KR102869752B1 - High-entropy carbide and manufacturing method thereof - Google Patents

Abstract

The high-entropy superhard material according to the present invention can replace or reduce the amount of tungsten and cobalt, which are the main components of WC-Co alloy-based superhard alloys used as conventional superhard materials, while satisfying equivalent or higher mechanical properties, by developing raw material powders and binders capable of high entropy and suggesting an optimal molding/sintering method for them, thereby increasing utilization in various industrial groups and effectively preparing for supply chain problems.

Description

High-entropy carbide and manufacturing method thereof

The present invention relates to a high-entropy superhard material and a method for manufacturing the same, and more particularly, to a high-performance powder metallurgy-based superhard material that can replace or reduce materials used in conventional superhard alloys and a method for manufacturing the same.

Traditionally, common alloy systems consist of major elements such as iron, copper, aluminum, magnesium, and titanium, along with various minor alloying elements. Typically, in conventional multi-element alloys, increasing the number and amount of alloying elements leads to the formation of intermetallic compounds, which degrade the mechanical properties of the material. However, the recent emergence of high-entropy alloys (HEAs) has significantly changed the paradigm of conventional alloy design.

High-entropy alloys (HEAs) are alloys composed of multiple elements as primary constituents. Because they possess high entropy of mixing, their Gibbs free energy of formation is low, preventing the formation of intermetallic compounds and resulting in superior ductility. In addition to high strength and elongation, HEAs possess exceptional properties such as high-temperature resistance, corrosion resistance, and oxidation resistance. Research is underway in various fields as a means of overcoming the limitations of existing materials.

High-entropy materials are attracting attention, particularly in the field of cemented carbides. Cemented carbides are a general term for alloys formed by mixing and sintering iron group metals such as Fe, Co, and Ni into powders of metal carbides belonging to groups IVa, Va, and VIa of the periodic table. These alloys are characterized by excellent hardness at room temperature, high temperature hardness, high strength, and stable physical properties. Among them, the mechanical properties of the WC-Co alloy are the best, and this alloy system is commonly referred to as cemented carbides. Cemented carbides are widely used in various fields, including various cutting tools, wear-resistant and impact-resistant tools, high-temperature and high-pressure parts, and superheat-resistant materials.

The components of this WC-Co alloy superalloy include tungsten carbide with a particle size of 0.5 to 16 ㎛ as the main component, cobalt with a particle size of 1.0 to 2.0 ㎛ added as a bonding metal, titanium carbide added as a solid solution to improve the hardness and heat resistance of the superalloy, and tantalum carbide that improves the oxidation resistance of the superalloy while suppressing the grain growth of tungsten carbide and titanium carbide and improving the wear resistance and strength of the superalloy.

However, to date, other than the WC-Co alloy-based cemented carbide described above, there has been no technological development on high-entropy-based high-performance cemented carbide materials and new cemented carbide materials using these materials. In other words, in order to develop high-entropy-based high-performance cemented carbide materials with excellent mechanical properties such as fracture toughness, relative density, and hardness, it is necessary to derive factors related to the advancement of the properties of cemented carbide materials, as well as conduct research on the selection of high-entropy carbide raw material powders, their synthesis, molding, and sintering methods. However, due to the difficulty of research and development, no research on this has been reported.

Accordingly, in order to fully utilize the excellent properties of high-entropy superalloys and maximize their utilization in various industrial groups, there is an urgent need for research on the selection of high-entropy carbide raw material powders with excellent mechanical properties such as fracture toughness, relative density, and hardness, as well as on their synthesis, molding, and sintering methods.

Republic of Korea Patent No. 1039631 (June 1, 2011)

The present invention has been conceived to overcome the aforementioned problems, and the problem to be solved by the present invention is to develop raw powders and binders capable of high entropy and to provide optimal mixing, molding, and sintering methods therefor. Through this, the present invention provides a high-entropy superhard material and a manufacturing method thereof that can replace or reduce the amount of tungsten and cobalt, which are the main components of conventional WC-Co alloy superhard alloys, while satisfying equivalent or higher mechanical properties.

The present invention is a method for manufacturing a high-entropy superhard material to solve the above-described problem, comprising a first step of manufacturing a high-entropy carbide using a high-entropy carbide raw material powder containing at least five kinds of transition metals, a second step of manufacturing a high-entropy binder, and a third step of manufacturing a high-entropy sintered body by mixing, molding, and sintering the high-entropy carbide and the high-entropy binder.

A high-entropy superhard material satisfying both the following relationships (1) and (2) is provided.

(1) Vickers hardness of 1,300 or more (HV30)

(2) Fracture toughness of 6 Mpaㆍm ^1/2 or more

In addition, according to one embodiment of the present invention, the high-entropy carbide raw material powder of the first step may be characterized by being five kinds selected from the group consisting of HfC, TaC, TiC, ZrC, NbC, VC, CrC, MoC, and WC.

