CN116162841A - Ultrahigh yield strength block nanocrystalline medium entropy VCoNi alloy and preparation method thereof - Google Patents
Ultrahigh yield strength block nanocrystalline medium entropy VCoNi alloy and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C30/00—Alloys containing less than 50% by weight of each constituent
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
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- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/02—Compacting only
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
Abstract
The invention relates to the field of nanocrystalline manufacturing and powder metallurgy, and discloses an ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy and a preparation method thereof, wherein the microstructure is a single-phase FCC (fluid catalytic cracking) structure, and the bulk nanocrystalline alloy has high purity, uniform structure, average grain size of less than 50nm and yield strength of up to 3.4 GPa; the chemical elements in the VCoNi alloy are as follows: v: co: ni=1:1:1; and the purity of each pure element of the smelting parent metal is more than or equal to 99.95 percent. The preparation process can be used for preparing the traditional block nanocrystalline, the block material with the high-purity average grain size smaller than 50nm is difficult to prepare, the whole preparation process of the preparation scheme is completed in the ultrahigh vacuum cavity, the condition that a sample is oxidized does not exist, the influence of impurity elements on the performance of the sample can be greatly avoided, and the preparation process has a great effect on the development of nanocrystalline theory and engineering application.
Description
Technical Field
The invention relates to the fields of nanocrystalline manufacturing and powder metallurgy, in particular to an ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy and a preparation method thereof.
Background
Metallic materials have become indispensable engineering structural materials by virtue of excellent workability, higher recyclability, and excellent mechanical properties. However, as the human society further develops, the requirements for the properties of metallic materials are also increasing. Designing and preparing metallic materials with more excellent properties is always a goal pursued by the materials community. Tissue nanocrystallization is considered to be an effective means of greatly improving the performance of metallic materials. However, the current mainstream preparation methods (such as multi-pass rolling, high-pressure torsion, equal-diameter angular extrusion, cold drawing, high-energy ball milling and powder sintering) cannot be widely used for preparing metal nanocrystalline bulk materials with high purity and average grain size less than 50 nm.
In recent years, the medium-high entropy alloy has a great deal of excellent physical and chemical properties as a hot spot for current research, and is a novel metal structural material with wide market application prospect. The entropy alloy in VCoNi has excellent mechanical properties due to the fact that the entropy alloy has a large lattice distortion effect and Hall-Petch coefficient: the yield strength is as high as approximately 1GPa at an average grain size of 1 μm. How to effectively improve the mechanical property through reasonable and scientific tissue regulation is a key for promoting the future development and application of the materials.
Chinese patent document with publication number CN 115478201A discloses a double ordered phase CoNiV-based entropy alloy and a preparation method thereof, wherein the publication date is 2022, 12 and 16. The patent successfully prepares the CoNiV-based medium-entropy alloy with double ordered phases based on arc melting and heat treatment processes by mainly regulating and controlling the contents of Al element and Ti element. The intermediate entropy alloy prepared by the method has good yield strength which can reach 1.2GPa. But is limited by the traditional arc melting preparation process, the grain size of the alloy material is still in the micron level, the advantage of larger entropy alloy Hall-Petch coefficient in VCoNi can not be exerted, if the grain size is further refined to the nanometer level through a specific preparation means, the yield strength of the material is expected to be obviously improved, and the application prospect of the material is further expanded.
The Chinese patent document with publication number CN 112663333A also searches for a method for depositing superfine metal powder on day 2021, month 4 and day 16. In the method, under the protection of inert gas, a metal target is excited by laser heating to prepare nano particles with uniform and controllable size and regular shape. The patent mainly provides a preparation process of pure metal nano powder, and the preparation process of bulk nano metal is not yet explored.
