WO1995016530A1

WO1995016530A1 - Polycrystalline diamond composite cutting insert for attachment to a tool

Info

Publication number: WO1995016530A1
Application number: PCT/US1994/013035
Authority: WO
Inventors: William P. Losch; Wayne H. Beach; Don C. Rowlett
Original assignee: Kennametal Inc.
Priority date: 1993-12-17
Filing date: 1994-11-14
Publication date: 1995-06-22
Also published as: ZA949230B; AU1095195A

Abstract

A polycrystalline diamond composite cutting insert (46) for attachment to a tool so that the cutting insert engages a work material when the tool is in operation. The cutting insert comprises a substrate (48) and an polycrystalline diamond composite layer on the substrate. The polycrystalline diamond composite layer has a transition region (50), bonded to the substrate, comprising a composite polycrystalline material in which the cemented carbide pieces, which comprise between about 40 volume percent and about 80 volume percent, and the diamond crystals are interspersed in one another. The polycrystalline diamond composite layer further includes an outer region (52), bonded to the transition region, comprising a composite polycrystalline material in which the cemented carbide pieces, which comprise between about 5 volume percent and about 45 volume percent, and the diamond crystals are interspersed in one another.

Description

POLYCRYSTALLINE DIAMOND COMPOSITE CUTTING INSERT FOR ATTACHMENT TO A TOOL BACKGROUND OF THE INVENTION The invention pertains to a polycrystalline diamond composite cutting insert having a polycrystalline diamond composite layer wherein the cutting insert attaches to a supporting tool body. More particularly, the invention pertains to a polycrystalline diamond composite cutting insert having a polycrystalline diamond composite layer wherein the outer region of the polycrystalline diamond composite layer contains less than 100 volume percent diamond crystals.

In the past, cutting tools, such as, for example, roof drill bits and point attack tools, used a cutting insert that comprised a cemented carbide substrate with a polycrystalline diamond composite layer thereon so that this layer presented the working surface of the cutting insert. For example, pending U.S. Patent Application Serial No. 07/935,956, filed on August 26, 1992, for a CUTTING BIT AND CUTTING INSERT, assigned to the assignee, Kennametal Inc. , of Latrobe, Pennsylvania, of the present patent application shows and describes a roof drill bit using cutting inserts comprising a cemented carbide substrate with a layer containing polycrystalline diamond thereon. As an. rher example, issued U.S. Patent No. 5,161,626, to Burkett, for an ATTACK TOOL INSERT WITH POLYCRYSTALLINE DIAMOND LAYER, shows a point attack style of tool using a cutting insert including a polycrystalline diamond composite layer over a portion of the cemented tungsten carbide substrate wherein the outer region of the layer consists of 100 volume percent polycrystalline diamond. See Column 3, lines 19 through 35, of U.S. Patent No. 5,161,627.

While cutting tools using a polycrystalline diamond composite as an external surface layer performed in a satisfactory fashion, these tools taught the use of a polycrystalline diamond composite layer wherein the outer region thereof comprised approximately 100 volume percent diamond crystals. One drawback with an outer region comprising 100 volume percent diamond crystals was that it had the tendency to fracture and peel due to its brittleness. This resulted in the loss of the polycrystalline diamond composite layer which led to the tool losing its operating efficiency, as well as its cost advantages over traditional bits using a cemented carbide insert. Another drawback with earlier tools that used an outer region having a composition of about 100 volume percent diamond crystals has been that it was necessary to provide a transition region between this outer region and the substrate. The presence of the transition region was necessary because of the use of an outer layer having about 100 volume percent diamond crystals. While the transition region played an important role when an outer layer of about 100 volume percent diamond crystals was used, its use increased the manufacturing costs. This is not to say, however, that a transition region is not useful. In fact, the inventors contemplate the use of a transition region in certain embodiments. But in other embodiments, the inventors do not contemplate the presence of a transition region. In light of earlier efforts, it becomes apparent that it would be desirable to provide a tool using a polycrystalline diamond composite cutting insert wherein the polycrystalline diamond composite layer does not contain an outer region having a content of approximately 100 volume percent diamond crystals thereby resulting in the cutting insert being less brittle than polycrystalline diamond composite cutting inserts of the past.

It also becomes apparent that in certain applications it would be desirable to provide a tool using a polycrystalline diamond composite cutting insert wherein there is an absence of a transition region between the substrate and the outer region. SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved polycrystalline diamond composite cutting insert that does not use approximately

100 volume percent diamond crystals in the outer region of the polycrystalline diamond composite layer.

It is another object of the present invention to provide an improved polycrystalline diamond composite cutting insert that is not as brittle as earlier polycrystalline diamond composite cutting inserts.

