CN109554638B - Preparation method of high-entropy alloy gradient nano material - Google Patents
Preparation method of high-entropy alloy gradient nano material Download PDFInfo
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- CN109554638B CN109554638B CN201910021541.5A CN201910021541A CN109554638B CN 109554638 B CN109554638 B CN 109554638B CN 201910021541 A CN201910021541 A CN 201910021541A CN 109554638 B CN109554638 B CN 109554638B
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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Abstract
The invention belongs to the technical field of material processing, and relates to a preparation method of a high-entropy alloy gradient nano material. The invention aims to prepare a gradient nano material from a high-entropy alloy through stepped high-pressure torsion, so that the problems of large and thick crystal grains and easiness in cracking of the high-entropy alloy are solved, and the application and development of the high-entropy alloy material in various fields are effectively promoted. The implementation method mainly comprises the following steps: preparing a cylindrical high-entropy alloy material, fixing the cylindrical high-entropy alloy material between an upper template and a lower template, applying high pressure to the upper template, twisting the lower template, adjusting a chuck to move downwards to realize graded twisting, and sampling for testing and evaluation. The high-entropy alloy gradient nano material is prepared by the invention, and mainly, the material is subjected to severe plastic deformation through high-pressure torsion, so that the recrystallization of the material is promoted to generate nano crystals, the materials with different heights are subjected to graded torsion through moving the position of a chuck, and the sizes of the generated nano crystals are different due to different torsion strengths, so that the aim of preparing the gradient high-entropy alloy nano material is fulfilled.
Description
Technical Field
The invention belongs to a preparation technology of a high-entropy alloy gradient nano material, and relates to a method for improving the comprehensive performance of the high-entropy alloy and forming the gradient nano material in a severe plastic deformation mode.
Background
The development of metal materials has great influence on human civilization, and with the rapid development of technologies such as aviation, aerospace, electronics, communication and the like, people put higher requirements on the comprehensive performance of the materials.
Conventional alloy designs have primarily been based on one or two elements as the major constituent, followed by the addition of other minor elements to improve the alloy's texture and the desired associated properties. In 1995, Taiwan scholars, Yeyu et al, provided a novel alloy design concept-high entropy alloy, which triggered the research heat trend on multi-principal element alloys.
The High-entropy alloy (High-entropy alloy) is a novel alloy system designed by adopting the concept of multi-principal-element alloy, is an alloy prepared by alloying five or more than five elements according to equal atomic ratio or close to equal atomic ratio, and has excellent properties of High strength, High hardness, High-temperature creep resistance, High-temperature oxidation resistance, corrosion resistance and the like.
The nano material is a material with the size of a structural unit between 1 nanometer and 100 nanometers, and as the size of the nano material is close to the coherence length of electrons, the property of the nano material is greatly changed due to self-organization caused by strong coherence, and various excellent performances are shown.
Obviously, if the excellent performance of the high-entropy alloy can be combined with the excellent performance of the nano material, the comprehensive performance of the high-entropy alloy is expected to be greatly improved, and the application range is expanded.
The gradient structure is a multi-level structure mode of a material structure, and the size of a structural unit of the material is continuously changed in a gradient manner in space, and is increased from a smaller scale, such as a nanometer scale, to a macroscopic scale. Compared with simple mixing or compounding of structures with different characteristic sizes (such as nano-crystalline grains, submicron crystalline grains and coarse crystalline grains), the gradient structure effectively avoids performance mutation caused by structural characteristic size mutation, can coordinate structures with different characteristic sizes, and simultaneously shows various action mechanisms corresponding to the characteristic sizes, so that the overall performance of the material is optimized.
The high-pressure torsion method is an important method for preparing the nano-structure material, and the working principle of the method is that a disc-shaped sample is placed between an upper die and a lower die, pressure is applied to the sample at room temperature or a certain heating temperature, the dies rotate, and the sample is subjected to shear deformation under the equal hydrostatic pressure due to the friction force between the sample and the dies, so that grains are refined, and the nano-structure material is obtained.
By combining the technical principles, the invention provides a technology for preparing a high-entropy alloy gradient nano material by a processing method for enabling high-entropy alloy to generate severe plastic deformation through graded high-pressure torsion. The gradient structure is realized by carrying out high-pressure torsion of different degrees on different positions of the high-entropy alloy, and the material is subjected to severe plastic deformation by applying high-pressure torsion, so that grains are refined to form a nano structure, the internal organization structure of the high-entropy alloy is optimized, the mechanical property of the high-entropy alloy is improved, and meanwhile, the performance problem of a common nano structure is improved by the gradient structure, so that the comprehensive performance of the high-entropy alloy is effectively improved, and the method has great theoretical and practical significance for the application of the high-entropy alloy in production practice.
Disclosure of Invention
The invention aims to provide a preparation technology of a gradient nano material of a high-entropy alloy, which is used for performing high-pressure torsion on a cylindrical high-entropy alloy at different heights to generate nano crystals and realizing grain refinement and grain size gradient control, so that the comprehensive performance of the high-entropy alloy is further improved, and the high-entropy alloy gradient nano material is prepared.
The purpose of high-pressure torsion is to enable the high-entropy alloy to generate violent plastic deformation, promote the transformation of crystal grains, generate nano-crystals and refine the crystal grains. Because the grain size is in direct proportion to the deformation degree, the more severe the deformation is, the finer the grains are, and therefore, the gradient nano material can be obtained by twisting the columnar high-entropy alloy at different heights in different degrees.
