WO2016084929A1 - Sintered object based on cubic boron nitride, and cutting tool constituted of sintered object based on cubic boron nitride - Google Patents

Abstract

A sintered object based on cubic boron nitride, the sintered object including 70-95 vol% cubic boron nitride grains. When the structure of a cross-section of the sintered object is examined, a binder phase having a width of 1-30 nm is observed between adjacent cubic boron nitride grains, the binder phase being constituted of a compound containing at least Al, B, and N, the ratio of the oxygen content to the Al content in the binder phase being 0.1 or less (in terms of atomic ratio).

Description

Cubic boron nitride-based sintered body and cutting tool made of cubic boron nitride-based sintered body

The present invention relates to a cubic boron nitride (hereinafter sometimes referred to as “cBN”)-based sintered body (hereinafter also referred to as “cBN sintered body”) having high hardness.
This application claims priority based on Japanese Patent Application No. 2014-240418 filed in Japan on November 27, 2014, and Japanese Patent Application No. 2015-229737 filed in Japan on November 25, 2015, and its contents Is hereby incorporated by reference.

cBN sintered body is a tool for cutting iron-based work materials such as steel and cast iron because it has the second highest hardness and thermal conductivity after diamond and has low affinity with iron-based materials. As such, it has been conventionally used favorably.
In order to improve the performance as a cutting tool, some proposals have been made so far in order to further improve the strength, toughness, hardness and the like of the cBN sintered body.

For example, Patent Document 1 discloses that when a cBN sintered body is produced by ultra-high pressure sintering, a binder phase is a skeleton structure, cBN particles which are hard particles in a binder phase structure, Al boride and nitride, and It has been proposed to improve the strength and toughness of a cBN sintered body by forming a structure in which a reaction product made of Ti boride is dispersed and distributed.

Further, in Patent Document 2, in the cBN sintered body, in order to remove oxygen adsorbed on the surface of the cBN grains when the cBN particles are combined, Ti and Al are used as raw materials to act as oxygen getters, Prevents alteration of cBN particles due to solid solution of oxygen inside the cBN grains, and forms a structure having a continuous structure in which the cBN particles are bonded to each other and a bonded structure in which the bonded phases are bonded to each other. By doing so, it has been proposed to achieve both improvement in heat resistance and improvement in toughness of the cBN sintered body.

JP-A-8-197307 Japanese Patent No. 5032318

Although proposals have been made to improve the characteristics of the cBN sintered body as shown in Patent Documents 1 and 2, it cannot be said that it is sufficient.
For example, a cBN sintered body for a cutting tool disclosed in Patent Document 1 has a binder phase as a skeleton structure, cBN particles which are hard particles in a binder phase structure, Al boride and nitride, and Ti boride. It has a structure in which a reaction product consisting of is distributed and distributed. When a cBN sintered body having such a structure is used as a cutting tool, if the cBN content in the sintered body is increased in order to apply to cutting conditions with a high load on the cutting edge, the cBN particles are brought into contact with each other and bonded. More unsintered parts that cannot react sufficiently with the phase. Since this unsintered portion has lower strength than the portion where the cBN grains and the binder phase are in contact with each other, there is a problem that the hardness according to the cBN content cannot be obtained as the cBN content increases. It was. In addition, when such a cBN sintered body having insufficient hardness is used as a tool, cracks starting from the portions where the cBN grains are in contact with each other tend to occur. Therefore, when such a tool is used for intermittent cutting with a high load on the cutting edge, there is a problem that the cutting edge tends to be lost and the tool life is short.
Further, in the cBN sintered body shown in Patent Document 2, the influence of oxygen on the cBN particles themselves can be prevented, but oxides such as Ti having relatively low strength are present in the bonded phase structure as cBN particles and cBN particles. Therefore, there is a problem that a cBN sintered body having low hardness as a whole can be obtained.

In order to solve the above-mentioned problems, the present inventors paid attention to the binder existing between the cBN particles and the cBN particles, and conducted earnest research to improve the hardness of the cBN sintered body. As a result, the following knowledge was obtained. Obtained.

In the conventional cBN sintered body, cBN powder, which is a constituent component of cBN sintered body, is mixed with TiN powder, TiAl ₃ powder, Al ₂ O ₃ powder, etc., which are binder phase forming components, and these are mixed under ultra high pressure and high temperature conditions. It was made by sintering underneath.

The inventors have found the following. That is, in the production of the cBN sintered body, in order to use as a raw material cBN particles having a high surface cleanliness obtained by pretreating the surface of the cBN particles to be used, For example, ALD (Atomic Layer Deposition) is a method of forming a film by reacting a raw material compound molecule layer by layer with a substrate in a vacuum chamber and repeatedly purging with Ar or nitrogen, and is a kind of CVD method .)) A very thin AlN film is formed by the method or the like, and then heated under vacuum, and then a pretreatment including a step of peeling the AlN film by ball mill mixing is performed.
By applying such pretreatment to the cBN particles, cBN particles having a high surface cleanliness from which impurity components such as oxygen adhering to and adsorbing on the surface of the cBN particles are removed are obtained.
Then, when this cBN particle was used as a raw material and sintered under a super high pressure condition together with a binder phase forming component to produce a cBN sintered body, the oxygen content in the binder phase existing between the cBN particles and the cBN particles ( However, the value of the atomic ratio of the oxygen content to the Al content) becomes a small value, the oxide in the binder phase between the cBN particles and the cBN particles can be reduced, and a strong binder phase can be formed. There are fewer unsintered parts where the particles are in contact with each other and cannot sufficiently react with the binder phase.
As a result, the present inventors have found that, in the cBN sintered body of the present invention, a cBN sintered body having high hardness can be obtained even when the content ratio of cBN contained in the sintered body is increased. It was.

