Self-renewing cutting surface, tool and method for making same using powder metallurgy and densification techniques

Abstract

A self-renewing cutting tool or cutting element is formed by bonding an overcoat, cladding or layer of highly abrasive, very durable material on a surface of a substrate or load-bearing element. The cutting layer is a composite structure and includes appropriately sized, multi-edged pieces of a superhard material, such as tungsten carbide, dispersed in a softer material which produces high strength bonds between and among the pieces and the substrate or load-bearing element.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of cutting tools and cutting elements and, more specifically, to self-renewing cutting tools and elements for cutting hard materials such as metals or metallic structures that may be in aqueous environments.

2. Background Information

Conventional cutting tools and elements for cutting metals and other tough surfaces may be made of a superhard material such as tungsten carbide. While conventional cutting tools and elements provide good performance under normal operating conditions and loads, they may not be suitable for applications in which harsh environmental conditions are present or high loads must be applied to cut large and or very complex structures. For example, in certain large scale demolition operations, it is often desirable or necessary to cut completely through a large objects comprised at least in part of metal or other difficult to cut surfaces in order to section them into more manageable sized to effect removal. Depending upon the environment in which the demolition takes place, including the orientation and balance of the object(s) to be cut, as well as the size and hardness of the object being cut or abraded, it may be impractical or unsafe to perform such cutting other than by tools which can be actuated some distance from the point of the cut.

Under normal operating conditions, conventional cutting tools will wear and eventually become dull or damaged which, in turn, reduces cutting performance. Under difficult operating conditions or sustained high loads (or both), conventional cutting tools tend to wear at an accelerated rate, leading to increased downtime to replace worn or broken tools. In addition, the basic geometries of conventional cutting tools may not be appropriate or effective for cutting objects that are massive and/or complex (e.g., an object made of multiple materials and/or systems, or a submerged structure).

As shown in the literature, one known approach to cutting massive and/or complex objects is to braze pieces of a superhard material, such as tungsten carbide, to a surface of a tool. That approach suffers from at least one major disadvantage. Because brazing does not provide a sufficiently strong bond between and among the pieces of superhard material, the braze material and the tool surface, the pieces of superhard material become dislodged during cutting operations. The loss of superhard pieces, in turn, degrades the performance of the tool thereby necessitating more frequent repair or replacement.

SUMMARY OF THE INVENTION

In brief summary, a self-renewing cutting tool or cutting element is formed by forming or bonding an overcoat, cladding or layer including superhard, very durable constituents on a surface of a substrate or load-bearing element. The cutting layer is a is composite structure and includes appropriately sized, multi-edged pieces of a superhard material, such as tungsten carbide, interspersed with a bonding material which produces high strength bonds between and among the pieces and the substrate or load-bearing element and forms an integral composite of the plurality of materials. When the cutting layer is initially formed, portions of at least some of the superhard pieces typically protrude from a wear surface of the layer and are thus available to remove material wear surface is worked against an object. As the wear surface is worked, the bonding material of the cutting layer may gradually wear away exposing additional edges of pieces and additional pieces of the superhard materials in a self-renewing cycle.

In accordance with another aspect of the invention, the cutting layer may be formed from a combination of superhard pieces and one or more powder materials having appropriate bonding characteristics. Through application of a hot isostatic pressing (HIP) process, the combination is densified and diffusion bonded between and among the superhard pieces, the bonding material and the substrate or load-bearing element. As used herein, densification and related terms refer to a process in which the mass density of a body or aggregation increases as a result of the controlled application of temperature and/or pressure.

In accordance with another aspect of the invention, the cutting layer may be formed from a combination of superhard pieces and one or more powder metals having appropriate bonding characteristics. Through the application of spark plasma sintering (SPS), the combination is densified and diffusion bonded to the substrate or load-bearing element.

