GB2509244A

GB2509244A - A composite material comprising diamond-silicon carbide particles in a metal matrix

Info

Publication number: GB2509244A
Application number: GB1322580.0A
Authority: GB
Inventors: Gerald Francis Flynn
Original assignee: Element Six GmbH
Current assignee: Element Six GmbH
Priority date: 2012-12-20
Filing date: 2013-12-19
Publication date: 2014-06-25
Also published as: WO2014096208A1; GB201223087D0; GB201322580D0

Abstract

A material which comprises composite particles 2 made of diamond particles 6 embedded in silicon carbide 8, the composite particles 2 themselves being embedded in a matrix 4 of a metal or alloy. The composite particles 2 occupy 20-80 % by volume of the material and the composite particles 2 comprise at least 20 % by volume diamond particles 6. Some residual silicon 10 is present in the composite particles 2. The material can be used for hard-facing substrates, forming a weld joint between two bodies and forming a body by pressing in a mould and sintering.

Description

MATERIAL COMPRISING COMPOSITE PARTICLES EMBEDDED IN A MATRIX

FIELD

This disclosure relates to a body of material comprising particles embedded in a matrix. In some described embodiments it relates to a body of material in which the particles that are embedded are relatively harder than the matrix in which they are embedded, and the matrix into which the particles are embedded is relatively tougher than the embedded particles.

BACKGROUND

One typical example of a body of material comprising particles embedded in a matrix is a material suitable for use as a so-called "hardfacing material" on surfaces or substrates, for example on metal substrates. Application of a hardfacing material onto surfaces and substrates is a well-known technique used to enhance the erosion and abrasion resistance of those surfaces or substrates or to refurbish those surfaces or substrates, and is used, for example, to extend the service life of metal drill bits and other metal downhole tools as used in the oil and gas industry, and may also be used in other applications where a tool or part is to be subjected to abrasive wear and erosion, for example in the mining industry.

Current hard face materials used for the refurbishment and/or protection of wear surfaces encountered on tool bodies e.g. drill bits or wear surfaces etc. generally consist of two phases -a hard phase additive and a binder matrix component. The hard phase additive is generally dispersed in a softer matrix component of fracture toughness significantly greater than that of the hard phase. The hard phase additive may typically consist of diamond or cBN (cubic boron nitride) particles, polycrystalline diamond material, cemented tungsten carbide, fused tungsten carbide, silicon carbide, silicon nitride, borides or similar hard additives. The matrix may typically comprise a metal or alloy. The hard material additive phase is typically selected in the field to exhibit a relatively high hardness and the other first matrix phase is generally selected to exhibit relatively high fracture toughness and good adhesion to the substrate. The effect of this is that overall the composite material will provide good wear and erosion resistance (as provided by the hard phase additive), but will not show brittle failure in operation (due to the good fracture toughness of the matrix).

The two-phase material can then be deposited on the surface of the substrate to be protected by a variety of deposition methods, and these methods often involve exposing the hard-face material to a period at high temperature during which time the super hard component may, depending on its nature, be vulnerable to thermal damage which is deleterious to the hardness of the material and its subsequent effectiveness in resisting wear. Diamond, for example is vulnerable to graphitisation at these high temperatures. The deposition of the two phase hard facing material onto the substrate to be refurbished or protected is generally done so as to form metallurgical bonds to the substrate, to ensure good adhesion thereto.

There are many examples of hardfacing materials in the prior art, some of which attempt to avoid or minimise the problems of the vulnerability of diamond as a component in a hard facing material.

