W-BN based sintered body and method for manufacturing the same using impact pressure

Abstract

To obtain: a w-BN-based sintered body having good properties without upper limit of producible dimension and without high equipment cost; or a w-BN-based composite impact sintered body added with a material having hardness of 20 GPa or more.SOLUTION: A method for producing a w-BN-based sintered body includes subjecting a starting particle aggregate containing wurtzite-type boron nitride (hereinafter referred to as w-BN) particles and a hard material single crystal particle to an instantaneous ultra-high pressure of 8 to 100 GPa to make the adjacent particles bond with each other, thereby collecting a sintered body of integrated particles, wherein: the particle aggregate comprises, in terms of composition ratio, 10 mass% or more of w-BN (raw material composition); and an ultra-high pressure is applied under close contact between w-BN and the hard material single crystal particle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention is a novel wurtzite boron nitride (w-BN) based The present invention relates to a sintered body and a method for producing the same. The sintered body of the present invention particularly includes a sintered body having a single phase of w-BN, and a composite sintered body of w-BN and hard material particles such as cubic boron nitride (c-BN) or diamond. . [Background technology]

[0002] Wurtzite boron nitride (w-BN) particles are an aggregate of fine crystalline particles with excellent mechanical properties, and are industrially produced by applying shock pressure to low-pressure phase h-BN through the explosion of explosives. Because the shock pressure application time is extremely short, on the order of microseconds, the product is obtained in the form of agglomerated particles of 200 nm (0.2 μm) or larger, in which fine primary particles of about several tens of nanometers are entangled.

[0003] Theoretical analysis has determined that w-BN has a hardness of 114 GPa, which is higher than the 90 GPa of diamond and significantly harder than the approximately 50 GPa of cubic boron nitride (hereafter c-BN), a high-pressure phase of the same compound that is considered to be a highly hard material. Regarding heat resistance, while diamond is about 600°C in air, c-BN is said to not undergo phase transformation to the low-pressure phase h-BN even at 1400°C (Non-Patent Documents 1 and 2).

[0004] On the other hand, although there is no data on w-BN itself, in addition to its excellent hardness, it has low reactivity with iron-group metals, just like c-BN. Therefore, sintered materials sintered alone (Patent Document 1) or mixed with c-BN (Patent Documents 2 and 3) are suitable materials for producing various tool components for cutting and grinding steel and the like.

[0005] Sintered bodies or chunks of w-BN, c-BN, or diamond are mainly obtained by adding a sintering aid such as a metal to powder or particles of these materials, loading them into a high-pressure, high-temperature apparatus (hereinafter referred to as a high-pressure apparatus), and treating them under high-pressure, high-temperature conditions of several GPa and 1200°C or higher (Patent Documents 1-3).

[0006] As mentioned above, the high-pressure apparatus used to sinter high-hardness materials is designed to withstand ultra-high pressures of several GPa and severe high pressures and temperatures of several thousand degrees Celsius, so the spatial shape and volume in which the sintered raw material can be stored are restricted, being limited to a maximum disk of 100 mm in diameter and 10 mm in thickness. Furthermore, the special structure of such apparatus increases the manufacturing costs, and the large stresses placed on the constituent parts shorten their lifespan, which inevitably makes the sintered product expensive.

[0007] Previously, there have been attempts to bond w-BN, c-BN, or diamond particles by using the high shock pressure associated with the explosion of explosives without using a static ultra-high pressure device, but no results suitable for industrial production have been obtained. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 61-100302 [Patent Document 2] Japanese Patent Application Publication No. 63-266030 [Patent Document 3] Japanese Patent Application Publication No. 176769 / 1983 [Non-patent literature]

[0009] [Non-Patent Document 1] DeVries, General Electric Report No. 72-CRD, 178, June (1972) [Non-patent document 2] Z. Pan et al., Physical Review Letters 102 (5), 055503-1, (2009). The American Physical Society Summary of the Invention [Problem to be solved by the invention]

[0010] w-BN is a thermodynamically metastable phase, and it is believed that a transition to c-BN occurs around 1000°C in the pressure and temperature range of the c-BN stable phase, which is stable under high pressure. Therefore, w-BN sintered bodies obtained by static pressing always exhibit a w-BN / c-BN mixed crystal structure, and no sintered bodies exhibiting the inherent hardness of w-BN are obtained.

