阅读说明：本技术 一种高硬度粉末高熵合金的制备方法 (Preparation method of high-hardness powder high-entropy alloy ) 是由 高卡 刘东岳 马天宇 孙德建 廉政政 赵峻良 高阳 樊磊 于 2021-08-13 设计创作，主要内容包括：本发明公开了一种高硬度粉末高熵合金的制备方法,该方法采用真空振荡热压烧结与热处理结合的方式,使高熵合金在热场和力场的多场耦合作用下,结合热处理的方式,促使粉体重排、气孔排出、消除偏析,从而凝固成形,减少内部缺陷,提升粉末高熵合金的硬度和致密度。且粉末内部在烧结过程中,相邻粉体间通过元素扩散效应,界面融合、消失,形成统一的整体,相结构发生改变,界面结合强度增强,样品的硬度增加。本发明制备得到的粉末高熵合金硬度可达451.5HV-(30),致密度可达99.2％。本发明的振荡热压烧结与热处理结合的方式用于制备高硬度粉末高熵合金,具有绿色、高效的特点。(The invention discloses a preparation method of high-hardness powder high-entropy alloy, which adopts a mode of combining vacuum oscillation hot-pressing sintering with heat treatment, so that the high-entropy alloy combines the heat treatment mode under the multi-field coupling action of a thermal field and a force field to promote powder rearrangement, air hole discharge and segregation elimination, thereby solidifying and forming, reducing internal defects and improving the hardness and density of the powder high-entropy alloy. In the sintering process of the powder, interfaces of adjacent powder bodies are fused and disappear through an element diffusion effect to form a unified whole, the phase structure is changed, the interface bonding strength is enhanced, and the hardness of a sample is increased. The hardness of the powder high-entropy alloy prepared by the invention can reach 451.5HV 30 The density canUp to 99.2 percent. The mode of combining the oscillating hot-pressing sintering and the heat treatment is used for preparing the high-hardness powder high-entropy alloy, and has the characteristics of greenness and high efficiency.)

1. A preparation method of a high-hardness powder high-entropy alloy is characterized by comprising the following steps:

(1) loading the high-entropy alloy mixed powder into a die, and then performing pre-pressing forming;

(2) putting the die which is pre-pressed and molded in the step (1) and is filled with the high-entropy alloy mixed powder into an oscillating pressure sintering furnace, applying constant pressure to the sample, and heating the sample by raising the temperature; when the temperature in the sintering furnace reaches the set temperature T₁Then, performing a heat preservation stage, simultaneously boosting pressure, and applying oscillation pressure to the sample until the heat preservation is finished; after the oscillation program is finished, cooling the sample along with the furnace, keeping applying pressure to the sample in the cooling process, wherein the pressure value is the median value of the oscillation pressure, and cooling to the room temperature;

(3) carrying out a heat treatment process on the cooled sample obtained in the step (2), heating the sample to reach a set temperature T₂And then entering a heat preservation stage, and cooling the sample to room temperature after heat preservation is finished to obtain a final product.

2. The method for preparing the high-hardness powder high-entropy alloy according to claim 1, wherein the high-entropy alloy mixed powder is Al_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2。

3. The method for preparing the high-hardness powder high-entropy alloy according to claim 1, wherein the pressure increase rate in the step (2) is 2MPa/min, the median value of the oscillation pressure is 30 to 60MPa, the amplitude is ± 1 to ± 10MPa, and the oscillation frequency is 1 to 10 Hz.

4. The method for preparing a high-hardness powder high-entropy alloy according to claim 1, wherein the temperature rise rate in the step (2) is 8 ℃/min, and the set temperature T is₁The temperature is 850-1000 ℃, and the heat preservation time is 0.5-2 h.

5. The method for producing a high-hardness powder high-entropy alloy according to claim 1, wherein the constant pressure in the step (2) is 1.4 MPa.

6. The method for preparing a high-hardness powder high-entropy alloy according to claim 1, wherein the temperature rise rate of the heat treatment process in the step (3) is 17.5 ℃/min, and the set temperature T is₂The temperature is 500-600 ℃, and the heat preservation time is 0.5-1 h.

7. The method for preparing the high-hardness powder high-entropy alloy according to claim 1, wherein the pressure for the pre-compaction molding in the step (1) is 6MPa, and the time is 15 min.

8. The method for preparing a high-hardness powder high-entropy alloy according to claim 1, wherein the steps (2) and (3) are performed in a vacuum environment.

