JP2014141359A - Sialon-base sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sialon-base sintered compact that contains cubic crystal-type sialon particles and has excellent toughness.SOLUTION: A sialon-base sintered compact of the invention includes equiaxial crystal, cubic crystal-type sialon particles, and columnar crystal β-type sialon particles, so that the sialon-base sintered compact has high toughness in addition to excellent wear resistance.

Description

  The present invention relates to a sialon-based sintered body, a cutting tool using the sialon-based sintered body, and a manufacturing method thereof, and more specifically, a sialon-based sintering containing equiaxed cubic sialon particles and columnar β-sialon particles. The present invention relates to a bonded body, a cutting tool using the same, and a manufacturing method thereof.

  Sialon has a structure in which aluminum and oxygen are dissolved in silicon nitride, and there are usually two types of crystal systems, α-sialon and β-sialon, which belong to the hexagonal system. A sialon-based sintered body using such sialon has a characteristic of low reactivity with a metal, and has been developed as a cutting tool material. Recently, in order to further increase hardness and improve wear resistance when used as a cutting tool material, cubic sialon crystal particles with higher hardness than α-sialon and β-sialon are used. A sintered body containing the same has been developed (Patent Document 1).

  However, cubic sialon has high hardness and excellent wear resistance, but is brittle, so when using a sialon-based sintered body containing cubic sialon particles for a cutting tool, There are aspects that are not always sufficient in terms of defectability, and further improvement in toughness has been desired.

JP 2011-121822 A

  The present invention reduces chipping and chipping of cutting edges during cutting in a cutting tool using a sialon-based sintered body containing cubic sialon particles having low reactivity with metal and excellent wear resistance. Therefore, an object is to improve the toughness of the sialon-based sintered body.

  In view of the above requirements, the present inventors have intensively studied a method for improving toughness by paying attention to the structure of a sialon-based sintered body containing cubic sialon particles, particularly the shape of crystal particles. As a result, the presence of the columnar β-type sialon particles in the sialon-based sintered body containing the equiaxed cubic type sialon particles makes the hardness of the cubic type sialon excellent in wear resistance. The inventors have found that the toughness of a sialon-based sintered body can be improved while taking advantage of the features, and have completed the present invention.

  That is, the first aspect of the present invention is a sialon-based sintered body including equiaxed cubic sialon particles and columnar β-sialon particles.

  The sintered body preferably has an average aspect ratio of the columnar crystal β-type sialon particles of 2 or more and an average minor axis diameter of 0.2 μm or more and 10 μm or less.

  In the sintered body, the equiaxed cubic sialon particles preferably have an average particle size of 0.05 μm or more and 5 μm or less.

In the sintered body, the ratio of the peak intensity I _{C (311)} of the (311) plane of cubic sialon and the peak intensity I _{β (200)} of the (200) plane of β-type sialon in X-ray diffraction ₍ I _{C ( 311)} / (IC ₍₃₁₁₎ + _{Iβ (200)} ) is preferably 0.2 or more and 0.9 or less.

The sintered body preferably further includes the following (a) and / or (b) as the third compound.
(A) A compound of at least one element selected from the group consisting of aluminum, boron, silicon, titanium, iron and nickel and at least one element selected from the group consisting of carbon, nitrogen and oxygen.
(B) A compound of at least two elements selected from the group consisting of aluminum, boron, silicon, titanium, iron, and nickel.

  In the sintered body, the content of the third compound is preferably 10% by volume or more and 50% by volume or less.

The sintered body preferably has a Vickers hardness of 22 GPa or more and a fracture toughness value of 5 MPa · m ^1/2 or more.

  The second aspect of the present invention is a cutting tool using the above sialon-based sintered body.

  In a third aspect of the present invention, a powder containing columnar crystal β-sialon particles having an average aspect ratio of 2 or more and an average minor axis diameter of 0.2 μm or more and 10 μm or less is a temperature of 1800 ° C. or more and 2000 ° C. or less. And a process of producing a mixed powder containing equiaxed cubic sialon particles and columnar β-sialon particles by treating at a pressure of 40 GPa or more and 60 GPa or less, and the mixed powder is processed at 1200 ° C. or more and 1800 ° C. A method for producing a sialon-based sintered body comprising a step of sintering at the following temperature.

  According to the present invention as described above, the brittleness of the sialon-based sintered body containing cubic sialon particles having low reactivity with metal and excellent wear resistance is improved, and toughness is improved. When the sialon-based sintered body is used as a cutting tool, chipping or chipping of the cutting edge during cutting can be reduced.

  Hereinafter, an embodiment of a sialon-based sintered body according to the first aspect of the present invention will be described.

  The sialon-based sintered body of the present invention is a sialon-based sintered body including equiaxed cubic sialon particles and columnar β-sialon particles. In machining of heat-resistant alloys such as Inconel, which are difficult to cut materials, tools made of β-type sialon sintered bodies that take advantage of low reactivity with metals have been used, but wear resistance and fracture resistance In order to further improve the properties, it has been required to simultaneously increase both the hardness and toughness of the sialon sintered body. In response to this requirement, the inventors examined the use of cubic sialon having high hardness and excellent wear resistance instead of β-sialon, but because cubic sialon is equiaxed, it has toughness. However, it was still not enough. Therefore, as a result of coexisting the equiaxed cubic sialon particles and the columnar β-sialon particles in the sialon-based sintered body of the present invention, the hardness of the equiaxed cubic sialon particles is increased. It was possible to achieve both increase and toughness increase by columnar β-sialon particles, and both wear resistance and fracture resistance could be improved at the same time.

