CA2163953C

CA2163953C - Diamond sintered body having high strength and high wear-resistance and manufacturing method thereof

Info

Publication number: CA2163953C
Application number: CA002163953A
Authority: CA
Inventors: Yasuyuki Kanada; Hirohumi Mizusuna; Tsutomu Nakamura; Tetsuo Nakai
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1994-11-30
Filing date: 1995-11-28
Publication date: 1999-05-11
Anticipated expiration: 2015-11-28
Also published as: EP0714695A2; CA2163953A1; EP1064991B1; EP1064991A2; EP1064991A3; DE69523117D1; DE69532541D1; KR0180769B1; US5759216A; DE69532541T2; KR960017589A; ZA9510177B; DE69523117T2; EP0714695A3; EP0714695B1

Abstract

A method of manufacturing a diamond sintered body includes the steps of preparing diamond powder having a particle size within the range of from 0.1 to 10 µm, coating the surface of each particle of the diamond powder with a sintering assistant agent including Pd within a range of from 0.01 to 40 percent by weight and at least one of an iron family metal as the remaining part, and sintering the coated diamond powder in liquid-phase under high pressure and high temperature conditions, so that a diamond sintering body having high strength and high wear-resistance containing 80 to 96 percent by volume of diamond particles can be obtained.

Description

CA 021639~3 1998-12-22 Diamond Sintered Body Having High Strength and High Wear-Resistance and Manufacturing Method Thereof The present invention relates to a diamond sintered body used as a material for cutting tools, digging tools, drawing dies, wear-resistant parts and the like and manufacturing method thereof. More particularly, it relates to a diamond sintered body having improved strength and wear-resistance and to the manufacturing method thereof.
A diamond sintered body generally has superior wear-resistance and strength as compared with other materials. Therefore, it is used for applications which require strength and wear-resistance, e.g. the field of cutting tools, digging tools and drawing dies. Such a diamond sintered body can be obtained by filling a container formed of WC-Co cemented carbide with diamond powder, infiltrating Co-W-C eutectic composition liquid-phase from the cemented carbide base material into the diamond powder under high pressure at high temperature and by sintering the same, as disclosed, for example, in Japanese Patent Publication No. 52-12126. Alternatively, as disclosed in Japanese Patent Laying-Open No. 54-114513, a diamond sintered body can be obtained by premixing diamond powder with powder containing an iron family solvent metal, and by holding the mixed powder at such high temperature and high pressure conditions that allow formation of diamond sinter.
The diamond sintered bodies obtained through the above described methods suffer from problems under sub-optimal sintering conditions. For example, if the diamond particles are too fine or if the solvent metal to be mixed in is in an insufficient amount, sintering is impossible since the solvent metal hardly infiltrates, or the CA 021639~3 1998-12-22 aggregate portions of diamond particles would not be sintered locally, since surface portions in contact with other diamond particles increase. Accordingly, it is not easy to obtain a diamond sintered body having high density, that is, a diamond sintered body having good wear-resistance and high diamond content.
In order to solve the problems of the prior art, a method to obtain a diamond sintered body having a high density has been proposed, for example, in Japanese Patent Laying-Open Nos. 63-190756 and 6-32655, and in Research Report No. 58, pp. 38 to 48 of National Institute for Research in Inorganic Materials, in which method a sintering assistant agent is applied, as coating, to the surface of each particle of diamond powder and the coated diamond powder is sintered. The diamond sintered body obtained through this method has a high diamond content, and therefore it has good wear-resistance. However, when the diamond particle size in the sintered body is large, the strength of the diamond sintered body is reduced and therefore it has insufficient reliability for practical use. Further, when a high density diamond sintered body is to be obtained by such a method, only a small amount of sintering assistant agent can be added. Therefore, depending on the composition of the sintering assistant agent and the method of coating, within the temperature range and pressure range allowing production of diamond sinter, relatively high temperature and pressure are required. In such a case, there would be a large strain remaining in the diamond sintered body, which degrades the strength of the diamond sintered body, and hence lowers reliability in practical use.
In order to prevent degradation of a diamond sintered body at a high temperature, a method has been proposed, for example, in Japanese Patent Laying-Open No.

