JP2803827B2 - Manufacturing method of high density and high hardness ceramics sintered body - Google Patents

Description

The present invention relates to a method for producing a high-density and high-hardness ceramic sintered body. More specifically, the present invention
A method for producing high-density and high-hardness ceramic sintered bodies that can be used simply and inexpensively to produce high-density and high-hardness ceramic sintered bodies that are useful as cutting tools and various other wear-resistant and heat-resistant materials. It is about.

(Prior art) Conventionally, high-pressure phase materials such as diamond, cubic boron nitride (CBN), or B ₄ C, S
iC, Al ₂ O _{3 and the} like are widely known. In addition, since these typical hard ceramics generally have a strong covalent bond between the constituent elements, if these raw material powders are sintered without being pressed, the entire compact sample shrinks, that is, It is also known that it is difficult to produce a dense sintered body because the diffusion of atoms that promotes densification does not easily occur, and the surface diffusion of particles takes precedence over the volume diffusion of atoms. . It is believed that this is because the energy required for diffusion of atoms through defects in the crystal is younger and larger than the surface diffusion energy. Since simple sintering of a hard ceramic material is extremely difficult as described above, usually, an additive serving as an auxiliary agent for assisting the transfer of atoms between powder particles is added, and sintering is performed under pressure. Have been adopted. For example, in the sintering of B ₄ C or SiC powder to which a sintering aid has been added, a hot press method using a graphite mold capable of pressurizing to about several tens MPa has been mainly performed.

However, in this hot press method, although the pressure to be applied is effective for densification of the structure, the pressure is restricted by the strength of the graphite mold at high temperatures, so that the pressure that can be generated at high temperatures decreases. There are drawbacks. Also,
The sintering temperature also needs to be low enough that the sample does not react with the graphite mold. Due to such restrictions, it has been difficult to produce a high-density hard ceramic sintered body having a sufficiently strong intergranular bond in the hot press method using a graphite mold.

On the other hand, as a method of lowering the sintering temperature and densifying the structure, a method of increasing the sintering holding time has been considered, but in this case, the particles are likely to be coarsened, thereby causing sintering. There is a problem that the strength of the unit is reduced.

Also, as a method for effectively densifying the hard ceramic powder, an ultra-high pressure sintering method capable of generating a pressure of several GPa or more is known. It was developed to synthesize and sinter diamond and cubic boron nitride (CBN), which are high-pressure phase materials and ultra-hard ceramics. There is an advantage that plastic deformation of the ceramic powder particles easily occurs and forced densification can be realized.
In this ultrahigh-pressure sintering method, a heater for heating a sample powder is first placed in a solid pressure medium, and then a high-hydrostatic pressure medium such as salt is inserted into the heater, and the metal is further placed in the medium. A compact sample filled in an insulative capsule or the like is inserted and heated and sintered in this state.

However, even if this method is used, the pressure can be increased to a certain degree in forming strong intergranular bonding of the ceramic powder particles, but the sintering temperature is generally set at 7 to the melting point of the target material. It requires some cost,
It is difficult to stabilize and raise the sintering temperature, and at least several tens of minutes are required for holding the sintering, so that the coarsening of the particles cannot be avoided except under special conditions. is there. This ultra-high pressure sintering method is indispensable for sintering high pressure phase materials such as diamond, but this method requires a larger and more expensive device than the hot press method, However, there is a problem that the driving cost is high and the driving technique is advanced. A more serious problem is that it is extremely difficult to produce a large sintered body having a complicated shape.

In order to overcome the disadvantages of each of the above-mentioned methods for producing a hard ceramic sintered body, the inventors of the present invention have developed ceramics, cermets, and ceramics of high strength and high hardness that do not utilize static ultra-high pressure. A method for producing a cermet composite sintered body material is proposed. In this manufacturing method, a powder obtained by mixing a component having self-exothermic reaction (SHS) properties with ceramic powder is formed, and the compact is subjected to impact compression to cause the self-exothermic reaction (SHS) to occur simultaneously with the densification of the structure. To produce a strong ceramic sintered body comprising a starting material and its reaction product.

Self-exothermic reaction (SHS)
-Propagating High-Temperature Synthesis (SHS), translated as self-heating or self-combustion, but there is no uniform name in Japan.
Therefore, the inventors of the present invention adopt the former self-exothermic reaction as a name.

In such a method for producing a high-strength and high-hardness ceramic sintered body that does not use a static ultra-high pressure, the pressure maintaining time during impact compression is generally on the order of 10 ^-6 seconds. Most of the self-heating reaction (SHS) is ignited by the impact compression of appropriate strength, and the synthesis reaction of the desired high-density and high-hardness ceramic sintered body is started. For example, it has been confirmed that the reaction rate at 1000 ° C. is about 0.17 m / s for the synthesis reaction of Ti + C → TiC, which has a relatively high reaction rate among the self-heating reactions.

