Patent Application
20160230473
This disclosure relates to a rock removal body for a drag bit rock drilling application and a rock removal body for a roller cone bit rock drilling application
Background
Polycrystalline diamond materials (PCD) typically comprise an intergrown network of diamond grains with an interpenetrating metallic network. The network of diamond grains is formed by sintering of diamond powders facilitated by molten metal catalyst/solvent for carbon at elevated pressures and temperatures. The diamond powders may have a monomodal size distribution whereby there is a single maximum in the particle number or mass size distribution, which leads to a monomodal grain size distribution in the diamond network. Alternatively, the diamond powders may have a multimodal size distribution where there are two or more maxima in the particle number or mass size distribution, which leads to a multimodal grain size distribution in the diamond network. Typical pressures used in this process are in the range of around 4 to 7 GPa but higher pressures up to 10 GPa or more are also practically accessible and may be used. The temperatures employed are above the melting point at such pressures of the metals. The metallic network is the result of the molten metal freezing on return to normal room conditions and will inevitably be a high carbon content alloy. In principle, any molten metal solvent for carbon which can enable diamond crystallization at such conditions may be employed. The transition metals of the periodic table and their alloys may be included in such metals.
Conventionally, the predominant custom and practice is to use the binder metal of hard metal substrates caused to infiltrate into a mass of diamond powder, after melting of such binders at the elevated temperature and pressure. This is infiltration of molten metal at the macroscopic scale of the conventional PCD construction, i.e., infiltrating at the scale of millimetres. By far the commonest conventional situation is the use of tungsten carbide, with cobalt metal binders, as the sintered hard metal substrate. This inevitably results in the sintered hard metal substrate being bonded in-situ to the resultant PCD. Successful commercial exploitation of PCD materials to date has been very heavily dominated by such custom and practice.
For the purposes of this disclosure, PCD constructs which use sintered hard metal substrates as a source of the molten metal sintering agent via directional infiltration and the bonding in-situ to that substrate, are referred to as “conventional PCD” constructions or bodies.
Historically, conventional PCD structures comprising PCD material bonded and attached to carbide hard metal substrates are used for material removal elements attached and arranged in housing bodies. General applications where the material to be removed is rock include drill bits for oil well and mining purposes and the like. PCD structures may also find application in, for example, as road planing and building construction where the material to be removed may be considered as synthetic or re-constituted rock-like materials such as asphalt, rock chipping containing asphalt, concrete, brick and the like, including combinations of such. Henceforth, as used herein the term “rock” will be considered to refer to both natural geological rocks and synthetic or re-constituted rock-like materials.
Very important applications such as oil well drilling use two main streams of drilling technology, either in competition with or complementing each other. These are drag bit and roller cone technologies. Both of these technologies exploit conventional PCD structures.1
Such drag drill bit designs have been extensively optimized over many years such that the dominant and convenient custom and practice is to exploit right cylindrical rock removal elements which are brazed into cylindrical recessed pockets such that, on rotation of the drill bit, overlapping of the sweep of the cutters or rock removal elements provides for rock removal across the full face of the drill bit. These highly established and optimized drill bit designs with the attendant brazing technologies for attachment of the cylindrical cutting elements are not lightly or conveniently altered. Thus, desired and improved rock removal elements or cutters are still conveniently restricted to overall right cylindrical shapes and geometries. Moreover, the establishment of the barrel of rock removal elements or cutters being made of hard and wear resistant hard metals, providing appropriate mechanical wear and brazability properties is a generally desired and not a lightly changed aspect of the present drilling paradigm.
Similarly to drag bit designs, roller cone designs are highly optimized and established. These too, therefore, are not lightly and conveniently altered. Thus, it would be advantageous for improved rock removal or rock crushing elements intended for roller cone bits to have shapes and geometries with a right cylindrical barrel made from easily brazable hard metal materials, whereby one end of the generally cylindrical shape forms a convex surface such as a dome, a rounded cone or a chisel shape involving edges.
Conventional PCD rock removal elements, be they intended for drag bit or roller cone bits, have been restricted to relatively thin layers of PCD material (typically from 1 to about 2.5 mm and rarely up to about 4 mm) formed attached to typically one side of large, substantially cylindrical hard metal substrates in the same high pressure high temperature processes. The required metal for the partial re-crystallisation and sintering of the diamond particles leading to the inter-grown polycrystalline diamond grains is predominantly derived from and infiltrated from the hard metal substrates. The long range infiltration of the required metal necessary for PCD layers between 2.5 and 4 mm progressively contributes to difficulties of producing well sintered diamond grains.
The dominant life limiting mechanism for conventional PCD rock removal elements or bodies involves crack propagation in the PCD body which extends to the free surfaces of the PCD material resulting in extremely damaging chipping and spelling behaviour. It is believed that a governing aspect for such crack propagation is the residual stress distribution in the PCD rock removal element or body which results from the differential thermal contraction of the PCD layer compared to the hard metal substrate material during the return-to-room pressure and temperature of the manufacturing process. Due to the conventional rock removal element or body designs involving the PCD layers being attached to one side of the hard metal substrates, the return-to-room pressure and temperature in the manufacturing process causes bending distortion to occur in the PCD layers, necessarily resulting in the residual stress distribution spanning the PCD layers involving substantial and significant tensile stress components. These tensile stress components govern the direction of crack propagation. Their particular magnitude, gradients and directional residual stress distributions for specific designs and arrangements for PCD layers and substrates distinguishes the poorest and the best designs.
Conventional PCD bodies comprising a thin layer of PCD material attached during manufacturing processes to substantial hard metal substrates also are restricted in both PCD layer thickness and composition of the PCD material itself. PCD layer thicknesses made conventionally are typically less than 2.5 mm, though exceptionally up to 4 mm. These thicker PCD layers are very difficult to make and progressively suffer from inferior structure and properties arising from poor diamond-to-diamond bonding as a consequence of impurity segregation and general difficulties of long range infiltration of the catalyst/solvent metals for sintering of the diamond particles. The compositional restrictions of the conventional PCD layers concern a dependence of the overall metal content of the PCD material to the diamond grain size distribution. This is illustrated in
Thus there is a need for improved rock removal or rock crushing elements which ameliorate or substantially overcome one or more of the abovementioned problems or disadvantages.
Viewed from a first aspect there is provided a rock removal body for a drag bit rock drilling application comprising a polycrystalline diamond (PCD) material volume bonded to a cemented hard metal substrate along an interface; wherein:
Viewed from a second aspect there is provided a rock removal body for a roller cone bit rock drilling application comprising a polycrystalline diamond (PCD) material volume bonded to a cemented hard metal substrate along an interface; wherein:
Examples will now be described with reference to the accompanying drawings in which:
As shown in
The presence of a cemented hard metal substrate 602 bonded in an axially asymmetric manner to the PCD material volume 601 during the high pressure high temperature manufacture of the PCD material volume causes residual stress distributions in both the PCD and cemented hard metal material volumes. The residual stress distributions are due to bending effects caused by differential expansion and contraction of the PCD and cemented hard metal material volumes during the return-to-room temperature and pressure at the end of the high pressure high temperature manufacturing process. These differential dilations are a result of the elastic modulus and thermal expansion properties of the PCD and cemented hard metal carbides being significantly different. In the experience of the inventors of the current application, the residual stress distribution in PCD, hard metal composite rock removal elements, in particular the tensile residual components in the PCD material volume, are the dominant aspects which may determine the useful life of such rock removal bodies. This is understood to be due to the fact that, typically, crack related failures such as chipping and spelling are the dominant life limiting considerations.