CA 021639~3 1998-12-22 6-6769 in which the surfaces of diamond particles are coated by transition metal, B or Si and the coated diamond powder is sintered in solid-phase. However, in this case it is considered that diamond particles are bonded with coating material which is carbonized by solid-phase reaction interposed. Therefore, the diamond sintered body obtained by liquid-phase sintering employing as a solvent an iron family metal allowing direct bonding between diamond particles with each other is superior in mechanical strength.
In view of the problems of the prior art, an object of the present invention is to provide a diamond sintered body having high strength and high wear-resistance and a manufacturing method thereof.
The diamond sintered body having high strength and high wear-resistance in accordance with one aspect of the present invention includes 80 to 96 percent by volume of sintered diamond particles and a remaining part of sintering assistant agent and unavoidable impurity, the sintered diamond particles having a particle size substantially in the range of from O.l to lO ~m and directly bonded to each other, the sintering assistant agent including Pd within the range of from O.Ol to 40 percent by weight, and as a remaining part, including at least one of Fe, Co and Ni.
In the diamond sintered body in accordance with the first aspect of the present invention, since fine diamond particles are sintered with high density in the presence of sintering assistant agent including an iron family element, high strength and high wear-resistance can be realized.
According to a second aspect of the invention, the method of manufacturing a diamond sintered body having high strength and high wear-resistance includes the steps of preparing diamond powder having a particle size CA 02l639~3 l998-l2-22 substantially within the range of from O.l to lO ~m;
preparing coated diamond powder by applying a sintering assistant agent to said diamond powder in a quantity within the range of from 4 to 20 percent by volume, which comprises precipitating Pd within the range of from 10-4 to 40 percent by weight on a surface of each particle of said diamond powder, and thereafter electroless plating at least one of Fe, Co and Ni to the surface of each particle of said diamond powder; and under high pressure and high temperature conditions at which diamond is stable, sintering said coated diamond powder in liquid-phase.
In the method of manufacturing a diamond sintered body in accordance with the second aspect of the present invention, a sintering assistant agent including an iron family element is applied as coating, within the range of 4 to 20 percent by volume to the surface of each particle of fine diamond powder, and the coated diamond powder is sintered in liquid-phase under high pressure and high temperature conditions in which diamond is stable, so that a diamond sintered body having high strength and high wear-resistance as well as high diamond content can be obtained.
According to a third aspect of the present invention, the method of manufacturing a diamond sintered body having high strength and high wear-resistance includes the steps of preparing diamond powder having particle size substantially in the range of from O.l to lO
~m; preparing coated diamond powder by applying a sintering assistant agent to said diamond powder in a quantity within the range of from O.l to l9.9 percent by volume, which comprises precipitating Pd in the range of from 10-4 to 40 percent by weight on a surface of each particle of said diamond powder and thereafter electroless plating at least one of Fe, Co and Ni to the surface of each particle of said diamond powder; molding a powder CA 021639~3 1998-12-22 compact body of said coated diamond powder; bringing into contact an additional sintering assistant agent including at least one of Pd, Fe, Co and Ni to said powder compact body; and sintering said powder compact body in liquid-phase while infiltrating said additional sintering assistant agent under high pressure and high temperature conditions at which diamond is stable.
In the method of manufacturing the diamond sintered body in accordance with the third aspect of the present invention, the sintering assistant agent including an iron family element is applied for coating to the surface of each particle of fine diamond powder within the range of O.l to l9.9 percent by volume, an additional sintering assistant agent is brought into contact with the coated diamond powder, and the coated diamond powder is sintered in liquid-phase under high pressure and high temperature in which diamond is stable while infiltrating the additional sintering assistant agent. Therefore, a diamond sintered body having high diamond content as well as high strength and high wear-resistance can be obtained.
First, the inventors studied strength of various diamond sintered bodies. As a result, it was found that the strength of the diamond sintered body depends on the size of a defect in the sintered body which serves as an initiation point of breakage. Here, the term defect means a larger diamond particle in the diamond sintered body, a pool of the sintering assistant agent, such as the solvent metal, or a void. The smaller the defect, the higher the strength of the diamond sintered body.
It was found that in order to improve strength of the diamond sintered body, first, the larger diamond particles must be reduced to the acceptable particle size of at most lO ~m. In order to provide coating of sintering assistant agent on the surface of diamond particles, which will be described later, the diamond CA 021639~3 1998-12-22 particle must have the particle size of at least O.l ~m.
In other words, the raw material diamond powder is required to have the particle size within the range of O.l to lO ~m.
It was found that in order to reduce pooled portions of sintering assistant agent and voids in the sintered body, it is preferable to sinter coated diamond powder having the sintering assistant agent coating the surface of each particle of diamond powder in liquid-phase. It was found that, preferably, the sintering assistant agent includes Pd and at least one selected from Fe, Co and Ni which are iron family metals. It was found that by preparing coated diamond powder to include such a sintering assistant agent within the range of 4 to 20 percent by volume and by sintering the coated diamond powder under high pressure and high temperature conditions in which diamond is stable, a uniform liquid-phase of sintering assistant agent is generated evenly throughout the diamond powder, so that a diamond sintered body having smaller pooled portions of sintering assistant agent and smaller void portions is obtained.
Further, it was found that by preparing coated diamond powder to include a sintering assistant agent including Pd and at least one of Fe, Co and Ni within the range of O.l to l9.9 percent by volume, and bringing into contact an additional sintering assistant agent including at least one of Pd, Fe, Co and Ni with the coated diamond powder, uniform infiltration of the additional sintering assistant agent occurs evenly throughout the coated diamond powder compact body, supplementing the sintering assistant agent coated on the diamond powder under high pressure and high temperature conditions in which diamond is stable, and hence a diamond sintered body having smaller pooled portions of sintering assistant agent and smaller void portions can be obtained.

