Patent Application
20240425953
The present invention relates to a cubic boron nitride sintered body.
Cubic boron nitride (hereinafter also referred to as “cBN”) has hardness second only to diamond, and excellent thermal conductivity. Cubic boron nitride also has a characteristic of low affinity with iron as compared with diamond. Therefore, a cubic boron nitride sintered body containing cubic boron nitride and a binder phase of a metal or ceramic is used in a cutting tool or a wear resistant tool.
Demand for improved cutting tool performance to difficult-to-cut materials such as heat-resistant alloys has been increasing in recent years. In particular, in processing sintered metals having high moldability, work materials have complicated shapes in many cases, and hence when they are processed with a tool, the tool is easily fractured by thermal shock. Besides, since sintered metals may contain hard particles in some cases, the tool is easily worn away. Therefore, cubic boron nitride is used in many cases of processing sintered metals, and in particular, many studies have been made on cubic boron nitride sintered bodies having a high cubic boron nitride content.
For example, Japanese Patent Laid-Open No. 2014-208889 discloses a sintered body containing: hard particles each consisting of one or more selected from the group consisting of cubic boron nitride, Al2O3, AlON, SiAlON, TiC, TiCN, TiN, WC, and diamond; and a metal phase represented by (Co,Ni)3(Al,W,V,Ti).
If the hard particles in the sintered body disclosed in Japanese Patent Laid-Open No. 2014-208889 are made of cubic boron nitride (also referred to as cBN), the sintered body may be insufficient in the interparticle binding strength of the cBN, thus leaving room for improvement in fracture resistance.
The present invention has an object to provide a cubic boron nitride sintered body capable of extending the tool life.
The present inventor has diligently examined to find that a cubic boron nitride sintered body capable of extending the tool life can be obtained if a cBN sintered body has a specific constitution. Finally, the present inventor has completed the present invention based on such findings.
The gist of the present invention is as set forth below.
[1]
A cubic boron nitride sintered body comprising cubic boron nitride and a binder phase, wherein a content ratio of the cubic boron nitride is 80 volume % or more and 94 volume % or less based on the total amount of the sintered body, a content ratio of the binder phase is 6 volume % or more and 20 volume % or less based on the total amount of the sintered body, the binder phase comprises a metal phase, a V compound, and an Al compound, the metal phase comprises one or more selected from a group consisting of Ni metal, a Ni-containing alloy, and a Ni-containing solid solution, the Ni-containing alloy and the Ni-containing solid solution each comprise Ni and one or more elements selected from a group consisting of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, and Co, the V compound comprises one or more selected from a group consisting of VN, VCN, and VC, the Al compound comprises one or more selected from a group consisting of Al2O3, AlN, and AlB2, a maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction is less than 51.60°, and I1/(I1+I2) is 0.40 or more and 0.80 or less, where I1 denotes an X-ray diffraction peak intensity of a (220) plane of the V compound, and I2 denotes an X-ray diffraction peak intensity of the (200) plane of the metal phase.
[2]
The cubic boron nitride sintered body according to [1], wherein a full width at half maximum (°) of a peak of the (200) plane of the metal phase in X-ray diffraction is 0.40° or more and 0.70° or less.
[3]
The cubic boron nitride sintered body according to [1] or [2], wherein I1/I3 is 0.70 or more and 1.50 or less, where I3 denotes an X-ray diffraction peak intensity of the (220) plane of the cubic boron nitride.
[4]
The cubic boron nitride sintered body according to any one of [1] to [3], wherein a maximum peak position 2θ (°) of the (220) plane of the V compound in X-ray diffraction is less than 63.40°.
[5]
The cubic boron nitride sintered body according to any one of [1] to [4], wherein a maximum peak position 2θ (°) of the (200) plane of the metal phase in X-ray diffraction is less than 51.40°.
According to the present invention, a cubic boron nitride sintered body capable of extending the tool life can be provided.