In conventional PCD cutters where the required metal for the liquid phase sintering of the PCD particulate network of the PCD material volumes is derived from long range infiltration of molten cementing metals of the carbide substrate, the residual stress distribution in the PCD material volume is of particular highly significance in this regard. The long range infiltration of the required metal into the PCD volume results in the restriction of the general thickness of the PCD material volume to typically less than 3 mm.
Some examples described herein provide for means whereby there is no such molten metal infiltration related limitation on PCD material volume dimensions and thicknesses. In order to provide a relatively unrestricted scale to the PCD material volume dimensions, the metal required for the PCD material may be independently derived and isolated from the cementing metal of the hard metal substrate. PCD material volumes of any general simple shape, up to dimensions limited by the high pressure high temperature apparatus available, may be made by providing the necessary metal for the PCD material from a starting mass of particulate diamond intimately and homogeneously combined with metallic particles. Thus, the metallic component of the PCD material volume and the cementing metal of the hard metal substrate are independent of one another, independently derived and have not interacted during the high pressure high temperature process. Moreover, in the rock removal elements of the examples described herein, the metal components of the PCD material volume and the hard metal substrate are measurably different and pre-selected to be different in their elemental composition.
The molten binder metal of the hard metal substrate may be precluded from infiltrating into the polycrystalline diamond volume of the composite and an example of a means of achieving this separation and isolation of the metallurgy of the PCD volume and the hard metal substrate volume is to provide a barrier layer 603 between the said volumes which is capable of preventing significant cross contamination of the molten metals of the substrate and PCD material volumes. Barrier layers which may operate in this way may comprise materials which have significantly higher melting points than the catalyst/solvent metals for the PCD material and also the binder metal of the hard metal substrate. In addition, such metals may alloy and react slowly with the molten catalyst/solvent metals for the PCD materials and the molten binder metal for the hard metal substrate. This latter point may assist in providing for sufficient barrier behaviour and also bonding behaviour with both the PCD material and the substrate material. Examples of metals which may satisfy these behaviours may comprise the refractory metals including tantalum, vanadium, niobium, molybdenum, zirconium and their alloys.
Certain ceramic materials such as nitrides, borides and carbides may also fulfil the required criteria. Some examples of such ceramics are tantalum nitride, titanium nitride, aluminium nitride, silicon nitride and mixed nitrides. In some examples, a 50 to 500 micro meter thick continuous zirconium metal barrier layer or bonding layer may be used. In some examples, the barrier layer may comprise a 50 micro meter thick tantalum metal or zirconium metal layer. Also, in some embodiments, a thin layer of nitrides/borides and/or carbides of the elements of groups IVa, Va and/or VIa of the periodic table and B, Si and Al, including, for example, TaN, TiB2, ZrB2, AIN, Si3N4, AIB2 and ZrN, refractory metals, solids solutions, e.g., (Ti, Al)N and mixtures of these, may be used and may be applied using physical vapour deposition (PVD) or chemical vapour deposition (CVD) techniques. In some examples, the barrier layer between the PCD volume and hard metal substrate may comprise a continuous titanium nitride (TiN) layer, greater than around 3 micro meters in thickness. These thin barrier layers may have particular utility when the interface geometry between the PCD layer and substrate has a non-planar geometry.
Thus, examples may comprise an interface bonding the polycrystalline material volume to the cemented hard metal substrate, which is comprised of a thin layer of a third material derived from a refractory material which acts as a metal diffusion blocking barrier material to the molten cementing material of the hard metal substrate and the molten catalyst sintering aid of the polycrystalline diamond material during the high pressure high temperature process.
The metallic component of the PCD material volume and the cementing metal of the hard metal substrate are independent of one another as a result of being prevented from interacting with one another during the high pressure high temperature process due to the presence of the barrier material layer.
This independence of the metallurgy of the PCD material volume and the cementing metal of the hard metal substrate may assist in allowing each of these metallic components to be independently pre-selected in regard to particular desired composition and properties for each of the PCD material volume and hard metal substrate. This is in contrast to much of the conventional prior art PCD where the metal of the PCD material volume is wholly or in part derived from the cementing metal of the hard metal substrate. For example, it may be desired to exploit a corrosion resistant grade of tungsten carbide hard metal based upon the cementing metal. This corrosion resistance is often and typically achieved by alloying the cobalt cementing metal with elements such as nickel and chromium, or completely replacing it with a more corrosion resistant alloy. These alloying agents may well not be ideal or desired components of the metal of the PCD material volume. In this regard, elements such as chromium and other stable carbide forming metals will always and necessarily form precipitated carbides in metal network of the PCD material volume. Such precipitated carbides may well undesirably alter the properties of the PCD material volume.
By contrast, some examples described herein may allow for the exploitation of a greatly expanded range of substrate materials without suffering from such potentially undesired metallurgies of the PCD material volume. A further example may well be the use of titanium carbide cemented with nickel hard metal material for the substrates while exploiting well established simple cobalt PCD material volume metallurgy. Thus, greatly expanded material design capabilities may be achievable in comparison with the conventional prior art where the metallurgies of the PCD material volume and the cemented hard metal substrate are co-dependent.
Thus, in some examples, the metallic component of the PCD material volume and the cementing metal of the hard metal substrate are independent of one another, are independently derived, have not interacted during the high pressure high temperature process, are measurably distinguishable and are pre-selected to be different with respect to the alloy composition. Since a role of the metal of the PCD material volume is to act as a molten catalyst/solvent for diamond recrystallization from solution, the metallic component of the PCD material volume may be a high carbon content alloy of transition metals which may be able to act as catalyst/solvent for diamond recrystallization from solution. These include, for example, transition metals such as cobalt, nickel, iron, manganese and their alloys. High carbon content cobalt may be a catalyst/solvent for the formation of the PCD network. In contrast, the cementing metal of the hard metal substrate will have acted as a liquid phase for the sintering of the carbide hard material. Such cementing metals will therefore tend to be alloys containing the hard metal carbide and the metallic element or elements of the carbide in solid solution. Typical of such cementing metals is, for example, cobalt with tungsten in solid solution for tungsten carbide cobalt based hard metal or nickel with titanium in solid solution for titanium carbide nickel based hard metal. Even if both the metal component of the PCD material volume and the cementing metal of the hard metal substrate are dominated and substantially the same metallic element, such as cobalt, they will be measurably distinguishable in such examples. The former will be a high carbon cobalt alloy as compared to a cobalt tungsten alloy for the latter. The metallic component of the PCD material volume and the cementing metal of the hard metal substrate of some examples may be preselected to be different with respect to their alloy composition. The metal component of the PCD material volume may be shown to be different in alloy composition using standard analytical techniques known in the art. These techniques include Energy Dispersive Analysis (EDS) on a Scanning Electron Microscope, X-Ray Diffraction and Wet Chemical Analysis.
It has been observed in general drag bit subterranean rock drilling that when the life of cylindrical rock removing elements such as those schematically depicted in
The commonest conventional rock removal elements, commonly known as cutters, are all generally right circular cylinders with the PCD material volume dimension at the barrel being typically around 2.5 mm and rarely and exceptionally around 3 to 4 mm. The diameter and length are usually selected according to the specifications given in the Table 1 below.
The examples described may be directed at any of the standard configurations. The 1616 configuration will be used to exemplify various features, which may be applied to all of the configurations in Table 1.