CA 021639~3 1998-12-22 More specifically, by using coated diamond powder on which the above described sintering assistant agent is coated, uniform melting or infiltration of the sintering assistant agent occurs, so that sintering becomes possible under conditions that are otherwise unsuitable for sintering, and hence a diamond sintered body having high diamond content, high strength and high wear-resistance can be obtained.
Here, any of Pd, Fe, Co and Ni may be used as the sintering assistant agent for the diamond powder by itself. However, it was found that when the sintering assistant agent includes Pd in addition to at least one of Fe, Co and Ni, the melting point of the sintering assistant agent lowers and the sintering property of the diamond powder is remarkably improved. Here, if the content of Pd in the sintering assistant agent is less than 0.0l percent by weight, the melting point lowering effect of the sintering assistant agent is insufficient.
By contrast, if the content of Pd exceeds 40 percent by weight, the melting point of the sintering assistant agent tends to increase, degrading the sintering property of the diamond powder. In other words, the content of Pd in the sintering assistant agent is preferably within the range of 0.0l to 40 percent by weight.
Further, the sintering assistant agent should preferably be included in a quantity of at least 4 percent by weight when the diamond powder coated with the sintering assistant agent is to be sintered, in order to prevent shortage of the sintering assistant agent, which shortage makes sintering of diamond powder practically impossible. On the other hand, the content of sintering assistant agent should preferably be 20 percent by volume at most, since wear-resistance of the sintered body is remarkably degraded as the diamond content lowers if the CA 021639~3 1998-12-22 sintering assistant agent in the diamond sintered body exceeds 20 percent by volume.
Similarly, when sintering of coated diamond powder is to be performed with an additional sintering assistant agent brought into contact with the powder compact body of the coated diamond powder, the amount of sintering assistant agent coating the diamond particle should preferably be at least 0.1 percent by volume. The reason for this is that if the amount of coating of the additional sintering assistant agent is less than 0.1 percent by volume, uniform coating by the additional sintering assisting agent on the surface of the diamond particle becomes difficult, making uniform infiltration of the additional sintering assistant agent impossible. On the other hand, the amount of coating of the sintering assistant agent should preferably be at most 19.9 percent by volume. The reason for this is that after sintering while infiltrating additional sintering assistant agent, if the sintering assistant agent in the sintered body exceeds 20 percent by volume, diamond content is lowered, and hence wear-resistance of the sintered body is significantly degraded.
As a method of providing coating of the sintering assistant agent on each particle of the diamond powder, CVD method, PVD method or solution precipitation method may be possible. However, electroless plating method is most preferably used, from an economical view and considering that uniformity of the sintering assistant agent coating the surface of the diamond particle plays a very important part in improving the sintering property of the powder and in the strength of the sintered body.
When the sintering assistant agent is to be precipitated on the surface of diamond particles by electroless plating, mixing of impurity in the sintering assistant agent should be prevented as much as possible, CA 021639~3 1998-12-22 in order to obtain high diamond content after sintering.
Considering the fact that catalytic nuclei having high catalytic action must exist on the surface of the diamond particle in the initial reaction of electroless plating, it is preferable that Pd exhibiting not only the function of a sintering assistant agent but also the catalytic action be coated first on the surface of the diamond particle. It was found that by providing coating of a sintering assistant agent including at least one of Fe, Co and Ni with Pd serving as catalytic nucleus, diamond particles coated with sintering assistant agent with minimal impurities can be obtained.
Here, it is preferable that the amount of precipitation of Pd on the surface of the diamond particle is at least 10-4 percent by weight. The reason for this is that if catalytic action is insufficient, the electroless plating reaction becomes insufficient, making it difficult to provide coating of the sintering assistant agent. On the other hand, the amount of precipitation of Pd should preferably be 40 percent by weight at most. The reason for this is to prevent degradation of the sintering property, which is caused by an elevated melting point of the sintering assistant agent caused by excessive Pd.
Further, it was found that if the sintering assistant agent includes at least one of Sn, P and B in addition to the iron family metal, Sn, P or B serves to lower the melting point of the sintering assistant agent, significantly improving sintering property of the diamond powder coated by the sintering assistant agent.
As for precipitation of P in addition to the iron family element, a sintering assistant agent having a desired P concentration can be precipitated by using a hypophosphite, for example sodium hypophosphite as a reducing agent in the electroless plating solution, and by adjusting concentration of the reducing agent in the CA 021639~3 1998-12-22 plating solution, pH of the plating solution and temperature during plating. Similarly, for precipitation of B in addition to the iron family element, a sintering assistant agent having a desired B concentration can be precipitated by using a boron hydride compound such as sodium borohydride, as the reducing agent in the electroless plating solution, and by adjusting concentration of the reducing agent in the plating solution, pH of the plating solution and the temperature during plating. Meanwhile, Sn has superior absorption property with respect to the surface of the diamond powder particle. Therefore, it can be directly absorbed to the diamond particle surface from a tin chloride solution, for example. Further, precipitation of Pd serving as the catalytic nucleus after absorption of Sn onto the diamond particle surface as pre-processing for electroless plating (sensitizing activating method) or precipitation of Sn and Pd simultaneously (catalyst accelerating method) is preferable, since it promotes absorption of Pd at the surface of the diamond particles.
At this time, if the total content of Sn, P and B
in the sintering assistant agent is less than 0.01 percent by weight, the melting point of the sintering assistant agent cannot be lowered. By contrast, if the total content of Sn, P and B exceeds 30 percent by weight, the melting of diamond to the iron family metal which serves as solvent metal in the sintering assistant agent at the time of sintering is hindered, so that strength with which diamond particles bind with each other is reduced, thus degrading the strength of the sintered body, and degrading thermal properties of the sintered body. The total content of Sn, P and B should more preferably be within the range of 0.01 to 11.5 percent by weight.
When the diamond particle is to be coated with the sintering assistant agent by electroless plating, the iron CA 021639~3 1998-12-22 family element precipitated by electroless plating is, in most cases, precipitated as an oxide. If sintering is performed using a sintering assistant agent including an oxide, oxygen derived from the oxide may possibly generate voids in the sintered body, which may hinder melting and precipitation reaction of diamond in the sintering assistant agent serving as the solvent. Therefore, it may degrade the property of the diamond sintered body. In order to prevent such undesirable effects of oxygen, the coated diamond powder after electroless plating should preferably be reduced by heat treatment under vacuum or in hydrogen atmosphere.
It was found that when electroless plating is performed on the diamond powder, the diamond powder can be coated uniformly by the sintering assistant agent if the plating solution including the diamond powder is agitated by at least one of stirring and ultrasonic vibration.
Further, in order to obtain a diamond sintered body having higher density, it is preferable to perform heat treatment at high temperature on the diamond powder under conditions that make diamond unstable so that the diamond particles are partially turned to graphite from the surface, to coat the partially graphitized diamond particle with the sintering assistant agent and to perform sintering thereafter, or to coat the diamond powder with the sintering assistant agent, to turn the coated diamond particle into graphite partially from the surface and then perform sintering. The reason for this is as follows.
Diamond powder is not susceptible to plastic deformation.
Therefore, even under high pressure, spaces tend to remain between diamond particles. However, if the surface of the diamond particle is turned into graphite, the graphite portion is more susceptible to plastic deformation, and hence density of the sintered body can be substantially improved. Further, considering melting of carbon and CA 021639~3 1998-12-22 reprecipitation in the sintering assistant agent during sintering, speed of reaction of graphite is faster than that of diamond, and hence sintering property is improved if the diamond surface is turned into graphite.
From these reasons, it would be understood that a diamond sintered body having higher density could be obtained if the diamond surface is partially converted to graphite. At this time, if the ratio of graphitization of diamond particle is less than 0.5 percent by volume, density of the sintered body is hardly improved.
Meanwhile, if the ratio of graphitization of diamond particle exceeds 80 percent by volume, converting graphite to diamond during sintering under such high pressure and high temperature that keeps diamond stable becomes imperfect, resulting in graphite left in the diamond sintered body. Therefore, the preferable range of partial graphitization of diamond particle is 0.5 to 80 percent by volume.
Now, if the above described diamond sintered body is to be obtained, it is possible that various materials are mixed in small quantity. For example, the coated diamond powder is generally filled in a container formed of a cemented carbide or a refractory metal and sintered.
Therefore, W, Ta, Mo, Cr which are the components of the container or carbide thereof may possibly be mixed in the sintered body. However, even if such material is mixed in the sintered body, such material does not cause any problem provided that diamond content in the sintered body is within the range of from 80 to 96 percent by volume.
Similarly, evenwhen additionalsintering assistant agent is brought into contact with the powder compact body as supplement to the sintering assistant agent in the coated diamond powder and infiltrated to the powder compact body during sintering, it does not cause any problem provided that the diamond content of the sintered CA 021639~3 1998-12-22 body is within the range of from 80 to 96 percent by volume. As for the composition of additional sintering assistant agent arranged in contact with such powder compact body, similar compositions as those for the sintering assistant agent used for coating of the diamond particle may be used.