An embodiment for carrying out the present invention (hereinafter simply referred to as the “present embodiment”) will hereinafter be described in detail. However, the present invention is not limited to the present embodiment described below. Various modifications may be made to the present invention without departing from the gist of the invention.
A cubic boron nitride sintered body according to the present embodiment is a cubic boron nitride sintered body including cubic boron nitride and a binder phase, wherein a content ratio of the cubic boron nitride is 80 volume % or more and 94 volume % or less based on the total amount of the sintered body, a content ratio of the binder phase is 6 volume % or more and 20 volume % or less based on the total amount of the sintered body, the binder phase contains a metal phase, a V compound, and an Al compound, the metal phase contains one or more selected from the group consisting of Ni metal, a Ni-containing alloy, and a Ni-containing solid solution, the Ni-containing alloy and the Ni-containing solid solution each contain Ni and one or more elements selected from the group consisting of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, and Co, the V compound contains one or more selected from the group consisting of VN, VCN, and VC, the Al compound contains one or more selected from the group consisting of Al2O3, AlN, and AlB2, a maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction is less than 51.60°, and I1/(I1+I2) is 0.40 or more and 0.80 or less, where I1 denotes an X-ray diffraction peak intensity of a (220) plane of the V compound, and I2 denotes an X-ray diffraction peak intensity of a (200) plane of the metal phase.
Including the above-described constitution, the cubic boron nitride sintered body according to the present embodiment can extend tool life.
The detailed reason why the cubic boron nitride sintered body according to the present embodiment provides an extended tool life is not clear, but the present inventor considers the reason as follows. However, the reason is not limited thereto.
Since the content ratio of the cubic boron nitride is 80 volume % or more based on the total amount of the sintered body in the cubic boron nitride sintered body of the present embodiment, the hardness of the cBN sintered body is improved, and hence the wear resistance is excellent. Since the content ratio of the cubic boron nitride is 94 volume % or less based on the total amount of the sintered body, the content ratio of the binder phase is relatively high, and hence the cBN particles can be inhibited from dropping off, and the wear resistance is excellent.
Since the content ratio of the binder phase is 6 volume % or more based on the total amount of the sintered body, the cBN particles can be inhibited from dropping off, and the wear resistance is excellent. Since the content ratio of the binder phase is 20 volume % or less based on the total amount of the sintered body, the content ratio of the cBN is relatively high and the hardness of the cBN sintered body is improved, and hence the wear resistance is excellent.
Since the maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction is less than 51.60°, the thermal resistance is improved, and the wear resistance is excellent.
Since I1/(I1+I2) is 0.40 or more, where I1 denotes an X-ray diffraction peak intensity of a (220) plane of the V compound, and I2 denotes an X-ray diffraction peak intensity of a (200) plane of the metal phase, the interparticle binding strength of the cBN is improved, and hence the fracture resistance is excellent. Since the effect of the binder phase to inhibit the cBN particles from dropping off is increased, the wear resistance is also improved.
Since I1/(I1+I2) is 0.80 or less, the sinterability is improved, and hence the toughness of the sintered body is improved, and the fracture resistance is excellent.
The cubic boron nitride sintered body of the present embodiment, owing to a combination of those effects, is excellent in fracture resistance.
The cubic boron nitride sintered body of the present embodiment contains the cBN and the binder phase. It is noted that the total content ratio of the cBN and the binder phase in the cubic boron nitride sintered body of the present embodiment is 100 volume %.
The binder phase contains a metal phase, a V compound, and an Al compound.
The content ratio (volume %) of the Al compound is preferably 0.5 volume % or more and 5.0 volume % or less, more preferably 0.8 volume % or more and 4.3 volume % or less, and further preferably 0.8 volume % or more and 3.2 volume % or less based on the total amount of the sintered body.
The total content ratio of the metal phase and the V compound is preferably 5.0 volume % or more and 18.0 volume % or less, more preferably 5.2 volume % or more and 16.3 volume % or less, and further preferably 6.6 volume % or more and 12.5 volume % or less based on the total amount of the sintered body.