(Problems to be Solved by the Invention) However, in the above method, assuming that the time for maintaining the impact compression is 1 μs, the starting material powder of titanium (Ti) and carbon (C) has a particle size of 0.34 μm or less. The synthesis reaction is completed during shock compression only when the material is used, and the reaction does not end when particles of a larger size are used, and pores remain in the recovered sintered body due to volume shrinkage accompanying this reaction. Will do. There is a problem that such residual pores cause a reduction in the strength of the sintered body.

This method is mainly used for the synthesis reaction of a transition metal carbide or boride of Group IVa, Va, VIa,
Generally, these metal powders have a high chemical activity, and particularly the activity of the submicron powder is extremely high, so that the handling thereof is difficult and dangerous. When such fine powder is used, a series of steps from mixing, molding, and impact treatment under special conditions are required, and it is actually troublesome to mix the raw material powder uniformly. there were. Furthermore, it was also difficult to obtain such a powder.

Furthermore, this method has a disadvantage that there is a time delay from the densification of the green compact by impact compression to the start of the synthesis reaction. In the self-exothermic reaction (SHS), the heat of reaction sequentially propagates and the reaction continues, but in regions where the density of the compact is high, heat conduction becomes excessive and the degree of heat diffusion becomes too large, so the next synthesis reaction Cannot be excited, and the reaction stops halfway. This inevitably left local unreacted parts.

The present invention has been made in view of the circumstances described above, and while utilizing the features of the conventional shock compression method utilizing self-heating reaction, the disadvantages are eliminated, and various kinds of cutting tools and the like are used. It is an object of the present invention to provide an improved method for producing a high-density and high-hardness ceramic sintered body that can easily and inexpensively produce a ceramic sintered body having good high density and high hardness as a wear-resistant material and a heat-resistant material. The purpose is.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention relates to a method for manufacturing a ceramic sintered body comprising 30% by volume or more and less than 99% by volume of hard ceramics, wherein the hard ceramic powder contains A powder consisting of at least one element and / or compound capable of self-exothermic reaction (SHS) with at least one or more elements of the above, and an element or an element thereof that independently performs self-exothermic reaction (SHS) With a powder consisting of at least one combination of the compounds of
A mixed powder prepared by blending at least one of them is molded, a part or all of the molded body is heated to cause a self-heating reaction (SHS), and then the molded body is subjected to impact compression. And a method for producing a high-density and high-hardness ceramic sintered body.

The method for producing a high-density and high-hardness ceramic sintered body according to the present invention is characterized by the above-mentioned disadvantages and problems in the method for producing a powder compact (JP-A-62-52183) previously proposed by the inventors of the present invention. As a result of intensive studies to improve the reaction, instead of igniting the reaction with the heat accompanying adiabatic compression by shock compression, the reaction is started by another method and shock-compressed at an arbitrary time interval from the start of the reaction By this, it was found that the densification of the sample powder was further facilitated, and that a strong bond was formed between grains, and the present invention was completed based on this finding.

That is, in the synthesis of certain types of ceramics, particularly ceramics having a high melting point, the heat of synthesis of compounds from the constituent elements reaches several tens to several hundreds of KJ per mole. This large heat of formation is successively propagated in the compact of the raw material mixed powder, and the excitation, initiation, and synthesis of the reaction are sequentially maintained. For example, titanium carbide (TiC) is replaced with titanium (Ti) and carbon (C)
When synthesizing from powder, titanium (Ti) and carbon (C) powders that match the stoichiometric ratio of titanium carbide (TiC) are mixed and molded. When used to ignite and initiate the reaction, the reaction proceeds throughout the compact and titanium carbide (TiC) can be synthesized without the need for external heating. Table 1 shows examples of typical high melting point ceramics that can be synthesized by this self-heating reaction (SHS). The characteristics of the self-exothermic reaction (SHS) are a remarkably large heat of reaction and a reduction in volume accompanying the reaction. The rate of this volume reduction depends on the material, but can be as high as 30%.

For this reason, in order to produce a dense sintered body at the same time as synthesis using the self-heating reaction (SHS), it is necessary to compensate for this volume shrinkage by some method.

The method for producing a high-density and high-hardness ceramic sintered body according to the present invention is characterized by adding a reaction component that causes a self-heating reaction (SHS) to hard ceramic powder.
As such a component, a powder composed of at least one or more of elements and / or compounds that cause a self-heating reaction (SHS) with at least one of the constituent elements of the hard ceramic is added to the hard ceramic powder. Can be.

