Note: Descriptions are shown in the official language in which they were submitted.
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TOOL INSERT
BACKGROUND OF THE INVENTION
This invention relates to tool inserts and more particularly to cutting tool
inserts for use in drilling and coring holes in subterranean formations.
A commonly used cutting tool insert for drill bits is one which comprises a
layer of polycrystalline diamond (PCD) bonded to a cemented carbide
substrate. The layer of PCD presents a working face and a cutting edge
around a portion of the periphery of the working surface.
Polycrystalline diamond, also known as a diamond abrasive compact,
comprises a mass of diamond particles containing a substantial amount of
direct diamond-to-diamond bonding. Polycrystalline diamond will generally
have a second phase which contains a diamond catalyst/solvent such as
cobalt, nickel, iron or an alloy containing one or more such metals.
In drilling operations, such a cutting tool insert is subjected to heavy loads
and high temperatures at various stages of its life. In the early stages of
drilling, when the sharp cutting edge of the insert contacts the subterranean
formation, the cutting tool is subjected to large contact pressures. This
results in the possibility of a number'of fracture processes.being activated
such as the initiation of fatigue cracks, high energy impacts, in the normal
direction, resulting in spelling of the PCD layer, and high energy impacts in
the cutting direction, resulting in chipping of the PCD layer.
As the cutting edge of the insert wears, the contact pressure decreases and
is generally too low to cause high energy failures. However, this pressure
can still propagate cracks initiated under high contact pressures, and will
eventually result in spelling-type failures.
CONFIRMATION COPY
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Spalling failures are particularly damaging in that these failures represent a
mechanism for the rapid removal of wear resistant material and
consequently reduce the life of the cutting tool insert. Localised spalling
leads to a localised thinning of the PCD table which in turn gives rise to a
grooving type of wear. This wear phenomenon redistributes the loading on
the wearflat and can result in an increase in the contact pressure. As the
grooving wear continues, the contact pressure will continue to increase,
eventually initiating new spalling type failures from the high contact
pressure areas. In a worst case scenario, this becomes a self sustaining
wear mode that will lead to the premature failure of the cutting tool due to
the rapid removal of the PCD layer by a spalling mechanism..
United States 5,135,061 describes a cutting tool insert for use in rotary
drill
bits of the kind generally described above. The cutting element has a layer
of superhard material such as PCD bonded to a cemented carbide
substrate. The layer of superhard material has a front layer at the cutting
face and a second layer behind the front layer. The front layer comprises a
form of superhard material which is less wear-resistant than the super-hard
material forming the second layer. Generally, a plurality of further layers
are stacked behind the second layer, ti,e further layers being of reducing
wear-resistance as they extend away from the second layer towards the
substrate.
US 6,290,003 discloses a PCD enhanced insert which includes a body
' portion adapted for attachment to ~n earth-boring bit and a top 'portion for
contacting an earthen formafiion. The top portion of the insert is provided
' with two different compositions of polycrystalline diamond. In the primary
surface of the top portion, a tougher or less wear-resistant polycrystalline
diamond layer is provided, whereas a more wear-resistant polycrystalline
diamond layer is provided in the remaining region of the top portion. In
addition to polycrystalline diamond, polycrystalline boron nitride and other
superhard materials may also be used.
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US 6,443,248 describes a cutter element for use in a drill bit, comprising a
substrate and a plurality of layers thereon. The substrate comprises a grip
portion and an extending portion. The layers are applied to the extending
portion such that at least one of the layers is harder than at least one of
the
layers above it. The layers can include.one or more layers of polycrystalline
diamond and can include a layer in which the composition of the material
changes with distance from the substrate.
SUMMARY OF THE INVENTION
According to the present invention, a tool insert comprises a working layer
of ultra-hard abrasive, particularly PGD, bonded to a substrate along an
interface, the working layer presenting a working surface and a periphery
around the working surface which provides a cufiting edge for the insert, the
working layer of ultra-hard abrasive having a first region extending into the
working layer from the working surface, and a second region in contact with
the first region, the wear resistance of the first region being less than that
of
the second region, wherein the wear resistance of the first region is
between 50°/~ and 95°/~ of that of the second region, preferably
between
60°/~ and 90°/~, most preferably between ~0°/~ and
89°/~.