The metal phase contains one or more selected from the group consisting of Ni metal, a Ni-containing alloy, and a Ni-containing solid solution; the Ni-containing alloy and the Ni-containing solid solution each contain Ni and one or more elements selected from the group consisting of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, and Co; the V compound contains one or more selected from the group consisting of VN, VCN, and VC; and the Al compound contains one or more selected from the group consisting of Al2O3, AlN, and AlB2.
[Cubic Boron Nitride (cBN)]
Since the content ratio of the cubic boron nitride is 80 volume % or more in the cubic boron nitride sintered body of the present embodiment, the ratio of the binder phase is relatively low, and hence the hardness is improved, and the wear resistance is excellent. On the other hand, since the content ratio of the cubic boron nitride is 94 volume % or less in the cubic boron nitride sintered body of the present embodiment, the cubic boron nitride particles can be inhibited from dropping off, and hence the wear resistance is excellent. In addition, surface roughness on a surface to be processed of a work material is reduced in cutting processing, and appearance obtained after the processing tends to be favorable. From a similar point of view, the content ratio of the cubic boron nitride is preferably 80.5 volume % or more and 93.7 volume % or less and more preferably 83.2 volume % or more and 92.3 volume % or less.
Since the content ratio of the binder phase in the cubic boron nitride sintered body of the present embodiment is 6 volume % or more, the cBN particles can be inhibited from dropping off, and the wear resistance is excellent. On the other hand, since the content ratio of the binder phase in the cubic boron nitride sintered body is 20 volume % or less, the content ratio of the cBN is relatively high, and hence the hardness is improved, resulting in excellent wear resistance. From a similar point of view, the content ratio of the binder phase is preferably 6.3 volume % or more and 19.5 volume % or less, and more preferably 7.7 volume % or more and 16.8 volume % or less.
In the cubic boron nitride sintered body according to the present embodiment, the binder phase contains a metal phase, a V compound, and an Al compound.
The metal phase contains one or more selected from the group consisting of Ni metal, a Ni-containing alloy, and a Ni-containing solid solution, preferably contains one or more selected from the group consisting of a Ni-containing alloy and a Ni-containing solid solution, and more preferably contains a Ni-containing alloy.
The Ni-containing alloy and the Ni-containing solid solution each contain Ni and one or more elements selected from the group consisting of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, and Co, preferably contain Ni and one or more elements selected from the group consisting of Al and V, more preferably contain Ni element and V element, and further preferably contain Ni3V.
The V compound contains one or more selected from the group consisting of VN, VCN, and VC, and the Al compound contains one or more selected from the group consisting of Al2O3, AlN, and AlB2, preferably contains one or more selected from the group consisting of Al2O3 and AlN, and more preferably contains Al2O3.
Since the maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction is less than 51.60°, the thermal resistance is improved, and the wear resistance is excellent. From a similar point of view, the maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction is preferably less than 51.40°, and more preferably 50.80° or more and less than 51.30°.
If the maximum peak position 2θ of a (200) plane of the metal phase in X-ray diffraction falls within a range below, for example, the metal phase is regarded as Ni3V or Ni. The crystal structures of Ni3V and Ni are each cubic.
Accordingly, non-limiting examples of methods for setting the maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction within the above range include a method of allowing the metal phase to contain Ni3V. Furthermore, for example, if the content ratio of Ni3V in the metal phase is increased, the maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction tends to be small.
In the cubic boron nitride sintered body according to the present embodiment, the full width at half maximum (°) of a peak of a (200) plane of the metal phase in X-ray diffraction is preferably 0.40° or more and 0.70° or less. Finer structures tend to exhibit larger values of the full width at half maximum. Finer metal structures tend to result in improved hardness but in lower toughness.