The PCD material volume may be made to any predetermined dimensions. In the context of the 1616 example, where also a flat planar interfacial boundary is specified, the PCD material volume therefore may be chosen to be of any thickness within the constraints of the overall length.
As already stated, in the experience of the inventors, the dimension of the functional working volume at end of life is chosen to be around 3 mm vertically down the barrel of the cylindrical surface.
The angle 704 the final wear scar 702 makes with respect to the vertical of the cylindrical barrel is dependent upon the chosen rake angle in relation to the rock surface. This angle is chosen to be 20° for the purpose of this analysis and is typical of what is used in practice. This means that the extent of the functional working volume at end of life radially from 703, along the top flat surface, will be about 1.1 mm.
The lines labelled 705 represent principle tensile iso-stress contour lines in the cemented carbide substrate. Between this line and the base and barrel free surfaces of the substrate, the volume is occupied by a principle tensile stress field of very low magnitude. Between 705 and the line representing the barrier layer 701, in the direction of the barrier 701, there is a principal tensile stress field increasing in magnitude with an increase in stress gradient becoming more and more intense as the barrier layer is approached. The line 706 represents an intermediate principal iso-stress contour line.
The dotted line 707 indicates the position of the maximum principal tensile stress in the substrate material immediately below the barrier layer 701. Note that at all positions in the cemented hard metal carbide the principal stresses are tensile. The line 708 in the PCD material volume represents the zero stress contour line which separates the hatched volume of PCD material which is in compression from a general tensile field occupying the remainder of the PCD material volume. Two positions of principal tensile stress maxima are indicated by 709 and 710, respectively. The principal stress tensile maximum 709 occupies a position at the circumferential barrel surface of the PCD material volume slightly above the barrier layer 701. This principal stress tensile maximum 709 is dominated by an axial tensile stress. The principal stress tensile maximum 710 occupies a position on the flat top free surface of the PCD material volume. This principal stress tensile maximum, 710, is dominated by a radial tensile stress.
In
It has been observed by the inventors that, when a wear scar interacts with such tensile stress maxima and high tensile stress gradients, macroscopic cracks propagate behind the wear scar in the PCD material volume guided by the general residual stress fields and gradients. Such cracks may lead to chipping and spalling and premature end to the useful life of such rock removing elements or cutters. The PCD construction depicted in
In comparison,
A distinguishing factor between the example of
The example depicted in
Table 2 gives the estimated values of the average principal tensile stress gradients, 711 and 712. It may be seen that these estimates indicate that, as the PCD material volume thickness increases from 2 to 8 mm, the tensile stress gradient 711 is progressively reduced by an order of magnitude and that the tensile stress gradient 712 is progressively reduced by about a factor of 4. This analysis, therefore, indicates that a less damaging tensile residual stress distribution in the functional working volume may progressively develop as the PCD material volume thickness increases from around 3 mm.
The trend of beneficial displacement of the tensile stress maxima, 709 and 710, at the free surface of the PCD material volumes, progressively becoming more and more remote from the functional working volume may continue as the PCD material volume thickness becomes larger and larger. However, as the PCD material volume thickness becomes larger, the principal tensile stresses in the cemented hard metal substrate may increase in magnitude and extent. This may be seen by comparing the maximum principal tensile stress 707 for
Moreover, it may also be seen from the comparison of
Experientially, the inventors have found that the occurrence of diametrical splitting of the hard metal substrate may be greatly reduced when the volume of the PCD material is less than 50 percent of the overall rock removal body volume, i.e., when the ratio of the PCD material volume thickness to the cemented hard metal substrate length or thickness measured from the circumferential edge of the body along the curved barrel surface of the cylinder is less than 1.0.
For a 16 mm diameter and 16 mm long right circular cylinder as illustrated
More generally, for the configurations listed in Table 1, encompassed by the diameter of the cylindrical body being in the range 12 to 20 mm and the overall length of the body 11 to 20 mm, the PCD material volume is a cylindrical layer with thickness 3 mm or greater and the combined thickness of the bonding boundary layer and the cemented hard metal substrate is 8 mm or greater, the bonding interface between the PCD material volume and the cemented hard metal substrate being flat, planar and parallel to the base of the cylindrical rock removal body.
One of the advantages and benefits of the PCD of some of the examples, is that the resulting PCD material exhibits a very high degree of homogeneity in that the diamond network to metallic network volume ratio is spatially constant and invariant at and above a scale directly related to the diamond grain size. This may be achieved by generating a starting particulate mass of diamond particles homogeneously mixed with an accurately determined amount of metal particles such that the metal is always smaller than the diamond particle sizes. The methods may involve suspending the diamond particles in a liquid and nucleating and growing precursor compound(s) for the required metals on the surfaces of the diamond particles. The precursor compound(s) are then conveniently converted to pure metals attached to the diamond surfaces by heat treatment in reducing furnace environment. Specifically, the homogeneity obtainable in the resulting PCD material by such methods may be demonstrated and measured at a scale greater than ten times the average diamond grain size. A further constraint on the diamond grain size distribution in the context of such homogeneous materials is that the maximum grain size be less than three times the average diamond grain size. Such homogeneous PCD materials may have best utility if they at least encompass the functional working volume. Homogeneity in this regard may allow the avoidance of local stress inducing inhomogeneity-based defect structures to occur. In turn this may allow the full exploitation of the residual stress minimizing aspects.
Thus, the PCD material in some of the examples that at least encompasses the functional working volume is homogeneous in that it is spatially constant and invariant with respect to diamond network and metallic network volume ratio, wherein the homogeneity is measured at a scale greater than ten times the average grain size, the maximum diamond grain size being less than three times the average diamond grain size.
The residual stress related criteria applied to the examples may allow the probability of macroscopic crack related behaviour, such as chipping and spelling, to be so reduced that they become of secondary consideration. The primary consideration for the performance of such examples intended for drag bit applications may now be considered to be normal wear behaviour during the rock removal application. PCD material compositions and structures which exhibit improved wear resistance may then be favourably exploited.
It is generally known in the art that high wear resistance is associated with finer diamond grain sizes, and also with high diamond concentration, i.e., low metal content. In the conventional prior art where the required metal for the sintering of the PCD material is derived from long range infiltration from a cemented hard metal substrate, finer diamond grain sizes are invariably associated with high metal content. The diamond grain size and metal content are not independently pre-selectable. For example, in the conventional prior art, when the average grain size is chosen in the range ten to one micro meters, the typical metal contents progressively increase from about nine volume percent to about twelve volume percent. Experientially, in such conventional prior art, metal contents as low as five volume percent are not obtainable for PCD materials with average diamond grain sizes less than ten microns.
By contrast, in some examples, the diamond grain size distribution and the metal content are independently pre-selected. Fine grained PCD material less than ten micro meters average grain size with a metal content between five and nine volume percent may be utilized to assist in exploiting high wear resistant behaviour of the PCD material in the functional working volume.
To enable the examples to be used in largely unaltered roller cone bit designs and custom and practice, the rock removal bodies of the examples intended for roller cone bit applications may comprise a body comprising a right circular cylinder body with one end extending to an apex, with the PCD material volume being axially asymmetrically disposed extending from or abutting the apex, the cemented hard metal substrate being disposed at the opposite cylindrical end. The apex may be formed by a generally convex curved surface or surfaces. Alternatively, the apex may be formed by a general chisel shape where two or more flat surfaces meet to form the apex.
The generally convex curved surface or surfaces may take a hemispheroidal form, for example, either a prolate hemispheroidal, oblate hemispheroidal or a hemispherical form, respectively.
