Tough-coated hard powders and sintered articles thereof

Technical field

The present invention relates to ceramic powders and sintered materials made from such powders. Such materials find specific use as metal forming components such as metal cutting and forming tools.

BACKGROUND OF THE INVENTION

During the mid-1930s, alloyed tool steels began to be replaced by sintered tungsten carbide powders, which quickly became the standard for their extraordinary hardness and high inherent toughness and mechanical bending strength. The hardness of such materials improved tool life and toughness and strength helped to increase productivity by allowing higher feed rates, speeds and more active forming parameters. The development of carbide tools and commercial availability increased considerably after World War II.

Even these materials eventually wear out and the mechanisms of such wear are not yet fully understood. Progressive wear causes a change in the materials being formed, and as a result of the need to maintain the dimensional tolerances of the part, the tool must be replaced when it is no longer able to mold the part to the correct dimension. The time or number of parts reshaped before such an event definitely determines the tool life limit. Subsequent loss of productivity during tool change and process re-managed as well, mismatched manufacturing, remodeling and missed completion dates were the determining force for obtaining materials that would provide longer tool life.

Tool life is determined by its resistance to multiple types of wear, its sensitivity to heavy loads and impacts. In general, the higher the chip removal rate (high feed rates and speeds), the tensile and forming pressures, and the long-lasting geometry of the tool, the better the tool is. At the same time, better quality cutting and forming tools must be hard, strong, rigid and resistant to chipping, breakage, thermal failure, fatigue, chemical reaction with the workpiece and abrasion wear. Accordingly, the desired mechanical properties sought for in the sintered tool are the strength, hardness, high modulus, fracture toughness, low chemical interaction with the workpiece and low coefficient of friction with the workpiece forming aid to reduce heat generation.

In recent years, the powder metallurgy industry has grown considerably, due to the ability of powders to flow cold into precision molds. This allows the mold to be reused, often to a large extent, dramatically reducing machining, forming and other process steps, since the sintered part is already very close to its intended outer shape or has an "almost pure shape". These parts, now produced more and more from aluminum, iron and copper powders, require some of the same desirable features as tools. For this reason, many powder metallurgy products undergo additional forging, plating or heat treatment operations to induce local hardness, toughness and strength. Many of these parts require impact and abrasion resistance, reminiscent of the same mechanical properties required for tools.

For tools and hard products, wear resistance is increased at the expense of strength. Today, the best tools show the best compromises and are therefore limited to use for special applications.

In addition to tungsten carbide, it has been found that not only allow longer tool life, but also increased cutting speeds and feeds of various alloys, coating techniques and combinations thereof. Powder metallurgy and sintering has led to the development of new materials with increased hardness and toughness and the addition of a hard coating to the sintered alloy, such as chemical vapor deposition (CVD), physical vapor deposition (PVD) or plasma assisted chemical vapor deposition (PACVD), increased wear resistance.

- 1 GB 302016 B6

There are many teachings in the art about the preparation of coatings on powders, coating substrates and other improvements of hard materials. The state of the art for tooling materials provides a lesson of six approaches that are now known and generally used to achieve such improved wear resistance and toughness, each with significant benefits and significant disadvantages: (1) mixing of hard and tough phase particles, (2) chemical or other vapor deposition coatings of sintered substrates with hard phase fibers, (3) combining approaches one and two, (4) cermetal moldings, (5) for special type tools (abrasive and sand media) chemical bonding of low concentrations of large diamond or cBN particles to a hard but relatively weak abrasive substrate; and (6) Functionally Grading Materials (FGM).

None of these solutions has produced a significant combination of the required tool properties, and for some mechanical parts requiring increased abrasion resistance, only chemical vapor deposition (CVD or PVD) coating is applicable today.

Mixing of hard and tough terrain systems

Despite the many auxiliary modifications and variations that exist and are discussed in the prior art, mixing hard particles of WD-TiN-Co alloy with carbide powder has several drawbacks before sintering. Since these harder particles have little mutual solubility with the binder, the bending strength of the substrate decreases rapidly above 6 to 10 percent by weight of the hard particles. Accordingly, the surface hardness and wear resistance are also reduced compared to the surface coating. Also, the wear mechanism is not significantly improved because few hard particles (less than one in ten at the surface where they are needed) glued weakly to the binder break out whole.

Chemical Vapor Deposition (CVD) Coatings

These hard outer coatings of hard intermetallic and cermet layers on tool steels or substrates of sintered products (after sintering) are valued for the high surface hardness they impart to them, which typically gives 2400 Vickers (TiN) to 5000 Vickers (cubic boron nitride) and up to 9000 (diamond). However, for all of these auxiliaries, combinations and sintering aids that exist and are disclosed in the prior art, including additional coating layers, locally treated substrate structures and accelerating or retarding agents to reduce grain size or finishes, the exterior coating solution has several major disadvantages including layer fracturing and cracks in use (from different thermal expansion rates of the coating and substrate and from bending and surface loads) and the required high CVD process temperatures (900 to 1200 ° C) cannot coincide with heat treatment required for the strength or geometry of the sintered part.

A conventional CVD coating of already sintered articles with several different coatings or layers allows them to withstand the challenges of two or three workpieces. However, since each layer must be deposited sequentially, one or two of the remaining special coatings must remain coated until the outer layers become blue. Thus, at the same time, only one of the competing challenges for substrate coating can be met.

Some categories of tools, such as punches and injection nozzles, are even more costly because there are additional costs to ensure that CVD vapor is circulated sufficiently through the hole of the punch to apply the coating where it is most needed. CVD gas diffusion is slow and the penetration is typically 0.5 to 10 microns or less. First, at these thicknesses, the coating is consumed down to the backing carbide before most of the wire or tube diameter tolerance is consumed. Secondly, normal re-use must be accomplished without this hard coating after use of the punches at larger diameters. In many cases, the overall tool life extension cannot be proportional to the additional cost of the CVD.

-2GB 302016 B6

Today, outer coatings are the most general commercial solution to improve the performance of simple sintered tungsten carbide products. Increasing the deposited thickness of the outer layers to obtain a longer service life has limiting responses. It tends to increase the susceptibility to cracking and rounding the sharp edges of the tool, which adversely affects the optimum cut or die geometry.

Combined mixtures and coatings

The CVD coating and the mixing of the cemented carbide particles, i.e. the combination of the above (1) and (2), gives a very limited additional benefit while having the same drawbacks.