Since the full width at half maximum (°) of a peak of a (200) plane of the metal phase in X-ray diffraction is 0.40° or more, the hardness of the metal phase is improved, and hence the wear resistance is excellent. Since the full width at half maximum (°) of a peak of a (200) plane of the metal phase in X-ray diffraction is 0.70° or less, the toughness of the metal phase is improved, and hence the fracture resistance is excellent. From a similar point of view, the full width at half maximum (°) of the peak of a (200) plane of the metal phase in X-ray diffraction is more preferably 0.42 or more and 0.67 or less, and further preferably 0.47 or more and 0.61 or less.
In the cubic boron nitride sintered body according to the present embodiment, the maximum peak position 2θ (°) of a (220) plane of the V compound in X-ray diffraction is preferably 62.60° or more and less than 63.40°.
Since the maximum peak position 2θ (°) of a (220) plane of the V compound in X-ray diffraction is less than 63.40°, the wear resistance tends to be further better. From a similar point of view, the maximum peak position 2θ (°) of a (220) plane of the V compound in X-ray diffraction is more preferably less than 63.10°.
If the maximum peak position 2θ of a (220) plane of the V compound in X-ray diffraction falls within a range below, the V compound is regarded as VC, VCN, or VN.
Accordingly, non-limiting examples of methods for setting the maximum peak position 2θ of a (220) plane of the V compound in X-ray diffraction within the above range include a method of allowing the V compound to contain larger amounts of VCN and/or VC, which are superior in hardness to VN.
Since I1/(I1+I2) is 0.40 or more, where I1 denotes an X-ray diffraction peak intensity of a (220) plane of the V compound, and I2 denotes an X-ray diffraction peak intensity of a (200) plane of the metal phase, the interparticle binding strength of the cBN is improved, and hence the fracture resistance is excellent. Since the effect of the binder phase to inhibit the cBN particles from dropping off is increased, the wear resistance is also improved.
Since I1/(I1+I2) is 0.80 or less, the sinterability is improved, and hence the toughness of the sintered body is improved, and the fracture resistance is excellent. From a similar point of view, I1/(I1+I2) is preferably 0.43 or more and 0.77 or less, and more preferably 0.53 or more and 0.64 or less.
In the cubic boron nitride sintered body according to the present embodiment, I1/I3 is preferably 0.70 or more and 1.50 or less, where I3 denotes an X-ray diffraction peak intensity of a (220) plane of the cubic boron nitride.
Since I1/I3 is 0.70 or more, the interparticle binding strength of the cBN is improved, and hence the fracture resistance is excellent. Since I1/I3 is 1.50 or less, the sinterability is improved, and hence the toughness of the sintered body is improved, and the fracture resistance is excellent. From a similar point of view, I1/I3 is preferably 0.72 or more and 1.45 or less, and more preferably 0.76 or more and 1.32 or less.
I1, I2 and I3 are each maximum intensity in a range of 20 below.
In the cubic boron nitride sintered body according to the present embodiment, the binder phase may contain an element other than the elements constituting the metal phase, the V compound, and the Al compound. Non-limiting specific examples thereof include Mn, Fe, and Si.
Such elements may be derived from, for example, a ball mill cylinder or ball, or a high-melting-point metal capsule used for filling, and may be unavoidably contained or intentionally added. The content ratio of such another element is not especially limited, and may be, for example, 0 mass % or more and 10 mass % or less based on 100 mass % in total of all the elements contained in the sintered body.
In the cubic boron nitride sintered body according to the present embodiment, the respective content ratios (volume %) of the cubic boron nitride and the binder phase can be determined by analyzing, using commercially available image analysis software, a structural photograph of the cubic boron nitride sintered body taken by a scanning electron microscope (SEM). More specifically, the cubic boron nitride sintered body is mirror-polished in a direction orthogonal to a surface thereof. Next, using a SEM, an observation is conducted on a backscattered electron image of the mirror-polished surface of the cubic boron nitride sintered body exposed via the mirror polishing. At this time, the mirror-polished surface of the cubic boron nitride sintered body is observed using a SEM via a backscattered electron image at a magnification such that 100 or more and 400 or less cubic boron nitride particles can be covered. Using an energy-dispersive X-ray spectroscope (EDS) included with the SEM, it can be determined that a black region is identified as cubic boron nitride, and a gray region and a white region are each identified as a binder phase. Thereafter, a structural photograph of the above cross section of the cubic boron nitride is taken using a SEM. With commercially available image analysis software, the respective occupied areas of the cubic boron nitride and the binder phase are obtained from the obtained structural photograph, and the content ratios (volume %) are obtained from the occupied areas.