It is still another object of the invention to provide an improved polycrystalline diamond composite cutting insert that in certain applications does not use a transition region between the substrate and the outer region of the polycrystalline diamond composite layer.

In one form thereof, the invention is a polycrystalline diamond composite cutting insert for attachment to a tool so that the cutting insert engages a work material when the tool is in operation. The cutting insert includes a substrate. The cutting insert further includes a transition region, bonded to the substrate, which includes a mixture of diamond crystals and cemented carbide pieces pressed under sufficient heat and pressure to create a composite polycrystalline material in which the diamond crystals and the cemented carbide pieces are interspersed in one another. The cemented carbide pieces comprise between about 40 volume percent and about 80 volume percent of the transition region. The cutting insert further includes an outer region, bonded to the transition region, and having at least one exposed surface that engages the work material. The outer region comprises a mixture of diamond crystals and cemented carbide pieces pressed under sufficient heat and pressure to create a composite polycrystalline material in which the diamond crystals and the cemented carbide pieces are interspersed in one another. The cemented carbide pieces comprise between about 30 volume percent and about 45 volume percent of the outer region.

In another form thereof, the invention is a tool for working in earth strata, earth surfaces, and the like. The tool comprises a tool body which has a polycrystalline diamond composite cutting insert at one end thereof. The cutting insert includes a cemented carbide substrate affixed to the body with a polycystalline diamond composite layer on the substrate. The polycrystalline diamond composite layer includes a transition region, bonded to the substrate, and which comprises a mixture of diamond crystals and cemented carbide particles wherein the cemented carbide pieces in the transition region comprise between about 40 volume percent to about 80 volume percent of the transition region. The polycrystalline diamond composite layer further includes an outer region bonded to the transition region. The outer region comprises a mixture of diamond crystals and cemented carbide particles wherein the cemented carbide pieces comprise between about 5 volume percent to about 45 volume percent of the outer region.

In yet another form thereof, the invention is a polycrystalline diamond composite cutting insert for attachment to a tool so that the cutting insert engages a work material when the tool is in operation. The cutting insert comprises a substrate and an outer region, which is bonded to the substrate. The outer region has at least one exposed surface that engages the work material. The outer region further comprises a mixture of diamond crystals and cemented carbide pieces pressed under sufficient heat and pressure to create a composite polycrystalline material in which the diamond crystals and the cemented carbide pieces are interspersed in one another. The cemented carbide pieces comprise between about 45 volume percent and about 80 volume percent of the outer region. BRIEF DESCRIPTION OF THE DRAWINGS The following is a brief description of the drawings which form a part of this patent application:

FIG. 1 is a side cross-sectional view of a pressing unit used to make one embodiment of the polycrystalline diamond composite cutting insert of the present invention;

FIG. 2 is a perspective view of the polycrystalline diamond composite cutting insert made by the pressing unit of FIG. 1;

FIG. 3 is a cross-sectional view of the cutting insert of FIG. 2 taken along section line 3-3 of FIG. 2;

FIG. 4 is a side view of a rotatable cutting tool using a plug-style cutting insert with a portion of the steel body near the forward end thereof cut away to reveal the joint between the cutting insert and the tool body;

FIG. 4A is a cross-sectional view of the cutting insert of the tool shown in FIG. 4 taken along section 4A-4A of FIG. 4; FIG. 5 is a side view of a concave drag bit using a cutting insert having a concavity in the forward surface thereof with a portion of the steel body near the forward end thereof cut away to reveal the joint between the cutting insert and the tool body;

FIG. 5A is a cross-sectional view of the cutting insert of the tool shown in FIG. 5 taken along section 5A-5A of FIG. 5;

FIG. 6 is a side view of a two-prong drill bit using cutting inserts of the present invention;

FIG. 6A is a cross-sectional view of the cutting insert of FIG. 6 taken along section line 6A-6A of FIG. 6;

FIG. 7 is a perspective view of a non-coring style of roof bit using cutting inserts of the present invention;

FIG. 7A is a cross-sectional view of the cutting insert of FIG. 7;

FIG. 8 is a side view of a rotatable cutting tool using a cutting insert made in accordance with the present invention with a portion of the steel body near the forward end thereof cut away to reveal the joint between the cutting insert and the tool body;

FIG. 8A is a cross-sectional view of the cutting insert of the tool shown in FIG. 8 taken along section 8A-8A of FIG. 8;

FIG. 9 is a side view of a radial style of tool using a polycrystalline diamond composite cutting insert of the present invention;

