Cermet Product And Method And Apparatus For The Manufacture Thereof

Abstract

The invention relates to a cermet product and a method and apparatus for the manufacture thereof in which carbonaceous material is placed in a cell in the presence of metal and converted to diamond form. The converted charge upon removal from the apparatus is shaped and mounted on a tool holder and it is then adapted for use as a turning tool. The invention contemplates conversion of the carbon-metal charge in a shaped cavity to reduce the amount of shaping required after the charge is removed from the chamber in which it is converted.

Description

This invention relates to diamond products and to methods of, and apparatus for, manufacturing such products.

Diamonds are a crystalline form of carbon and it has been found that nondiamond form of carbon can be converted to diamond form by subjecting the carbon to certain conditions of heat and pressure. The term carbon as employed herein is intended to mean substantially any material containing carbon in nondiamond form. Thus, materials which are partly carbon, or which contain carbon in the form of carbon compounds are included within the scope of the term carbon as employed herein. For practical reasons, the carbon employed is as nearly pure carbon as possible, with certain physical specifications, because any other material included therewith is merely excess and reduces the efficiency of any conversion cycle.

Different methods can be employed for establishing the conditions of pressure and temperature at which carbon converts to the diamond form but the present invention is concerned with the process wherein the carbon is confined within a cell and is subjected to mechanical pressure and to the development of heat within the cell by passing an electric current therethrough. It has been found that the process referred to operates with much greater efficiency and at the lowest temperatures and pressures when a metal is included in the cell with the carbon. A number of metals have been found suitable for this purpose such as one or more metals selected from the class consisting of iron, cobalt, nickel, rhodium, ruthenium, palladium, osmium, iridium, chromium, tantalum, manganese, and alloys thereof. Other metals such as titanium, zirconium, and copper can be included in the metal component in the cell if so desired. It is essential that at least one of the metals be a solvent for carbon because it is believed that, when the carbon converts from the nondiamond state thereof to its diamond state, the carbon is dissolved in the metal solvent therefor and, inasmuch as the conditions of heat and pressure are those at which the crystalline diamond form of carbon is stable, the carbon immediately, following the dissolving thereof in the metal, precipitates from the metal in the form of diamond. The pressures employed in such cells range upwardly to 50,000 atmospheres and more and temperatures established within the cell range from 1,000.degree. to 2,000.degree. Centigrade. Under these conditions of heat and pressure, the metal in the cell becomes molten and, as mentioned above, the carbon in the cell goes into solution in the metal and precipitates therefrom as diamond crystals. The carbon in the cell, whether in the form of one or more solid pieces, or in the form of powder. Excellent results have been obtained from the use of carbon having a density of from about 1.7 to about 1.9 but higher and lower density carbon is not excluded. This permits the metal to infiltrate throughout the carbon and promotes efficient conversion of the carbon to diamond.

According to the present invention it is desired for the metal included in the cell with the nondiamond form of carbon to be a tough high melting point material and it has been found that alloys of iron, nickel, and chromium of the class of alloys referred to as Inconels are suitable for this purpose either with or without the addition of small amounts of other metals such as manganese, tantalum, titanium, zirconium, and copper.

In the usual manner in which diamonds are manufactured, the charge is removed from the cell in which the diamonds are formed, and the diamond crystals are recovered by a complex and lengthy physical and chemical processing which results in completely freeing the diamond crystals from all the other material in the cell. The now clean diamonds are then sized and are ready for use as the abrasive component in abrading devices such as diamond wheels, drills, saws, and the like or for incorporation in lapping compounds.

Diamonds of a size sufficient to form large single point tools have not heretofore been produced by any manufacturing method because synthetic diamonds have always been recovered from the cell in which they are made in the manner referred to and which, as mentioned, will produce only small diamond crystals ranging in size from about 40 mesh down to micron sizes.

Examination of a charge from a cell of the nature referred to after conversion thereof will reveal that there are diamond crystals in the charge prior to crushing which are substantially larger than any of the diamond crystals which can be recovered from a cell by the aforementioned recovery process. The diamond crystals in the charge are of random sizes and random orientation and in intertwined relation and tend to break at the weak section or sections thereof when the charge in the cell is crushed thereby leading to the relatively small size crystals that are recovered by the aforementioned lengthy and time consuming chemical and physical recovery process. The diamonds recovered by such a process are similar to natural diamonds, with respect to hardness and can be employed for any cutting or abrading operations for which natural diamonds are employed.