In order to achieve the technical aim, the invention adopts the following technical scheme:
the first step is as follows: designing a high-pressure torsion die device. The equipment mainly comprises an upper template, a lower template, a fixture, a box body and a multi-stage hydraulic adjusting device. The upper template is pressurized, the lower template rotates, the clamp fixes the hydraulic adjusting device and the sample, the box fixes the clamp and the template, and the multistage hydraulic adjusting device adjusts the position of the sample twisted under high pressure.
The second step is that: and fixing the upper end of the processed cylindrical high-entropy alloy sample by a fixing device.
The third step: high pressure is applied to the high-entropy alloy sample through the upper template at room temperature or a certain heating temperature, and then the lower template rotates to enable the high-entropy alloy sample to generate high-pressure torsion at a certain angle.
The fourth step: the fixed position of the sample is moved downwards for a certain distance through the adjusting device, and the sample is continuously twisted in the same direction with a larger angle.
The fifth step: the fixed position of the sample is continuously moved downwards, and the torsion angle is continuously increased until the high-pressure torsion of the whole sample is completed.
And a sixth step: and continuously adjusting the torsion angle in the experimental process, and repeating the experiment until the gradient nano material with uniform gradient and excellent comprehensive performance is prepared.
Compared with the prior art, the invention has the following advantages
1. Combines the nanocrystalline and the gradient structure, and the nanocrystalline and the gradient structure are complementary, thereby improving the structure of the high-entropy alloy, refining the crystal grains and improving the comprehensive performance of the high-entropy alloy.
2. The process is simple and easy to realize, the nano material can be prepared through plastic deformation, the comprehensive performance of the high-entropy alloy is improved, and the application value is high.
Drawings
Fig. 1 is a schematic diagram showing preparation of a high-entropy alloy gradient nanomaterial, a cylindrical high-entropy alloy is fixed between an upper template and a lower template, the upper template applies high pressure to a bar, the lower template rotates to enable the bar to be twisted so as to generate severe plastic deformation, and plastic deformation with different degrees can be applied to materials at different parts of the bar in the height direction by moving the position of a chuck, so that the gradient nanomaterial is prepared.
Detailed Description
The high-entropy alloy sample having a height of 100mm shown in FIG. 1 will be specifically described as an example. The operation steps are as follows:
(1) fixing the prepared cylindrical high-entropy alloy sample between an upper template and a lower template, applying high pressure to the bar through the upper template without generating plastic deformation, and fixing the chuck at the uppermost end of the bar.
(2) Applying torque to the lower template to enable the bar to be twisted under a high-pressure state, rotating for 90 degrees along the direction shown in figure 1, and then stopping the rotation of the lower template, so that the whole bar is subjected to severe plastic deformation to generate nanocrystalline.
(3) And opening the chuck, moving the chuck downwards for 10mm, fixing the chuck, and rotating the bar material to 180 degrees in the same direction through the lower template, so that the bar material below the position of the chuck is twisted to a greater extent, and crystal grains at the position below the chuck are finer.
(4) And continuously repeating the steps, wherein the chuck moves downwards by 10mm each time, and the equidirectional rotation angle of the bar is increased by 90 degrees until the position of the chuck moves to the lowest end.
(5) And opening the chuck after the machining is finished, unloading the load, taking out the sample, detecting and evaluating whether the expected requirements are met, if the expected requirements are not met, adjusting the technological parameters such as pressure, rotation speed, rotation angle and the like, and repeating the test until the part meeting the expected performance requirements is machined.
Claims (2)
1. A preparation method of a high-entropy alloy gradient nano material comprises the following steps:
(1) fixing the prepared cylindrical high-entropy alloy sample between an upper template and a lower template, applying high pressure to the bar through the upper template without causing plastic deformation, and fixing a chuck at the uppermost end of the bar;
(2) applying torque to the lower template to enable the bar to be twisted under a high-pressure state, rotating the bar for 90 degrees along a specific direction, and then stopping the rotation of the lower template to enable the whole bar to be subjected to severe plastic deformation so as to generate nanocrystalline;
(3) opening the chuck, moving downwards for 10mm and then fixing, and rotating the bar material to 180 degrees in the same direction through the lower template, so that the bar material below the position of the chuck is twisted to a greater extent, and crystal grains at the position below the chuck are finer;
(4) continuously repeating the steps, wherein the chuck moves downwards by 10mm each time, the equidirectional rotation angle of the bar is increased by 90 degrees until the position of the chuck moves to the lowest end;
(5) and opening the chuck after the machining is finished, unloading the load, taking out the sample, detecting and evaluating whether the expected requirements are met, if the expected requirements are not met, adjusting the technological parameters of pressure, rotation speed and rotation angle, and repeating the test until the part meeting the expected performance requirements is machined.
2. The preparation method of the high-entropy alloy gradient nanomaterial according to claim 1, characterized in that: the material is subjected to severe plastic deformation by applying high pressure and twisting the material under the high-pressure state, and the severe plastic deformation can promote recrystallization of the material to realize crystal grain transformation, so that the nanocrystalline is prepared; the gradient material is prepared by twisting different parts of the material in stages, the materials at different parts have different twisting angles and different plastic deformation degrees, so that the nanocrystals with different sizes are prepared; the method has the advantages of simple device, easy realization, capability of preparing the gradient nano material by simple process equipment, fundamental improvement on the problems of large and large crystal grains of the high-entropy alloy and easy cracking in the deformation process, high processing efficiency and great application value.
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| CN106140950B (en) * | 2015-03-31 | 2020-08-14 | 南京理工大学 | High-pressure torsion superposition manufacturing method and device |
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