CA1149619A

CA1149619A - Diamond sintered body and the method for producing the same

Info

Publication number: CA1149619A
Application number: CA000334154A
Authority: CA
Inventors: Akio Hara; Shuji Yazu
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1978-08-26
Filing date: 1979-08-21
Publication date: 1983-07-12
Also published as: CA1149619A1; AU5032379A; GB2029389A; DE2934567A1; AU531126B2; DE2934567C2; FR2434130B1; SE442962B; FR2434130A1; SE7907095L; GB2029389B

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a diamond sintered body having a high wear resistance and enabling to obtain a processed surface of high dimensional precision and beautiful finish as a wear resisting tool blank for use particularly in a wire drawing die, shaving die and the like, as a tool blank for use in a cutting tool for a workpiece consisting of nonferrous metals, plastics, ceramic, etc., and as a cutting tool blank for use in a glass cutter, synthetic building material cutting blade, etc., and the method for producing the same. wherein a mixture comprising a diamond powder below 1µ and a powder below 1µ of one or more than two kinds of carbides, nitrides and borides of IVa, Va and VIa group metals of the periodic table, and further a powder of iron group metals is placed between a plurality of cemented carbide plates and then subjected to hot press sintering at a high temperature and high pressure under which diamond is stable thereby enabling to obtain a diamond sintered body having a high properties suitable for the aforesaid uses.

Description

~1~9619 1 Background of the Invention A cutting tool material wherein a sintered body consisting o~ more than 70 vol % of diamond and a metal chiefly comprising Co as a bonding material is bonded onto a ceme~ted carbide substrate is commercially avail-able. The said tool blank is commonly for use in a cutting tool for processing Al alloys containing a large amount of Si, Cu alloys, etc. despite the high price thereof.
~hejsaia tool blank is not only far better in respect of wear resistance than that of the conventional cemented carbide but also sufficiently tough against impact compared with the tool blalik produced from a single crystal natural diamond. ~he said cutting tool blank, however, has a disadvantage in that the processed surfaces of nonférrous metals and the like cut by said tool blank have greater roughness compared with those processed by the cutting tool of single crystal natural diamond thereby rendering it impo~sible to obtain a beautifully finished surface like a mirror. Moreover~
particularly when a small and thin workpiece, such as a part of a watch and the like, is processed, the said tool blank has a high cutting resistance, whereby the workpiece is liable to be deformed out of dimensional precision.

Summary of the Invention ~he invention relates to a dia~ond sintered body useful as a wear resisting tool blank for us~ particular-ly in a wire drawing die, shaving die and the like, as ~ 1 ~9 61~

1 a tool blank for use in a cutting tool for a workpiece made of nonferrous metals, plastics, ceramic, etc., and as a cutting tool blank for use in a glass cutter, synthetic building material cutting blade, etct, and the method for producing the same, wherein a mixture comprising 50-95 vol % of a diamond powder below lJU
the remainder consisting of a powder below lJ~ of one or more than two kinds of carbides, nitrides, borides of IVa, Va and VIa group metals of the periodic table lQ and solid~ solutions thereof, and further a powder of iron group metals, is interposed between a plurality of oemented carbide plates, and then subjected to hot press sintering at a high temperature and high pressure under which diamond is stable thereby enabling to obtain a diamond sintered body having high wear resistance.

Brief Des¢riptlon of the Drawings Fig.l(a) is a perspective view showing the con-struction of the marketed diamond sintered body for use in a wire drawing die.
Fig.l(b) is a sectional view of the same.
Fig.2 is a photograph showing the state of the surface of a copper wire drawn by a natural diamond die.
Fig.3 is a photograph showing the state of the surface of a copper wire drawn by means of a marketed diamond sintered body.
Fig.4 is a photograph showing the inner face of a die after the wire drawing, in which a marketed diamond sintered body is used.
Fig.5 is a diagram illustrating the shape and si~e 9~9 1 of a natural dia~ond. Fig. 5 appears on the same page as Figs. l(a)-(b).
Figs. 6 to 8 are typical diagrams describing the method conforming to the invention. Figs. 6 to 8 appear on the same page as Figs. l(a)-(bl.
Fig. 9 is a perspective view of a diamond sintered body obtained according to the invention. Fig. 9 appears on the same page as Figs. l(a~-~b).

Fig. 10 is a sectional view of wire drawing dies using diamond sintered body according to the invention. b is a case made of stainless steel, c is sintered metal mount and d is diamond sintered body.
Fig. 11 is a photograph of scanning electron micro-scope showing the micro structure of diamond sintered body according to the invention. The grey or black part is diamond particles and the white part is WC particles. Fig. 11 appears on the same page as Fig. 2.
Fig. 12 is a type view of micro structure of diamond sintered body according to the invention shown in Fig. 11. White

2~ particles is diamond and black particles is WC.