(Embodiment 1) Table 1 Powder Diamond Method of Content ofComposition of sintering assistant agentsampleparticle applying sintering (wt.%) size sintering assistant agent (llm)assistant agent (vol.%) L~ 0.1 - 4 electroless 6.092.9-Co, 0.05-Pd, 3.95-Fe, 3-P, 0.1-Sn plating lB 0.1 - 4 electroless 13.092.9-Co, 0.05-Pd, 3.95-Fe, 3-P, 0.1-Sn plating lC 0.1 - 4 electroless 26.0929-Co, 0.05-Pd, 3.95-Fe, 3-P, 0.1-Sn plating lD 0.1 - 4 PVD 6.092.9-Co, 0.05-Pd, 3.95-Fe, 3-P, 0.1-Sn lE 0.1 - 4 PVD 13.092.9-Co, 0.05-Pd, 3.95-Fe, 3-P, 0.1-Sn lF 0.1 - 4 PVD 26.092.9-Co, 0.05-Pd, 3.95-Fe, 3-P, 0.1-Sn lG 0.1 - 4miYing ultra 6.0 100-Co fine powder lH 0.1 - 4mLYing ultra 13.0 100-Co fine powder lI 0.1 - 4miYing ultra 26.0 100-Co fine powder lJ 0.1 - 4 cemented 6.0 25-Co, 75-WC
carbide ball mill lK 0.1 - 4 cemented 13.0 25-Co, 75-WC
carbide ball mill lL 0.1 - 4 cemented 26.0 25-Co, 75-WC
carbide ball mill CA 021639~3 1998-12-22 Table l shows various powder samples prepared for studying the influence of the method of applying sintering assistant agent, content and composition on mechanical properties of the diamond sintered body. More specifically, powder samples lA to lL shown in Table l are all raw material diamond powders having a particle size within the range of O.l to 4 ~m, while the method of applying sintering assistant agent, content and composition are changed variously.
For the samples lA, lB and lC, the following process was performed to coat diamond powder particles by the sintering assistant agent by electroless plating.
First, diamond powder was degreased in alcohol. The degreased diamond powder was cleaned in flowing water, cleaned in a hydrochloric acid solution of 5 percent by weight, and then again cleaned in flowing water. The diamond powder thus cleaned was immersed for one minute in a solution including stannous chloride and hydrochloric acid at room temperature as pre-processing, so as to cause absorption of Sn at the surface of the diamond particles (sensitizing). The sensitized diamond powder was washed by water and thereafter immersed for one minute in hydrochloric acid solution containing palladium chloride at room temperature, and thus Pd was precipitated at the surface of the diamond particles (activated).
The activated diamond powder was washed by water, and thereafter immersed for a prescribed time period in a Co-Fe-P electroless plating solution held at 75~C, containing cobalt sulfate, iron sulfate and sodium hypophosphite. The longer the time of immersion in the electroless plating solution, the larger the amount of sintering assistant agent coating the surface of the diamond particle, and the larger the content of the sintering assistant agent in the powder samples. In the CA 021639~3 1998-12-22 step of electroless plating, the pre-plating solution and plating solution were stirred and at the same time, subjected to ultrasonic vibration. The coated diamond powder which was subjected to electroless plating in this manner was cleaned, the surface of diamond particles was partially graphitized by heat treatment under vacuum at 1000~C for 60 minutes, and collected, whereby the coated powder samples lA to lC having such content and composition of the sintering assistant agent as shown in Table l were obtained.
For the samples lD to lF, the sintering assistant agent has the same composition as those for the samples lA
to lC. However, coating of the sintering assistant agent was performed in accordance with an arc ion plating method. More specifically, the sintering assistant agent is applied to the surface of diamond powder particles by arc ion plating method in which a target correspond to the composition of the sintering assistant agent and a bias voltage of 350 V were used in an argon atmosphere of l x lo-2 torr.
For samples lG to lI, ultra fine Co powder having the particle size of 500 A was used as the sintering assistant agent. Diamond powder and ultra fine Co powder corresponding to the prescribed content were put in a ball mill container formed of Teflon which contains mixing balls formed of Teflon. The powders were mixed for 4 hours, whereby the mixed powder samples lG to lI were obtained.
In preparing the samples lJ to lL, diamond powder was put in a ball mill having mixing balls and a container formed of cemented carbide WC-Co and the ball mill was driven for a prescribed time period. During the driving of the cemented carbide ball mill, the cemented carbide powder scraped off from the mixing balls and the container was mixed as sintering assistant agent to the diamond CA 021639~3 1998-12-22 powder. The content of the cemented carbide powder mixed in the diamond powder can be adjusted by changing the time of driving the cemented carbide ball mill.
The powder samples lA to lL shown in Table 1 were each sealed in a container formed of tantalum, kept at a pressure of 50 kb at a temperature 1400~C for 10 minutes by using a belt type high pressure apparatus, and thus sintered. Table 2 shows diamond content and wear-resistance of the diamond sintered body samples obtained 10in this manner.