FIG. 9A is a front view of the upper portion of the tool of FIG. 9; and

FIG. 10 is a perspective view of a cylindrical cutting insert that does not have a transition region between the outer region and the substrate.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 shows a cross-section of a pressing unit generally designated as 20 that may be employed to make the composite polycrystalline diamond body of the present invention. Although this pressing unit is described hereinafter, U.S. Patent No. 4,604,106, to Hall et al., also describes the pressing unit, and the disclosure of U.S. Patent No. 4,604,106, to Hall et al., is hereby incorporated by reference herein. The pressing unit disclosed in FIG. 1 herein makes a cutting insert of a generally cylindrical shape. It should be appreciated that for some of the tools disclosed hereinafter, the cylindrically shaped cutting insert may not be applicable; however, the cutting inserts for these other applications can be made according to the same principles and techniques used to make the cylindrical cutting inserts by the use of pressing assemblies which accommodate shapes corresponding to the shape of the desired cutting insert.

Referring now to the structure of the pressing unit 20, the pressing unit 20 is generally cylindrical in shape and is designed to fit within the central cavity of an ultra high pressure and temperature cell. According to U.S. Patent No.

4,604,106, those cells are described in U.S. Patent Nos. 3,913,280 or 3,745,623. The pressing unit 20 includes a hollow tube 22 with circular discs 24 and 26 located at the top and bottom of the tube 22, respectively. The hollow tube 22 and discs 24 and 26 together function as a plastic pressure transmitting medium. According to U.S. Patent No. 4,604,106, tube 22 and discs 24 and 26 preferably consist of pressed NaCl, although talc or hexagonal boron nitride may also be used for these structures.

A generally cylindrical protective metal enclosure 28, which is closed at its bottom end, is within the hollow tube 22. The protective metal enclosure 28 is preferably made from molybdenum because of its high melting temperature, but other metals such as zirconium or tantalum also work well according to U.S. Patent No. 4,604,106. A circular disc 30, usually comprising the same metal as the protective enclosure 28, is placed as a closure on the top of the protective enclosure 28.

A substrate 32 of a specific shape is placed in the bottom of the protective enclosure 28. In the embodiment illustrated in Fig. 1, the substrate 32 is of a generally cylindrical shape. It should be appreciated that substrates of different shapes may be positioned at the bottom of the protective enclosure 28. In the case of cutting inserts disclosed herein, the substrate will serve a supporting function for the polycrystalline diamond composite layer produced by the process described herein. In the case of the cutting inserts disclosed herein, it is typical that the substrate of the cutting insert will be directly attached to the tool. One common attachment technique is brazing.

In regard to the composition of the substrate 32, the substrate 32 preferably comprises cemented tungsten carbide wherein the binder is cobalt. The composition of some preferred grades of WC-Co are set out hereinafter. Grade No. 1 contains 5.4 wt% cobalt, the WC has a grain size of 1-18 microns, and the material has a hardness of 88.2 Rockwell A. Grade No. 2 contains 6.3 wt% cobalt, the WC has a grain size of 1-12 microns, and the material has a hardness of 89.6 Rockwell A. Grade No. 3 contains 6.0 wt% cobalt, the WC has a grain size of 1-9 microns, and the material has a hardness of 90.7 Rockwell A. It is also contemplated that a WC-Co composite comprising tungsten carbide of a submicron particle size with about 6 wt% Co and about .5 wt.% Cr could be useful for the cutting insert. Furthermore, a WC-Co composition having 12 wt.% cobalt with the WC having a grain size of 1-9 microns and a hardness of 88.3 R_A could be useful in certain applications. Substrates comprising WC-Co are typically chemically compatible with many of the catalyst/binder systems utilized to form the polycrystalline diamond compact. In addition to WC-Co, the substrate material may comprise other metallic, ceramic, or cermet compositions such as, for example, steel or other ferrous alloys. However, when using steel or any other material which is chemically reactive or otherwise incompatible with the system used to produce the polycrystalline diamond compact, it is desirable to include an additional layer, such as a layer of cemented tungsten carbide (WC-Co) to serve as a barrier between the substrate and the polycrystalline diamond layer. As can be seen from Fig. 1, the interior of the protective enclosure 28 contains a mixture of diamond crystals and cemented tungsten carbide (WC-Co) particles. The composition of the mixture is such so as to define two distinct regions. More specifically, adjacent to the substrate 32 is a transition region 34 (shown by the brackets in FIG. 1) comprising a mixture of pieces of cemented tungsten carbide (WC-Co) 36 and diamond crystals 38 together with a catalyst/binder material for the formation of the polycrystalline diamond composite. The mixture for the transition region may be produced by ball milling the cemented carbide pieces 36 with the diamond crystals 38 and a suitable catalyst/binder material together. The ball- milled mixture can then be poured into the protective enclosure 28 on top of the substrate 32 to a depth so as to produce a finished product with a transition region of the desired thickness.