Cermety

Cermets are ceramic particles dispersed in a metal oxide or carbide matrix. Cermets combine the resistance of ceramic materials to high temperatures with toughness and ductility as well as carbides. They are valued about as much as plain tungsten carbide, and wear is about the same, apart from fine finishing machining where it performs better than plain carbide.

Sintered abrasive mixtures

The fourth approach discussed in Dr. Randall M. German "Sintering of the liquid phase". Plenum

Press, New York 1985 (and practiced in Russia many years earlier) creates a class of super-abrasive compounds for abrasive and sanding media and niche deposition tools.

Such mixtures are made by mixing diamond particles (or cubic boron nitride, cBN) 25 and cobalt powders or trapping them in a galvanized (nickel) deposit and compressing them at low temperatures. One alternative is to coat the diamond (or cBN) with some intermediate layer of a transition metal carbide carcass that wets the diamond and chemically bonds it to other low melting, but malleable, low melting metal binders such as cobalt, iron or nickel. The transition metal is applied only as a chemical bridge at thicknesses not intended to transmit structural mechanical loads. The metals used as the main binder matrix have good sinterability, but relatively low melting points, modulus of elasticity and strength. Such materials have desirable properties in abrasive applications. In most of these applications, the diamond represents 10 to 60 percent by volume of the composition. The binder coatings are several micrometers thick to aid processing at low temperatures (to avoid graphite degradation of the diamond) and dilute the diamond content, but with greater loss in mechanical properties. The properties of these mixtures are determined by chemical agents, not by mechanical agents of modulus of elasticity, strength or fracture toughness. Accordingly, by the large particle size of the diamond and the high concentration of binder, the mechanical properties of the mixture are determined by the mixture rule. These mixtures are selected to ensure that the diamond particles in the final microstructure 40 are separated, ensuring that there may be few diamond-diamond interactions. There is a small increase in mechanical advantages as found in one micrometer according to the nanoscale of the sintered carbide grain size range.

The requirements for abrasive tools are relatively large grains (50 to 600 microns) to increase metal removal, adherence of these particles to the wheel, adequate clearance between the particles (low particle concentration with large binder phase bands) to allow removal of workpiece cleaner, and long retention grinding wheel geometry. Such materials form metals by removing the workpiece due to the shear differential between the abrasive particles and the workpiece itself. Such abrasive compounds are sometimes used in cutting tools used in machining particularly high-hardness materials at relatively high speeds, but at a very low chip removal rate (see Figure 6). The rough action of diamond cutting tools is very different from that of cemented carbide tools. Cutting diamonds or composites in cutting tools stems from their cutting behavior. Such composites work as abrasives, where they generally carry out a gradual drift of the workpiece rather than chip removal under high load. With this

The method is a very hard diamond particle held by a tensile binder. When sliding over a workpiece, the diamond is subjected to cutting the opposite surface, but resists wear, while the matrix prays and progressively exposes the diamond. It is a protruding diamond that makes a cut as long as it remains sharp. When the diamond dulls, it rounds and the matrix is ​​designed to fall out.

In this way, the diamond is pulled out by the workpiece and the matrix prays until another diamond is exposed.

Such hard, brittle abrasive composites are also used in some tool-like applications such as chisels and masonry saws. They can also be found in high cost wire drawing punches and some cutting tools where their performance is tolerated due to the presence of steel or other solid reinforcement.

Functional Gradient Materials (FGM)

The problem with coated products is the incompatibility between the mechanical, chemical or thermal properties of the layers. To remedy this problem by providing a gradual transition between the incompatible layers, the FGMs have one or more of the following variable parameters: chemical composition, microstructure structure, density, or variable forms of the same material. Another object is to change the electrical, thermal, chemical or optical properties of the sub20 strata to which FGM is applied as a coating layer. Substantial drawbacks of such materials are their tendency to sag at places where these properties change, and difficulties in manufacturing such materials.

SUMMARY OF THE INVENTION

It is an essential object of the present invention to provide sinterable materials in the form of particles called Tough Hard Powder (TCHP), which provide added value over the carbide product and tool materials known today. These particles and products made from them combine the best mechanical properties in strength, hardness, high modulus of elasticity, fracture toughness, low interaction with the workpiece and low coefficient of friction, which exist separately for conventional materials, into one product of incomparable properties.

Another object of the invention is to reduce the cost of providing such materials to users. For example, tool inserts must be provided in many geometric variations in order to fit into a series of tool holders. In addition, the tooling materials available today must be designed for high-precision, defined applications. Therefore, material selections (uncoated, CVD coated, PVD coated, cermet, ceramic, polycrystalline cBN, polycrystalline diamond) must be offered for each of these geometric variants. The combination of geometric and material variants requires costly catalogs, unnecessary tooling richness, costly suppliers, and user inventory with specific packaging and labeling, and the business effort to explain and sell the mesh assembly to users. It is a further object of the present invention to reduce the waste and costs associated with the present system by providing a more general intention for higher performance tools at justifiable costs.

In addition, the process of making an embodiment of an article of the invention aims to reduce the cost of manufacturing articles made according to the invention.

Another objective is to provide a significant cost reduction by extending the initial product life and reducing the manufacturing cost of the products concerned. The fact that the products of the present invention are macroscopically homogeneous rather than coated, offers users or suppliers the opportunity to economically re-grind and reuse the initially worn pieces.

Yet another object of the invention is to provide the same high representation of the mechanical properties of the materials of the present invention relative to other applications on hard metal pieces.

-4E 302016 B6

It is a further object of the present invention to provide a material that has improved wear resistance and toughness for use in a wide range of products including machining (such as broaching dies, die, die, die punches, dies, forging rolls, injection molds, shears, drills). , milling cutters and lathe cutting tools, saws, punches, broaching darkness, reamers, taps and dies); separate mechanical parts (such as gears, cams, bearing pins, injection nozzles, seals, valve seats, pump impellers, turret heads, pulleys, bearing and raceway surfaces); integrated sintered components to replace fasteners (connecting rods of internal combustion engines, bearings) and / or to provide hard surface areas in mechanical parts of powder metals (P / M) replaced by forged or machined steel parts with heat-treated zones (such as camshafts, transmission components, parts of printers / copiers); heavy industry products (such as deep hole drill bits, teeth for mining and earthmoving equipment, hot-rolling rolls for steel mills); and electromechanical components (such as memory drive read heads, special magnets). In addition to providing such novel products, it is essential to provide novel particulate composite materials (i.e., TCHP), new methods of making such materials, and novel methods of making articles of such materials.