Table 2 Sintered body Diamond content Flank wear 15 sample (vol.%) (~lm) 2A 93.8 31 2B 86.9 65 2C 74.2 131 2D 92.3 damaged 2E 86.8 damaged 2F 73.9 damaged 2G sintering not possible 2H 86.7 damaged 2I 74.0 damaged 2J sintering not possible 2K sintering not possible 2L 73.9 142 Sintered body samples 2A to 2L of Table 2 are obtained by sintering powder samples lA to lL shown in Table 1. As can be seen from Table 2, in samples 2G, 2J
and 2K, the amount of sintering assistant agent is small and distribution thereof is not uniform. Since uniform CA 021639~3 1998-12-22 melting of sintering assistant agent did not occur entirely in the diamond powder, sintering was insufficient, and hence a complete sintered body could not be obtained.
Meanwhile, samples providing complete sintered bodies were processed to be cutting tools, and performance was evaluated under the following cutting conditions.
Work piece: a round bar of A1-16 wt ~ Si having six grooves on the surface along the axial direction.
Peripheral surface velocity of the work piece: 500 (m/min) Byte cutting depth: 0.6 (mm) Byte feeding speed: 0.12 (mm/rev) Cutting time: 3 (min) The flank wear of the tools as a result of cutting test were as shown in Table 2. As can be seen from Table 2, sintering is possible in sintered body samples 2A and 2B in accordance with the present invention even when the amount of sintering assistant agent is small. Therefore, tools having high diamond content and superior wear-resistance can be obtained. Further, since the sintered body samples 2A and 2B have uniform sintered body texture, they have high strength, and it becomes apparent that they have good damage resistance as cutting tools.
By contrast, it is apparent that sintered body samples 2C and 2L having low diamond content are inferior in wear-resistance. Of the sintered body textures of samples 2D, 2E, 2F, 2H and 2I, uneven distribution of sintering assistant agent generated in the PVD method or Co pools derived from aggregation of ultra fine Co powder were observed, which pools lowered strength and hence caused damages to the sintered body during cutting. Thus the sintered bodies could not be used as cutting tools.

(Embodiment 2) Table 3 Powder DiamondMethod Or Method of Content ofComposition or sintering samplcparticlcapplying agitating sintcring assistant agcnt size sintering plating assistant agent (wt.%) (llm)assistant agent~olution (vol.%) 3A 1- 2 electrolessstirring+ultrasonic 9 97-Ni, 0.5-Pd, 2-P, 05-Sn D
plating vibration O
3B 1- 2 electrolessstirring+ultrasonic 9 89-Ni, 05-Pd, 10-P, 0.5-Sn plating vibration 3C 1- 2 electrolessstirring+ultrasonic 9 6~Ni, 05-Pd, 35-P, 05-Sn 1-ac plating vibration 3D 1 - 2 electroless not agitated 9 97-Ni, 05-Pd, 2-P, 05-Sn plating 3E 1- 2 electroless not agitated 9 89-Ni, 0.5-Pd, 10-P, 0.5-Sn plating 3F 1- 2 clc~tlole~ not agitated 9 64-Ni, 0.5-Pd, 35-P, 0.5-Sn plating 3G 1- 2mixing ultra - 9 100-Ni fne powder CA 021639~3 1998-12-22 Table 3 shows various powder samples prepared for studying influence of the method of applying sintering assistant agent, composition and conditions of electroless plating on mechanical properties of the sintered bodies.
For samples 3A to 3C, the surface of diamond particles was partially graphitized by heat treatment under vacuum at 1450~C for 30 minutes, then diamond powders were degreased and subjected to acid cleaning using the method of Embodiment 1 (Table 1) and thereafter the diamond powders were subjected to surface activation, in order to coat the diamond powder particles with sintering assistant agent by electroless plating.
Thereafter, the diamond powders were immersed in an Ni-P
electroless plating solution containing nickel sulfate and sodium hypophoshite and held at 60~C. During the step of electroless plating, the pre-plating solution and the plating solution were agitated by stirring and ultrasonic vibration. The composition of the sintering assistant agent was adjusted by changing the pH of the plating solution.
Samples 3D to 3F were prepared by electroless plating similar to samples 3A to 3C. However, agitation by stirring and ultrasonic vibration was not applied to the electroless plating solution.
As for sample 3G, diamond powder was put in a ball mill container formed of Teflon containing mixing balls formed of Teflon, together with ultra fine Ni powder having a particle size of 200 A, and mixed for 4 hours.
The powder samples of Table 3 were each sealed in a container of Mo and sintered for 15 minutes at a pressure of 45 kb at a temperature of 1350~C by using a belt type high pressure apparatus. Various properties of the sintered body samples obtained in this manner are as shown in Table 4.

CA 021639~3 1998-12-22 Table 4 Sintered DiamondComposition of sintering Three point body contentassistant agent after bending sample (vol.%j sintering strength (wt.%) (kgf/rnrn2) 4A 90.997-Ni, 0.5-Pd, 2-P, 0.5-Sn 263 4B 90.889-Ni, 0.5-Pd, 10-P, 0.5-Sn 254 4C 90.964-Ni, 0.5-Pd, 35-P, 0.5-Sn 193 1 0 4D 90.797-Ni, 0.5-Pd, 2-P, 0.5-Sn 179 4E 90.889-Ni, 0.5-Pd, 10-P, 0.5-Sn 164 4F 90.964-Ni, 0.5-Pd, 35-P, 0.5-Sn 142 4G sintering not possible The sintered body samples 4A to 4G shown in Table 4 were obtained from powder samples 3A to 3G of Table 3.
However, similar to the sample 2B of Table 2, locally unsintered regions were generated in sample 4G, and a complete sintered body could not be obtained.
The samples from which complete sintered bodies were obtained were each processed to a bar-shaped sample piece of 6 x 3 x 0.3 mm, and thereafter the strength 25 thereof was evaluated by three point bending test with the spun of 4 mm. As a result, as can be seen from Table 4, it is apparent that samples 4A to 4C have improved strength compared with samples 4D to 4F. More cg omega specifically, as the plating solution was stirred and subjected to ultrasonic vibration during electroless plating of diamond powder, a uniform coating of sintering CA 021639~3 1998-12-22 assistant agent was formed on the diamond particles, defects in the diamond sintered body were reduced and hence strength of the sintered body was significantly improved .
Further, in view of the fact that samples 4A and 4B have higher strength than samples 4C and 4F, it was found that when the sintering assistant agent includes P
and Sn, the total content thereof should preferably be in the range of 0.01 to 30 percent by weight. Further, it was found that when the sintering assisting agent includes B, the desired content thereof is from 0.01 to 30 percent by weight.