9. The method of producing a high-hardness powder high-entropy alloy according to claim 2, wherein the Al is_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2The purity of each element in the high-entropy alloy mixed powder is more than 99.6 percent.

Technical Field

The invention belongs to the field of powder metallurgy preparation of metal materials, and relates to a preparation method of a high-hardness powder high-entropy alloy.

Background

The high-entropy alloy is a brand-new alloy and consists of five or more than five metal elements, and the content of each element is between 5 and 35 percent. Due to the high entropy of mixing in the system, the alloy tends to form Face Centered Cubic (FCC) and Body Centered Cubic (BCC) phases with simple solid solutions. Under the interaction of various elements, four different effects of a high-entropy effect, a delayed diffusion effect, a lattice distortion effect and a cocktail effect are shown, so that the high-entropy alloy has excellent performances in the aspects of hardness, toughness, corrosion resistance, high temperature resistance, low temperature resistance, irradiation resistance and the like. At present, the high-entropy alloy is applied to a plurality of fields, such as high-speed cutting tools, oil pressure air pressure rods, hard surfaces of rolling cylinders, high-frequency soft magnetic films and the like, and can be subsequently applied to the fields of aerospace, war industry, ships, civil use and the like.

The existing preparation methods of the high-entropy alloy mainly comprise a vacuum melting method, a powder metallurgy method, a mechanical alloying method, a laser cladding method, an electrochemical deposition method and the like. Compared with the traditional process steps of solidification, solid solution, deformation, machining and the like, the powder metallurgy method has the advantages that the diffusion, fusion welding, combination, dissolution, recrystallization and the like occur among powder particles in the sintering process, the organization rearrangement among the metal powder particles is promoted, the combination is firmer, the metal powder becomes firm blocks, the obtained product has the advantages of near-net-shape forming, uniform grain size, fine grains, high utilization rate, excellent performance and the like, the hardness of the product can be effectively increased, the utilization rate of materials is improved, the waste of the traditional fusion casting mode is avoided, and the method is more applicable to casting the blocky high-entropy alloy. However, the existing powder metallurgy technology has the defects of high sintering temperature, long consumption time, process and internal defects and the like, so that the hardness of the obtained powder alloy is low, and the high requirements of the part in practical application cannot be met. Therefore, to overcome the above-mentioned problems, it is necessary to introduce new technical solutions to improve the properties of the powder alloy.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a preparation method of a high-hardness powder high-entropy alloy, and the powder high-entropy alloy prepared by the method has the characteristics of high hardness and high compactness.

One of the purposes of the invention is realized by adopting the following technical scheme:

a preparation method of a high-hardness powder high-entropy alloy comprises the following steps:

(1) loading the high-entropy alloy mixed powder into a die, and then performing pre-pressing forming;

(2) putting the die which is pre-pressed and molded in the step (1) and is filled with the high-entropy alloy mixed powder into an oscillating pressure sintering furnace, applying constant pressure to the sample, and heating the sample by raising the temperature; when the temperature in the sintering furnace reaches the set temperature T₁Then, performing a heat preservation stage, simultaneously boosting pressure, and applying oscillation pressure to the sample until the heat preservation is finished; after the oscillation program is finished, cooling the sample along with the furnace, keeping applying pressure to the sample in the cooling process, wherein the pressure value is the median value of the oscillation pressure, and cooling to the room temperature;

(3) carrying out a heat treatment process on the cooled sample obtained in the step (2), heating the sample to reach a set temperature T₂And then entering a heat preservation stage, and cooling the sample to room temperature after heat preservation is finished to obtain a final product.

Further, the high-entropy alloy mixed powder is Al_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2。

Further, the boosting rate in the step (2) is 2MPa/min, the median value of the oscillation pressure is 30-60 MPa, the amplitude is +/-1- +/-10 MPa, and the oscillation frequency is 1-10 Hz.

Further, the heating rate in the step (2) is 8 ℃/min, and the temperature T is set₁The temperature is 850-1000 ℃, and the heat preservation time is 0.5-2 h.

Further, the constant pressure of the step (2) is 1.4 MPa.

Further, the temperature rise rate of the heat treatment process in the step (3) is 17.5 ℃/min, and the set temperature T₂The temperature is 500-600 ℃, and the heat preservation time is 0.5-1 h.

Further, the pressure of the pre-pressing forming in the step (1) is 6MPa, and the time is 15 min.

Further, the steps (2) and (3) are carried out in a vacuum environment.