  In preparing a sialon-based sintered body containing cubic sialon, as will be described later, a part of β sialon is cubically crystallized using a method such as impact synthesis compression using β type sialon powder as a starting material. A powder transformed into a type sialon is prepared, and the sintered body is obtained by sintering the powder. At this time, the form of particles of β-sialon powder used as a starting material determines the structure of the sintered body. When β-sialon is synthesized by a general carbon reductive nitriding method under an atmospheric pressure nitrogen atmosphere, only equiaxed crystal powder particles can be obtained. When impact synthesis compression is performed using equiaxed β-sialon powder as a starting material, a powder containing equiaxed cubic sialon particles and equiaxed β-sialon particles is obtained. Even so, only a sialon-based sintered body including equiaxed cubic sialon particles and equiaxed β-sialon particles can be obtained, and improvement in toughness cannot be expected.

  On the other hand, when β-sialon is synthesized using a high temperature nitridation synthesis process utilizing a nitridation reaction of metal silicon and its reaction heat in a nitrogen atmosphere at atmospheric pressure or higher, abnormal grain growth of β-sialon particles occurs 2500 Since the reaction temperature can be increased to about 0 ° C., β-sialon powder having hexagonal columnar crystals grown in the c-axis direction can be obtained. When impact-compression compression is performed using such columnar β-sialon powder as a starting material, cubic sialon powder that has undergone phase transformation becomes equiaxed, but β-sialon powder that has not undergone phase transformation remains columnar. Thus, a powder containing equiaxed cubic sialon particles and columnar β-sialon particles is obtained. When this powder is sintered, a sialon-based sintered body containing equiaxed cubic sialon particles and columnar β-sialon particles can be obtained, and the hardness and toughness can be improved at the same time.

  In the above-described sialon-based sintered body, it is preferable that the average aspect ratio of the columnar β-type sialon particles is 2 or more and the average minor axis diameter is 0.2 μm or more and 10 μm or less. When stress is applied to the sialon-based sintered body from the outside and the crack progresses inside the sintered body, the crack progresses so as to bypass the columnar crystals, so the toughness increases by increasing the energy required for fracture. However, if the average aspect ratio of columnar β-sialon particles is less than 2, the distance by which cracks bypass is reduced and it becomes difficult to obtain the effect of improving toughness. The ratio is preferably 2 or more. In addition, if the average minor axis diameter of β-type sialon particles is less than 0.2 μm, cracks will progress by cutting the β-type sialon particles, and if the average minor axis diameter exceeds 10 μm, stress will be applied from the outside. When added, stress concentration may occur in the β-type sialon particles, which may be the starting point of fracture. Therefore, the average minor axis diameter of the columnar β-type sialon particles is preferably 0.2 μm or more and 10 μm or less. Furthermore, from the viewpoint of improving toughness while suppressing a decrease in hardness, it is more preferable that the average aspect ratio of β-sialon particles of columnar crystals is 3 or more and the average minor axis diameter is 1 μm or more and 5 μm or less.

  At this time, the average aspect ratio and the average minor axis diameter of the β-type sialon particles are the crystal phase by EBSD (Electron Back Scattering Diffraction Pattern) using SEM (Scanning Electron Microscope). Mapping and image analysis. Specifically, the structure observation surface of the sialon-based sintered body of the present invention is processed into a mirror surface by beam processing using a cross section polisher, and an FE-SEM (Field Emission Scanning Electron Microscope). Is observed at a magnification of 5000 times or more using a scanning electron microscope), and the crystal phase of the observation surface is mapped using an EBSD apparatus attached to the FE-SEM. At this time, by inputting the respective crystal structures and lattice constants of cubic sialon, β-sialon, third compound, etc., previously measured by X-ray diffraction as parameters for analysis, the observation is performed. A mapping diagram of the crystal phase and crystal orientation of the surface is obtained. Using the difference in crystal orientation from the mapping diagram, the grain boundaries of cubic sialon and β sialon are identified, and each of the 50 β sialon particles arbitrarily extracted is imaged using image analysis software. The diameter and the major axis diameter are obtained, and the average value of 50 short axis diameters is defined as the average minor axis diameter, and the average value of 50 major axis diameters is defined as the average major axis diameter. The average aspect ratio is calculated by dividing the average major axis diameter by the average minor axis diameter. When measuring the average aspect ratio and average minor axis diameter of β-type sialon particles, use other observation means that can identify the crystal phase, such as TEM (Transmission Electron Microscope) transmission analysis. Is also possible.

  In the above sialon-based sintered body, it is preferable that the average particle diameter of the equiaxed cubic sialon particles is 0.05 μm or more and 5 μm or less. When the average particle size of the cubic sialon particles is less than 0.05 μm, the sintered body becomes brittle and easily broken when used as a cutting tool. On the other hand, when the average particle size exceeds 5 μm, the hardness decreases. This is because wear tends to occur when used as a cutting tool. Further, from the viewpoint of improving the strength of the sintered body, the average particle diameter of the equiaxed cubic sialon particles is more preferably 0.1 μm or more and 2 μm or less.

  At this time, the average particle diameter of the cubic sialon particles can be determined by mapping the crystal phase by EBSD using SEM and image analysis, as with the average aspect ratio and average minor axis diameter of the β-sialon particles described above. . For each of the 50 cubic sialon particles arbitrarily extracted from the mapping diagram, the Haywood diameter is obtained using image analysis software, and the average value of the 50 Haywood diameters is defined as the average particle diameter.

In the above sialon-based sintered body, the peak intensity I _{C (311)} of the (311) plane of cubic sialon and the peak intensity I _{β (200)} of the (200) plane of β-type sialon in X-ray diffraction. The ratio I _{C (311)} / (I _{C (311)} + I _{β (200)} ) is preferably 0.2 or more and 0.9 or less. At this time, the sialon-based sintered body of the present invention was subjected to surface grinding using a No. 400 diamond grindstone, and a cubic crystal was obtained from an X-ray diffraction pattern obtained by measuring the surface ground surface using Cu- _Kα characteristic X-rays. The peak intensity I _{C (311)} of the (311) plane of the type sialon and the peak intensity I _{β (200)} of the (200) plane of the β type sialon can be obtained. When I _{C (311)} / (I _{C (311)} + I _{β (200)} ) is defined as Rc, Rc indicates the ratio of cubic sialon contained in the sialon-based sintered body of the present invention. When Rc is less than 0.2, the ratio of cubic sialon particles contained in the sialon-based sintered body is small, and it becomes difficult to obtain a sufficient increase in hardness compared to the β-type sialon sintered body. On the other hand, if Rc exceeds 0.9, the ratio of columnar β-type sialon particles contained in the sialon-based sintered body is reduced, and the toughness is lowered, which is not preferable.