As previously mentioned herein, the pieces of cemented carbide 36 comprise tungsten carbide with a cobalt binder. At present, for reasons of chemical compatibility, it is considered to be preferable for the pieces of cemented carbide 36 to have the same composition, including the binder content, as the substrate 32. However, it may alternatively be desirable to vary the binder content in the cemented tungsten carbide component to influence various physical properties, such as, for example, the modulus of elasticity, of the pieces of cemented tungsten carbide 36 from those of the cemented tungsten carbide substrate 32. In alternative embodiments with more than one transition region, the binder content or tungsten carbide grain size within the cemented carbide pieces may be varied from region to region to achieve selected physical properties. In this regard, the inventors contemplate that the WC-Co component for the transition region could be the WC-12% Co composition while the WC-Co component for the outer region could be another composition, such as, for example, any one of the WC-Co Grades Nos. 1 through 3 identified above.

The size and shape of the pieces of cemented carbide 36 can be varied to achieve different results. The shape can be regular or irregular. The most economical source of cemented carbide pieces is in the form of crushed grit, or flame-sprayed presintered grit so that irregulary shaped pieces are preferable. For convenience and clarity in the drawings, the size of the pieces of cemented carbide 36 have been exaggerated in this and other drawings over that which is preferable. In the actual microstructure, it is preferable to use cemented carbide pieces that would be too small to be seen with the naked eye without magnification. In addition, it is deemed preferable to use cemented carbide pieces that are significantly larger than the diamond crystals in order to lessen the degree to which the cemented carbide pieces interfere with the formation of diamond to diamond bonding in forming the polycrystalline diamond composite.

The size of the diamond crystals 38 can be varied by well known means to suit the needs of particular applications. In the preferred embodiment, a mixture of diamond crystals having a size ranging from about 1 to about 100 microns is used with the most preferable range being between about 4 microns to about 12 microns.

Various catalyst/binder materials for the formation of polycrystalline diamond compacts are well known in the art. In this preferred embodiment, a catalyst/binder is mixed with the diamond crystals which comprises cobalt powder and is present in about

1 to about 15 volummetric ratio with the diamond cobalt mixture. Alternatively, the catalyst for bonding the crystals together in this transition region 34 may be derived entirely from the binder (cobalt) present in the precemented carbide pieces. In other words, the cobalt or other binder in the cemented carbide pieces 36 may extrude out of the cemented pieces during the pressing cycle in sufficient quantity to function as the catalyst/binder for the diamond crystals 38. Adjacent to the transition region 34 is the outer region 40 (shown in brackets in FIG. 1) comprising a quantity of cemented tungsten carbide particles and diamond crystals together with a suitable catalyst/binder material. It is preferable to use the same catalyst/binder material in the outer region as in the transition region. Again, the catalyst binder in this outer region 40 may alternatively be either partially or entirely provided from the binder which migrates from the cemented carbide pieces 36. The mixture that forms the outer region 40 is formed by ball-milling as described above, and this mixture can be poured into the metal enclosure 28 on top of the transition layer 34 to the desired depth so as to form an outer region in the finished product having the desired thickness. The outer region 40 includes the exposed or working surface of the polycrystalline diamond composite produced by this process. In this embodiment, the diamond crystals 38 are present in the outer region 40 in a mixture of sizes equivalent to that in the transition region 34. However, because the outer region 40 includes the working surfaces of the ultimate compact, it may be preferable to use finer diamond crystals, such as those diamond crystals having a size up to about 5 microns, to improve the finish of the exposed surface.

FIG. 2 is a perspective view of the composite body generally designated as 46 made according to the present invention in the shape of a cylinder. It should be appreciated that compacts of other shapes are contemplated by the present invention as will become apparent from the other specific embodiments shown and described hereinafter.

Referring to the body 46 shown in FIGS. 2 and 3, it comprises a substrate 48 which is made of cemented tungsten carbide with a cobalt binder. As mentioned above, other materials may be used for the substrate 48. In some applications, the substrate 48 is brazed to a supporting structure so as to affix the entire polycrystalline diamond cutting composite insert to the tool which carries the same.

