A method for nanostructuring metal surface based on in-situ shear force

Abstract

The present invention is a method for nano-crystallizing a metal surface based on in-situ shear force, the method comprising the following steps: a) alternately layering a mixture of Ti powder, Al powder and WC powder in a mold and cold pressing to form a laminated structure, wherein the cold pressing obtains a block having a density of 50-60%; b) heating and pressurizing the cold-pressed block at a heating temperature of 500-600°C, and obtaining a block density of 70-80%; c) maintaining the heating and pressurizing state of step b and raising the temperature to 800-900°C, and then rotating the block at a rotation speed of 80-100 rad / min for 0.5-1 hour, wherein the WC powder particles act as a grinding agent and The adjacent Ti powder particles are broken into nano-size, and the final block density is 90-95%; d. Finally, the block is subjected to high-temperature sintering, the heating temperature is 1100-1200 ° C, the heat preservation is 0.5-1h, and after cooling to room temperature, a metal material with 100% density, nanostructure and multiple layers is obtained; in the method of the present invention, due to the mutual penetration of low-melting point components and high-melting point components, and the maintenance of the morphology and position of the strengthening particles during the penetration process, the strengthening particles play the role of internal grinding of the organization during the high-pressure torsion process, and the high-temperature and high-pressure sintering after grinding completely integrates the strengthening particles into the organization, making the entire block organization less likely to produce internal cracks.

Description

Technical Field

[0001] The invention relates to a metal surface tissue nano-structuring method based on in-situ shearing force, and belongs to the technical field of powder metallurgy. Background Art

[0002] The general solidification and forming methods of powder metallurgy block materials include hot isostatic pressing, hot pressing and sintering, and powder direct forging. Hot isostatic pressing and powder direct forging are suitable for the preparation of larger block materials, and the density of the block materials can reach 100%. Hot pressing and sintering are suitable for the preparation of smaller block materials. In the preparation process, since it does not require prefabricated powder packaging, the composition can be flexibly changed. However, the structure is relatively coarse and no recrystallization occurs. Recrystallization relies on subsequent heat treatment, which increases the manufacturing cost.

[0003] The present invention is designed to address the above-mentioned existing technical situation and provides a method for metal surface nanostructure preparation based on in-situ shear force. Its purpose is to obtain a fully dense bulk metal material with a gradient structure. Reinforcement particles are dispersed in the structure of the metal material, and the grain size on both sides of the reinforcement particles reaches the nanometer level. The grain size in the structure changes in a layered step manner. This bulk metal material can be used in the preparation of components such as stepped shafts.

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

[0005] The method for nanostructuring a metal surface based on in-situ shearing force proposed by the present invention comprises the following steps:

[0006] a. A mixture of Ti powder, Al powder and WC powder is alternately layered in a mold and cold pressed to form a laminated structure. Each time a layer of Ti powder or a mixture of Al powder and WC powder is laid, the entire block in the mold is cold pressed once. The density of the block after cold pressing is 50-60%.

[0007] b. Heating and pressurizing the cold-pressed block at a temperature of 500-600°C, at which the Al powder begins to soften, and the final block density is 70-80%;

[0008] c. Maintaining the heating and pressurizing state of step b, the temperature is raised to 800-900°C. At this temperature, the Al powder begins to melt and penetrate into the gaps between the Ti powder particles below. The block is then rotated at a speed of 80-100 rad / min for 0.5-1 hour. During the rotation, the WC powder particles act as a grinding agent and break the adjacent Ti powder particles into nano-size particles. The final block density is 90-95%.

[0009] d. Finally, the block is sintered at a high temperature of 1100-1200°C for 0.5-1 hour, and then cooled to room temperature to obtain a metal material with 100% density, nanostructure and multiple layers.

[0010] In addition, in the above step a, the particle size of the Ti powder, Al powder and WC powder is -300 to -400 mesh, and the purity is 99.99%.

[0011] In addition, in the above step b, the Ti powder and Al powder particles in each layer of the block undergo plastic deformation. The plastic deformation of the Ti powder and Al powder particles can buffer the WC powder particles and enable them to maintain their original morphology.

[0012] In addition, in the above step b, the thickness of the layer of the mixture of Al powder and WC powder is 70-80% of the thickness of the layer of Ti powder.

