Patent Grant
6892836
This invention relates to a method for forming cutting elements and specifically to a method for forming cutting elements having a non-uniform interface adjacent their cutting layers.
Cutting elements, such as shear cutters for rock bits, for example, typically have a body (or substrate) which has a cutting face. A cutting layer (sometimes referred to as a “cutting table”) is bonded to the cutting face of the body. The body is generally made from cemented tungsten carbide (sometimes referred to simply as “tungsten carbide” or “carbide”), while the cutting layer is made from a polycrystalline ultra hard material, such as polycrystalline diamond (“PCD”) or polycrystalline cubic boron nitride (“PCBN”). Moreover, these cutters may employ transition layers bonded between the substrate and the cutting layer. The transition layers typically have properties which are intermediate between the properties of the substrate and the cutting layer.
To reduce the residual stresses formed on the interface between the substrate and the cutting layer and to enhance the delamination resistance of the cutting layer, irregularities are sometimes incorporated on the cutting face of the substrate, forming a non-uniform interface between the substrate and the cutting layer. When transition layers are incorporated, one or both faces of the transition layers may also be non-uniform.
As used herein, a uniform interface is one that is flat or always curves in the same direction. This can be stated differently as an interface having the first derivative of slope always having the same sign. Thus, for example, a conventional polycrystalline diamond-coated convex insert for a rock bit has a uniform interface since the center of curvature of all portions of the interface is in or through the carbide substrate.
On the other hand, a non-uniform interface is defined as one where the first derivative of slope has changing sign. An example of a non-uniform interface is one that is wavy with alternating peaks and valleys. Other non-uniform interfaces may have dimples, bumps, ridges (straight or curved) or grooves, or other patterns of raised and lowered regions in relief.
There are a few methods currently being used for forming a non-uniform interface between the substrate and the cutting layer, or between a transition layer and the substrate, or between the a transition layer and the cutting layer. One method requires presintering the substrate. Grooves or other irregularities are then milled or EDM-sunk into the cutting face of the presintered substrate. If a transition layer is to be incorporated, the transition layer may be laid in powder form over the grooved cutting face of the substrate. The ultra hard material layer is then laid over the transition layer. The ultra hard material is also typically laid in powder form.
In situations where a non-uniform interface is required between the transition layer and the ultra hard material layer, grooves or other irregularities may be pressed on top of the powder transition layer during a presintering process. The ultra hard material is then applied over the presintered transition layer and the entire assembly consisting of the substrate, transition layer and ultra hard material is sintered in a conventional high temperature, high pressure process.
Other methods of forming non-uniform interfaces commonly require that the grooves are formed on the substrate cutting face during the substrate presintering process. Typically the substrate is formed from a powder tungsten carbide material. Grooves are pressed on a portion of the powder substrate that would form the cutting face while the substrate is being presintered.
As can be seen, the methods currently used for forming a cutting element having non-uniform interfaces between the cutting layer and the substrate, or between the cutting layer and a transition layer, or between the substrate and a transition layer may be labor intensive. As such, there is a need for a simpler method of forming a cutting element having a non-uniform interface.
To form a non-uniform interface between an ultra hard material cutting layer and a substrate, for example, a sheet of material which after the sintering process is the same as the substrate, is embossed on one face for forming the desired non-uniform interface. For illustrative purposes this sheet is referred to herein as the “substrate material sheet.” The substrate material sheet is cut and placed on an end of the substrate. A second sheet ultra hard material is formed and is embossed for forming a non-uniform face complementary to the embossed non-uniform face on the substrate layer. The sheet is cut and the two sheets are mated with each other over the substrate. The entire assembly consisting of the substrate, substrate material sheet and ultra hard material sheet are then sintered together, causing the substrate material sheet to become integral with the substrate, and the ultra hard material sheet to bond to the resulting substrate for forming a non-uniform interface between the resulting substrate and the ultra hard material.
Similarly, a transition layer may be formed from a sheet material which after the sintering process has properties intermediate to that of the substrate and the ultra hard material layer. The transition sheet may be embossed on one face and/or both faces to form a non-uniform interface with the ultra hard material sheet, and/or the substrate material sheet, respectively. A protective coating, such as tungsten, niobium, silicon, or aluminum oxide, may be placed on top of the ultra hard material layer prior to sintering. The coating may also be in sheet form. The coating protects the polycrystalline ultra hard material layer.
Multiple ultra hard material sheets may be used to form separate polycrystalline ultra hard material layers and each sheet may be of the same type of ultra hard material, or may be a different type of ultra hard material such as diamond or cubic boron nitride, or may be of the same type of ultra hard material but have a different ultra hard material particle size. Similarly, one or multiple sheets of a transition material may be employed to form one or more transition layers. These sheets will also be embossed as necessary so that they mate with their adjacent sheets on the substrate.