[0011] The objective of the present invention is to obtain a w-BN-based sintered body with good properties, or a w-BN-based composite impact sintered body with an added material having a hardness of 20 GPa or more, without any upper limit on the manufacturable dimensions and without requiring high equipment costs. The present invention also In one embodiment, Another objective is to obtain a dense sintered body consisting essentially of a single phase of 100% w-BN. [Means for solving the problem]

[0012] The gist of the present invention is a method for producing a w-BN-based sintered body, in which a starting particle aggregate containing wurtzite boron nitride (hereinafter referred to as w-BN) particles and single crystal particles of a hard material is subjected to an instantaneous ultra-high pressure of 8 to 100 GPa to bond adjacent particles together, and a sintered body of the integrated particles is recovered, in which the particle aggregate contains 10 mass % or more (raw material composition) of w-BN, and the ultra-high pressure is applied while the w-BN and the single crystal particles of the hard material are in close contact with each other. [Effects of the Invention]

[0013] In the present invention, the w-BN powder mixture is subjected to an impact pressure of a magnitude that cannot be achieved by conventional industrial-scale static pressure methods during explosive explosions, thereby densifying the w-BN powder. Furthermore, the instantaneous and short heating time under this explosion suppresses the phase transition to c-BN, making it possible to obtain a sintered body that is essentially 100% w-BN.

[0014] Previously, there have been attempts to bond high-hardness particles of c-BN or diamond using the high shock pressure generated by explosive explosions, without relying on static ultra-high pressure equipment, but no results suitable for industrial production have been achieved. The main reason for this is thought to be that, for example, when attempting to bond only c-BN particles, the fact that many c-BN and other high-hardness material particles are polyhedral crystals makes it difficult for adjacent particles to blend together, making it impossible to bond them together without gaps.

[0015] In contrast, in the present invention, w-BN is used as a high-hardness material to form the sintered body. w-BN is synthesized by narrowing the lattice spacing of hexagonal boron nitride (h-BN) by applying a momentary high pressure for about 1 μs, causing a phase transition, and individual particles are 100 nm (1 × 10 -4 It is an amorphous polycrystalline particle formed by the aggregation of minute crystals of size 0.1m or less, and therefore does not have the cleavage that is inevitably present in single crystal particles.

[0016] On the other hand, w-BN, being an aggregate of minute crystals, does not have the sharp corners or edges that single crystal particles have to serve as cutting edges. Therefore, when w-BN alone is formed into a mass by impact pressure and used as a cutting tool, it is suitable for machining the surface of a workpiece to a fine finish, but is not suitable for high-efficiency cutting processes that require deep cuts. Therefore, it is preferable to use w-BN as a mass integrated with single crystal particles other than w-BN, which have sharp corners and edges, when making cutting tools. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a configuration for the direct impact pressure method of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a configuration for the indirect impact pressure method of the present invention. Embodiments of the invention

[0018] The starting w-BN particles used in the impact pressure treatment of this invention are suitable for bonding with cleavable single-crystal particles such as diamond, c-BN, and other high-hardness substances with a Vickers hardness of 20 GPa or more to form a sintered body, taking advantage of the fact that they do not exhibit cleavage even when sintered alone. This is because, due to their lack of sharp corners or flat surfaces and their irregular shape, they easily penetrate between the single-crystal particles, making them suitable for compressing the entire body to a high density without cleaving the single-crystal particles.

[0019] The w-BN particles used in the present invention exist as secondary particles formed by aggregation of nanometer-sized primary particles, and these secondary particles form the constituent units of the sintered body. The w-BN particles synthesized using impact pressure have a short reaction time, and in addition to the fineness of the primary particles, they have many defects inside the crystals and an active surface. It is presumed that these factors work to promote bonding between particles during sintering, and a strong and stable sintered structure is obtained through bonding between primary particles and bonding between secondary particles. is the particle diameter The smaller the value, the larger the overall surface area and the more active the sintering reaction. These secondary particles Use with an average particle size of 5 μm or less This is considered to be desirable as it results in a high density and fine structure. .

[0020] In addition to sintering w-BN alone, to create a composite sintered body by bonding cleavable single crystal particles with polycrystalline w-BN, it is preferable to interpose w-BN particles between the single crystal particles. From this perspective, it is appropriate for the average particle size of the w-BN particles to be smaller than the average particle size of the combined single crystal particles, and it is particularly preferable for it to be 1 / 2 or less.