The present invention has been made based on the above findings,
“(1) In a cubic boron nitride-based sintered body containing 70 to 95 vol% of cubic boron nitride particles, when the cross-sectional structure of the sintered body was observed, the adjacent cubic boron nitride particles A binder phase having a width of 1 nm or more and 30 nm or less exists, the binder phase is composed of a compound containing at least Al, B, and N, and the ratio of the oxygen content to the Al content in the binder phase is A cubic boron nitride-based sintered body having an atomic ratio of 0.1 or less (however, the atomic ratio).
(2) In a cubic boron nitride-based sintered body containing 70 to 95 vol% of cubic boron nitride particles, when the cross-sectional structure of the sintered body is observed, There is a region having an interval of 30 nm or less, and the binder phase of the region is composed of a nitride containing either one or both of Al and B and an oxide of Al, and in the binder phase of the region A cubic boron nitride based sintered body characterized in that there is a region in which the ratio of the oxygen content to the Al content is 0.1 or less (however, the atomic ratio).
(3) In the cubic boron nitride-based sintered body, an average particle size of the cubic boron nitride particles is 0.5 to 8.0 μm, and a cross-sectional structure of the cubic boron nitride-based sintered body , When a field of view 5 times x 5 times the average particle diameter of the cubic boron nitride particles is taken as one field of view, the width between adjacent cubic boron nitride particles is The presence of the cubic boron nitride particles in which a binder phase of 1 nm to 30 nm is present and the ratio of the oxygen content to the Al content in the binder phase is 0.1 or less is the total number of viewing fields. The cubic boron nitride-based sintered body according to (1) or (2) above, which is observed in a field of view of 60% or more.
(4) When the cross-sectional structure of the cubic boron nitride-based sintered body is observed, the cubic boron nitride in which a binder phase having a width of 1 nm or more and 30 nm or less exists between the adjacent cubic boron nitride particles. Elementary particles are present in an average particle number ratio of 0.4 or more with respect to the total number of cubic boron nitride particles in the observation cross section, and between adjacent cubic boron nitride particles. In the cubic boron nitride particles in which a binder phase having a width of 1 nm to 30 nm is present, the ratio of the oxygen content to the Al content in the binder phase is 0.1 or less. The number is present at an average ratio of 0.5 or more with respect to the number of the cubic boron nitride particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between the adjacent cubic boron nitride particles. (1) No. characterized by A cubic boron nitride-based sintered body according to any one of (3) to (3).
(5) The binder phase having a width of 1 nm or more and 30 nm or less present between the cubic boron nitride particles is interspersed between the cubic boron nitride particles (1) The cubic boron nitride group sintered body according to any one of (4) to (4).
(6) A cubic boron nitride, wherein the cutting edge portion of the cutting tool is composed of the cubic boron nitride-based sintered body according to any one of (1) to (5). Cutting tool made of basic sintered body. "
It is characterized by.

The cBN sintered body of the present invention contains 70 to 95 vol% of cBN particles having an average particle diameter of preferably 0.5 to 8.0 μm, and when the cross-sectional structure of the sintered body is observed, adjacent cBN A bonded phase having a width of 1 nm to 30 nm exists between the particles, and the bonded phase is composed of a compound containing at least Al, B, and N, and has an oxygen content with respect to the Al content in the bonded phase. The ratio is 0.1 or less. Therefore, there are few oxides in the binder phase between cBN particles and cBN particles, the binder phase is strong, and there are few unsintered portions where the cBN particles are in contact with each other and cannot sufficiently react with the binder phase. As a result, this sintered body exhibits high hardness even when the content ratio of cBN particles is large.
Moreover, the cutting tool using the cBN sintered body of the present invention exhibits excellent fracture resistance and can extend the tool life.

HAADF (high angle scattering annular dark field) by STEM (scanning transmission electron microscope) of the interface between cBN particles of a cBN sintered body (hereinafter also referred to as “the present invention cBN sintered body”) according to an embodiment of the present invention. ) Image (80,000 times) is shown. The binarized image (80,000 times) of the B mapping image by STEM of the interface between the cBN particles of the cBN sintered body of the present invention is shown. The binarized image (80000 times) of the N mapping image by STEM of the interface between the cBN particles of the cBN sintered body of the present invention is shown. The binarized image (80000 times) of the Al mapping image by STEM of the interface between the cBN particles of the present invention cBN sintered body is shown. FIG. 5 is a diagram showing a region where B, N, and Al overlap in FIGS. It is a figure which shows the state which carried out the ellipse approximation of the area | region (island) where B, N, and Al of FIG. 5 overlap by image processing. In FIG. 6, it is the figure which drawn the interface outline line which consists of a polygonal line which connected the midpoint of the short axis of each ellipse with the straight line. The interface outline line between the cBN particles obtained from the Al mapping image, the B mapping image, and the N mapping image of the interface between the cBN particles of the cBN sintered body of the present invention is shown. The direction perpendicular to the interface outline (the arrow direction in FIG. 9) is shown. FIG. 6 shows the width of a binder phase between cBN particles and a partially enlarged view thereof obtained from FIG. 5 and an interface outline. The binarized image of the Al mapping image (80000 times) by STEM of the interface between the cBN particles of the cBN sintered body of the present invention and a measurement region with a width of 30 nm centering on the interface outline line are shown. The binarized image of the O (oxygen) mapping image (80000 times) by STEM at the interface between the cBN particles of the cBN sintered body of the present invention and the measurement region with a width of 30 nm centering on the interface outline. The method for measuring the number ratio (q / Q) of cBN particles in which a binder phase having a width of 1 nm to 30 nm exists between the cBN particles in the cBN sintered body of the present invention, and the oxygen content relative to the Al content in the binder phase It is a schematic diagram which shows the measuring method of the particle number ratio (n / N) whose ratio is 0.1 or less. It is a graph showing the relationship between the cBN content and the Vickers hardness HV of the cBN sintered body of the present invention and the comparative example cBN sintered body, and the curve in the graph is H = −0.42C ² + 81.5C (however, H represents Vickers hardness, and C represents cBN content by vol%).

An embodiment of the present invention (hereinafter also referred to as “this embodiment”) will be described below. The cBN sintered body according to the present embodiment includes cBN particles having a volume ratio of 70 to 95 vol% with respect to the volume of the entire cBN sintered body, and a binder phase that binds the cBN particles to each other. Further, when the cross-sectional structure of this sintered body is observed, a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles. Further, this binder phase contains at least Al (aluminum), B (boron), and N (nitrogen), and the ratio of O content to Al content in the binder phase is 0.1 or less (provided that (Atom ratio calculated from area ratio on the cross section). Note that the above-mentioned binder phase having a width of 1 nm or more and 30 nm or less that exists between adjacent cBN particles may be interspersed between adjacent cBN particles, and one binder phase extends between the cBN particles. (CBN particles may be adjacent to other cBN particles through one of the above-mentioned binder phases).

