Diamond single crystals, a process of manufacturing and tools for using same

An artificial diamond single crystal, a process for producing it, and tools for utilizing it are disclosed. The artificial diamond crystal has at least one surface which has a rough surface formed by suppressed crystal growth at that surface. The single crystal is produced by providing a diamond synthesis reaction system comprised of a reaction chamber, a carbon source and a solvent metal arranged in contact with the carbon source. A seed crystal is provided in the reaction chamber under elevated pressures and temperatures which permit diamond to be maintained thermodynamically stable. The reaction system is heated to provide a temperature gradient in such a way that a portion of the solvent metal in contact with the carbon source is higher in temperature than a portion of the solvent metal in contact with the seed crystal. This temperature gradient causes a migration of the carbon from the higher temperature portion to the lower temperature portion using the solvent metal as a medium. This allows the carbon to precipitate and grow as diamond on the seed crystal due to the difference in solubility caused by the temperature gradient. The conditions in the reaction chamber housing are maintained so as to suppress crystal growth in at least one direction perpendicular to the direction of the temperature gradient, at the end of the solvent metal. The suppressed crystal growth provides the rough surface of the single crystal which can be connected to a tool and thus provides good adherence between the crystal and the tool.

FIELD OF THE INVENTION 
The present invention relates to artificial diamond single crystals having 
a rough surface which are suitable for use in tools, and a process for 
manufacturing such crystals. 
BACKGROUND OF THE INVENTION 
Bits for drilling rocks and tip material of dressers for repairing grinding 
wheels have been made of diamond which has the highest hardness of all 
materials. Diamonds used in these tools must be approximately 1 mm or more 
in size. Natural diamond called "boart" is used at present since synthetic 
diamonds having such a size have not been manufactured on an industrial 
scale. 
The resistance to wear of a diamond varies to a great extent depending upon 
the orientation of crystals and it is essential in the use of these tools 
to select a proper orientation. On the other hand, natural diamonds are 
scarcely idiomorphic because of their being subjected to dissolution in 
the process of growth. Generally, natural diamonds have been rounded, and 
have a variety of shapes depending upon the degree of dissolution. As a 
result, it requires considerable skill to determine the proper orientation 
of crystals which can serve as tools. 
SUMMARY OF THE INVENTION 
An object of the present invention is to increase the adhesive strength of 
a diamond single crystal to a tool support by providing the crystal with a 
novel surface condition. 
Another object of the present invention is to provide a diamond single 
crystal having a shape suited for tools. 
Another object of the present invention is to provide a rodlike diamond 
single crystal having a sufficient length for use in a tool. 
The artificial diamond single crystal of the present invention is 
characterized in that at least a part of the surface of the crystal has a 
rough surface which was formed by suppressed crystal growth at that 
surface. 
The diamond single crystal of the present invention is formed by the 
following method. 
The disclosed process for manufacturing a diamond single crystal involves a 
diamond reaction system consisting of a carbon source, a solvent metal 
(molten catalyst metal) arranged in contact with said carbon source, and a 
seed crystal. The reaction system is held under elevated pressures and 
temperatures which permit diamond to be maintained in thermodynamically 
stable condition. The reaction chamber housing the reaction system is 
heated to provide a temperature gradient in such a way that the portion of 
the solvent metal in contact with the carbon source is higher in 
temperature than the portion of the solvent metal in contact with the seed 
crystal so as to migrate the carbon from the higher temperature portion to 
the lower temperature portion using the solvent metal as a medium. 
Accordingly, the carbon being precipitated and grown as diamond on the 
seed crystal due to the difference in solubility of carbon caused by said 
temperature gradient. The diamond single crystal of this invention is 
manufactured under the condition of that the crystal growth in at least 
one direction perpendicular to the direction of the temperature gradient 
(i.e., to the longitudinal direction) is suppressed at the end of the 
solvent metal. In the present invention the crystal growth suppression is 
carried out by using a solvent metal having a shape of the cross section 
perpendicular to the direction of the temperature gradient such that the 
crystal growth in the direction of the cross section plane suppressed at 
the solvent metal surface (the outer surface) due to insufficient size of 
the solvent metal in this direction.