For example, when cubic boron nitride (CBN) powder is used as the hard ceramic powder, one or both of its constituent elements, boron (B) and nitrogen (N), may be used as the component that causes the self-heating reaction (SHS). Metal powders such as Ti and Zr or compounds that deviate from normal stoichiometric ratios such as TiN _0.6 and NbC _0.7 , which react with and generate a self-heating reaction (SHS), that is, apparently surplus metal A compound having an element, a solid solution or a mixture thereof, or the like can be used. Further, in the present invention, the component that causes the self-heating reaction (SHS) is different from the hard ceramic component described above. It is also possible to use a powder composed of at least one or more elements independently generating a self-heating reaction (SHS) or a combination of compounds of the elements.

As an example, when TiB ₂ is used as a hard ceramic, a combination of elements such as (Ti + B) and (Mo + C), or (VN _0.5 + C), (HfN _0.6 + B)
And the like, and combinations of elements and compounds. When a mixed powder of (Ti + B) is used, a simple dense and high-hardness sintered body of TiB ₂ can be manufactured. Of course, the component causing the self-heating reaction (SHS) is composed of at least one element and / or compound capable of causing a self-heating reaction (SHS) with at least one or more of the constituent elements of the hard ceramic powder. The powder may be at least one of, or both of, a powder and a powder composed of at least one or more elements that independently react with each other or a combination of compounds of the element that independently react with each other.

Components that cause such a self-heating reaction (SHS)
It mainly has the following two excellent functions and effects. One is that some components of the high-temperature liquid phase accompanying the reaction activate the diffusion of the constituent atoms of hard ceramics between grains,
As a result, strong intergranular engagement is formed, and solidification of the liquid phase also forms strong intergranular bonds via reaction products. The high temperature is generated only between the grains necessary for sintering, and is not uniform heating accompanied with the growth of the grains, but the high temperature between the grains is also instantaneous. Therefore, there is no need to worry about a decrease in the strength of the sintered body due to coarsening of grains in normal sintering, the particle size of the starting material is maintained up to the sintered body, control of the composition and physical properties of the material, design is extremely simple and easy. Become. Another is that densification of the green compact sample becomes extremely easy. This is because an exothermic reaction before impact compression generates a partial liquid phase between the hard ceramic particles, and this liquid phase acts as a lubricant in densification by the movement of the hard particles in the next impact compression. It is thought to be. Therefore, densification of the structure by this manufacturing method is sufficient even with impact compression at a low pressure level, and the occurrence of residual stress in the obtained sintered body can be reduced. The reduction of the occurrence of residual stress in the sintered body is also one of the great features of the method of the present invention.

Further, in the method for manufacturing a high-density and high-hardness ceramic sintered body of the present invention, a high-pressure phase material such as diamond or cubic boron nitride (CBN) or a strong share of B ₄ C or SiC is used as the hard ceramic powder. A high hardness material having bonding properties can also be used. When a high-pressure phase material or a high-hardness material is used, a wide range of components can be appropriately selected as a component that causes a self-heating reaction (SHS).
If an appropriate one is selected from carbides, nitrides, borides, or solid solutions of IVa, Va, VIa group metals, a high-density, high-hardness sintered body can be easily produced.
As a method of adding such components, it is possible not only to mix them with the hard ceramic powder, but also to coat the surfaces of the hard ceramic particles as the starting material with a certain amount of the added components uniformly. By the coating on the surface of the starting material powder, the reaction occurs uniformly, and as a result, a sintered body having uniform properties can be produced.

The temperature increase due to heat associated with the self exothermic reaction (SHS) can be calculated assuming that all the heat of reaction is used to increase the temperature of the product. When the calculated heat insulation and the heat of synthesis reaction reach the melting point of the product, a part of the liquid phase appears during the reaction, the diffusion of atoms in this region becomes easy, and the synthesis reaction proceeds easily. The TiB ₂ synthesis reaction from Ti (titanium) and boron (B) powder is one example, and the heat of reaction involved in this reaction is extremely large, and the temperature of the reaction section is about 3,000.
It reaches more than ° C. Further, in the SiC synthesis reaction from silicon (Si) and carbon (C), the heat of formation is as small as 69 KJ / mol, and the temperature rise due to this reaction does not reach the melting point of SiC of 2400 ° C. For this reason, even if this reaction is ignited once at room temperature, it stops in the middle of the reaction. In such a synthesis reaction with a small heat of formation, the reaction can be continued by igniting in a state of being heated to about 1000 ° C. in advance so that a part of the liquid phase is generated during the reaction.