For example, in the binder phase, a gray region can correspond to the Al compound, and a white region can correspond to the metal phase or the V compound. This image is analyzed, and the proportion of the gray region is calculated as “the content ratio (volume %) of the Al compound”. The proportion of the white region is calculated as “the total content ratio (volume %) of the metal phase and the V compound”.
In the present embodiment, the content ratio (mass %) of each of the elements in the binder phase can be determined using an energy-dispersive X-ray spectroscope (EDS) in the same observation field as that of a structural photograph of the cubic boron nitride sintered body taken with a scanning electron microscope (SEM) for obtaining the content ratios (volume %) of the cubic boron nitride and the binder phase. More specifically, EDS analysis is performed in the entire observation field of the magnified mirror-polished surface, and a content ratio (mass %) of each element is calculated assuming that the total content of all the elements contained in the cubic boron nitride sintered body is 100 mass %.
Herein, the mirror-polished surface of the cubic boron nitride sintered body is a cross section of the cubic boron nitride sintered body obtained by mirror-polishing the surface of the cubic boron nitride sintered body or an arbitrary cross-section thereof. Examples of a method for obtaining a mirror-polished surface of a cubic boron nitride sintered body include a polishing method using diamond paste.
The composition of a binder phase can be identified using a commercially available X-ray diffractometer. For example, when an X-ray diffraction measurement is performed, using an X-ray diffractometer (product name “SmartLab”) manufactured by Rigaku Corporation, by means of a 2θ/θ focusing optical system with Cu-Kα radiation, the composition of the binder phase can be identified. Here, measurement conditions are, for example, preferably conditions described later in Examples. Analysis with a broader 2θ measurement range tends to allow more peaks to be detected, and materials contained in the sintered body can be more reliably specified. From such a point of view, measurement, for example, in the range of 2θ=20 to 140° is preferable.
In the present embodiment, the cubic boron nitride content ratio and the binder phase content ratio, and the binder phase composition can be determined by the methods described in the Examples mentioned below.
Specifically, the composition of the binder phase can be specified by analyzing a measurement result obtained with an X-ray analyzer, and an element mapping result obtained using an EDS.
The cubic boron nitride sintered body according to the present embodiment is manufactured, for example, in the following manner.
As raw material powder, cBN powder, VC powder, VN powder, Ni powder, and Al powder are prepared. Here, the average particle size of the cBN in an obtained cubic boron nitride sintered body can be controlled within the above specific range by appropriately adjusting the average particle size of the raw material cBN powder. In addition, the content ratios of the cBN and the binder phase in an obtained cubic boron nitride sintered body can be controlled within the above specific ranges by appropriately adjusting the proportion of each raw material powder. Next, the prepared raw material powder is put in a ball mill cylinder together with cemented carbide balls, a solvent, and paraffin, and then mixed. The raw material powder mixed with a ball mill is filled in a high-melting-point metal capsule made of Ta, and subjected to a vacuum heat treatment with the capsule left opened for removing moisture adsorbed onto the surface of the powder and another adhering component. In filling the raw material powder in the capsule, a substrate of cemented carbide may be put therein.
Next, the capsule is sealed, and the raw material powder filled in the capsule is sintered at a high pressure. For example, the conditions of the high-pressure sintering are a pressure of 6.0 to 9.0 GPa, a temperature of 1600 to 1900° C., and a sintering time of 15 to 60 minutes.