Fig. 13 is a diagram related to the production condition of the diamond sintered body conforming to the invention, showing the diamond stability range on the temperature and pressure phase chart.
Detailed Description of the Invention The invention relates to an inexpensive diamond-sintered body in the shape of a thin plate capable of replacing a natural diamond for industrial use, which is particularly suitable for a wire drawing die tool blank, a wear resisting member, and a cutting tool blank, and the method for producing the same.
At present, a cutting tool material for cutting ~..", ~1~9619 1 nonferrous metals~ plastics and ceramic wherein a sintered body consisting of more than 70 vol ~ of diamond and a metal chiefly comprising Co as a bonding material is bonded onto a cemented carbide substrate is commercial-ly available. Despite its high price, the said tool material is welcomed in some circles as a cutting tool blank for processing Al alloys containing a large amount of Si and copper alloys~
~he inventors of the pre~ent in~ention made careful studies on the properties of the aforesaid tool material.
Cutting tests were practically conducted with cutting tool produced by making use of the said material. As a result, it was found that the cutting tool was featured by its superiority over the Gonventional cemented carbide tool in respect of wear resistance with greater toughness against impact compared with a tool made of a !~`
single crystal natural diamond.
It was found, however, that the processed surface of, for example, a nonferrous metal showed greater rough-ness compared with the surface machined by a cutting tool made of single crystal naturi~l diamond. ~hus, it was impossible to obtain a machined surface as beautifully finished as a mirror.
Moreover, when a small and thin workpiece, such as a part of a watch, was machined, the workpiece waæ
liable to be deformed by high cutting resistance there-by rendering it impo3sible to sustain dimensional pre-cisionO Careful examinations revealed the following reasons.
~he marketed diamond sintered body is composed of -1 diamond crystals of 3-lQ ~, the diamond crystals being bonded to each other in a skeleton construction with metallic Co as a bonding material existing therebetween. The edge of the tool made of the sintered body shows convexities and concavities sub-stantially same as the size of the crystal particles, which is different from the sharp edges of the natural diamond cutting tool. This is one of the reasons why the beautifully finished surface is unobtainable by the marketed diamond sintered body cutting tool. Furthermore, the metallic Co bonding phase existing between the diamond particles is liable to adhere to the work-piece. This is another problem to be solved when a mirrorlike surface is required.
The marketed diamond sintered body available for use in a die consists of diamond particles of 50-6Q ~ with its outer periphery concentrically encircled by a cemented carbide.
Figs. l(a) and ~b~ show the construction of the said diamond sintered body for use in a wire drawing die, (a~ being a perspective view, whilst (b~ shows a sectional view of the same, where (Sl shows the diamond sintered body which is integrated with the encircling ring (A) of WC-Co cemented carbide.
According to U.S. Patent No. 3,831,428 which con-ce~vably covers the art of the aforesaid marketed article, the strong compressive stress of the outer peripheral cemented car-bide acting on the inner diamond sintered body helps to improve the properties of the wire drawing die. However, when the ~1~961 9 1 diamond is sintered under normal pressure, it trans-forms to graphite due to a high temperature. ~here-fore, an ultrahigh pressure high temperature apparatùs is necessitated which is as expensive as in the case of synthesizing a diamond~ According to the said ~aying-Open Gazette, the encircling cemented carbide is also sintered in the same expensive ultrahigh pre~sure high temperature apparatus. As a result, the diamond sintered body for use in a wire drawing die commerci~lly available at present is extravagantly high-priced.
A diamond die made of single crystal natural diamond has been in use for a long time. ~he price (y) t of single crystal natural diamond is substantially ;r represented by the formula of Y=(AX~B)2 depending on the size thereof (X) (wherein A and B are constants).
he price is very high when the size is large.
Conversely speaking, a small-sized single crystal natural diamond is relatively inexpensive. Single crystal natural dianond replaceable by a marketed diamond sintered body after processing into a wire drawing die is estimated at 1.2 mm and upward in bore size except a specific case. In many cases, it is said that the sintered diamond die has a longer life than the single crystal natural diamond die. If it is '~
possible to provide small-sized diamond sintered bodies t at low price,- it will have a great industrial signifi- i cance. ;
In recent years, the production of natural diamond `
has not been increased, the price showing a sharp uprise ~1~96~9 1 since the demand exceeds the supply. Great hopes are entertained of the said marketed diamond sintered body as a substitute for single crystal natural diamond.
However, it i~ high-priced and is not yet capable o~
replacing natural diamond altogether though it displays distinguished merits when used in a die.
~ he marketed diamond sintered body for use in a wire drawing die comprises coarse diamond particles of 50_60~sintered with a bonding material chiefly con-sisting of metallic Co.
~ he properties of the coarse-grained sintered body were examined by the inventors of the present invention by practically drawing a wire thereby. As a result~
there were some problems to be solved though great improvement over the conventional cemented carbide wire drawing die had been made in wear resistance and some other respects. One of the problems is that scars are left on the surface of the drawn wire. Figs,2 and 3 show examples thereof. Fig.2 ~hows the condition of the surface of a copper wire 0.5 mm in diameter drawn by use of a die made of single cryetal natural diamond, whilst Fig.3 shows that of the same wire drawn under the same condition by mal~ing use of the said marketed sintered body.
As is apparent from the comparison, the marketed sintered diamond die leave~ a great deal of scars on the drawn wire. Examination of the inside of the used die revealed that part of the sintered diamond particles was broken and missing as shown by the photograph of Fig.4, the scars being presumably caused when the metal ~1~9619 1 bit into the said defective part of the die whilst being drawn.
Another shortcoming of the marketed sintered diamod consists in greatne~s of the friction coefficient between the wire to be drawn and the die compared with the case of a natural diamond die. The greatness of the friction coefficient is liable not only to cause a breakage of the wire but also to render the control of the wire diameter difficult. ~he grBatness of the frictionjcoefficient may be attributable to the follow-ing reasons. ?he bonding material chiefly consi~ts of metallic C0 which is liable to adhere to the wire to be f drawn. Furthermore, since the wear re~istance of the diamond particles is largely different from that of the ¦i bonding material, the bonding material i~ worn earlier than the diamond particles, concavities thus formed permitting the wire to be drawn to bite thereinto.
The invcntors have made the present invention after careful studie~ on the method for developing a diamond sintered body capable of obviating the aforementioned disadvantages of the marketed diamond sintered body~ r having properties capable of entirely replacing single crystal natural diamond, and producible at low cost.
~o be more precise, the diamond sintered body conforming to the invention is characterized in that the diamond crystal is an extremely fine particle below 1JL, and preferably below 0.5J~ ~ the chief component ~
of the bonding material being not a metallic phase but ~-a powder below 1~ of carbides, nitrides and borides of IVa, Va or VIa group metals of the periodic table , ~

