HK1028368B - A kind of material - Google Patents

Description

Material

Background of the invention

RELATED APPLICATIONS

The present application was made on the basis of provisional application No. 60/046,885 filed on 13/5/1997.

Field of the invention

The present invention relates to ceramic powders and sintered materials made from such powders. Such materials are particularly suitable as metal forming devices, such as metal cutting and forming tools.

Background of the invention

In the mid-thirty years, sintered tungsten carbide powder tools began to replace alloy steel tools, which are rapidly becoming the norm due to their superior hardness, inherent high toughness and transverse mechanical strength. The hardness of this material improves tool life, and its toughness and strength can be fed faster, faster and more aggressive forging parameters to help increase productivity. The development and marketing of carbide tools after the second war are remarkably accelerated.

Even if this material eventually wears away, the mechanism of this wear is not completely understood. The progressive wear of the tool causes deformation of the material to be shaped and, in order to maintain the dimensional tolerances of the workpiece, the tool must be replaced when it is not capable of forming a workpiece of the correct dimensions. The time of use before changing the tool or the number of formed workpieces ultimately determines the life limit of the tool. The loss of productivity resulting from tool change and readjustment operations, manufacturing out of fit, rework and loss of work schedule is a driving force for seeking materials that will extend the life of the tool.

The life of a tool depends on its resistance to various wear, reaction to heavy loads and reaction to vibration. Generally, the greater the chip removal rate (fast feed and high cutting speed), the stretching and forming pressure, and the more durable the tool topography is maintained, the better the tool. A good cutting and forming tool must be simultaneously hard, strong, and inflexible, and resistant to chipping, cracking, thermal cracking, fatigue, chemical reaction with the workpiece, and wear. Thus, the main mechanical property requirements for sintered tools are strength, hardness, high elastic modulus, high fracture toughness, low chemical interaction with the workpiece, and low coefficient of friction in order to reduce heat build-up while the workpiece is being shaped.

In recent years, the Powder Metallurgy (PM) industry has seen significant development because of the ability of the powder to be cold-flowed into precision molds. This allows the mold, which is typically bulky, to be reused while greatly reducing machining, shaping, and other processing steps, since the sintered part is already very close to its desired shape, i.e., "near net shape. There is a tendency to require that these parts (which are currently made mainly of aluminium, iron and copper powders) have some quality which is the same as the tool. Accordingly, many PM articles are additionally forged, coated or heat treated to impart localized hardness, toughness and strength. Many of these parts require shock and wear resistance to give them the same mechanical properties as the tool.

In tools and hard articles, wear resistance is generally increased by sacrificing strength; currently, the best tools best meet various requirements, thus limiting their use in specific applications.

In addition to tungsten carbide, other alloys, coating techniques, and combinations of the two have been found to not only extend tool life, but also to increase cutting and feed rates. Powder metallurgy and sintering have developed new materials with enhanced hardness and toughness for improved wear resistance by applying a hard coating on the sintered alloy, for example by Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD) or Plasma Assisted Chemical Vapor Deposition (PACVD).

Many enhancements to the formation of coatings on powders, coating substrates and other hard materials have been reported in the prior art literature. The prior art in the field of tool materials discloses six methods currently known and commonly used to achieve such enhanced wear resistance and toughness; each method has obvious advantages and obvious disadvantages: (1) mixing hard and tough phase particles, (2) coating a hard phase layer on a sintered substrate by chemical vapor deposition (or other methods), (3) using method 1 and method 2 in combination, (4) ceramic metal (cermet) pressing, (5) chemically bonding low concentration diamond or cBN macroparticles to a hard but relatively brittle abrasive substrate for special types of tools (abrasive and sanding media), and (6) Functionally Graded Materials (FGM).

None of these solutions compromise the desired tool performance, and only chemical vapor deposition (CVD or PVD) methods are currently used in certain mechanical parts where increased wear resistance is desired.

Ternary system for mixing hardness and toughness

Despite the numerous secondary processing methods and variations thereof used and reported in the art, mixing hard WC-TiN-Co alloy particles with carbide powders prior to sintering has a number of disadvantages. Due to the low mutual solubility between these harder particles and the binder, the transverse strength of the substrate decreases rapidly at hard particle contents above 6-10 wt.%. The surface hardness and wear resistance are also reduced compared to surface coatings. The wear mechanism is not much improved either, since a very small number of hard particles (less than one on the surface where the hard particles are needed) that are weakly bonded to the binder fall off as a whole.

Chemical Vapor Deposition (CVD) coatings

The value of these hard intermetallic and hard outer coatings of cermet layers on tool steel or sintered article substrates (after sintering) is that they can form high surface hardness values, typically 2400 to 5000 vickers (TiN) to 9000 (diamond). Likewise, for all of the ancillary processing, modification and sintering aids used and disclosed in the art (including additional coatings, dopants or coatings that locally alter the substrate structure and reduce particle size), this overcoat approach has several major drawbacks, including coating delamination and cracking (caused by differences in thermal expansion rates of the coating and substrate, and by bending and surface stresses) when used, and the required higher CVD processing temperatures (900 ℃ C. and 1200 ℃ C.) are incompatible with the heat treatments required for the strength or morphology of the sintered part.

Conventional CVD coating of sintered articles with several different coatings or coatings can solve two or three unique workpiece problems. However, since the layers must be deposited in sequence, the remaining layer or layers of the particular coating are covered before the outer coating is abraded away. Thus, only one of the coatings of the shared substrate may be used to solve the problem over time.

Some tools, such as wire-drawing dies and nozzles, are prohibitively expensive because of the additional expense required to ensure that the CVD vapor is properly circulated through the die exit to deposit the coating where it is most needed. The diffusion of CVD vapors is slow and the penetration depth is typically about 0.5-10 microns or less. First, at this thickness, the coating has worn down to the carbide underlayer before the diameter tolerance of most metal wires or tubes is reached. Second, dies at larger diameters must be reused normally without a hard coating. In many cases, the overall life of the tool is disproportionate to the increased CVD cost.

Currently, overcoating is the most common industrial method to enhance the properties of common tungsten carbide sintered products. The return from the process of increasing the deposited thickness of the outer layer to achieve longer life is diminishing, increasing the thickness increases the tendency for cracking and rounding of sharp tool edges, adversely affecting the optimum cutting or die profile.

Using a combination of mixing and coating methods

CVD coating and mixing of hard alloy particles, i.e. using method 1 and method 2 in combination, offers limited benefits while having the same disadvantages as above.

Metal ceramic

Cermets are formed by dispersing ceramic particles in a matrix of metal oxides or carbides. The cermet has both the high temperature resistance of ceramic and the toughness and flexibility of carbide. They are the same price as ordinary tungsten carbide and have approximately the same wear resistance, but their light-polishing cutting performance is superior to ordinary carbide.