For illustrative purposes, this invention will be described in terms of a rock bit shear cutter 10 having a cylindrical body 12 (FIG. 1A). However, as it will be apparent to one skilled in the art, the present invention can be used to form other types of cutting elements. The body 12 of a shear cutter is typically made from cemented tungsten carbide. An end face of the body forms a cutting face 14. An ultra hard material layer 16 such as PCD or PCBN is bonded on the cutting face forming a cutting layer or cutting face. A transition layer 18 or multiple transition layers having properties which preferably are intermediate between the substrate and the cutting layer may also be incorporated between the cutting face and the cutting layer (FIG. 1B). A transition layer may for example be a layer of tungsten carbide, PCD or PCBN having varying particle grain sizes or may be formed from a combination these materials.
In a first embodiment, a presintered substrate 20 having an end face 22 is formed from a tungsten carbide material. A sheet material 24 having the properties of the substrate after sintering (referred to herein as the “substrate material sheet”) is embossed so as to form a non-uniform surface on one of its faces 26 (FIG. 3). The face 28 opposite the embossed face remains flat. This substrate material sheet is cut to an appropriate size for mating to the end face 22 of the substrate. This sheet can be cut and embossed simultaneously.
As used herein, embossing refers to forming a surface of the sheet material to have a design in raised relief. The design may be symmetrical or asymmetrical and have almost any desired configuration. Typically, embossing is obtained by pressing or coining with a steel die or the like, although if many repetitive designs are to be used, a die roller may be used. Moreover, as used herein, the term “sheet” should be construed to include beyond its regular meaning a strip, a ribbon and the like as well as a material form that may be as thick as it is wide and/or long. The term should also be construed to include within its meaning any material form comprising a plurality of particles that are bound together. The particles may be loosely or firmly bound together. For example, the particles may be very loosely bound together such that they would prevent one from lifting the “sheet” by itself without the sheet breaking apart. Moreover, the term “sheet” as used herein should not be limited to a material form having flat and/or parallel surfaces. A “sheet” as used herein may, for example, have non-uniform surfaces or even opposite surfaces that are not parallel to each other.
The cut sheet is placed with its flat face on the end face 22 of the presintered substrate 20 (FIG. 4). A sheet 30 of ultra hard material is then cut and embossed on one face 32 forming a non-uniform face complementary to the non-uniform face formed on the substrate material sheet 24 (FIG. 5). The ultra hard material sheet layer is also preferably cut and embossed simultaneously.
The ultra hard material sheet if formed by commingling ultra hard material particles, such a diamond or cubic boron nitride particles, and binder. For example, the sheet may be formed by commingling powderous ultra hard material with a binder such as a wax family binder, e.g., paraffin, polycarbonate, or polyethylene. In a preferred embodiment, a high shear compaction ultra hard material sheet is used. However ultra hard material sheets formed by other methods as for example, tapecasting, doctor blade forming or roll forming can also be used. When a high shear compaction sheet is used, it is preferable that it have rounded particles since layers formed from sheets of high shear compaction ultra hard material having rounded particles have been found to have increased abrasion and impact resistance.
The cut sheet of ultra hard material is placed over the substrate material sheet such that the non-uniform embossed faces 32, 26 of the two layers which are complementary to each other interface with each other. The assembly consisting of the substrate with the two embossed layers is then sintered in a high pressure, high temperature (HPHT) press, forming a cutter with a polycrystalline ultra hard material layer. The sintering process causes the substrate material sheet and the ultra hard material sheet to bond completely to each other and to the substrate body. The bond line between the substrate material sheet and the substrate is non-differentiable or nearly so. In essence, the substrate material sheet becomes integral with the substrate and a non-uniform interface is formed between the polycrystalline ultra hard material layer and the resulting substrate.
It should be noted that the substrate material sheet may be formed by the same methods used to form the ultra hard material sheet. Of course, instead of ultra hard material particles, tungsten carbide particles are commingled with a binder.
In a further embodiment (not shown), instead of placing an ultra hard material embossed sheet over the substrate material sheet, the ultra hard material may be placed in powder form over the non-uniform face of the substrate material sheet and then sintered together using conventional HPHT techniques.
In yet further embodiments, a sheet 34 of transition material having properties after processing intermediate between the tungsten carbide substrate and the ultra hard material layer is also employed (FIG. 6A). The intermediate properties, for example, may include an intermediate coefficient of thermal expansion. As discussed above, the transition material sheet may include tungsten carbide, diamond, cubic boron nitride particles of varying sizes and any combination thereof. The transition material sheet may be formed by the same methods as those used to form the ultra hard material sheet. In other embodiments, the transition material may not have properties after precessing intermediate between the tungsten carbide substrate and the ultra hard material layer. For example, the transition material may be an ultra hard material itself.