[0013] In addition, the pressures of the cold pressing in step a and the pressurizing in steps b and c are all 900 to 1000 MPa.

[0014] In addition, in the mixture of Al powder and WC powder, the volume fraction of Al powder is 60-70%.

[0015] In one embodiment, the steps of the metal surface nanostructure method based on in-situ shear force are as follows:

[0016] Step 1: Raw material preparation

[0017] Prepare Ti powder, Al powder and WC powder, the powder particle size is -300 to -400 mesh, and the purity is 99.99%;

[0018] Step 2: Powder cold pressing

[0019] In a vacuum environment, Ti powder is layered on the bottom of a cylindrical mold with a diameter of 100 to 200 mm to a thickness of 1 to 3 mm, and then cold pressed at a pressure of 900 to 1000 MPa for 0.5 to 1 hour to obtain a Ti powder layer. Then, a mixture layer of Al powder and WC powder is laid on the cold-pressed Ti powder layer to a thickness of 70 to 80% of the thickness of the Ti powder layer. The volume fraction of Al powder in the mixture of Al powder and WC powder is 60 to 70%. Then, cold pressed again at a pressure of 900 to 1000 MPa for 0.5 to 1 hour to obtain an Al powder and WC powder layer, wherein the Ti powder and Al powder undergo plastic deformation, and under the buffering effect of the plastic deformation of the Ti powder and Al powder, the WC powder maintains its initial morphology.

[0020] Step 3: Accumulate cold pressure

[0021] Repeat step 2 5 to 10 times until a Ti-Al / WC-Ti-Al / WC-…-Al / WC–Ti multilayer powder cold-pressed block is obtained. The Ti powder layer, Al powder layer, and WC powder layer in the block are mechanically bonded. As the plastic deformation of the Ti and Al powders gradually decreases from bottom to top, the density of the block also gradually decreases. After the cold pressing, the density of the block is 50 to 60%.

[0022] Step 4: Heating and pressing

[0023] The cold-pressed block is heated and pressurized at a temperature of 500-600°C. At this temperature, the Al powder begins to soften. Since the density of the block gradually decreases from bottom to top, the softened Al powder does not penetrate downward into the Ti powder layer. At the same time, the block is pressurized at a pressure of 900-1000 MPa for 0.5-1 hour. As the height of the block decreases, the density of the block tends to be uniform, the gas in the pores is discharged, and the combination of the Ti powder layer, Al powder and WC powder layer in the block is transformed into an adhesive bond. The final block density is 70-80%.

[0024] Step 5: High temperature and high pressure torsion

[0025] Maintaining the heating and pressurizing state of step 4 and raising the temperature to 800-900°C, at which temperature the Al powder begins to melt and penetrate into the gaps between the Ti powder particles below. The WC powder particles, due to their particle size being consistent with those of the Ti and Al powders, remain between the Ti powder layer and the Al and WC powder layers. The block is then rotated at a speed of 80-100 rad / min for 0.5-1 hour. During the rotation, the WC powder particles act as a grinding agent and break the adjacent Ti powder particles into nano-sizes. The resulting block has a density of 90-95%.

[0026] Step 6: High temperature sintering

[0027] Finally, the block is sintered at a high temperature of 1100-1200°C, kept warm for 0.5-1 hour, and then cooled to room temperature, ultimately obtaining a metal material with 100% density, nanostructure, and multiple layers.

[0028] The characteristics and beneficial effects of the technical solution of the present invention are:

[0029] 1. The present invention provides a powder metallurgy method for obtaining nanostructures. Unlike traditional methods such as hot isostatic pressing, hot pressing and sintering, and direct powder forging, this method can be used to prepare large-scale bulk materials and flexibly change the bulk composition. It does not require prefabricated powder coatings, and the bulk structure is fine, fully dense, and nano-scaled, with the strengthening particles dispersed throughout the microstructure.

[0030] Second, through the present invention, different temperature rise treatments during the preparation process are the key to obtaining a fully dense structure. By taking advantage of the difference in melting points between the bulk components, the low-melting-point component undergoes plastic deformation-softening-melting, fully combining with the high-melting-point component. Unlike interfacial reactions, this method is simpler and more efficient.