In addition, the first step may be characterized as a step of ball milling at a ball and powder ratio of 5 to 15:1 for 15 to 90 minutes at 500 to 1,100 rpm (gravitational acceleration of 40 G to 90 G) in an air atmosphere.

In addition, it can be characterized in that the high-entropy carbide raw material powder is FCC single-phased in a multi-component system through the first step.

In addition, the first step may be characterized as a multi-stage sintering step in which the temperature maintenance section is performed at least once.

In addition, the temperature maintenance range of the first step may be characterized as being 1,500 to 2,000°C.

Additionally, the first step may be characterized by being performed at a sintering pressure of 50 to 65 MPa.

In addition, the first step may be characterized by performing a first stage sintering for 10 minutes at a pressure of 55 to 65 MPa and a temperature of 1,750 to 1,850°C, and then performing a second stage sintering for 1 to 10 minutes at a pressure of 55 to 65 MPa and a temperature of 1,950 to 2,050°C.

Additionally, the high-entropy binder may be characterized by being gas-atomized with one or more materials selected from aluminum (Al), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), and nickel (Ni).

In addition, it may be characterized by crushing and refining high-entropy carbide before performing the third step.

In addition, the present invention provides a high-entropy superhard material comprising five kinds of high-entropy carbide raw material powders selected from the group consisting of HfC, TaC, TiC, ZrC, NbC, VC, CrC, MoC and WC and a high-entropy binder, and satisfying both the following relationships (1) and (2).

(1) Vickers hardness of 1300 or higher (HV30)

(2) Fracture toughness of 6 Mpaㆍm ^1/2 or more

By developing a raw material powder and binder capable of high entropy formation as suggested in the present invention and an optimal mixing, molding/sintering method for them, it is possible to replace or reduce the amount of tungsten and cobalt, which are the main components of WC-Co alloy-based superhard alloys used as conventional superhard materials, while manufacturing a high-entropy superhard material that satisfies mechanical properties equivalent to or better, thereby greatly increasing its utilization in various industrial groups.

In addition, there is a growing demand for replacement and reduction of tungsten (W) and cobalt (Co), which are the main components of conventional superhard materials, in relation to the supply chain stabilization issue (Global Value Chain: GVC), which has recently attracted significant social attention. The above two elements are representative supply chain management items that are almost entirely produced and supplied by China. In this respect, the high-entropy superhard material of the present invention has a composition that completely replaces W and Co or contains very small amounts, and high-entropy materials are generally composed of 3 to 5 or more types of elements in equivalent amounts. Therefore, when a supply chain problem occurs in some component materials, it can be replaced with other elements with similar properties excluding the element in question, so there is an advantage in that it is easy to respond to supply chain issues.

Figure 1 is a schematic diagram of a WC-Co alloy, a typical conventional superhard material.
Figure 2 is a schematic diagram of a high-entropy superhard material (carbide + binder) according to one embodiment of the present invention.
Figure 3a is an SEM image of raw material powders according to one embodiment of the present invention.
Figure 3b is a SEM image showing superhard powder after milling according to one embodiment of the present invention.
Figure 4 is an image showing a high-energy ball mill device according to one embodiment of the present invention.
Figure 5 is an SEM image showing the influence of ball and powder ratio according to one embodiment of the present invention.
Figure 6 is an SEM image showing the influence of rpm among milling conditions according to one embodiment of the present invention.
Figure 7 is an SEM image showing the influence of ball and magnet materials according to one embodiment of the present invention.
Figure 8 is an SEM image showing the effect of milling time according to one embodiment of the present invention.
Figure 9 is an EDS mapping image according to milling time of a transition metal carbide according to one embodiment of the present invention.
Figure 10 shows the results of XRD analysis according to milling time of transition metal carbide according to one embodiment of the present invention.
Figure 11 is an image showing a rapid sintering device according to one embodiment of the present invention.
Figure 12 is an image showing defects in sintered bodies according to the maximum sintering temperature range.
Figure 13 is a graph showing the sintering temperature range according to the present invention.
Fig. 14 is a graph showing the results of XRD analysis of a high-entropy carbide sintered body according to one embodiment of the present invention.
FIG. 15 is a graph showing the Vickers hardness and fracture toughness of high-entropy carbide sintered bodies using one-stage and two-stage sintering methods according to one embodiment of the present invention.
Figure 16 is a table showing the density and Vickers hardness of a high-entropy carbide sintered body according to one embodiment of the present invention.
Fig. 17 is an image showing the microstructure of carbide at a sintering temperature according to one embodiment of the present invention.
Fig. 18 is a graph showing particle size according to sintering temperature according to one embodiment of the present invention.
Figures 19 and 20 are graphs showing mechanical properties according to sintering temperature according to one embodiment of the present invention.
Figure 21 is an image showing the presence of coarse high-entropy carbide under 60-minute milling conditions of high-entropy carbide or high-entropy binder.
Figure 22 is a graph showing the mechanical properties of a superhard material according to one embodiment of the present invention.
Figure 23 is a graph showing the mechanical properties of conventional superhard materials.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

As described above, research on the improvement of mechanical properties of conventional superhard materials due to high entropy is limited, and thus their utilization is limited.