The transition material sheet is cut and embossed on one face 36 forming a surface complementary to the embossed face 26 of the substrate material sheet (FIG. 6A). Alternatively, the transition material sheet 34 may be embossed on both faces 36, 38 (FIGS. 6B and 13). In the latter case, the ultra hard material sheet 30 is cut and embossed such that its embossed face 32 is complementary to the upper embossed face 38 of the transition material sheet. The carbide, transition, and ultra hard material sheets are then positioned over the presintered substrate and the entire assembly is sintered together for forming a cutting element having a transition layer interposed between the substrate and the ultra hard material layer. Instead of a single transition material sheet, multiple transition material sheets may be used. Each transition material sheet has faces complementary to the corresponding faces of the other sheets or substrate with which they will interface.
In yet a further alternate embodiment as shown in
The substrate material sheet, the transition material sheet 34, and the ultra hard material sheet 30 may be embossed with raised designs to form various cross-sectional geometries. For example, the embossed non-uniform faces may have a continuous curvature 40 (FIG. 7), or may comprise multiple ridges and grooves or other irregularities 42 (FIG. 8). These ridges or grooves may be annular or linear or even wiggly. Moreover, the embossed transition material sheet may be cut to form a transition layer 34 that is smaller than the ultra hard material layer 30 (
Moreover, instead of one, multiple ultra hard material layers 30 may be formed over the transition layer 34, as shown for example in FIG. 12. The ultra hard material layers may interface with each other with their complementary non-uniform faces 32.
As will be apparent to one skilled in the art, with any of the above referenced embodiments, multiple sheets of embossed ultra hard material may be employed, each forming a separate ultra hard material layer. The ultra hard material layers may contain different grades of ultra hard material or may even be of different types of ultra hard material, as for example, diamond and cubic boron nitride. Different particle sizes of the same ultra hard material may be applied in separate embossed sheets. For example, the cutting element may be formed using two ultra hard material sheets 46, 48, one on top of the other, wherein each sheet contains a different grade of ultra hard material. With this embodiment, a sheet of a first grade diamond material is embossed on one side to form a non-uniform surface 50 (FIG. 10A). The face 52 opposite the embossed face remains flat. The sheet is cut to appropriate size. The flat face is placed on the cutting face 22 of the tungsten carbide substrate. A sheet 46 made from a second grade of ultra grade material is cut to approximate size and embossed, forming a non-uniform face 54 that is complementary to the non-uniform face 50 of the first cut sheet. The second cut sheet is placed over the first sheet such that the complementary non-uniform faces of the two sheets interface with each other. The whole assembly is then sintered in a HPHT process for forming a polycrystalline layer of ultra hard material.
With this embodiment the first grade ultra hard material sheet 48 may be embossed on both of its faces 56, 58 and interface with a substrate material sheet 24 that is positioned on top of the presintered substrate so as to form a non-uniform interface between the resulting substrate and the first ultra hard material layer (FIG. 10B). Alternatively, the ultra hard material sheet 48 may be positioned on top of the transition material sheet 34.
Embossing is used in the present invention to form a non-uniform face on the material sheets by creating a pattern of relief. However, with any of the aforementioned embodiments, the non-uniform faces on the material sheets may be formed by processes other than embossing such as stamping or coining. The embossing or stamping may occur by using a roller which is rolled along the length of the sheet to emboss or stamp the desired non-uniform pattern multiple times along the length of the sheet. To form the desired pattern the roller will have protrusions extending from its surface that are complementary to the pattern. The sheet may then be cut in sections whereby each section comprises a pattern. The section is then placed on the presintered substrate for forming the desired layer. Moreover, the roller may also simultaneously cut the sheet to the desired shape as it embosses it or stamps it so as to form the individual sheet sections containing the desired pattern.
With any of the above described embodiments, crack growth that travels chordwise 60 along the cutting layer is arrested once it grows horizontally through and across the layer in which it is initially formed and reaches a different grade or a different type of layer, as for example, when it reaches point 62 as shown in FIG. 10C.
With all of the above described embodiments, a coating 64 may be applied over the ultra hard material layer 30 to improve the thermal stability and to change the residual stresses in the ultra hard material layer, and to protect the cobalt in the ultra hard material layer from the corrosive environment during drilling (FIG. 11). In one embodiment, a tungsten coating in foil form 66 is placed over the ultra hard material sheet layer prior to sintering. Once the cutting element is sintered, the tungsten foil 66 forms into a tungsten carbide coating.
In other embodiments, instead of a tungsten coating, a tape 68 of niobium or a wafer 70 of silicon is placed over the ultra hard material 30. If niobium is used, the a coating of niobium carbide is formed over the ultra hard material layer after the sintering process is completed. If silicon is used, a coating of silicon carbide is formed after sintering. Alternatively, a powder of aluminum oxide may be placed over the ultra hard material layer to form a coating of aluminum oxide. The thickness of these coatings are preferably between 5 and 10 microns.
This application is a divisional of patent application Ser. No. 09/047,801 filed on Mar. 25, 1998 and issued as U.S. Pat. No. 6,193,001.
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 09047801 | Mar 1998 | US |
| Child | 09735389 | US |