The Chinese patent document with publication number of CN 115323241A also searches for 11 days of 2022, and discloses a preparation method of the nano refractory high-entropy alloy TiZrHfNb. The method successfully prepares the single-phase BCC structure nanocrystalline material with uniform structure and excellent thermal stability by an inert gas condensation method. The patent adds a one-step high-pressure process on the basis of the Chinese patent process with the publication number of CN 112663333A, and further successfully prepares the block nano metal material. However, the melting points of Ti and Zr in the four elements in the alloy system of the patent are close, the melting points of Hf and Nb are close, and no obvious lattice distortion effect exists, so that the bulk nanocrystalline material with uniform structure is easier to prepare. For a VCoNi alloy system, since the V element has a far higher melting point than the Co element and the Ni element, and there is a large lattice distortion effect, the related preparation process still needs to be further explored.
The Chinese patent document with publication number CN 112251644B, with publication number 2022, 5 and 31, also discloses a preparation method for preparing high-heat-stability equiaxed nanocrystalline Ti6Al4V-Ag alloy. The patent refines grains mainly by ECAP method, but the method has a remarkable disadvantage: the block material with the grain size smaller than 50nm cannot be prepared, so that various physical and chemical properties of the block material cannot be researched, and the development of the toughening theory and industrial application of the block material is seriously retarded.
In summary, although the metal bulk nanocrystalline materials can be prepared by some means, no preparation means is currently available for preparing entropy alloy in FCC structure VCoNi with high purity and larger lattice distortion.
Disclosure of Invention
The invention aims to provide an ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy and a preparation method thereof, and solves the problems that although a metal bulk nanocrystalline material can be prepared through certain means in the prior art, the preparation method of the high-purity medium entropy alloy with a large lattice distortion in FCC structure VCoNi is not available at present.
Aiming at the defects existing in the prior art, the preparation method aims at solving the problems of larger grain size and low purity of the preparation material, and further realizes the preparation of the high-purity ultrahigh yield strength face-centered cubic entropy nanocrystalline VCoNi alloy bulk material. The invention provides a means for combining arc melting, cold rolling, heat treatment, inert gas condensation and ultrahigh pressure compression, and realizes the preparation of the entropy VCoNi alloy in the nanocrystalline of the nanoscale bulk material with the grain size. The method can successfully prepare the bulk entropy VCoNi nanocrystalline alloy with high purity, uniform structure, average grain size smaller than 50nm and yield strength up to 3.4GPa. The successful preparation of the alloy lays a good foundation for the application of the material and the development of the related theory of the nanocrystalline material.
In order to achieve the above purpose, the present invention provides the following technical solutions: the nano-crystalline medium-entropy VCoNi alloy is a nano-crystalline medium-entropy VCoNi alloy with high purity, uniform structure, average grain size less than 50nm and yield strength as high as 3.4GPa, and the microstructure is mainly nano-crystalline;
the chemical elements in the VCoNi alloy are as follows: v: co: ni=1:1:1; the purity of each pure element of the smelting parent metal is more than or equal to 99.95 percent;
the method comprises the following specific steps:
firstly, preparing a high-purity coarse-grain VCoNi bulk material with equal atomic ratio in an arc melting furnace, homogenizing the structure of the prepared bulk material by a method combining cold rolling and heat treatment to obtain a target material, and finally preparing the bulk nanocrystalline material by a laser inert gas condensation method and an in-situ ultrahigh pressure method;
repeatedly cleaning the arc melting furnace with high purity argon gas for three times before smelting, and keeping the vacuum degree to be 1.5X10 after each cleaning -3 Pa; the rolling amount in the tissue homogenization process is 50-80%, and the annealing parameters are 1000-1200 ℃ for 3-6h;
third, inert gas condensing cavity is kept in high vacuum state (less than 10) -6 Pa), after high-purity helium is introduced, the pressure in the cavity is kept stable between 400 Pa and 600Pa, the distance between the laser emission lens and the target is controlled between 70 cm and 80cm, the emission power is 50W to 100W, 808 nm to 1064nm picosecond laser is selected, the single pulse energy is ensured to exceed 100 mu J, the pulse frequency is 500kHz, and the pulse width is less than 15ps; and (3) pre-pressing the powder under the pressure of 500-800MPa, and finally pressing the sample into a block sample with the diameter of 10mm and the thickness of 0.2-0.3mm by using the pressure of 5-6GPa in the room temperature environment.