Accordingly, the present invention seeks to solve the above-described problem by providing a method for manufacturing a high-entropy superhard material, comprising a first step of manufacturing a high-entropy carbide using a high-entropy carbide raw material powder containing at least five kinds of transition metals, a second step of manufacturing a high-entropy binder, and a third step of manufacturing a high-entropy sintered body by mixing, molding, and sintering the high-entropy carbide and the high-entropy binder, and satisfying both the following equations (1) and (2).

(1) Vickers hardness of 1300 or higher (HV30)

(2) Fracture toughness of 6 Mpaㆍm ^1/2 or more

Through this, through the development of raw material powder and binder capable of high entropy as suggested in the present invention and the optimal mixing, molding/sintering method for them, it is possible to replace or reduce the amount of tungsten and cobalt, which are the main components of WC-Co alloy-based superalloys used as conventional superalloys, while manufacturing high entropy superalloys that satisfy equivalent or higher mechanical properties, thereby greatly increasing their utilization in various industrial groups.

Referring to the drawings below, a method for manufacturing a high-entropy superhard material according to the present invention is described.

The first step of the method for manufacturing a high-entropy superhard material according to the present invention is a step of manufacturing a high-entropy carbide using a high-entropy carbide raw material powder containing at least five types of transition metals.

Referring to Figure 1, a schematic diagram of a typical WC-Co alloy, a conventional superhard material, can be seen. Such a conventional WC-Co alloy is made from tungsten as a raw material powder, with trace elements such as cobalt binder and aluminum added. Currently, there is a need to develop new high-entropy superhard materials containing various elements to expand the application areas of high-entropy alloys across various industries, maximize their utility, and reduce or replace the use of conventional materials.

Accordingly, the present invention can provide a new high-entropy superhard material by researching/developing and deriving a high-entropy raw material powder (High-Entory-Carbide, HEC) as shown in the schematic diagram of Fig. 2.

To this end, the high-entropy carbide raw material powder can be selected from materials capable of being made into high entropy. For example, the high-entropy raw material can be a transition metal belonging to groups IVa, Va, and VIa, and a carbide material thereof can be used by selecting a transition metal with a similar crystal structure. More preferably, the raw material powder can be five kinds selected from the group consisting of HfC, TaC, TiC, ZrC, NbC, VC, CrC, MoC, and WC. The above raw material powders have a high melting point, excellent mechanical strength, and can form a body-centered cubic structure high-entropy alloy when an alloy is produced at a similar fraction, which may be more advantageous. Accordingly, (Hf-Ta-Ti-Zr-Nb)C can be most preferably used as the high-entropy carbide raw material powder. In this case, the high-entropy carbide raw material powders HfC, TaC, TiC, ZrC, and NbC may each have a weight ratio composition of 25~32: 7~12: 27~32: 13~20: 14~20.

Meanwhile, as described above, the high-entropy carbide raw material powder must exhibit high-entropy characteristics. To achieve this, these raw material powders must be able to be uniformly mixed and refined. Only when these characteristics are satisfied can the present invention exhibit mechanical properties equivalent to or superior to those of conventional carbide materials. However, referring to Fig. 3a, the shape of the (Hf-Ta-Ti-Zr-Nb)C raw material powder according to a preferred embodiment of the present invention can be seen, and it can be seen that the surface generally has a sharp and irregular shape. Accordingly, the present invention can improve the refinement/homogenization and mixing characteristics of the powder by suggesting the optimal milling or molding/sintering conditions described below. That is, as shown in Fig. 3b, the raw material powder having an angular shape is refined as the milling time increases. It is possible to manufacture high-entropy carbide having an average particle size of 0.2 to 2 ㎛.

For this purpose, the first step may be a step of ball milling at high energy using equipment such as Fig. 4 with a ball and powder ratio of 5 to 15:1 for 15 to 90 minutes at 500 to 700 rpm in an air atmosphere.

At this time, if the milling speed of the first step is less than 500 rpm, the mixing characteristics may deteriorate due to uneven mixing or fine mixing as shown in the image in Fig. 5, and if the milling speed exceeds 700 rpm, there may be a problem of deposition on the wall or a decrease in the recovery rate.

