Method of brazing of diamond to substrate

A method of making a diamond cutting and abrading tool. The method includes the following steps: PA0 (A) Mixing molybdenum with a braze which alloys with the carbide forming substance and a temporary binder to provide a coating material; PA0 (B) Applying said coating material to a tool substrate; PA0 (C) Applying at least a monolayer of diamond particles thereover; and PA0 (D) Heating the product of step (C) at a temperature sufficient to initially form a metal carbide coating on the diamond and thereafter to braze the carbide coated diamond to the tool substrate.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to diamond tools. More particularly, the 
present invention relates to a method of brazing diamond abrasive 
particles to a substrate to make a monolayer diamond abrasive or cutting 
tool. The present invention facilitates control of the strength with which 
abrasive particles are held by the bonding agent. 
There are various methods of making diamond abrasive or cutting tools. The 
present invention is concerned with monolayer diamond abrasive tools which 
are tools having only a single layer of diamond abrasive particles on the 
tool substrate. Monolayer diamond abrasive tools encounter difficulties in 
regard to attaching the individual diamond abrasive particles to the tool 
substrate or core. This is especially the case where a brazing or 
soldering technique is employed. 
A variety of bonding methods have heretofore been used for bonding diamond 
or other carbon containing abrasives by brazing or soldering. At the 
present time, known brazing alloys for diamond abrasive materials include 
alloys based on copper, silver or gold doped with additives of iron, 
cobalt and nickel taken either separately or in combination with one 
another. 
Also known are brazing alloys such as, copper-titanium, silver titanium, 
gold titanium, tin titanium, lead-titanium, copper-molybdenum, copper 
zirconium, copper vanadium, gold-tantalum, gold-niobium, 
copper-silver-titanium, copper-gold titanium, bronze-titanium and 
copper-tin-titanium. The content of Ti, Mo, Zr and V in such alloys 
generally amounts up to 10 weight percent, see for examples, "Wetting and 
Interaction of Metal Melts with Surface of Diamond and Graphite", Yu. V. 
Naidich and G. A. Kolesuichenko, "Naukova dumku" Publishers, Kiev 1967 (in 
Russian). 
Another brazing alloy known for use with diamond is essentially an alloy of 
gold with 1-25 weight percent of tantalum, U.S. Pat. No. 3,192,620. This 
alloy, however, has a high liquid-phase point (above 1050.degree. C.) and 
therefore is restricted but to a narrow field of application, since at 
1050.degree. C. and over diamond is liable to vigorously pass into a 
hexagonal form of carbon which adversely affects the strength of the 
abrasive. 
Another diamond brazing alloy now in common use, consists of 75 weight 
percent copper and 25 weight percent of titanium. 
A disadvantage of this alloy is that it is brittle and its thermal 
expansion factor differs substantially from that of the diamond. These 
properties lead to thermal stresses in finished products which, in turn, 
lead to rapid failure in the course of operation and consequently, high 
and premature wear of the tool made of such abrasives. 
All of the brazing alloys described above are used also for metallization 
of abrasives made of diamond, cubic boron nitride, corundum, etc. Apart 
from the alloys discussed above, there are also known some alloys and 
single metals for surface metallization of abrasive, Viz., diamond, cubic 
boron nitride, silicon carbide, and tungsten carbide, the metallization 
being either single or multiple-layer. For establishing the initial layer, 
use is made of nickel, copper, zinc, tin, gold, lead or their alloys; if a 
second layer is desired, iron-nickel alloy is used or the like. For the 
third layer, copper or bronze is commonly used. 
The coated crystals are then used to make polycrystalline diamond compacts 
as are commonly used in sintered metal bonded abrasive and cutting tools. 
It is known in the art to metallize diamond and abrasives using alloys of 
silver-gold-titanium-cobalt-tantalum, copper-tin-tungsten and/or 
molybdenum-tantalum-nickel and/or cobalt-lead and/or bismuth-titanium 
and/or zirconium. Alloys used for brazing feature the use of an alloy of 
copper-tin-tungsten, molybdenum-tantalum-titanium and/or zirconium-cobalt 
and/or nickel-lead and/or bismuth, see for example, U.S. Pat. No. 
4,009,027). 
Yet another known brazing alloy contains nickel and/or 
cobalt-chromium-boron and/or silicon and/or phosphorous, see for example, 
U.S. Pat. No. 4,018,576). Chromium is claimed to wet the surface of the 
diamond causing tenacious adhesion of the diamond to the braze. 
One common disadvantage of the above methods is that they are limited in 
the scope of their ability to vary the strength with which the braze bonds 
to the diamond. Another disadvantage of some methods is their use of 
costly precious metals and vacuums of 10.sup.-5 torr. Even the use of 
metals such as copper is not economical as they cannot be processed 
without the use of a high vacuum or expensive dry hydrogen furnaces so as 
not to form hydrides of the active metals. 