Directly on top of the substrate 48 is a transition region 50 as shown by the brackets. The transition region 50 comprises an integrally bonded mixture of diamond crystals and cemented carbide pieces so as to form a polycrystalline diamond composite. In particular, the transition region 38 comprises polycrystalline diamond crystals together with a catalyst/binder material and pieces of cemented tungsten carbide. The initial mixture of diamond crystals, cemented tungsten carbide and the catalyst/binder has been pressed under sufficient heat and pressure to cause the adjacent diamond crystals to bond to each other and to the cemented tungsten carbide pieces. The transition region 50 also comprises an amount of residual catalyst/binder material left in polycrystalline structure after pressing. The preferred concentration of diamond crystals (including any pores and residual catalyst/binder) in the transition layer 50 is between about 20 volume percent and about 60 volume percent, and most preferably is about 40 volume percent. This means that the cemented carbide content ranges between about 40 to 80 volume percent, with the preferred content of cemented carbide being about 60 volume percent of the transition region.

On top of the transition region 50 is an outer region 52 (which is shown by the brackets in FIGS. 2 and 3) , which includes the exposed or working surface 54 of the polycrystalline diamond composite cutting insert. The outer layer 52 comprises a mixture of diamond crystals 38 together with a catalyst/binder material and pieces of cemented tungsten carbide which have been pressed under sufficient heat and pressure to cause the adjacent diamond crystals to bond to each other and to the cemented tungsten carbide pieces. The diamond crystals (and any residual catalyst/binder) are present in an amount from between about 55 volume percent to about 95 volume percent. This means that the content of the cemented carbide ranges between about 5 volume percent to about 45 volume percent in the outer region. One preferred range for the diamond crystal content (and residual catalyst/binder) is between about 60 volume percent and about 80 volume percent with the balance being cemented tungsten carbide. This means that the cemented carbide pieces range between about 20 volume percent to about 40 volume percent.

In another range, the diamond crystals (and residual catalyst/binder) are between about 55 volume percent and about 70 volume percent. This means that the cemented carbide ranges between about 30 volume percent and about 45 volume percent.

One specific composition comprises about 25 volume percent cemented carbide pieces with the balance being diamond crystals and residual catalyst/binder.

Preferably, the catalyst/binder material is a cobalt powder and is present in this outer region 52 and the transition region 50 in about 1 to about 15 volummetric ratio with the diamond crystals. Alternatively, the catalyst/binder for the outer region 52 can be derived either partially or entirely from the binder which has migrated from the transition region 50. FIG. 3 is a cross section taken along line 3-3 of FIG. 2. The transition region 50 meets the substrate 48 at an interface 55. In the typical prior art composite compact, the interface between the substrate and the adjacent polycrystalline diamond layer is a potentially weak point in the structure because of the stresses that can occur due to the thermal expansion differential. However, with the transition region 50 of the present invention, the thermal expansion problems are moderated by virtue of the fact that the transition region as a whole will have thermal expansion characteristics somewhere between those of the cemented carbide substrate 48 and the outer region 52. During the cooling stage, which is after the pressing of the compact 46, the transition region 50 should shrink more than the outer region 52, but less than the substrate 48. As a result, the strain to the overall structure of the composite compact is reduced, particularly at the interface 55. Referring to Figs. 4 and 4A, there is illustrated a rotatable cutting tool generally designated as 60. This style of tool (or bit) is called a point attack style of tool and may be used in a wide variety of applications, such t , for example, in coal mining or in road planing. Rotatable cutting tool 60 has an elongate steel body 62 with opposite axially forward and rearward ends 64 and 66, respectively. Typically, the tool 60 is rotatably mounted in the bore of a support block at the axially rearward end 66 thereof. U.S. Patent No. 4,201,421, to Den Besten et al., depicts a typical resilient cylindrical retainer used to rotatably connect the bit to the supporting block on a road planing machine. U.S. Patent No. 3,519,309, to Engle et al., shows a dimple ring clip used to typically rotatably connect a rotatable cutting tool to the supporting block on a coal mining machine. A bore 68 is in the axially forward end 64 of the body 62, and this bore 68 receives a polycrystalline diamond composite cutting insert generally designated as 70.

Insert 70 includes a substrate 72 made from cemented tungsten carbide (WC-Co) . The substrate is of a generally cylindrical configuration with an axie.Ily forwardly projecting protrusion 74, which is of a generally conical shape. It should be understood that the protrusion could present a shape other than conical. A polycrystalline diamond layer 76 overlays the surface of the protrusion 74.