[0021] The problem with the mechanism of sintering particle aggregates using explosive pressure is that the material is compressed strongly by the instantaneous pressure, causing a sudden rise in temperature throughout the material, which then drops in temperature during the process of releasing the compression pressure. This also makes it easy for uneven compression to occur, leading to the generation of localized residual stress. Therefore, it is preferable to perform stress-relief annealing as a post-process, if necessary.

[0022] Annealing is also effective in improving the bonding strength within sintered bodies, particularly those obtained by adding sintering aids and applying impact. The annealing conditions are set based on the material composition of the pressure-sintered product, but generally, heating at a temperature in the range of 700°C to 1700°C for 1 hour to 24 hours is also effective.

[0023] In the present invention, the mechanism of sintering w-BN particles or w-BN particles and added single crystal particles by explosion pressure is the same as in the case of explosive welding (explosive pressure bonding, explosive welding, explosive bonding, etc.), a metallurgical method that uses the explosion pressure of explosives to join metals, and between However, the particles are bonded to each other without forming any compounds. between There are also compounds that are inevitably produced by the molten state that accompanies the jet generated by the collision, and bonding by these cannot be ruled out.If a certain degree of reduction in hardness of the resulting sintered body can be tolerated, it is possible to add metal materials such as Al, Si, Ti, Zr, Hf, and Ta, either alone or in combination, as sintering aids, and sinter under lower pressure loads by using less explosives.

[0024] By adding the above metals, bonding occurs with the w-BN, involving the formation of metal nitrides or borides, or bonding occurs due to the affinity between the metals. In these cases, sintering is possible at lower pressures and temperatures than the sintering conditions for w-BN alone, and the hardness of the resulting sintered body is lower than that of a sintered body made only of w-BN. However, because the sintered body can be produced with a small explosive force, if the intended product can be achieved even with a sintered body with a slightly lower hardness, it is still within the realm of choice.

[0025] Furthermore, when stress relief annealing is performed according to the present invention, it is assumed that the material sintered with the sintering aids described above will not react with w-BN during the sintering process due to impact pressure and will remain as a metal. However, in this case, it is expected that the annealing heat will stabilize the material by reacting with w-BN to form a compound. Furthermore, it is expected that the sintered body will be stabilized by adding an appropriate amount of ceramic carbide, nitride, boride, or oxide of a specific metal that is chemically active against boron nitride.

[0026] The stress relief annealing operation in the present invention can be carried out in a non-oxidizing atmosphere under normal pressure, but is more effective in promoting densification if carried out under pressure. As a pressure application method, various means such as hot pressing, HIP, and ultra-high pressure can be used.

[0027] In the present invention, the pressure applied to the material to be treated is the impact force generated when an explosive explodes. By using this method, although there are environmental restrictions on the amount of explosive that can be detonated, there are no theoretical restrictions on dimensions, and since no static ultra-high pressure equipment is used, various problems that arise from the use of such equipment, such as restrictions on manufacturable dimensions and high manufacturing costs, can be avoided.

[0028] In the present invention, the impact pressure applied to the w-BN or the mixture of w-BN and sintering aid is calculated by first determining the explosion pressure of the explosive, then calculating the pressure value applied to the container of the impact object due to that pressure, and then determining the pressure transmitted from the container to the w-BN or the mixture of w-BN and sintering aid contained therein. In the present invention, the direct method and indirect method described in detail below can be used as a method for transmitting the explosion pressure of the explosive to the material sealed in the metal tube.

[0029] The direct method involves detonating explosives placed around a metal tube containing the material to be sintered, thereby transmitting pressure to the impacted material. On the other hand, the indirect method involves arranging metal tubes (flying tubes) with an inner diameter larger than the outer diameter of the metal tube containing the impacted material to be sintered concentrically, detonating explosives placed around the outside of the tube, causing the flying tube to collide centripetally at high speed with the material storage tube, thereby transmitting pressure.

