A powder metallurgy step sintering method of a multi-principal element alloy

Abstract

The application provides a powder metallurgy step-by-step sintering method of a multi-principal-element alloy, belongs to the technical field of metal material preparation, and successfully obtains a high-performance multi-principal-element alloy by using a step-by-step sintering method of a spark plasma sintering preparation process, so that various problems existing in the preparation of the multi-principal-element alloy by using traditional vacuum arc melting, mechanical alloying and magnetron sputtering can be solved, and the method has the advantages of high forming rate, size controllability and simple operation.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, and particularly relates to a stepwise sintering method for powder metallurgy of multi-principal element alloys. Background Technology

[0002] Traditional alloys generally consist of two parts: a matrix and alloying elements, with the alloying elements being called solutes. The most significant characteristic of novel multi-principal element alloys is that they do not distinguish between the matrix and the solute; the atomic percentage of each element does not exceed 50%, and each principal element is both the matrix and the solute. This results in unique properties that traditional alloys cannot achieve.

[0003] In terms of preparation methods, since the beginning of the 21st century, numerous researchers have developed various techniques for preparing multi-principal alloys. Currently, approximately 75% of published papers on multi-principal alloys describe alloys produced using the fusion casting method. Fusion casting (FC) generally includes two methods: vacuum arc melting and vacuum induction melting. Currently, lower-temperature vacuum induction melting is commonly used instead of vacuum arc melting, primarily including vacuum induction furnace melting, suspension melting, and cold crucible melting.

[0004] In addition, laser cladding (LC), also known as laser welding or laser powder deposition, is an interdisciplinary technology integrating laser technology, powder metallurgy, control science and engineering, and computer-aided manufacturing (CAM). Powder is spread or simultaneously fed onto a substrate material, and then irradiated with a high-energy laser, causing the multi-principal element alloy powder to rapidly melt, expand, and solidify, forming a multi-principal element alloy coating with fewer defects, high density, uniform microstructure, and good metallurgical bonding. This is a method of material surface modification. Because the energy-affected zone of laser irradiation is very small, the melting of the substrate material is minimal, and the dilution rate of the multi-principal element alloy coating is very small, which can meet the performance requirements of the material surface without changing the overall properties of the material. Multi-principal element alloy coatings prepared by laser cladding have advantages such as wear resistance, corrosion resistance, and strong oxidation resistance. With the continuous emergence of various high-performance multi-principal element alloys, the preparation of multi-principal element alloy coatings by laser cladding has a promising future.

[0005] Magnetron sputtering (MS) is a form of physical vapor deposition technique widely used for the preparation of multi-principal alloy thin films. The entire process is carried out in a vacuum environment. A large voltage device is applied between the cathode (target) and the anode (coating chamber wall). Under the coupling effect of a large electric field and an alternating magnetic field, a magnetron-controlled abnormal glow discharge phenomenon occurs. High-speed electrons collide with argon molecules, ionizing them. Argon ions, accelerated by the cathode, bombard the anode target surface, resulting in energy exchange. Atoms on the target surface escape from their original crystal lattice and move in a predetermined direction, depositing onto the substrate to form a film. The key to magnetron sputtering is target preparation. The preparation of multi-principal alloy targets is more difficult than that of traditional alloy targets. Magnetron sputtering requires high purity of both the target material and the reactant gas, which is beneficial for preparing multi-principal alloy thin films with uniform microstructures. The composition and thickness of the thin film can be adjusted by the target material and sputtering time. The elemental content of the film is monitored by plasma emission spectroscopy to regulate the reactive gas flow rate, thereby stabilizing the discharge voltage and thus the deposition rate, which is beneficial for obtaining a uniformly distributed multi-principal alloy thin film. The coating layer has a large area, is dense and uniform, has good wear resistance, strong corrosion resistance, low substrate temperature, fast film formation speed, and strong adhesion to the substrate. The prepared multi-principal alloy thin film can be used in wear-resistant cutting tools, anti-corrosion coatings, diffusion barrier layers, and other applications.