Generally, the first and second regions will comprise layers, typically
successive layers, extending from the working face into the working layer.
The regions, or at least one of the. regions, may comprise .an' annulus
extending inwards from a periphery of the layer of ultra-hard abrasive. In
some cases, the thickness of the first, thin region may be non-uniform
across the diameter of the cutter; so that the interface between the first and
second regions may be specifically designed for optimal behaviour.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A tool component of the invention comprises a layer of ultra-hard abrasive
that has a first region which is less wear resistant than a second region
thereof. Accordingly, essential to the invention is that the first region
differs
in material characteristics to that of the second region leading to a
controlled and reduced spalling and reduced fatigue in the layer of ultra-
hard abrasive. The first region will generally be relatively thin and extend
to
a depth of about 750 microns, preferably no more than about 500 microns,
and most preferably about 50 to 250 microns, for a wear ratio of between
50% and 95%, from the working surface.
In the tool component of the invention, there is a relationship between the
wear resistances of the two regions to achieve a minimising of the failure
problems of prior art tool inserfis described above. The first region
preferably has a wear resistance of between 50°/~ and 95°/~,
more
preferably between 60% and 90°/~, and most preferably between
70°/~ and
89% of the wear resistance of the second region. An example of such a
tool component, in one embodiment of the invention, is one in which the
first region comprises a composite structure of two or more materials. The
materials may be uniformly distributed fihroughout the region or randomly
distributed. For example, the one material may be the same material as
that of the second region and this will be combined with another material
which provides that first region with a wear resistance lower than that of the
second region.. ' - ' -
This type of arrangement can also be obtained in a number of other ways.
For instance, the tool component in a further embodiment of the invention
can be designed such that the first and second regions are both regions of
PCD and contain catalyst/solvent, the amount of catalyst/solvent in the first
region being higher than that in the second region. Alternatively, the tool
component in yet a further embodiment of the invention can be designed
such that the first region has ultra-hard abrasive particles of a unimodal
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particle size distribution only, and the second region has ultra-hard abrasive
particles which have a multimodal particle size distribution.
In both these cases, it is preferable that the average grain or particle sizes
in the two regions are similar. In other words, the range of particle sizes in
the second region will not differ materially from the range of particle sizes
of
the ultra-hard abrasive in the first region.
In a further alternative embodiment of the invention, the tool component is
one in which both the first and second regions comprise ultra-hard abrasive
particles of more than one particle size, the size distribution of the
particles
in the first region being coarser than that of the second region. In such a
case, the ultra-hard abrasive in the first region is preferably made from a
mass which comprises at least 25°/~ by mass particles having an average
particle size in the range 10 to 100 microns and consisting of particles
having three different average particle sizes and at least 4% by mass of the
particles having an average particle size of less than 10 microns. Further,
the ultra-hard abrasive in the second region preferably is made from a
mass of particles which has an average particle size of less than 20
microns and consists of particles having at least three different average
particle sizes.
In another embodiment of the invention, the ultra-hard abrasive is PCD and
the thermal stability of the PCD in the first region is less than fihat of the
PCD in the second' region. A metal or other material which has .thermal
expansion properties significantly different to that of PCD may be provided
in the first region. Also, the first region may have a second phase which
includes in it a metal such as iron or manganese which can react with the
diamond under high temperature.
In a further embodiment of the invention, the ultra-hard abrasive is PCD
and sinter quality of the PCD in the first region is compromised by the
introduction of a material such as a sintering agent in small quantities,
which is not introduced into the second region. The compromising material
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will generally not be present in quantities sufficient for the mechanical or
thermal properties of the material itself to affect the properties of the
first
region. The role of the compromising material is to influence the diamond
sintering process during synthesis. This may be achieved in one of two
ways. First, the material may act as an inhibitor/poison where the agent
interferes with the sintering. Second, the material may be more catalytic,
for example where the presence of the material encourages sintering, but
at a too rapid rate, producing a less well-sintered structure. Further
examples of compromising the quality. of the PCD is by treatment of the
diamond particle surface or the introduction of additional carbon material
into the first region.