DETAILED DESCRIPTION OF THE INVENTION 
Generally, a natural diamond has a diameter almost equal to its length as 
shown in FIG. 14, with its entire configuration close to that of a sphere. 
In addition, the surfaces are smooth, and the edges which serve as knives 
when used in tools are rounded because it has been subjected to 
dissolution in the process of growth as described hereinabove. For this 
reason, when a natural diamond is used in a dresser a particular type of 
diamond tools nearly half of it is embedded in the cementing material on 
its support as shown in FIG. 15, so that the usable portion becomes very 
small (only the tip portion p in FIG. 15 can be used). Furthermore, since 
the surfaces are smooth as described above, the adhering strength to the 
cementing material is weak. Accordingly, it may fall off during use. In 
FIG. 15, reference numerals 11, 12, and 13 designate a natural diamond, a 
support, and a cementing material, respectively. 
Further, in diamond bits used for drilling, there exists a problem that the 
bits lose their sharpness with progressing wear, resulting in increase of 
weight on bit. In addition, the adhering strength of the diamonds to the 
bit body is weak because only about half of each diamond is embedded in 
the bit body due to its nearly spherical shape, the surfaces are 
comparatively smooth, and because they are mounted to the bit body by 
powder metal method they are apt to fall of during drilling. 
The present invention provides diamond dressers and bits which solve the 
problems encountered with the conventional ones by using the synthetic 
diamonds of the present invention therein. 
The diamond single crystal of the present invention, the process for 
manufacturing them, and the diamond tools using them will be described 
below with reference to the accompanying drawings. 
FIG. 1 shows an arrangement for manufacturing an idiomorphic large diamond 
single crystal by a known process. Components including a diamond seed 
crystal 1, a solvent metal 2, and a carbon source 3 are arranged in layers 
in a cylindrical heater 5 interposing a pressure medium of, for example, 
sodium chloride between the heater and the components. In this case, in 
order to use the temperature gradient naturally formed in the arrangement 
in the axial direction (A--A'), the carbon source is arranged at the 
portion of the higher temperature, generally, at the central portion (in 
the direction of the axis A--A') and the seed crystal at the portion of 
the lower temperature in this arrangement, generally, at the portion apart 
from the center. These are arranged in a pressure medium cylinder made of, 
for example, pyrophylite, etc., which is housed in a superhigh pressure 
and temperature device. After being pressurized up to a predetermined 
pressure, they are heated by the heater 5. 
Then a temperature difference occurs between the carbon source and the seed 
crystal due to heat conduction at ends of the arrangement, causing carbon 
atoms to be migrated from the carbon source to the seed crystal to become 
a diamond and grow on the seed crystal. The growing diamond 7 continues to 
grow holding the same orientation as that of the face of seed crystal in 
contact with the solvent metal. That is, if the face of seed crystal is 
the face having index of a plan (100), the top face of growing diamond 7 
is (100), and if the face of the seed crystal is (111) the top face is 
(111) (conventional methods are disclosed in, for example, The Journal of 
Physical Chemistry, Vol. 76, No. 12, 1971, pp 1833-1837). 
