Hard composite materials

Abstract

A cBN sintered body which comprises cubic boron nitride particles and a binder phase, wherein: the binder phase contains Ti2CN and Co2B; and if ITi2CN is the peak intensity of Ti2CN appeared within the 2θ range of from 41.9° to 42.2° in XRD measurement and ICo2B is the peak intensity of Co2B appeared within the 2θ range of from 45.7° to 45.9° in XRD measurement, the peak intensity ratio, namely ITi2CN / ICo2B is from 0.5 to 2.0.

Description

[Technical Field]

[0001] The present invention relates to a hard composite material suitable for drilling tips of drilling tools. This application claims priority to Japanese Patent Application No. 2020-043694, filed on March 13, 2020. The entire contents of the Japanese Patent Application are incorporated herein by reference. [Background technology]

[0002] WC-based cemented carbide has high hardness and excellent toughness, and is therefore used not only in cutting tools but also as the drilling tips of excavation tools. Cubic boron nitride sintered compacts (hereinafter sometimes referred to as cBN sintered compacts) are less hard than diamond, but have low reactivity with Fe-based and Ni-based materials, and are therefore used not only in cutting tools but also as the drilling tips of excavation tools in Fe-based and Ni-based mines. Proposals have been made to improve the cutting and drilling performance of these WC-based cemented carbide and cBN sintered compacts.

[0003] For example, Patent Document 1 proposes a cemented carbide containing an iron-based metal, WC, and TiCN for use in the cutting edge of a deep drilling tool.

[0004] Furthermore, for example, Patent Document 2 proposes a cBN sintered body for cutting tools or wear-resistant tools that uses Ti2AlC as a binder phase-forming substance, and activates the surface of this binder phase-forming substance to stimulate the reaction between the cBN and the binder phase, thereby forming a two-layer reaction layer on the surface of the cBN particles, consisting of a first layer containing Ti and boron and a second layer containing Al and boron over the entire surface of this first layer, thereby increasing the adhesion between the cBN and the binder phase and improving the strength, toughness, etc. of the sintered body.

[0005] Furthermore, for example, Patent Document 3 proposes a self-sintering polycrystalline cubic boron nitride compact having a first phase of cBN particles and a ceramic binder phase containing a titanium compound, in which the first phase accounts for more than 80% by volume of the boron compact, and further, the compact contains a binder phase that is conductive or semi-conductive by using TiAlC as a binder precursor, resulting in a high-cBN sintered body that has excellent workability by electrical discharge machining. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 53-89809 [Patent Document 2] Japanese Patent Application Publication No. 5-310474 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-537116 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances and proposals, and aims to provide a hard composite material that has excellent fatigue wear resistance and abrasive wear resistance, and further has resistance to damage such as chipping caused by impacts and vibrations used to break rocks, even when used as an excavation tool. [Means for solving the problem]

[0008] The cBN sintered body according to the embodiment of the present invention is A cBN sintered body having cubic boron nitride particles and a binder phase, The binder phase contains Ti2CN and Co2B and TiB 2 includes, The peak intensity of Ti2CN appearing at 2θ = 41.9 to 42.2° in the XRD measurement is I Ti2CN The peak intensity of Co2B appearing at 2θ = 45.7 to 45.9° is defined as I Co2B When The ratio of the peak intensities, I Ti2CN / I Co2B Satisfies 0.5 to 2.0 death, The peak intensity of TiB2 appearing at 2θ = 44.4 to 44.6 in the XRD measurement is I TiB2 When this is done, the ratio of the peak intensity of Co2B to that of I Co2B / I TiB2 is 1.2 to 3.4 the law of nature, The binder phase further comprises AlN. [Effects of the Invention]

[0011] According to the above, a cBN sintered body is obtained which has excellent fatigue wear resistance and abrasive wear resistance, and further has resistance to damage such as chipping caused by impacts and vibrations used to break rocks when used as an excavation tool. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows an XRD measurement chart of Example sintered body 4. DETAILED DESCRIPTION OF THE INVENTION

[0013] As a result of examining the proposals described in the above-mentioned documents, the present inventors have come to the following realization.

[0014] The cemented carbide described in Patent Document 1 is intended for deep drilling, but because it is intended for drilling in a highly corrosive atmosphere, it has poor wear resistance in deep drilling depths and hard rock, and when used as the cutting edge of a drilling tool, it wears out quickly and has a short lifespan.