[0006] Mechanical alloying (MA) is also a commonly used method for preparing bulk multi-principal element alloys. Metal or alloy powders are placed in a planetary ball mill at a specific ratio. Under the action of the milling media (generally stainless steel / alumina balls with a diameter of 2-10 mm, in an argon atmosphere), and at a certain rotation speed, the metal or alloy powders undergo intense impact and collision with the milling media. After a period of operation, a multi-principal element alloy powder with uniform chemical composition is finally prepared. During this process, the metal or alloy powders are continuously flattened, cold-welded, broken, and re-welded. Ultimately, under conditions below the melting point temperature of the elements, metal elements with large differences in melting point or vapor pressure are alloyed, maximizing the solid solubility between the elements in the multi-principal element alloy and promoting the formation of a stable solid solution phase. This method is commonly used to prepare dispersion-strengthened materials, ultrafine-grained materials, gradient composite materials, or nano-multi-principal element alloy materials. However, during MA, impurities are introduced due to environmental inhalation gases, wear of the balls and canisters, process control agents, etc., and repeated collisions between the powder and the milling media exacerbate the contamination of the powder, leading to a decline in the overall performance of the alloy.

[0007] In summary, from the perspective of commonly used preparation processes, the significant advantage of vacuum arc melting is its extremely high temperature (~3000℃). In this environment, most common metallic elements can be melted, and the content of impurity elements such as O, N, and H can be minimized under vacuum and high temperature, thereby improving the application quality of the alloy. However, a major drawback of vacuum arc melting is that metallic elements with lower boiling points may undergo significant volatilization during the melting process, affecting the predetermined elemental ratio in the alloy. Currently, multi-principal element alloys prepared by magnetron sputtering have relatively small coating thicknesses, only at the nanometer and micrometer scale, and are mainly used in ultra-micro film fields such as solar cells, with very limited applications in the metal field. Commonly used mechanical alloying methods can effectively avoid volatilization caused by differences in melting points of metallic elements. However, during powder ball milling, many factors such as process control agents, milling media, and the airtightness of the planetary ball mill can adversely affect the sample. Especially for metal or alloy powders that are easily oxidized in air, the initial weighing and powder collection processes after ball milling must be carried out in a glove box, which is quite cumbersome. Summary of the Invention

[0008] To address the problem that the alloy melts into liquid and flows out from the mold gaps during the one-step sintering process due to the large differences in melting points of different alloying elements, making it difficult to form the final product and contaminating the cavity, this invention provides a multi-principal element alloy powder metallurgy stepwise sintering method.

[0009] To achieve the above objectives, this invention provides a stepwise powder metallurgy sintering method for multi-principal element alloys, employing a gradient sintering process:

[0010] First, rapidly increase the temperature to T at a rate of 20-100℃ / min. m1 The temperature is maintained for 0.5-1 hour, and the pressure is increased to 10-20 MPa. The heating rate is relatively fast in the first stage, which effectively saves sintering time and is also due to T... m1 The temperature is near the melting point of the lowest melting point alloy in the multi-principal alloy, so the effect on the material is small; the holding time (0.5-1 h) is chosen because this time range is sufficient for the melting and diffusion of each element; the pressure range (10-20 MPa) is chosen because the pressure is low in the early stage of sintering, and the forming is slow.

[0011] Secondly, the temperature is increased to T at a rate of 10-20℃ / min. m2The second stage involves holding the temperature for 0.5-1 hour, with the pressure increasing to 20-30 MPa. The slightly slower heating rate (compared to the first stage) is designed to gradually reach the lowest melting point alloying elements, preventing overheating. The holding time (0.5-1 hour) ensures stable temperature operation during this stage and facilitates the full diffusion of alloying elements near this melting point. The pressure range (20-30 MPa) is chosen to allow for a gradual increase in sintering pressure during the middle stages of sintering, resulting in slightly faster forming.

[0012] Next, the temperature is increased to T at a rate of 5-10℃ / min. m3 Hold at this temperature for 0.5-1 hour, and increase the pressure to 30-40 MPa. The reason for setting a slower heating rate in the third stage (compared to the first and second stages) is to gradually reach the melting point of the second-lowest melting point alloying element, and at this time, T... m3 Above 900℃, more pronounced temperature surge is more likely to occur. In the third stage, the target pressure can be set, as most alloying elements have essentially melted by this point, meeting the conditions for preliminary shaping and laying the foundation for the final forming stage.

[0013] Then, increase the temperature to T at a rate of 5-10℃ / min. m4 The holding time is 0.5-3 hours at a pressure of 30-40 MPa. The target temperature for the fourth stage is the final sintering temperature. Setting the heating rate too fast (compared to the first and second stages) will cause the alloying elements with the highest melting point to melt rapidly, posing a risk of leakage from the gaps in the graphite mold and hindering the long-term use of the thermocouples or infrared heating system in the hot-pressing sintering furnace (making it difficult to control the adjustment height of the temperature measuring holes). The holding time (0.5-3 hours) at the target pressure (30-40 MPa) is set to ensure that all alloying elements diffuse completely and sufficiently. Generally, 3 hours of holding time is sufficient for the diffusion of less reactive elements.