The aforementioned drawbacks of the state of the art are overcome and the achievement of these and other objects is achieved by a sintered material comprising a plurality of core particles according to the invention, which consists in the core particles consisting of a first metal compound having the_andX_b. M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum and silicon. X represents one or more elements selected from the group consisting of nitrogen, carbon, boron and oxygen; and (a) and (b) are numbers greater than zero up to and including four. One intermediate layer surrounds each of the core particles and consists essentially of a second metal compound, a composition different from said first metal compound. This second metal compound has a greater relative fracture toughness and is capable of binding with the first metal compound and is also capable of binding with iron, cobalt or nickel. The core particle with the intermediate layer on it forms a certain amount of coated particles. One outer layer overlaps the intermediate layer on the coated particles and acts as a binder. It consists of iron, cobalt, nickel, mixtures thereof, their alloys or their intermetallic compounds.

The coated particles preferably have an average size less than about 2 µm, and most preferably less than about 1 µm. It is also preferred that the intermediate layer has a thickness after sintering in the range of 5 to 25% of the core particle diameter. It is also preferred that the outer layer of binder has a thickness after sintering in the range of from 3 to 12% of the diameter of the coated particles. With such a thickness of the outer layer, it is believed that stress fields associated with offsets of one coated particle are transferred through the outer layer of binder to the immediately adjacent intermediate layer. Preferably, the first metal compound consists essentially of a stoichiometric compound such as TiN, TiCN, TiB₂, TiC, ZrC, ZrN, VC, HV, cBN, A1₂O₃, Si₃O₄ or A1N. It is also preferred that the second metal compound consists essentially of WC or W₂C and most preferably from WC. Such materials have a fracture toughness greater than cubic boron nitride.

One preferred embodiment of the sintered material comprises core particles consisting essentially of cubic boron nitride with an intermediate layer on each of the core particles consisting essentially of WC. The intermediate layer has a thickness after sintering in the range of 5 to 25% of the diameter of the core particles. The outer layer, which comprises cobalt or nickel, overlaps the intermediate layer, and the outer layer has a sintered thickness ranging from 3 to 12% of the diameter of the coated particles. This combination of core particles, intermediate layer and outer layer forming the coated particle preferably has an average particle size of less than about 1 µm.

Another embodiment of the present invention is a powder consisting essentially of a plurality of coated particles. Most of these coated particles have core particles consisting essentially of a first metal compound having the formula M_andX_b. M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum and silicon.

-5GB 302016 B6

X represents one or more elements selected from the group consisting of nitrogen, carbon, boron and oxygen; and (a) and (b) are numbers greater than zero up to and including Four. The core particles coated with a surrounding layer consisting essentially of a second metal compound different in composition from said first metal compound and having a higher relative fracture toughness. This layer is also capable of bonding to the first metal compound and is also capable of bonding to a metal selected from the group consisting of iron, cobalt and nickel. These coated particles preferably have an average particle size of less than about 2 µm and most preferably less than about 1 µm. It is also preferred that the layer surrounding the core particles after sintering has a thickness ranging from 3 to 200% of the diameter of the core particles.

Preferred mixtures of core particles and surrounding layers (intermediate layer) are the same for making powders as for the sintered article.

It is also preferred that the outer binder layer consists essentially of cobalt, nickel, iron, mixtures thereof, their alloys or their intermetallic composites deposited on the outer surface of the layer of the second metal compound in the form of a continuous layer.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to provide a further understanding of the invention, the accompanying drawings, which are incorporated in and represent a part of the background and together with the description, serve to explain the nature of the invention.

Giant. 1 is a schematic representation of a sintered material formed according to one aspect of the present invention.

Giant. 2 is a photomicrograph of 20,000x magnification of a sintered material produced according to one aspect of the present invention.

Giant. 3 is a schematic illustration of a powder forming apparatus according to one aspect of the present invention.

Giant. 4 is a schematic illustration of the interior of the apparatus of FIG. 3 showing the movement of particles within such apparatus during deposition of the intermediate layer by chemical vapor deposition.

Giant. 5 is an end view of one component in the preferred embodiment of the apparatus of FIGS. 3 and 4.

Giant. 6 is a graphical representation of the working area of ​​the sintered material of the present invention when used as a cutting tool relative to conventional materials.

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

DETAILED DESCRIPTION OF THE INVENTION

As specified herein, the present invention is a new type of powder material. In accordance with the invention, the powder is composed of a plurality of core particles. These core particles are intended to impart their physical properties to the entire powder structure. As specifically expressed herein, the core particles consist essentially of a first metal compound having the formula

M_andX_bwherein M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum and silicon, and X represents one or more elements selected from the group consisting of nitrogen , carbon, boron and oxygen, and the letters a and b represent digits greater than zero and up to four. Such metal compounds are hard, wear resistant and chemically resistant to most environments and workpieces. Significant to the present invention is that the core material can be stripped, such as where the powder is sintered to form a cutting tool, the sintered product is shaped to form the final product by grinding, lapping and polishing. This removes the intermediate layer of material on the core particles and exposes the core of the particles to be machined. As will be explained more fully below, this is a significant advantage.

As specifically disclosed herein, core powder particles consist essentially of at least one stoichiometric compound. In some embodiments, the core compounds are different to impart the properties of the various core particles to the articles formed therefrom. Preferably, the metal core compound consists essentially of a metal compound selected from the group consisting of: TiN, TiCN, TiB₂, TiC, ZrC, ZrN, VC, HV, cBN, A1₂O₃, Si₃N₄ and A1N. Such materials may be used in the form of commercially available powders, needles, or needles. whiskers, crystals, fibers or the like, since the shape of the core particle can be an important technique. The core particle is coated with a layer of another metal compound designated an intermediate layer. Thus, the core particle material must have a degree of compatibility with the intermediate layer material that is applied to it, and should have a composition different from that of the intermediate layer.