[0015] The cBN sintered bodies shown in Patent Documents 2 and 3 are designed to be pressed against a workpiece of uniform composition, and therefore, when used as a drilling tool for excavating rock, they do not have sufficient resistance to damage such as fatigue wear due to repeated impacts, abrasive wear due to the minute cutting action caused by hard components in the crushed rock getting between the tool cutting edge and the rock, and chipping due to impacts and vibrations used to break the rock.

[0016] Excavation tools are used to excavate and dig into the ground or bedrock. However, underground rocks are brittle materials with varying compositions and strengths. Therefore, unlike cutting processes that emphasize cutting and scraping performance, excavation tools must be able to withstand the impacts and vibrations required to break the rock, as well as the rotation required to efficiently remove the broken rock.

[0017] In other words, materials for drilling tools must be resistant to fatigue wear caused by repeated impacts, abrasive wear caused by the micro-cutting action that occurs when hard components of crushed rock get between the tool cutting edge and the rock as it surrounds the drilling tool, and damage such as chipping caused by the impacts and vibrations used to break the rock.

[0018] Based on this understanding, the present inventors conducted extensive research and found that, focusing on cBN sintered compacts as hard composite materials, it is possible to obtain cBN sintered compacts that have excellent fatigue wear resistance and abrasive wear resistance, and that are resistant to damage such as chipping caused by impacts and vibrations used to break rock, when used as drilling tools, if the peak intensities of Ti2CN and Co2B constituting the binder phase of the cBN sintered compacts are related to each other in a specific manner during XRD analysis.

[0019] The cBN sintered body according to the embodiment of the present invention will be described in more detail below. In this specification and claims, when a numerical range is expressed as "A to B" (A and B are both numerical values), this is synonymous with "A or more and B or less," and the range includes an upper limit (B) and a lower limit (A). The upper limit and lower limit have the same units. The numerical values ​​also include tolerances.

[0020] Cubic Boron Nitride (cBN) Particle Average Size: The average particle size of the cBN particles used in this embodiment is not particularly limited, but is preferably in the range of 0.5 to 30.0 μm.

[0021] The reason for this is that, in addition to the effect of enhancing fracture resistance by including hard cBN particles in the sintered body, if the average particle size is 0.5 to 30.0 μm, not only will fractures and chipping originating from the uneven shape of the cutting edge caused by cBN particles falling off the surface of the tool during use as a drilling tool be suppressed, but also cracks that develop from the interface between the cBN particles and the binder phase due to stress applied to the cutting edge during use as a drilling tool, or cracks that develop as the cBN particles break apart, will be reliably suppressed, resulting in better fracture resistance.

[0022] Here, the average particle size of the cBN particles can be determined as follows. The cross section of the cBN sintered body is mirror-polished, and the mirror-polished surface is observed using a scanning electron microscope (SEM) to obtain a secondary electron image. Next, the cBN grains in the obtained image are extracted using image processing, and the average grain size is calculated based on the maximum length of each grain determined by image analysis.

[0023] When extracting the cBN particle portion of the image by image processing, the image was displayed in 256-level monochrome, with 0 being black and 255 being white, in order to clearly distinguish between the cBN particle and the binder phase. 、 Perform binarization processing.

[0024] Furthermore, it is desirable to select an area of ​​approximately 0.5 μm × 0.5 μm as the area for determining the pixel value of the cBN particle portion, and to use the average value determined from at least three different locations within the same image area as the pixel value of the cBN.

[0025] After the binarization process, a process is performed to separate the cBN grains that are thought to be in contact with each other, for example, watershed processing is used to separate the cBN grains that are thought to be in contact with each other.

[0026] The areas corresponding to cBN particles (black areas) in the image (observation area) obtained after binarization were subjected to particle analysis, and the maximum length found was taken as the maximum length of each particle, which was then used as the diameter of each particle.In particle analysis to find the maximum length, the Feret diameter of one cBN particle was calculated, and the larger of the two lengths found was taken as the maximum length, which was then used as the diameter of each particle.

[0027] Then, assuming each particle is an ideal sphere with this diameter, the cumulative volume is calculated as the volume of each particle. Based on this cumulative volume, a graph is drawn with the vertical axis representing volume percentage (%) and the horizontal axis representing diameter (μm), and the diameter at a volume percentage of 50% is taken as the average particle size of the cBN particles. This is done for three observation areas, and the average value is taken as the average particle size (μm) of the cBN.