Further, in the method for producing a high-density and high-hardness ceramic sintered body of the present invention, an ignition method using a normal tungsten heating wire, an electron beam, or the like may be employed as a method for initiating the reaction. When a metal component or a compound containing a relatively excessive metal element is used, a heating and ignition method by direct energization utilizing these electrical properties can also be used. The heating by direct energization is mainly due to the discharge at the contact points of the metal components, such as grain contacts or carbon elements. Micro-uniform ignition in the
And the reaction can be started at the same time. By this ignition method, a sintered body having a more uniform structure and physical properties can be produced. In a normal reaction ignition method, the amount of a component related to the self-heating reaction (SHS) in a molded body is 50 vol. % Or less, it may not be possible to continue the reaction without preheating even if (Ti + B) is used. However, this discharge heating enables simultaneous instantaneous heating of the trial compact in such a case. It can be performed without the need for a special furnace, and is also effective for compositions having a low self-heating (SHS) component.

A reasonable rule of thumb for the appropriate time interval between the start of the self-exothermic reaction (SHS) and the shock compression for tissue densification is the time interval from the start to the end of the self-exothermic reaction (SHS). Yes, and the time interval is basically determined by the reaction rate. The reaction rate is determined by the self-exothermic reaction (SH
The time interval from the start of the reaction to the impact compression takes into account these factors because it varies depending on the initial density of the molded body, as well as the type, blending amount, particle size, temperature of the molded body, etc., of the components involved in S). Can be controlled.

As a method of impact compression, a shock wave generated by a collision of a high-speed flying object, a detonation wave caused by an explosion of an explosive, and the like can be used. For example, a low-speed shock wave by a dynapack device which has been used as a pretreatment for sintering a metal or a part of ceramic powder in the related art can be used. This method utilizes the pressure generated by the free fall or forced fall of a heavy object.
^It can last for about ^-3 to 10 ^-2 seconds and is effective for densification of powder.

FIG. 1 can be used in the method for producing a high-density and high-hardness ceramic sintered body of the present invention. It is sectional drawing which showed an example of the reaction apparatus which combined the said dynaback apparatus and the discharge heating apparatus. In the apparatus of this example, a piston (1), a high-pressure gas supply chamber (2), a high-pressure gas supply port (3a)
(3b), an O-ring (4), a space (5), and a mold (6) for integrally supporting them. The lower part of this device is for discharge heating of the sample,
A metal cylindrical mold (9) having an electrically insulating lining (8) on the inner surface for filling the sample (7) and an upper push rod (11) and a lower push connected to a discharge heating power supply (10). And a bar (12). In this apparatus, a sample (7) is filled in a mold (9), and a power supply for heat radiation (10) is used.
The sample (7) is energized and heated through the upper push rod (11) and the lower push rod (12).

When the sample (7) is subjected to impact compression, high-pressure gas of about 100 to 250 kg / cm ² is introduced into the high-pressure gas supply chamber (2) from the high-pressure gas supply port (3b), and the gas pressure of the piston (1) is applied. It accelerates downward at several tens to several hundreds m / s and collides with the upper push rod (11), and the impact is transmitted to the sample (7). That is,
The high-pressure gas supply chamber (2) and the O-ring (4) and the upper space (5) shown in this example serve as a trigger for accelerating the piston (1) downward, and the space (5) When the high-pressure gas is introduced from the high-pressure gas supply port (3a), the piston (1) comes off the O-ring (4), and the high-pressure gas introduced into the high-pressure gas supply chamber (2) is placed on the upper surface of the piston (1). It turns around and accelerates the piston (1) downward.

Such a dynapack method does not require explosives or explosives, and therefore has good safety and is advantageous for producing a hard ceramic sintered body. In addition, the method for producing a high-density and high-hardness ceramic sintered body of the present invention can easily perform densification of hard ceramic particles by utilizing the self-heating reaction (SHS) described above. Alternatively, a shock compression method with a low pressure level such as described above can be employed.

FIG. 2 is a cross-sectional view showing an example of a flat impact compression apparatus which can use the method for manufacturing a high-density and high-hardness ceramic sintered body of the present invention.

In the apparatus of this example, a primer (13) for obtaining a plane shock wave from above, an explosive lens (14), an explosive system comprising an explosive (15) and a driving plate (16), and a sample to be filled with a sample (7) A momentum trap (18) for facilitating the collection of the sample part (17a) (17b) and the sample (7)
a) It has the configuration of (18b).

The sample (7) is filled between the sample containers (17a) and (17b) and placed at a predetermined position of the momentum trap (18a). The sample containers (17a) (17b) and the momentum traps (18a) (18b) are formed of an electrically conductive material, and examples of such a material include iron and stainless steel. A power source (10) for discharge heating is connected to the momentum traps (18a) (18b). An electrically insulating lining (8) and a momentum trap (18a) (18) are provided on the inner wall surface of the sample container (17a).
b) An electric insulating sheet (19) is provided in a portion other than the sample container (17b) between them.