A particular embodiment of the powder of the present invention comprises an intermediate layer applied to the outer surface of the core particle. The intermediate layer essentially consists of a second metal compound, i.e. a compound different from the first metal compound forming the core of the particle. The compound of the second, intermediate layer has a higher relative fracture toughness than the core material. In addition, the second metal compound must be capable of bonding to the first metal compound and must be capable of bonding to iron, cobalt, nickel, mixtures thereof, alloys thereof or intermetallic mixtures thereof. Preferably, the second metal compound consists essentially of WC or W₂C. As will be shown below, the combination of a relatively tough and thick intermediate layer and a hard core provides a powder and a sintered material formed therefrom with outstanding mechanical properties. This is also the case with the size and thickness of the coated particles. Specifically, particle sizes and layer thicknesses provide properties that are not calculated by the classical rule of mixture calculations. This will be more fully described in the section relating to sintered articles. In any case, it is preferred that the coated particles have an average particle size of less than about 2 µm, and most preferably less than about 1 µm. It is also preferred that the intermediate layer has a thickness ranging from 5 to 25% of the diameter of the core particles.

The thickness of the intermediate layer has a considerable effect on the mechanical properties of the articles made therefrom. It is believed that when the coated particles (core with intermediate layer on top of them) have an average particle diameter as measured graphically in a cross-section micrograph using a medium free path method, less than about 2 µm, the resistance to displacement movement is within increased sintered particles, which improves the mechanical properties of the sintered product. Even using a classical mechanical approach that utilizes finite elemental analysis, it is apparent that increasing the thickness of the WC spherical shell surrounding the TiN sphere from about 0.1 to about 0.4 µm increases the theoretical toughness by over 40%.

It is further preferred that the intermediate layer has a thickness prior to sintering in the range of 3 to 200% of the core particle diameter. During sintering, there may be a reduction in the thickness of the intermediate layer due to interaction with the core material, particle / particle interaction, grain boundary and growth phenomenon. Thus, it may be necessary to have an initial thickness of up to 300% of the core particle diameter to achieve the desired thickness of the intermediate layer in the final sintered product.

One preferred powder would have an outer binder layer applied thereto. Usually, metal binders are applied to the metal compound particles by grinding them with metal powders. This physical operation is long and when only a minor percentage of powders to be ground (eg 6%) from the binder metal adversely affects the time to coat the binder metal on the surface of the remaining binders.

94 % of the particles can damage the economy of forming sintered articles using metal binders

-7EN 302016 B6 coated particles. The present invention contemplates applying such particles as a uniform coating to the outer surface of the particles of the metal compound in the form of a continuous layer. In accordance with the invention, the binder layer consists essentially of a metal selected from the group consisting of: iron, cobalt, nickel, a mixture thereof, their alloys and their intermetallic compounds. Preferably, the continuous binder layer is deposited by chemical vapor deposition, spraying, electroless plating, electroplating, physical vapor deposition, carbonyl deposition, solution spray deposition, or plasma assisted physical vapor deposition. Since cobalt and nickel are compatible with the preferred core material and intermediate layer materials and have exceptionally high thermal properties, they are preferred binder metal compounds.

Another embodiment of the invention is a sintered material. Such a sintered material is composed of a series of core particles consisting essentially of a first metal compound having the formula M_andX_b. M is a metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, boron, aluminum and silicon. X represents one or more elements selected from the group consisting of nitrogen, carbon, boron and oxygen and and b and b are numbers greater than zero up to and including four.

Preferably, the first metal compound is predominantly stoichiometric and consists essentially of a metal compound selected from the group consisting of: TiN, TiCN, TiB₂, TiC, ZrC, ZrN, VC, HV, cubic BN, A1₂O₃, Sí₃N₄ and A1N. Such metal compounds are hard, have some other useful mechanical properties, but have limited fracture toughness (the ability to stop a propagating crack). Other metal compounds may be useful with the present invention, but the above compounds are preferred.

The selection of compounds for the various parts of the particles can be based on conventional information regarding the known characteristics of the candidate materials at the macro level. For example, it is known that diffusion wear for various materials can be estimated by considering their standard free energy generation at working temperature. Taken into account, WC, TiC, TiN and A1₂O₃ As more and more negative energy is generated, it can be seen that TiN provides significantly reduced diffusion wear compared to standard WC cermets.

In addition, the solubility rates of various tool materials in iron (typical workpiece) at temperatures ranging from 1000 to 1100 ° C differ significantly from one another. The comparison shows that the noticeable presence of TiN on the tool surface will result in a significant decrease in the dissolution of WC into iron, for example at 500 ° C, the relative dissolution rates are:

WC: 5.4 x 10⁴

TiC: 1.0

TiN: 1.8 x 10 ³

A1₂O₃: 8.9 x 10 ·.

It is believed that these principles explain the improved wear behavior of WC tools against iron when the WC is associated with a TiN core, i.e., the exposed TiN core will represent less diffuse wear into the iron than the WC. It is believed that a continuous WC coating of the particle (Young's modulus 696 GPa compared to 250 GPa for TiN) is necessary to achieve a thick shell and high mechanical properties. TiN core (which has Vickers H hardness)_in = 2400 compared to H_in = 2350 for WC and has a variable coefficient of friction μ - 0.125 compared to μ = 0.200 for WC) will reduce friction wear compared to iron; the core will be exposed and exposed to the surface of the tool after final grinding and polishing.

It is also possible to have core particles that will be of a variety of different metal compounds, each being compatible and different from the material comprising the core coating layer. In this way, the properties of the article are composed of sintered material when the core particles are

B6 302016 B6 exposed by removing the portion covering the intermediate layers, determined essentially by the properties of the core particles, their concentrations in the sintered material, and combinations thereof. For example, when it is desired to form a sintered article in a cutting insert, the sintered article may be ground or shaped by EDM (electroerosion machining) to expose core particles. In one preferred conduit where the core particles are TiN and the intermediate layer is WC, the friction coefficient TiN, its hardness and wear resistance imparts these properties to the cutting insert, while the overall insert strength and its crack resistance are increased by the WC layer surrounding the core particles TiN. Significantly, wear of the liner will not result in deterioration of the characteristics of such liner, since TiN is not a coating to be abraded. It is an integral part of the liner material that restores the surface when worn. The preferred core material is cubic boron nitride (cBN), but this embodiment requires a specific particle size and layer thickness to realize the potential of the cBN core particle. It is believed that the extraordinary hardness of cBN must be integrated into the article by using a surrounding load-bearing layer of another metal compound of composition and thickness such that the resulting layered particle, when sintered, will have useful technical properties as a structure when used as an abrasive .

This embodiment of the sintered material comprises an intermediate layer on each of the cBN core particles that consists essentially of WC or W₂C.