In accordance with another aspect of the invention, the cutting layer may be formed on almost any substrate or load-bearing element geometry, as desired for a particular application including but not limited to planar, spherical, elliptical, conical, polyhedral, and cylindrical geometries. In order to meet the requirements of a particular application, a substrate or load-bearing element may include one or more features which are specially adapted or arranged to accommodate the cutting layer. Similarly, the cutting layer material may be formed in a desired pattern, as opposed to a continuous layer, on a substrate or load-bearing element.

In accordance with another aspect of the invention, the superhard pieces may be formed by crushing or fracturing recycled (used) tungsten carbide machine tool inserts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention description below refers to the accompanying drawings, of which:

FIG. 1 is a cross section of a finished cutting element having a cutting layer bonded to a substrate or load bearing element in accordance with a preferred embodiment of the present invention;

FIG. 2 is an enlarged cross section of the cutting layer of FIG. 1 showing a typical dispersion of superhard pieces bearing cutting edges within the cutting layer;

FIG. 3 is a cross section of an assembly of a load bearing element, located within a can, to which a cutting layer will be applied;

FIG. 4 is a cross section of the assembly of FIG. 3 in which a metal powder and superhard pieces have been introduced in preparation for a hot isostatic pressing;

FIG. 5 is a cross section of the assembly of FIG. 4 following the application of hot isostatic pressing and prior to removal of the can;

FIG. 6 is a cross section of a load bearing element which includes a recessed area or feature in which a cutting layer is disposed;

FIG. 7 is a schematic diagram of a spark plasma sintering system which may alternatively be used to form the cutting layer of FIG. 1;

FIG. 8 is an enlarged schematic view of the central portion of FIG. 7; and

FIG. 9 is a cross section of a finished cutting element having a cutting layer bonded to selected portions of a substrate or load bearing element.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

With reference to FIG. 1, a structure 10 serviceable as a cutting element includes a substrate or load-bearing element 20 on which a layer 26 is formed of particles or pieces 32 of a first material embedded in or bonded to a continuous second material 38. Layer 26 represents a substantially fully dense overcoat, cladding or cutting layer bonded to substrate 20. The thickness of second material 38 may vary from point to point on substrate 20, and may conformally coat pieces 32. Those skilled in the art will understand that second material 38 may comprise an alloy or a material comprising more than one type of compound. Those skilled in the art will further understand that substrate 20 and superhard pieces 32 may be fabricated from any number of materials and methods, provided that they will bond among and between themselves when interspersed with or dispersed within second material 38.

As is understood by those skilled in the art, cutting and abrading are different mechanisms of removing material. Cutting is a shearing action where a chip of the material to be removed is formed. Abrading is the wearing away of material through the use of friction. As used herein, the terms “cut” and “cutting” and their derivatives should be understood to include cutting or abrading or both.

Illustratively, pieces 32 are of a superhard material (>12 GPa Vickers) and provide multiple respective cutting edges 44 shown in FIG. 2. Examples of superhard materials include, but are not limited, to tungsten carbide, zirconium oxide, silicon carbide, cubic boron nitride and polycarbonate diamond. Alternatively, somewhat softer but appropriate material such as tool steel may be used. Pieces 32 are generally dispersed throughout or interspersed with second material 38. One or more of pieces 32 may protrude from second material 38 such that cutting edges 44 are typically randomly oriented and, in aggregate, provide a highly effective cutting surface. Alternatively, pieces 32 may be oriented in a preferential manner to better expose cutting edges 44 and provide a more effective cutting surface. Layer 26 is so constituted such that cutting edges 44 of those pieces 32 lying beneath the cutting surface of layer 26 are gradually exposed upon wearing of the second material 38. Thus, structure 10 may be adapted (e.g., secured to an appropriate fixture and power source) to cut an object worked against the cutting surface of layer 26 with continual self-renewal of the cutting surface.