In addition, if the ball and powder ratio exceeds 15:1, there may be a problem with the powder recovery rate as shown in the image in Fig. 6, which may result in a decrease in milling efficiency, and if the ball and powder ratio is less than 5:1, there may be a disadvantage in terms of uneven mixing or fine mixing, which may result in a decrease in mixing characteristics.

In addition, if the ball and shaft material is tungsten carbide as shown in the image in Fig. 7, it is appropriate, but if metal (SUS) or ceramic (ZrO ₂ ) is used, there may be a problem that sufficient impact is not transmitted or impurities increase.

In addition, if the milling time of the first step is less than 15 minutes, the mixing characteristics may deteriorate due to uneven mixing or fine mixing as shown in the image in Fig. 8, and if the milling time exceeds 90 minutes, there may be a problem of impurities increasing as the milling time increases.

More specifically, referring to FIG. 9, in a preferred embodiment of the present invention, when the transition metal carbide uses HfC, TaC, TiC, ZrC, and NbC, the EDS mapping image according to the milling time can be seen, through which it can be seen that the high-entropy transition metal cemented carbide powder according to the present invention exhibits excellent uniform dispersibility after a certain milling time. In addition, in the XRD analysis results of FIG. 10, it can be seen that although various carbide phases were observed at the initial milling time (1, 5, 15 minutes), the phases tend to be gradually synthesized as the milling time increases. That is, the present invention can synthesize the high-entropy carbide raw material powder in a multi-component phase close to FCC single phase through the first step.

At this time, the milling conditions of the first stage of the present invention described above describe the main milling conditions for achieving the purpose of the present invention, and conventional processes known in the art, such as grinding or heat treatment, may be added as long as they are consistent with the purpose of the present invention.

Meanwhile, the first step includes a step of molding and sintering high-entropy carbide milling powder. In order to manufacture high-entropy carbide with excellent mechanical properties using the above-described milling powder, it is generally necessary to optimize conditions such as heating rate, time, pressure, and sintering holding temperature so that cracks in the sintered body do not occur during the sintering process after the milling process and densification is possible. If even one of the conditions is not properly designed, it is difficult to exhibit the desired mechanical properties.

Accordingly, the first step of the present invention may preferably be a step of ultra-high pressure molding the high-entropy carbide milling powder at a pressure of 50 to 65 MPa in a vacuum atmosphere using the equipment of FIG. 12 and then sintering at a temperature of 1,500 to 2,000°C. At this time, if the temperature exceeds 2,000°C, defects in the carbide sintered body may occur, as shown in FIG. 13. In addition, if the temperature is less than 1,500°C, it may be disadvantageous in the uniformity and micro-screen of the carbide sintered body.

In addition, referring to FIGS. 13a and 13b, the temperature increase to the maximum temperature range can be achieved at a heating rate of 80 to 120°C/min. If the temperature increase is lower than 80°C/min, the heat treatment time becomes too long, which is undesirable. If the temperature increase is higher than 120°C/min, the process efficiency decreases compared to the energy input for heating, which is undesirable. In addition, the cooling can be achieved at a rate of 30 to 70°C/min.

More specifically, referring to FIG. 13a and FIG. 14, which are single-stage sintering methods having a single temperature holding section (1,700 to 2,000°C), the XRD results of the high-entropy carbide sintered body manufactured by the single-stage sintering method in which the temperature holding section is sintered only once for 10 minutes at 1,700 to 2,000°C show that as the sintering temperature increases, single elements of ZrC and HfC tend to be synthesized in an FCC single phase, and some peaks of HfO ₂ and ZrO ₂ oxides are also detected.

At this time, according to a preferred embodiment of the present invention, the sintering step of the first stage may be a multi-stage sintering step having at least one temperature maintenance section, as shown in FIG. 13b. That is, FIG. 13a described above shows that the sintering step of the first stage has only one temperature maintenance section (1,700 to 2,000°C), and FIG. 13b shows that it has two temperature maintenance sections.

More specifically, referring to FIGS. 13b and 15, it can be seen that when the first stage sintering is performed at a temperature of 1,750 to 1,850°C for 10 minutes and then the second stage sintering is performed at a pressure of 55 to 65 MPa and a temperature of 1,950 to 2,050°C for 1 to 10 minutes, the overall relative density and Vickers hardness are superior to those of the single-stage sintering method. In addition, through FIG. 15, it can be seen that the main process factor for improving the Vickers hardness is that the holding time of the final sintering temperature is important in minimizing grain size growth, and the pressure variable is most important for improving the relative density.