  For a tool used for high-speed finishing of a heat-resistant alloy that easily causes tool wear, it is preferable to use a material that places importance on the hardness of Rc in the range of 0.4 to 0.9. On the other hand, it is preferable to use a material with an emphasis on toughness in the range of Rc of 0.2 to 0.6 for a tool used for rough machining with an emphasis on fracture resistance.

The sialon-based sintered body preferably further includes the following (a) and / or (b) as the third compound.
(A) A compound of at least one element selected from the group consisting of aluminum, boron, silicon, titanium, iron and nickel and at least one element selected from the group consisting of carbon, nitrogen and oxygen.
(B) A compound of at least two elements selected from the group consisting of aluminum, boron, silicon, titanium, iron, and nickel.

  This is because such a third compound functions as a binder for cubic sialon particles and β-sialon particles, thereby further strengthening the bond between the cubic sialon particles and β-sialon particles. In addition, when the third compound itself is a substance having high toughness, the toughness of the sialon-based sintered body in which the third compound is dispersed is also improved.

  At this time, the content of the third compound is preferably 10% by volume or more and 50% by volume or less of the sialon-based sintered body. This is because when the content of the third compound is less than 10% by volume, the effect of adding the third compound cannot be sufficiently obtained as compared with the case where the third compound is not added. On the other hand, if the content of the third compound exceeds 50% by volume, the sialon-based sintered body inherently has a low reactivity with metals in addition to a decrease in hardness with a decrease in the content of cubic sialon particles. This is not preferable because the features of are lost.

  The third compound is subjected to impact synthesis compression using columnar β-sialon powder as a starting material to obtain powder containing equiaxed cubic sialon particles and columnar β-sialon particles, and then sintered. A predetermined amount is added and mixed in the state of powder before. When X-ray diffraction is performed before and after sintering, there is no significant change in the peak intensity ratio of cubic sialon, β-sialon and third compound, and the volume ratio of the third compound added in the powder state is It was confirmed that the body was maintained as it was. In addition to the above X-ray diffraction, the mirror-polished sintered body cross section is observed by SEM, and the elements constituting the crystal particles are examined using EDX (Energy Dispersive X-ray spectrometry). The volume ratio of the third compound contained in the sialon-based sintered body can also be specified by determining the area ratio by specifying the particles of the three compounds and regarding it as the volume ratio.

In the sialon-based sintered body of the present invention, it is preferable that the Vickers hardness is 22 GPa or more and the fracture toughness value is 5 MPa · m ^1/2 or more. Usually, a β-type sialon sintered body has a Vickers hardness of about 17 GPa and a fracture toughness value of about 6 MPa · m ^1/2 . When a cutting tool made of such a β-sialon sintered body is used to cut a heat-resistant alloy such as Inconel, which is a difficult-to-cut material, sufficient wear resistance as a tool cannot be obtained. On the other hand, when cubic sialon particles are contained as in the sialon-based sintered body of the present invention, when the Vickers hardness of the sintered body is 22 GPa or more, a heat-resistant alloy such as Inconel, which is a difficult-to-cut material, is used. On the other hand, it has sufficient wear resistance as a tool. At this time, if the fracture toughness value of the sialon-based sintered body is less than 5 MPa · m ^1/2 , it becomes difficult to ensure sufficient fracture resistance as a tool, so the fracture toughness of the sialon-based sintered body of the present invention The value is preferably 5 MPa · m ^1/2 or more. In the sialon-based sintered body of the present invention, the reduction in fracture toughness value due to the inclusion of cubic sialon particles having a high hardness but brittleness, columnar β-sialon particles in the sintered body It is suppressed by coexisting.

The Vickers hardness of the sialon-based sintered body of the present invention is determined by polishing a sintered body embedded in a bakelite resin for 30 minutes using 9 μm and 3 μm diamond abrasive grains, respectively, and then applying a Vickers hardness meter ( Measurement was performed by pushing a diamond indenter with a load of 10 kgf using AKASHI (HV-112). The Vickers hardness _Hv10 was determined from the indentation generated by pressing the diamond indenter. Furthermore, the crack length propagating from the indentation was measured, and the fracture toughness value was determined by the IF method in accordance with JIS R 1607 (room temperature fracture toughness (toughness test method for fine ceramics)).

  The second aspect of the present invention is a cutting tool using the above sialon-based sintered body. In the sialon-based sintered body of the present invention, taking advantage of the original characteristics of sialon that the reactivity with metal is low, the hardness is increased by equiaxed cubic sialon particles, and the toughness by columnar β-sialon particles Therefore, it can be suitably used as a tool used for applications such as cutting of heat-resistant alloys such as Inconel, which is a difficult-to-cut material. And when it uses for such a use, compared with the tool made from the conventional (beta) type sialon sintered compact, abrasion resistance and a fracture resistance can be improved significantly.

  An embodiment of the method for producing a sialon-based sintered body according to the third aspect of the present invention will be described below in the order of steps.