[0030] The present invention will now be described in detail with reference to the accompanying drawings. In Figure 1, which shows an outline of the components of the direct method, the opening at one end of a steel treated material storage tube 1 is sealed with a metal plug 2, filled with starting material 3 consisting of w-BN or a powder mixture of w-BN and a sintering aid, and the other end is sealed with a similar metal plug 4. The entire tube is placed coaxially within a larger diameter, bottomed steel explosive storage tube 5, filled with explosive 6, and sealed with an end plate 7 made of any material, and an electric detonator 8 is attached.

[0031] When explosive 6 is detonated by detonator 8, a detonation wave travels from the detonated side to the opposite side at a high speed characteristic of explosives, and the generated explosion pressure compresses steel tube 1 toward its central axis at high speed, and at the same time, the starting materials, including w-BN, stored inside are integrated by the compression load.

[0032] On the other hand, in the indirect method, metal tubes (flying tubes) with an inner diameter larger than the outer diameter of the metal tube containing the impacted material to be sintered are arranged concentrically, and explosives placed around the outside of the tubes are detonated, causing the flying tubes to collide centripetally with the material storage tube at high speed, transmitting pressure. In Figure 2, elements 1 to 8 are configured in the same way as in Figure 1, but a metal cylinder 11 is placed around the outside of the steel tube 1 containing the material to be treated, allowing the flying tubes to collide with the steel tube 1. A space 12 is left between the steel tube 1 and the metal cylinder 11.

[0033] When the explosive 6 is detonated by the detonator 8, a detonation wave travels from the detonated side to the opposite side at a speed specific to the explosive, and the generated explosion pressure causes the flying metal cylinder 11 to contract at high speed, and then passes through the space 12, impact-compressing the surface of the treated material storage tube 1, thereby compressing and integrating the w-BN or w-BN and single crystal particles and / or a powder mixture of these and sintering aids inside the steel tube.

[0034] The pressures generated in the direct and indirect methods are calculated below. Note that as a special example in the present invention, there is also a method in which impact pressure is applied to a flat material, and the pressure applied in that case can also be calculated in the same way by referring to the following description.

[0035] The explosive detonation pressure P required for both the direct and indirect methods can be roughly calculated using the following formula, where ρ0 is the initial density of the explosive and D is the detonation velocity. P = ρ0D 2 / 4 ..... 1) P: Pressure N / m 2 , ρ0: density kg / m 3 , D: Explosion velocity m / s Density 1.1×10 3 kg / m 3 , explosion velocity 2.8×10 3 The pressure P generated by the explosive in m / s is P = ρ0D 2 / 4 = 1.1×10 3 kg / m 3 ×(2.8×10 3 m / s) 2 / 4 = 2.156×10 9 kgm / m 2 s 2 = 2.156GPa The pressure obtained is an approximate value, so it can be rounded to 2.2 GPa.

[0036] In both the direct and indirect methods, 60% of the explosive energy is considered to be transferred to the metal tube in contact with the explosive, and this value is called the Gurney energy (US Pat. 3,667,911). Furthermore, when the material to be impacted is contained in a cylinder, the energy consumed by the deformation of the cylinder due to the impact is a small portion of the applied energy and can be ignored.

[0037] In the direct method, when a metal tube containing materials (hereinafter referred to as the material storage tube) receives the impact of an explosion, it contracts toward the central axis of the tube, compressing the stored material. Strictly speaking, since the material storage tube is in contact with the material, it does not fly through space, but since it is possible to calculate the speed at which metal is accelerated by the explosion pressure, as a convenience method, the material storage tube is assumed to fly a small distance and collide with the material.

[0038] To understand the behavior of w-BN particles subjected to impact pressure through a material storage tube, it is first necessary to determine the impact properties of w-BN. Since the impact properties of w-BN cannot be obtained from published data, we will use those of cubic boron nitride (hereafter c-BN), which is also a high-pressure phase of boron nitride. The specific volume V of c-BN with high true density under each pressure can be obtained by the following procedure.

