Patent Application
20080066388
An embodiment of the present invention will be shown in examples below.
In the present example, an average particle size of the sintered diamond object powder, the content of the sintered diamond particle in the sintered diamond object, and a composition of the binder are varied and the transverse rupture strength and a flank wear amount were measured. Specifically, a vacuum furnace containing a rotary mixer was used to dry-blend the diamond powder having an average particle size of 0.8 μm and mixture powder of Co metal and Ti metal serving as the binder under such a condition as a degree of vacuum of 0.1 Pa, a furnace temperature of 300° C., and the number of revolutions of 2000 rpm. The blended diamond powder and various binders were filled in a container made of Ta (tantalum) in a state that the mixture was in contact with a disk made of WC-6% Co hardmetal, and held for sintering for 10 minutes under a condition of a pressure from 5.7 GPa to 7.2 GPa and a temperature from 1500° C. to 1900° C. by using a belt-type extra-high-pressure apparatus. A sample in which Ti was added was presented for observation of the texture on the surface of the completed sintered object, so as to determine whether Ti is present continuously or discontinuously. The diamond particle that has grown to a particle size of not smaller than 300 μm during sintering was considered as the abnormally grown particle, and the number of such particles was counted. All sintered objects were worked into bar-shaped test pieces having a dimension of 6×3×0.3 mm, and thereafter its transverse rupture strength was measured in a three-point bending test under a condition of 4 mm span. In addition, a sintered object chip for cutting (ISO standard: TPGN160304) having a main surface shaped in a regular triangle was fabricated and subjected to a cutting test, in which a flank wear amount was measured. In the cutting test, an Al (aluminum) alloy round rod containing 16 mass % Si was used as a material to be cut, and the test was conducted with the use of a cutting liquid under a working condition of a cutting speed of 800 m/min, a cutting depth of 0.5 mm, a feed speed of 0.12 mm/rev, and a cutting time period of 5 minutes. The result is shown in Table 1. In Table 1, the sintered diamond object according to the present invention is represented by samples 1E and 1G. As a result of X-ray analysis of samples 1E and 1G, it was found that a part of added Ti was present as TiC.
As shown in Table 1, in samples 1A and 1D in which 100 mass % Co was used as a prepared composition of the binder and diamond powder has an average particle size of 0.8 μm, a large number of abnormally grown particles (258 and 231 particles) were observed in sample 1A and sample 1D respectively. In addition, some abnormally grown particles (11, 8 and 3 particles) were generated in 1C, 1F, and 1H respectively, in which W was added to the binder. On the other hand, in samples 1B, 1E, 1G, 1I, and 1N in which the binder phase contains at least 0.5 mass % Ti and diamond powder has an average particle size of 0.8 μm, abnormal particle growth was hardly observed. Therefore, it can be seen that abnormal particle growth can be suppressed by containing at least 0.5 mass % Ti in the binder phase.
In addition, when comparison is made between sample 1E in which diamond powder has an average particle size of 0.8 μm and sample 1L in which diamond powder has an average particle size of 2.5 μm, transverse rupture strength of sample 1E is larger than that of sample 1L. Therefore, it can be seen that chipping resistance is improved by setting the average particle size of the diamond particle to not larger than 2 μm.
Moreover, when comparison is made between samples 1B and 1C containing 78 volume % sintered diamond particle and samples 1E and 1F containing 90 volume % sintered diamond particle, the transverse rupture strength of samples 1E and 1F is larger than that of samples 1B and 1C, and flank wear amount of samples 1E and 1F is smaller than that of samples 1B and 1C. Therefore, it can be seen that chipping resistance and wear resistance are improved by setting the content of the sintered diamond particle to not smaller than 80 volume %.
Furthermore, when comparison is made between sample 1E containing 16.1 mass % Ti in the binder phase and sintered under the condition of a pressure of 7.2 GPa and a temperature of 1900° C. and sample 1F containing 25.6 mass % W in the binder phase and sintered under the condition of a pressure of 6.8 GPa and a temperature of 1800° C., the transverse rupture strength of sample 1E is larger than that of sample 1F, and flank wear amount of sample 1E is smaller than that of sample 1F. When comparison is made between sample 1G containing 46.2 mass % Ti in the binder phase and sintered under the condition of a pressure of 7.0 GPa and a temperature of 1900° C. and sample 1H containing 40.8 mass % W in the binder phase and sintered under the condition of a pressure of 6.7 GPa and a temperature of 1750° C., the transverse rupture strength of sample 1G is larger than that of sample 1H, and flank wear amount of sample 1G is smaller than that of sample 1H. As abnormal particle growth can be suppressed by containing Ti in the binder phase, a pressure and a temperature representing sintering conditions can be set higher. Therefore, it can be seen that chipping resistance and wear resistance can be improved.
Samples 1E and 1G according to the present invention attain higher transverse rupture strength and smaller flank wear amount than sample 1M representing a conventional product. In addition, it can be seen that abnormal particle growth did not occur in sample 1K having an average particle size of not smaller than 2 μm even if Ti was not added. Sample 1N containing 99 mass % diamond particle attains low transverse rupture strength and large flank wear amount. Therefore, it can be seen that neck growth achieved by the binder is insufficient.