Further, the Al_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2The purity of each element in the high-entropy alloy mixed powder is more than 99.6 percent.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides a preparation method of a high-hardness powder high-entropy alloy, which adopts a mode of combining vacuum oscillation hot-pressing sintering with heat treatment, so that the high-entropy alloy combines the heat treatment mode under the multi-field coupling action of a thermal field and a force field to promote powder rearrangement, air hole discharge, segregation elimination and other defects, thereby solidifying and forming, reducing internal defects, and improving hardness and density. In the sintering process of the powder, interfaces of adjacent powder bodies are fused and disappear through an element diffusion effect to form a unified whole, the phase structure is changed, the interface bonding strength is enhanced, and the hardness of a sample is increased. The hardness of the powder high-entropy alloy prepared by the invention can reach 451.5HV₃₀The compactness can reach 99.2%. The mode of combining the oscillating hot-pressing sintering and the heat treatment is used for preparing the high-hardness powder high-entropy alloy, and has the characteristics of greenness and high efficiency.

Drawings

FIG. 1 is an SEM photograph of four samples obtained in example 1 of the present invention and four samples obtained in comparative example 1, wherein FIGS. 1a to 1d correspond to 1-1, 1-2, 1-3 and 1-4, respectively, and FIGS. 1e to 1h correspond to HP-1, HP-3 and HP-4, respectively;

FIG. 2 is a graph showing hardness property profiles of samples obtained in examples 1 and 2, comparative examples 1 and 2 of the present invention;

fig. 3 is a density distribution chart of samples obtained in example 1 and example 2, comparative example 1 and comparative example 2 of the present invention.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and the detailed description, and it should be noted that any combination of the embodiments or technical features described below can be used to form a new embodiment without conflict.

Example 1

A preparation method of a high-hardness powder high-entropy alloy comprises the following steps:

(1) 25g of Al was taken_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2The high-entropy alloy mixed powder is filled into a graphite die coated with boron nitride powder, and then is subjected to pre-pressing forming for 15min under the pressure of 6 MPa; pressing into cylindrical sheet with diameter of 30mm and thickness of 4 mm. Al mentioned above_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2The atomic ratio of each element in the high-entropy alloy mixed powder is 1:1:1:1:1, the atomic percentage of each element is 20%, and the purity of each element is more than 99.6%.

(2) Prepressing and molding the step (1) and then filling Al_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2Putting a graphite mold of high-entropy alloy mixed powder on a pressure workbench of an oscillating pressure sintering (HOP) furnace chamber, aligning a mold base with the workbench in the furnace, adjusting an upper pressure head to descend through control parameters in DPL fatigue test software, stopping when the graphite mold is about to contact with the upper end of the mold, boosting at a loading speed of 1.4MPa/min, applying a constant pressure of 1.4MPa to a sample, observing whether the mold cracks when a load value reaches a set value, and stopping a pressure head descending program. Closing the furnace cavity door, performing a vacuumizing process, opening the upper valve and the lower valve in sequence after the mechanical pump is opened to reach a specified vacuum degree, and immediately opening the diffusion pump to vacuumize the interior of the furnace cavity.

Adjusting and setting heating process parameters through a control panel, heating the sample at a heating rate of 8 ℃/min, and preserving heat for 1h when the set temperature in the sintering furnace reaches 850 ℃; and increasing the pressure at the rate of 2MPa/min while heating to the set temperature, and applying oscillation pressure to the sample until the heat preservation is finished, wherein the median value of the oscillation pressure is 60MPa, the amplitude is +/-5 MPa, and the frequency is 1 Hz. And after the oscillation program is finished, cooling the sample along with the furnace, keeping pressure on the sample in the cooling process, wherein the pressure value is the median value of the oscillation pressure, and closing the furnace until the sample is cooled to the set temperature. And naturally cooling the inner cavity of the sintering furnace along with the furnace to room temperature, opening a furnace cavity door by breaking vacuum, enabling the upper pressure head to ascend through control parameters in software, removing the pressure of the upper pressure head, and taking out the graphite mold to obtain a sample in the mold.

(3) And (3) putting the cooled sample obtained in the step (2) into a crucible, then putting the crucible into a tube furnace, opening an air inlet valve of the tube furnace after the installation is finished, closing a power supply of a vacuum valve, and opening an air outlet valve. Heating the sample at a heating rate of 17.5 ℃/min, entering a heat preservation state after reaching the set temperature of 600 ℃, and preserving heat for 1 h. And after the heat preservation is finished, cooling the sample to room temperature along with the furnace to obtain the high-hardness powder high-entropy alloy, and marking as 1-1.