Sintered abrasive composites

The fourth method described above, which is published by dr. randall m.german, Liquid Phase Sintering, Plenum Press, new york1985 (and by Russian practice many years ago), forms a class of superabrasive composites useful as grinding and sanding media and tools for small spaces (niche).

This complex is prepared as follows: diamond particles (or cubic boron nitride, cBN) and cobalt powder are mixed or they are collected in a metal (nickel) electroplated layer and hot pressed at low temperature. Another approach is to coat the diamond (or cBN) with an intermediate layer of a transition metal carbide precursor that wets the diamond and chemically bond it to other particles with a low melting non-wetting but soft metal binder such as cobalt, iron or nickel. The applied transition metal acts primarily as a viscous chemical medium and does not bear the structural mechanical loads. The metal as the main binder matrix has good sinterability, but the melting point, elastic modulus and strength are low. Such materials have desirable properties in abrasive applications. In most of these applications the diamond comprises 10-60% by volume of the composite. The binder coating is several microns thick to facilitate processing at low temperatures (to prevent degradation of the graphitized diamond) and to dilute the diamond content, but with a large loss of mechanical properties. The performance of these composites is determined by chemical factors rather than by mechanical factors such as modulus of elasticity, strength or fracture toughness. Thus, for large particle size diamond and high binder concentrations, the mechanical properties of the composite are determined by the mixture rules. The composition should be selected to ensure that each diamond particle is independent and that the diamond-diamond interactions are small in the final microstructure. It does not improve the mechanical advantage of cemented carbides in the micron to nanometer size range.

Abrasive tools are required to have relatively large abrasive grain sizes (50-600 microns) to increase metal removal rates, proper spacing between abrasive grains when bonded into a wheel (low concentration of abrasive grains, large portion of binder phase matrix between abrasives) to remove workpiece particles and maintain wheel topography over long periods of time. Such abrasives utilize distinct hardness of abrasive particles and the workpiece itself to shape the metal workpiece by cutting the workpiece. These abrasive composites are sometimes used in cutting tools to process high hardness materials at relatively high speeds and low chip removal rates (loads) (see fig. 6). The cutting action of diamond cutting tools is distinct from cemented carbide tools. The limitation of diamond or composites in cutting tools comes from their cutting behavior. Such composites are used as abrasives, typically for abrading a workpiece, rather than removing debris under high load (load). In this manner, the very hard diamond particles are retained by the tensile bonding forces. The diamond is exposed to cut the opposite surface as it slides across the work piece surface, but it has wear resistance as the matrix erodes and the diamond is progressively exposed. The cutting is performed with protruding diamonds as long as they remain sharp. When the diamond becomes dull, it rounds and is designed to break the matrix. In this manner, the diamond is pulled out of the work piece and the matrix erodes until another diamond is exposed.

Such hard, brittle abrasive composites may also be used in certain tool-like applications, such as the cutter and saw of a masher. They have also been found to be useful in high cost wire-drawing dies, as well as cutting tools in the presence of steel and other strong backings.

Functionally Graded Material (FGM)

A problem with coated articles is that the mechanical, chemical or thermal properties are incompatible between the layers. To address this problem by forming a graded region between incompatible layers, FGMs have one or more of the following variations: chemical composition, microstructure, density, or different morphologies of the same material. It is another object to form a coating to improve the electrical, thermal, chemical or optical properties of the substrate to which the FGM is applied. The main disadvantage of this material is that it breaks at the transition in properties and that it is difficult to manufacture.

Summary of the invention

The main object of the present invention is to produce sinterable pellets called tough material coated hard powders (TCHPs) which have a higher value than the hard articles and tool materials known to date. The particles and articles made therefrom combine optimum strength, hardness, high elastic modulus, fracture toughness, low interaction with the workpiece, and low coefficient of friction, which combine the properties found in various conventional materials, respectively, into an article having incomparable properties.

It is another object of the present invention to reduce the cost of providing these materials to the user. For example, various cutting inserts of very different shapes must be provided to accommodate different holders. Additionally, currently available tool materials must be designed to suit different specific uses. Therefore, for each shape difference, a choice of materials (uncoated, CVD coated, PVD coated, cermet, ceramic, polycrystalline cBN, polycrystalline diamond) must also be provided. The addition of geometry and material changes requires an expensive inventory of products (catalog), the manufacture of useless spare tools, the storage of expensive inventory products with unique packaging and instructions by the producer and user, and the interpretation and effort to sell them to the user at the point of sale. It is another object of the present invention to reduce the waste and cost associated with existing systems by providing a more versatile higher performance tool at a reasonable cost.

In addition, the method of manufacturing embodiments of the inventive article has the objective of reducing the production costs of the inventive article.

Another object is to significantly reduce costs by extending the first time life of the article and reducing the manufacturing costs of the product. The fact that the articles of the present invention are macroscopically homogeneous rather than coated gives the user or supplier the opportunity to economically regrind and reuse the initially worn article.

Another object of the invention is to provide other hard articles with mechanical properties as high as those of the material of the invention.

It is another object of the present invention to provide a material having enhanced wear resistance and toughness suitable for use in a variety of articles including tools such as wire drawing dies, extrusion dies, forging dies, shearing and stamping dies, die plates, forming rolls, injection molds, shearing machines, drill bits, grinding and lathe tools, saws, hobs, shavers, reamers, taps and dies; individual mechanical components such as gears, cams, pivots, nozzles, seals, valve seats, pump impellers, winches, pulleys, bearings and wear surfaces; integral co-sintered components that replace mating components, such as internal combustion engine connecting rods, bearings, and/or provide a hard surface area in powder metal (P/M) mechanical components (such as camshafts, transmission components, printer or copier components) that replace forged or machined steel components with heat treated areas; heavy industrial articles such as deep well drill bits, teeth of mining and earthmoving equipment, hot rolls of steel mills; and electromechanical components such as memory driven read heads, dedicated permanent magnets. In addition to providing these new articles, the primary object of the present invention is to provide a new composite particulate material (i.e., TCHP), a new method of making such material and a new method of making articles from such material.

To achieve these and other objects, the present invention provides a sintered material comprising a plurality of core particles consisting essentially of a material having the formula M_aX_bOf a first metal compound of (a). M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and aluminum or M is silicon. X represents one or more elements selected from nitrogen, carbon, boron and oxygen, a and b represent a number greater than 0, up to and including 4. An intermediate layer surrounds each of the core particles and is composed mainly of a second metal compound different in composition from the first metal compound. The second metal compound has a higher relative fracture toughness and can be combined with the first metal compound and also with iron, cobalt or nickel. The core particles with the intermediate layer thereon form a series of coated particles. The intermediate layer on the core particle is covered with an outer layer as a binder. It includes iron, cobalt, nickel, mixtures thereof, alloys thereof, or intermetallic compounds thereof.