The raw materials used in the preparation method of the VCoNi alloy are high-purity block materials with the purity of more than 99.95 percent, and the quality precision of each raw material is controlled to be 5 multiplied by 10 -4 g is less than or equal to g.
The invention also discloses a method for preparing the ultrahigh yield strength bulk nanocrystalline medium-entropy VCoNi alloy, which is characterized by comprising the following specific steps:
s1: calculating the required mass of each element according to the equal atomic ratio, performing surface grinding on raw materials to remove an oxide layer possibly existing on the surface, then weighing and weighing in a high-precision balance, and then preparing an equal atomic block sample in an arc melting furnace (considering that the melting point of V element is obviously higher than that of the other two elements, three raw materials are placed on the other two raw materials when placed into a melting cavity, so as to ensure that the elements of the prepared sample are uniformly distributed), and repeatedly smelting for six times during the process to ensure that the elements of the prepared material are uniformly distributed;
s2: carrying out homogenizing annealing at 1100 ℃ for 10 hours on the bulk equal atomic ratio VCoNi medium entropy alloy prepared in the first step, and then carrying out cold rolling;
s3: the alloy sheet material prepared by the method is deposited into nanocrystalline powder material by adopting an inert gas condensation method and is prepared into a block material by in-situ ultrahigh pressure, and the specific flow is as follows:
(1) finely cleaning the whole cavity so as to avoid pollution, and placing the block material (target material) prepared in the second step on a sample tray in the cavity;
(2) pumping the inert gas condensation cavity to an ultrahigh vacuum state through a first-stage pump (mechanical pump) and a second-stage pump (molecular pump), then flushing high-purity helium into the cavity, and flushing liquid nitrogen into a cold trap;
(3) setting a position and adjusting the angle of the laser so that the light path is perpendicular to the target, and adjusting the distance between the laser and the sample;
(4) setting the power of a laser to perform a short test experiment, so that the laser evaporation, cold trap deposition and scraper collection of the powder can be successfully realized after the laser and the bulk material act;
(5) ensuring that the powder preparation experiment is started after the problem does not exist in the step (4), and observing the powder preparation process through an observation window;
(6) after collecting enough powder, transferring the powder collecting tank to a low-pressure chamber in situ, then placing a sample on a pressing head, transferring the sample to a high-pressure chamber in situ, and applying pressure of 5GPa for 3min to finally successfully prepare the high-purity bulk nanocrystalline material.
As a preferred embodiment of the invention, the three raw materials in S1 are placed on the other two raw materials when being placed into the smelting cavity, so that the element distribution of the prepared sample is ensured to be uniform.
As a preferred embodiment of the present invention, the rolling amount in S2 is controlled to 60%, and then annealing is performed at 1000 ℃ for 3 hours under vacuum environment, so as to ensure that a bulk material with uniform microstructure is obtained.
As a preferred embodiment of the present invention, the vacuum degree in (2) of S3<10 -6 Pa。
As a preferred embodiment of the present invention, the nano powder deposited on the cold trap is scraped off by a scraper in time in (5) of S3 and collected into a powder collecting tank.
In a preferred embodiment of the present invention, the pre-press molding is performed at a pressure of 500MPa in (6) of S3.
As a preferred embodiment of the invention, the smelting is repeated six times to ensure a uniform distribution of elements in the material produced.
Compared with the prior art, the invention has the following beneficial effects:
the beneficial effects of the invention are as follows:
a. the traditional preparation process of the bulk nano-crystal is difficult to prepare the bulk material with the high-purity average grain size smaller than 50nm, the whole preparation process of the preparation scheme is finished in an ultra-high vacuum cavity, the condition that a sample is oxidized does not exist, the influence of impurity elements on the performance of the sample can be greatly avoided, and the preparation process has a great effect on the development of nano-crystal theory and engineering application.