<Manufacturing method>
In the production of the cBN sintered body according to this embodiment, cBN particles obtained by pre-treating the surface of the cBN particles are used as the cBN raw material. Specifically, the cBN sintered body of the present embodiment includes a step of pre-processing the surface of the cBN particles, a step of mixing the pre-processed cBN particles with the raw material powder constituting the binder phase, And a process of sintering the body.
The pretreatment of the cBN particle surface is performed as follows, for example.
First, for example, in the ALD method, an AlN film is formed on the surface of cBN particles. For film formation, cBN particles are charged into a fluidized bed furnace, the temperature inside the furnace is raised to about 350 ° C., Ar + Al (CH ₃ ) ₃ gas inflow process, Ar gas purge process, Ar + NH ₃ gas inflow process, Ar gas purge The process is defined as one cycle, and this cycle is repeated until a desired AlN film thickness is obtained. For example, by forming the film over 30 minutes, an AlN film having a thickness of about 5 nm can be formed on the cBN particle surface.
Next, the cBN particles having an AlN film having a predetermined thickness formed thereon are heated at about 1000 ° C. under vacuum to diffuse impurity elements such as oxygen on the cBN surface into the AlN film. To capture.
Next, the AlN film in which the impurity element is trapped is peeled off from the cBN surface by ball mill mixing.
By applying such pretreatment to the cBN particles, cBN particles having a high surface cleanliness from which impurity components such as oxygen adsorbed on the cBN surface are removed are obtained. Note that the pretreatment of the cBN particle surface is not limited to the above-described ALD method, but may be any method that can remove the impurity component on the cBN particle surface.

The cBN particles subjected to the above pretreatment are used as raw materials, and further, for example, TiN powder, Al powder, TiAl ₃ powder, and Al ₂ O ₃ powder are used as raw material powders, and these raw material powders have a predetermined composition. Thus, a molded body having a predetermined size is prepared.
Next, the compact is charged into a normal ultra-high pressure sintering apparatus and subjected to ultra-high pressure and high temperature sintering for a predetermined time under sintering conditions of a pressure of 5 GPa or higher and a temperature of 1600 ° C. or higher. The cBN sintered body of the embodiment can be produced. Thus, the cBN sintered body according to the present embodiment can be obtained by producing the cBN sintered body using the cBN particles from which the impurity components on the surface have been removed by the pretreatment.

In addition, when using the cBN sintered compact of this embodiment as a cutting tool material, for example, in a state where the compact is superposed on a support piece made of a WC (tungsten carbide) -based cemented carbide, a normal ultra-high pressure is used. A cutting tool using the WC-based cemented carbide as the backing material and the cBN sintered body of the present embodiment as a cutting edge portion by charging into a sintering apparatus and performing ultra-high pressure and high-temperature sintering under the same conditions as described above. Can be produced.

<Content of cBN particles in the cBN sintered body>
In the cBN sintered body produced by the above method, when the content ratio of the cBN particles in the cBN sintered body is less than 70 vol%, the cBN particles are in contact with each other and cannot be sufficiently reacted with the binder phase. However, there are very few places where a binder phase having a width of 1 nm or more and 30 nm or less exists between the cBN particles, and binder phase components other than compounds containing at least Al, B, and N (for example, Ti and Ta). This compound, Al boride) increases between the cBN particles, and a structure exhibiting the effect of this embodiment cannot be formed. That is, compared with the binder phase containing at least Al, B, and N, this Ti compound and Al boride have low adhesion strength with cBN particles. For this reason, when used as a cutting tool, the interface between the Ti compound or Al boride and cBN particles tends to be the starting point of cracks, resulting in a decrease in fracture resistance. Therefore, it is not preferable that the content ratio of cBN particles in the cBN sintered body is less than 70 vol%. On the other hand, when the content ratio of cBN particles exceeds 95 vol%, when used as a cutting tool, voids that are the starting points of cracks are easily generated in the sintered body, and the fracture resistance is reduced. Therefore, the content ratio of cBN particles in the cBN sintered body is 70 to 95 vol%. The content ratio of cBN particles in the cBN sintered body is preferably 70 to 90 vol%, more preferably 75 to 85 vol%, but is not limited thereto.

<Content of cBN particles in the cBN sintered body>
In addition, the content ratio of the cBN particles in the cBN sintered body is determined by observing the cross-sectional structure of the cBN sintered body with the SEM, and the portion corresponding to the cBN particles in the obtained secondary electron image is the same image as described above. Extract by processing. The area occupied by the cBN particles is calculated by image analysis, the ratio of the cBN particles in one image is calculated, and the average value of the content ratio of the cBN particles obtained by processing at least three images is set in the cBN sintered body. Obtained as the content of occupied cBN particles. It is desirable that a square region having one side that is five times the average particle size of the cBN particles be an observation region used for image processing. For example, when the average particle size of cBN particles is 3 μm, a visual field area of about 15 μm × 15 μm is desirable.

<Average particle size of cBN particles>
The average particle size of the cBN particles used in the present embodiment is not particularly limited, but is preferably in the range of 0.5 to 8 μm.
This is due to the following reason.
When a cBN sintered body is used as a cutting edge part of a cutting tool, cBN particles having an average particle size of 0.5 μm to 8 μm are dispersed in the sintered body, so that cBN particles on the tool surface are used during tool use. Chipping that originates from the uneven shape of the cutting edge caused by dropping off can be suppressed. In addition, the propagation of cracks that propagate from the interface between the cBN particles and the binder phase caused by the stress applied to the blade edge during use of the tool, or the cracks that propagate through the cBN particles, is caused by the cBN particles dispersed in the sintered body. Can be suppressed. Therefore, such a cutting tool has excellent fracture resistance.
Therefore, the average particle size of the cBN particles used in this embodiment is preferably in the range of 0.5 to 8 μm, and more preferably in the range of 0.5 to 3 μm.