[0014] T m1 =600-800℃, T m2 =700-900℃, T m3 =900-1000℃, T m4 =1000-1500℃ and T m1 <T m2 <T m3 <T m4 ;

[0015] Finally, the gradient sintering process ends.

[0016] Preferably, before employing the gradient sintering process, the method further includes: using multi-principal alloy powder as a precursor, mixing it uniformly in a ball mill, and placing the uniformly mixed multi-principal alloy powder in a graphite mold.

[0017] Preferably, before gradient sintering, the uniformly mixed multi-principal powder is placed in a graphite mold and then pre-cooled and pressed at a pressure of 5-10 MPa for 5-10 min.

[0018] Preferably, after the gradient sintering process is completed, the furnace is cooled to room temperature.

[0019] Preferably, the powder metallurgy stepwise sintering method for multi-principal element alloys specifically includes the following steps:

[0020] (1) Use multi-principal alloy powder as a precursor and mix it thoroughly in a ball mill;

[0021] (2) Select a cylindrical graphite mold, first place a carbon sheet with a thickness of 0.02 mm on the inner surface, and then put the lower column into the inside of the graphite mold;

[0022] (3) After pouring the uniformly mixed multi-principal alloy powder into the graphite mold, place the upper column head and pad it with carbon sheet;

[0023] (4) Pre-cool and press the graphite mold containing multiple main alloy powders, and hold the pressure for 5-10 minutes. During this period, ensure that the upper and lower pressure heads are on the same axis to avoid centrifugal problems during subsequent pressure sintering, which could lead to mold damage.

[0024] (5) Place the pre-cooled graphite mold into the sintering cavity of the hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole;

[0025] (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, and wait for the vacuum level to drop before gradually closing the secondary valves around the chamber.

[0026] (7) Start the sintering process:

[0027] First, raise the temperature to T at a rate of 20-50℃ / min. m1 Keep warm for 0.5-1 hour, and increase the pressure to 10-20 MPa;

[0028] Secondly, the temperature is increased to T at a rate of 10-20℃ / min. m2 Keep warm for 0.5-1 hour, and increase the pressure to 20-30 MPa;

[0029] Next, the temperature is increased to T at a rate of 5-10℃ / min. m3 Keep warm for 0.5-1 hour, and increase the pressure to 30-40 MPa;

[0030] Then, increase the temperature to T at a rate of 5-10℃ / min. m4 Insulate for 0.5-3 hours at a pressure of 30-40 MPa;

[0031] T m1 =600-800℃, T m2 =700-900℃, T m3 =900-1000℃, T m4 =1000-1500℃ and T m1 <T m2 <T m3 <T m4 ;

[0032] Finally, the gradient sintering process ends;

[0033] (8) After the gradient sintering process is completed, the furnace is cooled to room temperature;

[0034] (9) Take out the cooled sample and polish the surface to obtain the target product.

[0035] Preferably, in step (2), the diameter of the cylindrical graphite mold is 30 mm, 40 mm or 50 mm.

[0036] Preferably, in step (5), if the sintering temperature is higher than 1000℃, infrared heating is used for sintering. At this time, the heating rate must be sufficient to ensure that there is enough time to adjust the displacement according to the infrared hole temperature.

[0037] Preferably, in step (8), the upper and lower pressure heads are turned on and the cooling system is turned on during the cooling process.

[0038] Throughout the sintering process, a vacuum or inert gas atmosphere must be maintained to prevent alloy oxidation.

[0039] Compared with the prior art, the present invention has the following advantages and technical effects:

[0040] This invention involves pre-pressing and high-temperature sintering alloy powder. During the sintering process, the alloy powder undergoes micro-plastic deformation, resulting in a certain degree of work hardening and increased activity of metallic elements. The multi-principal element alloy prepared by the method of this invention has advantages such as uniform microstructure and reduced segregation. Further heat treatment and large plastic deformation processes can significantly improve the overall performance of the alloy.