(Process of synthesizing columnar β-type sialon powder)
_{Si 6-Z Al Z O Z} N 8-Z (Z is greater than 0, 4.2 or less number) Upon synthesizing β-sialon represented by the chemical _formula, starting carbon and SiO 2, _Al 2 _{O 3} When synthesized using a carbon reductive nitriding method under a general nitrogen atmosphere at atmospheric pressure as a raw material, the β-sialon powder particles obtained are equiaxed crystals. On the other hand, for example, by using a high temperature nitriding synthesis method that applies a nitriding reaction of metal silicon under a nitrogen atmosphere at atmospheric pressure or higher, represented by the following formula (I), the synthesis temperature of sialon is changed to β-type sialon particles. Therefore, β-sialon powder in which hexagonal columnar crystals grow in the c-axis direction can be obtained.

3 (2-0.5Z) Si + ZAl + 0.5ZSiO ₂ + (4-0.5Z) N ₂
→ Si _6-Z Al _Z O _Z N _8-Z (I)
Si powder (average particle size 0.5 to 45 μm, purity 96% or more, more preferably 99% or more), SiO ₂ powder (average particle size 0.1 to 20 μm) and Al powder (average particle size 1 to 75 μm) Are weighed according to a desired Z value, and then mixed with a ball mill, a shaker mixer or the like to prepare a raw material powder for β-sialon synthesis. At this time, in addition to the above formula (I), it is also possible to use an appropriate combination of AlN or Al ₂ O ₃ as the Al component. When synthesizing β-sialon, if the synthesis temperature is 3000 ° C. or higher, β-sialon is decomposed and Al or Si is precipitated, and β-sialon having a desired composition may not be synthesized. In order to suppress such decomposition, for the purpose of adjusting the synthesis reaction and temperature, it is effective to add in advance a diluting component such as ceramic powder such as TiN or NaCl powder that can be removed in a subsequent process. If the pressure of the nitrogen gas is less than 1 MPa or the synthesis temperature is less than 2000 ° C., the desired columnar β-sialon powder may not be obtained or the nitriding reaction may not occur. The temperature for synthesizing the β-sialon powder having a columnar crystal with little necking and high aspect ratio is preferably 2300 to 2700 ° C. Further, the pressure of the nitrogen gas filled in the vessel for synthesizing β-sialon is preferably 1.5 MPa or more, and in order to promote the growth of columnar crystals, the synthesis is performed under a nitrogen gas pressure of 3 MPa or more. preferable. As a synthesis apparatus that can withstand such gas pressure, a combustion synthesis apparatus or a HIP (Hot Isostatic Pressing) apparatus is suitable.

  When β-sialon is synthesized as described above, an agglomerated powder in which the particles are necked together is obtained, and it is necessary to break up the agglomeration. If the agglomerated powder is pulverized for a long time using a media grinding process such as a ball mill or an attritor, the columnar crystals may be overmilled to become equiaxed crystals. Control of methods and conditions is important. For the crushing, a wet ball mill having a relatively small crushing force is suitable in the media crushing process. For example, after blending the synthetic powder and the solvent so that the solid content ratio of the slurry is 20 to 80% by mass, using a silicon nitride or alumina ball having a diameter of about 1 to 10 mm as a medium for 2 to 10 hours It is preferable to break up the agglomeration by ball milling.

  A more preferable crushing method is to use a medialess crushing process that does not involve crushing of powder particles, such as an ultrasonic homogenizer or a wet jet mill. For example, a slurry prepared by mixing the synthetic powder and the solvent so that the solid content ratio is 10 to 50% by mass is processed by a wet jet mill at a flow rate of Mach of 0.8 or more for 3 passes or more to form a β-type columnar crystal A slurry in which sialon powder is monodispersed can be obtained. For the jet mill, a collision plate type apparatus that collides the slurry with the diamond or ceramic sintered body may be used. In that case, aggregation can be crushed even if the injection pressure is reduced to 0.5 to 1.5 MPa. In addition, a medialess crushing process may be performed after the synthetic powder is preliminarily wet dispersed by a ball mill.

  In crushing, it is preferable to adjust the crushing conditions so that the half width of the X-ray diffraction peak of the (101) plane of the β-sialon powder after crushing is 0.35 ° to 2.0 °. . This is because if the half width is less than 0.35 °, phase transformation to cubic sialon is promoted in the subsequent impact synthetic compression process, and β-sialon having a desired columnar crystal may not remain. . Moreover, in the β-sialon refined until the half width exceeds 2.0 °, a desired cubic sialon may not be synthesized due to oxidation accompanying an increase in specific surface area.

  By performing high-temperature nitridation synthesis and crushing as described above, columnar β-sialon powder suitable as a starting material for the synthesis of cubic sialon can be obtained. In a 10,000 times electronic image taken using SEM or TEM, the average short axis diameter of 500 powder particles extracted arbitrarily is 0.2 to 10 μm, and the average long axis diameter is short. The aspect ratio obtained by dividing by the average value of the shaft diameter is 2 or more.

(Process of synthesizing cubic sialon powder)
The columnar β-sialon powder obtained as described above is treated at a temperature of 1800 ° C. or more and 2000 ° C. or less and a pressure of 40 GPa or more and 60 GPa or less to partially transform it into cubic sialon. Can be made. For example, when an impact compression process is used for the above-mentioned treatment, by setting the impact pressure to about 40 GPa and the temperature to 1800 to 2000 ° C., equiaxed cubic sialon and columnar β-sialon are mixed. Powder is obtained.

  In a 50,000-fold electron image obtained by imaging the treated powder using a TEM, equiaxed grains having a grain size of about 0.05 to 5 μm, a minor axis diameter of about 0.2 to 10 μm, and an aspect ratio of 2 The above columnar grains were observed. It was confirmed by diffraction analysis that the equiaxed grains were cubic sialon and the columnar grains were β sialon.

(Mixing process)
The following powder (a) and / or (b) is added and mixed as the third compound to the above-described treated powder containing cubic sialon and β-sialon.
(A) A compound of at least one element selected from the group consisting of aluminum, boron, silicon, titanium, iron and nickel and at least one element selected from the group consisting of carbon, nitrogen and oxygen.
(B) A compound of at least two elements selected from the group consisting of aluminum, boron, silicon, titanium, iron, and nickel.