Here, the average particle size of the cBN particles can be determined as follows.
The cross-sectional structure of the cBN sintered body is observed by SEM. For example, when the average particle size of cBN particles is 3 μm, a secondary electron image of 15 μm × 15 μm (5 times square of the average particle size of cBN particles) is obtained. A portion corresponding to cBN particles in the obtained image is extracted by image processing, and a maximum length of a portion corresponding to each particle extracted by image analysis is obtained by the following procedure. First, in order to clearly determine the cBN particles and the binder phase when extracting the portion corresponding to the cBN particles by image processing, the image is displayed in monochrome with 256 gradations, with 0 being black and 255 being white. Binarization processing is performed so that the cBN particles are black using an image of pixel values in which the ratio of the pixel value of the particle portion to the pixel value of the binder phase portion is 2 or more.
The pixel values of the cBN particle part and the binder phase part are obtained from an average value in a region of about 0.5 μm × 0.5 μm. It is desirable to obtain an average value of pixel values in at least three different regions in the same image, and use the average value as each contrast.
After binarization processing, cBN particles that are considered to be in contact using watershed, which is one of image processing operations, such as separation of parts that are considered to be in contact with each other. Separate each other.
The portion corresponding to cBN particles (black portion) in the image obtained after the above processing is subjected to particle analysis, and the maximum length of the portion corresponding to each particle is obtained. The obtained maximum length is defined as the maximum length of each particle, and this is defined as the diameter of each particle. From this diameter, the volume of each particle is calculated using each particle as a sphere. Based on the obtained volume of each particle, an integrated distribution of particle diameters is obtained. Specifically, for each particle, the sum of the volume and the volume of particles having a diameter equal to or smaller than the diameter of the particle is obtained as an integrated value. For each particle, a graph is drawn with the volume percentage [%], which is a ratio of the total value of each particle with respect to the total volume of all particles, as the vertical axis and the horizontal axis as the diameter [μm] of each particle. The value of the diameter (median diameter) at which the volume percentage is 50% is taken as the average particle size of cBN particles in one image. The average value of the average particle size values obtained by performing the above processing on at least three images is defined as the average particle size [μm] of the cBN particles of the cBN sintered body. When performing particle analysis, a length (μm) per pixel is set using a scale value known in advance by SEM. Further, in the particle analysis, in order to remove noise, a region having a diameter smaller than 0.02 μm is not calculated as a particle.

<Identification of a binder phase having a width of 1 nm to 30 nm between adjacent cBN particles, component analysis of the binder phase, and measurement of O / Al>
Identification of a binder phase having a width of 1 nm or more and 30 nm or less existing between adjacent cBN particles and component analysis of the binder phase can be performed as follows.
After producing the cBN sintered body, the cross section of the sintered body is polished. Then, the interface which cBN particle | grains and cBN particle | grains adjoin is observed using STEM (refer FIG. 1). FIG. 1 is a HAADF (high angle scattering annular dark field) image (80000 times) obtained by observing the interface between cBN particles and cBN particles using a STEM (scanning transmission electron microscope). The thickness of the observation sample is preferably 3 nm to 70 nm. If it is thinner than 3 nm, the amount of characteristic X-rays to be detected is small at the time of element mapping, which is not preferable because it takes time for measurement and the sample is easily damaged. On the other hand, if it is thicker than 70 nm, analysis of the image becomes difficult, which is not preferable. The observation image has an image size of about 500 nm in length × about 500 nm in width to about 150 nm in length × 150 nm in width, and a resolution of 512 × 512 pixels or more. Mapping images of boron (B), nitrogen (N), aluminum (Al), and oxygen (O) elements (see FIGS. 2 to 4, 11, and 12) are acquired at the observation site. These images are images converted to atm% of these four elements for the purpose of removing the background (images converted to the ratio of the content of each element (atm%) to the total content of the four elements). ). Based on this image, in the following procedure, between adjacent cBN particles, whether there are interspersed or intervening bonded phases between 1 nm and 30 nm in width, and between the cBN particles in this bonded phase Find the proportion of Al and O.
(A) From the mapping image of B and N (see FIGS. 2 and 3), it is confirmed that the observed region is a place where a plurality of cBN particles should be observed (a region where a plurality of cBN particles are present). .
(B) A mapping image of Al (see FIG. 4) and a mapping image of B (FIG. 2) and a mapping image of N (FIG. 3) in the above (a) are superposed and exist between cBN particles, and at least Al, The position of the binder phase containing B and N is specified. Then, the width of the binder phase is determined as follows.
(B1) When the binder phase is interposed between the cBN particles, that is, when there is one Al island overlapping the region where B and N exist (when one binder phase extends between the cBN particles) First, in the mapping image of Al, a long axis is obtained when the Al island corresponding to the binder phase is approximated as an ellipse. Specifically, the Al island overlapping the region where B and N are present is extracted by image processing in the same manner as the processing performed in the measurement of the average particle size of the cBN particles, and is analyzed by image analysis. The longest axis is the maximum length when the extracted island is approximated to an ellipse. This long axis is defined as an interface outline line between cBN particles.
(B2) When the binder phase is scattered at the interface between the cBN grains, that is, when the Al island overlapping the region where B and N exist is divided into two or more, B and N In the same manner as the processing performed when measuring the average particle size of the cBN particles described above, the Al islands that overlap the region where the slab exists are extracted by image processing (FIG. 5), and the islands extracted by image analysis are elliptical. Approximate (FIG. 6). Then, the minor axis of each ellipse is obtained. By obtaining a midpoint on each short axis and drawing a polygonal line T connecting the adjacent midpoints with straight lines, an interface outline line between the cBN particles is obtained (FIGS. 7 and 8).
(B3) In the Al island (FIG. 10) of the Al mapping image that overlaps the interface outline obtained in (b1) or (b2) above, Al in the direction perpendicular to the interface outline (FIG. 9) The width of the island is measured (see FIG. 10), and the average value of the width measured at least at three or more locations is defined as the width of the binder phase existing between the cBN particles. When the width is 1 nm or more and 30 nm or less, it is assumed that the width of the binder phase existing between the cBN particles is 1 nm or more and 30 nm or less.
In the cBN sintered body, when there is no binder phase having a width of 1 to 30 nm including Al, B, and N between adjacent cBN particles, sufficient strength to adhere between the cBN particles and the cBN particles cannot be obtained. Or breakage starting from the inside of the binder. As a result, a sintered body having a low hardness is obtained, which is not preferable.
(C) Next, the content of Al and the content of O contained in the binder phase are determined as follows. First, using a binarized image of the mapping image of Al and O (FIGS. 11 and 12), a measurement region M having a width of 30 nm around the interface outline confirmed in (b) above is determined. This region M was surrounded on both sides of the interface outline by two lines parallel to and congruent to the interface outline with a distance of 15 nm from the interface outline and two straight lines connecting the ends. It is an area. A content (area%) of Al and O in a portion where B, N, and Al included in the region M overlap is obtained. Specifically, the area of Al where B, N, and Al existing in this region M overlap is obtained from an image obtained by binarizing the Al mapping image, and the ratio of the area of Al to the area of this region is calculated as follows: The content of Al contained in the binder phase. Similarly, for O, the ratio of the area of O to the area of the region M is obtained, and this is defined as the content of O contained in the binder phase. The ratio (area%) of the area of Al and O contained in the binder phase thus obtained is defined as the content (atomic ratio) of Al and O, respectively.
(D) From the Al and O contents (area%) determined above, the ratio of the oxygen content to the Al content in the binder phase (hereinafter sometimes referred to as “O / Al”) is calculated. .
In accordance with the procedures (a) to (d) above, component analysis is performed on a binder phase having a width of 1 nm or more and 30 nm or less present in a region of 30 nm width centered on a rough interface line defined between adjacent cBN particles. At the same time, the value of O / Al in the binder phase can be obtained.
Note that the binder phase interspersed with or having a width of 1 nm or more and 30 nm or less at the interface between adjacent cBN particles is composed of a component containing at least Al, B, and N (see FIGS. 2 to 12). ).
According to the procedures (a) to (d), it is determined whether or not a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles. When such a bonded phase exists, component analysis in the bonded phase is performed, and the value of O / Al in the bonded phase can be obtained.
“Dispersed” indicates a state in which Al is present in a plurality of islands in a portion where Al, B, and N overlap, and “interposed” indicates that Al is present in a portion in which Al, B, and N overlap. Indicates a state that exists without interruption.
Note that the binder phase having a width of 1 nm or more and 30 nm or less that exists between the adjacent cBN particles contains at least Al, B, and N. In this embodiment, the main structure of the binder phase is composed of Al, B, and N (see FIGS. 2 to 12).