An electric current in which DC and AC overlap is effective for discharge heating. In this example, the power supply for discharge heating (1
0)-Momentum trap (18a)-Sample container (17a)
An electric current flows through a circuit including a sample (7), a sample container (17b), a momentum trap (18b), and a power supply for discharge heating (10), so that the green compact sample (7) can be energized. A voltage is applied to the discharge heating power supply (10) to start the reaction, and immediately after the reaction is completed, impact compression is performed.

The conical explosive lens (14) shown in FIG.
Detonated by the top detonator (13), the explosive lens (1
The combustion in 4) propagates downward in a planar manner. This planar combustion propagates to the explosive (15) located immediately below, where planar combustion occurs, and the detonation shock wave generated by this combustion accelerates the drive plate (16) at high speed. The drive plate (16) collides with the sample container (17a) and the sample container (17
A plane shock wave is generated in a) and the sample (7) is shock-compressed. In this example, the driving plate (16) and the sample container (17
A space is provided between the driving plate (a) and the driving plate (18) to accelerate to a predetermined speed in this space. Of course, there is no particular limitation on the configuration, and the explosive (15) is brought into contact with the sample container (17a) having no space, or the driving plate (16) is arranged on the upper surface of the sample container (17a). The explosive (15) may be arranged directly on the upper surface.

FIG. 3 is a sectional view showing an example of a cylindrical impact compression device that can be used in the method for producing a high-density and high-hardness ceramic sintered body of the present invention.

In the apparatus of this example, plugs (21a) and (21b) of electrical insulation 2 are provided on the upper and lower surfaces of a sample container cylinder (20) having an electrically insulating lining (8) on the inner wall surface. A pair of upper and lower electrodes (22a) (22b) facing each other is disposed between the plugs (21a) (21b), and these are connected to a discharge heating power supply (10). A sample (7) of a sintering raw material powder containing a component involved in the self-heating reaction (SHS) between the electrodes (22a) and (22b) in the sample container cylinder (20) is filled to a predetermined initial density and discharged. A voltage is applied to the heating power supply (10) to start the reaction, and shock compression is performed immediately after the reaction is completed. The explosive (15) is filled in a space partitioned by the sample container cylinder (20), the explosive container (23), the upper plate (24) and the lower plate (25). The explosive (15) is detonated by a detonator (13), and the detonation shock wave generated by the detonation is transmitted to the sample (7) via the sample container cylinder (20) and shock-compressed. In addition to the example illustrated in FIG. 3, in the cylinder impact compression device, a cylinder having an inner diameter larger than the outer diameter is arranged outside the sample container cylinder (20), and the cylinder is arranged outside the sample container cylinder (20). In some systems, a space on a thin cylinder is formed between the cylinders, and the explosive (15) is inserted into contact with the outer cylinder. In this method as well, the explosive (15) is detonated by the primer (13) in the same manner as the apparatus illustrated in FIG. 3, whereby the outer cylinder is focused in the direction of the central axis and collides with the sample container cylinder (20). As a result, the generated shock wave can be propagated to the sample (7) and shock-compressed.

The pressure level of impact compression using explosives as shown in FIGS. 2 and 3 may be relatively low. At least a pressure lower than the pressure level required for densification of the sintered body when it does not contain any self-heating (SHS) components is sufficient. If this pressure is too high, the adverse effects of rarefaction waves and residual stress may be reduced. This is undesirable. As described above, the pressure required for densification of the structure can be reduced because a partial liquid phase is generated between the hard ceramic particles by the exothermic reaction before the impact compression as described above, and this liquid phase is formed. This is because it plays a role as a lubricant when the structure is densified by the movement of the hard ceramic particles in the next impact compression. The lowering of the pressure level allows the use of a step-like rising shock wave or a gentle, continuous rising rising shock wave, which is usually unsuitable for impact sintering of ceramic powders.

The inventors of the present invention have confirmed that better shock densification can be obtained by using a shock wave by such a shock compression process than by a shock wave having a normal sharp pressure rise. ing. One of the reasons for this is that although the duration at the highest ultimate pressure is short, the rise of the pressure is gradual, so that the structure of the structure involving the rearrangement of particles through the liquid phase existing between the hard ceramic particles is generated. It is conceivable that densification occurred, and forced deformation and destruction of particles were reduced. Another reason is that a gradual or step-like rise in pressure also affects the strength and transmission of the subsequent rarefaction waves, and the slow gradual pressure process can lead to cracks in the sintered body and a reduction in residual stress. It is thought to be effective.