  The third compound is preferably added in the range of 10 to 50% by volume of the sialon-based sintered body. This is because by adding 10% by volume or more of the third compound, improvement in the toughness of the sintered body due to particle dispersion can be expected, and if the addition is 50% by volume or less, the hardness will not be greatly reduced.

  As the powder of the third compound, titanium nitride powder having an average particle size of about 0.05 to 2 μm, aluminum nitride powder having an average particle size of about 0.05 to 2 μm, cubic boron nitride having an average particle size of about 0.1 to 3 μm Powder, silicon carbide powder having an average particle size of about 0.1 to 3 μm, TiAl powder having an average particle size of about 0.5 to 10 μm, FeAl powder having an average particle size of about 0.5 to 10 μm, average particle size of 0.5 to 10 μm About NiAl powder or the like is preferably used.

  In mixing, silicon nitride or alumina balls having a diameter of about 3 to 10 mm are used as media, and ball mill mixing is performed for a short time within 12 hours in a solvent such as ethanol, or an ultrasonic homogenizer or a wet jet mill. By mixing using the medialess mixing apparatus, a mixed slurry in which cubic sialon powder, β-sialon powder and third compound powder are uniformly dispersed can be obtained. In particular, it is preferable to use a medialess mixing device from the viewpoint of maintaining a high aspect ratio without crushing columnar β-sialon powder. In addition, when adding a plurality of third compound powders, a slurry in which only the third compound powders are sufficiently mixed in advance using a ball mill or a bead mill is added to the sialon powders for short-time ball mill mixing or medialess mixing. It is effective to do.

  The slurry obtained as described above is dried by natural drying, a spray dryer or a slurry dryer to obtain a mixed powder.

(Sintering process)
The mixed powder is molded using a hydraulic press or the like, and then sintered in a temperature range of 1200 to 1800 ° C. under a pressure of 3 to 7 GPa using a high pressure generator such as a belt-type ultrahigh pressure press. Prior to sintering, it is also possible to pre-sinter the compact of the mixed powder and to sinter the compacted product to some extent. Moreover, it can also sinter by hold | maintaining for a time shorter than about 5 minutes in the temperature range of 1200-1600 degreeC under the pressure of 30-200 MPa using a pulse electric current sintering apparatus (SPS).

Example 1
Si powder (product of high-purity chemical, product name: SIE19PB, purity 99%, particle size 45 μm or less), Al powder (product of Minalco, product name: 300 A, particle size 45 μm or less) and SiO ₂ powder (manufactured by Denki Kagaku Kogyo, product name: FB) Β-sialon powder was synthesized according to the above formula (I) using -5D and an average particle diameter of 5 μm. As the composition of this case β-sialon is synthesized _{(Si 6-Z Al Z O} Z N 8-Z) becomes Z = 1, and a starting material by blending the Si powder, Al powder and SiO2 powder.

  200 g of NaCl powder added to 200 g of the starting material for the purpose of reaction dilution and temperature adjustment is put into a nylon pot containing 500 g of φ6 mm silicon nitride balls, and dry-mixed for 30 minutes with a shaker mixer. A mixed powder for high-temperature nitriding synthesis was prepared.

  Using a combustion synthesizer or HIP device, β-sialon was produced from the mixed powder by a high temperature nitriding synthesis method.

  Sample No. 1-1 to 1-11 and 1-14 produced β-sialon using a combustion synthesizer. After leaving the mixed powder in a porous carbon crucible having a capacity of 500 ml, pellets of Ti powder (made by Toho Titanium, product name: TC450, particle size of 45 μm or less) embossed into a shape having a diameter of 20 mm and a thickness of 5 mm are obtained. Then, it was set on the mixed powder as an ignition material. After the crucible was placed on the stage in the combustion synthesizer, an ignition source tungsten wire (made by Allied Material, wire diameter φ0.5 mm) was attached between the electrodes. After evacuating the inside of the combustion synthesis apparatus using a rotary pump, JIS class 2 high-purity nitrogen gas (purity 99.99 vol% or more) was introduced, and the nitrogen gas pressure in the apparatus was increased to 3 MPa. In starting the synthesis reaction, the tungsten wire is incandescent by increasing the voltage between the electrodes to ignite the titanium pellets, and the reaction heat propagates to the mixed powder, thereby causing a self-combustion reaction of β-sialon. I let you. At this time, the reaction temperature measured using a two-color radiation thermometer was 2500 ° C.

  Sample No. 1-12 and 1-13 produced β-sialon using a HIP device. The mixed powder was left in a carbon cylindrical crucible having a capacity of 100 ml, and then the crucible was set in an HIP apparatus. After evacuating the inside of the HIP apparatus using a vacuum pump, JIS class 2 high-purity nitrogen gas (purity 99.99 vol% or more) was introduced, and the nitrogen gas pressure in the HIP apparatus was increased to 20 MPa. In starting the synthesis reaction, the heater temperature was raised to 2500 ° C., and the Joule heat was propagated to the mixed powder, thereby causing β-sialon self-combustion reaction. The reaction temperature measured using a thermocouple installed in the vicinity of the heater was 2700 ° C.

The reaction product synthesized as described above was taken out from the apparatus, and after agglomeration was pulverized in an alumina mortar, NaCl was removed in pure water. X-ray diffractometer (Panalytic X'Pert Powder, Cu-Kα line, 2θ-θ method, voltage × current: 45 kV × 40 A, measurement range: 2θ = 10 to 80 °, scan step: 0.03 °, scan As a result of identifying the crystal phase of the reaction product after NaCl removal, all diffraction peaks were consistent with β-type Si ₅ AlON ₇ (JCPDS card: 01-077-0755). From this, it was judged that a β-type sialon with Z = 1 could be synthesized. As a result of SEM observation of this β-sialon powder, it was confirmed that the powder particles were growing in a needle shape.