Yet another example is illustrated in
In
The cemented hard metal substrate assists in enabling the standard custom and practice of braze technologies developed for roller cone bit manufacture to be applied in substantively unaltered form. Moreover, a chosen minimum size of substrate for each design of the examples may assist in enabling there to be sufficient cemented hard metal substrate free surface area to provide adequate bond strength to the braze layer for engagement.
Prior art rock removal elements utilizing PCD for roller cone bit applications conventionally exploit a thin layer of PCD material, typically 1.0 to 2.0 mm thick, forming a shell at a convexly curved surface or surfaces. This is illustrated in
In
For each of the examples illustrated in
The thin interfacial bonding layers, 803 and 903, may be flat and parallel to the circular cylindrical end of the substrates as illustrated. Alternatively, the thin interfacial layers 803 and 903 may be generally arcuately curved in regard to the flat end free surface of the substrate. The arcuate nature may be convex in regard to this free surface of the substrate.
Thus some examples may comprise an interface bonding the PCD material volume to the cemented hard metal substrate comprising a layer of third material, for example a thin layer, derived from a refractory material which acts as a metal diffusion blocking barrier material to the molten bonding material of the hard metal substrate and the molten catalyst solvent sintering aid of the PCD material during the high pressure high temperature manufacturing process.
Rock removal elements in roller cone bit applications operate by predominantly a crushing action by indentation on the rock surface. In such applications, therefore, it is necessary that the rock removal elements bearing on the rock have high compressive strength. Typical roller cone bit designs employ conical rollers with protruding rock removal elements inserted into the surface of the rollers. During drilling, the conical rollers roll around the surface of the rock so that the apices of the rock removing elements are cyclically brought to the bear on the rock surface. This cyclical rotary action, therefore, always involves a degree of impact loading to which the rock removal elements are exposed close to and at the apices of these bodies. Cemented hard metal rock removal elements have been traditionally used in this application in that they have adequate strength and impact resistance properties for such crushing actions particularly for soft rock formations. Cemented hard metal rock removal elements however are somewhat inadequate in respect to their wear resistance properties in such applications and suffer from often unfortunate excessive wear which can limit their usefulness. The systems of the prior art conventionally comprise a relatively thin PCD layer at the apices of cemented hard metal rock removal elements in an attempt to mitigate such wear resistance inadequacies by providing greatly improved wear resistance at the apices. However, these limited thicknesses of PCD material (up to about 1 mm) do not provide significant improvements in strength of the rock removal elements and may suffer from easy chipping and spelling due to the inevitable high tensile residual stresses in the PCD layers. The present applicants have appreciated that such stresses are a consequence of bending effects resulting from the differential shrinkage of PCD layers or volumes bonded to cemented hard metal substrates during manufacture.
The thin PCD layers of the conventional structures usually involve functional grading to deal with local high interfacial stresses. This conventional prior art may thus be viewed as using PCD to provide an enhanced wear resistance to the roller cone bullet which would still be dominated by the compressive properties of the carbide. In contrast, some examples described herein exploit the superior compressive strength of PCD over carbide by using large PCD material volumes and therefore may assist in enhancing the wear resistance of the PCD.
In some examples, the substantial volumes of PCD material may occupy at least the functional working volume. Thus the PCD material volume may provide the required strength and impact resistance for the crushing action of the rock removal element. The general bulk mechanical properties of homogeneous, well-sintered PCD materials may be far superior to general cemented hard metal materials for these purposes. Specifically, the hardness of PCD materials may be, in some examples, be two to five times greater than typical cobalt cemented tungsten carbide hard metals typically used in roller cone bit drilling applications. This means that the mechanical wear resistance of the PCD of some of the examples, may be greatly superior to such cemented hard metals, and the measured compressive strength of PCD material grades (greater than 6700 MPa) may be greater than those obtained for most cobalt cemented tungsten carbide hard metals (eg in the range 3500 to 5500 MPa). The fracture toughness of the PCD materials of some of the examples may be in the range 9 to 10.5 MPa.m−0.5, which is high for such a hard material. Thus, where the examples exploit large bulk volumes of PCD material, they may exhibit, due to this combination of properties, very good behaviour in this application which may be far better than typical cemented hard metals.
To assist in enabling the bulk properties of PCD materials to be exploited, the PCD material volume in some examples must be sufficiently large, and avoid thin layers such as those exploited in the typical prior art PCD. Moreover, large pieces of PCD material which have an increase of cross-sectional area at right angles to the direction of the applied forces during the crushing action may benefit from the concept of massive support as taught by P W Bridgman2 . Some of the examples described herein for roller cone drilling applications have this geometry as the PCD material volumes extend from an apex and have a general convex nature. These examples, may therefore enjoy the benefits of the high rigidity of PCD materials providing massive support to their apices when they are bearing upon and crushing the rock. The very high rigidity of such PCD materials may be superior to those exhibited by general cemented hard metals in these applications.
For roller cone drilling general applications, in some of the examples, the thickness of the PCD material volume from the apex in the axial direction of the cylindrical part of the body to the interface with the cemented hard metal substrate is equal to or greater than the radius of the right circular cylindrical body. The maximum extent of the functional working volume extending from the apex in the axial direction may be less than the PCD material volume thickness. This assists in achieving a minimum thickness of PCD material volume, and for a minimum volume of PCD material relative to the overall rock removal body volume.
The examples described may comprise a cemented hard metal substrate. To assist in enabling relatively large bulk pieces of PCD material to be made bonded to cemented hard metal substrates during manufacture, it may be advantageous for the molten cementing metal of the hard metal substrate to be prevented from interacting with the molten catalyst/solvent metal/s necessary for the sintering of the PCD material volume. As previously explained in the context of examples for drag bit applications, refractory metal layers or certain ceramic layers may be used as metal diffusion blocking barriers during the manufacture of PCD material bonded to cemented hard metal substrates.
For roller cone bit applications, the interface bonding the PCD volume to the cemented hard metal substrate may comprise, for example, a thin layer of a third material derived from the refractory material which acted as a metal diffusion blocking barrier material to the molten bonding material of the hard metal substrate and the molten catalyst sintering aid of the PCD material during the high pressure high temperature manufacturing process. Thus, the metallic component of the PCD material volume and the cementing metal of the hard metal substrate may be independent of one another, may be independently derived, have not interacted during the high pressure high temperature process, may be measurably distinguishable and may be pre-selected to be different with respect to the alloy composition.
As discussed above, one of the potential advantages/benefits of the PCD of the examples, may be that the resulting PCD material exhibits a very high degree of homogeneity in that the diamond network to metallic network volume ratio is spatially constant and invariant at and above a scale directly related to the diamond grain size. To assist in achieving this, a starting particulate mass of diamond particles is generated which is homogeneously mixed with an accurately determined amount of metal particles such that the metal is always smaller than the diamond particle sizes. The methods may involve suspending the diamond particles in a liquid and nucleating and growing precursor compound(s) for the required metals on the surfaces of the diamond particles. The precursor compound(s) is/are then conveniently converted to pure metals attached to the diamond surfaces by heat treatment in reducing furnace environment. Details of this method are set out in the examples below. The homogeneity obtainable in the resulting PCD material by such methods may be demonstrated and measured at a scale greater than ten times the average diamond grain size. A further constraint on the diamond grain size distribution in the context of such homogeneous materials is that the maximum grain size is preferably less than around three times the average diamond grain size. Such homogeneous PCD materials may have improved utility if they at least encompass the functional working volume. Homogeneity in this regard may allow the avoidance of local stress inducing inhomogeneity-based defect structures to occur. In turn this may allow for the full exploitation of the residual stress minimizing aspects as described above. Thus, for roller cone bit applications, the PCD material of some examples material at least encompass the functional working volume, and is homogeneous in that it is spatially constant and invariant with respect to diamond network and metallic network volume ratio, wherein the homogeneity is measured at a scale greater than ten times the average grain size, the maximum diamond grain size being less than around three times the average diamond grain size.