The coated particles preferably have an average particle size of less than about 2 microns, and most preferably less than about 1 micron. The thickness of the intermediate layer after sintering is preferably 5 to 25% of the diameter of the core particles. The thickness of the outer layer after sintering is preferably 3-12% of the diameter of the coated particles. It is believed that the outer layer has such a thickness that the strain field associated with dislocations in one coated particle passes through the outer layer of adhesive into the intermediate layer immediately adjacent thereto. The first metal compound is preferably composed mainly of stoichiometric compounds, such as TiN, TiCN, TiB₂、TiC、ZrC、ZrN、VC、VN、cBN、Al₂O₃、Si₃N₄Or AlN. The second metal compound is preferably composed mainly of WC or W₂C, wherein WC is preferred. The fracture toughness of the material is larger than that of the cubic boron nitride.

A preferred example of the sintered material includes a plurality of core particles composed mainly of cubic boron nitride, and an intermediate layer composed mainly of WC on each of the core particles. After sintering, the thickness of the intermediate layer is 5-25% of the diameter of the core particles. An outer layer comprising cobalt or nickel is applied over the intermediate layer, the outer layer having a thickness after sintering of from 3 to 12% of the diameter of the coated particles. The inner core particles, intermediate layer and outer layer together form a coated particle, preferably having an average particle size of less than about 1 micron.

Another embodiment of the invention is a powder consisting essentially of a plurality of coated particles. The majority of the core particles of the coated particles consist essentially of a compound of the formula M_aX_bOf a first metal compound of (a). M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and aluminum or M is silicon. X represents one or more elements selected from nitrogen, carbon, boron and oxygen, a and b represent a number greater than 0, up to and including 4. The core particles are coated with a covering layer consisting essentially of a second metal compound having a different composition than the first metal compound and having a higher relative fracture toughness. The layer can also be combined with a first metal compound and can be combined with a metal selected from the group consisting of iron, cobalt, and nickel. The coated particles preferably have an average particle size of less than about 2 microns, and most preferably less than about 1 micron. The thickness of the layer surrounding the core particle after sintering is 3 to 200% of the diameter of the core particle.

The preferred compositions of the core particles and the cover layer (i.e., the intermediate layer) are the same as the powder examples described for the sintered article.

The outer binder layer preferably consists essentially of cobalt, nickel, iron, mixtures thereof, alloys thereof or intermetallic compounds thereof deposited on the outer surface of the second metal compound layer in the form of a continuous layer.

Brief Description of Drawings

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. Together with the description, the drawings serve to explain the principles of the invention.

FIG. 1 is a schematic illustration of a sintered material formed in accordance with an aspect of the present invention;

FIG. 2 is a 20,000-fold scanning electron micrograph of a cross-section of a sintered material formed in accordance with an aspect of the present invention;

FIG. 3 is a schematic view of an apparatus for forming a powder according to one aspect of the present invention;

FIG. 4 is a schematic view of the interior of the apparatus of FIG. 3 illustrating the movement of particles within the apparatus during deposition of an intermediate layer by chemical vapor deposition;

FIG. 5 is an end view of a component of a preferred embodiment of the apparatus of FIGS. 3 and 4;

FIG. 6 is a schematic illustration of a sintered material operative field of the present invention as compared to a conventional material when used as a cutting tool;

FIG. 7 is a compilation of properties of the sintered materials described in the examples.

Detailed description of the preferred embodiments

As outlined herein, the present invention is a novel material made from powder. The powder of the invention comprises a plurality of core particles. The core particles impart their physical properties to the overall powder structure. As described herein, the core particle is composed of a core particle having the formula M_aX_bWherein M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and aluminum or M is silicon, X represents one or more elements selected from the group consisting of nitrogen, carbon, boron and oxygen, and the characters a and b represent a number greater than 0 and up to 4. Such metal compounds are hard, wear resistant and chemically resistant to most environments and workpieces. Significantly, the core material is exposed, for example, when the powder is sintered into a cutting tool, and the sintered article is formed by grinding, lapping and polishing into the shape of the final article. This method removes the interlayer material from the core particles and exposes the particle cores to the workpiece being machined. This is a great advantage, as will be described in detail below.

As described herein, the core particle of the powder consists essentially of at least one stoichiometric compound. In certain examples, the inner cores have different compositions so as to impart properties of different inner core particles to articles made therefrom. The core metal compound is preferably mainly composed of a metal selected from TiN, TiCN, TiB₂、TiC、ZrC、ZrN、VC、VN、cBN、Al₂O₃And AlN or a compound Si₃N₄And (4) forming. These materials can be used in the form of commercially available powders, whiskers, crystals, filaments, etc., as the shape of the core particles can be technically meaningful. The core particles are covered with a layer of another metal compound called the intermediate layer. Thus, the material of the core particles must be compatible to some extent with the interlayer material applied thereto, and its composition differs from that of the interlayer material.

Examples of the powder of the present invention include an intermediate layer applied to the outer surface of the core particle. The intermediate layer is composed mainly of a second metal compound (i.e., a compound having a composition different from that of the first metal compound forming the core particle). The relative fracture toughness of the intermediate layer second compound is higher than the toughness of the material forming the core. In addition, the second metal compound must be capable of binding to the first metal compound and to iron, cobalt, nickel, mixtures thereof, alloys thereof or intermediate metal compounds thereof. The second metal compound is preferably composed mainly of WC or W₂C, the composition is shown. As will be described below, the combination of a relatively tough and strong intermediate layer with a hard inner core provides a powder and sintered material made therefrom with exceptional mechanical properties. This can also be the case with the particle size and layer thickness of the coated particles. In particular, the properties provided by the particle size and layer thickness are difficult to specify by classical mixture calculation rules, which will be explained in more detail in the section of the present description discussing sintered articles. In general, the coated particles preferably have an average particle size of less than about 2 microns, and most preferably less than about 1 micron. The thickness of the intermediate layer is preferably 5 to 25% of the particle size of the core.

The thickness of the intermediate layer significantly affects the mechanical properties of the articles made therefrom. It is believed that when the average particle size of the coated particles (core with interlayer) is less than about 2 microns as measured graphically in a photomicrograph of a cross-section using the mean free path method, the resistance to dislocation movement in adjacent sintered particles is enhanced, improving the mechanical properties of the sintered article. Even with classical mechanical methods, using finite element analysis, the theoretical toughness increases by over 40% when the WC bowl thickness around the TiN sphere is increased from about 0.1 micron to about 0.4 micron.