Furthermore, after the high-pressure sintering, the temperature and/or the pressure is lowered and retained. For example, the retention conditions are a pressure of 2.0 to 5.0 GPa, a temperature of 600 to 1000° C., and a retention time of 60 to 150 minutes.
In the present embodiment, non-limiting examples of a method for setting high the content ratio of the cubic boron nitride include a method in which the blending proportion of the cBN in the blending composition is increased in the above-described production process of the cubic boron nitride sintered body.
In the present embodiment, non-limiting examples of a method for setting high the I1/(I1+I2) described above include a method in which the total proportion of the V-containing compound (for example, VC, VN) is set higher than the total proportion of Ni and the V-containing compound (for example, VC, VN) in the blending composition in the above-described production process of the cubic boron nitride sintered body.
In the present embodiment, non-limiting examples of a method for setting high the I1/I3 described above include a method in which the blending proportion of the cBN in the blending composition is decreased in the above-described production process of the cubic boron nitride sintered body.
In the present embodiment, non-limiting examples of a method for setting low the full width at half maximum (°) of a peak of a (200) plane of the metal phase in X-ray diffraction include a method in which the pressure in the retention is increased in the above-described production process of the cubic boron nitride sintered body.
In the present embodiment, non-limiting examples of a method for setting low the maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction include a method in which the temperature in the sintering is increased in the above-described production process of the cubic boron nitride sintered body, and a method in which the pressure in the retention is increased.
In the present embodiment, non-limiting examples of a method for forming the metal phase as Ni3V and a method for setting low the maximum peak position 2θ (°) of a (220) plane of the V compound in X-ray diffraction include a method in which VC is used as a raw material of the V compound in the above-described production process of the cubic boron nitride sintered body.
The cubic boron nitride sintered body according to the present embodiment may be used as a coated cubic boron nitride sintered body including a coating layer on a surface thereof. The coating layer formed on a surface of the cubic boron nitride sintered body further improves the wear resistance. The coating layer is not especially limited, and may include, for example, an element of at least one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and an element of at least one selected from the group consisting of C, N, O, and B. The coating layer may have a single-layer structure or a laminated structure including two or more layers.
When the coating layer has such structures, the coated cubic boron nitride sintered body according to the present embodiment tends to show further improved wear resistance.
Non-limiting examples of compounds forming the coating layer include TiN, TiC, TiCN, TiAlN, TiSiN, AlCrN, and the like. Among these, TiCN, TiAlN, and AlCrN are preferred. The coating layer may have a structure in which multiple layers each having a different composition are laminated.
The thickness of each layer that constitutes the coating layer and the thickness of the entire coating layer can be measured from a cross-sectional structure of the coated cubic boron nitride sintered body using an optical microscope, a SEM, a transmission electron microscope (TEM), or the like. It should be noted that, as to the average thickness of each layer and the average thickness of the entire coating layer in the coated cubic boron nitride sintered body, such average thicknesses can be obtained by measuring, near the position 50 μm from the edge of a surface facing the metal evaporation source toward the center of such surface, the thickness of each layer and the thickness of the entire coating layer from each of the cross sections at three or more locations, and calculating the average value thereof.
The composition of each layer that constitutes the coating layer can be measured from a cross-sectional structure of the coated cubic boron nitride sintered body using an EDS, a wavelength-dispersive X-ray spectroscope (WDS), or the like.
A method of manufacturing a coating layer is not particularly limited, and examples of such methods include chemical deposition methods and physical vapor deposition methods, such as an ion plating method, an arc ion plating method, a sputtering method, and an ion mixing method. Among them, arc ion plating methods are preferred because further better adhesiveness between the coating layer and the cubic boron nitride sintered body can be provided.
The cubic boron nitride sintered body or the coated cubic boron nitride sintered body according to the present embodiment is capable of extending tool life, and therefore preferably used as cutting tools and wear-resistant tools, and among them, is preferably used as cutting tools. The cubic boron nitride sintered body or the coated cubic boron nitride sintered body according to the present embodiment is further preferably used as cutting tools for sintered metals or cast iron. The tool life can be extended compared to conventional tools when the cubic boron nitride sintered body or the coated cubic boron nitride sintered body according to the present embodiment is used as cutting tools or wear-resistant tools.