~ 619 l including a small amount of iron group metals as an auxiliary agent, a sintered body comprising such fine diamond particles enabling to largely alleviate the surface scars of the drawn wire which were inevitable in case of the aforesaid marketed diamond sintered body.
~he bonding material for bonding the diamond particles chiefly consists of compounds having high hardness, wear resistance and adhesion, such as carbides, nitrides and borides of IVa, Va or VIa group metals of the periodicjtable, instead of simple metals. ~he compound is, *or example, a carbide, such as WC, TiC or ~aC, which is used as a principal wear resisting component of the cemented carbide. At present, such cemented carbide is for use in a cutting tool, wire drawing die, etc.
Since the bonding material of the diamond sintered '-body conforming to the invention chiefly comprises compounds having high wear resistance and adhesion with a small content of iron group metal~, the wire drawing die made of the diamond sintered body conforming to the invention causes less adhesion of the wire to be drawn with less friction coefficient compared with die m~de of the marketed diamond sintered body.
Furthermore, the invention i~ greatly characterized by its shape. '~he diamond sintered body conforming to the invention is intended for replacing the single crystal natural diamond. A sintered body of substantial-ly the predetermined shape of the currently used diamond can be produced particularly when it is for use in a wire drawing die~

_ g _ ~9619 ~ he size of a rough diamond for use in a die is as shown in ~'ig.5 accordillg to the Interna-tional Diamond A~sociation Standard (IDAS). The required effecti~e side length (~) is greater than the effective thick-ness (~), and ~ 1.2D~0.6(mm), ~- 1.5D~1.4(mm). What is required is to produce a plate-like sintered body such as will satis~y the said standard.
~ he wire drawing die of single crystal natural diamond produced at pre~ent has a hole diameter up to ~ about 3 ~m, the size of the sintered body required in this case being about 4 mm in thickness and about 6 mm in side length. In practice, the dies in which natural diamond is mostly used are those having a still smaller hole diameter.
The inventors of the present invention, after care-ful ~tudie~ on the method for industrially producing a thin diamond sintered body in the shape of a plate~
have found that such a thin diamond sintered body iB
readily producible by interposing a powder material of the sintered body including a fine powder of di~mond between cemented carbide plates of high rigidity and subjecting same to high pressure and temperature.
~he cemented carbide in the aforesaid case i9 chief-ly composed of WC, (Mo~)C~ TiC, ~aC, etc. bondea by a metal, WC, (Mo,W)C being particularly preferred for the high deformation resistance t-hereof. A green compact of a sandwich structure with a layer 3 of powder material containing a fine diamond powder interposed between cemented carbide thin plates 1, 2 (Figs.6 and 7) is placed in an ultrahigh pressure high temperature appara~u~.