Furthermore, most processes in the art heretofore required that two 
separate costly operations be performed; first coating the abrasive by 
metallizing or the like and then applying a braze in an additional 
operation. 
There remains a need, however, for an improved low cost practical method of 
brazing a monolayer of diamond particles to a tool substrate. In 
accordance with the present invention, an improved method of forming a 
brazed monolayer of diamond particles is provided which is simpler and 
more effective than these prior methods. In the present invention, a 
carbide forming substance including a carbide forming element is mixed 
with a braze material in a temporary binder. This coating is coated onto 
the tool substance and a layer of diamonds is applied thereover. The 
resultant tool is heated to an effective temperature for allowing the 
carbide forming substance to form an initial element carbide layer on the 
surface of the diamond after which the braze may readily attach to the 
carbide layer to securely hold the diamond to the tool substrate. The 
method of the present invention also has the advantage that the carbide 
and braze layers tend to climb up the side of the diamond particle as the 
heating step progresses, thereby allowing for increased strength in the 
final brazed tool. Additionally, the bond strength can be varied by 
varying the amount of carbide forming material used in the initial mixture 
utilized and the processing time which controls the climb of the carbide 
formation in the present invention. 
Additional benefits and advantages of the present invention will become 
apparent from the subsequent description and the appended claims taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE INVENTION 
Generally speaking, the present invention involves the steps of: (A) Mixing 
a carbide forming substance containing an element capable of forming a 
carbide, a braze which alloys with the carbide forming substance and a 
temporary binder to provide a coating material; 
(B) Applying said coating material to a substrate; 
(C) Applying at least a monolayer of diamond particles thereover; and 
(D) Heating the product of step (C) at a temperature sufficient to 
initially form a an element carbide coating on the diamond and thereafter 
to braze the carbide coated diamond to the substrate. 
Referring to the drawings, in accordance with the first step of the present 
invention, a mixture of a carbide forming substance 10, a brazing material 
12 and a temporary binder 18 is prepared and thereafter applied to a tool 
substrate 16. 
The carbide forming substance preferably includes a metal which will form a 
metal carbide layer on the diamond particles during the heating step. 
Suitable carbide forming metals are well known in the art and include, for 
example, iron, molybdenum, chromium, tantalum, titanium, zirconium, 
tungsten, niobium, vanadium, maganese, germanium and silicon, and mixtures 
thereof. It will be appreciated that such carbide forming metals can be 
used in the form of their carbide forming compounds such as molybdenum 
silicide or tungsten carbide, the free metal of which can form carbides. 
Iron and molybdenum are preferred metals and may be used singly or in 
combination. In the preferred embodiment from about 2 to about 30% of the 
carbide forming substance is mixed with 20% to 80% braze. 
The temporary binder selected must be temporary in that it is easily driven 
off in the heating step but allows temporary suspension of the carbide 
forming substance component and the brazing material component of the 
coating. It is preferable that the binder is somewhat viscous such that 
the above components may be easily suspended. It is also preferable that 
the binder utilized will be somewhat tacky such that the diamond particles 
are retained on the tool surface coated with the above mixture. A 
preferred binder is a urethane based adhesive, such as a Wall Colmonoy "S" 
type binder. Other suitable binders include acrylic resins, 
methylmethacrylate resins, lacquers paints and the like. The binder used 
also must be relatively inert in that it must not adversely affect the 
components in the final heating step. 
The braze material selected is chosen to be compatible with the particular 
carbide forming metal utilized in the carbide forming substance, i.e. to 
alloy with the carbide forming metal. Suitable brazes include nickel, 
silver, gold or copper based brazes. Suitable brazes are commercially 
available, for example, from Wall Colmonoy Corporation of Detroit, Mich. 
under the Nicrobraz.RTM. line. 
In accordance with the second step of the present invention, the mixture of 
carbide forming substance, braze material and binder is coated onto the 
desired surface of tool substrate 16 in a somewhat uniform layer. This may 
be accomplished by brushing, spraying or dipping of the surface of the 
tool 16 in the mixture. While this layer is still tacky, a monolayer of 
diamond particles 14 is applied to the tacky layer. The diamond particles 
14 may be applied either singly by hand application or could be applied by 
sprinkling of diamond particles onto the tool. 
According to the fourth step of the present invention, the "green" tool, as 
shown in FIG. 1, with the layer of the coating mixture and diamond 
material is heated at an effective temperature to allow formation of an 
initial metal carbide layer 10a which is chemically bonded to the diamond 
surface. This ensures that the braze has a compatible metal carbide 
surface coating on which to attach to the diamond. In the preferred 
embodiment the heating step is accomplished in a vacuum of about 10.sup.-4 
torr. However, the method of the present invention may be practiced in 
hydrogen containing atmospheres or in substantially reducing atmospheres 
with good results. 