[0041] A stepwise sintering method using spark plasma sintering has been successfully developed to obtain high-performance multi-principal alloys. This method not only solves various problems associated with traditional vacuum arc melting, mechanical alloying, and magnetron sputtering methods for preparing multi-principal alloys, but also offers advantages such as uniform material composition and microstructure distribution, controllable dimensions, and ease of operation. Attached Figure Description

[0042] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0043] Figure 1 This is a graph showing the relationship between sintering time and sintering temperature in this invention;

[0044] Figure 2 This is a schematic diagram of the apparatus for the stepwise sintering method of the present invention;

[0045] Figure 3 The image shows a physical picture of the CoCrFeNiCu alloy prepared by the one-step sintering method in Comparative Example 1, where (a) is the final product obtained after the one-step sintering method is completed, and (b) is the block sample taken out of the graphite mold.

[0046] Figure 4 The images show the physical samples of the CoCrFeNiCu alloy (a) prepared by stepwise sintering in Example 1, the AlCrFeNi alloy (b) prepared by stepwise sintering in Example 2, and the CoCrNiFeMn alloy (c) prepared by stepwise sintering in Example 3.

[0047] Figure 5 Quasi-static uniaxial tensile stress-strain curves of the CoCrFeNiCu alloy prepared by stepwise sintering in Example 1 and the CoCrFeNiCu alloy prepared by one-step sintering in Comparative Example 1.

[0048] Figure 6 Quasi-static uniaxial tensile stress-strain curves of AlCrFeNi alloy prepared by stepwise sintering in Example 2 and AlCrFeNi alloy prepared by one-step sintering in Comparative Example 2.

[0049] Figure 7 Quasi-static uniaxial tensile stress-strain curves of the CoCrNiFeMn alloy prepared by stepwise sintering in Example 3 and the CoCrNiFeMn alloy prepared by one-step sintering in Comparative Example 3.

[0050] Figure 8 The image shows the engineering stress-strain curve of the block specimen obtained in Comparative Example 4.

[0051] Figure 9 The image shows the engineering stress-strain curve of the block specimen obtained in Comparative Example 5.

[0052] Figure 10 The diagram shows the engineering stress-strain curve of the block specimen obtained in Comparative Example 6. Detailed Implementation

[0053] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0054] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0055] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0056] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0057] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0058] In the embodiments of this invention, room temperature refers to 25±2℃.

[0059] Surface polishing is a conventional technique in this field and is not the focus of this invention, so it will not be described in detail here.

[0060] The relationship between sintering time and sintering temperature in this invention is shown in the graph. Figure 1 A schematic diagram of the apparatus for the stepwise sintering method of the present invention is shown below. Figure 2 .

[0061] Comparative Example 1: Preparation of CoCrFeNiCu alloy by one-step sintering method

[0062] (1) Weigh Fe, Co, Cr, Cu and Ni powders with a particle size of 500 mesh (all with a purity of 99.95%) according to the equiatomic ratio to obtain 180 g of multi-principal alloy powder, put it into a ball mill jar, add stainless steel balls with a diameter of 10 mm, the ball-to-material ratio is 5:1, put it into a vertical planetary ball mill, the speed is 400 r / min, rotate forward for 2 min and stop for 18 min, rotate backward for 2 min and stop for 18 min, the effective ball milling time is 60 min, and uniform multi-principal alloy powder is obtained.

[0063] (2) First, place a carbon sheet with a thickness of 0.02 mm on the inner surface of the cylindrical graphite mold, and then put the lower column into the inside of the graphite mold. The diameter of the graphite mold is 40 mm and the height is 80 mm.

[0064] (3) After pouring the well-mixed multi-principal alloy powder into the graphite mold, place the upper column head and pad it with carbon sheet.

[0065] (4) Pre-cool the graphite mold containing multiple main alloy powders (5 MPa) and hold the pressure for 10 min. During this period, ensure that the upper and lower pressure heads are on the same axis to avoid centrifugal problems during subsequent pressure sintering, which could damage the mold.

[0066] (5) Place the pre-cooled graphite mold into the sintering cavity of the rapid hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole;

[0067] (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, and wait for the vacuum level to drop before gradually closing the secondary valves around the chamber.

[0068] (7) Start the sintering program: raise the temperature to 1000℃ at a rate of 20℃ / min and hold for 1 h, while maintaining a pressure of 30 MPa;

[0069] (8) After the one-step sintering process is completed, the furnace is cooled to room temperature. During the cooling process, the upper and lower pressure heads are kept open and the cooling system is turned on.

[0070] The physical image of the CoCrFeNiCu alloy prepared by the one-step sintering method in this comparative example is shown below. Figure 3 ,Depend on Figure 3 It can be seen that the CoCrFeNiCu alloy block obtained by the one-step sintering method is incomplete, and a lot of liquid alloy flows out during the sintering process, forming an extremely irregular block material.