96~9 1 The pressure is applied by a pair of piston~ 4~ 5.
l~lus, it is pr~ferable that the green compact of the sandwich structure is disposed normally to the pistons. As is apparent from Fig.8, a plurality o~
green compacts may be placed in the apparatus sim~-taneously. Since heating is e~fected by applying a heavy current to a graphite heater 10 through the piston~ 4, 5, a temperature distribution arises in the vertical direction. A plurality of green compacts lo may be p}aced simultaneously within the scope o~ this tolerance. Re~erring to the drawings, the nt~erals 6 and 7 de~ignate cylinders~ 8 and 9 designating pre~sure mediums, 11 and 12 de~ignating partition members.
Accordin~ to the invention, the powder material of the diamond sintered body comprises a mixture of fine powder of diamond and fine powder of carbides, nitrides and borides of I~a, Va or VIa group metals of the periodic table which are principQl cornponents of the bonding material. A fine powder o-~ iron group metal~
may be added as an at~xiliary agent.
In the former case, the green compacts are dispos-ed as shown in Fig.6 and heated after pressurized in the t~trahigh presst~re apparatus. Then~ an eutectic liquid phase appears on the upper and lower cemented carbide thin plates 1~ 2~ a small ~mount of said so-lution phase infiltrating into the layer o~ the powder material containing diamond ss as to act as an ~uxiliary agent.
In the latter case, a predetermined amo~l~t of iron group metal powder as an at~iliary agen-t has been ~.

96~9 1 preliminarily added to the powder material, and no infiltration of the liquid phase from the upper and lower cemented carbide thin plates i~ necessitated in this case. In order to stabilize the composition of the bonding matçrial in the diamond sintered body, it is preferable to adopt the latter method wherein partition members 11, 12 for precluding displacement of the liquid phase appearing in the course o~ sintering between the powder mixture 3 containing diamond and the upper and lower cemented carbide thin plates 1, 2, as shown in Fig.7. The partition member may be selected from the materials unfusible at the high temperature and pressure to which the sintered body is exposed, for example, metals of high fusing point, such a~ Ti, Zr, Hf, ~a, Nb, Cr, Mo, W, Pt, etc. or compounds of high fusing point, such as ~iN, ZrN, H~N, BN, A1203, etc. In view ,;
of its end, the partition member requires no great thickness, a thickness less than 0.5 mm being suf~icient.
The aforesaid metal foil may be used as a partition member, or the cemented carbide thin plate may be plated.
In case of use of a compound, it may be applied to the cemented carbide thin plate in the state of fine powder, or by any known art, for example, the chemical vapor deposition method (abbreviated as CVD).
~he diamond sintered body con~orming to the invention is characterized in that the diamond crystal particles in the sintered body consist of ultrafine particles below l~(preferably below 0.5~).
According to the experiments by the inventors of the present invention, however, such ultrafine grain ~ .

~ 3619 1 diamond sintered body is not obtainable by the method o~ simply mixing a diamond powder below 1 ~ as the powder material and iron group metal powder as a bonding material, or by the method of causing a liquid phase containing iron group metals to infiltrate into the diamond powder from the surrounding cemented carbide during the sintering process.
In such a case~ the iron group metals, such as aO, Fe, Ni, etc., act as a solvent of diamond thereby inducingjthe phenomenon of dissolution and precipita-tion of diamond into the solvent at the high temper-ature and high pressure under which diamond is stable.
In case of using a diamond powder below 3 ~ ~ and particularly 1 ~ , the abnormal growth of diamond crystals arises, a sintered body consisting of uni-formly fine crystals being unobtainable as a result.
On care~ul ~tudies of the method for producing a sintered body of fine crystals below lJu, the inventors of the present invention have found that the grain growth of diamo~d can be controlled even in the state of coexistence with an iron group metal li~uid i~ the diamond powder is mixed with a fine powder of carbide~
nitride~ and boride of IVa group metals (Ti, Zr, Hf), Va group metals (V, Nb, Ta) and VIa group metals (Cr, Mo, W) of the periodic table.
It is presumable that the grain growth is con-trolled by the existence of the compound particles between the fine diamond crystal particles which act as impurities, or the grain growth i9 controlled by the dissolution of part of the compounds into the iron 1.

.... .