The second step of the method for manufacturing a high-entropy superhard material according to the present invention is a step of manufacturing a high-entropy binder for mixing with the high-entropy carbide manufactured in the first step.

The high-entropy binder may be a material capable of high entropy, and a known, conventional material may be used as long as it is suitable for the purpose of the present invention. However, it is preferable to use a gas-atomized binder made of manganese (Mn), aluminum (Al), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), and nickel (Ni), which may be more advantageous in terms of powder uniformity and fine screen, which will be described later.

According to one embodiment of the present invention, when the high-entropy binder comprises manganese (Mn), cobalt (Co), iron (Fe), and nickel (Ni), reduction in materials used as conventional binders may be possible, and further, according to another embodiment of the present invention, when the high-entropy binder comprises aluminum (Al), chromium (Cr), iron (Fe), and nickel (Ni), cobalt used as conventional binders may be replaced.

At this time, the binder can be manufactured using a known, conventional method for a material capable of high entropy including the above-described material, and is not particularly limited.

The third step of the method for manufacturing a high-entropy superhard material according to the present invention is a step of manufacturing a high-entropy sintered body by mixing, molding, and sintering the high-entropy carbide and the high-entropy binder.

The purpose of the present invention is to provide a new material having higher performance than conventional superhard materials by replacing tungsten as a conventional superhard material with high-entropy carbide and replacing the conventional cobalt binder with a high-entropy binder as described above. Therefore, uniform mixing of the high-entropy carbide and the high-entropy binder is required.

To this end, the third step may be a step of performing ultra-high pressure molding of the high-entropy transition metal carbide superhard powder using the equipment of FIG. 12 described above at a pressure of 40 to 60 MPa in a vacuum atmosphere, and then maintaining the temperature at 1,200 to 1,400°C for 5 to 15 minutes to rapidly sinter it. At this time, the temperature of 1,200 to 1,400°C is maintained as the maximum temperature range for 5 to 15 minutes, thereby enabling densification of the sintered body. At this time, if the temperature exceeds 1,400°C, sintered body defects may occur. In addition, if the temperature is lower than 1,200°C, it may be disadvantageous in uniformity and fine screen of the sintered body.

At this time, the temperature can be increased to the above maximum temperature range at a heating rate of 80 to 120°C/min. If the temperature is increased at a rate lower than 80°C/min, the heat treatment time becomes too long, which is undesirable. If the temperature is increased at a rate higher than 120°C/min, the process efficiency decreases compared to the energy input for heating, which is undesirable. In addition, cooling can be performed at a rate of 40 to 60°C/min.

Meanwhile, referring to FIG. 21, it can be seen that coarse high-entropy carbide exists under 60-minute milling conditions of high-entropy carbide or high-entropy binder. In order to manufacture the desired high-performance high-entropy superhard material, coarse grinding and refinement of the high-entropy carbide may be additionally required prior to mixing the carbide and binder powders.

Accordingly, the method for manufacturing a high-entropy superhard material according to the present invention may further include a step of coarsely crushing and refining the high-entropy carbide before performing the third step. In this case, the degree of mixing of the carbide and the binder and the density of the sintered body can be significantly increased during the mixing and molding with the high-entropy binder in the third step.

The following describes a high-entropy superhard material according to the present invention. However, to avoid duplication, descriptions of parts that share the same technical concept as the manufacturing method for the high-entropy carbide described above are omitted.

The high-entropy superhard material according to the present invention comprises five kinds of high-entropy carbide raw material powders selected from the group consisting of HfC, TaC, TiC, ZrC, NbC, VC, CrC, MoC and WC and a high-entropy binder, and satisfies both the following relationships (1) and (2).

(1) Vickers hardness of 1300 or higher (HV30)

(2) Fracture toughness of 6 Mpaㆍm ^1/2 or more

More specifically, referring to FIGS. 22 and 23, the high-entropy superhard material according to the present invention can have a Vickers hardness of 1,300 or more. That is, it can be seen that it exhibits mechanical properties (Vickers hardness) that are equivalent to or superior to the conventional WC-Co superhard material shown in FIG. 23. If the Vickers hardness of the high-entropy superhard material according to the present invention is less than 1,300, the cutting, processing, and polishing performance of the workpiece may deteriorate.

In addition, it can be seen that the high-entropy superhard material according to the present invention exhibits a fracture toughness of 6 Mpaㆍm ^1/2 or more. If the fracture toughness of the high-entropy superhard material according to the present invention is less than 7 Mpaㆍm ^1/2 , the tool life may be significantly reduced.

In summary, the high-entropy superhard material of the present invention can replace or reduce the amount of tungsten and cobalt, which are the main components of WC-Co alloy superhard alloys used as conventional superhard materials, while satisfying equivalent or higher mechanical properties by developing raw material powders and binders capable of high entropy and suggesting an optimal molding/sintering method for them, thereby manufacturing a high-entropy superhard material that can sufficiently utilize the excellent intrinsic properties of superhard alloys and can greatly increase their utilization in various industrial groups, and can effectively respond to supply chain problems that arise.