[0071] Example 1: Stepwise sintering preparation of CoCrFeNiCu alloy

[0072] (1) Weigh Fe, Co, Cr, Cu and Ni powders with a particle size of 500 mesh (all with a purity of 99.95%) according to the equiatomic ratio to obtain 180 g of multi-principal alloy powder, put it into a ball mill jar, add stainless steel balls with a diameter of 10 mm, the ball-to-material ratio is 5:1, put it into a vertical planetary ball mill, the speed is 400 r / min, rotate forward for 2 min and stop for 18 min, rotate backward for 2 min and stop for 18 min, the effective ball milling time is 60 min, and uniform multi-principal alloy powder is obtained.

[0073] (2) First, place a carbon sheet with a thickness of 0.02 mm on the inner surface of the cylindrical graphite mold, and then put the lower column into the inside of the graphite mold. The diameter of the graphite mold is 40 mm and the height is 80 mm.

[0074] (3) After pouring the well-mixed multi-principal alloy powder into the graphite mold, place the upper column head and pad it with carbon sheet.

[0075] (4) Pre-cool the graphite mold containing multiple main alloy powders (5 MPa) and hold the pressure for 10 min. During this period, ensure that the upper and lower pressure heads are on the same axis to avoid centrifugal problems during subsequent pressure sintering, which could damage the mold.

[0076] (5) Place the pre-cooled graphite mold into the sintering cavity of the rapid hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole;

[0077] (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, and wait for the vacuum level to drop before gradually closing the secondary valves around the chamber.

[0078] (7) Start the sintering process:

[0079] First, the temperature was increased to 660℃ at a rate of 100℃ / min and held for 0.5 h, during which time the pressure increased to 10 MPa.

[0080] Secondly, the temperature was increased to 800℃ at a rate of 10℃ / min and held for 0.5 h, while maintaining a vacuum state throughout the heating and holding process, during which the pressure increased to 20 MPa.

[0081] Next, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 0.5h, while the pressure was increased to 30 MPa.

[0082] Then, the temperature was increased to 1000℃ at a rate of 10℃ / min and held for 1 hour, during which the pressure was maintained at 30 MPa.

[0083] Finally, the gradient sintering process ends;

[0084] (8) After the gradient sintering process is completed, the temperature is reduced to 100°C at a cooling rate of 30°C / min, and then cooled to room temperature with the furnace. During the cooling process, the upper and lower pressure heads are kept open and the cooling system is turned on.

[0085] (9) The cooled block sample is removed and its surface is polished to obtain the target product. A physical image of the stepwise sintering preparation of the CoCrFeNiCu alloy in this embodiment is shown below. Figure 4 In (a), the quasi-static uniaxial tensile stress-strain curves of the CoCrFeNiCu alloy bulk specimens obtained after sintering in Example 1 and Comparative Example 1 are shown in Figure (a). Figure 5 As shown, it can be seen that compared with the one-step sintering method, the step-by-step sintering method can not only obtain complete and regular bulk materials ( Figure 4 In addition, its tensile strength under quasi-static uniaxial tensile loading increased from 356 MPa to 458 MPa, an increase of about 28.7%. Furthermore, the elongation increased from 4.3% to 7.4%, resulting in a significant improvement in overall mechanical properties.

[0086] Comparative Example 2: Preparation of AlCrFeNi Alloy by One-Step Sintering Method

[0087] (1) Weigh Al, Cr, Fe and Ni powders with a particle size of 500 mesh and a purity of 99.95% according to the equiatomic ratio to obtain 200 g of multi-principal alloy powder, put it into a ball mill jar, add stainless steel balls with a diameter of 10 mm, the ball-to-material ratio is 5:1, put it into a vertical planetary ball mill, the speed is 400 r / min, rotate forward for 2 min and stop for 18 min, rotate backward for 2 min and stop for 18 min, the effective ball milling time is 60 min, and uniform multi-principal alloy powder is obtained.

[0088] (2) First, place a carbon sheet with a thickness of 0.02 mm on the inner surface of the cylindrical graphite mold, and then put the lower column into the inside of the graphite mold. The diameter of the graphite mold is 30 mm and the height is 80 mm.

[0089] (3) After pouring the well-mixed multi-principal alloy powder into the graphite mold, place the upper column head and pad it with carbon sheet.