1 group metal liquid and the precipitation thereof as carbides on the surface of the diamond crystals.
In order to have the aforesaid action it is necessary that the compound particles are interposed between the ~ine diamond crystal particles. Thus, the compounds should be pulverized to a granularity same as or below that of the diamond crystals and mixed with the diamond crystal powder uniformly.
The experiments show that, among the compounds, carbides of IVa group, Va group and VIa group metals have 0 the greatest effect of controlling the grain growth. When viewed from the performance of a cutting tool, it is necessary that the compounds have high strength and wear resistance since they are retained in the sintered body as the bonding material of the diamond crystals together with the iron group metals.
Thus, the use of carbides will enable to obtain a sintered body having a higher strength and wear resistance.
As a diamond powder for use in the sintered body conforming to the invention, both synthetic diamond and natural diamond are suitable insofar as the diamond is micronized less than 1 ~, and preferably less than 0.5 ~.
A mixture comprising the diamond powder, one or more than two kinds of said compound powders, and a powder of iron group metals such as Fe, Co, Ni is uniformly milled by means of a ball mill or the like.
The iron group metals may be caused to permeate at the time of sintering instead of preliminary mixing.
As described in the prior application by the inventors, U.S. Patent No. 4,171,973, the pot `'', ~ ~k9 619 1 and balls may be produced by means of a sintered body comprising iron group metals and compounds, æuch as carbides and the like.
~hus, a fine powder, which comes out of the pot and balls, of sintered body of iron group metal~ and com-pounds, such as carbides and the like, is mixed with the diamond powder whilst it is milled in the ballmill.
~he powder mixture thus prepared iQ placed direct-ly between cemented carbide thin plates as shown in Fig.6 when the iron group metals are not preliminarily mixed, or placed between said thin plates with inter-position of partition members as shown in Fig.7 when a required amount of iron group metals is preliminarily -mixed, green compacts of such sandwich structure being placed in a single layer or multiple layers in the ultrahigh pressure high temperature apparatus as shown in Fig.8.
In case of the arrangement as shown in Fig.6, an eutectic liquid phase arises on the upper and lower cemented carbide thin plates 1, 2 when heated after application of pressure, said liquid phase infiltrat-ing into the powder mixture 3 of diamond, carbides and the like.
In case of the arrangement of Fig.7, sintering is e~fected at a higher temperature than the level at which an eutectic liquid phase appears between the iron ~-groups metals used in the powder mixture containing r,`
diamond and the compounds, such as carbides and the like. ~
. . .
For example, when ~iC is used as a compound and Co as an iron group metal~ a liquid phase arises at about 9ti1~

1 1260 C under normal pressure. Under high pre~sure, the eutectic temperature will be higher by scores of degrees C.
In this case~therefore, sintering is e*fected at a temperature higher than 1300 C.
In this invention, however, there is also a upper limit to a sintering temperature. ~his temperature should not be higher than 200 C from eutectic temperature~
when grain growth of diamond becomes remarkable.
In all the cases~ the conditions pressure and temperature under which sintering i8 effected should be within the stability range of diamond as shown in Fig.
13, otherwise diamond will trans~orm into graphite in the course o~ sintering.
~ hus~ a sintered body rigidly integrated in a sand-wich structure iB obtainable when the temperature i5 lowered and the pressure is released.
~ he upper and lower surface are ground by means of~
for example, a cLiamond grinder.
~inor concElvities of the ceme~ted carbide and the partition member need not be removed completely~ since a high degree of parallel between the upper and lower surfaces of a sintered body very much *acilitates the production of a die.
In reverse, a relatively small resi~ual of the cemented carbide is almost harmless.
The diamond sintered body of which the greater parts of the upper and lower sur~aces are in parallel is cut by a diamond cutter or laser. Fig.9 is a perspective

3 view o~ a diamond sintered body thus obtained.

- 16 _ 1 The principal use of the diamond sintered body conforming to the invention is a replacement of the natural single crystal as described hereinbefore. Though the single crystal is susceptible to cleavage and breakage with relatively low strength, the sintered body conforming to the invention has an advantage in respect of strength since it consists of fine crystals since it has been developed as a substitute for fragile single crystals, it necessitates no reinforcement as described in U.S. Patent No. 3,831,428.
If a greater strength is required, the dimensions of the sintered body may be increased longitudinally and transversely, or the sintered body may be formed into the shape of a triangle.
The diamond sintered body conforming to the invention contains diamond within the scope of 95-50 vol %. In case the diamond content exceeds 95 ~, the grain growth of diamond can not be controlled with effect during the sintering process since the amount of the interposed compounds is not sufficient. If the diamond content is less than 50 vol % of the sintered body, the wear resistance is reduced and the properties equal to those of natural diamond are no longer obtainable.
The ratio of the compounds, such as carbides and the like to the iron group metals acting as bonding agents of diamond in the sintered body can not be readily determined.
However, the amount should be at least such that the compounds are permitted to remain as solids at the time of sintering. For e~ample, in case WC is used ~ ~ ~9 61~