is us 8079428 describes diamond-based hard facing materials used to increase the wear resistance of earth boring tools and components. The materials described are particles of polycrystalline diamond (PCD) material embedded within a matrix material of a metal or metal alloy. The particles of polycrystalline diamond comprise a plurality of inter-bonded diamond grains; the inter-grain bonding is said to be formed by subjecting the diamond grains to a temperature greater than about 1,500°C and a pressure greater than about 5GPa in the presence of a catalyst such as cobalt. The reference describes methods whereby the hard facing material is applied to a surface to be protected using a welding rod that comprises the hardfacing material and a torch used to heat the rod until the matrix begins to melt, at which stage the hardfacing material is applied to the surface to be protected, the hard particles within the matrix being applied together with the matrix to the surface to be protected. In some embodiments described in US8079428 the PCD particles are at least partially encapsulated with a coating, and certain metals, alloys, carbides, borides and nitrides for example are mentioned as candidates for this coating, the purpose of which is said to be to protect the polycrystalline diamond material within the PCD particles against thermal degradation (e.g. graphitisation) that might occur during formation at high temperatures of the hard facing. In certain embodiments in us 8,079,428 the PCD particles are subject to a leaching process to remove catalyst material such as cobalt from interstitial spaces between the diamond grains. Such a catalyst, if present, promotes graphitisation of the diamond at the temperatures used to apply the hard-facing material, thereby reducing the abrasive resistance of the diamond layer. These additional steps of coating and leaching disadvantageously involve additional cost, and in addition the leaching process may be hazardous.

US 5,755,299 describes coated diamond particles embedded in a matrix, used as a hard facing material. The coating encapsulates the diamond to protect the diamond particles from the heat associated with the hardfacing procedure, and is selected to be metallurgically and chemically compatible with the material forming the matrix.

US 6,138,779 describes hardfacing material comprising coated ceramic particles and/or other coated particles of super-abrasive and superhard materials (for cubic boron nitride (cBN) integrated into a less hard but much tougher matrix deposit formed for example from cobalt, copper, nickel, iron, and alloys of these elements.

In addition to the hard facing materials described above that are known in the prior art which describe superhard material embedded in a metal matrix material typically applied onto a substrate on site, there is also known in the prior art stand-alone articles comprising diamond material embedded in a metal matrix. For example US 7,350,599 describes an insert from a drill bit that may be made by coating diamond particles with a variety of materials including tungsten carbide, cobalt, copper and polymer binder, and blending these with a matrix material which may be a metal component selected from alloys of cobalt, iron, nickel or copper.

Similarly, US 8,069,936 describes earth boring tools and components thereof including encapsulated diamond particles embedded in a metal or alloy matrix In addition, and relevant to certain embodiments of this invention, EP 1019338 describes a method of making abrasive grains by crushing a composite material comprising separate diamond particles placed in a matrix formed by silicon carbide and silicon.

SUMMARY

It is an aim of certain embodiments of the present invention to provide alternative composite materials to those known in the prior art with a phase that is relatively harder than another phase, but relatively less tough. It is another aim of certain embodiments of the present invention to provide an alternative material that may be used as hard facing materials with enhanced ease of application. It is a further aim of certain embodiments of the invention to provide an alternative composite material to that disclosed in the prior art for use in applications other than as a hard facing material. It is another aim of certain embodiments of the invention to provide an abrasive wear resistant, thermally stable, additive material which can be co-deposited with an appropriate tough matrix binder phase whilst retaining its wear resistant properties and also capable of being retained within the co-deposited hard-face matrix during application. It is another aim of certain embodiments of the invention to provide composite materials that may be formed in situ or in a factory, and methods of their formation.

Viewed from a first aspect there is provided a body of material comprising: (i) a plurality of particles which are composite particles and (U) a matrix which comprises a metal or alloy; the plurality of composite particles being embedded in the metal or alloy matrix, and the composite particles themselves comprising a plurality of superhard sub-particles which are diamond particles and a sub-matrix which comprises silicon carbide in which the diamond sub-particles are embedded.

The body of material comprises a plurality of composite particles embedded in a matrix. Therefore the body of material is itself a composite, and contains within it particles that are themselves composite particles. The terms sub-particles" (of diamond material, which is a superhard material) and "sub-matrix" (of silicon carbide which is a ceramic material) are used in this specification to distinguish them from the particles (of composite material) and the matrix (of metal or alloy) in which those composited particles are embedded.

As used herein, the term "composite material" means a complex material in which two or more distinct, structurally complementary substances combine to produce structural or functional properties not present in any individual component.

As used herein, the term "superhard material" means a material having a Vickers hardness, Hv, of at least about 2800, and often a hardness of at least Hv 4000.