[0039] Shock wave velocity U of the material under impact s , sound speed C0, particle speed U p , the coefficient S is expressed as U s = C0+ SU p ..... 2) P = ρ0U s U p = ρ0(C0U p +SU p 2 ) ..... 3) from, U p = [{(ρ0C0) 2 +4ρ0SP} 1 / 2 ] / 2ρ0S ..... 4) In c-BN, C0 = 1.19 × 10 4 m / s, S = 1.11, ρ0 = 3.48×10 3 kg / m 3 and [4] , so equation 4) becomes: U p = [{(3.48×10 3 × 1.19×10 4 ) 2 + 4 × 3.48×10 3 × 1.1 × P} 1 / 2 The specific volume V is given by the following equation: V = V0(U s -U p ) / U s ..... 5) [4]: N. Kawai et al., Shock compression of cubic boron nitride, J. Appl. Phys. 106, 033508 (2009)

[0040] The true density w-BN (substituted with the value of c-BN) at each pressure can be obtained using equations 3), 4), and 5). However, the material subjected to impact is a powder-filled material with a low density, and the behavior of the material under impact differs from that of a true density material under high pressure. Therefore, the behavior of the material with voids under impact must be calculated using the following equation: [5] . P = P H [1-ρ γ (V0-V) / 2] / [1- ρ γ (V0* - V) / 2] ..... 6) P: Pressure P of the porous material H : Pressure of the true density material ρ γ : Defined in Equation 7) V0: Initial specific volume of the material with true density V0*: Initial specific volume of the material with voids [5] : RG McQueen et al. (1970) "The equation of solids from shock wave studies" in High-Velocity Impact Phenomena (ed. R. Kinslow), Academic Press, New York, pp.293-417

[0041] ρ in Equation 6) γ is defined by equation 7), and γ or γ0 is called the Gruneisen coefficient and is defined by equation 7). ρ0γ0= ρ γ ..... 7) ρ0: initial density of material ρ: density at any pressure γ0: Gruneisen coefficient at the initial density of the material γ: Gruneisen coefficient at density ρ The meaning of this formula is that even if the density of a material changes due to pressure, the value obtained as the product of density and the Gruneisen coefficient does not change. From physical considerations, the initial value of the Gruneisen coefficient γ0 is defined by the following formula.

[0042] γ0= 2S-1 ..... 8) S in equation 8) is S in equation 2). Therefore, γ0 of c-BN is γ0= 2S - 1 = 2 × 1.11 - 1 = 1.22 is.

[0043] When calculating the various values ​​when impact is applied to c-BN with voids using formula 6), the ratio of the packing density to the true density is taken as the packing rate, which in the present invention is set to 75% based on past experience. V0= 1 / ρ0= 1 / 3480 = 0.2874 ×10 -4 m 3 / kg V0* = 1 / (ρ0× 0.75) = 1 / (3480×0.75) = 1 / 2610 = 0.3831×10 -3 m 3 / kg

[0044] Once the PV relationship for c-BN with voids is obtained, the particle velocity U at each pressure can be calculated using equations 9 and 10. p1 and shock wave speed U s1 You can get the following. U p = [(P - P0)(V0- V)] 1 / 2 ..... 9) U s = V0[(P - P0) / (V0- V)] 1 / 2 ..... 10) Table 1 shows the true density of c-BN calculated by equations 2) to 5). H , U p .U s , V are calculated, and then, using equations 6) to 10), P and U of the c-BN with voids are calculated. p1 .U s1 The results of the relationship are shown below.

[0045] [Table 1]

[0046] High-pressure data for true density c-BN P H , U p , U s , V High-pressure data P, U of c-BN with voids p1 , U s1 , V (true density common to high-pressure data for c-BN) Table 1. U of c-BN with voids p1 and U s1 When the two-dimensional correlation was analyzed, the reliability was r = 0.994. U s1 = 1446.5 + 2.504U p ..... 11) The relationship was obtained.

[0047] The metal tube inscribed in the cylindrical explosive contracts toward its central axis, and in the direct method, high pressure is applied directly to the material stored inside the metal tube, while in the indirect method, the material flies through space and collides with the metal tube containing the material. In both the direct and indirect methods, it can be assumed that most of the energy generated by the explosion and directed toward the central axis is transferred to the stored material, and in the indirect method, the speed of the metal tube flying under the pressure of the explosion can be calculated using the following formula. V pm =(2E g ) 1 / 2 [{(1+2M d / M x ) 3 +1} / {6(1+M d / M x )}+M d / M x ] -1 / 2 ... 12), however V pm : The maximum flight tube speed obtainable by the system E g :Explosive energy × 0.6 M d : Explosive mass per unit area of ​​the flight tube kg / m2 M x : Mass per unit area of ​​the flight tube kg / m 2 YP x / (M d V pm 2 ) = -ln(1 - V p / V pm )-V p / V pm .....13) Y: Flight distance until the flying tube hits the material storage tube m P x : Explosive explosion pressure P a V p : The speed of the tube when it reaches the distance Y (m / s)