b. The invention can prepare the nanocrystalline VCoNi medium entropy alloy with uniform structure and larger lattice distortion. Multiple means are adopted in the preparation process, so that the prepared nanocrystalline bulk material is ensured to have uniform tissue: the V element is placed above the other two elements in the raw material smelting stage; the tissue homogenization stage adopts a cold rolling 60% large deformation means and 1100 ℃ annealing temperature calculated according to a phase diagram theory; the inert gas condensation stage adopts high-power laser to uniformly excite the target material, so that atoms are uniformly excited to prepare the bulk nanocrystalline material with uniform tissues.
c. Compared with the traditional chemical preparation method, the preparation method has relatively simple process and does not have a plurality of complicated preparation processes; on the other hand, the preparation process does not have any reagent with safety risk, and the safety coefficient is far higher than that of the chemical means reported at present.
d. The yield strength of the entropy alloy in the nanocrystalline VCoNi prepared by the method is up to 3.4GPa, which is more than twice of the reported value of the material of the system at present, and the potential engineering application prospect of the material is greatly expanded.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of an inert gas condensing unit.
Fig. 2 is an XRD pattern of the entropy alloy in the as-prepared nanocrystalline VCoNi.
FIG. 3 is a graph showing TEM characterization results and grain size distribution of an entropy alloy in a prepared nanocrystalline VCoNi: (a) bright field image; (b) grain size distribution profile.
Fig. 4 is a compressive true stress strain curve.
Detailed Description
The invention is further described in connection with the following detailed description, in order to make the technical means, the creation characteristics, the achievement of the purpose and the effect of the invention easy to understand.
Example 1:
referring to fig. 1-2, the present invention provides a technical solution: the entropy VCoNi alloy in the ultra-high yield strength bulk nanocrystalline is an ultra-high yield strength alloy, the microstructure is a single-phase FCC structure, and the bulk nanocrystalline alloy has high purity, uniform structure, average grain size of less than 50nm and yield strength of up to 3.4 GPa;
the chemical elements in the VCoNi alloy are as follows: v: co: ni=1:1:1; the purity of the simple substance element of the smelting parent metal is more than or equal to 99.95 percent;
the method comprises the following specific steps:
firstly preparing a high-purity coarse-grain VCoNi bulk material with equal atomic ratio in an arc melting furnace, homogenizing the structure of the prepared bulk material by a method combining cold rolling and heat treatment to obtain a target material, and finally preparing the bulk nanocrystalline material by a laser inert gas condensation method and an in-situ ultrahigh pressure method; repeatedly cleaning the arc melting furnace with high purity argon gas for three times before melting, and keeping vacuum degree to 1.5X10 after each cleaning -3 Pa; the rolling amount in the tissue homogenization process is 50-80%, and the annealing parameters are 1000-1200 ℃ for 3-6h; the inert gas condensation cavity is kept in a high vacuum state (less than 10) -6 Pa), after high-purity helium is introduced, the pressure in the cavity is kept stable between 400 Pa and 600Pa, the distance between the laser emission lens and the target is controlled between 70 cm and 80cm, the emission power is 50W to 100W, 808 nm to 1064nm picosecond laser is selected, the single pulse energy is ensured to exceed 100 mu J, the pulse frequency is 500kHz, and the pulse width is less than 15ps; and (3) pre-pressing the powder under the pressure of 500-800MPa, and finally pressing the sample into a block sample with the diameter of 10mm and the thickness of 0.2-0.3mm by using the pressure of 5-6GPa in the room temperature environment. The raw materials used in the preparation method of the VCoNi alloy are high-purity block materials with the purity of more than 99.95 percent, and the quality precision of each raw material is controlled to be 5 multiplied by 10 -4 g is less than or equal to g.