As used herein, the term "ceramic" means an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling".

The body of material comprises composite particles embedded in a matrix of a metal or alloy. It is also envisaged that additional particles may also be present in the body of material to enhance properties of the body of material according to its application.

For example it is envisaged that particles of titanium, boron carbide (B4C), tungsten carbide, silicon carbide, silicon nitride or cBN (cubic boron nitride) could be present in the matrix interspersed with the composite particles. In preferred embodiments there should be substantially no catalyst metals present within the composite particles. By catalyst metals we mean metals such as nickel, cobalt, iron or manganese. By substantially no presence of these elements we mean less than 2 volume percent, or optionally less than 1 volume percent, or even less than 0.5 volume percent. This zero or minimal level of catalyst metals in the composite particles distinguishes the body of material fuither from those materials in the prior art comprising PCD material, since such catalyst metals are invariably present in such POD material as a consequence of its manufacturing process. The metal or alloy matrix may or may not be substantially free from catalyst metals.

In some embodiments the hardness of the composite particles that are embedded in the metal matrix is at least Hv 2400, or even at least Hv 3000. In some embodiments the hardness of the composite particles is at most Hv 5000 or even at most Hv 3500.

In contrast the hardness of POD is much higher, typically having a Knoop hardness of 5OGPa ASTM C1326-03). Similarly the hardness of single crystal diamond is much higher at Hv 10,000. In some embodiments the range of Vickers Hardness is 2400- 4000, or optionally 3000-3500. Vickers Hardness of the composite is measured according to ASTM E384 liel as mentioned earlier. It should be noted that composite hardness consists of measuring the hardness of both the binder phase and hard phase, the overall hardness then being determined as described in ASTM Standard E384 liel. This hardness determination is defined in the above mentioned ASTM measuring standard. In some embodiments the fracture toughness of the composite particles is at least 5 MPa. In some embodiments the fracture toughness of the composite particles is at most 8 MPa. Fracture toughness values as given in this specification are measured according to ASTM E1820-01.

In some embodiments the hardness of the metal matrix is at least Hvoi 300. In some embodiments the hardness of the metal matrix is at most HvOA 1,000. In some embodiments the hardness range is Hvo.i 300 to Hv 1,000. In some embodiments the fracture toughness of the metal matrix is at least 40 MPa.

It is noted that Vickers hardness values may be written as Hvo.i indicating the use of a 0.1 kg test force. Often the force is omitted as the hardness number is largely independent although caution is advised when comparing values at the lower end of scale.

In some embodiments the hardness of the composite particles is at least 2 times the hardness of the metal matrix. In some embodiments the fracture toughness of the metal matrix is at least 5 times the toughness of the composite particles. Thus advantageously the body of material provided has a high hardness as a result of its composite particles contained therein, and good toughness as a result of the matrix component, making the body of material suitable for hard-facing applications amongst others.

In some embodiments the composite particles comprise at least 20 volume percent, or at least 29 volume percent, or even at least 46 volume percent or at least 54 volume percent superhard diamond sub-particles.

The superhard diamond sub-particles within the composite particles may be mono-modal or multi-modal in size.

As used in this specification, a "multi-modal" size distribution of a mass of particles or sub-particles is understood to mean that the particles or sub-particles have a size distribution with more than one peak, each peak corresponding to a respective "mode". In contrast a "mono-modal" size distribution of a mass of particles or sub-particles is one having a size distribution with a single peak corresponding to the single "mode".

The superhard diamond sub-particles may be, for example, single crystals, or broken or partial single crystals, or fragments of single crystals. In some embodiments diamond crystals forming the sub-particles are anhedral, and in other embodiments they are euhedral. Euhedral crystals are those that are well-formed with sharp, easily recognised faces. The opposite is true of anhedral crystals. Typically the minimum size of the diamond sub-particles (taking a mean dimension) is 5 microns, or optionally 20 microns. Typically the maximum size of the diamond sub particles is 250 microns, or optionally 50 microns. In some examples the size of the diamond sub-particle is about 30 microns. In some embodiments the size range is 5-250 microns, optionally 20 to 50 microns.