Usually, in such a known manufacturing process, a solvent metal having a 
diameter larger than that of the growing diamond is used, so that an 
idiomorphic diamond having smooth surfaces may be obtained. This invention 
has been derived from the finding that, if the diameter of solvent metal 
is limited to less than the size of the idiomorphic diamond crystal which 
could be obtained at those conditions, i.e., the pressure, temperature and 
the carbon concentration in the metal, the diamond obtained has the same 
outside profile as that of the solvent metal, and has outer surfaces 
presenting a novel and industrially useful surface condition. In other 
words, if the growth of the diamond crystal is suppressed due to the 
insufficient size of the solvent metal in the direction perpendicular to 
the direction of the temperature gradient (the direction of axis A--A') a 
rough surface with irregularities forms at the portion where the crystal 
growth is suppressed. Therefore, to obtain rough surface at least at a 
part of the surface of the diamond it is necessary to make at least a part 
of the diamond crystal grow until the crystal reaches the end portion 
(side surface) of the solvent metal in the direction perpendicular to the 
axis A--A'. Thus the crystal growth is suppressed and a rough surface 
forms at that portion. 
It is difficult to express the irregular state of the rough surface 
quantitatively, but it may be defined optically as an irregular state by 
which light is diffusibly reflected. The surface has a surface texture 
having a macro projection value (by ASTM) of not more than about 0.5 mm, 
usually, not more than 0.1 mm. 
The shape of the diamond single crystal of the present invention is not 
limited to a special shape. The diamond may have a variety of cross 
sections in the direction perpendicular to the axis A--A', such as circle, 
a polygon, such as triangle, tetragon, or special form including 
star-shape, etc. as shown in FIGS. 10 to 13. The polygonal cross section 
may be such that at least one of angles forms a circular arc. It is 
preferable that the length l (in the direction of the axis A--A') is 
longer than the diameter of the cross section D, more preferably 
l.gtoreq.1.5 D. As the diameter D in the cases of FIGS. 11 to 13, the 
diameters for circles converted from the cross section area are used, 
which is referred to as "equivalent diameter" and can be calculated by the 
following equation: 
##EQU1## 
where S=cross-sectional area. 
(Hereinafter "equivalent diameter" refers to both "diameter" and 
"equivalent diameter".) 
For obtaining a diamond crystal having a predetermined shape, for example, 
as shown in FIGS. 10, 11, 12 or 13, solvent metal having the same shape of 
the cross section as that of the aimed, predetermined shape is used. In 
such a case a seed crystal should be put at the center of the cross 
section of the end of the solvent metal where it contacts with the seed 
crystal. 
For forming a diamond crystal having a rough surface only at a part of the 
side surface of the crystal, a solvent metal having a shape such that the 
crystal growth is suppressed only at a part of the side surface of the 
crystal is used, or the seed is placed at a position other than or apart 
from the center. 
Generally, the solvent metal has a rodlike shape as shown in FIGS. 2 and 3. 
The length in the direction of the axis is not limited. In order to 
produce a sufficient concentration of carbon in the metal solvent it is 
preferred to provide a plate of the metal generally in the shape of a 
disk, which has a larger cross sectional area (in the direction 
perpendicular to the axis A--A') than that of the rodlike portion ("leg") 
at the end (top of FIGS.) of the rodlike solvent metal so that it contacts 
with the carbon source. The ratio of the equivalent diameter of the plate 
to the equivalent diameter of the rodlike solvent metal is more than 1, 
preferably from 2 to 5, and the ratio of the equivalent diameter of the 
plate to the thickness of the plate is usually 2 to 7. Since the contact 
area of the solvent metal with the carbon source can be made to be wider 
than that of the end area of the rodlike solvent metal the amount of 
carbon dissolved into the metal from the source is greater than that of 
the solvent metal having no such plate. 
To manufacture diamond of the present invention, it is important to select 
the diameter of solvent metal. That is, a solvent metal having a 
comparatively large equivalent diameter may be used when the diamond 
growing rate is high. However, when the growing rate is low, it is 
necessary to reduce the equivalent diameter depending upon the growing 
rate. 
The use of a solvent metal having an equivalent diameter which is too large 
would cause growth of an idiomorphic diamond with smooth surfaces which 
does not have the same cross-sectional shape as that of the solvent metal, 
and a rodlike crystal can not be obtained. There exists a proper 
equivalent diameter corresponding to a growing rate. 