The embodiment also discloses a method for preparing the entropy VCoNi alloy in the ultra-high yield strength block nanocrystalline, which comprises the following specific steps:
s1: calculating the required mass of each element according to the equal atomic ratio, performing surface grinding on raw materials to remove an oxide layer possibly existing on the surface, then weighing and weighing in a high-precision balance, and then preparing an equal atomic block sample in an arc melting furnace (considering that the melting point of V element is obviously higher than that of the other two elements, three raw materials are placed on the other two raw materials when placed into a melting cavity, so as to ensure that the elements of the prepared sample are uniformly distributed), and repeatedly smelting for six times during the process to ensure that the elements of the prepared material are uniformly distributed;
s2: carrying out homogenizing annealing at 1100 ℃ for 10 hours on the bulk equal atomic ratio VCoNi medium entropy alloy prepared in the first step, and then carrying out cold rolling;
s3: the alloy sheet material prepared by the method is deposited into nanocrystalline powder material by adopting an inert gas condensation method and is prepared into a block material by in-situ ultrahigh pressure, and the specific flow is as follows:
(1) finely cleaning the whole cavity so as to avoid pollution, and placing the block material (target material) prepared in the second step on a sample tray in the cavity;
(2) pumping the inert gas condensing cavity to an ultrahigh vacuum state through a primary pump (mechanical pump) and a secondary pump (molecular pump), wherein the vacuum pressure value is<10 -6 Pa, then flushing high purity helium into the cavity, flushing liquid into the cold trapNitrogen;
(3) setting a position and adjusting the angle of the laser so that the light path is perpendicular to the target, and adjusting the distance between the laser and the sample;
(4) setting the power of a laser to perform a short test experiment, so that the laser evaporation, cold trap deposition and scraper collection of the powder can be successfully realized after the laser and the bulk material act;
(5) ensuring that the powder preparation experiment is started after the problem does not exist in the step (4), observing the powder preparation process through an observation window, scraping off the nano powder deposited on the cold trap by a scraper at proper time, and collecting the nano powder into a powder collecting tank;
(6) after collecting enough powder, transferring the powder collecting tank to a low-pressure chamber in situ, then placing a sample on a pressing head, transferring the sample to a high-pressure chamber in situ, performing pre-pressing molding by adopting 500MPa, and pressing for 3min by adopting 5GPa pressure, thereby finally successfully preparing the high-purity bulk nanocrystalline material.
The three raw materials in S1 are placed on the other two raw materials when placed in the smelting cavity, so that the element distribution of the prepared sample is ensured to be uniform, and smelting is repeated for six times during the period to ensure that the element distribution in the prepared material is uniform; the rolling amount in S2 is controlled at 60%, and then annealing is carried out for 3 hours at 1000 ℃ under a vacuum environment, so as to ensure that a block material with uniform microstructure is obtained.
Experimental example:
the preparation process of the invention mainly comprises three main steps of processes, namely: smelting an entropy alloy target in VCoNi, homogenizing the structure of the target, depositing nano particles and forming at high pressure.
The specific experimental process is as follows:
(1) Calculating and weighing the mass required by each element of VCoNi according to the equal atomic ratio, wherein the purity of each element is more than 99.95%, and the mass accuracy is controlled to be 5 multiplied by 10 -4 Within g, polishing the raw materials to remove an oxide film possibly existing on the surface before weighing, and then performing alcohol ultrasonic cleaning;
(2) Cleaning the furnace cavity of arc melting furnace, and vacuumizing until the vacuum degree reaches 1.5X10 -3 Backflushing high-purity argon to about 500Pa during Pa, and then vacuumizing, wherein the step is repeated for three times;
(3) The raw materials after weighing and cleaning are put into an arc melting furnace (the melting point of V element is far higher than that of the other two elements, the V element is placed at the top to ensure the uniformity of a melting structure), three times of pure Ti are repeatedly melted in a cavity to ensure lower oxygen content in the cavity before melting, then a VCoNi target is melted, repeatedly melted for 6 times, and then the VCoNi target is sucked and cast into a structure of 6 multiplied by 20 multiplied by 18mm 3 Is a bulk material of (a) a block material of (b);