One example of composite particle that may be used in the body of material of the present invention is so called silicon-carbide cemented diamond (ScD). ScD is a material known in the art in which diamond particles are embedded and bonded in a matrix of silicon carbide, especially predominantly beta phase silicon carbide, and sometimes also some free silicon. Unlike in most diamond composite bodies where very high diamond concentrations are used to form direct diamond to diamond contact and a direct chemical bonding between adjacent diamond particles resulting in a diamond skeleton structure, in ScD composite material a direct bonding of diamonds is not an important or needed factor in the material, and in general the structure is a skeleton of silicon carbide around diamond particles, with substantially no direct diamond-diamond contact, although in some high diamond content ScD composites some diamond to diamond contact may occur. Therefore in this specification when we talk about substantially no direct diamond-diamond contact being present we mean less than 5% of the diamond particles being in contact with any adjacent diamond particle. Methods of ScD manufacture are described for example in US 6,447,852, US 6,709,747, US 6,709,747, EP1019337 and EP 1253123 and typically involve: forming a work piece having a predetermined size and shape from a blend of diamond particles and a binder; heating the work-piece at a pressure below 50 bar and a temperature below 1900°C so that graphite is created by the partial graphitisation of the exposed diamond surface or complete graphitisation of fine diamond crystals, thereby creating an intermediate body; and infiltrating silicon or silicon alloy into the body. In view of the method of manufacture, free silicon, and sometimes other elements e.g. titanium or boron (from the infiltrating silicon alloy when one is used) may also be present in the ScD composite structure, within interstices in the silicon carbide and embedded diamond structure.

In certain embodiments the silicon carbide sub-matrix is hetero-epitaxially bonded to the diamond sub-particles. When we say the silicon carbide sub-matrix is hetero- epitaxially bonded to the diamond sub-particles, we mean that there is hetero-epitaxial bonding over at least 50% of the surfaces of the diamond particles.

An advantage of using ScD material for the composite particles is that the silicon carbide stabilises the diamond at high temperature as it provides an encapsulating layer around each diamond particle, thereby substantially eliminating graphitisation of the diamond at temperatures above 750 °C where graphitisation of exposed diamond would be expected to take place in a non-inert atmosphere. This makes it possible to use the body of material incorporating the SCD composite particles within a metal or alloy matrix in hard facing applications for example, where temperatures typically exceed 950 °C. In contrast in the prior art, such as US8079428 where polycrystalline diamond (POD) particles are embedded in a metal matrix, such PCD material would be expected to graphitise at temperatures used for applying hard facing materials, especially as cobalt (or another Group VIII element) is usually present as a residue from the catalyst metal infiltration during the synthesis manufacturing process of the POD material (and very difficult to remove), and this acts as a catalyst to the graphitisation process, meaning that special particle encapsulation steps need to be taken to stop thermal degradations, as described in the US 8,079,428 reference.

As defined above, within the body of material the composite particles (comprising the superhard diamond sub-particles and silicon carbide sub-matrix) are embedded within a metal or alloy matrix. The coniposite particles themselves may have a variety of shapes and sizes and occupy a variety of volume percent of the overall body of material. The average shape, size and percentage volume addition of the composite particles can be selected according to the application of the body of material, fol example where the body of material is to be a hardfacing material the average shape, size and percentage volume addition of the composite paiticles may be selected to enhance the abrasive wear resistance of the coated substrate. In the case of exposure to a slurry erosion environment the packing density and shape of the composite particles may be designed to minimise the mean free path in the metal matrix thereby creating a torturous path for the slurry and significantly impeding its harmful erosive action on the body.