In general, pieces 32 are of irregular and nonuniform shape but characterizable in terms of an average of the shortest diameters of respective pieces 32, which may be up to several inches. A powder used to prepare second material 38, as described below, may be, e.g., spherical or dendritic in morphology and has an average longest particle diameter of respective particles of the powder. The average longest particle diameter of the powder form of second material 38 before densification may be on the order of 0.05, 0.005, or 0.00005 times the average shortest diameter of pieces 32 or less. For example, pieces 32 may have average shortest diameter on the order of up to several inches, whereas the average longest particle diameter may be several thousandths of an inch to tenths of inches. Illustratively, second material 38 has a hardness that is less than ½ the hardness of the first material of which pieces 32 are made.

The strength of the bonds between a given one of pieces 32 and second material 38 in structure 10 is preferably greater than the strength of an individual one of pieces 32, so that under stress layer 26 loses pieces 32 more readily by breaking a piece 32 or removing a portion of the second material 38 than by detachment of the second material 38 from one of the pieces 32. Thus, the continuous second material 38 is configured to transfer load, during contact between layer 26 and an object to be cut or abraded from cutting edges 44 to substrate 20.

The material for substrate 20 of structure 10 is selected for its preferred properties, including but not limited to its ability to bear load, strength, resistance to corrosion in relevant environments, expense or other considerations. Illustratively, where strength is a very important consideration substrate 20 may be a steel such as 4340 alloy steel. There is no requirement that substrate 20 be metallic in nature. Illustratively, pieces 32 are of a material that is at least three times, five times, or ten times as hard as second material 38. Tungsten carbide is a superhard material available commercially as recycled fragments (Dynalloy Industries, Inc., Tomball, Tex.) having sharp cutting edges and suitable for pieces 32. The second material 38 in layer 26 is illustratively a metallic alloy, for example having the composition of a powder such as B27 (Carpenter Powder Products, Inc., Bridgeville, Pa.) which includes nickel, silicon, boron and carbon.

Layer 26 is illustratively formed by placing a powder substantially identical in composition to second material 38 in intimate contact between and among pieces 32 and between pieces 32 and substrate 20 and then subjecting substrate 20, pieces 32 and the powder form of second material 38 to a densification process such as HIP. In an illustrative method for forming structure 10 (FIG. 1), with reference to FIG. 3, a can 50, alternatively designated a skin or encapsulation, as is used to contain pieces 32 and the powder form of second material 38 during HIP, is disposed over a surface 56 on substrate 20. Can 50 is spaced apart from surface 56 of substrate 20 to form a cavity 62. Inert material 68, for example alumina, may be disposed upon or applied to an interior surface 58 to prevent interior surface 58 of can 50 from bonding to pieces 32, and to facilitate removal of can 50 from substrate 20 later in the method. Alternatively, a material that does not bond with pieces 32 or the powder, for example a piece of carbon paper such as Grafoil® (Graftech International Holdings, Inc., Parma, Ohio) whose thickness is selected based on the desired characteristics may be used. Those skilled in the art will recognize that it may be preferable to fabricate can 50 from a material that does not bond with pieces 32 or second material 38.

A substantially uniform mixture of pieces 32 (FIG. 1) and the powder to be densified into second material 38 is introduced into cavity 62. FIG. 4 shows can 50 holding the mixture which substantially fills the volume between neighboring ones of pieces 32 and between the pieces and can 50 and surface 56. Substrate 20, pieces 32 and powder 74 thus assembled constitute a precursor to the final structure 10 (FIG. 1).

Returning to FIG. 4, the mixture is illustratively created in cavity 56 stepwise by first loading pieces 32 into the cavity from its top end and then pouring powder 74 to appropriately fill remaining space between can 50 and surface 56. Preferably, pieces 32 may occupy about 40% to 60% of cavity 62. Preferably, powder 74 may occupy the volume in the cavity 62 not occupied by the pieces 32 at the tap density of powder 74.