Usually, when the growing rate exceeds 5 mg/H, the diamond synthesized 
includes a great quantity of solvent metal as impurities, which may cause 
cracks in the diamond attached to the tool support or during operation. 
For this reason, a growing rate not more than 5 mg/H is preferable. 
Experiments have indicated that the equivalent diameter of solvent metal 
to be used in the synthesis should be approximately 4 mm or less. Further 
experiments have indicated that a diameter no more than 3 mm is proper for 
a growing rate of 1 to 3 mg/H, and a diameter no more than 4 mm is 
preferable for a growing rate of more than 3 and up to 5 mg/H. 
The solvent metals used include known materials such as Fe, Ni, Co and 
alloys consisting principally of them. Useful alloy elements include Cr, 
Mn, Al, Ti, Zr, B, etc. 
As the carbon source for the synthesis of diamond (3 in Figs.), known 
sources such as powder of pure graphite, diamond or a mixlture thereof are 
used. 
The conditions for growth of the crystal may be the same as in a 
conventional method. 
The requirements for the synthesis of diamond are that both the seed 
crystal portion and carbon source are under pressures and temperatures 
which permit diamond to be stable and that they are at temperatures at 
which the metal is able to be in a molten state and which is not less than 
the eutectic temperature for the solvent metal and carbon used. Good 
results may be obtained when the temperature difference between the seed 
crystal portion and the carbon source is kept in the range of 10.degree. 
C. to 50.degree. C. 
The heating temperature is usually from about 1300.degree. to 1600.degree. 
C., and preferably 1400.degree. to 1500.degree. C., and the pressure is 
usually from 45 to 65 kb, and preferably 50 to 60 kb. These conditions are 
maintained until the crystal grows to the predetermined shape. The period 
of time for growth is generally about 10 to 100 hours. After the crystal 
growth to the predetermined shape the heating is stopped, the reaction 
system was cooled to about lower than 500.degree. C., and then the 
pressure is released. The crystal is then taken out of the arrangement. 
The position of the seed crystal at the position contacting with the 
solvent metal is optional so long as at least a part of the crystal can 
grow until it reaches the side surface (in FIGS. 2 and 3 parallel to the 
axis A--A') of the solvent metal. Generally, the seed crystal is placed at 
the center of the cross sectional area of the solvent metal at the 
contacting position to obtain a crystal of which all side surfaces have a 
rough surface, in other words, to obtain a crystal of which crystal growth 
is suppressed at all side surface. 
The seed crystal face which contacts with the solvent metal may have a 
plane index of (1,0,0), (1,1,1) or (1,0,1). However, two or more faces of 
a crystal may be contacted with the solvent metal. In this case the top 
face of the crystal is comprised of the same two or more faces to form an 
edge or edges. 
In the present invention the face of the side surface may be controlled by 
selecting the placing position of sides of the seed crystal with respect 
to the mutual relationship with the sides of the cross sectional shape of 
the end of the rodlike solvent metal. 
FIG. 2 shows an embodiment of this invention in which one cylindrical 
diamond single crystal is synthesized. In such a case, a solvent metal 8 
which has been formed to a cylindrical shape is used. FIG. 4 is the top 
plan view of the solvent metal. The diamond forming arrangement is charged 
into a superhigh pressure and temperature device to pressurise up to a 
predetermined pressure and to heat it to a predetermined temperature. The 
high pressure and the high temperature are held for at least a period of 
time until the growing diamond crystal reaches the side surface of the 
solvent metal. That is, the conditions are maintained until the growing 
diamond crystal reaches the contact surface of the solvent metal with the 
pressure medium. A cylindrical (rodlike) diamond as shown in FIG. 10 is 
obtained when the conditions are maintained for a sufficient period of 
time. The side surface of this cylindrical diamond is rough. 