Considering first the shape of the composite particles, this may be regular, for example approximately spherical or irregular in shape, for example with an irregularly shaped suiface, for example a suiface exhibiting re-entrant angles. The particles may have an aspect ratio in the range 1 to about 3, typically less than 1.5. Where the composite particle comprises SoD material it is noted that this material is relatively easy to process with a variety of methods such as jet milling, tumbling, high energy air milling, crushing and screening to produce particles of a variety of physical shapes and sizes. ScD is much more workable in this way than, for example, polycrystalline diamond, because ScD is a monolithic material which contains substantially no harmful catalytic metals, unlike polyclystalline diamond which is typically manufactured as a dual pail article consisting of a cemented tungsten carbide portion onto which the polycrystalline layer is grown and includes catalyst solvent metals which require to be removed. The processing of the polycrystalline diamond material into a granulate form is complicated by both these issues and by its extreme hardness which is typically higher than that of ScD. In some embodiments the composite particles are engineered to have a surface area to volume ratio of at least 3. Optionally also the composite particles are engineered to have an irregular surface, by which we mean not a rounded surface. Engineering the relatively large surface area to volume ratio and optionally also the irregular surface advantageously enhances mechanical engagement with the metal matrix material to complement any chemical/metallurgical bonding between the composite particles and the metal matrix with mechanical interlocking.

The size of the composite particles, even if irregular, may be expressed in terms of equivalent circle diameter (ECD). As used herein, the "equivalent circle diameter" (ECD) of a particle is the diameter of a circle having the same area as a cross section through the particle. The ECD size distribution and mean size of a plurality of particles may be measured for individual, un-bonded particles or for particles bonded together within a body, by means of image analysis of a cross-section through or a surface of the body. The size of the composite particles in the present invention may, in certain embodiments have a minimum ECD of 500 microns, or even 800 microns. The size of the composite particles may, in certain embodiments have a maximum ECD of 2,000 microns, or optionally 1300 microns.

The composite particles in the body of material may be mono-modal or multi-modal.

This allows the packing density to be engineered depending on the wear properties desired.

Within the overall body of material, the composite particles in some embodiments occupy at least 20 optionally at least 30 volume percent of the body of material. In some embodiments the composite particles occupy at most 80, optionally at most 45 volume percent of the body of material. In some embodiments the composite particles occupy 20-80, optionally 30-50 volume percent of the body of material In general there are substantially no interstices in the body of material, therefore the metal matrix makes up the remainder of the body of material, unless other components are added for additional application properties. Examples of other materials that may be added include tungsten carbide particles, including both mono crystalline tungsten carbide and cemented tungsten carbide particles and cubic boron nitride particles, as mentioned earlier.

Where the composite particles comprise ScD material, they may be made according to the method described in EF1019338. This method typically involves following the method described above with reference to US 6,447852, US 6,709,747, EP1O1 9337 and EP 1253123 to form a body of polycrystalline ScD material, and then crushing the polycrystalline body into grains The composite particles of superhard diamond and ceramic silicon carbide may be over-coated with an additional layer prior to incorporation into the metal or alloy matrix. For example, the composite particles may be over-coated using a continuous vapour deposition (CVD) or physical vapour deposition (PVD) technique to produce an optimised metallurgical or carbide forming layer on the composite particles, to improve further the matrix retention, for a desired composite particle/matrix combination.

The body of material comprising the composite particles in a metal or alloy matrix may be made on site or in a factory depending on the application.

Considering first on-site formation of the body of material, a method may be employed for example, in which (i) the composite particles are mixed with powder particles of the metal or alloy which is to form the matrix of the body of material, (ii) the mixture delivered to a substrate under the application of heat, the heat causing the metal powder particles to melt and flow around the composite particles, and (üi) the composite particles and molten metal or alloy allowed to cool, or actively cooled, thereby solidifying and thereby forming the body of material. This method may be used, for example to apply the body of material as a hard facing wear enhancement to a substrate, or for example to supply the body of material between two substrates to form a durable hard face weld between those substrates.

In another method of on-site application of the body of material, (i) the composite particles may be pre-encapsulated with metal or alloy powders of varying composition selected as those that are to form the matrix of the body of material, and then (ii) delivered to a substrate under the application of heat, for example by flame spraying, causing the metal or alloy coating to melt around the composite particles on the substrate, and then (ii) allowed to cool or actively cooled to solidify the metal or alloy, thereby forming the body of material. As with the previous method this method may be used for example to apply the body of material as a hard facing wear enhancement to a substrate or for example to supply the body of material between two substrates to form a durable hard face weld between those substrates.