Hereinafter, the present invention will be described in more detail through examples, but the following examples do not limit the scope of the present invention, and should be interpreted as helping to understand the present invention.

Preparation Example 1 - Ball Milling

HfC, TaC, TiC, ZrC, and NbC were mixed to have the composition shown in Table 1 below, and milled under the milling conditions shown in Table 2 below using ultra-high energy milling equipment as shown in Fig. 4 to manufacture high-entropy carbide powder.

　 HfC TiC TaC ZrC NbC Composition at.% 1 1 1 1 1 (HfTiTaZrNb)C wt.% 29.2 9.2 29.6 15.8 16.1

Preparation examples 2 to 9

A high-entropy carbide sintered body was manufactured in the same manner as in Preparation Example 1 above, but with different milling conditions as shown in Table 2 below.

Milling conditions Self-made material Ball material/size BPR RPM Milling time atmosphere Preparation Example 1 WC Carbide ball/5 ø 10:01 600 30 minutes * 2 cycles = 60 minutes atmosphere Preparation Example 2 Ceramic Carbide ball/5 ø 10:01 600 30 minutes * 2 cycles = 60 minutes atmosphere Preparation Example 3 metal Carbide ball/5 ø 10:01 600 30 minutes * 2 cycles = 60 minutes atmosphere Preparation Example 4 WC Carbide ball/5 ø 15:01 600 30 minutes * 2 cycles = 60 minutes atmosphere Preparation Example 5 WC Carbide ball/5 ø 20:01 600 30 minutes * 2 cycles = 60 minutes atmosphere Preparation Example 6 WC Carbide ball/5 ø 10:01 200 30 minutes * 2 cycles = 60 minutes atmosphere Preparation Example 7 WC Carbide ball/5 ø 10:01 400 30 minutes * 2 cycles = 60 minutes atmosphere Preparation Example 8 WC Carbide ball/5 ø 10:01 600 5 minutes atmosphere Preparation Example 9 WC Carbide ball/5 ø 10:01 600 10 minutes atmosphere

Experimental Example 1 - SEM Image Analysis

SEM images of the raw material powder according to the above Preparation Example 1 and the high-entropy carbide powder milled from the same were measured and shown in Figs. 3a and 3b.

Referring to Fig. 3a, the shape of the (Hf-Ta-Ti-Zr-Nb)C raw material powder according to a preferred embodiment of the present invention can be seen, and it can be seen that the surface generally has a sharp and irregular shape. However, as shown in Fig. 3b, in which the milling step for Preparation Example 1 was performed under the milling conditions according to the present invention, the raw material powder having an angular shape was refined as the milling time increased. It can be seen that it is possible to manufacture high-entropy transition metal superhard powders having an average particle size of 0.2 to 2 ㎛.

Experimental Example 2 - Analysis according to milling conditions

The results of varying the milling conditions for the above preparation examples 1 to 9 were analyzed and shown in Figures 5 to 10.

Referring to Fig. 5, it can be seen that in the case of Preparation Examples 6 and 7 where the milling speed of the first step is less than 500 rpm, the mixing characteristics may deteriorate due to uneven mixing or refinement.

Referring to Fig. 6, it can be seen that if the ball and powder ratio exceeds 15:1, in the case of Preparation Example 5, there may be a problem with the powder recovery rate, resulting in a decrease in milling efficiency.

Referring to Fig. 7, it can be seen that in the case of Preparation Examples 2 and 3, when metal (SUS) or ceramic (ZrO ₂ ) is used in relation to the material of the ball mill, there may be a problem in that sufficient impact is not transmitted or impurities increase.

Referring to Fig. 8, it can be seen that in the case of Preparation Examples 8 and 9 where the milling time of the first step is less than 30 minutes, the mixing characteristics may be deteriorated due to uneven mixing or fine mixing, and if the milling time exceeds 90 minutes, there may be a problem of impurities increasing as the milling time increases.

Referring to Fig. 9, EDS mapping images according to milling time for Preparation Example 1 of the present invention can be seen, through which it can be seen that the high-entropy transition metal cemented carbide powder according to the present invention exhibits excellent uniform dispersibility after a certain milling time. Furthermore, from the XRD analysis results of Fig. 10, it can be seen that although various carbide phases were observed at the initial milling time, the phases tended to be gradually synthesized as the milling time increased.