(4) Homogenizing the suction cast material for 10 hours in a vacuum environment at 1100 ℃, then carrying out cold rolling experiments on the sample, wherein the pressing amount is 5% each time, the final rolling amount is controlled to be about 60%, and then carrying out recrystallization treatment on the material for 3 hours in a vacuum environment at 1000 ℃ to ensure that a target material with uniform tissue is obtained;
(5) The whole chamber is finely cleaned to avoid pollution, the block material (target material) prepared in the previous step is put on a sample tray in the chamber, and the inert gas condensation chamber is pumped to an ultra-high vacuum state by a primary pump (mechanical pump) and a secondary pump (molecular pump)<10 -6 Pa), then high-purity helium is injected into the cavity, and liquid nitrogen is injected into the cold trap (shown in figure 1);
(6) Setting the position and adjusting the angle of the laser to enable the light path to be perpendicular to the target, adjusting the distance between the laser and the sample to be 75cm, setting the power of the laser to be 100W, ensuring that the single pulse energy exceeds 100 mu J, the pulse frequency is 500kHz, and the pulse width is less than 15ps, performing a short test experiment, and ensuring that the laser and the bulk material can successfully realize the laser evaporation, cold trap deposition and scraper collection of the powder after the action;
(7) Starting a powder preparation experiment after ensuring that the problem does not exist in the previous step, observing the powder preparation process through an observation window, scraping off the nano powder deposited on the cold trap by a scraper at proper time, and collecting the nano powder into a powder collecting tank;
(8) After collecting enough powder, transferring the powder collecting tank to a low-pressure chamber in situ, pre-pressing and molding by adopting the pressure of 500MPa, then placing a sample on a pressing head, transferring the sample to a high-pressure chamber in situ, pressing for 3min by adopting the pressure of 5GPa, and finally successfully preparing the high-purity block nanocrystalline material with the diameter of 10mm and the thickness of 0.3 mm.
The bulk materials prepared as described above were subjected to microstructure characterization and mechanical property testing as shown in fig. 2-4 to give a single FCC structure, then the sample was prepared by focusing an ion beam to give a sample transmission, and the results of the characterization were again followed by a small column preparation experiment with a diameter of about 2 μm and a height of about 5 μm using a focused ion beam, and finally nanoindentation (strain rate 10 -2 s -1 ) The mechanical property is characterized, and the yield strength is as high as 3.4GPa.
The invention relates to an ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy and a preparation method thereof, wherein each part is a universal standard part or a part known by a person skilled in the art, and the structure and the principle of the alloy are known by the person skilled in the art through technical manuals or through routine experimental methods.
Claims (9)
1. The ultrahigh yield strength block nanocrystalline medium entropy VCoNi alloy is characterized in that: the nanocrystalline medium-entropy VCoNi alloy is an ultrahigh yield strength alloy, has a microstructure of a single-phase FCC structure, and is a block nanocrystalline alloy with high purity, uniform structure, average grain size of less than 50nm and yield strength of up to 3.4 GPa;
the chemical elements in the VCoNi alloy are as follows: v: co: ni=1:1:1; the purity of each pure element of the smelting parent metal is more than or equal to 99.95 percent;
the method comprises the following specific steps:
(1) Firstly preparing a high-purity coarse-grain VCoNi bulk material with equal atomic ratio in an arc melting furnace, homogenizing the structure of the prepared bulk material by a method combining cold rolling and heat treatment to obtain a target material, and finally preparing the bulk nanocrystalline material by a laser inert gas condensation method and an in-situ ultrahigh pressure method;
(2) Repeatedly cleaning the arc melting furnace with high purity argon gas for three times before melting, and keeping vacuum degree to 1.5X10 after each cleaning -3 The method comprises the steps of carrying out a first treatment on the surface of the The rolling amount in the tissue homogenization process is 50-80%, and the annealing parameters are 1000-1200 ℃ for 3-6h;
(3) Inert before experimentThe condensing chamber of the sex gas keeps high vacuum state (less than 10 -6 Pa), after high-purity helium is introduced, the pressure in the cavity is kept stable between 400 Pa and 600Pa, the distance between the laser emission lens and the target is controlled between 70 cm and 80cm, the emission power is 50W to 100W, 808 nm to 1064nm picosecond laser is selected, the single pulse energy is ensured to exceed 100 mu J, the pulse frequency is 500kHz, and the pulse width is less than 15ps;
(4) And (3) pre-pressing the powder under the pressure of 500-800MPa, and finally pressing the sample into a block sample with the diameter of 10mm and the thickness of 0.2-0.3mm by using the pressure of 5-6GPa in the room temperature environment.