[0031] 3. Through the scheme of the present invention, due to the mutual penetration of low-melting point components and high-melting point components, and the maintenance of the morphology and position of the strengthening particles during the penetration process, the strengthening particles play a role of internal grinding of the tissue during the high-pressure torsion process. The high-temperature and high-pressure sintering after grinding completely integrates the strengthening particles into the tissue, making it difficult for the entire block tissue to produce internal cracks. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be further described in detail below with reference to the embodiments:

[0033] In this embodiment, the steps of the metal surface nanostructure method based on in-situ shear force of the present invention are as follows:

[0034] Step 1: Raw material preparation

[0035] Prepare Ti powder, Al powder and WC powder, the powder particle size is -300 to -400 mesh, and the purity is 99.99%;

[0036] Step 2: Powder cold pressing

[0037] In a vacuum environment, Ti powder is layered on the bottom of a cylindrical mold with a diameter of 100 to 200 mm to a thickness of 1 to 3 mm, and then cold pressed at a pressure of 900 to 1000 MPa for 0.5 to 1 hour to obtain a Ti powder layer. Then, a mixture layer of Al powder and WC powder is laid on the cold-pressed Ti powder layer to a thickness of 70 to 80% of the thickness of the Ti powder layer. The volume fraction of Al powder in the mixture of Al powder and WC powder is 60 to 70%. Then, cold pressed again at a pressure of 900 to 1000 MPa for 0.5 to 1 hour to obtain an Al powder and WC powder layer, wherein the Ti powder and Al powder undergo plastic deformation, and under the buffering effect of the plastic deformation of the Ti powder and Al powder, the WC powder maintains its initial morphology.

[0038] Step 3: Accumulate cold pressure

[0039] Repeat step 2 5 to 10 times until a Ti-Al / WC-Ti-Al / WC-…-Al / WC–Ti multilayer powder cold-pressed block is obtained. The Ti powder layer, Al powder layer, and WC powder layer in the block are mechanically bonded. As the plastic deformation of the Ti and Al powders gradually decreases from bottom to top, the density of the block also gradually decreases. After the cold pressing, the density of the block is 50 to 60%.

[0040] Step 4: Heating and pressing

[0041] The cold-pressed block is heated and pressurized at a temperature of 500-600°C. At this temperature, the Al powder begins to soften. Since the density of the block gradually decreases from bottom to top, the softened Al powder does not penetrate downward into the Ti powder layer. At the same time, the block is pressurized at a pressure of 900-1000 MPa for 0.5-1 hour. As the height of the block decreases, the density of the block tends to be uniform, the gas in the pores is discharged, and the combination of the Ti powder layer, Al powder and WC powder layer in the block is transformed into an adhesive bond. The final block density is 70-80%.

[0042] Step 5: High temperature and high pressure torsion

[0043] Maintaining the heating and pressurizing state of step 4 and raising the temperature to 800-900°C, at which temperature the Al powder begins to melt and penetrate into the gaps between the Ti powder particles below. The WC powder particles, due to their particle size being consistent with those of the Ti and Al powders, remain between the Ti powder layer and the Al and WC powder layers. The block is then rotated at a speed of 80-100 rad / min for 0.5-1 hour. During the rotation, the WC powder particles act as a grinding agent and break the adjacent Ti powder particles into nano-sizes. The resulting block has a density of 90-95%.

[0044] Step 6: High temperature sintering

[0045] Finally, the block is sintered at a high temperature of 1100-1200°C, kept warm for 0.5-1 hour, and then cooled to room temperature, ultimately obtaining a metal material with 100% density, nanostructure, and multiple layers.

Claims

1. A method for nanostructuring a metal surface based on in-situ shear force, characterized by: The steps of the method include: a. A mixture of Ti powder, Al powder and WC powder is alternately layered in a mold and cold pressed to form a laminated structure. Each time a layer of Ti powder or a mixture of Al powder and WC powder is laid, the entire block in the mold is cold pressed once. The density of the block after cold pressing is 50-60%. b. Heating and pressurizing the cold-pressed block at a temperature of 500-600°C, at which the Al powder begins to soften, and the final block density is 70-80%; c. Maintaining the heating and pressurizing state of step b, the temperature is raised to 800-900°C. At this temperature, the Al powder begins to melt and penetrate into the gaps between the Ti powder particles below. The block is then rotated at a speed of 80-100 rad / min for 0.5-1 hour. During the rotation, the WC powder particles act as a grinding agent and break the adjacent Ti powder particles into nano-size particles. The final block density is 90-95%. d. Finally, the block is sintered at a high temperature of 1100-1200°C for 0.5-1 hour, and then cooled to room temperature to obtain a metal material with 100% density, nanostructure and multiple layers.