In general roller cone bit applications for subterranean rock drilling, the rock removal elements operate primarily by crushing rock as indicated in
The example shown in
In particular,
In
In
In
In some examples with generally convex curved surfaces for the PCD material volume, where they take up hemispheroidal form, these examples have the interfacial bonding material separating the PCD material volume and the cemented hard metal substrate intersecting the free surface of the body in the cylindrical barrel surface below the shoulder, this being defined as the line of departure of the barrel cylindrical surface extending into the generally curve surface of the PCD material volume. The hemispheroidal form of the generally convex curved surface of the PCD material volume may be prolate hemispheroidal, oblate hemispheroidal or hemispherical, as depicted in
In applications where these examples will bear on the rock surface with applied load very close to the axial direction, these low tensile stresses in the functional working volume immediately adjacent to the apex may be largely cancelled out by the applied load. Clearly, in progressively moving from the example of
Such examples may be expected to have lowered probabilities of chipping, spelling and delamination. Moreover, since residual stress related premature failure phenomena in and close to the functional working volume are relegated to secondary considerations, such examples may allow the exploitation of the exceptional properties of PCD materials (with average diamond grain sizes in the range 1 to 30 micro meters) in regard to the loading situation typical of the roller cone bit applications, where the rock is predominantly removed by a crushing action. These properties are predominantly a combination of the high stiffness of PCD materials exhibited by property measurements such as modulus of elasticity at about a 1000 GPa, transverse rupture strength greater than 1200 MPa and adequate impact resistance exhibited by fracture toughness measurements (Klc) at about 9.5 MPa.m0.5. Such measurements may be made with the techniques well established in the art and technical literature. The PCD material in the examples intended for roller cone bit applications thus may have an average grain size in the range 1 to 30 micro meters, be homogeneous with well intergrown diamond structure such the transverse rupture strength is greater than 1200 MPa as measured in three point bend tests. In this broad range of PCD materials, in this particular application PCD materials with the highest compressive strength may be favoured. This implies PCD material types with higher diamond content, with good intergrowth. Typically, these would be materials with larger average grain sizes, such as in the range 10 to 30 micro meters.
As described above, one or more of the examples, be they intended for drag bit or roller cone bit applications, may have a refractory metal diffusion blocking barrier of material may assist in preventing the molten cementing metal of the hard metal substrate and the molten catalyst/solvent metal of the PCD material volume from interacting with one another during the manufacturing process at high pressure high temperature. In addition, such materials may also provide bonding between the PCD material volume and the cemented hard metal substrate. Typical materials which can serve such purposes, may be, for example, thin (eg around 20 to around 100 micro meters thickness) refractory metal layers chosen, for example, from any combination of one or more of tantalum, vanadium, molybdenum, zirconium, tungsten and alloys thereof. During the high temperature high pressure manufacturing process, these layers of refractory metals may be chosen such that they do not melt but will be subject to exposure to high carbon content molten transition metals such as molten cobalt-carbon alloy. Thus, these transition metals become partially carburised during the process.
Also, certain thin ceramic layers deposited using PVD or CVD techniques may also assist in providing a barrier, bonding layer for one or more of the examples. The refractory bonding interfacial layer separating the PCD material volume and the cemented hard metal substrate may be, for example, a CVD or PVD deposited continuous ceramic layer of greater than, for example, around 3 micro meters thickness, chosen for example, from any combination of nitrides of the elements of Group IVa, Va or VIa of the periodic table, such as titanium nitride, TiN.
Some of the examples, be they intended for drag bit or roller cone bit applications, may enjoy the benefits of the tensile residual stress distribution in and around the functional working volume being radically reduced in magnitude and intensity of gradient. Moreover, the principal tensile residual stress maxima may be significantly removed from and remote from the functional working volume and its environs. This may provide for a beneficial, significantly lowered possibility or probability of chipping and spelling in and close to the functional working volume. The common feature which may assist in providing this is if the PCD material volumes are large and are comparable in volume to the cemented hard metal substrate or indeed are greater in volume than the cemented hard metal substrate. The latter being the case for rock removal bodies intended for roller cone bit applications. For rock removal bodies intended for drag bit applications, which may be restricted to an overall right cylindrical shape, the desired size of the PCD material volume is expressed by stipulating that the PCD material volume thickness is around 3 mm or greater. The examples of
Similarly, the tensile stress maxima are illustrated in
In PCD materials made with cobalt as the catalyst solvent metal, the high linear coefficient of thermal expansion at the top of the range may restrict the PCD material to having a high metal cobalt content of at least above 9 volume percent. The cemented hard metal grades typically used in subterranean rock drilling applications are cobalt cemented tungsten carbide grades chosen within the range of 6 to 14 weight percent cobalt. Cemented hard metal carbide with low coefficient of thermal expansion may be restricted to grades with low cementing metal contents at most 10 weight percent (16.3 volume percent) cobalt.
Examples which exhibit lowered tensile stress maxima may be used where the metallic network of the PCD material is, for example, a cobalt-carbon alloy and the cementing metal of the hard metal substrate is, for example, a cobalt-tungsten-carbon alloy and the average metal content of the PCD material volume is, for example, greater than around 9 volume percent (20 weight percent) together with the average cobalt content of the hard metal substrate being less than around 16.3 volume per cent (10 weight percent).
Some of the examples employ PCD material volumes where the composition and structure of the PCD material is macroscopically invariant and homogeneous across the dimensional extent of the PCD material volume. The composition and structure of the cemented hard metal substrates may also be invariant across the dimensional extent of the substrate, i.e., made of one grade of cemented hard metal for these examples. Residual stress distributions extending across the macroscopic dimensions of high pressure high temperature PCD material bodies may be altered, manipulated and chosen by grading the composition of PCD material across the dimensions of the bodies. This may be done by graduating and changing the metal composition as a function of position in the PCD material volume such that the linear coefficient of thermal expansion is different as a function of position in the PCD material volume. The differential shrinkage of the PCD material from position to position during the cooling and pressure reduction phase of high pressure high temperature manufacturing process then induces residual stress from position to position. This method may be used by such positional choice of PCD material composition and structure to assist in reducing the intensity of tensile stress maxima and thus render them less likely to cause undesirable crack related fracture events such as chipping, spelling and delamination. This may be done by altering the composition and structure in a graduated way across the dimensions of the PCD material volume and/or by using discrete adjacent volumes of PCD materials differing appropriately in composition and linear coefficient of thermal expansion.