[0048] For example, the density explained in 0035 is 1.1×10 3 kg / m 3 , explosion velocity 2.8×10 3 Assume that an explosive of m / s is filled between an SGP150A steel explosive storage tube (outer diameter 165.2 mm x inner diameter 155.2 mm) and an STPG370 125A steel flight tube (outer diameter 139.8 mm x inner diameter 126.6 mm) and is then caused to collide with an STPG370 80A steel material storage tube (outer diameter 89.1 mm x inner diameter 78.1 mm). Explosive energy E of explosives is 4×10 3 In kJ / kg, the Gurney energy E g teeth, Eg = E × 0.6 = 2.4×10 3 kJ / kg Amount of explosive per unit area of ​​the flight tube M x and the mass per unit area of ​​the flight tube M d teeth, M x = 24.9 kg / m 2 ; M d = 54.5 kg / m 2 and by equation 12), V pm = 680.4 m / s is obtained.

[0049] The flight distance of the flight tube is (Inner diameter of flight tube - Outer diameter of material storage tube) / 2 = (0.1266 - 0.0891) / 2 = 0.01875 Therefore, the left side of equation 13) is YP x / (M d V pm 2 ) = 0.01875 × 2.2×10 9 / (54.5 × 680.4 2 ) = 1.6349 To find the right-hand side that is equal to that value, V = 627.5 m / s This balances the left side of the equation. Therefore, we can assume that the flying tube will collide with the material storage tube at 627.5 m / s.

[0050] When the flying tube collides with the material storage tube, it shrinks and becomes thicker. The impact mass per surface area of ​​the material storage tube is calculated as M d When the flight tube with an outer diameter of 139.8 mm and an inner diameter of 126.6 mm collides with the material storage tube, the inner diameter becomes equal to the outer diameter of the material storage tube, 89.1 mm, and the M d M d1 Then, M d1 = 77.4 kg / m 2 This becomes:

[0051] The energy of a moving object is E = MV 2 / 2 ..... 14) In this case, E = 77.4 kg / m 2 × (627.5m / s) 2 / 2 = 15.2MJ / m 2 As the flight tube contracts, it consumes energy due to deformation, but this amount is a small portion of the total energy and can be ignored. The material storage tube also deforms due to the impact, but this can also be ignored. Therefore, we can treat it as if all of the flight tube's kinetic energy is transmitted to the material through the material storage tube.

[0052] Surface area of ​​material storage pipe: 1m 2 The mass of the 75% w-BN per particle is 45.68 kg, and the energy given by the flight tube is 15.2 MJ / m 2 When w-BN receives E1= 332.7kJ / kg The impact properties of c-BN, which is assumed to have similar impact properties to w-BN, at a filling rate of 75%, are as follows: U s1 = 1446.5 + 2.504U p ..... 11) From U s1 If we set the speed of the explosion to 2800m / s, U p = 550.5 m / s From equations 2) and 3), P = 4.06GPa V0 = 0.6061 × 10 -3 m 3 / kg V = 0.4891×10 -3 is obtained, and from 5) E = (P+P0)(V0-V) / 2 ..... 15) = 231kJ / kg Energy of 2.8 x 10 3 A shock wave of m / s is generated in the material.

[0053] This value is calculated based on the shock wave velocity U generated by the energy input from the flight tube of 332.7 kJ / kg. s Therefore, in this case, for the w-BN with a material filling rate of 75% located at the collision point of the flight tube, there is a Us =3409m / s, particle velocity U p At the pressure point where the pressure drops to P=4.06GPa in front of the direction of explosion, centered on the maximum pressure P=7.266GPa, which corresponds to P=816m / s, the velocity is 2.8×10 3 It forms a shock wave front of m / s.

