GB2573405A

GB2573405A - Method of processing polycrystalline super hard material

Info

Publication number: GB2573405A
Application number: GB1906233.0A
Authority: GB
Inventors: Anthony Spits Raymond
Original assignee: Element Six Ltd
Current assignee: Element Six Ltd
Priority date: 2018-05-03
Filing date: 2019-05-03
Publication date: 2019-11-06
Anticipated expiration: 2039-05-03
Also published as: GB2573405B8; GB201906233D0; GB201807270D0; GB2573405B; WO2019211438A1

Abstract

A method of processing a body of polycrystalline super hard material 2 having a first phase including grains of super hard material and a second phase of non-super hard material includes the steps of applying a cover layer 42 to at least a portion of the surface of the body of super hard material to be treated and applying a laser shock wave peening treatment 40 to the surface through the cover layer. The cover layer may be a solid body such as a silica plate, or a liquid phase material such as water. Preferably, the laser shock wave peening treatment comprises generating a high pressure shockwave in the super hard material to create a region of plastically deformed material at the surface 44. The first phase may comprise diamond grains or cubic boron nitride (cBN) grains, and the second phase may comprise a binder catalyst material. The body may be subjected to further post-processing, e.g. removal of the catalyst material in the second phase by leaching.

Description

METHOD OF PROCESSING POLYCRYSTALLINE SUPER HARD MATERIAL

FIELD

This disclosure relates to a method of processing a body of polycrystalline super hard material including but not limited to polycrystalline diamond (PCD) material and to a construction formed of such material so processed.

BACKGROUND

Cutter inserts for machining and other tools may comprise a layer of polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PcBN) bonded to a cemented carbide substrate. PCD is an example of a superhard material, also called superabrasive material, which has a hardness value substantially greater than that of cemented tungsten carbide.

Components comprising PCD and PcBN are used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. PCD comprises a mass of substantially inter-grown diamond grains forming a skeletal mass, which defines interstices between the diamond grains. PCD material comprises at least about 80 volume % of diamond and may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa, typically about 5.5 GPa, and temperature of at least about 1200°C, typically about 1440°C, in the presence of a sintering aid, also referred to as a catalyst material for diamond. Catalyst material for diamond is understood to be material that is capable of promoting direct intergrowth of diamond grains at a pressure and temperature condition at which diamond is thermodynamically more stable than graphite.

Examples of catalyst materials for diamond are cobalt, iron, nickel and certain alloys including alloys of any of these elements. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. During sintering of the body of PCD material, a constituent of the cemented-carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent the volume of diamond particles into interstitial regions between the diamond particles. In this example, the cobalt acts as a catalyst to facilitate the formation of bonded diamond grains. Optionally, a metalsolvent catalyst may be mixed with diamond particles prior to subjecting the diamond particles and substrate to the HPHT process. The interstices within PCD material may at least partly be filled with the catalyst material. The intergrown diamond structure therefore comprises original diamond grains as well as a newly precipitated or re-grown diamond phase, which bridges the original grains. In the final sintered structure, catalyst/solvent material generally remains present within at least some of the interstices that exist between the sintered diamond grains.

The sintered PCD has sufficient wear resistance and hardness for use in aggressive wear, cutting and drilling applications.

A well-known problem experienced with this type of PCD compact, however, is that the residual presence of solvent/catalyst material in the microstructural interstices has a detrimental effect on the performance of the compact at high temperatures as it is believed that the presence of the solvent/catalyst in the diamond table reduces the thermal stability of the diamond table at these elevated temperatures. For example, the difference in thermal expansion coefficient between the diamond grains and the solvent/catalyst is believed to lead to chipping or cracking in the PCD table of a cutting element during drilling or cutting operations. The chipping or cracking in the PCD table may degrade the mechanical properties of the cutting element or lead to failure of the cutting element. Additionally, at high temperatures, diamond grains may undergo a chemical breakdown or back-conversion with the solvent/catalyst.

At extremely high temperatures, portions of diamond grains may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof, thereby degrading the mechanical properties of the PCD material.

A potential solution to these problems is to remove the catalyst/solvent or binder phase from the PCD material.

Chemical leaching is often used to remove metal-solvent catalysts, such as cobalt, from interstitial regions of a body of PCD material, such as from regions adjacent to the working surfaces of the PCD. Conventional chemical leaching techniques often involve the use of highly concentrated, toxic, and/or corrosive solutions, such as aqua regia and mixtures including hydrofluoric acid (HF), to dissolve and remove metallic-solvent/catalysts from polycrystalline diamond materials.

However, methods used to improve the abrasion resistance of a PCD composite often result in a decrease in impact resistance of the composite.