As shown in FIGS. 10, 11, 12 and 13, a rodlike diamond single crystal 
according to this invention is allotromorphic. It may have an optional 
cross section such as a circular, triangular, polygonal, or star-shaped 
cross section. The dotted surfaces 10 in the figures represent the 
irregular condition on surfaces like ground glass. Rodlike diamonds having 
a triangular or tetragonal cross section as shown in FIGS. 11 and 12 may 
be synthesized by the use of solvent metal having a shape as shown in 
FIGS. 5 and 6. The longitudinal sectional views of these shapes are the 
same as FIG. 2. FIG. 3 shows the case where a plurality of rodlike 
diamonds are synthesized at a time. In this case, a solvent metal 9 having 
a form which has a top plan view as shown in FIGS. 7, 8 or 9 is preferably 
used. 
In some cases, the end of the thus obtained crystal does not form a plane 
surface as shown in FIGS. 10a, 11-13, but forms a convex surface as shown 
in FIG. 10b. 
The diamond single crystal of this invention can be synthesized with the 
orientation previously selected toward the longitudinal direction 
(direction of the axis A--A'), so that the necessity for selecting the 
orientation as mentioned above may be eliminated, and the orientation 
suited to tools may be easily determined. In addition, it has an advantage 
that, when attached to a tool support by soldering or sintering, it has an 
adhesive strength higher than that of natural diamond having comparatively 
smooth surfaces because of the larger surface area of the diamond of the 
present invention due to a surface having irregularities like ground glass 
so that the chances of the diamonds falling off of the tool support during 
use are greatly reduced. 
Diamond dressers according to this invention are formed as shown, for 
example, in FIGS. 16 and 17, by joining an artificial rodlike diamond 14 
to a support 12 using a cementing material 13. In joining, an artificial 
rodlike diamond or diamonds 14 are embedded in a recess 15 provided at the 
end of the support 12 together with a cementing material 13 such as 
soldering material, powder sintering material, etc., and joined to the 
support 12 by heating to 800.degree. to 1000.degree. C. FIG. 16 shows a 
dresser using a single diamond, and FIG. 17 a dresser using a plurality of 
diamonds. 
As shown in FIG. 18 a diamond bit according to this invention comprises 
rodlike synthetic diamonds 14 plated in a ring-shaped sintered matrix 16 
being attached to a bit body 17, and joined to the bit body 17 through 
heat treatment using a soldering material or metal powder. To increase 
further the adhering strength, the surfaces of said diamonds 14 may be 
plated with titanium, nickel, etc. 
In the dressers and bits according to this invention as mentioned above, 
the diamonds have a sufficient length preferably such that l.gtoreq.1.5 D, 
and, in the case of polygonal diamonds, have long edges over the length, 
which permits the diamonds to be used to the last extremity resulting in a 
reduction in costs. 
In addition, since rodlike synthetic diamonds planted project from the tool 
body, the edges forming knives are always held in a sharp condition even 
when the wear has progressed to such an extent that only a short portion 
of the diamonds project beyond the tool body, so that the sharpness of 
tool will not be reduced. 
Furthermore, since diamonds of this invention can be embedded deep enough 
in tools because of their large length, and since they have an increased 
adhering strength because of their large surface area due to irregular 
faces, they are much less likely to fall off the support during use. In 
addition, metal plating treatment may be easily applied to them because of 
their rough surfaces. Further, since the orientation of synthetic diamonds 
is determined at the time of synthesis, it requires no skill to determine 
the orientation, and it is possible to easily find the orientation in 
which superior resistance to wear is ensured. 
The present invention may be more fully understood from the following 
examples. However, the scope of the invention is not limited to these 
examples. 