This embodiment further comprises an outer layer overlying the intermediate layer on the coated particles. The function of this outer layer is to form a binder and to bond the coated particles at appropriate sintering times and temperatures into a dense sintered material. As specifically indicated herein, this outer layer acts as a binder. It consists of iron, cobalt, nickel, mixtures thereof, their alloys or their intermetallic compounds. As noted above with respect to the powder embodiment, the present invention contemplates applying such binders as a uniform coating to the outer surface of the metal compound particles in the form of a continuous layer.

The size of the core particles coated with an intermediate layer (referred to collectively as "coated particles") has a considerable effect on the mechanical properties of the sintered material and the product made therefrom. As mentioned above in the powder description, it is preferred that the coated particles have an average particle size of less than about 2 µm and preferably less than about 1 µm. It is also preferred that the intermediate layer has a thickness after sintering in the range of 5 to 25% of the diameter of the core particles. Moreover, it is believed that the thickness of the binder layer also affects the properties of the sintered material.

It is preferred that the outer binder layer has a thickness after sintering in the range of 3 to 12% of the diameter of said coated particles.

It is believed that the sintered material having such dimensions has improved properties because the stress fields associated with dislocations in one coated particle are transferred through the intermediate layer to the immediately adjacent core particle. It is known that the invention is functional with an intermediate layer having a sintered thickness in the range of 3 to 200% of the core particle diameter, but a thickness in the range of 5 to 25% is preferred.

It is known that increased toughness is a normal result of reduced grain size. A preferred core particle diameter is in the range of 0.1 nanometer to 1.0 micrometer. This range of particle sizes interacts with the thickness of the intermediate layer.

The strength of the crystalline mass depends on the atomic bond and the structure failure. Faults are line defects of the atomic lattice that are normally locked and stationary. In a mixture of two atomically bonded crystalline materials, there are upper and lower limit estimates of the modulus of elasticity of the composite, as calculated by the mixture rule and the inverse of the mixture rule. When subjected to increased load, the material deforms elastically until the grain breaks begin to flow or slip, resulting in a puff of permanent compliance and a reduction in useful strength. For particle sizes approximately one

-9E 302016 B6 micrometers and less develop in such materials with an extremely high strength mainly due to the projection of fault voltages.

Around each fault is a cylindrical voltage field that extends out into the surrounding grid. Theoretically, this stress field must be balanced by the opposite stress fields around each fault, otherwise the fault will move away from the surfaces. When the crystal size is large compared to its stress field, no mirror voltage is created around the failure as long as it is at the crystal surface. In a sintered material having a binder joining a series of crystalline particles, the mirror stress equals less bonding matrix strength, but for large crystals it is a non-existent remedy, since most failures are not near the surface.

At the submicrometric poles of the crystalline particles, the stress field may interfere with adjacent grains whose atomic lattice is not aligned with the lattice of the grain field. This equalization of the stress field outside the grain surface impedes the movement of the failure and thus suppresses slippage. As the grain size decreases further, more disturbances are near the surfaces and the stress may decrease.

It is believed that when the thickness of the intermediate layer and the binder layer connecting the coated particles to the sintered material is sufficiently thin, then the stress field actually passes through the binder matrix and into adjacent particles. This creates a high strength that is not familiar with the bonding material (in this case binder) between the hard coated particles. In other words, the mechanical properties of the sintered product are independent of the properties of the binder phase, provided it is crystalline and very thin.

Thus, the thickness of the intermediate layer should be relatively thin relative to the core to form a mechanical cellular support matrix everywhere between and around the core particles. In addition to this goal and the expected mirror stress, strength increases with core powders 1.0 microns and less, surprising strength properties realized in sintered TCHP alloys can be realized apparently due to the interplay of particle size, core material properties and intermediate layer properties and thickness and binder.

The cause of this is not yet fully understood, but a tungsten carbide (WC) coating of 5 to 10 percent core particles of 1.0 micron or smaller is indeed very thin and may appear to be much smaller in the impact phase itself (50 to 100%). nanometers), which effectively achieves nanoscale mechanical properties at considerably larger and more manageable particle sizes.

The TCHP structure with a small hard core particle size and tough, nanoscale skin separated by thin cobalt bonds below one micron between the grain maximizes flexibility, hardness, fracture toughness and strength. The most interesting is the possible loss of “alloy” character in sintered TCHP mechanical properties due to thin bonding bonds. Even with low hardness material (such as cobalt) with mirror stresses from near surface failures (and for grains smaller than a micrometer, all are near the surfaces), the properties of the compound are higher than possible with abrasive compositions. It may also be that since the bonds of the binder matrix become very thin and the strength of the compound becomes independent of the plastic properties of the cobalt binder, the structural strength of the cellular coatings can prevail and actually approach the strength of the WC.

The present invention provides particulate sinterable metal materials that can be designed to provide a balance of properties (e.g., toughness, strength, low friction coefficient, and hardness). The functional improvements to be expected for dies and other tools made of TCHP are three of the following: (a) less coefficient of friction at the workpiece-tool interface, heat-reducing yield, wear, and grinding, and requiring less working power and auxiliary use external lubricants, which ultimately results in longer tool life and better process control; (b) low reactivity with iron, reduced adhesion and diffusion, wear on the back of the knife or die, and consequently the extension of the die life; and (c) a sintered microstructure

A tool in which a tough, thick coating material (e.g., WC) forms on the particles a cell-supporting macrostructure for the tool, while at the same time providing a perfectly fitting and tightly adhered protective layer for hard particles in the form of particles (e.g., TiN) This ensures that it is in a certain position and allows optimum exposure and deposition of the hard phase on the wear-resistant surface of the tool.

This is in contrast to articles made by conventional techniques (in which the relatively low bonding strength that exists between the particles and the binder reduces the level of toughness and flexural strength), or in which the sintered product is fully coated to provide hardness life limited coating or cracking).

Placing hard and alloyed carbide alloys inside as core particles (instead of on the outside) divides the cemented carbide phases (exposed after final grinding on external surfaces) throughout the sintered microstructure in much larger proportions (or thicknesses) than is possible in any known conventional material. This in itself increases the wear resistance, reduces the chemical interaction with the workpiece and greatly reduces the coefficient of friction. Tool life is increased by constantly removing surface changes that are worn or pulled away by the opposite sliding surface.