The diamond layer 76 comprises a transition region 78, bonded to the substrate, and an outer region 80, bonded to the transition region 78, which presents an outer working surface 82. The composition of the transition region 78 is within the same ranges, and has the same preferred specific composition, as the transition region 50 of the earlier specific embodiment. The composition of the outer region 80 is within the same ranges, and has the same preferred composition, as the outer region 52 in the earlier specific embodiment. Referring now to Figs. 5 and 5A, there is shown a concave drag bit generally designated as 86. The concave drag bit 86 is shown and described in detail in U.S. Patent No. 5,078,219, to Morrell et al. , for a CONCAVE DRAG BIT CUTTER DEVICE AND METHOD, and this patent is hereby incorporated by reference herein. A brief description of the concave drag bit 86 now follows.

Concave drag bit 86 includes an elongate steel body 88 having opposite axially forward and rearward ends 90 and 92, respectively. The concave drag bit 86 is typically connected to a support at the axially rearward end 92 thereof. The axially forward end 90 presents a flat surface to which the polycrystalline diamond cutting insert, generally designated as 94, is affixed as by brazing or the like.

Referring to the structure of the cutting insert 94, it includes a generally cylindrical substrate 96 having an axially rearwardly facing surface which attaches to the flat surface of the elongate body 88. The substrate 96 also includes an axially forwardly facing surface 98 which defines a concavity 100. In the specific embodiment illustrated in Figs. 5 and 5A, the surface 98 takes on a conical shape; however, the shape could be curved (such as illustrated in Fig. 3(b) of U.S. Patent No. 5,078,219) or of a truncated cone (such as illustrated in Fig. 4(b) of U.S. Patent No. 5,078,219) .

A polycrystalline diamond composite layer generally designated as 102 overlays the axially forward surface 98. A polycrystalline diamond composite layer 102 includes a transition region 104 bonded to the substrate 96 and an outer region 106 bonded to the transition region 104. The composition of the transition region 104 is within the same ranges, and has the same preferred specific composition, as the transition region 50 of the earlier specific embodiment. The composition of the outer region 106 is within the same ranges, and has the same preferred specific composition, as the outer region 52 in the earlier specific embodiment. Referring to Figs. 6 and 6A, there is illustrated a two-prong roof bit generally designated as 120. Roof bit 120 has a body 122 with a shank 124 projecting rearwardly therefrom. The body has a pair of prongs 125 projecting axially forwardly therefrom. The distal end of each prong 125 has a polycrystalline diamond composite cutting insert 126 affixed thereto by brazing or the like.

Referring to FIG. 6A, each cutting insert 126 comprises a substrate 128 typically made of cemented tungsten carbide. The substrate 128 has an exposed flat surface on which there is a polycrystalline diamond composite layer 130. The polycrystalline diamond composite layer 130 comprises a transition region 132 bonded to the substrate 128 and an outer region 134 bonded to the transition region 132. The outer region 134 presents the working surface 138 of the cutting insert 126.

The composition of the transition region 132 is within the same ranges, and has the same preferred specific composition, as the transition region 50 of the earlier specific embodiment. The composition of the outer region 134 is within the same ranges, and has the same preferred specific composition, as the outer region 52 in the earlier specific embodiment. Referring to Figs. 7 and 7A, there is illustrated a two-insert roof bit generally designated as 140. The roof bit 140 includes a drill bit body 142 having an axially forward end and an opposite axially rearward end. The bit body 142 contains a pair of oppositely disposed substantially identical pockets 144 in the axially forward end thereof. Each pocket 144 receives its corresponding polycrystalline diamond composite cutting insert 146 which is affixed in its corresponding pocket by brazing or the like.

The preferred braze alloy is the EASY-FLO 45 braze alloy made by Handy & Harman, New York, New York. Physical properties of the braze alloy are set forth in product literature available from Handy & Harman. These properties include a solidus of 1125°F (605°C) and a liquidus of 1145°F (620°C) . The nominal composition of this braze alloy is (in weight percent) : 45wt% Ag; 15 wt% Cu; 16 wt% Zn; 24 wt% Cd. This braze alloy is a low temperature alloy that brazes at a low enough temperature so as to not harm the polycrystalline diamond composite cutting insert. Cutting insert 146 comprises a polycrystalline diamond composite having a substrate 148 and a polycrystalline diamond composite layer 150. The substrate is made from cemented tungsten carbide. The diamond layer 150 comprises a transition region 152 adjacent to the substrate and an outer region 154 adjacent to the transition region 152. The composition of the transition region 152 is within the same ranges, and has the same preferred specific composition, as the transition region 50 of the earlier specific embodiment. The composition of the outer region 154 is within the same ranges, and has the same preferred specific composition, as the outer region 52 in the earlier specific embodiment. In regard to the geometry of the cutting insert 146, pending United States patent application Serial No.07/935,956, filed August 26, 1992, for CUTTING BIT AND CUTTING INSERT, and assigned to the assignee, i.e., Kennametal Inc., of Latrobe, Pennsylvania, of this patent application, describes the geometry in detail, and this patent application is hereby incorporated by reference herein. Referring to Figs. 8 and 8A, there is illustrated a rotatable cutting tool generally designated as 160. This style of tool (or bit) is called a point attack style of tool and may be used in a wide variety of applications, such as, for example, in coal mining or in road planing. Rotatable cutting tool 160 has an elongate steel body 162 with opposite axially forward and rearward ends 164 and 166, respectively. Typically, the tool 160 is rotatably connected to a support block 168 at the axially rearward end 166 thereof by a resilient sleeve 170 such as shown by the Den Besten et al. patent referred to hereinabove. A recess 172 is in the axially forward end 164 of the body 162, and this recess 172 receives a polycrystalline diamond cutting insert generally designated as 174.