In the present example, an average particle size of Ti contained in the binder was varied and the transverse rupture strength and the flank wear amount were measured. Specifically, a ball mill was used to blend the diamond powder having an average particle size of 0.8 μm and attaining the content of 90 volume % and the binder containing 75 mass % Co and 25 mass % Ti. Ti in the binder having different average particle sizes of 0.1 μm, 0.8 μm, 0.9 μm, and 1.0 m was used. Thereafter, a belt-type extra-high-pressure apparatus was used for sintering, in which the mixture was held for 10 minutes under a condition of a pressure of 7.2 GPa and a temperature of 1900° C. The transverse rupture strength of the obtained sintered object was measured by using the method the same as in Example 1 and the flank wear amount thereof was measured through a cutting test. The result is shown in Table 2.
As shown in Table 2, the flank wear amounts of samples 2A to 2D are substantially the same, and the flank wear amounts of samples 2E to 2H are substantially the same. Meanwhile, the transverse rupture strength of samples 2A and 2B is larger than that of samples 2C and 2D, and the transverse rupture strength of samples 2E and 2F is larger than that of samples 2G and 2H. In addition, the number of diamond particles that have grown to a particle size of not smaller than 300 μm during sintering was counted. Consequently, abnormal particle growth was not observed in samples 2A, 2B, 2E, and 2. On the other hand, abnormal particle growth was observed in samples 2C, 2D, 2G, and 2H (3, 25, 4, and 25 particles respectively). Therefore, it can be seen that setting the average particle size of Ti in the binder to not larger than 0.8 μm effectively suppresses abnormal particle growth, and chipping resistance is improved because neck growth is not suppressed.
In the present example, a method of adding Ti that should be added to the binder was varied and the transverse rupture strength and the flank wear amount were measured. Specifically, a sample 3A was prepared by blending, by means of the ball mill, diamond powder having an average particle size of 0.8 m and attaining the content of 90 volume % and the binder containing 75 mass % Co and 25 mass % Ti. In addition, a sample 3B having a similar composition was prepared by coating the diamond powder with Ti by using an RF (Radio Frequency) sputtering PVD apparatus. Moreover, a sample 3C having a similar texture was prepared by coating the diamond powder with Ti by using a CVD (Chemical Vapor Deposition) apparatus such that a coating layer has a thickness of 0.1 μm on an entire surface of the diamond particle. Each of samples 3A to 3C was filled in a container made of Ta (tantalum) in a state that the sample is in contact with a disk made of WC-6% Co hardmetal, and held for sintering for 10 minutes under a condition of a pressure of 7.2 GPa and a temperature of 1900° C. by using a belt-type extra-high-pressure apparatus. The transverse rupture strength of the obtained sintered object was measured by using the method the same as in Example 1 and the flank wear amount thereof was measured in a cutting test. The result is shown in Table 3.
As shown in Table 3, sample 3B coated by using the RF sputtering PVD apparatus exhibited the transverse rupture strength and the flank wear amount superior to sample 3A in which Ti was added by blending by means of the ball mill and sample 3C in which the diamond particle was coated with Ti by using the CVD method. The texture and the surface of each sample were observed by using a metallurgical microscope. In sample 3A, segregation of Co or Ti was observed and the uniform texture was not obtained. In addition, the average particle size of Ti carbide was 1.0 μm, which was larger than that at the time of addition. In samples 3B and 3C, segregation of Co or Ti was not observed and the uniform texture was obtained. In sample 3C, however, the texture of TiC was continuous, because the entire surface of the diamond particle was uniformly coated, and not only abnormal particle growth but also neck growth between the diamond particles were suppressed. In sample 3B, coating of the diamond particle with Ti was not entirely uniform but partial, that is, discontinuous, and the average particle size of Ti powder was maintained at approximately 0.1 μm. Therefore, it was found that Ti is preferably added by coating by means of the RF sputtering PVD apparatus. It was also found that lowering in the transverse rupture strength or increase in the flank wear amount is caused if carbide has an average particle size larger than 0.8 μm or if the texture of the carbide itself is continuous.
In the present example, variation in the transverse rupture strength when samples 3A to 3C in Example 3 were subjected to dissolution treatment was observed. Specifically, a test piece cut out from the sintered diamond object represented by samples 3A to 3C in Example 3 in a planar rectangular shape having a length of 6 mm, a width of 3 mm, and a thickness of 0.4 to 0.45 mm was subjected to dissolution treatment in a sealed container at a temperature of not lower than 120° C. and lower than 150° C. for 3 hours by using fluoro-nitric acid obtained by mixing 40 ml of twice-diluted nitric acid having a concentration of at least 60% and less than 65% and 10 ml of hydrofluoric acid having a concentration from 45 to 50%. Among the test pieces (samples) obtained in the above-described manner, a sample that had been identified as sample 3A was identified as a sample 4A, a sample that had been identified as sample 3B was identified as a sample 4B, and a sample that had been identified as sample 3C was identified as a sample 4C. Using each sample, the transverse rupture strength was measured under a condition of 4 mm span. The result is shown in Table 4.