[0054] As a specific example, the direct method in which explosives are directly attached to the material storage tube shown in Figure 1 will be explained. (1) Impact material: w-BN 100% by mass, filling density 50% of theoretical density (2) Explosive storage steel pipe: SPG65A, outer diameter 76.3 mm, inner diameter 69.6 mm, length 300 mm (3) Filled explosive: outer diameter 69.6 mm, inner diameter 27.2 mm, loading density 1450 kg / m 3 , length 300mm Explosion speed 5×10 3 m / s, explosive energy 5×10 3 KJ (4) Impact material storage tube: Carbon steel STPG370 SCH40 20A, outer diameter 27.2 mm, inner diameter 21.4 mm, Length: 250mm (5) Metal plug to seal the material: outer diameter 21.4 mm, length 25 mm

[0055] From the above, the amount of explosive per unit area of ​​the material storage tube M x and the mass per unit area of ​​the flight tube M d teeth, M x = 55.44 kg / m 2 , M d = 20.51 kg / m 2 Then, by equation 12), V pm teeth, V pm = 230 m / s According to 0037, if we consider that the material storage tube flies a very small distance of 1 mm and collides with the material, then according to equation 13), the material storage tube will be V p = 816 m / s The object will collide with the material at a speed of

[0056] The kinetic energy of the material storage tube is calculated by Equation 14). E = 20.51 kg / m 2 × (2300 m / s) 2 / 2 = 54.2MJ / m 2 and all of this is transmitted to the material in the material storage pipe. The surface area of ​​the material storage pipe is 1m 2 Amount of material per unit M s teeth, M s = 17.5 kg / m 2 It becomes. M s If the kinetic energy E of the material storage pipe is transmitted to the s teeth, E s = E / E s = 54.2MJ / m 2 / 17.5kg / m 2 = 3.10MJ / kg is.

[0057] When analyzing the impact conditions where the material subjected to the impact is 100% w-BN by mass and the filling density is 75% of the theoretical density, the w-BN density and hardness are very close to those of w-BN and c-BN, so the impact characteristics at high pressure shown by c-BN with a filling rate of 50% obtained earlier are: U s1 = 1.4465×10 3 + 2.504U p ..... 11) Here, let us assume that the explosive velocity of the explosive in the material is 5×10 3 E s If a shock wave occurs, the pressure generated in the material is as follows: 3) and 11) From this, the estimated value is 18.5 GPa, and the introduced energy E s1 From equation 15), E s1 = 1.0MJ / kg The introduced energy E s This is less than 3.10MJ / kg.

[0058] Energy introduced E s The shock wave velocity U when is 3.10MJ / kg s and particle velocity U p The corresponding pressure P is U s = 7435E s , U p = 2490E s , P = 48.5GPa and the shock wave velocity U s The explosion speed is 5 x 10 3 The pressure is much faster than m / s, and at the highest pressure point close to the explosion impact point, it reaches 48.5 GPa.A shock wave precedes the explosion impact point, and when the pressure decays, it becomes a shock wave with a speed equal to the explosion speed. The following examples illustrate embodiments of the present invention. Example 1

[0059] Using the configuration shown in Figure 2, w-BN powder consisting of 45% particles with an average particle size of 10 μm, 40% particles with an average particle size of 3 μm, and 15% particles with a particle size of 1 μm was sintered into a sintered body by indirect impact pressure. (The particle size here refers to the secondary particle size.) 150 g of w-BN powder with the above particle size distribution was pressure-filled into a material storage tube made of STPG37015A steel with an outer diameter of 27.2 mm, an inner diameter of 21.4 mm, and a length of 300 mm, and the tube was then evacuated to a pressure of 1 Torr or less, sealed, and subjected to impact treatment. The w-BN powder used in this example was a mixture of three types of powder with different average particle sizes, and the overall average particle size calculated by the weighted average of these was approximately 4.8 μm. .

[0060] The explosive tube was made of SGP 90A steel, with an outer diameter of 101.6 mm, an inner diameter of 93.2 mm, and a length of 400 mm. The flight tube was made of STPG370 50A steel, with an outer diameter of 60.5 mm, an inner diameter of 52.7 mm, and a length of 400 mm. Both tubes were filled with 1.9 kg of ANFO explosive. The impact pressure from this configuration was estimated to be approximately 35 GPa.

