Patent Application
20080302578
Cutting elements, as for example cutting elements used in rock bits or other cutting tools, typically have a body (i.e., a substrate), which has an interface face. An ultra hard material layer is bonded to the interface surface of the body by a sintering process to form a cutting layer, i.e., the layer of the cutting element that is used for cutting. The substrate is generally made from tungsten carbide-cobalt (sometimes referred to simply as “cemented tungsten carbide,” “tungsten carbide” “or carbide” ). The ultra hard material layer is a polycrystalline ultra hard material, such as polycrystalline diamond (“PCD”), polycrystalline cubic boron nitride (“PCBN”) or thermally stable product (“TSP”) material such as thermally stable polycrystalline diamond.
Cemented tungsten carbide is formed by carbide particles being dispensed in a cobalt matrix, i.e., tungsten carbide particles are cemented together with cobalt. To form the substrate, tungsten carbide particles and cobalt are mixed together and then heated to solidify. To form a cutting element having an ultra hard material layer such as a PCD or PCBN ultra hard material layer, diamond or cubic boron nitride (“CBN”) crystals are placed adjacent the cemented tungsten carbide body in a refractory metal enclosure (e.g., a niobium enclosure) and subjected to a high temperature and high pressures so that inter-crystalline bonding between the diamond or CBN crystals occurs forming a polycrystalline ultra hard material diamond or CBN layer. Generally, a catalyst or binder material is added to the diamond or CBN particles to assist in inter-crystalline bonding. The process of heating under high pressure is known as sintering. Metals such as cobalt, iron, nickel, manganese and alike and alloys of these metals have been used as a catalyst matrix material for the diamond or CBN.
The cemented tungsten carbide may be formed by mixing tungsten carbide particles with cobalt and then heating to form the substrate. In some instances, the substrate may be fully cured. In other instances, the substrate may be not fully cured, i.e., it may be green. In such case, the substrate may fully cure during the sintering process. In other embodiments, the substrate maybe in powder form and may solidify during the sintering process used to sinter the ultra hard material layer.
TSP is typically formed by “leaching” the cobalt from the diamond lattice structure of polycrystalline diamond. This type of TSP material is sometimes referred to as a “thermally enhanced” material. When formed, polycrystalline diamond comprises individual diamond crystals that are interconnected defining a lattice structure. Cobalt particles are often found within interstitial spaces in the diamond lattice structure. Cobalt has a significantly different coefficient of thermal expansion as compared to diamond, and as such, upon heating of the polycrystalline diamond, the cobalt expands, causing cracking to form in the lattice structure, resulting in the deterioration of the polycrystalline diamond layer. By removing, i.e., by leaching, the cobalt from the diamond lattice structure, the polycrystalline diamond layer becomes more heat resistant. In another exemplary embodiment, TSP material is formed by forming polycrystalline diamond with a thermally compatible silicon carbide binder instead of cobalt. “TSP” as used herein refers to either of the aforementioned types of TSP materials.
Prior art interface surfaces on substrates have been formed having a plurality of projecting spaced apart concentric annular bands. Tensile stress regions are formed on the upper surfaces of the bands, whereas compressive stress regions are formed on the valleys between such bands. Consequently, when a crack begins to grow it may grow along the entire annular upper surface of the annular band where it is exposed to compressive stresses, or may grow along the entire annular valley between the projections leading to the early failure of the cutting element. In other prior art cutting element substrate interfaces incorporating spaced apart projections 62, the projections have relative flat upper surfaces or non-planar upper surface due a plurality of shallow depressions as shown in
Common problems that plague cutting elements are chipping, spalling, partial fracturing, cracking and/or exfoliation of the ultra hard material layer. Typically, these problems are caused by cracking on the interface between the ultra hard material layer and the substrate and by the propagation of the crack across the interface surface. These problems result in the early failure of the ultra hard material layer and thus, in a shorter operating life for the cutting element. Accordingly, there is a need for a cutting element having an ultra hard material layer with improved cracking, chipping, fracturing and exfoliating characteristics, and thereby having an enhanced operating life.