  Since β-sialon powder synthesized by high-temperature nitriding is agglomerated, it was coarsely pulverized in an alumina mortar until the secondary particles became 150 μm or less, and then agglomerated using a ball mill, an attritor, or a wet jet mill.

  Sample No. 1-1 to 1-5, 1-12 and 1-14 were crushed using a ball mill. 200 g of β-sialon powder synthesized by high-temperature nitriding, 600 ml of ethanol, and 2 kg of φ5 mm silicon nitride balls are sealed in a 2 liter polystyrene pot, and wet ball milling is performed for 1 to 15 hours as shown in Table 1, respectively. A dispersion slurry was obtained.

  Sample No. In 1-6 to 1-8, aggregation was crushed using an attritor. Using slurry in which 200 g of β-sialon powder synthesized by high-temperature nitridation in 500 ml of ethanol is dispersed, as shown in Table 1, attritors (agitator peripheral speed 50 m / min, cemented carbide ball φ3 mm, cemented carbide) The slurry was prepared by crushing for 0.5 to 5 hours using an agitator.

  Sample No. 1-9 to 1-11 and 1-13 were crushed using a wet jet mill. Using a slurry in which 200 g of β-sialon powder synthesized by high-temperature nitridation in 2 liters of ethanol is dispersed, a wet jet mill (slurry flow rate Mach 1 during injection) is passed through 1 to 5 passes as shown in Table 1, respectively. Adjusted.

  Each of the above-mentioned slurries was naturally dried, and then the dried powder was passed through a sieve having an opening of 45 μm to obtain a raw material for impact synthesis of cubic sialon. Sample No. As a result of SEM observation of the powders crushed under the conditions of 1-1 to 1-7 and 1-9 to 1-14, β-sialon powder particles of columnar crystals were confirmed. In 1-8, columnar powder particles were not confirmed, and only equiaxed powder particles were observed. In addition, when the crystal structure of the powder after pulverization was analyzed using the same X-ray diffractometer used to identify the crystal phase of the β-sialon powder before pulverization, In the sample, the half-value width of the X-ray diffraction line on the (101) plane of the β-type sialon powder was in the range of 0.35 ° to 2.0 °.

After crushing and sieving, β-sialon powder is mixed with copper powder as a heat sink. By compressing, cubic sialon was synthesized. After impact compression, the mixed powder in the steel pipe was taken out, and copper powder was removed by acid cleaning to obtain a synthetic powder. When the synthetic powder was analyzed using the same X-ray diffractometer as used to identify the crystalline phase of the β-sialon powder before pulverization described above, cubic Si ₅ AlON ₇ (JCPDS card: 01-074-3494) and β-type Si ₅ AlON ₇ were identified.

  As a result of TEM observation of the synthetic powder, Sample No. In 1-1 to 1-7 and 1-9 to 1-13, columnar crystal particles and equiaxed crystal particles having a particle size of 5 μm or less were mixed. On the other hand, Sample No. In 1-8, all the powder particles were equiaxed crystals. When the crystal structure of each particle was identified using the TEM fraction, sample no. The equiaxed crystal particles observed in 1-1 to 1-7 and 1-9 to 1-13 are cubic crystals, and the columnar crystal particles are β-type crystals. It was confirmed that the equiaxed crystal particles observed in 1-8 are cubic crystals and β-type crystals.

  Sample No. For each of 1-1 to 1-13, after weighing 22.5 g of the synthetic powder and 7.5 g of TiN powder (manufactured by Shin Nippon Metal Co., Ltd., product name: TiN-01, average particle size: 1 μm), 60 ml of ethanol Along with 200 g of silicon nitride balls having a diameter of 5 mm and a polystyrene pot having a capacity of 150 ml, the mixture was ball milled for 3 hours to prepare a slurry. After the slurry taken out from the pot was naturally dried, a powder for sintering was produced through a sieve having an opening of 45 μm.

  For comparison, Sample No. The β-sialon powder 22.5 g which was synthesized by high-temperature nitriding under the same conditions as in 1-3, crushed and sieved was used as it was without impact compression, and 7.5 g of the TiN powder was added thereto. As in 1-3, ball mill mixing, natural drying and sieving were conducted. 1-14 powder for sintering was produced.

  Sample No. manufactured as described above was used. The powder for sintering 1-1 to 1-14 was vacuum sealed in a refractory metal capsule having a diameter of 20 mm, and then heated to 1500 ° C. while being pressurized to 6 GPa using a belt type ultra-high pressure press. Thus, a sintered body was produced.

After the surface of the sintered body is ground polished using a No. 400 diamond grindstone, the above-mentioned grinding is performed using the same apparatus used for identifying the crystal phase of the β-sialon powder before pulverization described above. Surface X-ray diffraction was performed. From the obtained diffraction pattern, the peak intensity I _{C (311)} of the (311) plane of cubic sialon and the peak intensity I _{β (200)} of the (200) plane of β-type sialon are obtained, and the intensity ratio Rc ( IC ₍₃₁₁₎ / (IC ₍₃₁₁₎ + I [ _{beta] (200)} )) was calculated. The results are shown in Table 1. Sample No. 5 was sintered using β-sialon powder synthesized by high-temperature nitriding without impact compression. In 1-14, Rc was 0.