The thickness of the intermediate layer before sintering is also preferably 3% to 200% of the diameter of the core particles. During sintering, the thickness of the intermediate layer decreases due to interactions with the core material, particle/particle interactions, particle boundaries and growth phenomena. Thus, in order to obtain the desired intermediate layer thickness in the sintered article, it is necessary to have an initial thickness of up to 300% of the diameter of the core particle.

A preferred powder form is one having an outer layer of adhesive applied thereto. Typically, the metal binder is applied to the metal compound particles by milling the metal binder with the metal powder. Such physical operations are time consuming and, when the binder metal is present in a minority (e.g., 6%) of the powder to be milled, the time required to coat the binder metal on the surface of the other 94% of the particles can adversely affect the economics of using the metal binder to form sintered particles and can compromise the coated particles. The present invention contemplates uniformly coating such particles in the form of a continuous layer on the outer surface of the metal compound particles. The binder layer of the present invention consists essentially of a material selected from the group consisting of iron, cobalt, nickel, mixtures thereof, alloys thereof, and intermetallic compounds thereof. The continuous layer of binder is preferably deposited by chemical vapor deposition, cathodic sputtering, electroless plating, electroplating, physical vapor deposition, carbonyl deposition, solution spray deposition, or plasma-assisted physical vapor deposition. Cobalt and nickel are preferred binder metal components because they are compatible with the preferred core particle materials and the preferred interlayer materials and have excellent high temperature properties.

Another example of the invention is a sintered material. The sintered material is composed of a plurality of core particles consisting essentially of the formula M_aX_bThe first metal compound of (a). M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, boron and aluminum or M is silicon, X represents one or more elements selected from the group consisting of nitrogen, carbon, boron and oxygen, a and b are numbers greater than 0, up to and including 4.

The first metal compound is preferably predominantly stoichiometric and consists essentially of a metal selected from the group consisting of TiN, TiCN, TiB₂TiC, ZrC, ZrN, VC, VN, cubic BN, Al₂O₃And AlN or a compound Si₃N₄And (4) forming. This metal compound is hard and has some other useful mechanical properties, but has limited fracture toughness (ability to inhibit crack propagation). Other metal compounds may be used in the present invention, but the compounds listed above are preferred.

The composition of the different parts of the particles can be selected on the basis of conventional information (known properties of the candidate material macroscopically). For example, it is known that the diffusion wear of various materials can be evaluated by their standard free energy of formation at operating temperatures. WC, TiC, TiN and Al₂O₂The negative formation energy of (a) increases in order, and thus, the diffusion wear of TiN is significantly reduced compared to standard WC cermets.

In addition, the dissolution rates of the various abrasives in iron (a common workpiece) vary greatly over the temperature range of 1000-. Comparative tests show that the presence of a large amount of TiN on the tool surface ensures a large reduction in the amount of WC dissolved in iron; for example, at 500 ℃, the relative dissolution rates are as follows:

WC：5.4×10⁴

TiN：1.0

TiN：1.8×10^-3

Al₂O₃：8.9×10^-11

when WC is used with TiN cores, it is believed that these principles illustrate the improvement in grinding performance of WC tools when grinding iron; i.e., the exposed TiN core is less diffusion worn in iron than WC. It is believed that WC continuous particle coatings are necessary to obtain a strong shell and high mechanical properties (young's modulus of 696GPa compared to TiN, which has a young's modulus of 250 GPa). TiN core (Vickers hardness H)_vAs compared with 2350 WC, its vickers hardness is 2400, when compared to WC having a sliding friction coefficient μ of 0.200, μ of 0.125) will reduce the frictional wear to iron; the core will expose the surface of the tool after final grinding and polishing.

The core may also be composed of many different metal compounds, so long as the various compounds are compatible with and compositionally different from the coating material that coats the core particles. In this case, when a portion of the intermediate coating layer is removed to expose the core particles, the properties of the article composed of the sintered material are determined primarily by the properties of the core particles, their concentration in the sintered material, and a combination of the two. For example, if the sintered article is to be made into a cutting insert, the sintered article may be ground or shaped by EMD (electro discharge machining) to expose the core particles. In a preferred embodiment where the core particles are TiN and the intermediate layer is WC, the coefficient of friction, hardness and wear resistance of the TiN are imparted to the cutting insert, while the WC layer coating around the TiN core particles enhances the overall strength and crack propagation resistance of the cutting insert. It is clear that the wear of the cutting insert does not lead to a degradation of its properties, since TiN is not a coating to be worn. It is an integral part of the material of the cutting insert, which renews its surface when the material is worn. One preferred core material is cubic boron nitride (cBN), however, this example requires a particular grain size, and layer thickness to achieve the potential of cBN core grains. It is believed that the exceptional hardness of cBN must be incorporated into an article using a load bearing cap layer of another metal compound of a composition and thickness such that the multilayer particles formed after sintering have useful engineering properties as a structure in addition to their use as abrasives.

An example of this sintered material includes an intermediate layer consisting essentially of WC or W on each cBN core particle₂C, the composition is shown.

This example also includes an outer layer overlying the intermediate layer of coated particles. The outer layer serves to form a binder and agglomerate the coated particles into a dense sintered material at reasonable sintering times and temperatures. The outer layer functions as a binder, as described herein. It is composed of iron, cobalt, nickel, mixtures thereof, alloys thereof, or intermetallic compounds thereof. As described above in the description of the powder examples, the present invention applies this binder as a uniform coating in the form of a continuous layer on the outside of the metal compound particles.

The particle size of the core particles covered with the intermediate layer (the intermediate layer and the core are together referred to as coated particles) has a great influence on the mechanical properties of the sintered material and the articles made therefrom. As described above in connection with the powders, the coated particles preferably have an average particle size of less than about 2 microns, and more preferably less than about 1 micron. The thickness of the intermediate layer after sintering is preferably 5 to 25% of the diameter of the core particles. In addition, the thickness of the binder layer is also believed to affect the properties of the sintered material.

After sintering, the thickness of the outer binder layer is preferably 3 to 12% of the diameter of the coated particles.

Sintered materials having such dimensions are believed to have improved performance because the strain fields associated with dislocations in one coated particle are transported through the interlayer to the core particle immediately adjacent thereto. It is known that the present invention can use an intermediate layer having a thickness of 3 to 200% of the diameter of the core particle after sintering, but a thickness of 5 to 25% is preferable.

It is known that increased toughness is a common result of decreased particle size. The preferred particle size of the core is 0.1nm to 1.0 micron. This particle size range can be adapted to the thickness of the intermediate layer.