[0061] The w-BN was in the form of a tightly sintered round rod with a diameter of approximately 15 mm. This was cut using a diamond blade, and 15 mm long specimens were taken from three locations: the initial location of the explosive shock, the center of the tube, and the end of the tube. The density was measured and found to be 3.43 g / cm3 in the above order. 3 , 3.44g / cm 3 , 3.46g / cm 3 These values ​​give a true density of c-BN of 3.48 g / cm 3 These correspond to 98.6%, 98.9%, and 99.4%, respectively. When the micro Vickers hardness of each of these samples was measured, the average value of five points was in the range of 56 GPa to 58 GPa, and no difference was observed depending on the sample collection position. Example 2

[0062] The material subjected to impact loading in Example 1 was placed in a high-pressure apparatus, and the pressure and temperature were increased to 2 GPa and 1350°C, and held for 15 minutes. The pressure and temperature were then returned to normal pressure and normal temperature, and the sample was recovered. The density of the recovered sample was 3.47 g / cm3, regardless of the impact position, as measured by the Archimedes method. 3 ~3.48g / cm 3 This was almost equal to the theoretical density of c-BN (Non-Patent Document 1). The Vickers hardness was also 78 GPa to 81 GPa regardless of the impact position, which was significantly higher than before treatment with the high-pressure device, and is thought to be due to the treatment further tightening the bonds between the constituent particles. X-ray diffraction measurement revealed a single phase of w-BN. Example 3

[0063] Ten samples were prepared by mixing w-BN powder with the metals, diamond, c-BN, metal carbides, oxides, or nitrides shown in Table 2. Each sample was packed into a material storage tube made of STPG37015A steel, measuring 27.2 mm in outer diameter, 21.4 mm in inner diameter, and 300 mm in length. The tube was then evacuated to a pressure of 1 Torr or less and sealed. Each sample was subjected to impact pressure treatment by indirect pressure using the configuration shown in Example 1. The ultimate pressure and the products identified by X-ray diffraction of the recovered material are also shown in the same table.

[0064] [Table 2]

[0065] In Table 2, (1) The composition ratio of each component is expressed in mass %. (2) The particle size is the average value (μm), and single crystal particles other than w-BN include composite crystals consisting of unit single crystals of 1 μm or more. (3) Hardness is measured in terms of Vickers hardness GPa (Hv) of the sintered body. (4) Hardness and load pressure values ​​are rounded. (5) The hardness of sintered products containing Al, Mg, Ti, Hf, Si, Ta, and Mo was measured after impact and subsequent heating at 1400°C for 1 hour in a nitrogen atmosphere. [Industrial Applicability]

[0066] Sintered w-BN is an ultra-hard material that is expected to have many applications in a variety of fields, such as abrasive tool components and wear-resistant components. [Explanation of symbols]

[0067] 1. Processing material storage pipe 2. Metal plug 3 Starting material 4 Metal stopper 5 Explosives storage steel pipe 6 Explosives 7 Metal end plate 8 Electric detonator 11 Metal cylinder 12 Space

Claims

1. A w-BN-based sintered body comprising secondary particles which are agglomerates of primary particles of wurtzite boron nitride (w-BN) and particles of one type of hard material selected from cubic boron nitride (c-BN) and diamond, which are bonded together to form an integrated body, wherein the w-BN phase content in the sintered body is 10 mass% or more of the total, and the hard material particles are tightly bonded together by the w-BN secondary particles interposed between the particles.

2. The w-BN-based sintered body according to claim 1, wherein the average particle size of the w-BN secondary particles is 5 μm or less.

3. The w-BN-based sintered body according to claim 1, wherein the ratio of the average particle size of the hard material particles to the w-BN secondary particles is 2 or more.

4. A method for producing a w-BN-based sintered body, comprising mixing, as a first component of 10% by mass or more, w-BN secondary particles which are agglomerates of wurtzite boron nitride (w-BN) primary particles and have an average secondary particle size of 5 μm or less, and as a second component of the remainder, single-crystal particles of a hard material selected from cubic boron nitride (c-BN) and diamond, having a particle size ratio to the w-BN secondary particles of 2 or more, to form a raw material particle aggregate in which the two are in close contact, and subjecting the raw material particle aggregate to an instantaneous ultra-high pressure of 8 to 100 GPa generated by the explosion of an explosive, thereby causing the w-BN particles to be interposed between the hard material particles and sintering, and thereby recovering the sintered body retaining the hard material particles.

5. A method comprising the step of further heat treating the sintered body recovered from claim 4 at a temperature of 700°C or higher and 1700°C or lower in a non-oxidizing atmosphere.

6. A method in which the heat treatment in the method according to claim 5 is carried out under pressure by hot pressing or HIP.

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