a cooling jacket (2) and a hot pressing chamber (3); the cooling plate (1) can rotate around its central axis and has fan-shaped blades installed at its edge; a cooling jacket (2) containing liquid nitrogen is arranged around the cooling plate (1); and a hot pressing chamber (3) is arranged below the cooling jacket (2).

3. The powder metallurgy method for improving strength and obtaining a cohesive microstructure according to claim 2, characterized in that: The fan-shaped blades are distributed radially along the rotation circumference of the cooling disk (1).

4. The powder metallurgy method for improving strength and obtaining a cohesive microstructure according to claim 2, characterized in that: The cooling jacket (2) and the hot pressing chamber (3) are made of stainless steel.

5. The powder metallurgy method for improving strength and obtaining a cohesive microstructure according to claim 2, characterized in that: The steps of preparing Mg-Al-Ti-Cu compound by using the device are as follows: Step 1, prepare Mg powder, Al powder, Ti powder and Cu powder with a powder particle size of -300 to -400 mesh, wherein the volume percentage of Mg powder and Cu powder is 20% and 10% respectively, and the volume percentage of Ti powder and Al powder is 35%; Step 2: Start the cooling disk (1) at a rotation speed of 50-200 rad / s, sprinkle Ti powder from the top of the cooling disk (1), and allow the Ti powder to pass through the cooling disk (1) and the cooling chamber (2) into the hot pressing chamber (3) to form a layer. During this process, the Ti powder is hit by the fan-shaped blades of the cooling disk (1) and collides with the inner wall of the cooling chamber (2), causing plastic deformation. However, due to the cooling effect of the liquid nitrogen in the cooling jacket (2), recovery and recrystallization do not occur. Step 3: The molten Al powder droplets are passed through the cooling plate (1) and the cooling chamber (2) into the hot pressing chamber (3) to form a layer. During this process, the aluminum powder droplets are hit by the fan-shaped blades of the cooling plate (1) and collide with the inner wall of the cooling chamber (2) to form a plate shape, but due to the cooling effect of the liquid nitrogen in the cooling jacket (2), recovery and recrystallization do not occur; Step 4: hot press sintering the two metal layers in a hot press chamber (3) at a sintering temperature of 600° C. and a pressure of 800-1000 MPa for 30 minutes. During this process, the morphology of the Ti and Al metals is restored, so that the Al metal softens and wraps the Ti metal. Step 5, repeat step 2 to lay the Ti powder in the hot pressing chamber (3); Step 6: Repeat step 3 twice to lay Mg powder and Al powder in the hot pressing chamber (3) respectively; Step 7, hot pressing and sintering the whole layer in the hot pressing chamber (3), the sintering temperature is 600°C, the pressure is 800-1000MPa, and the temperature and pressure are kept for 30 minutes. During this process, the morphology of Ti, Mg and Al metals is restored, and Al metal and Mg metal are softened and wrap Ti metal; Step 8: Repeat step 2 to lay Ti powder in the hot pressing chamber (3); Step 9, repeat step 3 three times, and respectively lay Mg powder, Cu powder, and Al powder in the hot pressing chamber (3); Step 10, repeat step 2 to lay Ti powder in the hot pressing chamber (3); Step 11: hot press sintering the entire laminate in the hot press chamber (3) at a sintering temperature of 600°C and a pressure of 800-1000 MPa for 30 minutes, then raising the temperature to 1000-1100°C and the pressure to 1500-1700 MPa for 30 minutes. After cooling to room temperature, a powder block material with a high strength and cohesive microstructure can be obtained.

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