The content of the hard ceramic in the sintered body which can be used in the method for producing a high-density and high-hardness ceramic sintered body of the present invention is at least 30% by volume in order to maintain the hardness of the sintered body sufficiently high. Is necessary, and preferably 50% by volume or more. The type of hard ceramic used need not be one, and if necessary, a mixture of two or more types of hard ceramics may be used. In addition, when the content of the hard ceramics in the sintered body is 99% by volume or more, the effect of the component that causes the self-heating reaction (SHS) is reduced. Therefore, in the present invention, the upper limit is less than 99% by volume. I do.

(Example) Hereinafter, an example is shown and the manufacturing method of the high-density and high-hardness ceramics sintered body of the present invention will be described in more detail.

Example 1-2 (Comparative Examples 1-2) boron carbide particle size 10~20μm as hard ceramic (B ₄ C) used, this self-heating reaction (SHS) particle size 5μm or less of titanium as a component that occurs the ( Ti) powder having a volume ratio of B ₄ C / Ti of 28/72 (Comparative Example 1), 60/40 (Example 1),
80/20 (Example 2) and 99/1 (Comparative Example 2) were blended and mixed to prepare starting material powders. A compact having a relative density of about 60% was formed from each mixed powder, and the reaction ignition of each compact was performed by a tungsten wire method and a discharge heating method. In the tungsten wire method in which a large current was passed for several seconds, the samples of Example 1 and Comparative Example 1 ignited, but the samples of Example 2 and Comparative Example 2 did not ignite. Meanwhile, AC 500A of DC and 500Hz units per cm ² 600A
In the discharge heating method using both, the samples of Examples 1 and 2 and Comparative Example 1 ignited, but the sample of Comparative Example 2 was difficult to ignite. It was confirmed that the self-heating reaction (SHS) did not occur when the content of the hard ceramic exceeded 99% of the volume of the sintered body.

The reaction of each of the samples of Examples 1 and 2 was ignited by this discharge heating method, and the reactivity of each of the obtained sintered bodies was examined.
And TiB ₂ were generated. However, each of the sintered bodies has many pores of various sizes, and the apparent porosity of the sintered bodies manufactured from the samples of Example 1 and Example 2 is 35% and 30%, respectively. It was confirmed that it was extremely porous.

The reaction time required for ignition for the samples of Examples 1 and 2 and Comparative Example 1 was longer in the order of Comparative Example 1, Example 1, and Example 2. Based on this data, each sintered body was compressed using an apparatus as illustrated in FIG.
Densification was performed. In this apparatus, a high alumina sintered body is used as a material for the lining (8) of a cylinder for forming a mixed powder, and a high-strength and good electric conductor is used as a material for the upper and lower push rods (11) and (12). Carbide sintered body (WC-20
% Co) was used. The reaction was started by discharge heating for the samples of Examples 1 and 2 and Comparative Example 1 in which the reaction was confirmed by ignition by the tungsten wire method. Immediately after the reaction was completed, the impact speed of the piston (1) was set to 40 m / s. Impact compression was performed. For this impact compression, an iron piston weighing about 200 kg was used, and high-pressure nitrogen gas compressed to 175 kg / cm ² was used as a piston acceleration gas.

The sintered body having the composition of Examples 1 and 2 could be easily recovered from the sintered body after the impact treatment, whereas the sintered body having the composition of Comparative Example 1 had a mold (9) and a push rod (11) ( They were broken and collected because they were welded or adhered to 12). Each of the collected pellet-shaped sintered bodies is cut into two in the vertical direction,
After polishing one of the cross sections, the presence or absence of a reaction product and unreacted Ti was examined by X-ray diffraction. The hardness was measured and the structure was observed using a microhardness tester.

As a result, the sintered bodies having the compositions of Example 1 and Example 2 differed in the relative amounts from each other, but the respective reaction products were both TiC and TiB ₂ , and any of the unreacted Ti It was not detected from the sintered body. Each of these products has a particle size of 1 μm or less, uniformly fills the gaps of boron carbide (B ₄ C) as the starting material, and shows residual pores and cracks in the structure. I couldn't. The micro hardness of the sintered body of Example 1 is about 3200 kg.
/ mm ² , and about 3300 kg / mm ^{2 of the} sintered body of Example 2, all of which had high hardness.

On the other hand, a sintered body having a composition of Comparative Example 1, but the reaction composition was TiC and TiB _2, the presence of unreacted Ti traces is confirmed, hardness 2500 kg / mm ² and low, the organization With regard to, abnormal growth of particles and coarsening of the whole particles were confirmed in a part of the reaction product. In addition, cracks occurred around the indentations in the hardness measurement. This is considered to be due to coarsening of the particles.