<Abundance ratio of cBN particles in which a binder phase with a width of 1 nm to 30 nm exists between adjacent cBN particles>
An abundance ratio of cBN particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles is measured. In other words, the abundance ratio (q / Q) of cBN particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles to all cBN particles is measured. For example, this measurement can be specifically performed as follows.
First, as shown in the schematic diagram of FIG. 13, a square region in which the length L of one side is five times the average particle size of cBN particles is defined as one measurement visual field range A. For example, when the average particle size of cBN particles is 1 μm, a square region of 5 μm × 5 μm is set as one measurement visual field range.
Then, pull the diagonal D from the top of the measurement region A which forms a square, it counts the number of particles to Q ₁ cBN particles 1 according to the diagonal D.
Next, for each cBN particle 1 present on the diagonal line D, whether or not the binder phase 2 having a width of 1 nm or more and 30 nm or less exists between the adjacent cBN particles 1 is specified by the above-described method. Then, the number of particles q ₁ of the cBN particles 1 specified to be present between the adjacent cBN particles 1 and having a width of 1 nm or more and 30 nm or less is counted, and the value of q ₁ / Q ₁ is calculated.
Next, the same measurement is performed for at least five visual fields, the value of q _n / Q _n in each visual field is calculated, and then the average value of these values is obtained as the value of q / Q.
By the above method, it is possible to identify cBN particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles, and to determine the ratio (q / Q) at which the cBN particles are present. In the present embodiment, the q / Q value is desirably 0.4 or more. The upper limit value of q / Q is preferably 1, and q / Q is more preferably 0.6 or more and 1 or less.

<Presence / absence of a region where O / Al is 0.1 or less in a bonded phase having a width of 1 nm to 30 nm between adjacent cBN particles>
Presence of cubic boron nitride particles having a binding phase of 1 nm to 30 nm in width between adjacent cBN particles and having an O / Al value of 0.1 or less in the binding phase. It is desirable to observe in a field of view that is 60% or more of the total number of fields of observation. Specifically, with respect to the cross section of the cBN sintered body, five or more fields of view are observed using a field of 5 times the average particle size of the cBN particles as an observation field. In each field of view, O / in the binder phase present between the adjacent cBN particles identified as described above and having a width of 1 nm to 30 nm and present in the region measured as described above. The presence or absence of a region where the Al value is 0.1 or less is observed. It is preferable that the number of fields in which at least one binder phase is observed is 60% or more of the total number of fields. It is more preferable that observation is performed in a field of view of 80% or more of the total number of observation fields, and it is further preferable that the region is observed in all observation fields of view (observed in 100% of the total number of observation fields).
In addition, if there is a binder phase having a width of 1 nm or more and 30 nm or less that exists between adjacent cBN particles, and there are many regions in which the value of O / Al in the binder phase is 0.1, adjacent cBN Many networks in which particles and cBN particles are sufficiently adhered with a strong binder phase can be formed, and the hardness is excellent. The lower limit value of O / Al is 0.

