Superhard cutting element utilizing tough reinforcement posts

This invention relates to superhard cutting elements. Specifically, this invention relates to polycrystalline diamond and cubic boron nitride cutting elements produced by means of high pressure and high temperature. The cutting element of this invention features cylindrical reinforcement posts to toughen the cutting surface in the same fashion that rebar strengthens concrete. This invention also discloses an economical means of producing the substrate of the present invention.

CROSS-REFERENCES TO RELATED APPLICATIONS NONE 
BACKGROUND OF THE INVENTION 
This invention relates to superhard cutting elements useful in rock 
drilling and machining wear resistant materials. Specifically, this 
invention relates polycrystaline diamond and cubic boron nitride cutting 
elements produced by means of high pressure and high temperature. Although 
these two super materials have divergent properties, it is not uncommon in 
the literature to speak in terms of one or both when addressing common 
issues. Since the issues raised in this application apply generally to 
both materials, the application will speak in terms of a superhard 
material. Those skilled in the art will readily understand the utility of 
this invention as it applies to both supermaterials. 
Superhard cutting elements are now so widely accepted in the drilling and 
tooling industries that they have become the standard and preferred tool 
for difficult applications. But these tools are not without limitations. 
Superhard materials have high hardness and abrasion resistance, but 
generally speaking, standing alone, they lack the toughness required by 
most difficult drilling and cutting jobs. By mounting the superhard 
material on a tough substrate, such as tungsten carbide, a certain amount 
of synergism is achieved; the superhard cutting element acquires the 
toughness of the substrate to go along with the hardness and abrasion 
resistance of the superhard material, itself. 
In the art, varied attempts have been made to improve the utility of 
superhard cutting elements. These efforts have largely centered on 
improving the bond between the substrate and the superhard material. An 
example of this issue is addressed but not fully taught in U.S. Pat. No. 
5,460,233. The problem ostensibly addressed in that patent was to provide 
a means of protecting the cutting table of a rock drilling element from 
damage as the cutting element first contacted formation being drilled. 
That is to say, as the bit was lowered into the hole and impacted the 
formation to be drilled, there was a tendency for the superhard surface of 
the cutting elements to fracture and delaminate. The applicants discovered 
that by contouring the substrate away from the superhard cutting surface, 
they were able to sufficiently protect the superhard materials long enough 
for it to wear into a safe mode. The published data showed that the 
substrate thus configured could withstand more than double the WOB of 
conventional cutting elements. What the disclosure failed to find was a 
means of actually imparting the toughness of the substrate into the 
superhard cutting table itself. 
Therefore, it would be useful to provide a means for reinforcing the 
superhard cutting surface and give it the toughness inherent in the 
tungsten carbide substrate, while at the same time providing an inherently 
tougher superhard cutting surface. 
SUMMARY OF THE INVENTION 
It is an object of this invention to impart the toughness of the substrate 
into the superhard surface of the cutting element. This is achieved by 
providing reinforcing posts that project from the substrate into the 
superhard surface, lending it the toughness of the substrate, much like 
rebar strengthens concrete. 
It is another object of this invention to provide a simpler and more 
economical means of producing the posts. 
It is another object of this invention to provide a substrate configuration 
that reduces stress concentrations, and at the same time facilitates 
mounting the superhard material on the substrate prior to processing at 
high pressure and high temperature.

DETAILED DESCRIPTION 
Although not as hard and abrasion resistant, the tungsten carbide substrate 
is actually tougher than the superhard cutting surface it supports. The 
diverse properties between the substrate and the superhard cutting surface 
are well documented in the art, and many attempts have been made to lessen 
the effects of those differences when the two are bonded together. These 
effects and differences are well taught in U.S. Pat. Nos. 5,662,720 and 
5,564,511 and are incorporated herein by this reference. While the present 
invention acknowledges the teachings of the prior art, it departs from the 
commonly held conclusion that internal stresses may only be diffused by a 
substrate that "does not ejaculate in any cross-section to cause abrupt 
angular changes." The present invention discloses an equally effective, 
less complex, and more economical solution for reinforcing the superhard 
cutting surface. 
The first aspect of the present invention is to impart to the superhard 
cutting surface the toughness of the substrate. This is achieved by 
providing tungsten carbide posts that project into the cutting surface 
from the substrate. These posts impart toughness to the superhard surface 
much like rebar adds toughness to concrete. Although the configuration of 
the reinforcement posts of the present invention departs from the 
teachings of the cited patents, the applicant has surprisingly discovered 
that the impact toughness of a cutting element having the posts doubled 
over prior art elements having a planar interface. Also, the elements of 
the present invention did not manifest the spalling and delamination of 
the superhard cutting surface as predicted in the prior art. It appears to 
the applicant that the posts of the present invention lend sufficient 
toughness to the superhard material to overcome whatever stresses build up 
due to the different properties in the superhard material and the 
substrate. 
FIG. 1 is a perspective illustration of a preferred embodiment of a 
substrate of this invention. The posts are arrayed across the surface of 
the substrate in either a regular or random pattern. They should be tall 
enough to impart strength to the superhard material, but not so tall as to 
protrude above the cutting surface. In thin layer applications, the height 
of these posts could be a little as 0.1 mm. In thick layer applications of 
over 1.5 mm, the height should be at least 0.5 mm. It is critical to this 
application that the posts extend at least one third of the way into the 
superhard material of the cutting surface. For example, in the tests 
conducted by the applicant, the posts projected 1 mm into a superhard 
cutting surface approximately 2.5 mm 
FIG. 2 is a frontal view of the substrate of the present invention. The 
nominal surface (6) of the substrate is depicted as being convex, and the 
posts (5) are depicted at right angels to the convex surface. The convex 
surface acts to increase the surface area of attachment as well as to 
evenly redistribute interfacial stresses known to exist between the 
substrate and the superhard material. The heights of the posts may vary 
according to the application of the cutting element. For example, the 
peripheral posts could be taller while the interior posts may be shorter. 
The posts may be removed from the outer periphery or they may actually be 
sectioned by the periphery so that their pattern is visible on the outside 
of the cutting element. 
FIG. 3 is a perspective view of the cutting element of the present 
invention depicting a cutaway view of the superhard cutting surface (3) 
and the reinforcement posts (4). The posts (4) extend at least a third of 
the way into the superhard material Another aspect of this invention is 
that the substrate is less complex and more economical to manufacture. The 
posts of the present invention are preformed into the substrate by means 
of a negative impression mold. Because the posts stand apart and are 
essentially cylinders with rounded tops, they can be machined into the 
mold using conventional milling techniques. This allows for more 
economical production and maintenance of the molds. It also facilitates 
varying the post patterns depending upon the specific application of the 
cutting element. Whereas it may be very expensive to alter the complex 
patterns disclosed in the prior art, the design of the present invention 
can be altered inexpensively using standard milling equipment. 
Another feature of the less complex pattern disclosed herein is that it 
also facilitates the mounting of the superhard material onto the substrate 
prior to processing at high pressure and high temperature. In mounting the 
superhard material, it is important to pre-compact the layers of superhard 
material in order to achieve sufficient pre-processing density and 
eliminate voids in the mass. The more complex the surface onto which the 
superhard material is mounted, the more difficult it is to sufficiently 
pre-compact the material. Low density and voids in the mass contribute to 
excessive shrinkage and low internal pressures and prevent superhard grain 
intergrowth, which leads to catastrophic failure of the element. The 
complex interfacial patterns also make it more difficult to manufacture 
and mount pre-formed layers of superhard material.