(Comparative Examples 3 to 5) A molded body having the same composition as in Example 1 was molded, this molded body was ignited by using a tungsten wire method, and after the reaction was completed, it was subjected to impact compression under the same conditions as described above and fired. A compact was produced (Comparative Example 3).

As for the sintered body of Comparative Example 3, a reaction composition similar to that of the sintered body having the composition of Example 1 was confirmed, but the hardness of the sintered body had a distribution, and the upper part where the reaction started was observed. is about 3000 kg / mm ^2, at the opposite side was about 3150kg / mm ^2. Corresponding to this, the particle size of the reaction products TiC and TiB ₂ was slightly larger in the former part than in the latter part.

A compact having the same composition as in Example 1 was subjected to impact compression almost simultaneously with the start of the reaction by discharge heating under the same conditions as above to produce a sintered body (Comparative Example 4).

Although generation of TiC and TiB ₂ was recognized in the recovered sintered body,
Unreacted Ti is clearly recognized and its hardness is 2200kg / m
m ^2, and generation of minute cracks in the sintered body was also confirmed.

A molded body having the same composition as in Example 1 was subjected to impact compression under the same conditions as described above without causing reactive ignition by discharge ignition, thereby producing a sintered body (Comparative Example 5).

Although the recovered sintered body was densified to some extent, it had many cracks and no reaction was observed.

Examples 3 to 4 (Comparative Example 6) Diamond powder having a particle size of 5 to 7 µm was vacuum-
The treatment was carried out at a temperature of 30 ° C. for 30 minutes to graphitize the surface of the diamond particles. The amount of graphitization under these conditions was about 16% by volume. The partially graphitized diamond powder was uniformly mixed with 10% by volume of silicon (Si) powder adjusted to an average particle size of 1 μm or less. This mixed powder was filled in a flat impact compression apparatus as shown in FIG. Momentum trap (18
a) (18b) is made of iron, and the sample containers (17a) (17
The material of b) is stainless steel and its sample container (17a)
An electrically insulating alumina sintered body was lined inside (17b). In addition, a thin Teflon sheet was used as an electrical insulating sheet (19) except for the sample container between the momentum traps (18a) and (18b).

First, the mixed powder is filled between the sample containers (18a) and (18b) so that the relative density becomes 60%, and then a direct current of 600 A per unit cm ² and an alternating current of 500 Hz at 500 A by a discharge heating power source (10).
Were simultaneously introduced to ignite and start the reaction. After the reaction is completed, the collision speed is measured using a 3.2 mm thick iron drive plate (16).
Impact compression treatment was performed at 1.5 mm / s (Example 3). Explosives (15)
The plane detonation liquid was generated by an explosive lens (14). After recovering the pellet-shaped sintered body, the sintered body was cut into two pieces vertically.
After polishing one of the cross-sections,
The presence or absence of reaction products and unreacted Si was examined by line diffraction. The hardness was measured and the structure was observed using a microhardness tester.

As a result, the reaction product was SiC, and no unreacted Si was detected. The hardness is as high as about 6700kg / mm ^2,
No residual pores and no growth of particles were confirmed in the structure, and a good sintered body having a dense structure could be produced.

The surface of partially graphitized diamond diamond powder similar to that used in Example 3 was coated with Si to about 10% by volume by a CVD method. Using a device similar to the above-described device, this powder was subjected to discharge heating and impact compression under the same conditions to produce a sintered body (Example 4).

The reaction product of this sintered body was SiC as in Example 3, and the hardness thereof was about 1000 kg / m2 more than that of the sintered body of Example 3.
It was 7,700 kg / mm ² , which was m ² higher. The structure had no residual pores, cracks, etc., and was more uniform than the sintered body of Example 3.

For comparison with these, a powder formed by mixing partially graphitized diamond and silicon (Si) powder as in Examples 3 and 4 was mixed under the same conditions as in Examples 3 and 4 using an apparatus. 1.5k flying plate speed without igniting the reaction due to discharge heating
A sintered body was produced by impact compression at g / s (Comparative Example 6).

No reaction occurred in this sintered body. The initial density of this compact was increased from 60% to 35 to increase the impact temperature.
% And subjected to impact compression under the same conditions as in Examples 3 and 4. X-ray diffraction confirmed the presence of many residual pores and many large and small cracks, although a reaction was observed. A practical sintered body could not be manufactured.