Encapsulation of the composite particles may be carried out by any suitable method known in the art, for example the method described in W02008/018048. According to that method, which is a two stage process, pellets containing an ultra-hard core coated with an encapsulating material are formed by suspending the core material in a flow of gas, contacting the core material with encapsulating material to form pellets, introducing the pellets into a rotating vessel, and contacting the pellets with further encapsulation material to form pellets of greater mass than the pellets introduced into the rotating vessel. When used for the present invention the encapsulation material may be powder comprising the metal or alloy that is to form the metal or alloy matrix and the superhard core the composite particles.

One advantage of the encapsulation approach is to avoid the potential problem of segregation occurring between the metal or alloy powders and the composite particles where these are used in a blended mixture. This is beneficial when the deposition method used for coating of the substrate requires a delivery system involving spraying the material onto the surface e.g. cold spray or thermal flame spray techniques since such techniques involve a time of flight trajectory which can result in de-segregation if separate composite particles and powder particles are used.

Other methods of application of particles or powders of components of the body of material that may be used to supply a body of material onto a substrate in situ to form the body of material (usually after cooling) include thermal spraying, laser deposition, cold spraying (MIG) welding, tungsten inert gas (TIG) welding, and plasma-transferred arc (PTA) welding.

Considering now factory formation of the body of material, this may be achieved by a number of methods. In one method, (i) the composite particles and powder of the metal or alloy that is to form the matrix are blended, (ii) those blended particles are poured into a mould of the form of the desired final part, (iii) pressed with a suitable binder into a green body in that mould, and then (iv) sintered to compact the body and remove the binder.

As an alternative factory method (i) composite granules may be encapsulated in a metal layer, for example in the manner described earlier, to form free flowing precursor materials, and then (ii) pressed (usually hot pressed) in the mould and (üi) sintered as above.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will now be described in more detail, by way of example only, with reference to the accompanying drawing in in which: Figure 1 is a schematic representation of the microstructure of the body of material according to an embodiment of the invention: Figure 2 is a schematic representation of the microstructure of one of the components shown in Figure 1; Figures 3 and 4 are schematic representations which show alternative methods for forming the body of material 1 of Figure 1 on a substrate as a hard facing material; Figure 5 is a schematic representation which shows the formation of a durable hard face weld by formation of the body of material of Figure 1 between two substrates; and Figures 6a and 6b are schematic representations showing stand-alone parts being a gage wear part and a cutting pick insert, each comprising the body of material shown in Figure 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, Figure 1 shows a body of material 1 comprising a plurality of ScD composite particles 2 embedded in a nickel/iron/boron/chrome alloy matrix 4. The ScD particles all have an irregular shape, and shaped surface with re-entrant angles as referenced 5. This irregular shape enhances the mechanical engagement of the ScD composite particles 2 with the matrix 4.

The ScD particles 2 occupy about 30 volume percent of the body of material 1, and the matrix 4 occupies the balance. In this illustrated embodiment no other components are present, but it is envisaged that additional hard material components could be added to compliment the superhard particles and engineer characteristics in the body of material according to its application, e.g. according to the tribological wear conditions the body of material will experience in use depending on application.

Sub-particles of diamond material 6, which may be single crystal diamond or fragments of single crystal diamond, are also illustrated in Figure 1 within the ScD composite particles 2. These are described in more detail with reference to Figure 2.

Figure 2 is an enlarged view of one of the SOD composite particles 2 shown in Figure 1. It illustrates the composition of each of these composite particles 2. Each comprises a plurality of diamond sub-particles 6 embedded in a sub-matrix 8 of silicon carbide. There is also some residual silicon 10 present. This is a residue from the manufacturing process for the SCD particle 2. The silicon carbide sub-matrix 8 provides a skeleton structure in which the diamond sub-particles 6 are embedded, and there is substantially no diamond-diamond 6-6 contact at all.