The most wear resistant grades of PCD usually suffer from a catastrophic fracture of the cutter before it has worn out. During the use of these cutters, cracks grow until they reach a critical length at which catastrophic failure occurs, namely, when a large portion of the PCD breaks away in a brittle manner. These long, fast growing cracks encountered during use of conventionally sintered PCD, result in short tool life.

Furthermore, despite their high strength, polycrystalline diamond (PCD) materials are usually susceptible to impact fracture due to their low fracture toughness. Improving fracture toughness without adversely affecting the material’s high strength and abrasion resistance is a challenging task.

There is therefore a need for a polycrystalline super hard composite such as a PCD composite that has good or improved abrasion, fracture and impact resistance and a method of forming such composites.

SUMMARY

Viewed from a first aspect there is provided a method of processing a body of polycrystalline super hard material having a first phase comprising grains of super hard material and a second phase of non-super hard material, the method comprising:

applying a cover layer to at least a portion of the surface of the body of super hard material to be treated; and applying a laser shock wave peening treatment to the surface through the cover layer.

In some examples, the method further comprises leaching an amount of residual catalyst/solvent from interstitial spaces between inter-bonded grains of the body of super hard material after the step of applying the laser shock wave peening treatment to the surface.

Viewed from a second aspect there is provided a polycrystalline super hard material treated by the above defined method.

BRIEF DESCRIPTION OF THE DRAWINGS

Various versions will now be described by way of example and with reference to the accompanying drawings in which:

Figure 1 is a perspective view of an example super hard cutter element or construction for a drill bit for boring into the earth;

Figure 2 is a schematic cross-section of a portion of a conventional PCD micro-structure with interstices between the inter-bonded diamond grains filled with a non-diamond phase material;

Figure 3a is schematic side view of an example treatment process being applied to cutter element;

Figure 3b is a schematic cross-sectional view through the cutter of Figure 3a during treatment;

Figure 4 is a plot showing the results of a vertical borer test comparing an unleached conventional PCD cutter element and four example cutter elements, also unleached, but which have been subjected to the treatment process of Figures 3a and 3b; and

Figure 5 is a plot showing the results of an analysis of wear scar area comparing a conventional PCD cutter element and four example cutter elements which have been subjected to the treatment process of Figures 3a and 3b.

The same reference numbers refer to the same respective features in all drawings.

Detailed Description

As used herein, a “super hard material” is a material having a Vickers hardness of at least about 28 GPa. Diamond and cubic boron nitride (cBN) material are examples of super hard materials.

As used herein, a “super hard construction” means a construction comprising a body of polycrystalline super hard material. In such a construction, a substrate may be attached thereto or alternatively the body of polycrystalline material may be free-standing and unbacked.

As used herein, polycrystalline diamond (PCD) is a type of polycrystalline super hard (PCS) material comprising a mass of diamond grains, a substantial portion of which are directly inter-bonded with each other and in which the content of diamond is at least about 80 volume percent of the material. In one example of PCD material, interstices between the diamond grains may be at least partly filled with a binder material comprising a catalyst for diamond. As used herein, “interstices” or “interstitial regions” are regions between the diamond grains of PCD material. In examples of PCD material, interstices or interstitial regions may be substantially or partially filled with a material other than diamond, or they may be substantially empty. PCD material may comprise at least a region from which catalyst material has been removed from the interstices, leaving interstitial voids between the diamond grains.

A “catalyst material” for a super hard material is capable of promoting the growth or sintering of the super hard material.

The term substrate as used herein means any substrate over which the super hard material layer is formed. For example, a substrate as used herein may be a transition layer formed over another substrate.

As used herein, the term “integrally formed” regions or parts are produced contiguous with each other and are not separated by a different kind of material.

In an example as shown in Figure 1, a cutting element 1 includes a substrate 3 with a layer of super hard material 2 formed on the substrate 3. The substrate 3 may be formed of a hard material such as cemented tungsten carbide. The super hard material 2 may be, for example, polycrystalline diamond (PCD), or a thermally stable product such as thermally stable PCD (TSP). The cutting element 1 may be mounted into a bit body such as a drag bit body (not shown) and may be suitable, for example, for use as a cutter insert for a drill bit for boring into the earth.

The exposed top surface of the super hard material opposite the substrate forms the cutting face 4, which is the surface which, along with its edge 6, performs the cutting in use.

At one end of the substrate 3 is an interface surface 8 that forms an interface with the super hard material layer 2 which is attached thereto at this interface surface. As shown in Figure 1, the substrate 3 is generally cylindrical and has a peripheral surface 14 and a peripheral top edge 16.