Examples 1 to 6 - High-entropy carbide production (one-step sintering)

After performing the milling step for the above Preparation Example 1, high-entropy carbide was manufactured using equipment such as Fig. 12 by varying the sintering temperature and particle size characteristics, maximum temperature maintenance time, and pressure as shown in Table 3 below.

　 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Maximum temperature range
(℃) 1700 1800 1900 2000 1800 1800 Retention time
(min) 10 10 10 10 10 10 Pressure (MPa) 50 50 50 50 55 60

Experimental Example 3 - Analysis according to sintering conditions (single-stage sintering)

Referring to FIG. 13a and FIG. 14, the XRD results of the high-entropy carbide sintered body manufactured by a single-step sintering method in which the temperature is maintained at 1700 to 2000°C and sintered only once for 10 minutes show that as the sintering temperature increases, single elements of ZrC and HfC tend to be synthesized as a FCC single phase, and some peaks of HfO ₂ and ZrO ₂ oxides are also detected.

More specifically, through Figs. 16 and 17 showing the mechanical properties of high-entropy carbides manufactured by the one-step sintering method, it can be seen that as the sintering temperature increases, the fraction of micropores shows a tendency to steadily decrease, and it can be seen that (Hf-Ta-Ti-Zr-Nb)C has a crystal grain size of 1-3 ㎛ according to a preferred embodiment of the present invention.

In addition, through Fig. 18, it can be seen that the particle size changes according to the sintering temperature, and through Fig. 19, it can be seen that as the sintering temperature increases, the relative density of the high-entropy carbide sintered body also tends to increase. At this time, the effective pressure for producing high-density high-entropy carbide is confirmed to be 60 MPa.

In addition, through Fig. 20, it can be seen that as the sintering temperature increases, the Vickers hardness of the high-entropy carbide sintered body also tends to increase, and similarly, it can be seen that a sintering pressure of 60 MPa is effective in improving the hardness of the high-entropy carbide.

Example 7 - High-entropy carbide production (two-stage sintering)

After performing the milling step for the above Preparation Example 1, high-entropy carbide was manufactured using equipment such as FIG. 12 by varying the sintering temperature, pressure, and maximum temperature maintenance time as shown in FIG. 13b and FIG. 16 below.

Referring to Fig. 15, it can be seen that when single-stage sintering is performed for 10 minutes under a pressure of 60 MPa and a temperature of 1800°C, and then double-stage sintering is performed for 10 minutes under a pressure of 60 MPa and a temperature of 2000°C, the overall relative density and Vickers hardness are superior to those of the single-stage sintering method. In addition, through Fig. 15, it can be seen that the main process factor for improving Vickers hardness is the maintenance time of the final sintering temperature, which is important in minimizing grain size growth, and the pressure variable is the most important for improving the relative density.

Preparation Example - Manufacturing of High-Entropy Binder (Gas Atomization Method)

At least four elements among manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), chromium (Cr), and aluminum (Al) were manufactured in equal proportions. The composition was designed as an alternative composition that did not contain any cobalt, and a reduced composition that contained trace amounts, as shown below.

Manufacturing variables Manufacturing conditions orifice Ceramic, inner diameter (3-7 mm) Type and pressure of injection gas Argon (Ar), 5~15 bar Crucible types high purity graphite Chamber atmosphere nitrogen Nozzle spray angle 15 degrees

Manufacturing Example - High-Entropy Binder (Gas Atomization Method)

Among the high-entropy binder compositions of the above preparation examples, AlCoCuCrFeNi was prepared into powder using a gas atomization method. Argon (Ar) gas was used as the carrier gas in the gas atomization process, and to prevent oxidation, the inside of the chamber was evacuated and then nitrogen gas (N2) was injected several times to create an inert atmosphere. Each metal element was placed in a high-purity graphite crucible and melted and alloyed by high-frequency heating. The molten metal was maintained for 10 minutes to ensure complete alloying, and then atomized by colliding with high-pressure argon gas while flowing through a nozzle. The atomized powder was classified to collect only powders smaller than 200 microns in size.

Manufacturing variables Manufacturing conditions orifice Ceramic, inner diameter (3-7 mm) Type and pressure of injection gas Argon (Ar), 5~15 bar Crucible types high purity graphite Chamber atmosphere nitrogen Nozzle spray angle 15 degrees

Manufacturing Example - Goenprofi Superhard Powder Mixing (Crushing and Mixing)

The high-entropy carbides manufactured in Examples 6 and 7 were coarsely ground and refined for mixing with the binder manufactured in the above manufacturing example. To this end, coarsely ground and refined were performed several times using a conventional coarse grinder or a molding device capable of momentarily applying an ultra-high pressure of 1 to 2?quot;.