Referring to FIG. 8A, cutting insert 174 includes a substrate 176 made from cemented tungsten carbide (WC-Co) . The substrate 176 presents a specific shape wherein it has a tip section 178, a frusto- conical intermediate section 180, a cylindrical base section 182, and a valve seat portion 184. A polycrystalline diamond composite layer 186 overlays the surface of the tip section 178, the surface of the intermediate section 180, and the surface of the base section 182.

The diamond layer 186 comprises a transition region, bonded to the substrate, and an outer region, bonded to the transition region, which presents an outer working surface. The composition of the transition region is within the same ranges, and has the same preferred specific composition, as the transition region 50 of the earlier specific embodiment. The composition of the outer region is within the same ranges, and has the same preferred specific composition, as the outer region 50 in the earlier specific embodiment. Referring to FIG. 9 and FIG. 9A, there is illustrated a radial style of tool 188. A typical radial tool is shown and described in U.S. Patent No. 3,305,274, to Goodfellow et al. , and this patent is hereby incorporated by reference herein. Radial tool 188 has a body 190 with a forward recess 192 which receives the cutting insert 194. Polycrystalline diamond composite cutting insert 194 includes a substrate 196 with a polycrystalline diamond composite layer 198 thereon.

The diamond layer 198 comprises a transition region, bonded to the substrate, and an outer region, bonded to the transition region, which presents an outer working surface. The composition of the transition region is within the same ranges, and has the same preferred specific composition, as the transition region 50 of the earlier specific embodiment. The composition of the outer region is within the same ranges, and has the same preferred specific composition, as the outer region 52 in the earlier specific embodiment.

Referring to FIG. 10, there is shown a another embodiment of the present invention in which there is no transition region between the outer region and the substrate. Cylindrical cutting insert 200 presents a substrate 202 and a single outer region 204. Outer region 204 comprises between about 25 to about 80 volume percent cemented tungsten carbide particles with, the balance being diamond crystals and residual binder/catalyst. One preferred composition for the outer region 204 is about 50 volume percent comprising cemented carbide pieces, and the balance is diamond crystals and residual catalyst/binder. The outer region 204 presents a working surface 206. There is an interface 208 between the substrate and the outer region 204.

This embodiment is manufactured in a way similar to that for the earlier embodiments except that only one layer is positioned on top of the substrate within the mold, rather than two layers being positioned on top of the substrate.

It should be appreciated that the other specific embodiments illustrated in FIGS. 1 through 9A could also use a single outer region as opposed to a combination of a transition region and an outer region.

Claims

WHAT IS CLAIMED IS;

1. A polycrystalline diamond composite cutting insert for attachment to a tool so that the cutting insert engages a work material when the tool is in operation, the cutting insert comprising: a substrate; a transition region, bonded to the substrate, comprising a mixture of diamond crystals and cemented carbide pieces pressed under sufficient heat and pressure to create a composite polycrystalline material in which the diamond crystals and the cemented carbide pieces are interspersed in one another, the cemented carbide pieces comprising between about 40 volume percent and about 80 volume percent of the transition region; and an outer region, bonded to the transition region, having at least one exposed surface that engages the work material, the outer region comprising a mixture of diamond crystals and cemented carbide pieces pressed under sufficient heat and pressure to create a composite polycrystalline material in which the diamond crystals and the cemented carbide pieces are interspersed in one another, the cemented carbide pieces comprising between about 5 volume percent and about 45 volume percent of the outer region.

2. The polycrystalline diamond composite cutting insert of claim 1 wherein the substrate comprises cemented tungsten carbide with a cobalt binder.

3. The polycrystalline diamond composite cutting insert of claim 1 wherein the total volume percent of cemented carbide pieces in the outer region is between about 30 volume percent and about 45 volume percent.