1as a compound and Co as a bonding metal~ the quantita-tive ratio of WC to Co should be such that the former is contained in more than about 50 ~ by weight. ~hen the diamond sintered body conforming the invention is used as a wire drawing die, the greater is the diamond content, the higher is the wear resistance.
If the diamond content is 95-70 %, a wire drawing die having a longer life than a natural diamond die i~
obtainable.
10In jthis case, the performance will be further improved if a carbide containing Mo, and preferably (~o, W)C having the same crystal structure at that of WC, is used a~ the principal component of the diamond bonding material. he reason why the performance of the wire drawing d~!e i5 improved when a carbide con-taining Mo i~ used aa a bonding material may be attribut-able to the fact that Mo is less liable to adhere to the workpiece compared with other compounds, such as WC
and the like. ~his iB presumably due to the properties ~ of oxides produced on the friction surface. To be more precise, MoO3 which oxidize~ Mo carbide is produced.
The said oxide, having a layer-like structure, is a self-lubricator belonging to the group having the lowest friction coefficient among the oxides. The sintered body conforming to the invention and the method for producing the same have been desoribed hereinbefore with reference to a tool blank fo~ use in a thin wire drawing die in which the effect of the inYention iB
best displayed.
30The invention has a great effect also as a wear .

.. .. ..

s3f~l9 1 resisting tool blank for use in a thicker wire drawing die, a shaving die and the like, as well as a cutting tool blank of a glass cutter and a synthetic building material cutting blade. In other words, it is use-ful where the single crystal diamond tool is used at present, for example, a wire drawing die in which a particularly beautifully finished surface is required, and Al alloys and Cu alloys which are required to be finished with mirror-like sur~aces.
Thejinvention will be described in more detail in reference to the following examples. f Example I
; A powder of 0.5f~ of synthetic diamond and a powder of WC and Co were milled by means of a pot and balls made of a WC-Co cemented carbide. ~he powder mixture thus produced was of the following composition.
~able 1 L
I .
No Volume % Sintered Body Diamond WC Co Vickers Hardness A 96 2 2 Grain Growth B 90 3 7 Grain Growth C 90 5 5 8,000 D 80 15 5 7,200 E 50 45 5 5~300 !:.
F 25 70 5 2~100 No. a to E represent the sintered bodies conforming to the invention.
The powder mixtures were stuffed into containers made of Ta and placed in an ultrahigh pressure apparatus.
After the pressure was raised to 55 Kh, sintering was ' - -- 19 -- .

9~;19 1 effected at 1450 C for 30 minutes. Examination of the micro structures of the sintered bodies thus obtained showed that no sintered bodies of uniform micro structure were obtainable from the samples No.A and No.B, coarse diamond crystals of about 300 ~ being produced.
The samples No.C to No.~ were fine crystal ~inter-ed bodies oontaining diamond below 1 ~ and WC below 1 ~ ~ respectively.
The vickers hardnes~ of the respective sintered -- i bodies is shown in Table lo A tip for use in a cutting tool ~as produced by cutting the sintered body of No.C, and a cutting test t was conducted on an Al alloy.
~he workpiece was an Al alloy round bar having a diameter of 60 mm.
It was cut under the condition of cutting speed 250 m/min, feed 0.02mm/rev, cutting depth 0.07mm.
- ` A finished face almo~t as beautiful as the mirror was J , o Wained,~hich was sub~tantlally same as the surface~
2~ finished by a natural diamond tool under the same ~ E~
- - ~ condition.
Example 2 A powder mixture of the compo~ition of No.C in Example 1 was stuffed into a container made of ~a 5 mm t in inside diameter, 5 mm in depth and 50~ in thickness, and then filted into a ring 15 mm in outside diameter~ i 5.2 mm in inside diameter and 5 mm in height made of preliminarily sintered WC-10% Co alloy.
~he compound sam~le thus prepared was p~aced in an ultrahigh pressure apparatus and sintered under the . ... . ......... . . . . .

1 same conditions as in Example 1. The sintered body thus obtained was a compound body with a diamond sinter-ed body brought into contact with the inner periphery of a W~-10% Co cemented carbide ring.
~ he ~a container 50 ~ in thickness remained on the inter~ace, part o~ which had turned into TaC
through reaction with diamond or cemented carbide. The existence of the interface apparently obviated in-filtration of Co liquid phase from t~e cemented carbide ring during the sintering process thereby enabling a diamond sintered body o~ a very fine micro structure below 1 ~ .
The sintered body was mounted on a stainless steel ring in the same manner as when a natural diamond die is produced.
A wire drawing die was produced by drilling a hole through the diamond sintered body.
~ he die thus produced wa~ used to draw a stainless steel wire 1 mm in diameter for which a natural diamond die was conventionally used. The life of the diamond sinterea body die was three times as long as that of the natural diamond die~ and the surface of the drawn wire was no less smooth than the ease of the natural diamond die.
Example 3 A powder mixture of the composition as shown in ~able 2 was produced by making use of a diamond powder below 1 ~ .

3o _ 21 -.....