Example 5 Cubic boron nitride (CBN) powder having an average particle diameter of 20 μm, wurtzite-type boron nitride (WBN) powder having an average particle diameter of 5 μm, and tantalum boride (TaB ₂ ) powder having an average particle diameter of 5 μm or less were converted to a volume of 3%. : 2: 1 to obtain a hard ceramic powder. This powder is mixed with Ti powder 20 having a particle size of 5 μm or less.
By volume, 20% by volume of an equimolar mixture of Mo powder having an average particle size of 2 μm and carbon powder having an average particle size of 1 μm were uniformly mixed to prepare a mixed powder of starting materials. This mixed powder was filled into a sample container cylinder (20) having an electrically insulating lining (8) of a cylindrical impact compression apparatus as shown in FIG. For the sample container cylinder (20), an iron pipe having a thin alumina lined inner wall was used. An iron block is used for the electrodes (22a) and (22b) for discharge heating, and electrically insulating plugs (21a) and (21b)
A wooden processed product was used. Mixed powder was filled in the apparatus so that the relative density is 58%, by flowing the electrodes (22a) (22b) simultaneously for about 10 seconds and AC 600A DC and 500Hz of 700A per cm ² through the reaction Was ignited and started, and after completion of the reaction, it was subjected to impact compression. In this shock compression, the thickness in the radial direction is 30 mm outside the sample container cylinder (20).
An ANFO explosive was charged and this was detonated by a primer (13). The obtained columnar sintered body is vertically
Then, the cross section was polished, and the presence or absence of a reaction product and unreacted Ti and Mo was examined by X-ray diffraction in the same manner as in Examples 1 and 2. The hardness was measured and the structure was observed using a microhardness tester.

As a result, the reaction product Mo ₂ C, generation of TiN and a TiB ₂ slightly MoB ₂ was also confirmed. Unreacted Ti, Mo and carbon were not detected.

Further, the hardness of this sintered body is about 3000 kg / mm ² , there is no hardness distribution in the cross section of the sample, and the structure has pores,
It was uniform without cracks.

Of course, the present invention is not limited by the above examples. Structure and structure of discharge heating method, shock compression method, etc., hard ceramics and self-heating reaction (SHS)
It goes without saying that various aspects are possible for details such as the types and ratios of the components.

(Effects of the Invention) As described in detail above, the method for manufacturing a high-density and high-hardness ceramic sintered body of the present invention makes it possible to easily manufacture a high-density and high-hardness ceramic sintered body at low cost and with a simple device. it can. The manufactured high-density and high-hardness ceramic sintered body can be applied to wear-resistant materials such as cutting tools and heat-resistant materials.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of an apparatus combining a dynapack apparatus and a discharge heating apparatus which can be used in the method for producing a high-density and high-hardness ceramic sintered body of the present invention. FIG. 2 is a cross-sectional view showing an example of a flat impact compression device that can be used in the method for manufacturing a high-density and high-hardness ceramic sintered body of the present invention. FIG. 3 is a cross-sectional view showing an example of a cylindrical impact compression device that can be used in the method for producing a high-density and high-hardness ceramic sintered body of the present invention. DESCRIPTION OF SYMBOLS 1 ... Piston 2 ... High-pressure gas supply chamber 3a, 3b ... High-pressure gas supply port 4 ... O-ring, 5 ... Space 6 ... Mold, 7 ... Sample 8 ... Electrical insulating lining, 9 ... … Mold 10… Power supply for discharge heating 11… Top push rod 12… Bottom push rod 13… Primer primer 14… Explosive lens 15… Explosive 16 …… Drive plate 17a, 17b …… Sample container 18a, 18b … Momentum trap 19… Electrical insulating sheet 20… Sample container cylinder 21a, 21b… Plug 22a, 22b… Electrode 23… Explosive container 24… Upper plate 25… Lower plate

Claims (4)

(57) [Claims] Claims: 1. A hard ceramic comprising at least 30% by volume and at least 99% by volume.
In the production of a ceramic sintered body consisting of at least one element and / or a compound capable of self-exothermic reaction with at least one or more of its constituent elements in a hard ceramic powder, Is formed by mixing at least one of a powder consisting of at least one of an element and a combination of compounds of the elements that independently react with each other and a self-exothermic reaction, and heating a part or all of the mixed powder. Producing a self-heating reaction, and then subjecting the compact to impact compression. 2. The method according to claim 1, wherein the hard ceramic comprises at least one of diamond, cubic boron nitride, and wurtzite boron nitride. 3. The method for producing a high-density and high-hardness ceramic sintered body according to claim 1, wherein a self-heating reaction is caused by heating the molded body by applying electric current. 4. The method for producing a high-density and high-hardness ceramic sintered body according to claim 1, wherein the compact is shock-compressed by a shock wave caused by a collision of a high-speed flying object or a detonation wave caused by an explosion of an explosive.