Also, the wear resistance and adhesion characteristics of most of the preferred core materials are known from their function in conventional materials, so their function as core particle materials is predictable in light of the present invention. Since the core particles are coated with known materials (e.g. WC), mixing and sintering the coated particles having several different core materials will increase a number of characteristics together. Accordingly, development and testing costs are reduced while providing the final material with unique properties. The sintered microstructure thus designed, wherein each particle has a tough shell (intermediate layer) that adheres very strongly to its adjacent particles to form a tough cellular support system throughout the substrate of the sintered article, forms a sintered product with the highest possible combination of strength, high modulus, fracture toughness and cemented carbide content.

The resulting piece macrostructure is a cellular microstructure skeleton composed of tough, rigid, tightly interconnected skin of coated particles, each containing and supporting one or more mechanically and chemically bonded core particles, crystals, fibers or whiskers exposed during final grinding and cross-sectional polishing outer surfaces. This principle of optimizing the combination of different materials for the core particles and surrounding the intermediate layer allows the combination of normally incompatible product performance characteristics (e.g. strength and hardness) at levels not previously seen in powder metallurgy prior art.

This concept gives material designers a range of tools (used alone or in combination) and a direct way to provide easy and complete control of the TCHP particle structure (intermediate layer thickness, size and core materials) and blend (joining different powders into tool and article zones) to meet many different unique, combined and special requirements conditions with a single piece or tool.

In addition, the use of a standard solid material (such as WC) as a stiff outer shell of a particle dramatically reduces the search, development, and industrialization efforts, since only one batch of complicated precursor and reactive gaseous components used on many outer substrate coatings will have to be used to coat powder particles. a material reaction precursor gas (e.g., tungsten carbide). Such particulate materials will sinter as if they were made of tungsten carbide particles which are already known for very strong bonding to adjacent tungsten carbide particles such as cobalt. In this way, the standard tough material used for more than sixty years will penetrate and solidify the entire structure. Increasing the tungsten carbide coating thickness per particle to accommodate more demanding strength applications,

Or reducing it in more critical wear applications should solve most design problems. Increasing the core particle size can be easily accomplished to meet more stringent wear resistance requirements or reduce it for higher strength applications. The use of different core particle materials with characteristics (hardness, coefficient of friction) known or found for better performance in specific applications (such as back wear or potholes) is also improved by the choice of core material. It is also possible to mix the above-mentioned thickness, diameter and powder parameters of the core material to solve most applications with many criteria.

It is also possible to use pre-heated wax / powder extruded parts for gradual transition of TCHP from regions or layers rich in harder phases to regions or layers with tougher materials. This is a more flexible and efficient approach than the one used for functionally graded material (FGM), which is used simultaneously,

The present invention can also be used to join layers of different powders (or mixtures) in different parts of the same piece to better withstand a variety of performance problems. This is the ultimate degree of refinement of the microstructure design that is possible without an atomic level gradient. TCHP sintered together with other metal powders to give local hardening in “non-hard” sintered parts will allow steel parts requiring heat treatment to be replaced with powder metal (P / M) parts that require fewer processing operations.

Turning now to the accompanying drawings in detail, Figure 1 shows a sintered material in a schematic cross-section. In this embodiment, one or more of the carbide compound particles 10 with an intermediate layer 14 of a hard, tough metal compound such as tungsten carbide.

The coated particle comprises an outer layer of a suitable sintering binder 16, preferably of the group of ferrous metals, typically cobalt or nickel. The resulting coated powder 18 is finally sintered into a semi-finished or finished piece whose microscopic cut is generally designated by the number 20.

The microstructure of this sintered piece 20 is the cellular framework of an interconnected, uniform WC layer 14, each containing and supporting its own tightly bonded metal compound core 10 held in the matrix 16 and in cross-section exposed on the outer surfaces 22 during final grinding and polishing.

The scanning electron microscope image shown in Figure 2 is a TCHP unit particle image consisting of a 1.6 micron titanium nitride core particle 6 coated with 7W₃C having a thickness of approximately 0.25 microns (15 percent). It is one of the many TCHP grains placed in the resin metallurgical sample shown in substrate 9 and polished. It is well known that cemented carbide particles often do not sinter sufficiently close to the theoretical density due to (a) irregularities of such grains (causing poor fluidity necessitating hot pressing) and (b) low plastic deformation during consolidation.

The shape of the core particle 6 in the form of the figure eight showed concave irregularities typical of the samples. The CVD coating process typically filled these concavities at 8, giving the coated particles a rounder, smoother shape that actually promoted flowability and densification of the powders. This should reduce processing costs, result in a more uniform and thin binder layer, and promote the densification of the powders, which in turn will increase the mechanical properties of the sintered product.

The unique powders of the present invention were made in a chemical vapor deposition reactor (CVD). Due to the size of the particles to be coated, the reactor included components to prevent caking of the particles to be coated. A schematic representation of the reactor is shown in Figures 3 to 5.

-12GB 302016 B6

The CVD reactor system of Figure 3 consists of a rotating CVD reactor vessel 20 contained within the furnace 22 for heating the powder and the reaction gases, the gases being supplied to the reactor and discharged through the gas inlet and outlet lines 36, 26 at opposite ends thereof. Line 30 supplies a tungsten hexafluoride precursor (WF_Ď), while the ducts 28 supply 99.999 percent pure hydrogen, the two gases that react in the reactor vessel 20 to form a CVD coating, connected to the rotating seal and the inlet pipe 36 through the flowmeters 32. The duct 28 also passes through the gas scrubber 34 containing 99.9% pure isopropyl benzene. At the outlet side of the reactor 20, a filter 38 is inserted upstream of the discharge line 26, which line is operatively connected to an exhaust system (not shown) and separator 40 and flow meter 42. The reactor 20 may be in the shape of a hollow cylinder of refractory metal or graphite capable of rotation at a variable speed in the range of 50 to 150 revolutions per minute depending on the diameter of the drum and the specific gravity of the coated powder and its change of orientation. Thus, the inclination angle 24 and the rotational speed can be adjusted to provide a suitable residence time of the coated powder in the formed high temperature reaction gas (500 to 1600 ° C). In the practical implementation of the CVD process for the production of particulate matter TCHP below one micrometer, there are four major challenges: (1) the current cost of the tungsten hexafluoride precursor gas (WF)_Ď), (2) controlling the harmful characteristics of WF_O(3) premature reaction of the precursors on surfaces other than the core powder, and (4) crushing the agglomerates. The last three have technical solutions. Although the benefits of additional processing costs can offset the first task, the ultimate success of CVD will be determined by its cost relative to other methods, such as metal carbon coating.