And (3) adjusting the set temperature of 850 ℃ in the step (2) to 900 ℃, 950 ℃ and 1000 ℃, and keeping the rest unchanged to obtain high-hardness powder high-entropy alloys which are respectively marked as 1-2, 1-3 and 1-4.

Example 2

A preparation method of a high-hardness powder high-entropy alloy comprises the following steps:

(1) 25g of Al was taken_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2The high-entropy alloy mixed powder is filled into a graphite die coated with boron nitride powder, and then is subjected to pre-pressing forming for 15min under the pressure of 6 MPa; pressing into cylindrical sheet with diameter of 30mm and thickness of 4 mm. Al mentioned above_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2The atomic ratio of each element in the high-entropy alloy mixed powder is 1:1:1:1:1, the atomic percentage of each element is 20%, and the purity of each element is more than 99.6%.

(2) Step (1)) Al is loaded after the prepressing forming_0.2Co_0.2Cr_0.2Ni_0.2Fe_0.2The graphite die of the high-entropy alloy mixed powder is placed on a pressure workbench of an oscillating pressure sintering furnace chamber, a die base is aligned with the workbench in the furnace, an upper pressure head is adjusted to move downwards through control parameters in DPL fatigue test software, the graphite die stops when the graphite die is about to contact with the upper end of the die, the pressure is increased at a loading speed of 1.4MPa/min, a constant pressure of 1.4MPa is applied to a sample, whether the die cracks or not is observed when a load value reaches a set value, and a pressure head moving program is stopped. Closing the furnace cavity door, performing a vacuumizing process, opening the upper valve and the lower valve in sequence after the mechanical pump is opened to reach a specified vacuum degree, and immediately opening the diffusion pump to vacuumize the interior of the furnace cavity.

Adjusting and setting heating process parameters through a control panel, heating the sample at a heating rate of 8 ℃/min, and preserving heat for 1h when the set temperature in the sintering furnace reaches 850 ℃; and increasing the pressure at the rate of 2MPa/min while heating to the set temperature, and applying oscillation pressure to the sample until the heat preservation is finished, wherein the median value of the oscillation pressure is 60MPa, the amplitude is +/-5 MPa, and the frequency is 1 Hz. And after the oscillation program is finished, cooling the sample along with the furnace, keeping pressure on the sample in the cooling process, wherein the pressure value is the median value of the oscillation pressure, and closing the furnace until the sample is cooled to the set temperature. And naturally cooling the inner cavity of the sintering furnace along with the furnace to room temperature, opening a furnace cavity door by breaking vacuum, enabling the upper pressure head to ascend through control parameters in software, removing the pressure of the upper pressure head, and taking out the graphite mold to obtain a sample in the mold.

(3) And (3) putting the cooled sample obtained in the step (2) into a crucible, then putting the crucible into a tube furnace, opening an air inlet valve of the tube furnace after the installation is finished, closing a power supply of a vacuum valve, and opening an air outlet valve. Heating the sample at a heating rate of 17.5 ℃/min, entering a heat preservation state after reaching a set temperature of 500 ℃, and preserving heat for 1 h. And after the heat preservation is finished, cooling the sample to room temperature along with the furnace to obtain the high-hardness powder high-entropy alloy, and marking as 2-1.

And (3) adjusting the set temperature of 850 ℃ in the step (2) to 900 ℃, 950 ℃ and 1000 ℃, and keeping the rest unchanged to obtain high-hardness powder high-entropy alloys which are respectively marked as 2-2, 2-3 and 2-4.

Comparative example 1

Comparative example 1 differs from example 1 in that: comparative example 1 the oscillatory pressure sintering in step (2) in example 1 was replaced with conventional hot-press sintering (HP), the sintering temperatures were 850 ℃, 900 ℃, 950 ℃, 1000 ℃, the sintering pressure was 65MPa, and the holding times were all 1 h; the procedure (3) in example 1 was omitted, and the same procedures as in example 1 were repeated to obtain final products, which were designated as HP-1, HP-2, HP-3 and HP-4, respectively, for the different sintering temperatures.