The strength of crystalline materials depends on the atomic bond and dislocation structure. Dislocations are linear defects of the atomic lattice, usually immobile. In a mixture of two atomically bonded crystalline materials, the upper and lower limits of the composite's modulus of elasticity can be calculated using the mixture rule and the inverse mixture rule. As the load increases, the material deforms elastically until dislocations in the particles begin to flow or slip, causing permanent flow and exceeding the limit of useful strength. At particle sizes of about 1 micron and less, exceptionally high strengths are produced in this material, primarily due to image dislocation stress.

A cylindrical strain field surrounding each dislocation point extends outward into the surrounding lattice. Theoretically, the strain fields around the dislocation points must be balanced by opposite strain fields, or the dislocations will be removed from the surface. When the crystal size is large compared to its strain field, no mirror stress is generated around the dislocation point unless at the crystal surface. In sintered materials where the binder agglomerates many crystal grains, the mirror stress matches the low strength of the binder matrix, but for larger crystals this is a minor correction, since most of the dislocation points are not close to the surface.

In submicron polycrystalline grains, the strain field may protrude into adjacent grains, and the atomic lattice of such grains may not be in accordance with the lattice orientation of the strain field grains. This balanced strain field protruding from the particle surface suppresses the movement of dislocations, thereby suppressing flow. When the particle size is further reduced, more dislocation points are close to the surface, and the strength is lowered.

It is believed that if the thickness of the intermediate layer and the thickness of the binder layer that agglomerates the coated particles into a sintered article are sufficiently thin, then the strain field actually penetrates through the binder matrix and into the adjacent particles. This results in high strength independent of the intermediate material (in this case the binder) between the hard coated particles. In other words, the mechanical properties of the sintered article are independent of the properties of the binder phase, assuming it is crystalline and very thin.

The thickness of the intermediate layer should also be sufficiently thick compared to the inner core to form a mechanical honeycomb support matrix throughout and around each core particle. In addition to this objective and the expected increase in mirror stress strength when using core particles of 0.1 microns and less, surprising strength properties can be obtained in sintered TCHP alloys, apparently due to a combination of particle size, core particle properties, and properties and thicknesses of the intermediate layer and binder.

The reason for this is not entirely clear, but the 5-10% thickness of the tungsten carbide (WC) coating of the 1.0 micron or smaller core particles is in fact very thin, as is itself a very small ductile phase particle (50-100 nm), but is effective to achieve mechanical properties on the order of submicron at much larger and more easily handled particle sizes.

TCHP structures having small hard core particle sizes and tough nano-shells are isolated by cobalt intermediate regions of less than 1 micron between the particles, thereby maximizing elasticity, hardness, fracture toughness and strength. Most interesting is the loss of "composite" properties in sintered TCHP mechanical properties due to the thin binder middle zone. Even with the use of low hardness materials such as cobalt, the mirror stress from near surface dislocations (all near the surface for submicron particles) can cause the composite performance to be higher than possible in abrasive composites. It is also possible that the structural strength of the honeycomb coating dominates, in fact approaching that of WC, when the binder matrix middle zone becomes very thin and the strength of the composite becomes independent of the plasticity of the cobalt binder.

The present invention provides a sinterable metal particulate material that optimally combines various properties (e.g., toughness, strength, low coefficient of friction, and hardness). There are three areas of operational improvement that can be expected in TCHP made dies and other tools: (a) lower coefficient of friction at the interface of the workpiece and tool, thereby reducing heat, wear and cratering, requiring less machining energy and the additional use of external lubricants, ultimately resulting in longer tool life and better machining control; (b) low reactivity with iron, reduced stickiness and diffusion, rib (flank) or die wear, thus extending the life of the die; and (c) a sintered tool microstructure with a tough, strong coating (e.g., WC) on the particles to provide the tool with a cellular supporting macrostructure while providing a well-fitting and tightly-adhering protective layer to the hard particle core (e.g., TiN), positioning it on the surface of the wear resistant tool, and allowing it to well expose and retain the hard phase.

This is in contrast to articles made by conventional methods where there is relatively low binder strength between the particles and the binder, toughness and flexural strength are reduced, or where the sintered article is fully coated to impart hardness (where thin coatings have limited life or can crack).

The hard phase alloy is placed internally as core particles (rather than externally) so that the hard phase alloy (exposed to the outer surface after polishing) is distributed throughout the sintered microstructure in a much larger proportion (or thickness) than any conventional material known. This in turn increases wear resistance, reduces chemical interaction with the workpiece and significantly reduces the coefficient of friction. The life of the tool is extended by constantly renewing the surface particles that are worn and pulled away by the opposing moving surface.

Also, the wear resistance and bonding characteristics of most preferred core materials are known from their performance in conventional materials, and thus their performance as core particles can be predicted in accordance with the present disclosure. Since the core particles are coated with known materials (e.g., WC), mixing and sintering together coated particles having several different core materials helps to enhance various properties. Thus, development and testing costs can be reduced while providing a final material with unique properties. This results in a sintered microstructure in which each particle has a tough shell (intermediate layer) which bonds very strongly to its neighbouring particles, forming a tough cellular support system throughout the sintered article substrate, making it possible for the sintered article to have an optimum combination of strength, high modulus of elasticity, fracture toughness and hard alloy capacity.

The resulting article microstructure has a cellular microstructure framework consisting of tough, strong, tightly inter-bonded, coated particle shells, each containing and supporting one or more mechanically and chemically bonded core particles, crystals, fibers or whiskers, with a cross-section that exposes the outer surface during final grinding and polishing. This principle of optimizing the combination of different materials as core particles and intermediate coating layers can combine generally conflicting article properties (e.g., strength and hardness) to a degree not previously seen in the powder metallurgy art.

This concept provides the material designer with a variety of tools (used alone or in combination) and straightforward methods to facilitate and overall control of TCHP particle structure (interlayer thickness, size, and core material) and blends (combining different powders within each region of the tool and article) to give them the appropriate properties to meet a variety of unique, comprehensive, and specific requirements with a single article or tool.

In addition, the use of standard robust materials (e.g., WC) as the tough outer particle shell introduction has significantly reduced the effort for research, development, and industrialization (effort) because only one substantial reactive precursor gas (e.g., tungsten carbide) is used to coat the powder particles, replacing many of the complex precursor and reactive gases used in multilayer substrate topcoats. Such particulate material will sinter like the material made from tungsten carbide particles, which are known to be strongly bonded to adjacent tungsten carbide particles by a binder such as cobalt. Thus, such standard ductile materials, which have been used for over 60 years, will penetrate and strengthen the entire structure. Increasing the thickness of the tungsten carbide coating on the particles to meet the more demanding strength applications, or decreasing the thickness for the more demanding wear applications, will solve most structural (design) problems. The particle size of the inner core can be easily increased to meet more stringent wear resistance requirements or decreased for higher strength applications. Different core particle materials, whose properties (hardness, coefficient of friction) are known or found to be good for particular applications (e.g. flank wear or crater wear), can also be used by selecting the core material. The above thickness, diameter and core material powder parameters can also be combined to address most multi-standard uses.