In an exemplary embodiment a cutting element is provided including a substrate having a periphery and an interface surface. An ultra hard material layer is formed over the substrate and interfaces with the interface surface. A plurality of spaced apart projections extend from the interface surface. These spaced apart projections are formed inwardly and spaced apart from the periphery and arranged around an annular path. Each projection includes a convex upper surface defining the projection. Each upper surface continuously and smoothly curves in the same direction increasing and then decreasing in height as viewed in cross-section along a plane through a diameter of the substrate. In a further exemplary embodiment, the interface surface includes a first annular section extending to the periphery, a second section extending radially inward and above the first annular section, and a third annular section between the first annular section and the second section. Each of the plurality of spaced apart projections straddles the first annular section and the second annular section and extends across the first, second and third sections. Furthermore, the second section extends to a height level, such that each of the projections extends above such height level, and such that the projections are spaced apart from the periphery.
In yet a further exemplary embodiment, each of the spaced apart projections is wider over the first section than over the second section. In yet another exemplary embodiment, each of the spaced apart projections when viewed in plan view has a first end having a first width opposite a second end having a second width and a third section between the first and second ends having a third width. The second width is narrower than the first width, and the third width is not greater than, or is smaller than, the second width. In a further exemplary embodiment, each of the spaced apart projections has a width as measured along a plane perpendicular to a central longitudinal axis of the substrate, such that the width decreases as the distance of said plane away from said interface surface increases. In another exemplary embodiment, the interface surface further includes a first annular projection formed radially inward from the spaced apart projections, such that the first annular projection is spaced apart from the spaced apart projections. In yet another exemplary embodiment, the interface surface further includes a second annular projection formed radially inward from the first annular projection, such that the second annular projection is spaced apart from the first annular projection. In yet a further exemplary embodiment, the interface surface further includes a central projection formed radially inward from the first annular projection, such that the central projection is spaced apart from the first annular projection.
In one exemplary embodiment, the first annular projection is polygonal in plan view. In a further exemplary embodiment, each of the spaced apart projection upper surfaces defines a parabola when viewed along the plane through a diameter of the substrate. In another exemplary embodiment, each of the spaced apart projections is trapezoidal in plan view. In yet a further exemplary embodiment, each of the spaced apart projections is widens in a radial direction toward the periphery.
In a further exemplary embodiment, a bit is provided incorporating any of the aforementioned exemplary embodiment cutting elements.
In order to improve the cracking, chipping, fracturing and exfoliating characteristics of the cutting elements, Applicants have invented cutting elements having an interface surface between the ultra hard material layer and the substrate having a geometry which improves such characteristics.
In the exemplary embodiments described herein, the interface surface is formed on the substrate which interfaces with the ultra hard material layer. It is to be understood that a negative of such interface surface is formed on the ultra hard material layer interfacing with the substrate.
The term “substrate” as used herein means any substrate over which is formed the ultra hard material layer. For example, a “substrate” as used herein may be a transition layer formed over another substrate. Moreover, the terms “upper,” “lower,” “upward,” and “downward” as used herein are relative terms to denote the relative position between two objects, and not the exact position of such objects. For example, an upper object may be lower than a lower object.