The finely divided carbide was mixed with a binder through an ultra-high energy milling process, and the mixing ratio of the high-entropy carbide and the high-entropy binder varied in the range of (100-85) wt% HEC + (0-15) wt% depending on the intended use. However, in this example, a superhard material was manufactured with a composition of 90% HEC + 10% HEB.

Manufacturing Example - Manufacturing of High-Entropy Superhard Materials

The high-entropy carbide according to the above Example 6 was rapidly sintered using the equipment of Fig. 12 at a pressure of 50 MPa and a temperature of 1300°C for 10 minutes in a vacuum atmosphere with a high-entropy binder (composition ratio) of AlCoCuCrFeNi, to produce the final high-entropy superhard material.

Experimental Example 4 - Mechanical Properties Analysis of Superhard Materials

For the above manufacturing example, Vickers hardness and fracture toughness were measured and shown in Fig. 22, and Vickers hardness for conventional general superhard materials was measured and shown in Fig. 23.

More specifically, referring to FIGS. 22 and 23, the high-entropy superhard material according to the present invention can have a Vickers hardness of 1,300 or more. That is, it can be seen that it exhibits mechanical properties (Vickers hardness) that are equivalent to or superior to the conventional WC-Co superhard material shown in FIG. 23. In addition, it can be seen that the high-entropy superhard material according to the present invention exhibits a fracture toughness of 6 Mpaㆍm ^1/2 or more.

Claims (11)

A method for manufacturing a high-entropy superhard material, comprising: a first step of manufacturing a high-entropy carbide raw material powder comprising at least five kinds of transition metal carbides selected from the group consisting of HfC, TaC, TiC, ZrC, NbC, VC, CrC, MoC and WC;
A second step of manufacturing a high-entropy binder comprising at least three metals selected from the group consisting of Al, Co, Cu, Cr, Fe, Ni, and Mn; and
A third step of manufacturing a high-entropy sintered body by mixing, molding, and sintering the high-entropy carbide and the high-entropy binder;
A method for manufacturing a high-entropy superhard material, characterized in that both the following relations (1) and (2) are satisfied, and the high-entropy carbide has a single-phase structure that does not form an intermetallic compound due to the high-entropy effect.
(1) Vickers hardness of 1300 or higher (HV30)
(2) Fracture toughness of 6 Mpaㆍm ^1/2 or more
In the first paragraph,
A method for manufacturing a high-entropy superhard material, characterized in that the first step includes a ball milling step at 400 to 800 rpm for 10 to 120 minutes with a ball to powder ratio of 3 to 20:1, and the ball milling step allows uniform mixing and micronization of the high-entropy carbide raw material powder.

In the first paragraph,
A method for manufacturing a high-entropy superhard material, characterized in that the high-entropy carbide raw material powder is synthesized into an FCC or BCC single phase in a multi-component system through the first step.
In the first paragraph,
A method for manufacturing a high-entropy superhard material, characterized in that the first step includes a sintering step in which the temperature maintenance section is performed at least once, and the sintering step is performed at a sintering pressure of 50 to 70 MPa.
In paragraph 4,
A method for manufacturing a high-entropy superhard material, characterized in that the sintering step of the first step comprises first-stage sintering at a pressure of 50 to 70 MPa and a temperature of 1,700 to 1,900°C for 5 to 15 minutes, and then second-stage sintering at a pressure of 50 to 70 MPa and a temperature of 1,900 to 2,100°C for 1 to 20 minutes.
In the first paragraph,
A method for manufacturing a high-entropy superhard material, characterized in that the high-entropy carbide is crushed and refined before performing the third step to have an average particle size of 0.2 to 2 μm.
In paragraph 5,
A method for manufacturing a high-entropy superhard material, characterized in that the high-entropy binder is manufactured by a gas atomizing method.
In the first paragraph,
A method for manufacturing a high-entropy superhard material, characterized in that the third step is sintering at a pressure of 40 to 65 MPa and a temperature of 1,200 to 1,400°C for 5 to 15 minutes.
A high-entropy carbide comprising at least five transition metals selected from the group consisting of HfC, TaC, TiC, ZrC, NbC, VC, CrC, MoC and WC; and
A high-entropy binder comprising at least three metals selected from the group consisting of Al, Co, Cu, Cr, Fe, Ni, and Mn;
A high-entropy superhard material characterized by satisfying both the following relations (1) and (2), and having a single-phase structure in which the high-entropy carbide does not form an intermetallic compound due to the high-entropy effect.
(1) Vickers hardness of 1,300 or more (HV30)
(2) Fracture toughness of 6 MPa·m¹/² or more
In paragraph 9,
A high-entropy superhard material characterized in that the high-entropy carbide has an average particle diameter of 0.2 to 2 μm and the high-entropy binder is manufactured by a gas atomizing method.
A cutting tool comprising the high-entropy superhard material described in Article 9.