[0090] (4) Pre-cool the graphite mold containing multiple main alloy powders (5 MPa) and hold the pressure for 10 min. During this period, ensure that the upper and lower pressure heads are on the same axis to avoid centrifugal problems during subsequent pressure sintering, which could lead to mold damage.

[0091] (5) Place the pre-cooled graphite mold into the sintering cavity of the rapid hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole;

[0092] (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, and wait for the vacuum level to drop before gradually closing the secondary valves around the chamber.

[0093] (7) Start the sintering program: raise the temperature to 1500℃ at a rate of 20℃ / min and hold for 0.5 h, during which the pressure is maintained at 40 MPa;

[0094] (8) After the sintering process is completed, the furnace is cooled to room temperature. During the cooling process, the upper and lower pressure heads are turned on and the cooling system is turned on.

[0095] Example 2: Stepwise sintering preparation of AlCrFeNi alloy

[0096] (1) Weigh Al, Cr, Fe and Ni powders with a particle size of 500 mesh and a purity of 99.95% according to the equiatomic ratio to obtain 200 g of multi-principal alloy powder, put it into a ball mill jar, add stainless steel balls with a diameter of 10 mm, the ball-to-material ratio is 5:1, put it into a vertical planetary ball mill, the speed is 400 r / min, rotate forward for 2 min and stop for 18 min, rotate backward for 2 min and stop for 18 min, the effective ball milling time is 60 min, and uniform multi-principal alloy powder is obtained.

[0097] (2) First, place a carbon sheet with a thickness of 0.02 mm on the inner surface of the cylindrical graphite mold, and then put the lower column into the inside of the graphite mold. The diameter of the graphite mold is 30 mm and the height is 80 mm.

[0098] (3) After pouring the well-mixed multi-principal alloy powder into the graphite mold, place the upper column head and pad it with carbon sheet.

[0099] (4) Pre-cool the graphite mold containing multiple main alloy powders (5 MPa) and hold the pressure for 10 min. During this period, ensure that the upper and lower pressure heads are on the same axis to avoid centrifugal problems during subsequent pressure sintering, which could lead to mold damage.

[0100] (5) Place the pre-cooled graphite mold into the sintering cavity of the rapid hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole;

[0101] (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, and wait for the vacuum level to drop before gradually closing the secondary valves around the chamber.

[0102] (7) Start the sintering process:

[0103] First, the temperature is increased to 660℃ at a rate of 50℃ / min and held for 1 hour, during which the pressure increases to 10 MPa.

[0104] Secondly, the temperature was increased to 900℃ at a rate of 20℃ / min and held for 1 hour, while maintaining a vacuum state throughout the heating and holding process, during which the pressure increased to 20 MPa.

[0105] Next, the temperature was increased to 1000℃ at a rate of 5℃ / min and held for 0.5h, while the pressure was increased to 40 MPa.

[0106] Then, the temperature was increased to 1500℃ at a rate of 10℃ / min and held for 0.5 h, during which time the pressure was maintained at 40 MPa.

[0107] Finally, the gradient sintering process ends;

[0108] (8) After the gradient sintering process is completed, the temperature is reduced to 90°C at a cooling rate of 100°C / min, and then cooled to room temperature with the furnace. During the cooling process, the upper and lower pressure heads are kept open and the cooling system is turned on.

[0109] (9) The cooled sample is then polished to obtain the target product. A physical image of the AlCrFeNi alloy prepared by stepwise sintering in this embodiment is shown below. Figure 4 In Figure (b), the quasi-static uniaxial tensile stress-strain curves of the AlCrFeNi alloy bulk specimens obtained after sintering in Example 2 and Comparative Example 2 are shown in Figure (b). Figure 6 As shown in the figure. It can be seen that, compared with the one-step sintering method, the step-by-step sintering method can not only obtain complete and regular bulk materials ( Figure 4 In addition, its tensile strength under quasi-static uniaxial tensile loading increased from ~613 MPa to ~843 MPa, an increase of about 37.5%. Furthermore, the elongation increased from 1.8% to 6.2%, resulting in a significant improvement in overall mechanical properties.

[0110] Comparative Example 3: Preparation of CoCrNiFeMn Alloy by One-Step Sintering Method

[0111] (1) Bulk alloys were prepared by mechanical alloying using pure elemental powders (Co, Cr, Ni, Fe, and Mn, all with a purity of 99.9%) with a particle size of 500 mesh. 200 g of multi-principal element alloy powder was obtained by weighing according to an equiatomic ratio, where the ball-to-powder weight ratio was 1:2, and the balls used for ball milling were Al2O3 balls. The total effective time for mechanical alloying was 10 h, and the rotation speed was 400 rpm, resulting in uniform multi-principal element alloy powder.