In another embodiment of the invention, where both the first and second
regi~ns are regions of PCD containing a catalyst/solvent in a second
phase, the catalyst/solvent in the first region is cobalt with another
transition
metal such as nickel, or the other transition metal; and the catalyst/solvent
in the second region is essentially cobalt. The nickel will tend to increase
the thermal stability of the PCD in the first region. However, the sintering
action of the nickel is less effective than another transition metal such as
cobalt. Thus, the presence of nickel in the PCD in the first region, where
the ~ther catalysfi/solvent is cobalt, will have the effect of reducing the
overall strength of the sintered PCD in the first region and hence rendering
it less wear resistant.
The invention will now be described in more detail, by way of example ~nly,
with reference to the following non-limiting examples.
Example 1
A number of tool inserts as generally described above (A1, B1 and C1)
were manufactured with respective first PCD abrasive regions or top layers
each 150pm in depth from their respective working surface. The respective
top layers of the tool inserts had different wear resistances relative to
their
respective second regions of PCD abrasive as follows:
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i) A1 - 0.94 (94%) wear resistance ratio;
ii) B1 - 0.91 (91 %) wear resistance ratio; and
iii) C1 - 0.88 (88%) wear resistance ratio.
These were then tested in a vertical borer test against a base PCD product
X1, and the results of these tests are depicted schematically in Figure 1 of
the accompanying drawings. In a vertical borer test, the wearflat area is
measured as a function of the number of passes (or the total distance
bored) of the cutter element boring into the workpiece, which in this case
was SW granite. It will be noted that the wear behaviour improved as the
wear ratio moved away from 1 at the 150pm depth for the respective top
layers. Referring to the base PCD product X1, the "deviations" from the
curve are due to instances of spelling behaviour.
In the vertical borer test, dafia was collected in the range of 0 -100 passes.
Example 2
A number of tool inserts (A2, B2, C2 and D2) were manufactured with a
wear ratio of the respective first regions or top layers to the respective
second regions or top layers of 0.91 (91 °/~). The respective tool
inserts had
different depths of the top layers from their working surfaces as follows:
i) A2 - 750Nm'depth of first region;
ii) B2 - 500pm depth of first region;
iii) C2 - 250pm depth of first region; and
iv) D2 - 150pm depth of first region.
These were again tested in a vertical borer test against a base PCD
product X2, and the results of these tests are depicted schematically in
Figure 2 of the accompanying drawings. It will be noted that at a wear ratio
of 0.91, wear behaviour improved as the top layer become thinner.
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In the vertical borer test, data was collected in the range of 0 -100 passes.
From the above Examples, the following observations can be made.
As the thickness of the top layer is increased, spalling behaviour will be
reduced, but this can be at the cost of cutting efficiency. At the extreme,
the wear resistance of the top layer will dominate the overall wear
resistance of the cutter. Hence a thinner top layer is desirable for achieving
most benefit from the more wear resistant underlying PCD. Where the
wear ratio is close to 1, thinner layers will not yield the desired stress-
reducing behaviours because of inadequate "rounding" of this layer.
Maximum cutting efficiency will be achieved by optimising the thickness of
the top layer and the wear ratio between the top layer and the underlying
PCD. The top layer must be thick enough to reduce contact pressures on
the cutting edge, but still thin enough that it does nofi negatively impact on
the overall wear resistance of the cutter. The closer that the wear ratio is
t~
1, the less efficient this optimisation will be. In the case of lower wear
ratios, the top layer will yield the required reduction in spalling behaviour,
in
an appropriate thickness region which still allows optimal cutter
performance.
However, it is believed that this behaviour is not just a function of the
relative wear ratio of the two layers and the top layer thickness, but will
also
be decided by the absolute sfirength of the material. Where this approach
is' applied to PCD material 'of lower strength, which is therefore less prone
to spalling type failure, maximum benefit is unlikely t~ be realised.
The invention has particular application to tool inserts wherein the ultra-
hard abrasive is PCD and, more particularly, to such inserts which are
intended to be used as cutting inserts for drill bits in the drilling or
coring of
drill holes or the like in subterranean formations.