As used herein, a PCD grade is a PCD material characterised in terms of the volume content and size of diamond grains, the volume content of interstitial regions between the diamond grains and composition of material that may be present within the interstitial regions. A grade of PCD material may be made by a process including providing an aggregate mass of diamond grains having a size distribution suitable for the grade, optionally introducing catalyst material or additive material into the aggregate mass, and subjecting the aggregated mass in the presence of a source of catalyst material for diamond to a pressure and temperature at which diamond is more thermodynamically stable than graphite and at which the catalyst material is molten. Under these conditions, molten catalyst material may infiltrate from the source into the aggregated mass and is likely to promote direct intergrowth between the diamond grains in a process of sintering, to form a PCD structure. The aggregate mass may comprise loose diamond grains or diamond grains held together by a binder material and said diamond grains may be natural or synthesised diamond grains.

Different PCD grades may have different microstructures and different mechanical properties, such as elastic (or Young’s) modulus E, modulus of elasticity, transverse rupture strength (TRS), toughness (such as so-called KiC toughness), hardness, density and coefficient of thermal expansion (CTE). Different PCD grades may also perform differently in use. For example, the wear rate and fracture resistance of different PCD grades may be different.

All of the PCD grades may comprise interstitial regions filled with material comprising cobalt metal, which is an example of catalyst material for diamond. The PCD structure 2 may comprise one or more PCD grades.

Figure 2 is a cross-section through conventional PCD material which may form the super hard layer 2 of Figure 1 in a conventional cutter. During formation of a conventional polycrystalline diamond construction, the diamond grains 22 are directly interbonded to adjacent grains and the interstices 24 between the grains 22 of super hard material such as diamond grains in the case of PCD, may be at least partly filled with a non-super hard phase material. This non-super hard phase material, also known as a filler material, may comprise residual catalyst/binder material, for example cobalt, nickel or iron. The typical average grain size of the diamond grains 22 is larger than 1 micron and the grain boundaries between adjacent grains is therefore typically between micron-sized diamond grains, as shown in Figure 2.

Polycrystalline diamond (PCD) is an example of a super hard material (also called a super abrasive material or ultra hard material) comprising a mass of substantially inter-grown diamond grains, forming a skeletal mass defining interstices between the diamond grains. PCD material typically comprises at least about 80 volume % of diamond and is conventionally made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa, and temperature of at least about 1,200°C, for example. A material wholly or partly filling the interstices may be referred to as filler or binder material.

PCD is typically formed in the presence of a sintering aid such as cobalt, which promotes the inter-growth of diamond grains. Suitable sintering aids for PCD are also commonly referred to as a solvent-catalyst material for diamond, owing to their function of dissolving, to some extent, the diamond and catalysing its re-precipitation. A solvent-catalyst for diamond is understood be a material that is capable of promoting the growth of diamond or the direct diamond-to-diamond inter-growth between diamond grains at a pressure and temperature condition at which diamond is thermodynamically stable. Consequently the interstices within the sintered PCD product may be wholly or partially filled with residual solvent-catalyst material. Materials that do not promote substantial coherent intergrowth between the diamond grains may themselves form strong bonds with diamond grains, but are not suitable solvent - catalysts for PCD sintering.

In accordance with some examples of the method, a sintered body of super hard material, in one example PCD material is created having diamond to diamond bonding and having a second phase comprising solvent/catalyst dispersed through its microstructure together. The body of PCD material may be formed according to standard methods, using HpHT conditions to produce a sintered PCD table. The PCD tables to be treated in accordance with examples may have a thickness, for example of about 1.5 mm to about 3.5 mm.

Once the super hard construction of Figures 1 and 2 has been sintered, various treatments may be applied to produce the finished end product. According to one example, a treatment process shown in Figures 3a and 3b is applied to the sintered construction prior to treatment of the construction to remove residual catalyst/binder from interstitial spaces.

The surface of the super hard construction to be treated, such as the working surface 4 of the body of super hard material covered by an inertial tamping layer or cover 42. In some examples this may be a solid body such as a silica plate, and in other examples it may be a liquid phase material such as water. The surface is subjected to laser radiation 40.The laser generates a material plasma 46 which is trapped by the inertial tamping layer or cover 42. This generates a high pressure shockwave 48 that propagates through the underlying material and creates a ‘skin’ or region 44 of plastically deformed material that is under significant compressive stress. The plastically deformed region 44 may be, for example around 100 microns to around 2mm thick and the thickness may be controlled as desired by the intensity of and duration for which the surface is exposed to the laser radiation. This technique is termed laser shock wave peening.

In some examples, the laser radiation is pulsed, for example between 1 to 10 Hz on the target material, and is of sufficiently high peak intensity to create the plastically deformed region 44, having a spot diameter of between 2microns to around 300 microns in some examples.