EXAMPLE 1 
The diamond forming arrangement as shown in FIG. 2 was used. The seed 
crystal 1 was a synthetic diamond of 30/40 mesh. As the face in contact 
with the solvent metal, the face (100) was selected. The solvent metal 8 
was an alloy of 58Fe--42Ni which was worked to a shape having a circular 
leg as shown in FIG. 4. The leg was 2 mm in diameter and 4 mm long, and 
the top disk was 7 mm in diameter and 1 mm thick. The carbon source 3 was 
a mixture of 160 mg of graphite powder for spectrochemical analysis and 
240 mg of synthetic diamond powder of 325/400 mesh pressed to a disk 7 mm 
in diameter and 4 mm thick, which was placed on said top disk. These were 
arranged in a pressure medium 4 of sodium chloride, and a diamond forming 
arrangement was formed using a cylindrical graphite heater 5 and a 
pyrophylite pressure medium 6. The arrangement was pressurized up to 54 Kb 
at which diamond can remain stable using a superhigh pressure and 
temperature device. The heater 5 was used to hold the temperature at 
1420.degree. C. for 20 hours. Releasing temperature and pressure in this 
order, a cylindrical synthetic diamond 2 mm in diameter and about 3.5 mm 
long was obtained. The diamond weighed about 30 mg, and was an opaque 
crystal having irregular outside peripheral surfaces like ground glass. It 
was found through the identification of the orientation of the crystal 
using the Laue method that the bottom of the cylinder was (100) as with 
the seed crystal. 
EXAMPLE 2 
The solvent metal used was an alloy of Fe-5 Al having a leg with regular 
triangular cross section with 2 mm sides, as shown in FIG. 5. The face of 
the seed crystal selected for contact with the solvent metal was the face 
(111). The arrangement was held under 56 Kb and 1480.degree. C. for 15 
hours. The other conditions were the same as in Example 1. A rodlike 
diamond having a triangular cross section as shown in FIG. 11 was 
obtained. It was about 3 mm long, and weighed about 15 mg, having opaque 
and irregular outer surfaces. It was found by means of the Laue method 
that the bottom of the triangular prism was (111). 
EXAMPLE 3 
The arrangement as shown in FIG. 3 was used. The solvent metal 9 was pure 
Ni. Four square legs each of 2 mm sides and 5.5 mm length were formed, and 
a disk of 7 mm diameter and 1 mm thickness was placed on them as shown in 
FIG. 9. On the bottom of each leg, a diamond of 30/40 mesh was arranged as 
the seed crystal 1. Two of them took the face (100) as the seed crystal 
face, and the others (111). The arrangement was held under 56 Kb and 
1400.degree. C. for 25 hours. The other conditions were the same as in 
Example 1. Four rodlike diamonds having a square cross section as shown in 
FIG. 12 were obtained. Two of the four were about 5 mm long, and the other 
two about 3.5 mm long. Each of them weighed about 70 mg or about 50 mg. 
The identification of the orientation of crystals indicated that the 
bottom faces of the longer crystals were (100), and those of the shorter 
ones (111). 
EXAMPLE 4 
In the same way as in the Example 2, a rodlike diamond of about 100 mg 
having a triangular cross section was synthesized. The diamond was 
embedded in the recess 15 having a 6 mm diameter provided in a tool 
support 12 having a 10 mm diameter together with silver powder as in FIG. 
16, and soldered to the support by heating to 900.degree. C. to make a 
dresser. When used in dressing a SiC grinding wheel, the dresser could be 
used without losing its sharpness until the portion projecting from the 
tool support had been worn out. 
EXAMPLE 5 
In the same way as in the Example 1, rodlike diamonds having a circular 
cross section were synthesized. Using these, a core bit of 46 mm outside 
diameter was made as shown in FIG. 18. With this core bit, granite having 
a compressive strength of about 1500 kg/mm.sup.2 was drilled at 250 rpm 
and at a drilling speed of 5 cm/min. A bit using natural diamonds 
decreased in drilling speed and wore out when it had drilled a distance of 
20 m, while the bit using the rodlike diamonds of this invention wore out 
when it had drilled a distance of about 28 m, a displaying a performance 
1.4 times that of the former. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.