(Embodiment 3) Table 5 PowderDiamond Amount oEComposilion of coatingCompoistion sampleparticlecoating oEsintering assistant agentof additional size sintering (~v1.%) sintering (ILm) assiatant assistant agent agent (vol.%) (~t-%) SA 2 - 3 0.192.0-Ni, 7.0-Pd, 1.0-Sn 100-Ni 5B 2 - 3 0.192.0-Ni, 7.0-Pd, 1.0-Sn 98-Ni, 2-B
5C 2 - 3 0.192.0-Ni, 7.0-Pd, 1.0-Sn 89-Ni, 11-B
SD 2 - 3 0.192.0-Ni, 7.0-Pd, 1.0-Sn 79-Ni, 21-B
SE 2 - 3 0.192.0-Ni, 7.0-Pd, l.O-Sn 66-Ni, 34-B

Table 5 shows various powder samples prepared for studying influence of composition of additional sintering assistant agent on the strength of the sintered bodies, when the additional sintering assistant agent which is CA 021639~3 1998-12-22 brought into contact with coated diamond powder compact body is infiltrated into the powder compact body during sintering.
For samples 5A to 5E, diamond powder was degreased and subjected to acid cleaning using the method of Embodiment 1 (Table 1), to coat the diamond powder particles with the sintering assistant agent by electroless plating. Thereafter, catalysting was performed as pre-processing of electroless plating, by immersing the diamond powder in a solution containing palladium chloride, stannous chloride and hydrochloric acid for two minutes at room temperature. Thereafter, accelerating of the diamond powder was performed by immersing the powder in a sulfuric acid solution for two minutes at room temperature.
The pre-processed powders were washed with water, and thereafter immersed for two minutes in an Ni-B plating solution including nickel sulfate and sodium borohydride at 90~C, and thus coated diamond powders including the coating sintering assistant agent having such compositions and amounts as shown in Table 5 were obtained. During these steps of alkali degreasing, acid cleaning, preprocessing and plating, while the diamond powders are immersed in the solutions, the solutions were agitated by stirring and ultrasonic vibration.
The coated diamond powders were molded into powder compact bodies, and metal plates having the compositions shown in Table 5 were stacked as additional sintering assistant agent and sealed into a container of Ta. The Ta container was held at a pressure of 60 kb at a temperature of 1550~C for 10 minutes by using a girdle type high pressure apparatus, and the sintered body samples shown in Table 6 were obtained.

CA 021639~3 1998-12-22 Table 6 Sintcred DiamondTotal content of Sn and BStrength of body contentin sintering assistant agentsintered body sample (vol.%) (wt.%) (kgf/mm2) 6A 85 0.005 197 6B 85 1.99 234 6C 85 11.0 222 6D 85 20.9 208 6E 85 33.8 135 The sintered body samples 6A to 6E shown in Table 6 were obtained from powder samples 5A to 5E of Table 5.
Each of the sintered body samples was processed to a bar-shaped sample piece of 6 x 3 x 0.3 mm, and the strength thereof was evaluated by three point bending test with the spun of 4 mm.
As can be seen from Table 6, it is apparent that samples 6B, 6C and 6C are stronger than samples 6A and 6E.
More specifically, it can be understood that when the additional sintering assistant agent includes B, the content should preferably be in the range of 0.01 to 30 percent by weight. Further, it was found that if the additional sintering assistant agent includes P and Sn, the preferable content thereof is from 0.01 to 30 percent by weight.

(Embodiment 4) CA 021639~3 1998-12-22 Table 7 Powdcr Diamond Method of Content ofComposition of sintering sampleparticle applying sintering assistantassistant agent size (ILm) sintering agent (wt.%) assistant agent (vol.%) 7A 1- 2 electroless 5.0 99.6-Co, 0.1-Pd, 0.3-Sn plating 7B 2 - 8 electroless 5.0 99.6-Co, 0.1-Pd, 0.3-Sn plating ~ 7C 5 -15 electroless 5.0 99.6-Co, 0.1-Pd, 0.3-Sn plating 7D 1- 2 CVD 5.0 99.6-Co, 0.1-Pd. 0.3-Sn 7E 2 - 8 CVD 5.0 99.6-Co, 0.1-Pd. 0.3-Sn 7F 5 -15 CVD 5.0 99.6-Co, 0.1-Pd, 0.3-Sn 7G 1 - 2mixing ullra fine 5.0 100-Co powder 7H 2 - 8mixing ultra fine 5.0 100-Co powder 71 5 -15mixing ultra fme 5.0 100-Co powder 7J 1- 2 cemented 5.0 15-Co, 85-WC
carbide ball mill 7K 2 - 8 cçmen~d 5.0 15-Co, 85-WC
carbide ball mill 7L 5 -15 cemell~ed 5.0 15-Co, 85-WC
carbide ball mill Table 7 shows various powder samples prepared for studying influence of the raw material diamond particle size, method of applying sintering assistant agent and composition on mechanical properties of the sintered bodies.
For samples 7A to 7C, the catalytic layer for electroless plating was applied to the surface of diamond powder particles using the method described in Embodiment CA 021639~3 1998-12-22 3 so as to coat the diamond powders with sintering assistant agent by electroless plating.
The pre-processed diamond powder was washed by water, and thereafter immersed in a Co electroless plating solution containing cobalt chloride and hydrazinium chloride and held at 80~C, and thus Co coating was provided on the surface of diamond particles. During pre-processing related to electroless plating and during plating, the solutions together with diamond powder were agitated by stirring and ultrasonic vibrations. The electroless plated diamond powder was washed and collected, thereafter heated in vacuum at 1250~C for 60 minutes, so that the sintering assistant agent was reduced and diamond particles were partially graphitized from the surface. As a result, powder sample 7A to 7C having such content and composition of sintering assistant agent as shown in Table 7 were obtained. The amount of oxygen contained in the powders of samples 7A to 7C was 0.05 percent by weight.
For samples 7D to 7F, coated diamond powders having the same composition of sintering assistant agent as samples 7A to 7C were fabricated by using microwave plasma CVD method.
For samples 7G to 7I, diamond powders were put together with ultra fine Co powder into a ball mill container formed of Teflon including mixing balls of Teflon, and mixed for three hours. For samples 7J to 7L, diamond powders were put in a cemented carbide ball mill container including mixing balls formed of cemented carbide, and the cemented carbide ball mill was driven for a prescribed time period, so that diamond powders mixed with cemented carbide powder were obtained. As already described, the cemented carbide powder was scraped off from the cemented carbide balls and the container and mixed with the diamond powders.