961~

1 ~able 2 No. Diamond Bonding Material & Vol.
Vol.~o Compound Iron Group Metal G 80 15 ~aC 5 Co H 80 15 ~iC 5 Co I 80 15 ~iB2 5 Ni J 80 15 ZrN 5 ~i E 80 15 WC 5 ~i ~ 80 15(~o7W3)~ 2.5Co- 2.5Ni j Sintered bodies were obtained under the complete-ly same sintering condition~ as in Example 1. All the sintered bodies thus obtained comprised fine crystals below 0.5 ~ formed into a skeleton structure.
However, the sintered bodies, No. I and J, had stratiform cracks extending thereon, and the strength thereof was inferior to that of the other samples.
Example 4 A pair of thin plates 1, 2 20 mm in diameter and 1.5 mm in thickness of a composition of WC-10 ~0 Co were prepared. A powder mixture ¢omprising 90 vol %
of synthetic diamond powder below 1 ~ (average granularity 0.3 ~ ) for use in lapping and 10 vol % of WC powder below 1~ was interposed between the thin plates 1, 2 in the form of a sandwich 90 that the interposed powder layer 3 has a thickness of 1~7 mm as shown in Fig.6.
~he ~ample thus prepared was placed in an ultrahi~h pressure high temperature apparatus called a girdle apparatus as shown in Fig.8 in such manner that the sample is normal to pistons 4, 5. Sintering was effected _ 22 -~ 619 1 under a pressure of 55 Kb and at a temperature of 1400 C for 10 minutes. The ~intered body thu~ obtain-ed was free from warp macroscopically. The upper and lower surfaces of the sintered body were subjected to plane grinding by means of a diamond grinder until the diamond layer was exposed to obtain a diamond sinter-ed body 1.2 mm in thickness. The diamond ~intered body thus obtained was lap-finished in part and examin-ed under an electron microscope. The examination showed ~ that thejdiamond sintered body was completely compact, its crystal granularity being about 0.3 ~ , as shown in the photograph of Fig.ll and the typical drawing of Fig.12. The diamond sintered body was cut 2.7 mm square .
by means of YAG laser (Fig.9) to produce a wire drawing die capable of drawing a 0.5 mm wire as shown in Fig.10.
~ i ; This die, when used for drawing SUS304, showed that it~
life was twice as long as that of the conventional single crystal die. The result showed that this die was advantageous to wire drawers in re~pect of cost, too.
Example 5 ;~ A mixture comprising a diamond powder same as was used in Example 4 and a fine powder of tMog, Wl)C
~ pulverized below 1 ~ in the ratio of 90 % to 10 % was ; sandwiched in between a pair of thin plates 20 mm in - diameter and 2 mm in thickness made of an alloy of (MogJ Wl)C-10 wt % Co - 10 wt % Ni in such manner that the powder mixture will have a thickness of 1.5 mm.
~he sample thus prepared was ~intered under a pressure of 52 Eb and at a temperature of 1250 C for ten minutes ~ in the same ultrahigh pressure apparatus as in Example 4 _ 23 -96~9 to obtain a diamond sintered body sandwiched between (Mo, W)C base alloy. ~he (~o, W)C base alloy on one side was completely removed, whilst that on the other side was ground until it was 0.2 mm in thickness thereby enabling to obtain a plate-like diamond sinter-ed body 1.0 mm in thickness having a 0.2 mm layer o~
(Mo, W)C base alloy bonded to one side thereof. It was cut into pieces 2.5 mm square by means of laser, and the same die as in Example 4 was produced by mak-ing use pf one of the pieces. As a result of a stain-less steel wire drawing test, the said die was ~ound to have higher properties than that of the die obtain-ed according to Example 4, and enable to draw wire about 3.5 time~ as much as in the case o~ a natural diamond single crystal die.
Example 6 A diamond powder below 1 ~ was subjected to wet ball milling for 24 hour~ with alcohol as a ~olvent and by m~ing use of a millpot lined with (Mo7, W3)~-10 wt % Co - 5 wt % Ni Qlloy and balls made of the same alloy. Subsequently the pulverized powder was reclaim-ed by evaporating the alcohol. Q~ analysis, it was found that the powder was mixed with (Mo, W)C, Co and Ni from the pot and balls in 15 vol ~ of the whole powder.
Independently, there were prepared a pair of disks 20 mm in diameter and 2 mm in thickness made of (~o7, W3)C-5 wt % Co - 5 w~ % Ni alloy. A Ta foil 0.1 mm in thickness and 20 mm in diameter was placed on the inside of each disk, and then the aforesaid powder was placed between the Ta foils 30 that the powder layer :, I' 1 was 105 mm in thickness. ~he sample thus prepared was sintered under a pressure of 52 Eb and a temperature of 1300 C for 10 minutes in the same apparatus as in Example 4 to obtain a sintered body comprising a diamond sintered body part about 1 mm in thickness with 8 Q l mm partition member and a (Mo7~ W3)C-5 % A, ~, Co - 5 % Ni alloy thin plate bonded to the upper and lower face, respectively.
The upper and lower (Mo7~ W3)C alloy parts were substantially completely ground away. ~hen, the disk-shaped diamond sintered body havin~ a ~a layer about 0.1 mm in thickness on each face thereof was cut by t laser in~o sintered bodies 2 mm square and 1.2 mm in thickness. One of the sintered bodies was fixed to a stainless steel ring by hot pressing at about 750 a hy making use of a mounting powder comprising silver blaz- ~r:
ing alloy powder mixed with iron powder, and a die hav-ing a hole diameter of 0.18~ was produced by the same method as in the case of a natural diamond die. For comparison, dies of the ~ame hole diameter were produced by making use of a diamond sintered body for use in a die in which marketed diamond crystals 50 - 60~ are bonded by Co~ and by making use of natural diamond !,`
single crystals. ~u wire was drawn at a speed o~ 300 m/mnn by means of the three kind~ of dies to measure ij the friction coefficient. In the case of the sintered t"
- body conforming to the in~ention, the ~alue was sub-stantially same as in the case of the natural diamond single crystal die, whilst it was about 1.5 times as high in the case of the marketed diamond sintered body.