This approach to manipulation and control of the residual stress distribution may also be applied to the cemented hard metal substrate. Similarly, different grades of cemented hard metal materials with differing linear coefficients of thermal expansion may be employed in various positions in the substrate to advantageously lower tensile residual stress. These teachings may be applied to the examples so far disclosed herein. To illustrate this,
In both
As described above, during the reduction of pressure and temperature at the end of the high pressure high temperature manufacturing process both the PCD material volume and the cemented hard metal substrate shrink. The shrinkage of typical PCD material volumes is always less than that of the cemented carbide material volume. This is because the linear coefficient of thermal expansion of typical PCD materials is always less than that of cemented hard metal materials. The arrows 1109 and 1110 in
Examples where the linear coefficient of thermal expansion of the PCD material increases in the general direction away from a point which is part of the functional working volume which initially bears upon the rock in use, towards the interfacial barrier layer separating the PCD material volume and the cemented hard metal substrate may be advantageous due to the reduction of the residual stress maxima. The value of the linear coefficient of thermal expansion of the PCD material at any given position in the PCD material volume is determined by the elemental composition and quantity of the metal component of the PCD material at and close to that given position. Where the metal type or alloy is invariant across the dimension of the PCD material volume, the linear coefficient of thermal expansion is varied by the metal content alone. The higher metal contents correspond to PCD materials of the highest coefficient of thermal expansion. The converse is also true.
Examples where the metal of the PCD material is invariant as regards the metal type or alloy across the dimensions of the PCD material volume and where the metallic content of the PCD material increases in the general direction away from a point which is part of the functional working volume which initially bears upon the rock in use, towards the interfacial barrier layer separating the PCD material volume and the cemented hard metal substrate may be advantageous due to the reduction of the magnitude of the residual stress maxima. A convenient way of generally increasing the linear coefficient of thermal expansion across a macroscopic dimension in a particular direction may be to employ discrete adjacent volumes of PCD materials differing in linear coefficient of thermal expansion and metal content. The differential shrinkage of the appropriately differing PCD material adjacent volumes may thus provide for a reduction in the overall shrinkage of the overall PCD material volume. Thus, one or more examples may comprise a PCD material volume comprising two or more layers of differing PCD material, the first layer of lowest linear coefficient of thermal expansion and metal content extends from the free surface and encompasses the functional working volume, with the second or subsequent layers of higher linear coefficient of thermal expansion and metal content separating the first layer from the interfacial barrier which separates the PCD material volume and the cemented hard metal substrate. Such examples using simple layers of differing PCD material may be very conveniently made and may significantly reduce the magnitude of critical residual stress tensile maxima. An example which demonstrates this is shown in
The functional working volume is indicated as the volume of material between the specific point 1206 and the dotted line 1207. 1206 is the specific point on the circumferential edge of the PCD volume which is chosen to initially bear on the rock during the application. The functional working volume extends down the circumferential free surface by a chosen 3 mm. The principal tensile residual stress maximum, 1208, is at a position on the circumferential free surface of the PCD material volume immediately above the interfacial barrier layer 1204, forming a ring around the circumference in the second PCD material layer 1203. This residual stress maximum, 1208, is dominated by an axial tensile stress and corresponds in position to the maximum tensile residual stress indicated in
When the magnitude of the tensile stress maxima in
As discussed above, graduating the properties of the cemented hard metal substrate may also be employed to reduce the differential shrinkage indicated by the arrows 1109 and 1110 in
A convenient way of generally decreasing the linear coefficient of thermal expansion of the cemented hard metal substrate across a macroscopic dimension in a chosen general direction may be to employ discrete adjacent volumes of cemented hard metal materials differing in linear coefficient of thermal expansion and cementing metal content. A set of examples in this regard may use parallel layers of differing hard metal material of varying thickness. In some examples, where, for example, the cemented hard metal substrate comprises two or more layers of differing hard metal material, the first layer of highest linear coefficient of thermal expansion and metal content may extend from the basal free surface of the substrate, with the second or subsequent layers of lower linear coefficient of thermal expansion and metal content separating the first layer from the interfacial barrier which separates the PCD material volume and the cemented hard metal substrate.
The positions of the axial dominated tensile principal residual stress maximum, 1306, in the PCD material volume, 1301, corresponds to 709 in
The examples of
In some examples, the metal network in the PCD material volume is cobalt and the cemented hard metal substrate is tungsten carbide cobalt.
The examples for drag bit applications shown in
Most of the examples so far described above exhibit a flat planar thin interfacial barrier layer derived from a refractory material which acts as a metal diffusion blocking barrier to the molten bonding material of the hard metal substrate and the molten catalyst solvent sintering aid of the polycrystalline material during the high pressure high temperature manufacturing process. However, the residual stress distribution in the PCD material volume of general composite PCD hard metal substrate bodies may be favourably altered by employing a non-flat, non-planar interface or boundary between the PCD material volume and the hard metal substrate. More explicitly, such non-planar interfaces or boundaries may have improved value in reducing tensile residual stress maxima, for example if they exhibit a general arcuitly convex curvature towards the PCD material volume.
Some further examples are now described in more detail and are not intended to be limiting.
Rock removal bodies intended for subterranean rock drilling using drag bit designs and technology were made corresponding to the embodiment illustrated in
The bodies each comprised a right circular cylinder of 16 mm diameter and overall length 16 mm with one end forming a cylindrical PCD material volume of thickness 6 mm, with a cemented hard metal substrate disposed at the opposite cylindrical end of the body. The PCD material volume of each body was comprised of a first cylindrical layer, 1202, of 3.5 mm thickness extending from the flat top circular free surface of the body and a second layer, 1203, of 2.5 mm thickness separating the first PCD layer from an extant barrier boundary layer and the cemented hard metal substrate. It is intended that the first layer will completely encompass the functional working volume in use, which extends about 3 mm down the barrel free surface of the PCD material volume from a chosen point at a circumferential edge of the body, this point being the point of initial contact with the rock strata.
This first layer was made from a multimodal PCD material with an average grain size of close to 10 micro meters, with the grain size distribution extending from about 1 to 30 micro meters. The term multimodal in this context refers to the starting diamond powder, which was produced by combining five separate powers, differing in average particle size distribution. The first layer was made from five component diamond powders having a single maximum in particle size distribution and hence each component being monomodal. The metal employed as catalyst solvent for partial re-crystallization of the diamond was cobalt, resulting in the interpenetrating network of the resultant PCD material being high carbon containing cobalt. The PCD material had a cobalt content of 6.7% by volume (15.4% by weight). This composition of PCD material is known to have a linear coefficient of thermal expansion of 3.7 ppm ° K−1.
This second layer was made from a multimodal PCD material with an average grain size of close to 6 micro meters, with the grain size distribution extending from about 1 to 20 micro meters. This layer was made from three component diamond powders having a single maximum in particle size distribution and hence each component being monomodal. The metal employed as catalyst solvent for partial re-crystallization of the diamond was cobalt, resulting in the interpenetrating metallic network of the resultant PCD material being high carbon containing cobalt. The PCD material had a cobalt content of 11.5% by volume (24.7% by weight). This composition of PCD material is known to have a linear coefficient of thermal expansion of 4.4 ppm ° K−1.
The two layer hard metal substrate was made from tungsten carbide cemented with cobalt. The layer at the base of the substrate, 1303 in
Note that for these bodies the linear coefficient of thermal expansion of the PCD material increased in the general direction away from a point which is part of the functional working volume which initially bears upon the rock in use, towards the interfacial barrier layer separating the PCD material volume and the cemented hard metal substrate, with the linear coefficient of thermal expansion of the hard metal substrate decreasing in the general direction away from the central point of the base of the body towards the interfacial barrier layer separating the PCD material volume and the cemented hard metal substrate.
Precursor compounds for the metal, in this case cobalt, are precipitated, nucleated and grown on the surface of the diamond particles by using reactions between soluble reactants whilst suspending the diamond powder in water. After removal from suspension, drying and subsequent heat treatment in reducing environments the diamond particle surfaces are decorated in pure metal particles, thus ensuring an extremely high degree of homogeneity of mixing with respect to the diamond and metal components.