CA 021639~3 1998-12-22 Each of the powder samples 7A to 7L shown in Table 7 was molded to a powder compact body, and a Co plate was stacked on the powder compact body and the powder compact body with the plate stacked was sealed in a container of cemented carbide. The cemented carbide container was held at a pressure of 50 kb and at a temperature of 1500~C for 15 minutes by a belt type high pressure apparatus, so that the stacked Co plate was melted and infiltrated in the powder compact body during sintering, and as a result, sintered body samples such as shown in Table 8 were obtained.

Table 8 Sintercd Diamond content Composition of sintering Flank~vear body (vol.~o) assistant agent aftersintering (llm) sample (~vt.5Z) 8A 86.9 99.88-Co, 0.03-Pd, 0.09-Sn 88 8B 8~.3 99.85-Co, 0.04-Pd, 0.11-Sn 67 8C 90.2 99.93-Co, 0.02-Pd, 0.05-Sn blade chipping 8D 86.7 99.88-Co, 0.03-Pd, O.09-Sn damaged 8E 87.9 99.85-Co, 0.04-Pd, 0.11-Sn damaged 8F 90.3 99.93-Co, 0.02-Pd, 0.05-Sn damaged 8Csintering not possible 8H 87.1 100Co damaged 8~ 90.0 100Co damaged 8J 79.6 57.7-Co, 42.3-WC 211 8K 79.8 48.3-Co, 51.7-WC 153 8L 8S.3 35.5-Co, 64.5-WC blade chipping The sintered body samples 8A to 8L shown in Table 8 were obtained from powder samples 7A to 7L of Table 7.

CA 021639~3 1998-12-22 In sample 8G, since the raw material diamond powder has fine particles as shown in Table 7, space between particles is narrow and mixed Co powder is not uniformly distributed. Therefore, when Co plate was stacked on the powder compact body of the mixed powder for infiltration, infiltration proceeded unevenly in the powder compact body. As a result, unsintered portions were generated partially in sample 8G and complete sintered body could not be obtained.
Samples providing complete sintered bodies were processed to cutting tools, and performance thereof was evaluated under the following cutting conditions.
Work piece: round bar of Al-lO wt ~ Si having four grooves along the axial direction Peripheral surface velocity of the work piece: 500 (m/min) Byte cutting depth: l.5 (mm) Byte feeding speed: 0.2 (mm/rev) Cutting time: 160 (min) Table 8 shows flank wear of sintered body samples as a result of cutting test. As can be seen from Table 8, sintered body samples 8D, 8E, 8F, 8H and 8I including pools of sintering assistant agent were damaged at initial stage of cutting and continuous cutting was impossible.
In sintered body samples 8C and 8L having large diamond particle size, chipping was observed at the blade of the tool during cutting test. As for sintered body samples 8J
and 8K having low diamond content, though there was not a damage, the flank wear was too large to be practical.
Meanwhile, sintered body samples 8A and 8B in accordance with the present invention had small diamond particle size, and uniform sintered body texture without void or Co pool could be obtained, and hence the sintered bodies had high strength and were free of chipping or CA 021639~3 1998-12-22 damage. In addition, it becomes apparent that samples 8A
and 8B have sufficient wear-resistance as shown in Table 8, since they have sufficiently high diamond content.

(Embodiment 5) Table 9 PowderConditionc forAmount of coating Contli~ionc for Degree of sampleheat treatment of sintering heat treatment grArhi~i7A~ion of ~liAn-ond assistant agent of coated (vol.%) powder (YOI.%) rli~mond powder 9A1400~C, 60 min. 4 heat treatment 5.3 not performed gB1450~C, 60 min. 4 heat treatment 52.6 not performed 9C1500~C, 60 min. 4 heat treatment 93.8 not performed 9Dheat treatment 4 heat treatment 0 not performed not performed 9Eheat treatment 4 1200~C, 60 min. 5.2 not performed 9Fheat treatment 4 1350~C, 60 min. 32.1 not performed Table 9 shows various powder samples prepared for studying influence of the degree of graphitization of diamond powder on diamond content in the sintered body.
In samples 9A to 9C, raw material diamond powders having the particle size of 5 to lO ~m were heat treated under vacuum under the conditions shown in Table 9 so as to partially graphitize the powders from the surface of the particles. The partially graphitized diamond particles were coated by the sintering assistant agent using the method described in Embodiment l.
In samples 9D to 9F, raw material diamond powder particles having the particle size of 5 to lO ~m were CA 021639~3 1998-12-22 coated by the sintering assistant agent using the method described in Embodiment 1, and thereafter the coated diamond particles were partially graphitized from the surface under the heat treatment conditions shown in Table 9 under vacuum.
The partially graphitized coated diamond powders were molded to powder compact bodies, a metal plate of 100 ~ Co was stacked as additional sintering assistant agent, and then the powder compact bodies were sealed in a container of Mo and sintered under a pressure of 50 kb at a temperature of 1550~C for 10 minutes. Table 10 shows diamond contents of the sintered body samples obtained in this manner.
Table 10 Sintered bodyDiamond content sample (wt.%) 10A 94.4 10B 95.1 10Cpartial sintering (Gr left) 10D 92.2 10E 94.5 10F 94.8 The sintered body samples lOA to lOF of Table 10 were obtained from powder samples 9A to 9F of Table 98.
As can be seen from Table 10, it is apparent that sintered body samples lOA, lOB, lOE and lOF have higher diamond contents than sample lOD. Meanwhile, sample lOC partially included remaining graphite (Gr), and hence a complete sintered body could not be obtained.
More specifically, the degree of graphitization of the coated diamond powder should preferably be in the range of 0.5 to 50 percent by volume.