4. The polycrystalline diamond composite cutting insert of claim 1 wherein the total volume of cemented carbide pieces in the outer region is between about 20 volume percent and about 40 volume percent.

5. The polycrystalline diamond composite cutting insert of claim 1 wherein the total volume of cemented carbide pieces in the outer region is about 25 volume percent.

6. The polycrystalline diamond cutting insert of claim 1 wherein the total volume percent of cemented carbide pieces in the transition region is between about 50 volume percent and about 70 volume percent.

7. The polycrystalline diamond cutting insert of claim 1 wherein the total volume percent of cemented carbide pieces in the transition region is about 60 volume percent.

8. The polycrystalline diamond composite cutting insert of claim 1 wherein the volume percent of diamond crystals in the outer region is higher than the volume percent of diamond crystals in the transition region.

9. The polycrystalline diamond composite cutting insert of claim 1 wherein the diamond crystals are distributed throughout the outer region in a relatively uniform fashion.

10. The polycrystalline diamond composite cutting insert of claim 6 wherein the diamond crystals are distributed throughout the transition region in a relatively uniform fashion.

11. The polycrystalline diamond composite cutting insert of claim 1 wherein the binder content of the cemented carbide in the transition region is higher than the binder content in the cemented carbide in the outer region.

12. The polycrystalline diamond composite cutting insert of claim 1 wherein the diamond crystal particle size is smaller in the outer region than the diamond crystal particle size in the transition region.

13. The polycrystalline diamond composite cutting insert of claim 1 wherein the particle size of the cemented carbide pieces in the transition region is different than the particle size of the cemented carbide pieces in the outer region

14. A tool for working earth strata, earth surfaces, and the like comprising: a tool body having a polycrystalline diamond composite cutting insert at one end thereof; the cutting insert including a cemented carbide substrate affixed to the body with a polycystalline diamond composite layer on the substrate; the polycrystalline diamond composite layer including a transition region bonded to the substrate, the transition region comprising a mixture of diamond crystals and cemented carbide particles wherein the cemented carbide pieces in the transition region comprise between about 40 volume percent to about 80 volume percent of the transition region; and the polycrystalline diamond composite layer further including an outer region bonded to the transition region, the outer region comprising a mixture of diamond crystals and cemented carbide particles wherein the cemented carbide pieces comprise between about 5 volume percent to about 45 volume percent of the outer region.

15. The tool of claim 14 wherein the cemented carbide pieces comprise between about 30 volume percent to about 45 volume percent of the outer region.

16. The tool of claim 14 wherein the tool body has opposite forward and rearward ends, the polycrystalline diamond composite cutting insert being attached to the tool body at the forward end thereof, the tool body having a recess at the forward end thereof which receives a portion of the substrate of the cutting insert, and the polycrystalline diamond composite layer covering the surface of the substrate that is axially forward of the forward end of the tool body.

17. The tool of claim 16 wherein the surface of the substrate that is axially forward of the ^orward end of the tool body is generally conically shaped.

18. The tool of claim 16 wherein the surface of the substrate that is axially forward of the forward end of the tool body presents a generally frusto- conically shaped surface extending axially forwardly of the forward end of the tool body, and a generally conically shaped surface contiguous with and extending axially forwardly from the generally frusto-conically shaped surface.

19. The tool of claim 16 wherein the tool body has opposite forward and rearward ends, the cutting insert being affixed to the forward end of the tool body, the substrate of the cutting insert having an axially forwardly facing surface presenting a concavity, and a polycrystalline diamond composite layer on the axially forwardly facing surface.

20. The tool of claim 19 wherein the concavity is of a generally conical shape.

21. The tool of claim 14 wherein the tool body has opposite forward and rearward ends, a plurality of the cutting inserts being affixed at the forward end of the tool body.

22. The drilling tool of claim 21 wherein the tool is a non-coring roof bit.

23. The drilling tool of claim 21 wherein the tool is a two-prong coring roof bit.

24. A polycrystalline diamond composite cutting insert for attachment to a tool so that the cutting insert engages a work material when the tool is in operation, the cutting insert comprising: a substrate; and an outer region, bonded to the substrate, having at least one exposed surface that engages the work material, the outer region comprising a mixture of diamond crystals and cemented carbide pieces pressed under sufficient heat and pressure to create a composite polycrystalline material in which the diamond crystals and the cemented carbide pieces are interspersed in one another, the cemented carbide pieces comprising between about 45 volume percent and about 80 volume percent of the outer region.

25. The cutting insert of claim 24 wherein the outer region comprises about 50 volume percent cemented carbide pieces and the balance being diamond crystals and residual catalyst/binder.