[0028] When performing this particle analysis, the length per pixel (μm) is set using the scale value known in advance from the SEM. As the observation area used for image processing, if the average particle size of the cBN particles is about 3 μm, a field of view of about 15 μm x 15 μm is desirable.

[0029] The content (volume %) of cBN particles in the cBN sintered compact is not particularly limited. If the content of cBN particles is less than 65 volume %, the sintered compact contains little hard material, and when used as a drilling tool, the chipping resistance may decrease. On the other hand, if it exceeds 93 volume %, voids that can become crack starting points may be generated in the sintered compact, and the chipping resistance may decrease. Therefore, to further demonstrate the effects of this embodiment, the content of cBN particles in the cBN sintered compact is preferably in the range of 65 to 93 volume %.

[0030] The cBN particle content of a cBN sintered body can be determined as follows: the cross-sectional structure of the cBN sintered body is observed using an SEM, the cBN particle portion of the obtained secondary electron image is extracted using image processing, the area occupied by the cBN particles is calculated using image analysis, and the average of the values ​​obtained from at least three images is taken as the cBN particle content (volume %). For an average cBN particle diameter of 3 μm, a viewing area of ​​approximately 15 μm × 15 μm is desirable for the observation area used in image processing.

[0031] Bonded phase: The ceramic binder phase of this embodiment can be made using Ti2AlC powder, Ti3AlC2 powder, TiN powder, TiC powder, TiCN powder, TiAl3 powder, and Co powder.

[0032] When the peak intensities of TiCN and CoB, which are components of the binder phase, are in a predetermined relationship during XRD measurement, that is, The peak intensity of Ti2CN appearing at 2θ = 41.9 to 42.2° in the XRD measurement is I Ti2CN The peak intensity I of Co2B appearing at 2θ = 45.7 to 45.9° is Co2B Then, the peak intensity ratio, I Ti2CN / I Co2B If the value is 0.5 to 2.0, the cBN sintered body has excellent wear resistance and abrasive wear resistance during rock excavation, and is highly resistant to damage such as chipping due to impacts and vibrations during rock excavation, which is preferable.

[0033] The reason why Co2B is produced in sintered bodies after ultra-high-pressure, high-temperature sintering is speculated to be as follows: First, during sintering under ultra-high pressure, Ti2AlC or Ti3AlC2 reacts with Co to produce TiAlCo. This TiAlCo reacts with cBN to produce Co2B. When this Co2B is produced, TiB2 is also produced.

[0034] Based on this assumption, I Ti2CN / I Co2B The reasons for setting the range are as follows:Ti2CN / I Co2B If the ratio is less than 0.5, the proportion of Co2B generated by the reaction between TiAlCo and cBN is high in the sintered body, and this Co2B is brittle and can become the starting point of fracture when excavating rock. Ti2CN / I Co2B If the value is greater than 2.0, the amount of Co2B in the sintered compact produced by the reaction of cBN with the binder phase raw material will be small. In this case, the adhesive strength between cBN and the binder phase will be reduced, resulting in a decrease in the abrasive wear resistance of the sintered compact and resistance to damage such as chipping caused by impacts and vibrations during rock excavation.

[0035] Here, the peak intensity of TiCN (I Ti2CN ) and Co2B peak intensity (I Co2B ) is confirmed by XRD measurement using a Cu tube. That is, the peak position (angle) of the 111 diffraction line of cBN is set to 2θ = 43.3, and based on this, the peak between 2θ = 41.9 to 42.2° is determined to be Ti2CN, and the peak between 2θ = 45.7 to 45.9° is determined to be Co2B. After background removal, a peak search is performed to confirm the intensity of each peak.

[0036] The binder phase contains TiB2, and the peak intensity of TiB2 appearing at 2θ = 44.4 to 44.6 in XRD measurement is shown as I TiB2 When this is done, the ratio of the peak intensity of Co2B to that of I Co2B / I TiB2 It is more preferable that the ratio is 1.2 or more and 3.4 or less.

[0037] The reasons are as follows: Co2B / I TiB2 If the ratio is less than 1.2, excessive TiB2, which is hard but has low toughness, is produced in the sintered body, forming coarse TiB2 particles, which can become the starting point for fractures during rock excavation.