[0112] (2) First, place a carbon sheet with a thickness of 0.02 mm on the inner surface of the cylindrical graphite mold, and then put the lower column into the inside of the graphite mold. The diameter of the graphite mold is 50 mm and the height is 80 mm.

[0113] (3) After pouring the well-mixed multi-principal alloy powder into the graphite mold, place the upper column head and pad it with carbon sheet.

[0114] (4) Pre-cool the graphite mold containing multiple main alloy powders (10 MPa) and hold the pressure for 5 min. During this period, ensure that the upper and lower pressure heads are on the same axis to avoid centrifugal problems during subsequent pressure sintering, which could lead to mold damage.

[0115] (5) Place the pre-cooled graphite mold into the sintering cavity of the rapid hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole;

[0116] (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, and wait for the vacuum level to drop before gradually closing the secondary valves around the chamber.

[0117] (7) Start the sintering program: raise the temperature to 1300℃ at a rate of 20℃ / min and hold for 3 hours, during which the pressure is maintained at 40MPa;

[0118] (8) After the gradient sintering process is completed, the furnace is cooled to room temperature. During the cooling process, the upper and lower pressure heads are kept open and the cooling system is turned on.

[0119] Example 3: Stepwise sintering preparation of CoCrNiFeMn alloy

[0120] (1) Bulk alloys were prepared by mechanical alloying using pure elemental powders (Co, Cr, Ni, Fe, and Mn, all with a purity of 99.9%) with a particle size of 500 mesh. 200 g of multi-principal element alloy powder was obtained by weighing according to an equiatomic ratio, where the ball-to-powder weight ratio was 1:2, and the balls used for ball milling were Al2O3 balls. The total effective time for mechanical alloying was 10 h, and the rotation speed was 400 rpm, resulting in uniform multi-principal element alloy powder.

[0121] (2) First, place a carbon sheet with a thickness of 0.02 mm on the inner surface of the cylindrical graphite mold, and then put the lower column into the inside of the graphite mold. The diameter of the graphite mold is 50 mm and the height is 80 mm.

[0122] (3) After pouring the well-mixed multi-principal alloy powder into the graphite mold, place the upper column head and pad it with carbon sheet.

[0123] (4) Pre-cool the graphite mold containing multiple main alloy powders (10 MPa) and hold the pressure for 5 min. During this period, ensure that the upper and lower pressure heads are on the same axis to avoid centrifugal problems during subsequent pressure sintering, which could lead to mold damage.

[0124] (5) Place the pre-cooled graphite mold into the sintering cavity of the rapid hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole;

[0125] (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, and wait for the vacuum level to drop before gradually closing the secondary valves around the chamber.

[0126] (7) Start the sintering process:

[0127] First, the temperature is increased to 800℃ at a rate of 40℃ / min and held for 1 hour, during which the pressure increases to 10 MPa.

[0128] Secondly, the temperature was increased to 900℃ at a rate of 20℃ / min and held for 1 hour, while maintaining a vacuum state throughout the heating and holding process, during which the pressure increased to 20 MPa.

[0129] Next, the temperature was increased to 1000℃ at a rate of 5℃ / min and held for 0.5 h, while the pressure was increased to 40 MPa.

[0130] Then, the temperature was increased to 1300℃ at a rate of 10℃ / min and held for 3 hours, during which the pressure was maintained at 40 MPa.

[0131] Finally, the gradient sintering process ends;

[0132] (8) After the gradient sintering process is completed, the temperature is reduced to 110°C at a cooling rate of 50°C / min, and then cooled to room temperature with the furnace. During the cooling process, the upper and lower pressure heads are kept open and the cooling system is turned on.

[0133] (9) Remove the cooled sample and polish its surface to obtain the target product. A physical image of the stepwise sintering preparation of the CoCrNiFeMn alloy in this embodiment is shown below. Figure 4 In (c), the quasi-static uniaxial tensile stress-strain curves of the CoCrNiFeMn alloy bulk specimens obtained after sintering in Example 3 and Comparative Example 3 are shown in Figure 3. Figure 7 As shown in the figure. It can be seen that, compared with the one-step sintering method, the step-by-step sintering method can not only obtain complete and regular bulk materials ( Figure 4 In addition, its tensile strength under quasi-static uniaxial tensile loading increased from ~560 MPa to ~665 MPa, an increase of about 18.8%. Furthermore, the elongation increased from 3.4% to 11.4%, resulting in a significant improvement in overall mechanical properties.