<Number and ratio of cBN particles in which O / Al is 0.1 or less in the bonded phase among cBN particles in which a bonded phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles>
In the schematic diagram of FIG. 13, after identifying cBN particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles by the method described above, a width of 1 nm or more and 30 nm or less existing between the cBN particles. In this binder phase, the number and proportion of cubic boron nitride particles having O / Al of 0.1 or less are obtained. In other words, among cBN particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles, the number of cBN particles in which the O / Al of this binder phase is 0.1 or less (n) And the ratio (n / N) to the number (N) of cBN particles in which a binder phase having a width of 1 nm to 30 nm is present between the cBN particles and the adjacent cBN particles. The measurement of the number and the calculation of the ratio can be performed as follows.
For example, among the cBN particles 1 on the diagonal line D drawn from the top of one square measurement visual field region A whose side length L is five times the average particle size of the cBN particles 1, adjacent cBN particles 1 and CBN particles 1 in which a binder phase 2 having a width of 1 nm or more and 30 nm or less is present in between, and the number N ₁ is counted.
Next, among the cBN particles 1 in which the binder phase 2 having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles 1, O / Al in the binder phase 2 is 0.1 or less (however, the area ratio). The number n ₁ of cBN particles 1 is counted, and the value of n ₁ / N ₁ is calculated.
Next, the same measurement is performed for at least five visual fields, and the value of n _n / N _n in each visual field is calculated. Then, an average value of these values is obtained and set as a value of n / N.

According to the above method, the number (n) and the abundance ratio (n / N) of cBN particles in which O / Al is 0.1 or less in a binder phase having a width of 1 nm or more and 30 nm or less existing between adjacent cBN particles. Can be sought. In the present embodiment, the value of n / N is desirably 0.5 or more. That is, the number (n) of cBN particles having an O / Al ratio of 0.1 or less in the binder phase existing between adjacent cBN particles and having a width of 1 nm or more and 30 nm or less is the width between adjacent cBN particles. It is desirable to exist at an average ratio of 0.5 or more with respect to the number (N) of cBN particles in which a binder phase of 1 nm or more and 30 nm or less exists.
When the average number of regions ratio (n / N) is 0.5 or more, a strong binder phase can be formed between the cBN particles and the cBN particles, and high hardness is exhibited. The value of n / N is preferably 0.6 or more, and more preferably 0.8 or more and 1 or less.

In addition, the cBN sintered body of the present embodiment is composed of cBN particles and a binder phase as described above. Regarding the binder phase, the configuration of the binder phase formed in the sintered body other than the binder phase having a width of 1 nm to 30 nm existing between adjacent cBN particles is not particularly limited, but the binder phase formed in this region is not limited. Is composed of one or more of Ti nitride, carbide, carbonitride, boride, Al nitride, boride, oxide and two or more of these solid solutions and unavoidable impurities. It is preferable.

The cBN sintered body according to the present embodiment described above has a high content ratio of cBN particles and exhibits a hardness higher than the hardness according to the cBN content. Specifically, the Vickers hardness H of the cBN sintered body satisfies the following formula.
H> −0.42C ² + 81.5C (C is the content of cBN particles (vol%))

Hereinafter, the cBN sintered body of the present embodiment will be described based on examples.

Preparation of cBN particle powder with high surface cleanliness:
CBN particles having a median diameter (D50) shown in Table 1 were used as a base material, and an AlN film having an average film thickness shown in Table 1 was coated on the cBN particles by an ALD (Atomic Layer Deposition) method. More specifically, cBN particles having a median diameter (D50) shown in Table 1 are charged into the furnace, the temperature inside the furnace is raised to 350 ° C., and a precursor of Al is used as a film forming gas. A certain Al (CH ₃ ) ₃ gas and NH ₃ gas as a reaction gas,
(1) Ar + Al (CH ₃ ) ₃ gas inflow process,
(2) Ar gas purge step,
(3) Ar + NH ₃ gas inflow process,
(4) Ar gas purging step The above (1) to (4) were set as one cycle, and this cycle was repeated until the AlN film reached the target film thickness. As a result, an AlN film having a predetermined thickness was formed on the surface of the cBN particles.
The cBN particle powder coated with the AlN film obtained by the above procedure was observed using an SEM (scanning electron microscope). As a result, an AlN film having an average film thickness shown in Table 1 was formed on the surface of the cBN particle. It was confirmed that it was coated.
Next, the cBN particles on which the AlN film was formed were heat-treated under a vacuum at a temperature of about 1000 ° C. for 30 minutes to diffuse impurity elements such as oxygen on the cBN surface into the AlN film. Next, the AlN film in which the impurity element was captured was peeled off from the cBN surface by ball mill mixing using a tungsten carbide container and balls.

CBN particle powder having a predetermined median diameter prepared by the above procedure, and TiN powder, TiC powder, Al powder, TiAl ₃ powder, and WC powder having an average particle diameter in the range of 0.3 to 0.9 μm. It was prepared as a raw material powder for forming a binder phase. Blended so that the content ratio of cBN particle powder is 70 to 95 vol% when the total amount of some raw material powder selected from these raw material powders and cBN particle powder is 100 vol%, wet-mixed, Dried. Then, it was press-molded into a size of diameter: 50 mm × thickness: 1.5 mm at a molding pressure of 1 MPa with a hydraulic press to obtain a molded body. Next, the compact was heat-treated in a vacuum atmosphere at a pressure of 1 Pa at a predetermined temperature within a range of 1000 to 1300 ° C. for 30 to 60 minutes, and charged into a normal ultrahigh pressure sintering apparatus under normal conditions. The cBN sintered bodies 1 to 17 of the present invention shown in Table 2 were prepared by sintering under high pressure and high temperature under the conditions of pressure: 5 GPa, temperature: 1600 ° C., and holding time: 30 minutes.
The binder phase structure other than cBN of the sintered body shown in Table 2 was confirmed by XRD (X-ray Diffraction) of the cBN sintered body.
The above production process is preferably performed so as to prevent oxidation of the raw material powder in the process up to ultra-high pressure sintering. Specifically, the raw material powder and the molded body are handled in a non-oxidizing protective atmosphere. It is preferable to do.

 

 

 

For comparison, as a raw material powder, cBN particle powders a, b, e to i having a median diameter (D50) shown in Table 4 that were not coated with an AlN film by an ALD (Atomic Layer Deposition) method were used. (The heat treatment under vacuum of the film and the peeling process of the AlN film from the cBN surface were not performed). Further, like the above-mentioned cBN sintered bodies 1 to 17 of the present invention, after coating an AlN film having an average film thickness shown in Table 4, after heat treatment under vacuum at a temperature of about 1000 ° C. for 30 minutes, by ball mill mixing, CBN particle powders c and d having a median diameter (D50) shown in Table 4 were prepared by peeling off the AlN film from the cBN surface. TiN powder, TiC powder, Al powder, TiAl ₃ powder, and WC powder having an average particle diameter in the range of 0.3 to 0.9 μm are prepared as binder phase forming raw material powders, and selected from these raw material powders. The cBN sintered bodies 1 to 17 of the present invention were blended so that the content ratio of the cBN particle powder was 55 to 98.2 vol% when the total amount of the raw material powder and the cBN particle powder was 100 vol%. Comparative Example cBN sintered bodies 1 to 10 shown in Table 5 were produced in the same manner as described above.