Although the present invention will be described in further detail below with examples, the present invention is not limited to such examples.
As raw materials of cBN sintered bodies, raw material powders having average particle sizes shown in Table 1 were prepared.
The average particle size of each raw material powder was measured in accordance with the Fisher process (Fisher Sub-Sieve Sizer (FSSS)) disclosed in the American Society for Testing Materials (ASTM) standard B330.
The raw material powders were weighed so as to give a blending composition (volume %) shown in Table 2. The weighed raw material powder, hexane solvent, and paraffin were put in a ball mill cylinder together with an alumina ball, and mixed for 2 hours.
The mixed raw material powder was filled in a disc-shaped high-melting-point metal capsule made of Ta. For removing moisture adsorbed onto the surface of the filled raw material powder and organic components, a vacuum heat treatment was performed with the capsule left opened to remove moisture adsorbed onto the surface of the powder and another adhering component, and the capsule was then sealed.
Thereafter, the raw material powder filled in the capsule was sintered at a high pressure. The following Table 3 shows the conditions for the high-pressure sintering.
Next, the temperature and pressure were lowered to the retention conditions shown in Table 3, and retained for a period of time shown in Table 3; thus, a sintered body was obtained.
The content ratios (volume %) of the cubic boron nitride and the binder phase in the cubic boron nitride sintered body obtained by high-pressure sintering was determined by analyzing a structural photograph of the cubic boron nitride sintered body, which had been taken by a scanning electron microscope (SEM), using commercially available image analysis software. More specifically, the cubic boron nitride sintered body was mirror-polished in a direction orthogonal to a surface thereof. Next, a backscattered electron image of the mirror-polished surface of the cubic boron nitride sintered body exposed via the mirror polishing was observed using a SEM. At this time, the mirror-polished surface of the cubic boron nitride sintered body was observed using the SEM via a backscattered electron image at a magnification such that 100 or more and 400 or less cubic boron nitride particles could be covered. Using an energy-dispersive X-ray spectroscope (EDS) included with the SEM, a black region was identified as cubic boron nitride, and gray and white regions were identified as binder phases. Thereafter, a structural photograph of the mirror-polished surface of the cubic boron nitride was taken using the SEM. With commercially available image analysis software, the respective occupied areas of the cubic boron nitride and the binder phase were determined from the obtained structural photograph, and the content ratios (volume %) were determined from the occupied areas.
Here, the mirror-polished surface of the cubic boron nitride sintered body was a cross section of the cubic boron nitride sintered body obtained by mirror-polishing the surface of the cubic boron nitride sintered body or an arbitrary cross-section thereof. Polishing using diamond paste was adopted as the method for obtaining a mirror-polished surface of a cubic boron nitride sintered body (hereinafter also referred to as the “cross section”). In the binder phase, a gray region was found to correspond to an Al compound, and a white region was found to correspond to a metal phase or a V compound. This image was analyzed, and the proportion of the gray region was calculated as “the content ratio (volume %) of the Al compound”. The proportion of the white region was calculated as “the total content ratio (volume %) of the metal phase and the V compound”.
The composition of the binder phase was identified using an X-ray diffractometer (product name “SmartLab”) manufactured by Rigaku Corporation. Specifically, a result of X-ray diffraction measurement of a 2θ/θ focusing optical system performed using Cu-Kα ray under the following conditions and an element mapping result using an EDS were analyzed to identify the composition of the binder phase.
Specifically, it was specified, through the X-ray diffraction measurement performed by the above-described method, that the obtained cubic boron nitride sintered body contained the materials shown in Table 4.