[0134] Comparative Example 4

[0135] Same as Example 1, except that the pre-cooling and pressing in step (4) was not performed.

[0136] The engineering stress-strain curve of the block specimen obtained in this comparative example is shown in the figure below. Figure 8 As shown.

[0137] Comparative Example 5

[0138] Same as Example 1, except that step (7) is as follows:

[0139] First, the temperature was increased to 660℃ at a rate of 50℃ / min and held for 0.5 h, during which time the pressure increased to 10 MPa.

[0140] Secondly, the temperature was increased to 1000℃ at a rate of 10℃ / min and held for 2 hours, during which the pressure was maintained at 30 MPa.

[0141] Finally, the gradient sintering process ends.

[0142] The engineering stress-strain curve of the block specimen obtained in this comparative example is shown in the figure below. Figure 9 As shown.

[0143] Comparative Example 6

[0144] Same as Example 1, except that step (7) is as follows:

[0145] First, the temperature was increased to 660℃ at a rate of 50℃ / min and held for 0.5 h, during which time the pressure increased to 20 MPa.

[0146] Secondly, the temperature was increased to 1000℃ at a rate of 5℃ / min and held for 2 hours, during which the pressure was maintained at 30 MPa.

[0147] Finally, the gradient sintering process ends.

[0148] The engineering stress-strain curve of the block specimen obtained in this comparative example is shown in the figure below. Figure 10 As shown.

[0149] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A stepwise powder metallurgy sintering method for multi-principal element alloys, characterized in that, Includes the following steps: (1) Use multi-principal alloy powder as a precursor and mix it thoroughly in a ball mill; (2) Select a cylindrical graphite mold, first place a carbon sheet with a thickness of 0.02mm on the inner surface, and then put the lower column into the inside of the graphite mold; (3) After pouring the uniformly mixed multi-principal alloy powder into the graphite mold, the upper column head is placed in and a carbon sheet is placed on top. (4) Pre-cool and press the graphite mold containing multiple main alloy powders, and hold the pressure for 5-10 minutes, ensuring that the upper and lower press heads are on the same axis during the process; (5) Place the pre-cooled graphite mold into the sintering cavity of the hot pressing sintering furnace and insert the thermocouple into the corresponding heating hole. (6) Close the sintering chamber door, turn on the pressure setting, turn on the vacuum switch, wait for the vacuum level to drop until it is below 20Pa, and then gradually close the secondary valves around the chamber. (7) Start the gradient sintering program: First, raise the temperature to T at a rate of 20-50℃ / min. m1 Keep warm for 0.5-1 hour, and increase the pressure to 10-20 MPa; Secondly, the temperature is increased to T at a rate of 10-20℃ / min. m2 Keep warm for 0.5-1 hour, and increase the pressure to 20-30 MPa; Next, the temperature is increased to T at a rate of 5-10℃ / min. m3 Keep warm for 0.5-1 hour, and the pressure will rise to 30-40 MPa; Then, increase the temperature to T at a rate of 5-10℃ / min. m4 Insulate for 0.5-3 hours at a pressure of 30-40 MPa; T m1 = 600 - 800 °C, T m2 = 700 - 900 °C, T m3 = 900 - 1000 °C, T m4 = 1000 - 1500 °C and T m1 <T m2 <T m3 <T m4 ; Finally, the gradient sintering process ends; (8) After the gradient sintering process is completed, the furnace is cooled to room temperature; (9) Take out the cooled sample and polish the surface to obtain the target product.

2. The powder metallurgy stepwise sintering method for multi-principal element alloys according to claim 1, characterized in that, In step (4), the pressure during pre-cooling is 5-10 MPa.

3. The powder metallurgy stepwise sintering method for multi-principal element alloys according to claim 1, characterized in that, In step (2), the diameter of the cylindrical graphite mold is 30mm, 40mm or 50mm.

4. The powder metallurgy stepwise sintering method for multi-principal element alloys according to claim 1, characterized in that, In step (5), if the sintering temperature is higher than 1000℃, infrared heating is used for sintering.

5. The powder metallurgy stepwise sintering method for multi-principal element alloys according to claim 1, characterized in that, In step (8), ensure that the upper and lower pressure heads are open and the cooling system is turned on during the cooling process.

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