The stock mass for the material of the first PCD layer was produced using the following procedural steps.
100 g of diamond powder was suspended in 2.5 litres of de-ionised water. The diamond powder comprised 5 separate monomodal diamond fractions each differing in average particle size. The diamond powder was thus considered to be multimodal. The 100 g of diamond powder was made up as follows: 5 g of average particle size 1.8 micro meters, 16 g of average particle size 3.5 micro meters, 7 g of average particle size 5 micro meters, 44 g of average particle size 10 micro meters and 28 g of average particle size 20 micro meters. This multimodal particle size distribution extended from about 1 micro meter to about 30 micro meters.
The diamond powder had been rendered hydrophilic by prior acid cleaning and washing in de-ionised water. To the suspension an aqueous solution of cobalt nitrate and a separate aqueous solution of sodium carbonate were simultaneously slowly added while the suspension was vigorously stirred. The cobalt nitrate solution was made by dissolving 93 g of cobalt nitrate hexahydrate crystals, Co(NO3)2.6H2O, in 200 ml of de-ionised water. The sodium carbonate solution is made by dissolving 33.9 g of pure anhydrous sodium carbonate, Na2CO3 in 200 ml of de-ionised water. The cobalt nitrate and sodium carbonate reacted in solution precipitating cobalt carbonate CoCO3, as per the following equation,
In the presence of the suspended diamond powder particles, with their hydrophilic surface chemistry, the cobalt carbonate crystals nucleated and grew on the diamond particle surfaces. The cobalt carbonate precursor compound for cobalt, took the form of whisker shaped crystals decorating the diamond particle surfaces. The sodium nitrate product of reaction was removed by a few cycles of decantation and washing in de-ionised water. The powder was finally washed in pure ethyl alcohol, removed from the alcohol by decantation and dried under vacuum at 60° C.
The dried powder was then placed in an alumina ceramic boat with a loose powder depth of about 5 mm and heated in a flowing stream of argon gas containing 5% hydrogen. The top temperature of the furnace was 750° C. which was maintained for 2 hours before cooling to room temperature. This furnace treatment dissociated and reduced the cobalt carbonate precursor to form pure cobalt particles, with some carbon in solid solution decorating the surfaces of the diamond particles. In this way it was ensured that the cobalt particles were always smaller than the diamond particles with the cobalt being homogeneously distributed. The conditions of the heat treatment were chosen with reference to the standard cobalt carbon phase diagram of the literature. At 750° C. it may be seen that the solid solubility of carbon in cobalt is low. At these conditions the formation of amorphous non-diamond carbon at this temperature is low and traces of non-diamond carbon could be detected in the final diamond-metal particulate mass. The resultant powder mass of multimodal diamond particles with an overall 15.4 weight % of cobalt metal decorating the diamond particle surfaces had a pale light grey appearance. This powder stock mass for the first PCD material layer was stored under dry nitrogen in an air-tight container to prevent oxidation of the fine cobalt decorating the diamond surfaces.
The stock mass for the material of the second PCD layer was produced using the following procedural steps.
100 g of diamond powder was suspended in 2.5 litres of de-ionised water. The diamond powder comprised 3 separate monomodal diamond fractions each differing in average particle size. The diamond powder was thus considered to be multimodal. The 100 g of diamond powder was made up as follows: 18 g of average particle size 4 micro meters, 70 g of average particle size 6 micro meters and 12 g of average particle size 12 micro meters. This multimodal particle size distribution extended from about 1 micro meter to about 20 micro meters.
The same sequential steps were then carried to precipitate a cobalt carbonate precursor for the cobalt metal onto the surfaces of the diamond particles as that for the stock mass for the first PCD layer material save that the cobalt nitrate solution was made by dissolving 160 g of cobalt nitrate hexahydrate crystals, Co(NO3)2.6H2O, in 200 ml of de-ionised water. The sodium carbonate solution is made by dissolving 60 g of pure anhydrous sodium carbonate, Na2CO3 in 200 ml of de-ionised water. The resultant powder mass of multimodal diamond particles with an overall 24.7 weight % of cobalt metal decorating the diamond particle surfaces was stored under dry nitrogen in an air-tight container to prevent oxidation of the fine cobalt decorating the diamond surfaces.
For each rock removal body, so called green body assemblies were constructed using thin walled tantalum canisters. The qualitative and geometric arrangement of the green body assemblies is schematically illustrated in
A 2.0 mm thick tungsten carbide 6 weight % (10.1 volume %) cobalt hard metal disc, 1504, was then inserted into the bottom of a tantalum canister, 1506, followed by 8.5 mm thick tungsten carbide 14 weight % (22.2 volume %) cobalt hard metal disc, 1505. These two hard metal discs together formed the substrate. The tantalum encompassed end of the substrate was then inserted into the open end of the diamond mass containing canister, 1503, such that the end wall of the canister, 1506, separated the diamond mass from the substrate, and further uniaxial compacted to form the assembly. After appropriate trimming of the open end of the canisters, the assembly was inserted into a third canister of slightly larger diameter, 1507, vacuum degassed and sealed under vacuum using procedures known in the art. To consolidate further, to a higher green density and to eliminate or radically reduce spatial density variations, the canister assembly was then subjected to a cold isostatic compaction procedure at a pressure of 200 MPa. Several so called green body assemblies were produced in this manner.
Note that the end wall of canister, 1506, separates the diamond particulate masses which will form the PCD material volume and the hard metal substrate. This thin, about 50 micro meters thick, tantalum end wall layer acted as a barrier to both the molten cementing cobalt of the substrate and the molten cobalt of the PCD material layer during sintering of the diamond PCD layer at high pressure and temperature. In this way the metallic component of the PCD material volume and the cementing metal of the hard metal substrate were independent of one another, independently derived and did not interacted during the high pressure high temperature manufacturing process. After the high pressure sintering of the PCD material volume an extant partially carburised tantalum layer separated the PCD material volume from the substrate.
To sinter the diamond particles of PCD material volume, by partial re-crystallisation of the diamond, each green body assembly was then placed in an assembly of compactable ceramic, salt components suitable for high pressure high temperature treatment as well established in the art. The material immediately surrounding the encapsulated green body was made from very low shear strength material such as sodium chloride. This provides for the green bodies being subjected to pressures which approach a hydrostatic condition. In this way pressure gradient induced distortions of the green body may be mitigated.
The green body canister assemblies were then subjected to a pressure of 6 GPa and a temperature of approximately 1560° C. for 1 hour using a belt type high pressure apparatus as well established in the art. During the end phase of the high pressure high temperature procedure the temperature was slowly reduced over several minutes to approximately 750° C., maintained at this value and then the pressure was reduced to ambient conditions. The high pressure assembly was then allowed to cool to ambient conditions before extraction from the high pressure apparatus. This procedure during the end phase of the high pressure high temperature treatment was thought to allow the surrounding salt media to remain in a plastic state during the removal of pressure and so prevent or inhibit shear forces bearing upon the now sintered PCD body.
The fully dense, right cylindrical bodies were then brought to dimensions of 16 mm diameter and 16 mm long, by finishing procedure such as fine diamond grinding and polishing as well established in the art. Several samples of the embodiment represented by
Rock removal bodies intended for subterranean rock drilling using roller cone bit designs and technology were made corresponding to the example illustrated in
The PCD material volume was made of a multimodal PCD material with an average grain size of close to 10 micro meters, with the grain size distribution extending from about 1 to 30 micro meters. The term multimodal in this context refers to the starting diamond powder, which was produced by combining five separate powers, differing in average particle size distribution. Each made of five component diamond powders having a single maximum in particle size distribution and hence being monomodal. The metal employed as catalyst solvent for partial re-crystallization of the diamond was cobalt, resulting in the interpenetrating network of the resultant PCD material being high carbon containing cobalt. The PCD material had a cobalt content of 9% by volume (20% by mass).