In an exemplary embodiment as shown in
In a further exemplary embodiment, at least one projecting annular band 34 is formed radially inward extending above the second section 24 and spaced apart from the annular riser 26. In a further exemplary embodiment, a second annular band 36 may be formed radially inward from the first annular band, extending above the second section and spaced apart from the first annular band. The annular bands may be polygonal or circular in plan view. In the exemplary embodiment shown in
In an exemplary embodiment, a plurality of spaced apart projections 44 are formed on the interface surface along an annular path straddling the first and second sections 22, 24 and extending across the riser 26, as for example shown in
In another exemplary embodiment shown in
By using spaced apart projections having continuously curving outer surfaces in cross-section and arranged around the interface surface as shown in
In another exemplary embodiment, the interface surface may be formed without the second section 24. In other words, the spaced apart projections 44 and any of the optional annular bands 34, 36 and central projection 38 may all extend from a single surface which may be planar or non-planar and/or non-uniform. Any of the aforementioned exemplary embodiment cutting elements may have sharp cutting edges 50 or beveled cutting edges 52, as for example shown in
Applicant conducted comparative impact tests using cutting elements incorporating two prior art substrate interfaces and the inventive cutting elements incorporating the inventive interface. The first prior art interface design included a plurality of shallow depressions 60 formed across the entire interface as shown in
Three samples each having a cutting layer with the sharp cutting edge and the first prior art interface design were subjected to the five Joule impact test. Of the three samples, sample 1 had a 100% delamination of the cutting layer from the substrate after five impacts. Sample 2 had a 100% delamination of the cutting layer from the substrate after 25 impacts. Sample 3 had a small chip formed on the cutting layer after 25 impacts. Three samples each having a cutting layer with the sharp cutting edge and the second prior art interface design were subjected to the five Joule impact test. Sample 1 had 20% of the cutting layer chip and spall after three impacts. Sample 2 had 45% of the cutting layer chip or spall after 23 impacts. Sample 3 had 3% of the cutting layer chip after 25 impacts. Three samples of the inventive cutting element each having the substrate shown in
Three samples each having a cutting layer with the beveled cutting edge and the first prior art interface design were subjected to the ten Joule impact test. Sample 1 had no damage after 100 impacts. Sample 2 had no damage after 200 impacts. Sample 3 had 100% delamination of the cutting layer from the substrate after 300 impacts. Three samples each having a cutting layer with the beveled cutting edge and the second prior art interface design were subjected to the ten Joule impact test. Sample 1 had no damage after 100 impacts. Sample 2 had no damage after 200 impacts. Sample 3 had half of the cutting layer delaminated after 300 impacts. Three samples of the inventive cutting element each having the substrate shown in
Additional advantages were seen by testing samples of cutting elements having the first and second prior art interfaces and the inventive interface shown in
Also, samples having the first and second prior art interfaces and the inventive interface shown in
where Δω is the shift in the Raman frequency, γ is the Grunesian constant, equaling 1.06, B is the bulk modulus, equaling 442 GPa, and σH is the hydrostatic stress. σH is defined as:
where σ1, σ2, and σ3 are the three orthogonal stresses in an arbitrary coordinate system, the sum of which equals the first stress invariant. In the center of the apex of an insert, it is reasonable to assume equibiaxial conditions σ1=σ2=σB and σ3=0). In which case, the relation between the biaxial stress σB and the peak shift is given by:
The equipment used to collect the Raman spectra employed a near-infrared laser operating at 785 nm, a fiber optic lens/collection system, and a spectrometer incorporating a CCD-array camera. The peak centers are determined by fitting a Gaussian curve to the experimental data using intrinsic fitting software. The Gaussian expression is given by:
where I(x) is the intensity as a function of position, I0 is the maximum intensity, ωC is the peak center, and w is the peak width, i.e., the full width at half maximum intensity. In this analysis, the fitted peak center was used to determine the residual stress. To facilitate accurate estimation of the residual stress, unsintered PCD powder was used to obtain the stress-free reference (1332.5 cm−1).
To assess the comparative residual stresses, the laser probe described above was used to measure the stresses in nine locations along the top PCD surface of cutting elements having the first and second prior art interfaces, and the inventive interface. The measured residual compressive residual stresses were found to be:
Use of the interface of the present invention showed a 12% reduction in residual stress in comparison to use of the first prior art interface, and a 6% reduction in residual stress in comparison to use of the second prior art interface. The results clearly indicated that a substantial reduction in residual stresses was achieved with the use of the inventive interface. The benefit of reduction in residual stress as a general design principle has been well established. For example, PCD cutting elements having lower residual stresses as measured by Raman spectroscopy have proven to have improved overall field performance. Thus it is expected that the reduced residual stress seen with the inventive interface will prove likewise beneficial to performance.
Although the present invention has been described and illustrated with respect to multiple embodiments thereof, it is to be understood that the present invention should not be so limited, since changes and modifications may be made therein which are within the full intended scope of this invention as hereinafter claimed.