It has been found that the solution to the above-mentioned third task (inefficient use of reactants) is to keep the gas below the reaction threshold temperature until it is close to the core particles. This can be further improved by keeping the gases of the reactants separate, mixing them with the turbulent heated powders themselves.

It was found that microwave energy (but not induction frequencies) would heat particles. At 2.45 Ghz, heating for about 2 seconds, 500 watts produced a temperature rise of about 37-40 ° C. The concept of high heating rates for a concentrated, turbulent stream of reactants heated by powder alone (heated microwave energy) in a recirculating quartz tube has a high efficiency in achieving homogeneous agglomeration, mixing, recirculation and coating of powders below one micrometer.

Figure 4 shows one solution found to solve the problem of powder agglomeration. Fluidization in a rotating reactor does not normally use the forces required to break pieces that are constantly forming. In fact, if left uncontrolled, the agglomerates tend to sort by size, which further prevents homogeneous processing. In addition, a conventional horizontal reactor has end zones that reduce the uniformity of coating thickness across the batch. As shown in FIG. 4, one solution to the sintering problem and end zones that formed the uneven coating involved tilting the reactor and installing a rigid rack-like line 80 for (a) recirculating and homogenizing the batch, and (b) applying sufficient shear to the powder to deagglomerate. Inside the furnace, the reaction chamber 62 is constructed of graphite lined with a quartz cylinder 60. The rotational speed 66 must be such that the gravitational force acting on the core particles is certainly greater than the centrifugal force, so that falling powder grains thus swirled to maximize exposure to the gaseous reactants accumulate an intermediate coating thereon. The purpose is to fall freely, roll, fall cascading like a waterfall, and roll the core powder with the right combination of centrifugal force, gravity, and rotational inertia from roller rotation to maximize exposure of the powder to precursor gases. This means a practical diameter 64 greater than 120 mm. In order to aid in the separation of the agglomerate pieces that prevent the application of homogeneous layers on each particle, the reactant gases can be introduced at high flow rates through the falling powder to break up the agglomerates by shear force.

The shear is applied to the powder in duplicate in the two zones of the guides 80 shown in cross section 67 at the lower end of the drum. The first zone 68 exerts a light pressure and shear on a portion of the powder when it is entrained under the guidance of the rotating drum 60,62.

The contact angle 69 13 degrees, this angle generating a sufficient pressure shear to break the agglomerates. The second zone 70 consists of a long 72 angular toothing forming the ridge itself cut out as a stainless steel quadrilateral with little mixing at the edges. This zone 70 allows the compressed powder to escape under a light shear force that serves to further deagglomerate and homogenize the particles when subjected to further rotation. At a distance of 5 inches (74 mm) from the quartz sleeve (60), the increasing ridge toothing angle is determined by the bending point, which increases the down pressure just when the toothing holes (72) reach their maximum. A small clearance 76 of 0.5 to 1.0 mm protects the quartz from scratching by the comb.

The spiral region 80 of the comb provides a conduit 78 which is shown at the lower end of the reactor and at its upper end is shown by dotted lines. This screw guide gives the powder stroke to ensure lateral recirculation and batch homogeneity.

Figure 5 shows the helical comb such that the helical guide 80 is shown more clearly. Holes 92 are cut into the upper deck to allow the powder collected there to fall through for further recirculation. The teeth of the comb 90 are also shown more clearly.

As currently observed, a preferred embodiment of the invention utilizes core powders of pre-ground titanium nitride particles. This powder was coated with a CVD intermediate layer of tungsten carbide. It is preferred to use a cobalt binder for sintering. In the TiN / WC / Co system, the good solubility of W in Co is a good reaction between C and TiN to form Ti (C, N), resulting in a solid boundary phase of the TiN / WC grains and extraordinary mechanical properties of the sintered article. less strong than a binder that can be formed between W and Co.

The TiN phase is located inside the material and there is no decrease in performance from surface wear (as with traditional ceramic coated tools). Thus, dies, tools or other cemented carbide articles made with such TCHP could be reused for larger dimensions or reground for other applications. When it is later determined that the formation of the Ti (C, N) boundary and stratum must be minimized in order to increase binder efficiency, an increase in WC coating thickness and sintering time and vapor deposition temperature on the particles can be used. On the other hand, at Vickers hardness, H_in= 3200 Ti (C, N) considerably harder than TiN at H_in= 2400 or TiC at H_in= 2800. This may prove positive in some applications. Zirconium nitride, ZrN, harder than TiN has a coefficient of friction two-thirds less than that of TiN, and is considered better for back wear. It is also a preferred core material.

Figure 6 shows the compilation of working spheres of several common tool materials and the expected working area of ​​an embodiment of the present invention used as a cutting tool material. By using conventional hard materials as the core, reducing the particle size to the desired range, and applying to the core a tough coating (such as WC) of appropriate thickness, the TCHPs of the present invention extend the working areas of such conventional materials. The extent of the increment of the tool feed rate, i.e., the extreme limit of the right side of the area defining the TCHP working area of ​​the present invention, is based on increasing the toughness provided by the tough coating and utilizing the hardness and other properties of the core material.

Using a reactor system such as that shown in Figure 3, sinterable particulate composite materials embodying the present invention could be prepared using each of the following alloys in powder form with a diameter of 1.0 to 1.5 microns: titanium nitride, titanium carbide, zirconium nitride, vanadium carbide, aluminum oxide and cubic boron nitride. (Other alloys such as titanium diboride, zirconium carbide, tantalum nitride and niobium carbide could also be used.) Chemical vapor reactants used for toilet deposition_X are tungsten hexafluoride (WF₆) in the presence of hydrogen and an aliphatic or aromatic carbon compound, these additives react at temperatures in the range of 500 to 700 ° C to form WC coatings_X with highly reproducible characteristics. A low pressure, for example less than 100 millibars, would be used in the reactor to increase the diffusivity of the reactants in the gas and to allow a homogeneous coating on the powder surface. This technique is commonly referred to as LPCVD (Low Pressure Chemical Vapor Deposi-13). The reactor is operated at a speed sufficient to roll the core powder in a continuous, free-falling stream and the rate of reaction gas is set as a function of other parameters (pressure and total flow). A gas scrubber is used in those cases where an aromatic liquid mixture is used as the reaction additive.