The present invention is based on the observation that the converted charge in a cell consists of the diamond crystals and the metal in the cell and an insignificant amount of unconverted carbon all intimately bonded together and with the diamond crystals having random orientation. Sometimes no unconverted carbon at all can be found in the converted charge. In particular, the bond between the diamonds and the metal, and which is referred to herein as the "matrix metal," is particularly intimate because the diamonds are precipitated from the metal-carbon melt and, thus, at the interface where each diamond crystal engages the matrix metal there is a bond which forms, and which is, of course, the most intimate possible bond between the diamond and metal and one which is not possible to establish except when the diamond is in a thermodynamically stable state. This bond is destroyed by the lengthy process ordinarily employed for the recovery of diamonds.

The diamond crystals, once recovered from the charge and cleaned of all adherent metal, cannot again have such an adherent metal coating applied thereto for the reason given above. It has been attempted to plate diamonds in various manners, such as by electrolytic plating, and by vapor plating, and the like, but no process known to applicant can reproduce the intimate molecular bond existing between the diamond and metal which is formed while the diamond is under conditions in which the diamond is thermodynamically stable.

Tests and experiments performed on the charge material following conversion reveal that the charge exhibits considerably physical strength in the form of compressive strength and in resistance to abrasion. It appears that the charge material, compacted at the extremely high pressures employed during the conversion process produces an extremely solid material in which the matrix metal and diamonds support one another and wherein the diamonds have random orientation so that the converted material in the charge presents the possibility for use as cutting and abrading material without recovering the diamonds in a completely clean form and thereafter forming a useful abrading material by again combining the diamond with a supporting substance or matrix therefor. For the material of the charge to be employed as a cutting material, however, it is required that, in addition to the matrix material possessing a high compressive strength and physically supporting the diamonds, it be resistant to high temperatures and tough so that it will withstand conditions that are encountered in cutting operations.

With the foregoing in mind, a principal objective of the present invention is the provision of a diamond product and a method of making the diamond product in which the customarily followed process for recovery of the diamonds in clean form is eliminated.

A particular object of the present invention is the provision of a diamond product and a method of, and apparatus for, making the product in which the charge in the cell in which the diamonds are produced is formed directly into cutting members such as cutting inserts for use in metal forming operations and the like.

A still further object of the present invention is the provision of a diamond product and a method of, and apparatus for, making the product in which end products can be obtained at greatly reduced costs over anything that has been possible heretofore.

A still further object of the present invention is the provision of a diamond product and a method of, and apparatus for, manufacturing the product in which the diamond product, as removed from the cell in which the diamonds are formed, requires the absolute minimum in forming operations to convert it into a cutting insert.

The nature of the present invention will be more clearly understood upon reference to the following detailed specification taken in connection with the accompanying drawings in which:

FIG. 1 is a sectional view showing a typical apparatus employed for effecting the conversion of nondiamond carbon to diamond;

FIG. 2 illustrates the charge in a cell after conversion and with the outer sleeves of the cell removed;

FIG. 3 is a fragmentary perspective view showing a cutting element made from the charge of FIG. 2 and mounted on a holder;

FIG. 4 is a view showing various cross sectional shapes possible for the cell in which the charge is converted;

FIG. 5 is a photomicrograph of a section through a typical charge shown at 200 times natural size;

FIG. 6 is a view like FIG. 5 but at 500 times natural size;

FIGS. 7, 8, 9, and 10 are perspective views showing still other tools that can be manufactured using the cutting elements according to the present invention;

FIG. 11 shows a cell in vertical cross section in which divider members separate the charge into discrete portions;

FIG. 12 is a cross sectional view of the cell of FIG. 11 and is indicated by line XII--XII on FIG. 11; and

FIG. 13 is a perspective view of a typical discrete portion of the cleavage in the cell of FIGS. 11 and 12 after conversion and removal from the cell.