  In order to obtain crystal grain sizes of cubic sialon and β-sialon contained in the sintered body, EBSD analysis of each sintered body was performed. First, the end surface of the sample for tissue observation cut out from the sintered body was subjected to argon ion etching using a CP processing machine (manufactured by JEOL Ltd., SM-09020CP) to smooth the sample end surface. The sample end face was observed at a magnification of 10,000 using an FE-SEM (manufactured by JEOL, JSM-7000F), and the crystal phase of the observation surface was mapped using an EBSD apparatus (manufactured by TSL, OIM-TM5.2). Went. As parameters for analysis, for cubic sialon, space group: Fd3m (cubic), lattice constant a = 0.78 nm, and for β-type sialon, space group: P63 (hexagonal), lattice constant a = 0.76 nm. , C = 0.29 nm was input. Using the difference in crystal orientation from the obtained mapping diagram, the grain boundaries of cubic sialon and β sialon are identified, and each of the 50 cubic sialon particles arbitrarily extracted is image analysis software (Winroof , Mitani Corporation) was used to determine the Haywood diameter, and the average value of the 50 Haywood diameters was taken as the average particle diameter of the cubic sialon particles. Further, for each of the arbitrarily extracted 50 β-type sialon particles, the minor axis diameter and the major axis diameter are obtained using image analysis software, and the average value of the 50 minor axis diameters is calculated as the average minor axis diameter, 50 particles. The average value of the major axis diameter was taken as the average major axis diameter. The average aspect ratio was calculated by dividing the average major axis diameter by the average minor axis diameter. The results are shown in Table 1.

Vickers hardness and fracture toughness were measured as mechanical property evaluation of the sintered body. The sintered body embedded in the bakelite resin was polished with 9 μm and 3 μm diamond abrasive grains for 30 minutes using a lapping machine manufactured by Musashino Electronics Co., Ltd., and then a Vickers hardness tester (manufactured by AKASHI, HV-112) Was used to indent a diamond indenter with a load of 10 kgf, and Vickers hardness _Hv10 was determined from the resulting indentation. Furthermore, the crack length propagating from the indentation was measured, and the fracture toughness value was determined by the IF method in accordance with JIS R 1607 (room temperature fracture toughness (toughness test method for fine ceramics)). The results are shown in Table 1.

  Next, the sintered body was processed into a CNGA12041 type brazing tip shape (blade edge treatment: chamfer shape with an angle of -20 ° and a width of 0.1 mm), and turning of Inconel 718 (Daido Special Metal Co., Ltd., registered trademark). Tool life in machining was evaluated. The outer diameter cylindrical turning test is performed under the following conditions. The cutting distance at which the flank wear amount of the tool edge reaches 0.2 mm is the wear life (km), and the cutting distance at which the defect amount reaches 0.2 mm is the defect life (km). The tool life (km) was defined as the smaller one of the wear life and the defect life. The results are shown in Table 1.

<Cutting conditions>
· Workpiece: Inconel 718 (溶態reduction and aging treatment material, Rockwell hardness _H RC = 45 equivalent)
・ Tool shape: CNGA120212 (ISO model number)
・ Cutting speed: 200 m / min ・ Incision: 0.5 mm
・ Feeding speed: 0.15mm / rev
・ Wet conditions (water-soluble oil)
For comparison, Sample No. As 1-15, a commercially available β-type sialon ceramic tool (manufactured by SANDVIK, CC6060) was evaluated. Evaluation was made with sample no. In the same manner as 1-1 to 1-14, the peak intensity ratio Rc of X-ray diffraction, the average minor axis diameter and average aspect ratio of β-type sialon particles, Vickers hardness and fracture toughness, wear life, fracture life and tool life It was measured. The results are shown in Table 1.

Sample No. In 1-1, since the time of the ball mill for crushing agglomeration after high-temperature nitridation synthesis of β-sialon powder was short, coarse columnar crystals β having an average minor axis diameter exceeding 10 μm in the sintered body Type sialon particles existed, and the number of columnar β-type sialon particles present in the sintered body decreased, and stress concentration occurred in coarse particles and cracks developed. As a result, the fracture toughness value stopped at 4.8 MPa · m ^1/2, and the chipping occurred at the cutting distance of 0.2 km, reaching the tool life.

Sample No. In 1-5, after β-sialon powder was subjected to high-temperature nitriding synthesis and then agglomeration was crushed, a long-time ball mill was performed, so that the average minor axis diameter of columnar β-sialon particles in the sintered body was It became smaller than 0.2 μm. As a result, the fracture toughness value was only 4.6 MPa · m ^1/2, and chipping occurred at a cutting distance of 0.2 km to reach the tool life.

  Sample No. In 1-6, the average particle size of cubic sialon particles in the sintered body was 5 μm because the time of the attritor for crushing agglomeration after high-temperature nitriding synthesis of β-sialon powder was short. It became too coarse. As a result, the Vickers hardness stopped at 20.2 GPa, and the tool life was reached due to wear at a cutting distance of 0.2 km.

Sample No. In 1-8, β-sialon particles in the sintered body were impact-synthesized using β-sialon powder that was over-pulverized at the time of crushing the aggregate after high-temperature nitriding synthesis as a raw material. The average aspect ratio of was less than 2. As a result, the fracture toughness value stopped at 4.8 MPa · m ^1/2, and the chipping occurred at the cutting distance of 0.2 km, reaching the tool life.

  Sample No. In 1-9, since the number of passes of a wet jet mill for crushing agglomeration after high-temperature nitriding synthesis of β-sialon powder was small, the peak intensity ratio Rc of the X-ray diffraction of the sintered body was smaller than 0.2. became. As a result of the small proportion of cubic sialon contained in the sintered body, the Vickers hardness was only 21.7 GPa, and the tool life was reached due to wear at a cutting distance of 0.3 km.

Sample No. In No. 1-11, since the number of passes of a wet jet mill for crushing agglomeration after high-temperature nitridation synthesis of β-sialon powder was high, the peak intensity ratio Rc of the X-ray diffraction of the sintered body was larger than 0.9. became. As a result of the small proportion of β-sialon of the columnar crystals contained in the sintered body, the fracture toughness value was only 4.6 MPa · m ^1/2, and chipping occurred at a cutting distance of 0.2 km, reaching the tool life.