[0038] Also, I Co2B / I TiB2When the ratio exceeds 3.4, there is extremely little TiB2 compared to Co2B, and the sintered body will contain a lot of Co2B formed by the direct reaction of Co with cBN, rather than Co2B formed by the TiAlCo formed by the initial reaction of Ti2AlC or Ti3AlC2 with Co reacting with cBN. This reduces the adhesive strength between the cBN and the binder phase, which can reduce the abrasive wear resistance of the sintered cBN and its resistance to damage such as chipping caused by impacts and vibrations during rock excavation.

[0039] Bonded phase manufacturing method: The binder phase of the cBN sintered body of this embodiment can be produced, for example, as follows.

[0040] That is, prior to ultra-high pressure, high temperature sintering, Ti2AlC or Ti3AlC2 with a particle size in the range of 1 to 500 μm and Co with an average particle size of a few microns or less are prepared. This is mixed with other raw materials and heat-treated at 250°C to 900°C under vacuum. This reduces the amount of water adsorbed on the surface of the raw materials without decomposing the coarse-grained Ti2AlC or Ti3AlC2 into TiO2 and Al2O3. This reduces the oxidation of Co during ultra-high pressure, high temperature sintering and also allows the Ti2AlC or Ti3AlC2 and Co to react first.

[0041] By not finely crushing the Ti2AlC or Ti3AlC2, the grains do not react with oxygen, and ultra-high pressure sintering is performed to produce Ti2CN within the sintered body. Co first reacts with Ti2AlC or Ti3AlC2 to produce TiAlCo. This TiAlCo then reacts with cBN to produce Co2B, TiB2, and AlN. This increases the bonding strength between the cBN and the binder phase.

[0042] Furthermore, the decrease in toughness due to the coarse grains of the binder phase can be compensated for by the improved toughness that results from the dispersion of fine Co2B particles in the sintered body. As a result, it is possible to obtain a cBN sintered body that is highly resistant to wear and abrasive wear during rock excavation, as well as to damage such as chipping caused by impacts and vibrations during rock excavation. [Example]

[0043] Next, examples will be described, but the present invention is not limited to the examples in any way.

[0044] This example was produced by the following steps (1) to (3).

[0045] (1) Preparation of raw powder As the hard raw material, cBN raw material with an average particle size of 0.5 to 35 μm was prepared, and as the raw material powders constituting the binder phase, Ti2AlC or Ti3AlC2 raw material and Co raw material were prepared. The Ti2AlC or Ti3AlC2 raw material had an average particle size of 50 μm, and the Co raw material had an average particle size of 1 μm. In addition, TiN powder, TiC powder, TiCN powder, and TiAl3 powder were separately prepared as raw material powders constituting the binder phase. The average particle sizes of these separately prepared powders were 0.3 μm to 0.9 μm. The blending compositions of these raw materials are shown in Table 1.

[0046] (2) Mixture These raw material powders were mixed, and then filled into a cemented carbide-lined container together with cemented carbide balls and acetone. After the container was closed, mixing was carried out using a ball mill. The mixing time was 1 hour so as not to crush the raw material powder into small pieces. Although not performed in this example, it is more preferable to use an ultrasonic agitator to break down the agglomerates of the raw material powder while mixing.

[0047] (3) Molding and sintering The obtained sintered body raw material powder was then molded under a predetermined pressure to produce a compact, which was then pre-heat treated. After that, it was charged into an ultra-high pressure sintering apparatus and sintered at a pressure of 5 GPa and a temperature of 1600°C to produce cBN sintered bodies 1 to 15 of the examples shown in Table 2 (referred to as example sintered bodies).

[0048] The preliminary heat treatment was performed in a vacuum atmosphere with a pressure of 1 Pa or less, at a temperature between 250°C and 900°C (referred to as the "heat treatment temperature after mixing" in Table 2). The reason for this is as follows: Below 250°C, adsorbed water does not sufficiently dissociate from the raw material surface. This moisture oxidizes Co during ultra-high-pressure, high-temperature sintering, inhibiting its reaction with Ti2AlC or Ti3AlC2. Furthermore, Ti2AlC or Ti3AlC2 reacts with the moisture adsorbed on the raw materials during ultra-high-pressure, high-temperature sintering, decomposing into TiO2 and Al2O3. As a result, the amount of Ti2CN in the binder phase of the sintered compact after ultra-high-pressure, high-temperature sintering decreases, reducing the toughness of the sintered compact.