The surface to which the treatment is to be applied may be the entire working surface 4 or a portion thereof, or at least a portion of the peripheral side surface of the construction. The tamping layer or cover 42 may therefore be chosen to extend to the peripheral side edge of the working surface or be spaced therefrom by a radial distance. In some examples, the distance by which the layer or cover 42 is spaced form the peripheral side edge of the working surface 4 is around 1mm.

In some examples, the laser shock wave peening treatment of the examples is applied after some initial processing of the construction has taken place such as polishing of the surface to be treated and in some examples the formation of a chamfer at the cutting edge 6.

Once the construction has been subjected to the laser shock wave peening process of the examples, the construction may be subjected to one or more further processing treatments, for example, catalyst material may be removed from a region of the PCD structure adjacent the working surface 4 or the side surface or both the working surface and the side surface. This may be achieved by treating the PCD structure with acid to leach out catalyst material from between the diamond grains, or by other methods such as electrochemical methods. A thermally stable region, which may be substantially porous, extending a depth of at least about 50 microns or at least about 100 microns from a surface of the PCD structure, may thus be formed which may further enhance the thermal stability of the PCD element.

The prepared PCD constructions treated according to the above methods were compared in a vertical boring mill test. The results are shown in Figure

4.

Two PCD constructions were tested first that were formed of conventional unleached PCD material which had not been subjected to a laser shock wave peening process and the results are shown in Figure 4 by lines 100 and 200. Two further PCD constructions were tested whose entire working surface 4 had been treated with the above described treatment process, and the results are shown in Figure 4 by lines 300 and 600. An additional two PCD constructions were then tested whose working surface 4 had been treated up to a distance of around 1mm from the peripheral side edge of that surface 4 with the above described treatment process, and the results are shown in Figure 4 by lines 400 and 500.

In this test, the wear flat area was measured as a function of the number of passes of the construction boring into the workpiece and the results obtained are illustrated graphically in Figures 4 and 5, Figure 5 showing the wear scar area at 30 passes of the vertical borer test for each of the tested constructions.

The results provide an indication of the total wear scar area plotted against cutting length. It will be seen that the PCD constructions formed according to the examples (lines 300, 400, 500 and 600) were able to achieve a significantly greater cutting length than that occurring in the conventional PCD compact (shown by lines 100 and 200 in Figure 4) which was subjected to the same test for comparison and the PCD constructions formed according to the examples were able to achieve a significantly smaller wear scar area than that occurring in the conventional PCD construction tested, as shown in Figure 5.

Thus it will be seen from Figure 4 that the PCD constructions treated in the manner described above to introduce a plastic deformation in the working surface which creates favourable compressive stress in the structure showed a significant improvement in both cutting distance and abrasion resistance over the conventional PCD construction when such a treatment process was applied to the construction prior to leaching any residual catalyst binder therefrom.

While various versions 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 examples or versions disclosed.

Claims

1. A method of processing a body of polycrystalline super hard material having a first phase comprising grains of super hard material and a second phase of non-super hard material, the method comprising:

2. The method of claim 1, further comprising leaching an amount of residual catalyst/solvent from interstitial spaces between inter-bonded grains of the body of super hard material after the step of applying the laser shock wave peening treatment to the surface.

3. The method of any one of the preceding claims, wherein the step of applying a cover layer to at least a portion of the surface of the body of super hard material to be treated comprises applying a solid cover to the surface to be treated.

4. The method of any one of claims 1 or 2, wherein the step of applying a cover layer to at least a portion of the surface of the body of super hard material to be treated comprises applying a liquid phase cover to the surface to be treated.

5. The method of any one of the preceding claims, wherein the step of applying a laser shock wave peening treatment to the surface comprises generating a high pressure shockwave in the super hard material to create a region of plastically deformed material at the surface.

6. The method of claim 6, wherein the region of plastically formed material has a thickness of around 100 microns to around 2mm.

7. The method of any one of the preceding claims, wherein the body of super hard material has a working surface, and the step of applying a cover layer to at least a portion of the surface of the body of super hard material to be treated comprises applying a cover that extends across substantially the entire working surface.

8. The method of any one of claims 1 to 6, wherein the body of super hard material has a working surface bounded by a peripheral side edge, and the step of applying a cover layer to at least a portion of the surface of the body of super hard material to be treated comprises applying a cover that extends across a portion of the working surface, the cover being spaced from the peripheral side edge.

9. The method of claim 8, wherein the cover is spaced form the peripheral side edge by a distance of up to around 1 mm.

10. The method of any one of the preceding claims, wherein the first phase comprises diamond grains or cBN grains, and the second phase comprises a binder catalyst material, the body of polycrystalline super hard material being polycrystalline diamond material or polycrystalline cubic boron nitride material.

11. A polycrystalline super hard material treated by the method of any one of claims 1 to 10.