FIG. 1 shows one type of apparatus in which nondiamond graphite or carbon can be converted to diamond under proper conditions. In FIG. 1, reference numeral 10 is a ring, such as a ring of cemented tungsten carbide material, which is press fitted into a heavy surrounding steel ring in order to withstand the stresses to which it is subjected. Pressure pistons enter the ring 10 from opposite ends to exert pressure on the charge therein. One such piston is indicated at the top of the cell by reference numeral 12, with the not-shown piston at the bottom of ring 10 being identical to piston 12. The prepared cell containing the charge comprises an inner sleeve 16 of alumina, a tube 18 of graphite surrounding tube 16, and a further insulating tube 20, of alumina, for example, surrounding tube 18.

Within tube 16, in the particular cell arrangement shown in FIG. 1, there is placed body 22 of carbon which preferably has a density of from about 1.7 to 1.9. Holes are drilled into the body 22 of carbon from the opposite ends thereof with each hole receiving a rod or wire 24 of the metal or metal alloy in which the carbon goes into solution during the conversion process. The holes in the block or body 22 of carbon, one of said holes being indicated at 25, are laterally offset from each other so that the rods or wires 24 therein do not interfere with movement of the pressure pistons toward each other during conversion of the charge.

Each end of tube 16 has therein a pair of alumina discs 26 in closing relation to the ends of the tube. Larger metal discs 28 extend over the ends of the cell the full diameter of outer tube 20 and are in electrically conductive engagement with the adjacent end of graphite tube 18. Graphite tube 18 is a heater tube and becomes hot by passing an electric current therethrough which is conveyed to and from tube 18 by discs 28.

A metal ring 29 may be provided resting on an adjacent disc 28 and inside ring 29 is an alumina plug 31. Ring 29 brings the adjacent pressure piston into electrically conductive relation with the adjacent disc 28.

Disposed between the cell and the ring 10 and between the pressure pistons and the ring 10 are sealing sleeves 30 which are of an electrical insulating material which are, and have the characteristics of, pyrophyllite, or talc. Advantageously, sleeves 30 are of the shape illustrated with a metal sleeve 32 disposed therebetween. The material of the sleeves 30 is such that they will become somewhat deformed under the pressure exerted thereon by the piston 12 at the top of the cell and the corresponding pressure piston at the bottom of the cell so as to permit the pressure pistons to advance toward the cell as the charge in the cell reduces in volume during conversion, but will not extrude between ring 10 and the pressure pistons which would cause the pressure on the cell to be lost.

After the cell as described has been placed in the apparatus shown, the pressure pistons are pressed toward each other to develop a certain pressure on the material within the cell while simultaneously electric current is passed through the cell between the pressure pistons and through tube 18 whereby the tube 18 becomes heated quickly and material in the cell also becomes heated. When the conditions of pressure and temperature in the cell reach the diamond stable region, there is a sudden conversion of the carbon in the cell to diamond. The conditions of pressure and temperature and other parameters established in the cell and leading to the conversion of the carbon to diamond, might, for example, be 50,000 to 75,000 atmospheres, and 1,200.degree. to 2,000.degree. Centigrade. The metal of the rods or wires becomes molten under the conditions at which diamonds will form and this molten metal infiltrates the carbon in the cell and dissolves the carbon to form a metal carbon melt and it is from this molten mass that the carbon converts or crystallizes into diamond form with simultaneous precipitation from the melt.

When the cell is removed from the die, it has somewhat the appearance as shown in FIG. 2 except that the sleeves 16, 18, and 20 still have at least fragments in place on the converted material when it is removed from the cell. FIG. 2, more exactly, shows the appearance of the converted charge after the outer sleeves of the cell have been removed. This converted charge, shown in ideal form in FIG. 2 consists of relatively solid member 40.

In view of the fact that the metal becomes molten and dissolves the carbon, there is sufficient migration of the metal and carbon that there is uniform distribution of metal in member 40.

The present invention takes advantage of the fact that diamond crystals are grown in a matrix of metal, and are tightly adherent to the metal, to produce novel diamond products having particular merit in respect of the forming of cutting tools.

What is proposed by the present invention is the forming of the converted charge into one or more inserts for mounting on holders so that the inserts can be employed as turning tools. It has been found that inserts or cutting elements manufactured in this manner have extremely long life and can be employed in substantially any situation in which single point natural diamond tools are now utilized.