[0049] Furthermore, at temperatures above 900°C, Ti2AlC or Ti3AlC2 reacts with the oxygen in the adsorbed water during the pre-heat treatment and decomposes into TiO2 and Al2O3. This leaves no Ti2AlC or Ti3AlC2 to react with Co during ultra-high-pressure sintering. As a result, TiAlCo is not produced, and the reaction with cBN is insufficient, reducing the adhesive strength between the cBN and the binder phase. This reduces the abrasive wear resistance of the sintered compact and its resistance to damage such as chipping caused by impacts and vibrations during rock excavation.

[0050] For comparison, comparative sintered bodies were prepared. The raw material powders were prepared as follows: cBN raw material with an average particle size of 1.0 to 4.0 μm as the hard raw material; and raw material powder containing Ti2AlC or Ti3AlC2 and Co as the raw material powder constituting the binder phase. The Ti2AlC and Ti3AlC2 raw materials had an average particle size of 50 μm, and the Co raw material had an average particle size of 1 μm. These were blended to obtain the compositions shown in Tables 1 and 3, and mixed in a ball mill under the same conditions as in the examples.

[0051] The mixture was then molded at a predetermined pressure to produce a green compact, which was then pre-heat treated at a predetermined temperature within the range of 100°C to 1200°C (referred to as "heat treatment temperature after mixing" in Table 4), and then loaded into an ultra-high pressure sintering apparatus and sintered at a pressure of 5 GPa and a temperature of 1600°C to produce comparative cBN sintered bodies 1 to 5 shown in Table 4 (referred to as comparative sintered bodies).

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] [Table 4]

[0056] Here, Fig. 1 shows an XRD measurement chart of Example sintered body 4. As is clear from the figure, the sintered body has a peak intensity of Ti2CN appearing at 2θ = 41.9 to 42.2° in the XRD measurement. Ti2CN The peak intensity of Co2B appearing at 2θ = 45.7 to 45.9° is defined as I Co2B When the ratio of the peak intensities is Ti2CN / I Co2B It can be seen that satisfies 0.5 to 2.0.

[0057] Next, from the sintered bodies 1 to 15 of the examples and the sintered bodies 1 to 5 of the comparative examples, Examples 1 to 15 and Comparative Examples 1 to 5 were used as tools having the shape specified in ISO standard RNGN090300. comparison Examples 1 to 5 were prepared, and these tools were attached to an NC lathe, and the following wet cutting test was carried out.

[0058] Cutting speed: 150m / min Depth of cut: 0.3mm Feed rate: 0.1mm / rev Material: Granite (Takine) Shape: Φ150mm x 200mmL

[0059] The amount of wear and condition of the cutting edge were checked when the cutting length (cutting distance) was 800 m. However, the cutting edge was observed every 100 m of cutting length to measure the presence or absence of chipping and the amount of wear, and if the amount of wear exceeded 2000 μm, the cutting test was stopped at that point. The results are shown in Table 5.

[0060] [Table 5]

[0061] As is clear from Table 5, all of the Examples exhibited little wear and no chipping, and therefore had excellent abrasive wear resistance, and were resistant to damage such as breakage caused by impacts and vibrations used to break rock, even when used as drilling tools. On the other hand, the Comparative Examples exhibited breakage or large wear even after only a short cutting length, and therefore had poor abrasive wear resistance and were prone to breakage, making them difficult to use as drilling tools.

[0062] The above-disclosed embodiments are merely illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, not by the above-disclosed embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

Claims

[Claim 1] A cBN sintered body having cubic boron nitride particles and a binder phase, The binder phase contains Ti ２ CN and Co ２ B and TiB2, Ti appearing at 2θ = 41.9 to 42.2° in XRD measurement ２ The CN peak intensity is I Ｔｉ２ＣＮ Co appears at 2θ=45.7 to 45.9° ２ The peak intensity of B is I Ｃｏ２Ｂ When The ratio of the peak intensities, I Ｔｉ２ＣＮ / I Ｃｏ２Ｂ satisfies 0.5 to 2.0, TiB appears at 2θ = 44.4 to 44.6 in XRD measurement ２ The peak intensity of I ＴｉＢ２ When Co ２ Ratio of the peak intensity of B to the peak intensity of I Ｃｏ２Ｂ / I ＴｉＢ２ is 1.2 to 3.4, The binder phase further comprises AlN. A cBN sintered body characterized by:

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