It is also possible to gradually transition the TCHP from a hard phase rich region or layer into a region or layer with more ductile interlayer material using a preheated extruded wax/powder unit (section). This is a more flexible and efficient method known than the methods used in the currently used Functionally Graded Materials (FGM).

The present invention can also be used to integrate different powder layers (or mixtures) in different parts of the same part to best address the problem of multiple properties. This is the limit of possible fine-design processing of microstructures in addition to atomic-scale gradients. TCHP, co-sintered with other material powders to form localized hardening in "non-hard" sintered parts, would allow steel parts requiring heat treatment to be replaced with powder metal (P/M) parts requiring fewer manufacturing operations.

The drawings are described in detail below, and fig. 1 is a schematic cross-sectional view of a sintered material. In this example, one or more hard metal compound particles (10) are provided with an intermediate layer (14) of a hard, tough metal compound, such as silicon carbide. The coated particles include an outer layer (16) of a suitable sintering binder, which is preferably an iron group metal, typically cobalt or nickel. The resulting coated powder (18) is finally sintered into a semi-finished or finished article, the microtome section of which is generally indicated by the numeral 20.

The microstructure of the sintered article (20) is a honeycomb structure of strongly interconnected monolithic WC layers (14), each WC layer containing and carrying its own tightly interconnected compound core (10) contained within a matrix (16) whose cross-section is exposed at the outer surface (22) during final polishing and grinding.

The scanning electron micrograph shown in fig. 2 is a single TCHP particle, which is coated with 1.6 micron titanium nitride core particles (6) and a layer thickness of about 0.25 micron (15%) W₂C layer (7). The particle is one of many TCHP particles that were placed on a resin metallurgy sample (shown in background (9)) and polished. It is known that hard alloy particles are often difficult to sinter close enough to theoretical density because (a) such particles are irregular (resulting in poor flowability and necessitating hot pressing) and (b) plastic deformation during solidification is small.

The 8-shaped core particles (6) in the test specimen generally showed a concave irregular shape. The CVD coating process fills the recess as generally described in (8), giving the coated particles a more rounded, smoother shape, in fact contributing to the flow and densification of the powder. This reduces processing costs, results in a more uniform and thin binder layer, and helps to densify the powder, thereby enhancing the mechanical properties of the sintered article.

The unique powders of the present invention are produced in a Chemical Vapor Deposition (CVD) reactor. Due to the size of the particles to be coated, the reactor comprises means to prevent agglomeration of the particles to be coated. Schematic diagrams of the reactor are shown in FIGS. 3-5.

The CVD reactor system of fig. 3 includes a CVD spin tank (20) housed in a furnace (22) for heating the powder and reactant gases that enter and exit the reactor through gas inlet (36) and outlet (26) tubes at opposite ends, respectively. The pipeline (30) is filled with tungsten hexafluoride (WF)₆) The precursor, line (28) supplies 99.999% pure hydrogen, and these two gases react in the reaction tank (20) to form a CVD coating, which is connected to the rotary seal and inlet line (36) by a flow meter (32). Line (28) also leads to a bubbler (34) containing 99.9% pure cumene. On the outlet side of the reaction tank (20) is placed a filter (38) which is located in front of the exhaust pipe (26) and which connects the exhaust pipe to a vacuum system (not shown), a trap device (40) and a flow meter (42). The reaction vessel (20) may be a refractory metal or graphite cylinder which can be rotated at different speeds in the range of 50-150rpm depending on the diameter of the cylinder and the specific gravity of the particles to be coated and the direction of the cylinder; thus, the tilt angle (24) and the rotation speed can be adjusted so that the coating powder has a suitable residence time in the resulting high temperature (500- & 1600 ℃) reactive gas environment.

There are four major problems in the manufacture of submicron TCHP particulate matter by CVD: (1) current tungsten hexafluoride (WF)₆) Cost of precursor gas, (2) control of WF₆The deleterious characteristics of (1), (3) premature reaction of the precursor on surfaces other than the core powder, and (4) de-agglomeration. The latter three have the technical proposal. Although the cost advantages of other processing steps may offset the first problem, the ultimate success of CVD will depend on its cost relative to other methods (e.g., deposition using metal carbonyls).

A solution to the third problem above (underutilization of reactants) was found to be to maintain the gas at a temperature below the reaction threshold until it approached the core particle. This process can be further improved by isolating the reactant gases, which are then mixed from the turbulent heated powder and mixed with the powder itself.

Microwave energy (but not induction frequencies) was found to heat the particles. Heating at a frequency of 2.45GHz for about 2 minutes at 500 watts may increase the temperature by about 37-40 ℃. The concept of heating the concentrated turbulent reactants at high rates by the powder itself (heated by microwave energy) in a circulating quartz tube is attractive to achieve uniform deagglomeration, mixing, circulation and coating of submicron powders.

Figure 4 shows a solution that was found to solve the problem of powder agglomeration. Fluidization in a rotating reactor generally does not apply the force required to break up the lumps, which are constantly re-agglomerated. In fact, without being inhibited, the agglomerates can be classified according to their particle size, further hindering uniform processing. In addition, conventional horizontal reactors have end regions that reduce the uniformity of the coating thickness of the batch. One way to address the problem of non-uniform agglomeration and end-capping of the coating is to tilt the reactor and install a fixed comb deflector (guide)80, as shown in fig. 4, to (a) recycle the batch material and homogenize it, and (b) apply sufficient shear to the powder to cause it to deagglomerate.

In the furnace, the reaction chamber (62) is made of graphite and lined with a quartz cylinder (60). The rotational speed (66) must be such that the gravitational force acting on the core particles is just greater than the centrifugal force, so that the falling powder particles are thus fluidized and maximally exposed to the reaction gas, on which the intermediate coating accumulates. The objective is to maximize the exposure of the core powder to the precursor gas by properly combining centrifugal force, gravity and the rotational inertia of the cylinder rotation to cause the core powder to flow, roll, cascade and tumble. This means that the actual diameter (64) is greater than 120 mm. To help break up agglomerates so as not to interfere with the deposition of a uniform layer on each particle, the added reactant gas can be passed through the falling powder at a high flow rate to break up agglomerates with shear.