Comparative example 2

Comparative example 2 differs from example 1 in that: comparative example 2 the same procedure as in example 1 was repeated except that step (3) of example 1 was omitted, that is, the heat treatment process was not performed, to obtain a final product. The products obtained at 850 deg.C, 900 deg.C, 950 deg.C and 1000 deg.C corresponding to different sintering temperatures are respectively marked as HOP-1, HOP-2, HOP-3 and HOP-4.

Experimental example 1

The four samples (1-1, 1-2, 1-3, 1-4) obtained in example 1 and the four samples (HP-1, HP-2, HP-3, HP-4) obtained in comparative example 1 were subjected to microscopic morphology characterization, the results of which are shown in FIG. 1. In fig. 1a, more dark intercrystalline regions appear, and the boundaries between particles are more distinct, indicating that the temperature has less influence on the microstructure of the high-entropy alloy, the sintering has not been fully performed, and the grain size is larger. With the increase of the temperature of the oscillatory hot-pressing sintering, as can be seen from fig. 1b-1d, sintering necks are formed between grain boundaries, powder bodies are bonded, the sintering process can be fully performed, a large number of closed pores are formed, and the pore size and the pores are gradually reduced with the increase of the temperature. The heat treatment step enables the original particle boundary to gradually disappear, the structure is more uniform while dendrites are formed, and the deepening of the densification degree and the increase of the hardness of the alloy powder are facilitated. Therefore, the mode of combining the oscillating hot-pressing sintering and the heat treatment is adopted, so that the powder high-entropy alloy can promote the powder to be rearranged, discharge air holes, eliminate segregation and reduce internal defects under the multi-field coupling action of a thermal field and a force field. The interface is fused and disappears between the adjacent powder bodies through the element diffusion effect, a unified whole is formed, the phase structure is changed, and the internal structure of the high-entropy alloy is combined more tightly, so that the hardness and the density of the alloy are improved.

Fig. 1e-1h are microstructure diagrams of samples obtained by the conventional hot-pressing sintering technology, and it can be seen from comparison with fig. 1a-1d that the sample obtained by the conventional hot-pressing sintering technology has clear particle boundaries, sparser particle distribution and more pores. The sample obtained by adopting the mode of combining the oscillating hot-pressing sintering and the heat treatment has more uniform structure, the number of air holes is greatly reduced, boundary precipitates are generated among the crystals, the sintering process among the powders is more thorough, and the hardness of the obtained alloy is more favorably improved.

The four samples (1-1, 1-2, 1-3, 1-4) obtained in example 1, the four samples (2-1, 2-2, 2-3, 2-4) obtained in example 2, the four samples (HP-1, HP-2, HP-3, HP-4) obtained in comparative example 1, and the four samples (HOP-1, HOP-2, HOP-3, HOP-4) obtained in comparative example 2 were each tested for hardness (Vickers hardness tester) and density, and the results are shown in FIGS. 2 and 3. The result shows that the hardness of the powder high-entropy alloy prepared by the invention can reach 451.5HV₃₀The compactness can reach 99.2%. When sintering is carried out at a lower temperature, the mode of combining the oscillating hot-pressing sintering and the heat treatment adopted by the invention is compared with the mode of only carrying out the traditional hot-pressing sintering or only carrying out the one-step oscillating hot-pressing sintering without carrying out the heat treatment, and the obtained powder high-entropy alloy has higher hardness and higher density.

In conclusion, the invention provides a preparation method of high-hardness powder high-entropy alloy, which adopts a mode of combining vacuum oscillation hot-pressing sintering and heat treatment, firstly, the oscillation hot-pressing sintering can ensure that continuous circulation pressure is applied to a sample, pores among powder are promoted to be discharged, the powder activity is improved, the solute diffusion is promoted, the rapid growth of crystal grains is inhibited, the sintering temperature can be effectively reduced, the sintering time is shortened, the internal defects of the material are reduced, the toughness of the alloy is increased, and the hardness of the alloy is improved. Meanwhile, the density of the sample is improved, the tissue distribution is more uniform, the number of air holes among powder particles is reduced, and the defects of the existing powder metallurgy technology are greatly overcome. After the oscillation hot pressing sintering, the one-step heat treatment process is carried out, so that the growth of crystal grains can be inhibited, the segregation of components is reduced, the internal stress is reduced, and the performance of the alloy is improved, so that the obtained powder high-entropy alloy has more excellent structure and performance. The mode of combining the oscillating hot-pressing sintering and the heat treatment is used for preparing the high-hardness powder high-entropy alloy, and has the characteristics of greenness and high efficiency.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.