Cavity 62 is then evacuated, sealed, placed in a hot isostatic press and heated under isostatic pressure, as understood by those skilled in the art. The operating parameters of the hot isostatic pressing operation are selected in view of the physical and sintering properties of the materials of which substrate 20, pieces 32 and powder 74 are made to consolidate the powder 74 and pieces 32 and substrate 20, as known to those skilled in the art. By way of illustration, and not limitation, typical process temperatures are 0.9 to 0.95 times the melting temperature of powder 74 with typical pressures around 10 to 30 Ksi. During HIP, particles of powder 74 (FIG. 4) consolidate into a continuous phase 38 (FIG. 2) which is diffusion bonded to pieces 32 and substrate 20. Illustratively, substrate 20 and pieces 32 need not densify during HIP.

FIG. 5 shows the assembly of FIG. 4 after densification of powder 74, with commensurate reduction of the volume it occupies following HIP. Can 50 has assumed a conformal profile accommodating the relatively reduced volume of second material 38 and pieces 32 protruding therefrom due to the HIP process. Removal of can 50 by, e.g., a mechanical or chemical process exposes protruding portions of pieces 32 illustratively bearing cutting edges 44 as shown in FIG. 2.

Using the method described above, a cutting layer, overcoat or cladding similar in composition to layer 26 may be formed on a wide variety of substrate or load-bearing element geometries including planar, spherical, elliptical, conical, polyhedral and cylindrical.

FIG. 6 shows an alternative configuration of substrate 20 in which a concavity 80 is disposed. Concavity 80 is substantially filled with the mixture of pieces 32 and powder 74 as described above. In preparation for a HIP process, concavity 80 is sealed by can 50. Those skilled in the art will recognize that a concavity 80 may be combined with a specifically configured can 50 to provide for the formation of custom layer 26 profiles.

As an alternative to HIP, spark plasma sintering (SPS) may be used to provide densification in order to form a structure like structure 10 (FIG. 1). SPS may be employed to fabricate layer 26 using similar, if not identical materials as those described above. With reference now to FIGS. 7 and 8, in the SPS process, powder 74 and superhard pieces 32 are disposed in a volume within tooling 100 between an upper press platen 110 and a lower press platen 120. An appropriate volume of respective superhard pieces 32 and powder 74 of appropriate ratios are placed within the tooling volume. Densification and sintering takes place under mechanical pressure that is applied by lowering upper press platen 110 and/or raising lower press platen 120 in opposition. The necessary temperature is produced by passing a pulsed high electrical current from a power source 140 through the tooling, as well as the powder and/or superhard pieces, thereby generating heat from the electrical resistance. In SPS a layer of electrically conductive powder 130, such as carbon powder, is placed in contact with an electrode, tooling, powder 74 and pieces 32, to accommodate the rough surface morphology of powder 74 and pieces 32.

Initially, powder 74 is at tap density and there are points of contact between and among powder particles, substrate and other powder particles. In some instances it may be necessary or desirable to mechanically compress powder 74 and pieces 32 prior to the application of the electrical current.

Once pressure is applied these contacts are effected and any oxide layers that may have been present may be broken down. The electric current produces high heating rates (>300° C./min are attainable) and heat is generated internally as opposed to being provided from the outside. Substantial densification results and cycle times on the order of minute(s) are possible. Custom tool designs can provide a wide range of desired post SPS tool geometries.

FIG. 9 shows a cross section of a structure 140 which includes a substrate or load-bearing element 20 similar that described above. In contrast to structure 10 of FIG. 1, however, substrate 20 does not have a continuous composite cutting layer bonded to it. Instead, as those skilled in the art will recognize, powder manufacturing techniques allow for patterning or selective application of a cutting layer to substrate 20. Material 26a-26c, which is similar in composition to layer 26 described above, is preferentially disposed on substrate 20, leaving at least one untreated area 142. Such material may be applied in any number of more complex patterns or shapes including a simple, substantially uniform layer 26a disposed over a portion of the substrate 20, a layer with varying thickness 26b, or a more complex feature, such as a cone, rail, or ridge 26c. In addition, the composition of material 26a-26c may also change as a function of its depth, depending on the desired properties.