While not wishing to be bound by any particular theory, it is believed that 
initially the diamond is in contact with at least some of the metal 
carbide forming particles or comes into contact with carbide forming 
metals during flow of the molten braze solution which includes the carbide 
forming metals in the molton solution. Upon heating to an effective 
temperature, a metal carbide layer 10a begins to form on the diamond from 
the carbide forming metal immediately adjacent the graphitized diamond 
surface. Thereafter, the molten braze 12a has an appropriate place to 
attach to the diamond. 
The reaction taking place in the present invention proceeds in a 
quasi-capillary manner up along the side of the diamond to allow the final 
braze material to progress up the diamond surface to a desired level or 
even to entirely cover the diamond with a braze layer if desired. It is 
believed that this phenomenon occurs by the initial formation of the 
carbide layer after which the braze attaches allowing more of the carbide 
forming substance to come into contact and chemically bond to the diamond 
surface forming another suitable location for brazing to attach. In this 
manner the brazing metal is drawn up the side of the diamond particles in 
a quasi-capillary manner to the desired level. The height of the braze 
layer may be controlled by varying the time of the heating step. 
Thus, during the heating step, the diamond can be heated to a temperature 
sufficient to cause free carbon atoms at the diamond surface and to form 
the desired metal carbide coating from the localized carbide forming 
metal. Formations of the metal carbide facilitates wetting of the diamond 
surface by the braze metal. The time and temperature of the heating step 
is determined by the particular carbide forming metal and braze 
composition chosen for use. Upper limits are determined by excessive 
graphitization or even complete breaking down of the diamond. Lower limits 
are functionally determined in that sufficient heating must be maintained 
to form the metal carbides and to melt the braze composition. 
Additionally, time and temperature may be utilized to control the amount 
of coverage of the diamond surface by the braze and the amount of 
filleting which is desired about the diamond particles. 
As stated above, the braze is selected to be compatible, i.e. to alloy with 
the metal carbide on the diamond surface. Thus, good wetting of the 
diamond carbide interface is achieved and a strong braze bond is obtained. 
Further understanding of the present invention will be had from the 
following examples: 
EXAMPLE I 
For the brazing of a peripheral diamond grinding wheel, a steel core of 
6.00" diameter and 0.625" thick was used. The 0.625" surface was coated by 
brushing on a paste consisting of Wall Colmonoy "S" cement and a mixture 
of Wall Colmonoy Nicrobraze.RTM. #10 Fe and Mo in the following weight 
percents: 
______________________________________ 
Nicrobraze #10 86% 
(P = 10%, C = .06% 
BAL. = NI) 
Fe(-325 Mesh, Hydrogen 
3.2% 
Reduced) 
Mo(6-12 Micron) 10.8% 
______________________________________ 
While the paste was still wet, 80/100 mesh diamond was sprinkled onto the 
paste. The coated core was allowed to air dry. The coated core was placed 
in a vacuum furnace that was computer controlled to carefully control the 
heat up and cool down cycle. The core and diamond mixture was heated to 
1745.degree. F. at 10.sup.-4 torr and heated for 45 seconds. The results 
were a diamond wheel suitable for bevel edging CR-39 plastic ophthalmic 
lenses. The diamonds were found to be tenaciously held in the braze with 
about twenty five percent of the diamond exposed. 
EXAMPLE II 
For the brazing of a cup type wheel used to generate the optical curvature 
in an ophthalmic lens, a 31/2" diameter with a 0.125" radius face steel 
core was coated with a paste of Wall Colmonoy "S" cement and a mixture of 
Wall Colmonoy Nicrobraze.RTM. #10 with Fe and Mo in the weight percents as 
follows: 
______________________________________ 
Nicrobraze .RTM. #10 80% 
Fe (Same as in Example I) 10% 
MO (Same as in Example I) 10% 
______________________________________ 
40/45 mesh diamond was sprinkled onto the wheel core as in Example I and 
processed as in Example I except the heating step used was 1730.degree. F. 
at 10.sup.-4 for 45 seconds. The resultant tool was successfully used for 
grinding CR-39 ophthalmic lenses. The diamonds were found to be 
tenaciously held in the braze with about twenty five percent of the 
diamond surface exposed. 
EXAMPLE III 
A router bit core made of steel was coated as in Example I with the 
following braze mixture constituent: 
______________________________________ 
Nicrobraze #130 80% 
(B = 3.1%, Si = 4.5% 
C = .06% BAL. -Ni) 
Fe (Same as in Example I) 10% 
Mo (Same as in Example I) 10% 
______________________________________ 
The coated router bit was furnaced at a temperature of 1900.degree. F. at 
10.sup.-4 torr for 12 seconds. 
The resultant tool was very successful in the grinding of marble. The 
diamonds were tenaciously held in the braze (but to a lesser extent than 
in Examples I and II) with about seventy five percent exposure of the 
diamond surface.