  On the other hand, after processing the columnar β-sialon powder synthesized by high-temperature nitriding under more preferable crushing conditions, sample no. In 1-2 to 1-4, 1-7, 1-10, 1-12, and 1-13, Vickers hardness and fracture toughness can be well balanced, resulting in tool life due to wear or fracture. The cutting distance could be extended to 0.4 km or more.

  On the other hand, in the sintered body, sample No. 1 containing only columnar β-type sialon particles and no hard cubic sialon particles. 1-14 and 1-15 had small Vickers hardness of 17.2 GPa and 16.7 GPa, respectively, and both reached the tool life due to wear at a cutting distance of 0.1 km.

(Example 2)
Sample No. 1 of Example 1 Using a synthetic powder containing equiaxed cubic sialon and columnar β-sialon produced under the same conditions as in 1-3, various third compound powders were added thereto to produce sintered bodies. . As the powder of the third compound, TiN, AlN, cBN, SiC, TiAl, FeAl, and NiAl powder each having an average particle diameter of 1 μm were used.

  The synthetic powder and the third compound powder are added so that the third compound powder is contained in a ratio shown in Table 2 in a total weight of 20 g of the sintering powder including the synthetic powder and the third compound powder. After weighing, it was put into a polystyrene pot having a capacity of 150 ml together with 60 ml of ethanol and 200 g of φ5 mm silicon nitride balls, and ball mill mixing was performed for 3 hours to prepare a slurry. The slurry taken out from the pot was naturally dried, and then passed through a sieve having an opening of 45 μm. Powders for sintering 2-1 to 2-11 were prepared.

  Sample No. The powders for sintering of 2-1 to 2-11 were sample No. 1 of Example 1, respectively. Sintering was performed under the same conditions as in 1-3. As a result of X-ray diffraction before and after sintering, there was no significant change in the peak intensity ratio of cubic sialon, β-sialon and third compound, and the volume ratio of the third compound added in the powder state was It was confirmed that it was maintained as it was even in the ligation.

  The obtained sample No. Each of the sintered bodies of 2-1 to 2-11 was sample No. 1 of Example 1. Evaluated by the same method as 1-3, peak intensity ratio Rc of X-ray diffraction, average particle diameter of cubic sialon particles, average minor axis diameter and average aspect ratio of β-type sialon particles, Vickers hardness, fracture toughness, The wear life, chip life and tool life were determined. The results are shown in Table 2.

Sample No. In 2-1, since the content of the third compound is less than 10% by volume, and the bond between the cubic sialon particles and the β sialon particles becomes weak, the fracture toughness value is 4.8 MPa · m ^1/2. However, the chipping occurred at a cutting distance of 0.2 km and the tool life was reached.

  Sample No. In 2-5, the content of the third compound exceeds 50% by volume, and the Vickers hardness stops at 21.7 GPa with the decrease in the content of cubic sialon particles. Since the original characteristic of the sialon-based sintered body, which is low in reactivity, is lost, wear occurs at a cutting distance of 0.2 km, leading to the tool life.

  On the other hand, Sample No. in which the content of the third compound is in the range of 10 to 50% by volume. In 2-2 to 2-4 and 2-6 to 2-11, the tool life was 0.6 km or more, and good results were obtained.

  The embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The technical scope of the present invention is shown not by the above description but by the scope of claims, and includes all modifications within the scope equivalent to the scope of claims.

  The sialon-based sintered body of the present invention is low in reactivity with metals by combining hard equiaxed cubic sialon particles and columnar β-sialon particles that suppress the growth of cracks. In addition to the original features of Sialon, we provide tool materials that have both hardness and fracture toughness. In the examples, the effect of the present invention in cutting Inconel was disclosed, but the sialon-based sintered body of the present invention has excellent resistance to cutting difficult-to-cut materials such as Ti in addition to heat-resistant alloys such as Inconel. Exhibits wear and fracture resistance, and is particularly applicable to high-speed cutting.

Claims (9)

  A sialon-based sintered body comprising equiaxed cubic sialon particles and columnar β-sialon particles.   2. The sialon-based sintered body according to claim 1, wherein the columnar crystal β-type sialon particles have an average aspect ratio of 2 or more and an average minor axis diameter of 0.2 μm or more and 10 μm or less.   3. The sialon-based sintered body according to claim 1, wherein the equiaxed cubic sialon particles have an average particle size of 0.05 μm to 5 μm. Ratio I _{C (311)} / (I _C ) of peak intensity I _{C (311)} of (311) plane of cubic sialon and peak intensity I _{β (200)} of (200) plane of β-type sialon in X-ray diffraction ₍₃₁₁₎ + _{Iβ (200)} ) is 0.2 or more and 0.9 or less, The sialon-based sintered body according to any one of claims 1 to 3. The sialon-based sintered body according to any one of claims 1 to 4, further comprising the following (a) and / or (b) as the third compound.
(A) A compound of at least one element selected from the group consisting of aluminum, boron, silicon, titanium, iron and nickel and at least one element selected from the group consisting of carbon, nitrogen and oxygen.
(B) A compound of at least two elements selected from the group consisting of aluminum, boron, silicon, titanium, iron, and nickel.   The sialon-based sintered body according to claim 5, wherein the content of the third compound is 10% by volume or more and 50% by volume or less. The sialon-based sintered body according to any one of claims 1 to 6, having a Vickers hardness of 22 GPa or more and a fracture toughness value of 5 MPa · m ^1/2 or more.   A cutting tool using the sialon-based sintered body according to claim 1. A powder containing columnar crystal β-sialon particles having an average aspect ratio of 2 or more and an average minor axis diameter of 0.2 μm to 10 μm at a temperature of 1800 ° C. to 2000 ° C. and a pressure of 40 GPa to 60 GPa. Processing to produce a mixed powder comprising equiaxed cubic sialon particles and columnar β sialon particles;
Sintering the mixed powder at a temperature of 1200 ° C. or higher and 1800 ° C. or lower;
A method for producing a sialon-based sintered body.