2. The ultra-high yield strength bulk nanocrystalline medium entropy VCoNi alloy according to claim 1, characterized by: the raw materials used in the preparation method of the VCoNi alloy are high-purity block materials with the purity of more than 99.95 percent, and the quality precision of each raw material is controlled to be 5 multiplied by 10 -4 g is less than or equal to g.
3. A method for preparing the ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy according to any one of claims 1-2, characterized by the specific steps of:
s1: calculating the required mass of each element according to the equal atomic ratio, performing surface grinding on raw materials to remove an oxide layer possibly existing on the surface, then weighing and weighing in a high-precision balance, and then preparing an equal atomic block sample in an arc melting furnace (considering that the melting point of V element is obviously higher than that of the other two elements, three raw materials are placed on the other two raw materials when placed into a melting cavity, so as to ensure that the elements of the prepared sample are uniformly distributed), and repeatedly smelting for six times during the process to ensure that the elements of the prepared material are uniformly distributed;
s2: carrying out homogenizing annealing at 1100 ℃ for 10 hours on the bulk equal atomic ratio VCoNi medium entropy alloy prepared in the first step, and then carrying out cold rolling;
s3: the alloy sheet material prepared by the method is deposited into nanocrystalline powder material by adopting an inert gas condensation method and is prepared into a block material by in-situ ultrahigh pressure, and the specific flow is as follows:
(1) finely cleaning the whole cavity so as to avoid pollution, and placing the block material (target material) prepared in the second step on a sample tray in the cavity;
(2) pumping the inert gas condensation cavity to an ultrahigh vacuum state through a first-stage pump (mechanical pump) and a second-stage pump (molecular pump), then flushing high-purity helium into the cavity, and flushing liquid nitrogen into a cold trap;
(3) setting a position and adjusting the angle of the laser so that the light path is perpendicular to the target, and adjusting the distance between the laser and the sample;
(4) setting the power of a laser to perform a short test experiment, so that the laser evaporation, cold trap deposition and scraper collection of the powder can be successfully realized after the laser and the bulk material act;
(5) ensuring that the powder preparation experiment is started after the problem does not exist in the step (4), and observing the powder preparation process through an observation window;
(6) after collecting enough powder, transferring the powder collecting tank to a low-pressure chamber in situ, then placing a sample on a pressing head, transferring the sample to a high-pressure chamber in situ, and applying pressure of 5GPa for 3min to finally successfully prepare the high-purity bulk nanocrystalline material.
4. The method for preparing the ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy according to claim 3, wherein: the three raw materials in the S1 are placed on the other two raw materials when placed into the smelting cavity, so that the element distribution of the prepared sample is ensured to be uniform).
5. The method for preparing the ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy according to claim 3, wherein: the rolling amount in S2 is controlled at 60%, and then annealing is carried out for 3 hours at 1000 ℃ under a vacuum environment, so as to ensure that a block material with uniform microstructure is obtained.
6. The method for preparing the ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy according to claim 3, wherein: the vacuum pressure value in (2) of S3 is<10 -6 Pa。
7. The method for preparing the ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy according to claim 3, wherein: and (5) scraping the nano powder deposited on the cold trap by a scraper at proper time and collecting the nano powder into a powder collecting tank.
8. The method for preparing the ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy according to claim 3, wherein: and (3) in the step (6) of the step S3, the pre-pressing molding is carried out by adopting the pressure of 500 MPa.
9. The method for preparing the ultrahigh yield strength bulk nanocrystalline medium entropy VCoNi alloy according to claim 4, wherein: smelting is repeated six times to ensure that the elements in the prepared material are uniformly distributed.
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| CN116536562B (en) * | 2023-07-03 | 2023-09-19 | 中国科学院力学研究所 | High-uniform-elongation 2.0 GPa-level multi-principal-element alloy and preparation method thereof |
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