Shear forces are applied doubly to the powder in two regions of the deflector (80), as shown by the shaded area (67) at the lower end of the drum. The first zone (68) applies a slight pressure and stress to the portion of powder as the rotating drums (60, 62) transport the powder below the deflector. A gradual crush angle (69) of 13 ° is formed between the drum and the support (67) which applies sufficient pressure to break up the agglomerates. The second zone (70) comprises long angled teeth (72) formed by the carrier itself, with the backlash cut into the stainless steel at right angles and the edges not chamfered. This zone (70) allows the compressed powder to escape with little shear force which causes the particles to further de-agglomerate and become uniform, exposing them for the next revolution. The taper angle of the stent teeth ends at an inflection point at 5mm (74) from the quartz liner (60) to increase the compressive force as the opening of the teeth (72) reaches their maximum. A small gap (76) of 0.5-1.0mm protects the quartz from being scratched by the holder.

The helical region (80) of the support forms a flow director (78), as shown at the lower end of the reactor, (and as shown by the dotted line at its upper end). The helical deflector provides lift to the powder to ensure lateral circulation and batch uniformity.

Fig. 5 shows the helical stent to more clearly show the helical deflector (80). Holes (92) are cut in the upper platform to allow the powder it collects to pass through for repeated circulation. The teeth (90) of the bracket are also more clearly shown in the figure.

As presently contemplated, a preferred embodiment of the present invention uses a pre-milled particulate core powder composed of titanium nitride. The powder was CVD coated with an intermediate layer of tungsten carbide. Preferably, a cobalt binder is used for sintering. In the TiN/WC/Co system, W has good solubility in Co, and C and TiN react effectively to form Ti (C, N), forming a strong TiN/WC grain boundary phase and excellent mechanical properties in the sintered article, although the bond is weaker than the bond formed between W and Co.

TiN is phase-locked within the material and does not degrade as a result of surface wear as is the case with conventional tools protected with ceramic coatings. Thus, dies, tools, or other hard articles made with such TCHPs can be reused for larger diameters or reground for other uses. If it is later decided that the Ti (C, N) interfacial layer must be reduced to increase the effectiveness of the binder, the sintering time and temperature can be reduced by increasing the thickness of the WC coating and vapor depositing the binder on the particles. On the other hand, Ti (C, N) has a Vickers hardness of 3200 significantly harder than TiN with a Vickers hardness of 2400 or TiC with a Vickers hardness of 2800. This may prove beneficial in certain applications. Zirconium nitride (ZrN), which is harder than TiN, has a lower coefficient of friction 2/3 than TiN and performs better in terms of facet wear. It is also a preferred core material.

FIG. 6 is a compilation of a series of workplaces of conventional tool material and an example intended workplace for use as a cutting tool material in accordance with the present invention. The TCHP of the present invention can broaden the operating range of conventional hard materials by using these materials as the core, reducing the particle size to the desired range, and applying a tough coating (e.g., WC) of appropriate thickness over the core. The degree of increase in feed speed (i.e., the limit to the right of the area defining the working zone of the present invention) is determined by the increased toughness resulting from the tough coating and the hardness and other properties of the core material.

The sinterable composite particulate material used in the present invention can be made using a reactor system such as that shown in FIG. 3, using the following various powdered alloys having a diameter of 1.0 to 1.5 microns: titanium nitride, titanium carbide, zirconium nitride, vanadium carbide, alumina, and cubic boron nitride. Other alloys, such as titanium diboride, zirconium carbide, tantalum nitride, and niobium carbide, may also be used. For depositing WC_xThe active ingredient of the chemical gas of (2) is tungsten hexafluoride (WF) in the presence of hydrogen₆) And aliphatic or aromatic carbon-containing compounds, which react at a temperature of 500-700 ℃ to form WC with high reproducibility_xAnd (4) coating. A low pressure (e.g. less than 100 mbar) may be used in the reactor to enhance diffusion of the reactants in the gas and to form a uniform coating on the powder surface. This technique is commonly referred to as LPCVD (low pressure chemical vapor deposition). The rotation speed of the reactor is sufficient to make the core powder roll in a continuous self-falling avalanche mode, and the speed of the active gas is adjusted according to other parameters (pressure and total flow rate); in the case of using an aromatic liquid compound as an active ingredient, a gas bubbler may be used.

If the required strength is full WC_x90-95% of the cemented carbide, with a target coating thickness of 2-25% of the average grain size based on minimum CVD residence time. Using a computer program, CVD operating parameters are adjusted to optimize them according to a primary "indicator", e.g., according to WC, at various points in the reactor_xCoating thickness. Comparing the intensity peaks of tungsten and titanium and the W measured at different points and times in the furnace by EDX microscopy of the treated powder_M∶Ti_KRatio of M and K, where M and K are atomic proportionality coefficients, to estimate the WC deposited on the powder_xThe amount of (c). This provides uniformity, deposition rate and WC prior to sintering_xSurface and WC_xInformation of/core particle interface properties. Observation of WC on a specimen with TCHP particles embedded in resin and polished exposed particle cross-section using an optical microscope and a scanning electron microscope_xThe cross-sectional thickness of the coating; x-ray analysis can also be used to show the presence of WC on the powder_xAnd (4) phase(s).

Examples

Three groups of sintered samples were prepared: a group of WC coated with_xOf titanium nitride particles (inventive sample, formulations C, D, E and F), a group of uncoated tungsten carbide powders (reference bar, formulation A), a group of comparison made of a mixture of uncoated tungsten carbide powder and TiN (formulation B), and coatings of TiN, TiC and Al₂O₃Standard Sandvik material (formulation G, see column 7G).

Tungsten carbide (WC) used to prepare each formulation was purchased from h.c. starck Company, grade DS100, and a typical average particle size was about 1.0 micron (+ -0.1 micron). The cobalt powder used was Starck II grade, with a typical average particle size of 1.5 microns (+ -0.2 microns); the titanium nitride powder used was Starck C grade, with a typical particle size of 1.0 micron (in the range of 0.8-1.2 microns); the nickel powder used is commercially available with a typical particle size of 2.2 microns.

The inventive formulation comprises TiN core particles, CVD coated with tungsten carbide (W) having a thickness of about 0.16 microns₂C) Formed to a particle size of about 1.0 micronThe composite particulate material (TCHP). The TiN powder was CVD coated using the apparatus described above with reference to fig. 3-5. The apparatus was run at a 20 ° helix angle and the comb was fixed at a 13 ° compression angle. Adding a proper amount of TiN powder into a reaction chamber of a graphite reactor. The system was purged and the flow of hydrogen was started, and the internal pressure was adjusted to 11.25 torr. Subsequently, the electric furnace was powered on, the reaction drum rotated at 90rpm was heated to about 550 deg.C (about 1 hour), and WF was then turned on₆And a cumene bubbler flow meter to adapt the molar ratios of the reactants for W deposition on TiN substrate powders₂C; the bubbler was operated at 20 c using hydrogen as a carrier gas for the liquid cumene. The duration of the operation is sufficient to form the desired W on the TiN particles₂Thickness of C, followed by closing of WF₆The flow meter and cumene bubbler, and the furnace was cooled under hydrogen.