2. The metal surface nanostructure method based on in-situ shear force according to claim 1, characterized in that: In the above step a, the particle size of the Ti powder, Al powder and WC powder is -300 to -400 mesh, and the purity is 99.99%.

3. The metal surface nanostructure method based on in-situ shear force according to claim 1, characterized in that: In the above step b, the Ti powder and Al powder particles in each layer of the block undergo plastic deformation. The plastic deformation of the Ti powder and Al powder particles can buffer the WC powder particles and enable them to maintain their original morphology.

4. The metal surface nanostructure method based on in-situ shear force according to claim 1, characterized in that: In the above step b, the thickness of the layer of the mixture of Al powder and WC powder is 70-80% of the thickness of the layer of Ti powder.

5. The method for nanostructuring a metal surface based on in-situ shear force according to claim 1, characterized in that: The pressures of the cold pressing in step a and the pressurizing in steps b and c are all 900 to 1000 MPa.

6. The metal surface nanostructure method based on in-situ shear force according to claim 1, characterized in that: In the mixture of Al powder and WC powder, the volume fraction of Al powder is 60-70%.

7. The method for nanostructuring a metal surface based on in-situ shear force according to claim 1, characterized in that: The steps of this method are as follows: Step 1: Raw material preparation Prepare Ti powder, Al powder and WC powder, the powder particle size is -300 to -400 mesh, and the purity is 99.99%; Step 2: Powder cold pressing In a vacuum environment, Ti powder is layered on the bottom of a cylindrical mold with a diameter of 100 to 200 mm to a thickness of 1 to 3 mm, and then cold pressed at a pressure of 900 to 1000 MPa for 0.5 to 1 hour to obtain a Ti powder layer. Then, a mixture layer of Al powder and WC powder is laid on the cold-pressed Ti powder layer to a thickness of 70 to 80% of the thickness of the Ti powder layer. The volume fraction of Al powder in the mixture of Al powder and WC powder is 60 to 70%. Then, cold pressed again at a pressure of 900 to 1000 MPa for 0.5 to 1 hour to obtain an Al powder and WC powder layer, wherein the Ti powder and Al powder undergo plastic deformation, and under the buffering effect of the plastic deformation of the Ti powder and Al powder, the WC powder maintains its initial morphology. Step 3: Accumulate cold pressure Repeat step 2 5 to 10 times until a Ti-Al / WC-Ti-Al / WC-…-Al / WC–Ti multilayer powder cold-pressed block is obtained. The Ti powder layer, Al powder layer, and WC powder layer in the block are mechanically bonded. As the plastic deformation of the Ti and Al powders gradually decreases from bottom to top, the density of the block also gradually decreases. After the cold pressing, the density of the block is 50 to 60%. Step 4: Heating and pressing The cold-pressed block is heated and pressurized at a temperature of 500-600°C. At this temperature, the Al powder begins to soften. Since the density of the block gradually decreases from bottom to top, the softened Al powder does not penetrate downward into the Ti powder layer. At the same time, the block is pressurized at a pressure of 900-1000 MPa for 0.5-1 hour. As the height of the block decreases, the density of the block tends to be uniform, the gas in the pores is discharged, and the combination of the Ti powder layer, Al powder and WC powder layer in the block is transformed into an adhesive bond. The final block density is 70-80%. Step 5: High temperature and high pressure torsion Maintaining the heating and pressurizing state of step 4 and raising the temperature to 800-900°C, at which temperature the Al powder begins to melt and penetrate into the gaps between the Ti powder particles below. The WC powder particles, due to their particle size being consistent with those of the Ti and Al powders, remain between the Ti powder layer and the Al and WC powder layers. The block is then rotated at a speed of 80-100 rad / min for 0.5-1 hour. During the rotation, the WC powder particles act as a grinding agent and break the adjacent Ti powder particles into nano-sizes. The resulting block has a density of 90-95%. Step 6: High temperature sintering Finally, the block is sintered at a high temperature of 1100-1200°C, kept warm for 0.5-1 hour, and then cooled to room temperature, ultimately obtaining a metal material with 100% density, nanostructure, and multiple layers.