As shown in Table 4, the transverse rupture strength of sample 4B, in which Ti was added by using the RF sputtering PVD apparatus, reduced solely by 0.22 GPa, from 2.88 GPa to 2.59 GPa. In contrast, the transverse rupture strength of sample 4A, in which Ti was added by blending by means of the ball mill, significantly reduced by 0.57 GPa, from 2.59 GPa to 2.02 GPa. In addition, the transverse rupture strength of sample 4C, in which Ti was added by using CVD, also significantly reduced by 0.48 GPa, from 2.46 GPa to 1.98 GPa. Therefore, it can be seen that neck growth between the diamond particles has developed and a strong structure has been formed by adding Ti by means of the RF sputtering PVD apparatus, that is, by developing a discontinuous texture of Ti itself.
In the present example, a proportion of Ti in the binder was varied and an intensity ratio between the diffraction beam of TiC in a direction of (200) and the diffraction beam of diamond in a direction of (111) in the obtained sintered object was measured. Specifically, three types of samples were prepared: a sample 5A containing 78 volume % diamond powder and a material to be sintered containing 75 mass % Co and 25 mass % Ti; a sample 5B containing 90 volume % diamond powder and a material to be sintered containing 75 mass % Co and 25 mass % Ti; and a sample 5C containing 90 volume % diamond powder and a material to be sintered containing 50 mass % Co and 50 mass % Ti. In all samples, the average particle size of the diamond powder was set to 0.8 μm. Thereafter, a belt-type extra-high-pressure apparatus was used for sintering, in which the sample was held for 10 minutes under a condition of a pressure of 7.2 GPa and a temperature of 1900° C. A characteristic X-ray generated from electron of K shell of Cu was used to measure an X-ray diffraction pattern of the obtained sintered diamond object under a condition of acceleration of electron beam for irradiating a Cu target of 40 kV, a current of 25 mA, an angle of diffraction 2θ=20 to 80°, and a scanning speed of 0.1° C./second, and the intensity ratio between the diffraction beam of TiC in the direction of (200) and the diffraction beam of diamond in a direction of (111) was measured. The result is shown in Table 5. In Table 5, sample 5B represents the sintered diamond object according to the present invention.
As shown in Table 5, the X-ray diffraction intensity ratio of sample 5B attaining the smallest flank wear amount was 40%. On the other hand, samples 5A and 5C attained the intensity ratio larger than 50%. Therefore, it can be seen that the flank wear amount tends to increase in a sample attaining the intensity ratio of TiC exceeding 50%. In addition, it can also be seen that the intensity ratio of the diffraction beam of TiC in a direction of (200) is preferably in a range of not lower than 0.01% and less than 50% of the diffraction beam of diamond in a direction of (111), because abnormal particle growth occurs in the sintered object without containing Ti in the binder composition.
In the present example, an amount of oxygen contained in the sintered diamond object was varied and the transverse rupture strength and the flank wear amount were measured. Specifically, the diamond powder having an average particle size of 0.8 m and attaining the content of 90 volume % and the binder containing 75 mass % Co and 25 mass % Ti were blended. Thereafter, the resultant mixtures were subjected to thermal treatment for 60 minutes in vacuum at temperatures of 1000° C., 1100° C., and 1250° C. respectively, so as to reduce the binder and partially graphitize the diamond particle from the surface. Thereafter, a belt-type extra-high-pressure apparatus was used for sintering, in which the sample was held for 10 minutes under a condition of a pressure of 7.2 GPa and a temperature of 1900° C. Among the obtained samples, a sample that had been subjected to thermal treatment at the temperature of 1000° C. was identified as a sample 6A; a sample that had been subjected to thermal treatment at the temperature of 1100° C. was identified as a sample 6B; and a sample that had been subjected to thermal treatment at the temperature of 1250° C. was identified as a sample 6C. An amount of oxygen contained in samples 6A to 6C was measured by using ICP (Inductively Coupled Plasma). In addition, the transverse rupture strength of samples 6A to 6C was measured with the method the same as in Example 1. The result is shown in Table 6.
As shown in Table 6, if the temperature for thermal treatment before sintering was changed, an amount of oxygen contained in the sintered diamond object varied. If the amount of oxygen is not larger than 0.15 mass %, the transverse rupture strength is significantly improved. Therefore, it can be seen that chipping resistance is improved by containing oxygen in an amount of less than 0.15 mass %.
In the present example, the sintered diamond objects represented as sample 1E (present invention) and sample 1H (conventional example) in Example 1 were treated with acid and microphotographed.
Referring to
The examples disclosed above are by way of illustration and are not to be taken by way of limitation, the spirit and scope of the present invention being limited not by the examples above but by the claims and intended to include all modifications and variations within the scope of the claims. ductivity can thus be obtained.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/13621 | 7/26/2005 | WO | 00 | 5/19/2006 |