Figure 3 shows one method of formation of the body of material 1 of Figure 1 as a hard facing material on a substrate 12. In this method a hollow steel cylindrical rod 14, closed at both ends is pre-loaded with a free flowing mixture comprising: (i) the composite particles 2, and (ii) metal alloy powder 4', e.g. nickel/iron/boron/chrome alloy powder. Metal/alloy powder 4' is a powder form of the metal/alloy which will form the matrix 4 in the formed hard facing material. One end of the rod is placed adjacent, and at an angle to the substrate 12 to be protected by the hard facing, and an oxyacetylene torch is used to produce a flame 16 with sufficient heat (typically about 800°C) to melt the end of the steel rod adjacent the substrate and to melt the metal powder 4'. The metal powder 4' therefore flows onto the substrate carrying with it the ScD composite particles 2, which do not melt. When a sufficient volume of material has flowed onto the substrate to provide the required hard facing layer, the flame 14 is removed and the body of material 1 allowed to cool so that the molten metal matrix 4 solidifies, around the composite particles 2 that it carries. This method as described in Figure 3 for forming the body of material 1 may be referred to as rod deposition method.

Figure 4 shows an alternative method for applying a hard facing material being the body of material of Figure 1 to a substrate. In this case composite particles 2 as illustrated in Figure 1 are encapsulated by a layer of a metal or alloy, this metal or alloy layer being the metal or alloy that will form the metal or alloy matrix in the final body of material that is the hard facing material. Encapsulation is not illustrated in the Figure but may be carried out by any suitable technique described in the prior art for encapsulating hard materials, for example the method described in W02008/01 8048 which has been described earlier. As shown in Figure 16 these metal or alloy encapsulated pellets which we will reference 2' are placed in a hopper 16 and flame sprayed in a conventional way using ignited propellant gas 18, so that a flame 20 containing the encapsulated composite particles (referenced 2') are sprayed onto the substrate 22 where the metal encapsulating material on the particles 2' melts and forms the matrix 4 around the composite ScD particles 2, thereby forming the body of material 1 of Figure 1. This method of application of the body of material to a substrate may be referenced flame spraying application.

Figure 5 shows the production and application of a body of material 1 as shown in Figure 1 between two substrates to form a durable hard face weld. In this embodiment particles of ScD composite material 2 and particles of metal or alloy powder 4' of the type used in the Figure 3 embodiment are fed through a vibration feed 24 from a hopper (not illustrated) into a space 26 between two substrates 28. An oxyacetylene flame 30 is applied to the join area which melts the metal/alloy powder 4' causing it to flow to form a matrix around the carried composite particles 2. The flame 30 is then removed, and the flowed matrix and particles allowed to cool, thereby forming the body of material 1 illustrated in Figure 1, and forming a durable hard face weld.

Figures 6a and 6b show respectively a gage wear part 32 and a cutting pick insert 34 each made of the body of material 1 shown in Figure 1. Specifically each part comprises ScD composite particles 2 embedded in a matrix of a metal or alloy 4, and the composite particles 2 occupy 30 volume percent of the part. Each ScD composite particle contains diamond 6 which may be in the form of single crystals or single crystal fragments embedded in silicon carbide 8, optionally with some free silicon (not illustrated). Unlike the hard facing material illustrated in Figures 3-4 and the durable hard face weld of Figure 5 which are all formed in situ on site applications, the gage wear part and cutting pick insert are stand-alone parts which may be formed in a factory. These may be made in a number of ways. For example SCD composite granules 2 may be blended with powdered metal particles 4', then poured into a suitable graphite mould of the form of the final part e.g. frusto-conical pick insert shape or domed part or cylinder, then hot pressed with a suitable binder into a green body in that mould, and then sintered to compact the body and remove the binder. Suitable materials for the matrix metal particles may be nickel or copper.