Precursor compounds for the metal, in this case cobalt, are precipitated, nucleated and grown on the surface of the diamond particles by using reactions between soluble reactants whilst suspending the diamond powder in water. After removal from suspension, drying and subsequent heat treatment in reducing environments the diamond particle surfaces are decorated in pure metal particles, thus ensuring an extremely high degree of homogeneity of mixing with respect to the diamond and metal components.
The procedural sequential steps of the method for this example are as follows.
100 g of diamond powder was suspended in 2.5 litres of de-ionised water. The diamond powder comprised 5 separate monomodal diamond fractions each differing in average particle size. The diamond powder was thus considered to be multimodal. The 100 g of diamond powder was made up as follows: 5 g of average particle size 1.8 micro meters, 16 g of average particle size 3.5 micro meters, 7 g of average particle size 5 micro meters, 44 g of average particle size 10 micro meters and 28 g of average particle size 20 micro meters. This multimodal particle size distribution extended from about 1 micro meter to about 30 micro meters.
The diamond powder had been rendered hydrophilic by prior acid cleaning and washing in de-ionised water. To the suspension an aqueous solution of cobalt nitrate and a separate aqueous solution of sodium carbonate were simultaneously slowly added while the suspension was vigorously stirred. The cobalt nitrate solution was made by dissolving 125 grams of cobalt nitrate hexahydrate crystals, Co(NO3)2.6H2O, in 200 ml of de-ionised water. The sodium carbonate solution is made by dissolving 45.5 g of pure anhydrous sodium carbonate, Na2CO3 in 200 ml of de-ionised water. The cobalt nitrate and sodium carbonate reacted in solution precipitating cobalt carbonate CoCO3, as per the following equation,
In the presence of the suspended diamond powder particles, with their hydrophilic surface chemistry, the cobalt carbonate crystals nucleated and grew on the diamond particle surfaces. The cobalt carbonate precursor compound for cobalt, took the form of whisker shaped crystals decorating the diamond particle surfaces. The sodium nitrate product of reaction was removed by a few cycles of decantation and washing in de-ionised water. The powder was finally washed in pure ethyl alcohol, removed from the alcohol by decantation and dried under vacuum at 60° C.
The dried powder was then placed in an alumina ceramic boat with a loose powder depth of about 5 mm and heated in a flowing stream of argon gas containing 5% hydrogen. The top temperature of the furnace was 750° C. which was maintained for 2 hours before cooling to room temperature. This furnace treatment dissociated and reduced the cobalt carbonate precursor to form pure cobalt particles, with some carbon in solid solution decorating the surfaces of the diamond particles. In this way it was ensured that the cobalt particles were always smaller than the diamond particles with the cobalt being homogeneously distributed. The conditions of the heat treatment were chosen with reference to the standard cobalt carbon phase diagram of the literature. At 750° C. it may be seen that the solid solubility of carbon in cobalt is low. At these conditions the formation of amorphous non-diamond carbon at this temperature is low and traces of non-diamond carbon could be detected in the final diamond-metal particulate mass. The resultant powder mass of multimodal diamond particles with an overall 20 weight % of cobalt metal decorating the diamond particle surfaces had a pale light grey appearance. The powder mass was stored under dry nitrogen in an air-tight container to prevent oxidation of the fine cobalt decorating the diamond surfaces.
For each rock removal body 11.4 g of the stock particulate mass was then pre-compacted into a hemispherical ended tantalum canister in a uniaxial hard metal compaction die to form a semi-dense hemispherical ended right cylindrical body. The 12.75 weight % cobalt, tungsten carbide cylindrical substrate for each body was inserted into a tantalum canister with wall thickness of 50 micro meters. The tantalum encompassed end of the substrate was then inserted into the open end of the diamond mass containing canister such that the end wall of the canister separated the diamond mass from the substrate, and further uniaxial compacted to form an assembly. After appropriate trimming of the open end of the canisters, the assembly was inserted into a third canister of slightly larger diameter, vacuum degassed and sealed under vacuum using procedures known in the art. To consolidate further, to a higher green density and to eliminate or radically reduce spatial density variations, the canister assembly was then subjected to a cold isostatic compaction procedure at a pressure of 200 MPa. Several so called green body assemblies were produced in this manner.
Each green body assembly was then placed in an assembly of compactable ceramic, salt components suitable for high pressure high temperature treatment as well established in the art. The material immediately surrounding the encapsulated green body was made from very low shear strength material such as sodium chloride. This provides for the green bodies being subjected to pressures which approach a hydrostatic condition. In this way pressure gradient induced distortions of the green body may be mitigated.
The green body canister assemblies were then subjected to a pressure of 6 GPa and a temperature of approximately 1560° C. for 1 hour using a belt type high pressure apparatus as well established in the art. During the end phase of the high pressure high temperature procedure the temperature was slowly reduced over several minutes to approximately 750° C., maintained at this value and then the pressure was reduced to ambient conditions. The high pressure assembly was then allowed to cool to ambient conditions before extraction from the high pressure apparatus. This procedure during the end phase of the high pressure high temperature treatment was thought to allow the surrounding salt media to remain in a plastic state during the removal of pressure and so prevent or inhibit shear forces bearing upon the now sintered PCD body.
The fully dense, hemispherical ended right cylindrical bodies were then brought to dimensions of 16 mm diameter and 27 mm long by finishing procedure such as fine diamond grinding and polishing as well established in the art.
In summary, one or more examples including polycrystalline bodies not deriving their required metal from substrate materials may be formed of PCD bodies of high homogeneity with their greatest dimensions possibly being around 150 mm or more, limited only by the design and scale of high pressure and high temperature apparatus known in the art and currently available. In addition, the PCD materials exploited in such examples may include PCD material compositions not accessible using conventional PCD manufacture, such as fine grained PCD with low metal contents, coarse grain PCD with high metal contents, both outside the band 501 of
The rock removal bodies of the examples may maintain the conventional overall shape of a simple right cylinder and the well-established custom and practice of brazing these cylinders into the housing bodies of the tools into which they are to be inserted via the cemented hard metal substrate may also be maintained. Thus, some of the examples may provide a means of exploiting the key advantages of free standing PCD bodies but with the inclusion of a substrate attached during the PCD material manufacturing procedure. In this way, the standard extremely well-established designs of drill bits and housing bodies together with the brazing related attachment procedures may be exploited and modifications and re-designs of such aspects may not be required. Thus some examples thus concern the means of making rock removal bodies, of general right cylindrical shape, where the attributes of the procedures of making free standing PCD bodies are made use of but substrates of general hard metal materials are attached in-situ during the manufacturing procedures.
While various embodiments have been described with reference to a number of examples, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof and that these examples are not intended to limit the particular embodiments disclosed.
1. Scott D E, Skeem M R, “Diamond enhanced shear cutting elements on roller cone bits”, Finer Points 2002 pp25-29 Fall-Winter and Proc Engineering Technology Conf on Energy, Houston, Tex., 2001 Vol A pp121-135.
2. Bridgman, P W, 1935, Physical Review, vol. 48, pages 825-832.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1316456.1 | Sep 2013 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/069587 | 9/15/2014 | WO | 00 |