1 E~ample 7 ~ hin plates made of WC-10 % Co alloy same as in Example 4 were prepared. ~urthermore, a fine powder of natural diamond below 1 ~ was mixed with compounds and metallic Co in compositions as sho~n in Table 30 ~able 3 Fine powder of No. Natural Diamond ~iC ~aC ~iN HfB2 Co j 60 35 5 `

On the inside of a pair of ~C-10 Co disks were placed 0.1 mm Mo foils as partition membiers~ and then a powder mixture of the respective composition in Table 3 was placed therebetween to a thickness of about 1.5 mm to obtain a sintered body by the same method as in Example 4. All the sintered bodies thus obtained were rigid with their diamond crystal granularity below 1 ~ . Il` -~he sample No. N in ~able 3 was selected from these sintered bodies. After grinding away the upper and lower cemented carbide, the sintered body was cut by laser into pieces 3 mm x 2 mm in side lengths and 1 mm ~-in thickness. One of the pieces was welded with æilver blazing alloy to a steel shank to produce a bite for use in a cutting tool in the same manner as in the case of a natural diamond single crystal bite. A bronze column was cut by making use of this bite, and the finished surface was as beautiful as that finished by a natural diamond bite.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A diamond sintered body comprising 50-95 vol % of diamond below 1 µ, the remainder being a bonding material comprising carbides, nitrides and borides of IVa, Va or VIa group metals of the periodic table, solid solutions or mixture crystals thereof below 1 µ, and iron group metals.

2. A diamond sintered body as defined in claim 1 characterized in that the bonding material comprise carbides of IVa, Va or VIa group metals of the periodic table and iron group metals, the carbide content in the ratio of carbides to iron group metals being greater than that corresponding to eutectic compositions.

3. A diamond sintered body as defined in claim 1 or 2, characterized in that the carbide in the bonding material is WC.

4. A diamond sintered body as defined in claim 1 or 2, characterized in that the carbides in the bonding material contain Mo.

5. A diamond sintered body as defined in claim 1 or 2, characterized in that the upper and lower surfaces of the sintered body are formed in the shape of plates substantially parallel to each other.

6. A method for producing a diamond sintered body characterized in that a mixture of a diamond powder below 1 µ
and a powder below 1 µ of one or more than two kinds of carbides, nitrides and borides of IVa, Va or VIa group metals of the periodic table and the solid solutions thereof, and a

Claim 6 continued.....

mixture in which a powder of iron group metals is further added, or a mixture of alloy powders of the said compounds and the iron group metals preliminarily alloyed are produced, said mixture being interposed between a plurality of cemented carbide plates directly or with interposition of partition members for precluding displacement of liquid phase in the course of sintering, the diamond containing mixture being sintered by hot pressing it under the condition of high temperature and high pressure in which diamond is stable, thereafter reducing temperature and removing pressure thus taking out sintered body, subsequently part or whole of the cemented carbide plates being removed substantially in parallel.

7. A method for producing a diamond sintered body as defined in claim 6, characterized in that a carbide powder of IVa, Va and VIa group metals of the periodic table and iron group metals are used as a bonding material forming powder, a mixture of diamond powder and the said bonding material powder being sintered at a high temperature and high pressure under which diamond is stable and at a temperature above the level where eutectic arises between the carbides and the iron group metals in the bonding material, the temperature not being higher than 200°C from eutectic temperature, thereby enabling to control the grain growth of diamond.

8. A diamond sintered body as defined in claim 1 or 2, wherein the carbide in the bonding material is WC and characterized in that the upper and lower surfaces of the sintered body are formed in the shape of plates substantially parallel to each other.

9. A diamond sintered body as defined in claim 1 or 2, wherein the carbides in the bonding material contain Mo and characterized in that the upper and lower surfaces of the sintered body are formed in the shape of plates substantially parallel to each other.