As to the compound containing Al element, no clear peak was obtained in the X-ray diffraction measurement, and hence the identification was performed through the element mapping using an EDS. As a result, it was found that all the cubic boron nitride sintered bodies obtained contained an Al compound.
Also found was a material that was not identified through X-ray diffraction measurement but identified only from an element mapping result. Specifically, for invention sample 16, no clear peak was detected in X-ray diffraction measurement, but a phase that was expected to be AlB2 from an element mapping result was observed. Also in other invention samples and comparative samples, AlB2 can be present as such a fine phase that is unidentifiable at the magnification in the present example.
The measurement results thus obtained are all listed in Table 4.
Simultaneously with the above X-ray diffraction measurement, the X-ray diffraction peak intensity I1 of a (220) plane of a V compound, the X-ray diffraction peak intensity I2 of a (200) plane of a metal phase, the X-ray diffraction peak intensity I3 of a (220) plane of cubic boron nitride, the maximum peak position 2θ (°) of a (200) plane of a metal phase in X-ray diffraction, and the maximum peak position 2θ (°) of a (220) plane of a V compound in X-ray diffraction were acquired.
From the X-ray diffraction peak intensity I1 of a (220) plane of a V compound, the X-ray diffraction peak intensity I2 of a (200) plane of a metal phase, the X-ray diffraction peak intensity I3 of a (220) plane of cubic boron nitride, and the maximum peak position 2θ (°) of a (200) plane of a metal phase in X-ray diffraction, I1/(I1+I2), I1/I3, and the full width at half maximum (°) of a peak of a (200) plane of a metal phase in X-ray diffraction were calculated.
The X-ray diffraction peak for each crystal plane was specified on the bases of the corresponding range shown below. The values thus obtained are summarized in Table 5.
A V compound was regarded as VC, VCN, or VN when the maximum peak position 2θ fell within the corresponding range in the following.
A metal phase was regarded as Ni3V or Ni when the maximum peak position 2θ in X-ray diffraction fell within the corresponding range in the following.
The obtained cubic boron nitride sintered body was cut out so as to correspond to the insert-shaped tool shape defined in the ISO standard CNGA 120408 using a wire electric discharge machine. The cut-out cubic boron nitride sintered body was joined to a cemented carbide base metal via brazing.
By using the obtained cutting tools, a cutting test was performed under the following conditions.
Evaluation items: The tool life was defined as when the width of the flank wear of the tool had reached 0.15 mm, or when the tool had been fractured, and the processing time to the tool life was measured. Besides, damage forms obtained when the tool life reached were observed. Measurement results are shown in Table 6.
Based on the results shown in Table 6, the following was found: The invention samples, in each of which the cubic boron nitride sintered body contains the cubic boron nitride and the binder phase, the content ratio of the cubic boron nitride is 80 volume % or more and 94 volume % or less based on the total amount of the sintered body, the content ratio of the binder phase is 6 volume % or more and 20 volume % or less based on the total amount of the sintered body, the binder phase contains a metal phase, a V compound, and an Al compound, the metal phase contains one or more selected from the group consisting of Ni metal, a Ni-containing alloy, and a Ni-containing solid solution, the Ni-containing alloy and the Ni-containing solid solution each contain Ni and one or more elements selected from the group consisting of Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, and Co, the V compound contains one or more selected from the group consisting of VN, VCN, and VC, the Al compound contains one or more selected from the group consisting of Al2O3, AlN, and AlB2, a maximum peak position 2θ (°) of a (200) plane of the metal phase in X-ray diffraction is less than 51.60°, and I1/(I1+I2) is 0.40 or more and 0.80 or less, where I1 denotes an X-ray diffraction peak intensity of a (220) plane of the V compound, and I2 denotes an X-ray diffraction peak intensity of a (200) plane of the metal phase, are excellent in wear resistance and fracture resistance and have extended tool life as compared with the comparative samples not having these features.
The cubic boron nitride sintered body of the present invention can extend the tool life compared to conventional ones, and is highly industrially applicable in that point.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-102325 | Jun 2023 | JP | national |