Those skilled in the art will recognize that powder manufacturing techniques make it possible to use various materials for pieces 32, powder 74, second material 38 or substrate 20, as long as the materials will bond to and among each other. In particular ceramics, intermetallics, stellites, diamond, alumina, silicon carbides, titanium nitrides, may be used for each of the above mentioned elements.

Claims

1. A structure comprising: a substrate;a layer bonded to said substrate, said layer including a plurality of pieces of a first material having an average shortest diameter, and a second material in which said plurality of pieces are embedded, said layer constituting a substantially fully dense composite cladding formed by placing a powder of the second material, having an average longest particle diameter smaller than 0.05 of the average shortest diameter, on the substrate in intimate contact with the plurality of pieces and then subjecting the substrate, the plurality of pieces and the powder to a densification process.

2. The structure as in claim 1 where the densification process comprises hot isostatic pressing.

3. The structure as in claim 1 wherein the densification process comprises spark plasma sintering.

4. The structure as in claim 1 where the first material is substantially harder than the second material.

5. The structure as in claim 1 wherein the first material has a hardness greater than 12 GPa Vickers.

6. The structure as in claim 1 wherein said first material substantially comprises tungsten carbide.

7. The structure as in claim 1 wherein said plurality of pieces comprise fragments of crushed used tungsten carbide machine tool inserts.

8. The structure as in claim 1 wherein said plurality of pieces are substantially the same size.

9. The structure as in claim 1 wherein said layer cuts an object which is worked against said layer and the structure presents a renewed cutting surface upon wearing of the second material of the cladding to expose underlying ones of said plurality of pieces.

10. The structure as in claim 1 wherein a sintering temperature of the second material is less than a sintering temperature of the first material.

11. The structure as in claim 1 wherein said first material comprises one or more of silicon carbide, cubic boron nitride, polycarbonate diamond, zirconium oxide and tool steel.

12. The structure as in claim 1 wherein said plurality of pieces are substantially randomly dispersed within said layer.

13. A structure comprising: a substrate;a plurality of pieces of a first material;a layer of a second material, bonded to said substrate, from which one or more of said plurality of pieces protrude and to which the plurality of pieces are bonded such that breaking one of the plurality of pieces requires less force than breaking a bond between one of the plurality of pieces and the second material, the plurality of pieces and layer together constituting a substantially fully dense composite cladding formed by placing a powder of the second material in intimate contact with the plurality of pieces and then subjecting the substrate, the plurality of pieces and the powder to a densification process.

14. A structure comprising: a substrate;a plurality of pieces of a first material, each of said plurality of pieces having respective cutting edges;a layer of a second material, bonded to said substrate, less than ½ as hard as the first material in which the plurality of pieces are embedded, the plurality of pieces and layer together constituting a substantially fully dense composite cladding formed by placing a powder of the second material in intimate contact with the plurality of pieces and then subjecting the substrate, the plurality of pieces and the powder to a densification process, wherein the structure presents a renewed cutting surface upon wearing of the second material of the cladding to expose underlying pieces of the first material.

15. A method of manufacturing a composite structure comprising the steps of: providing a substrate;providing a plurality of pieces of a first material;placing a powder of a second material on the substrate in intimate contact with the plurality of pieces to form a precursor; andsubjecting the precursor to a densification process, thereby converting the powder and plurality of pieces to a substantially fully dense composite cladding bonded to the substrate.

16. A method of manufacturing a self renewing cutting tool having a substrate and a renewable cutting layer bonded thereto, the layer formed from interspersing pieces of a first hard material providing a cutting function in a powder of a second softer material providing a binding function, an average size of the pieces of first material being substantially larger than that of the second material, and thereafter consolidating the first and second materials to form a unitary structure in which the second material is bonded to the first material and to the substrate and in which the bonding and the material hardnesses enable the cutting layer to renew itself by exposing further pieces of the first material in response to wearing of the second material.