CA 021639~3 1998-12-22 (Embodiment 6) Table 11 Powder DiamondAmount ofArnount o~ coatingComposilion of sintering samplcparticleabsorption ofof sintering assistant agent size Pd assistant agent (wt.%) (~lm) (~vt.%) (vol.%) 1~A S -10 Sx10-s not precipitated 11B 5 -10 8x10-3 5 Pd-0.08, Co-99.82, Sn-û.1 11C 5 -10 8x103 5 Pd-2.7, Co-97.2, Sn-0.1 11D 5 - 10 8x103 5 Pd-38.7, Co-61.2, Sn-0.1 11E 5 -10 8x103 5 Pd-52.1, Co-47.8, Sn-0.1 Table 11 shows various powder samples prepared for 15 studying influence of the amount of application of Pd on catalytic property in electroless plating and sintering property of diamond powder at the time of sintering.
For samples llA to llE, Pd was applied to the surfaces of diamond particles, using the method described in Embodiment 4, so as to coat diamond powder particles by sintering assistant agent by electroless plating.
Thereafter, diamond powder particles were electroless-plated by Pd, using electroless plating solution including palladium tetra chloride. Further, diamond powder 25 particles were coated by Co using an electroless plating solution containing hydrazine.
As a result, as shown in Table 11, the amount of absorption of Pd by the particles of diamond powder was too small in sample llA, so that catalytic action by Pd was insufficient and Co was not successfully precipitated at the surface of the diamond particles.
Each of the powder samples llB to llE coated with Co was molded into a powder compact body and sealed in a container formed of cemented carbide. The cemented 35 carbide container was held under a pressure of 50 kb at a CA 021639~3 1998-12-22 temperature of 1500~C for 15 minutes to perform sintering, by using a belt type high pressure apparatus. Sample llE
containing much Pd did not result in a complete sintered body, since melting of the sintering assistant agent did not occur. Meanwhile, complete sintered bodies could be obtained from samples llB to llD.
In other words, the preferable content of Pd in the sintering assistant agent is within the range of 0.01 to 40 percent by weight.
As described above, according to the present invention, a diamond sintered body having both high strength and high wear-resistance can be provided, which can be preferably used for cutting tools, digging tools, drawing dices and wear-resistant parts.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims

1. A diamond sintered body comprising 80 to 96 percent by volume of sintered diamond particles and a remaining part of sintering assistant agent and unavoidable impurity, said sintered diamond particles having a particle size substantially in the range of from 0.1 to 10 µm and directly bonded to each other, said sintering assistant agent including Pd within a range of from 0.01 to 40 percent by weight and as a remaining part, at least one of Fe, Co and Ni.

2. The diamond sintered body according to claim 1, wherein said sintering assistant agent further includes at least one of Sn, P and B.

3. The diamond sintered body according to claim 2, wherein said sintering assistant agent includes at least one of Sn, P and B within the range of from 0.01 to 30 percent by weight.

4. A method of manufacturing a diamond sintered body comprising the steps of:
preparing diamond powder having a particle size substantially within the range of from 0.1 to 10 µm;
preparing coated diamond powder by applying a sintering assistant agent to said diamond powder in a quantity within the range of from 4 to 20 percent by volume, which comprises precipitating Pd within the range of from 10-4 to 40 percent by weight on a surface of each particle of said diamond powder, and thereafter electroless plating at least one of Fe, Co and Ni to the surface of each particle of said diamond powder; and under high pressure and high temperature conditions at which diamond is stable, sintering said coated diamond powder in liquid-phase.

5. The method of manufacturing a diamond sintered body according to claim 4, wherein said sintering assistant agent further includes at least one of Sn, P and B.

6. The method of manufacturing a diamond sintered body according to claim 5, wherein said sintering assistant agent includes at least one of Sn, P and B within the range of from 0.01 to 30 percent by weight.

7. The method of manufacturing a diamond sintered body according to claim 4, wherein from 0.5 to 80 percent by volume of each particle of said diamond powder is graphitized from its surface by heat treatment at a high temperature at which diamond is unstable, and thereafter said sintering assistant agent is applied as coating.

8. The method of manufacturing a diamond sintered body according to claim 4, wherein from 0.5 to 80 percent by volume of each particle of said coated diamond powder is graphitized from its surface by heat treatment at a high temperature at which diamond is unstable, and thereafter said sintering in liquid-phase is performed.

9. The method of manufacturing a diamond sintered body according to claim 4, wherein during said electroless plating, the plating solution in which said diamond powder is immersed is agitated by at least one of stirring and ultrasonic vibration.

10. A method of manufacturing a diamond sintered body comprising the steps of:
preparing diamond powder having particle size substantially in the range of from 0.1 to 10 µm;
preparing coated diamond powder by applying a sintering assistant agent to said diamond powder in a quantity within the range of from 0.1 to 19.9 percent by volume, which comprises precipitating Pd in the range of from 10-4 to 40 percent by weight on a surface of each particle of said diamond powder and thereafter electroless plating at least one of Fe, Co and Ni to the surface of said particle of said diamond powder;
molding a powder compact body of said coated diamond powder;
bringing into contact an additional sintering assistant agent including at least one of Pd, Fe, Co and Ni to said powder compact body; and sintering said powder compact body in liquid-phase while infiltrating said additional sintering assistant agent under high pressure and high temperature conditions at which diamond is stable.

11. The method of manufacturing a diamond sintered body according to claim 10, wherein said sintering assistant agent coating said diamond particles further includes at least one of Sn, P and B.

12. The method of manufacturing a diamond sintered body according to claim 11, wherein said sintering assistant agent coating said diamond particle includes at least one of Sn, P and B within the range of from 0.01 to 30 percent by volume.

13. The method of manufacturing a diamond sintered body according to claim 10, wherein 0.5 to 80 percent by volume of each particle of said diamond powder is graphitized from its surface by heat treatment under a high temperature at which diamond is unstable, and thereafter said sintering assistant agent is applied as coating.

14. The method of manufacturing a diamond sintered body according to claim 10, wherein 0.5 to 80 percent by volume of each particle of said coated diamond powder is graphitized from its surface by heat treatment under a high temperature at which diamond is unstable, and thereafter said sintering in liquid-phase is performed.

15. The method of manufacturing a diamond sintered body according to claim 10, wherein said additional sintering assistant agent further includes at least one of Sn, P and B.

16. The method of manufacturing a diamond sintered body according to claim 15, wherein said additional sintering assistant agent further includes at least one of Sn, P and B within the range of from 0.01 to 30 percent by weight.

17. The method of manufacturing a diamond sintered body according to claim 10, wherein during said electroless plating, the plating solution in which said diamond powder is immersed is agitated by at least one of stirring and ultrasonic vibration.