Formulation a is a binary mixture consisting of 94 wt% WC and 6 wt% Co; formulation B is a ternary mixture consisting of 87 wt% WC, 6 wt% Co and 7 wt% TiN; formulation C was composed of 84 wt% of the TCHP complex and 16 wt% Ni; formulation D was composed of 84 wt% TCHP complex and 16 wt% Co; formulation E consisted of 90 wt% TCHP complex and 10 wt% Co.

Formulation B is a sintered rod of size 53X 16X 11mm weighing about 130 grams and was sintered by mixing the formulation with Acrawax C (an ethylenebisstearamide processing aid available from Lonza Inc., of Fair Lawn, NewJersey) and hexane, ball milling with WC balls for 16 hours, vacuum drying, 300 micron screening, cold pressing at 2000 bar isostatically for 5 minutes and holding at 1450 ℃ for 20 minutes under vacuum of 1-3 torr. The heating and cooling rates were 150-.

Sample discs were made from formulations A, C, D, E and F. The preparation is prepared by mixing the formulation with a camphor temporary binder and an ethanol solvent, ball milling with a tungsten carbide ball planetary (planet) for 5 minutes, drying at 80 ℃ for 15 minutes, and sieving at 300 μm. For samples A, C and D, discs were made with a diameter of 10mm and were described above for samples A and BSintering under vacuum condition. To produce samples E and F, 200kg/cm were measured at 1400 deg.C²The ball-milled, dried and sieved formulation was pressed under uniaxial pressure to form 50mm diameter discs.

A series of samples of the various sintered articles described above were tested to evaluate various properties. The formulation, sintering conditions (vacuum or hot pressing), article shape (rod or disk), binder content after sintering and various measured performance values are shown in figure 7. The measurements of facet wear and crater wear were carried out on standard material (CK45) at a tangential surface speed of 200m/min, a 2mm deep cut and a feed speed of 0.2 mm/rev. The values of hardness, flexural strength and modulus of elasticity of sample 1 are from the literature. In the above embodiments, the metal powders of the sintered samples of the present invention are particularly useful in the manufacture of tools and other articles, as described herein.

It is apparent that the properties of the particulate material and articles made therefrom can be highly controlled by varying not only the metal components (including the auxiliary binder or sintering aid) used to make the sinterable particulate article of the present invention, but also the relative thicknesses of the core particles and the overlying intermediate layer. For example, varying the thickness of the outer shell (e.g., typically, but not necessarily, by 5%, 10%, or 15% of the diameter of the TCHP particles) can provide a good compromise between hardness, toughness, strength, abrasiveness, and heat transfer capability, and impart these properties to the sintered article.

The present invention provides a new class of powder materials, namely ductile coated hard powders (TCHPs), which combine the inherent transverse mechanical strength of metal carbides (or corresponding ductile metal composites) with the superior wear resistance of the hard metal compounds in the core particles to produce sintered articles having overall properties that exceed those of conventional materials. The tool or article made from this material has better performance in a wider range of conditions than the current proprietary methods allow, and its performance/cost ratio or value ratio is also significantly improved.

The invention has been described above using examples and preferred embodiments. It is not intended that the scope of the invention be limited thereto, but rather by the claims appended hereto and their equivalents.

Claims (17)

1. A material, comprising:

a plurality of core particles, said core particles consisting essentially of one or more metal compounds, said metal compounds comprising a compound of the formula M_aX_bWherein M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and aluminum or M is silicon, X represents one or more elements selected from the group consisting of nitrogen, carbon, boron, and oxygen, a and b represent a number greater than 0, up to and including 4;

an intermediate layer on each of said core particles consisting essentially of a second metal compound having a different composition than said first metal compound, said second metal compound having a higher relative fracture toughness and being capable of bonding with said first metal compound and also being capable of bonding with iron, cobalt or nickel to form coated particles; and

a layer of binder overlying said coated particles with an intermediate layer, the outer binder layer comprising iron, cobalt, nickel, mixtures thereof, alloys thereof or intermetallic compounds thereof.

2. The material of claim 1, wherein said coated particles have an average particle size of less than about 2 microns.

3. The material of claim 1, wherein said coated particles have an average particle size of less than about 1 micron.

4. The material of claim 1, wherein the material is dense and heated to form a sintered material.

5. The material of claim 4, wherein the thickness of the intermediate layer after sintering is between 5 and 25% of the diameter of the core particles.

6. The material of claim 4, wherein the thickness of the interlayer is such that strain fields associated with dislocations in one coated particle pass through the interlayer into the core particle immediately adjacent thereto.

7. The material of claim 4, wherein the thickness of the intermediate layer after sintering is from 3 to 200% of the diameter of the core particles.

8. The material of claim 4, wherein the thickness of said outer layer after sintering is from 3 to 12% of the diameter of said coated particles.

9. A material according to claim 4, wherein the outer layer has a thickness such that the strain fields associated with dislocations in one coated particle pass through the binder and into the intermediate layer directly adjacent thereto.

10. The material of claim 1, wherein the first metal compound consists essentially of a stoichiometric compound.

11. The material of claim 1, wherein said first metal compound consists essentially of a metal selected from the group consisting of TiN, TiCN, TiB₂、TiC、ZrC、ZrN、VC、VN、Al₂O₃And AlN or a compound Si₃N₄And (4) forming.

12. The material of claim 1, wherein the second metal compound consists essentially of WC or W₂C, the composition is shown.

13. The material of claim 1, wherein portions of said intermediate layer and said binder are removed to expose interior portions of said core particles.

14. The material of claim 4, wherein the fracture toughness of the sintered material is greater than the fracture toughness of cubic boron nitride.

15. The material of claim 1, wherein said material is a powder comprising said core particles, each core particle having said intermediate layer and each having said outer layer of adhesive on said intermediate layer.

16. The material of claim 15, wherein said binder outer layer consists essentially of a metal selected from the group consisting of iron, cobalt, nickel, mixtures thereof, alloys thereof, or intermetallic compounds thereof, and said binder layer is deposited as a continuous layer on the outer surface of said second metal compound layer.

17. The material of claim 15 wherein said outer binder layer is deposited by chemical vapor deposition, cathodic sputtering, carbonyl deposition, solution spraying, electroless plating, electroplating or physical vapor deposition.