 

 

 

For the cBN sintered bodies 1 to 17 of the present invention and the comparative cBN sintered bodies 1 to 10 produced as described above, the average particle size (μm) of cBN particles and the content ratio (vol%) of cBN particles were calculated.
About the average particle diameter of cBN particle | grains, it calculated | required by the above-mentioned method. That is, the cross-sectional structure of the cBN sintered body was observed with a scanning electron microscope (SEM) to obtain a secondary electron image. The portion of cBN particles in the obtained image is extracted by image processing, the maximum length of each particle obtained by image analysis is obtained, and the volume is assumed to be the diameter of each particle and each particle is an ideal sphere. Was calculated.
The median diameter in the volume integration% and diameter distribution curve was obtained from one image, and the average value obtained from at least three images was defined as the average particle size (μm) of cBN. The observation area used for image processing was 15 μm × 15 μm. The calculated average particle diameters are shown in Tables 2 and 5.

In addition, component analysis and measurement of O / Al in a binder phase having a width of 1 nm to 30 nm existing between adjacent cBN particles were performed as described above.
That is, after polishing the cross section of the cBN sintered body, the interface where the cBN particles and the cBN particles are adjacent to each other is observed using a TEM, and mapping images of B, N, Al, and O elements are observed at the observation points (FIG. 2 to FIG. 2). 4, 11, 12).
Next, it was confirmed from the mapping image of B and N that it was an observation place between the cBN particles.
Next, the Al mapping image, the B mapping image, and the N mapping image were superposed, and an interface outline line between the cBN particles was obtained from the portion where Al, B, and N overlapped as described above. Moreover, it confirmed that the width | variety of the binder phase between cBN particle | grains was 30 nm or less by the above-mentioned method based on the obtained interface outline line.
Next, using the image obtained by binarizing the mapping image of Al and O, the content (area ratio) of Al and O was determined in a region having a width of 30 nm centered on the interface outline line confirmed above. .
From the Al and O contents (area ratio) determined above, O / Al in the binder phase of the region was calculated.
In accordance with the above procedure, at least five O / Al were measured, and the average value was determined as the value of O / Al in the binder phase having a width of 1 nm or more and 30 nm or less existing between adjacent cBN particles. The results are shown in Tables 3 and 6.

In addition, the identification of the cBN particle in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles and measurement of the abundance ratio (q / Q) of the cBN particles were performed as described above. That is, as shown in the schematic diagram of FIG. 13, a region of 5 times the average particle size of cBN particles is defined as one measurement visual field range, a diagonal line is drawn from the top of the measurement region forming a square, and the cBN particles applied to the diagonal line counting the number of particles Q ₁ of. Then, among the cBN particles diagonally, with the width 1nm or 30nm or less of the binder phase to identify the cBN particles present between the adjacent cBN particles were counted number of particles _{q 1} of the cBN particles. The value of q ₁ / Q ₁ was calculated. The same measurement was performed for a total of 10 visual fields, and the value of q _n / Q _n in each visual field was calculated. Subsequently, these average values were obtained as q / Q values. This value is shown in Tables 3 and 6 as an average particle number ratio (q / Q) of cBN particles in which a binder phase having a width of 1 nm to 30 nm exists between adjacent cBN particles.
Also, the number of observation fields in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles and a region having an O / Al value of 0.1 or less in the binder phase is obtained. It was. The results are shown in Tables 3 and 6 as the number of viewing fields. Note that the number of observation fields in the table is centered on the interface outline line obtained from the bonding phase in which a bonding phase having a width of 1 nm to 30 nm exists between adjacent cBN particles in a total of 10 observation fields. The number of visual fields in which a region where the value of O / Al in the binder phase in the region having a width of 30 nm is 0.1 or less is observed. “-” In the table indicates that a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles, but there is no overlap of Al, B, and N elements by element mapping (including at least Al, B, and N). This means that O / Al cannot be calculated because the interface outline line cannot be defined.
Further, as shown in the schematic diagram of FIG. 13, a region 5 times the average particle size of cBN particles was defined as one measurement visual field range, and a diagonal line was drawn from the top of the measurement region forming a square. Of cBN particles according to the diagonal, specifies a cBN particles present width 1nm or 30nm or less of the binder phase between the adjacent cBN particles were counted these numbers _{N 1.} Next, among cBN particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles, the number of cBN particles in which the O / Al in the binder phase is 0.1 or less (however, the area ratio) n ₁ was counted. The value of n ₁ / N ₁ is calculated, the same measurement is performed for a total of 10 visual fields, the value of n _n / N _n in each visual field is calculated, and then the average value of these values is the value of n / N Asked. The results are shown in Tables 3 and 6. Note that n / N in the table is O / Al in the binder phase in the region having a width of 30 nm centered on the interface outline line, with a binder phase having a width of 1 nm to 30 nm between adjacent cBN particles. Is the average ratio (n / N) to the number of cBN particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists at the interface with adjacent cBN particles. “-” In the table indicates that there is a binder phase with a width of 1 nm or more and 30 nm or less between adjacent cBN particles, but there is no overlap of Al, B, and N elements by element mapping, and the interface outline is defined. This means that O / Al cannot be calculated because it is not possible.

Further, with respect to the polished surfaces of the cBN sintered bodies 1 to 17 of the present invention and the comparative cBN sintered bodies 1 to 10, Vickers hardness (HV) was measured at a measurement point of 10 with a load of 5 kg, and these were averaged. The hardness of the sintered body was measured. In addition, about the value of hardness, the 1st digit was rounded off.
Tables 2 and 5 show these values.
FIG. 14 is a graph plotting the relationship between the cBN content C (vol%) obtained from Tables 2 and 4 and the Vickers hardness H (HV).