Determined coating thickness based on the required 90 to 95 percent strength of all cemented WC carbide_X and based on minimizing CVD residence time ranges from 2 to 25 percent of the average particle diameter. The CVD operating parameters are set using a computer program, thus allowing them to be optimized, which is guided by the main indicator, such as the WC coating thickness_X at different points in the reactor. Quantity of WC_X deposited on the powder is pre-calculated by microanalysis of the EDX-treated powder comparing the highest tungsten and titanium intensities and the W ratio_M: Ti_TO (where M and K are atomic ratio coefficients) determined on particulate samples taken at different furnace points and at different times. This provides data on the homogeneity, the degree of settling and the WC surface_X characteristics of the WC interface_x/ core particle before sintering. Thickness of cross-section of WC coating_X Examine by optical microscope and scanning electron microscope using a sample consisting of TCHP grains embedded in resin and polished to expose the cut of the slurry. To show the presence of the WC phase_X on powder, X-ray analysis is also used.

Three series of sintered samples were prepared: one series was made with titanium nitride particulate material coated with WC_X (embodying the present invention, compositions C, D, E and F), one series of reference bars was made with tungsten carbide powder without any coating (composition A), one comparative series was made with a mixture of nepo in treated tungsten carbide powder and TiN addition ( composition B) and there was a standard Sandvik material (see column G in Fig. 7 + legend on page 58) coated with TiN, TiC and A1₂O₃ (composition G).

The tungsten carbide (WC) powder used in the manufacture of these compositions is commercially available from HC Starek Company as stage DS100 and typically has an average particle size of about 1.0 µm (± 0.1 µm). The cobalt powder used was Starek Grade II, which has a typical particle size of 1.5 µm (± 0.2 µm). The titanium nitride powder used is Starek grade C, which has a typical particle size of 1.0 µm (in the range between 0.8 to 1.2 µm) and the powder used nickel commercially available, having a typical particle size of 2.2 µm.

The compositions embodying the present invention were composed of CVD-coated TiN core grains (W₂C) to a thickness of about 0.16 µm forming a composite particle material (TCHP) having a particle size of about 1.0 µm. The apparatus described hereinabove with reference to Figures 3 to 5 was used to perform CVD coating of TiN powder. It is operated with an inclination angle of 20 ° and a ridge mounted at a 13 ° ramming angle. An appropriate amount of TiN powder was introduced into the graphite reactor chamber. This system was vented, triggered by a stream of hydrogen, and the internal pressure was set at 1500 Pa. Then, power was supplied to the electric furnace to bring the reactor drum at 90 rpm to a temperature of about 550 ° C (about one hour). The flow meters were then opened to feed the WF₆ and a cumene washer to provide a molar ratio of reactants suitable for W storage₂C on the TiN substrate powder. The washer is operated at 20 ° C and hydrogen gas is used as the liquid cumene carrier. Operation was continued for a time delay sufficient to produce the desired thickness W₂C on TiN particles after which the flowmeter WF₆ and the cumene washer was closed and the furnace was cooled under hydrogen.

Composition A is a binary mixture consisting of 94 weight percent WC and 6 weight percent Co; composition B is a mixture consisting of 87 weight percent WC, 6 weight percent Co and 7 weight percent TiN; composition C consists of 84% by weight of the described mixture of TCHP and 16% by weight of Ni; composition D consists of 84 weight percent blend of TCHP and 16 weight percent Co; and composition E consists of 90 weight percent blend of TCHP and 10 weight percent Co.

- 15 GB 302016 B6

Composition B was formed into a 53 x 16 x 11 mm sintered rod weighing about 130 grams by mixing this composition into Acrawax C (ethylene bistearamide processing aid available from Lonza Inc, Fair Lawn, New Jersey and hexane). It was milled in a ball mill for 16 hours with WC balls, vacuum dried, sieved at 300 pm, cold isostatically pressed at 2x10⁸ Pa for 5 minutes and sintered for 20 minutes at 1450 ° C under a vacuum of 1 to 3 Pa. The applied heating and cooling rates were 150-200 ° C per hour and the total sintering operation required about two hours.

Sample discs were prepared from compositions A, C, D, E and F. To do this, the composition was mixed into a camphor intermediate binder and alcohol solvent, ground five minutes in a planetary mill with tungsten carbide grinding balls, dried at 80 ° C for 15 minutes and sieved to 300 µm. For samples A, C and D, the discs formed are 10 mm in diameter and are sintered under the vacuum conditions described above for samples A and B. To form samples E and F, the ground, dried and sieved composition is subjected to unidirectional compression at 1400 ° C at a pressure of 1.96x10⁷ Pa to form discs measuring 50 mm in diameter.

To evaluate each of several properties, a number of samples from each of the above-described sintered products were tested. The composition, sintering conditions (vacuum or hot pressing), the shape of the product (bar or disc), the binder content after sintering and the values ​​for several measured properties are shown in Figure 7. The back wear and pothole measurements were on standard material (CK 45) surface speed 200 m / min, cutting depth 2 mm and feed speed 0.2 mm / revolution. The values ​​of hardness, flexural strength and modulus of elasticity for Sample No. 1 are from the literature. In the foregoing examples, it has been found that sintered samples embodying the present invention operate in a manner that provides a component metal powder that is particularly well suited for making machining and other objects as contemplated herein.

It will be appreciated that the ability to vary not only the composition of the metals used to make these sintered particulate materials of the invention (including any additional binder or sintering aid), but also the relative thickness of the core particle and surrounding interlayers allows a high degree of control to be used. for those properties which are exhibited by particulate materials and products made from them. For example, by varying the thickness of the shell (e.g. to a value that typically, but not necessarily represents 5, 10, or 15 percent of the diameter of the TCHP particle) can achieve and impart to the sintered product an optimal balance of hardness, toughness, strength, wear and attractiveness of heat transfer.

The present invention provides a new class of powdered materials, i.e. TCHP, to produce sintered products that exceed the current compromise performance level of conventional materials by combining the basic bending mechanical strength of metal carbides (or comparable tough metal compounds) with exceptional wear resistance of hard metal compounds at the core particle level. Tools or articles made of such materials work well in far wider ranges of conditions than today's specialized procedures allow, and their performance / price or price ratio should increase considerably.

The present invention has been elucidated on the basis of examples and preferred embodiments. The scope of the invention is not limited thereto but is defined in the appended claims and their equivalents.