The parts may also include tungsten carbide/cobalt (spherical or crushed), which may be sintered tungsten carbide/cobalt (spherical or crushed). The hot pressing and sintering stage involves the uniaxial compaction of the encapsulated materials of the admixed powders whilst heating the matrix metal materials thereby resulting in a melting of the binder metal matrix allowing infiltration of the ScD composite parts within the matrix while being compacted, thereby producing a solid sintered body metal matrix body containing the ScD composite granule phase. As an alternative method ScD granules may be encapsulated in a metal layer, for example in the manner described above with reference to Figure 4, to form free flowing precursor materials, and these may be hot pressed in the mould as described above and subjected to the final sintering step. Both methods produce the same result which is a stand-alone article made from the body of material illustrated in Figure 1 comprising composite particles embedded in a metal or alloy matrix 4. There may optionally be further particles of other hard materials, e.g. tungsten carbide or silicon carbide in these stand-alone parts shown in Figures 6a and 6, depending on the application and wear and thermal requirements of the parts. These other components are not illustrated in the Figures.

Claims

CLAIMS1. A body of material comprising: (i) a plurality of particles which are composite particles and (U) a matrix which comprises a metal or alloy; the plurality of composite partices bençj embedded in the metal or alloy matrix, and the composite particles themselves comprising a plurality of superhard sub-particles which are diamond particles and a sub-matrix which comprises silicon carbide in which the diamond sub-particles are embedded.
2. A body of material according to claim 1, wherein the diamond sub-particles have a size range from 5 to 250 microns.
3. A body of material according to claim 1 or 2, wherein the superhard sub-particles are mono-modal or multi-modal within each composite particle, and the composite particles are mono-modal or multi-modal.
4. A body of material according to any of claims 1-3, wherein the composite particles comprise silicon-carbide cemented diamond (ScD) material, comprising a silicon carbide sub-matrix which provides a skeletal structure within which diamond sub-particles are embedded, and optionally some free silicon in interstices within the structure.
5. A body of material according to claim 4, wherein the silicon carbide sub-matrix is hetero-epitaxially bonded to the diamond sub-particles.
6. A body of material according to any preceding claim, wherein the composite particles have an irregular shape to enhance mechanical engagement with the metal or alloy matrix.
7. A body of material according to any preceding claim, wherein the composite particles occupy 20-80 volume percent of the body of material.
8. A body of material according to any preceding claim wherein the sub particles of superhard diamond material comprise single crystal diamonds or fragments of single crystal diamonds.
9. A body of material according to any preceding claim, wherein the composite particles comprise at least 20 volume percent diamond sub-particles.
10. A method of forming the body of material defined in any preceding claim in situ on a substrate, the method comprising: (i) mixing the composite particles which are the composite particles of the body of material with powder particles of the metal or alloy which is to form the matrix of the body of material; (ii) delivering the mixture to a substrate under the application of heat, the heat causing the metal powder particles to melt and flow around the composite particles; and (iii) allowing, or actively causing the composite particles and molten metal to cool and solidify, thereby forming the body of material.
11. A method of forming the body of material defined in any of claims 1-9 in situ on a substrate, the method comprising: (i) encapsulating the composite particles with metal or alloy powders of varying composition selected as those that are to form the matrix of the body of material; (H) delivering the encapsulated composite particles to the substrate under the application of heat sufficient to cause the metal or alloy coating to melt around the composite particles on the substrate, and then (Hi) allowing or actively cooling of the melted metal or alloy thereby forming the body of material.
12. The method according to claim 10 or 11, wherein the body of material so formed provides a hard facing material thereby providing wear enhancement to the substrate.
13. A method according to claim 10 or 11, wherein the body of material so formed provides a weld joint between the substrate and another body.
14. A method of forming an article made of the body of material defined in any of claims 1-9, the method comprising: (i) mixing the composite particles which are the composite particles of the body of material with powder particles of the metal or alloy which is to form the matrix of the body of material; (H) placing those mixed particles in a mould of the desired shape of the article to be formed; (Hi) pressing the particles in the mould; and (iv) sintering.
15. A method of forming an article made of the body of material defined in any of claims 1-9, the method comprising: (I) encapsulating the composite particles with a coating of the metal or alloy that is to form the matrix of the body of material; (H) placing those mixed particles in a mould of the desired shape of the article to be formed; (Hi) pressing the particles in the mould; and (iv) sintering.
16. A body of material or a method of applying a body of material substantially as described herein with reference to the accompanying drawings.