From the results shown in Tables 3 and 6, in the cBN sintered bodies 1 to 17 of the present invention, when the cBN particles are pretreated, the binder phase between the cBN particles and the cBN particles has an average O / Al of 0.10 or less. However, there was little oxide and the strong binder phase was formed. Furthermore, the number of visual fields in which a binder phase having a width of 1 nm or more and 30 nm or less exists between adjacent cBN particles and the O / Al value in the binder phase is 0.1 or less was observed. Since it was 60% or more of the number of fields of view, there were many unsintered portions where the cBN particles were in contact with each other and could not sufficiently react with the binder phase. Therefore, a high hardness of Vickers hardness (HV) of 3720 or higher was exhibited when the cBN content was in the range of 70 to 95 vol%.
On the other hand, in the comparative example cBN sintered body 3, since the treatment for increasing the surface cleanliness was performed on the cBN particles, the O / Al was 0.10 or less on average and the oxide was small, but the cBN contained The amount was less than the range defined in this embodiment. Therefore, the Vickers hardness (HV) was as low as 3190.
Moreover, since the comparative example cBN sintered body 4 is subjected to a treatment for increasing the surface cleanliness like the comparative example cBN sintered body 3, O / Al is 0.10 or less on average, and the oxide is There were few. In addition, the Vickers hardness (HV) remained at 3690 although the cBN content was higher than the range specified in the present embodiment. Incidentally, in the cBN sintered bodies 6 and 8 of the present invention, the cBN content is smaller than that of the comparative example cBN sintered body 4, but HV = 4050, 4210, which is much higher than that of the comparative example cBN sintered body 4. High hardness was shown.
Moreover, the comparative example cBN sintered body 6 has a high cBN content ratio and a Vickers hardness (HV) of 3710, which is the same as the Vickers hardness (HV) 4210 of the present cBN sintered body 8 having the same cBN content ratio. And it was low hardness.
In addition, the other comparative cBN sintered bodies 1, 2, 5, and 7 to 10 each had an O / Al average of 0.73 or more and a Vickers hardness (HV) of 3560 or less and a low hardness. It was.

Further, as can be seen from FIG. 14 in which the cBN content and the value of Vickers hardness are plotted for the cBN sintered bodies 1 to 17 of the present invention and the cBN sintered bodies 1 to 10 of the comparative examples, the cBN sintered bodies 1 to 17 was located above the curve represented by H = −0.42C ² + 81.5C (where H represents Vickers hardness and C represents the cBN content by vol%). On the other hand, the comparative cBN sintered bodies 1 to 10 were all located below the curve. From these facts, when comparing the hardness of the cBN sintered body with the same cBN content, the hardness of the cBN sintered body of the present invention is much higher than that of the comparative cBN sintered body. it is obvious. In addition, the curve in FIG. 14 represents the relationship between the cBN particle content of the cBN sintered body obtained empirically and the Vickers hardness.

As described above, the cBN sintered body of the present invention has high hardness and high bond strength between the cBN particles and the binder phase. Therefore, for example, when used as a cBN cutting tool in which a high load acts on the cutting edge, it is excellent in abnormal damage resistance such as defects, and exhibits excellent wear resistance over a long period of use. Application as fracture-resistant materials such as tool materials is expected.

Claims (6)

1. In a cubic boron nitride-based sintered body containing 70 to 95 vol% of cubic boron nitride particles, when the cross-sectional structure of the sintered body is observed, the width between adjacent cubic boron nitride particles is There is a binder phase of 1 nm or more and 30 nm or less, and the binder phase is composed of a compound containing at least Al, B, and N, and the ratio of the oxygen content to the Al content in the binder phase is 0.1 or less. A cubic boron nitride-based sintered body having an atomic ratio.
2. In a cubic boron nitride-based sintered body containing 70 to 95 vol% of cubic boron nitride particles, when the cross-sectional structure of the sintered body is observed, the interval between adjacent cubic boron nitride particles is 30 nm. The following region exists, and the binder phase in the region is composed of a nitride containing one or both of Al and B and an oxide of Al, and Al content in the binder phase in the region A cubic boron nitride based sintered body characterized in that there is a region in which the ratio of the oxygen content to the amount is 0.1 or less (however, the atomic ratio).
3. In the cubic boron nitride-based sintered body, the cubic boron nitride particles have an average particle size of 0.5 to 8.0 μm, and the cross-sectional structure of the cubic boron nitride-based sintered body is When viewing at least 5 or more fields with a field of view 5 times x 5 times the average particle diameter of the cubic boron nitride particles as one field of view, a width of 1 nm or more and 30 nm between the adjacent cubic boron nitride particles The presence of the cubic boron nitride particles in which the following binder phase is present and the ratio of the oxygen content to the Al content in the binder phase is 0.1 or less is 60% or more of the total number of viewing fields 3. The cubic boron nitride-based sintered body according to claim 1, wherein the cubic boron nitride-based sintered body is observed in the field of view.
4. When the cross-sectional structure of the cubic boron nitride-based sintered body is observed, the cubic boron nitride particles in which a binder phase having a width of 1 nm to 30 nm exists between adjacent cubic boron nitride particles. And an average particle number ratio of 0.4 or more with respect to the total number of the cubic boron nitride particles in the observed cross section, and a width of 1 nm between the adjacent cubic boron nitride particles. In the cubic boron nitride particles in which a binder phase of 30 nm or less is present, the number of the cubic boron nitride particles in which the ratio of the oxygen content to the Al content in the binder phase is 0.1 or less, It is present in an average ratio of 0.5 or more with respect to the number of the cubic boron nitride particles in which a binder phase having a width of 1 nm or more and 30 nm or less exists between the adjacent cubic boron nitride particles. Claims 1 to 3 Cubic boron nitride containing groups sintered body according to the deviation or claim.
5. 5. The binder phase having a width of 1 nm to 30 nm existing between the cubic boron nitride particles is interspersed between the cubic boron nitride particles. The cubic boron nitride base sintered body according to any one of the above.
6. A cubic boron nitride-based sintered body, wherein a cutting edge portion of the cutting tool is composed of the cubic boron nitride-based sintered body according to any one of claims 1 to 5. Cutting tool made.

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