17. The method as in claim 16 wherein the consolidation is performed by hot isostatic pressing.

18. The method as in claim 16 wherein the consolidation is performed by spark plasma sintering.

19. The method as in claim 16 wherein the materials are selected so that a bonding force required to break the bond between the first and second materials is greater than that required to break the bond between the second material and the substrate.

20. The method as in claim 16 wherein, in the unitary structure, the strength of the bonds between a given one of the pieces of the first material and second material is greater than the strength of the given one piece, thereby enabling the cutting layer to lose pieces more readily by breaking or removing a portion of the first material than by detachment of the first and second materials.

21. The method as in claim 16 wherein the bonding and the material hardnesses enable the second material to wear and expose further cutting surfaces of the first material below an original outer surface of the cutting layer.

22. The method as in claim 16 wherein an average size of the powder is less than 0.10 times the average size of the pieces of the first material.

23. The method as in claim 16 wherein the first material is a superhard material having a hardness on the order of that of tungsten carbide, silicon carbide, cubic boron nitride, polycarbonate diamond, or zirconium oxide.

24. The method as in claim 16 wherein the first material has a hardness greater than 12 GPa Vickers.

25. The method as in claim 16 wherein the first material is selected from a group consisting of ceramics, intermetallics, stellites, diamond, alumina, silicon carbides, titanium nitrides.

26. A method of manufacturing a self renewing cutting tool that is particularly adapted to hostile environments such as marine salvage operations, the tool being formed from a substrate having a renewable cutting layer bonded thereto, the cutting layer being formed from interspersing pieces of a first superhard material having a hardness on the order of that of tungsten carbide, silicon carbide, cubic boron nitride, polycarbonate diamond, or zirconium oxide and providing a cutting function in a powder of a second softer material, the average size of the pieces of first material being substantially larger than that of the second material, and the first and second materials being consolidated into a fully dense structure in which the second material is bonded to the first material and to the substrate and in which the bonding and the material hardnesses enable the cutting layer to renew itself by exposing further pieces of the first material in response to wearing of the second material.

27. The method as in claim 26 wherein the consolidation is performed by hot isostatic pressing.

28. The method as in claim 26 wherein the consolidation is performed by spark plasma sintering.

29. A method of manufacturing a self renewing cutting tool having a load bearing substrate and a renewable cutting layer bonded thereto, comprising the steps of interspersing pieces of a first hard material providing a cutting function in a powder of a second softer material providing a binding function, the average size of the pieces of first material being substantially larger than that of the second material, and thereafter consolidating the first and second materials by hot isostatic pressing to form a unitary structure in which the second material is bonded to the first material and to the substrate and in which the bonding and the material hardnesses enable the cutting layer to renew itself by exposing further pieces of the first material in response to wearing of the second material.

30. A method of manufacturing a self-renewing cutting tool comprising forming a cutting layer on a load-bearing substrate, the cutting layer comprising a composite structure which includes multi-edged pieces of a superhard material dispersed within a softer material that is bonded to both the pieces of superhard material and the load-bearing substrate by consolidation to form a fully dense cutting layer, wherein, the cutting layer is enabled to renew itself by exposing further pieces of the superhard material in response to wearing of the softer material.

31. The method as in claim 30 wherein the superhard material is selected from a group consisting of tungsten carbide, silicon carbide, cubic boron nitride, polycarbonate diamond, and zirconium oxide.

32. A method of manufacturing a self-renewing cutting tool comprising the steps of dispersing pieces of crushed cutting inserts of a superhard material in a relatively soft material that is diffusion bonded to the superhard material and to a substratee so that fresh sharp cutting edges of the superhard material are successively exposed by wearing of the soft material during cutting or abrasion.

33. The method as in claim 32 wherein the substrate has a cylindrical geometry.

34. The method as in claim 32 wherein the substrate has a planar geometry.

35. The method as in claim 32 wherein the substrate has a spherical geometry.

36. The method as in claim 32 wherein the substrate has an elliptical geometry.

37. The method as in claim 32 wherein the substrate has a conical geometry.

38. The method as in claim 32 wherein the substrate has a polyhedral geometry.