Single point diamond tools, as is known, are tools having a single large natural diamond mounted on a holder, by brazing, for example, and sharpened. Such tools are employed for shaping green carbide compacts, alumina, other ceramics, and similar materials which are so hard and abrasive that ordinary cutting tools cannot be used. Single point diamond tools, however, are expensive and are limited as to size, shape, and availability, and are extremely difficult and expensive to resharpen once they become dull.

Inserts or cutting tips made from the material removed from the cell in accordance with the teachings of the present invention can be roughly shaped as by a silicon carbide wheel and finish shaped by using a diamond wheel of from 180 grit to 300 or 400 grit. While the inserts or cutting elements according to the present invention can be shaped relatively simply, they nevertheless are possessed of extreme resistance to wear and can exhibit length of life and a quality of performance as good as that of a single point diamond tool.

Returning to FIG. 2, the compact taken from the cell may have weak regions or cleavage planes therein, as at 44 and if a portion is broken off from member 40, it will be a rather roughly formed disc. This small disc can be shaped by grinding to form a cutting element 45 that can be mounted on a holder 46 as shown in FIG. 3 as by brazing. Alternatively, the cutting tip can be clamped to the holder by any conventional insert clamping arrangement. The final grinding of the insert or cutting tip can take place after it is mounted on the holder if so desired. Such final shaping might take the form of finishing the top and periphery of the insert or cutting tip to provide it with a sharp edge, or grinding the tool to provide it with a clearance angle.

Alternatively, a piece can be cut from member 40 and then shaped to a cutting element. The cell illustrated in FIG. 1 is circular in cross section so that member 40, after conversion, is roughly cylindrical, but other cross sectional configurations are possible as shown in FIG. 4. FIG. 4, for example, shows a triangular form at 48, a square form at 50 and a somewhat elliptical form at 52. Round cells, and cells of the configurations shown in FIG. 4, are quite practical, as well as other cell shapes so long as the loading imposed at the pressure pistons does not cause the pistons to tilt and interfere with development of uniform pressure on the entire charge in the cell.

FIG. 1 shows the charge in the cell placed therein in the form of a block or rod of carbon with metal wires inserted therein but it is also quite practical to insert the carbon charge into the cell in the form of powder. The metal can also be in the form of powder and, further, the carbon and metal powder can be admixed in the proper proportions and then charged into the cell. In a cell charged with admixed carbon and metal powders, it is possible to induce the formation of cleavage planes by the introduction of layers of material within the cell which will not interfere with the conversion process in any way and which will part freely from the connected charge. Further, as will be seen hereinafter, the charge in the cell can be placed therein in such a manner that, after conversion, it is in the form of discrete members of predetermined size and shape. Still further, the charge can be made up of discs of carbon and metal arranged in alternating relation in the cell.

The nature of the charge removed from the cell shows that there is growth of diamond crystals, therein of substantial size and some of which are relatively complex in shape. The space between the individual diamond crystals, and, even sometimes regions inside the diamond crystals, are filled with the matrix metal that is charged into the cell with the carbon and which matrix metal, as mentioned, is tightly adherent to the diamond crystals.

FIGS. 5 and 6 demonstrate the structural nature of the material when it is taken from the cell. FIG. 5 is a photograph 200 times natural size of a sample of material taken from the cell and ground to a smooth finish. FIG. 6 is a photograph of a portion of FIG. 5 but at 500 times natural size and has been etched to sharpen the contrast between the diamond crystals and the matrix metal in which the crystals are embedded and bound.

The conversion of the carbon in the cell is often as high as 95 per cent or better to diamond and a fully converted charge is thus substantially completely diamond with a metal matrix completely filling the space between the diamonds and integrally bonded to the diamonds. The diamond crystals are thus extremely tightly and strongly supported and inserts formed of this material are extremely strong and wear resistant.

The bond of the metal to the diamond crystals in the charge as removed from the cell is different in kind from the bond of metal to diamond that can be obtained from any known plating process. The metal is intimately bonded to all exposed surfaces of the diamond crystals and can be removed therefrom only by prolonged chemical and physical treatment. If the charge is crushed, the diamonds tend to break before the diamond to metal bond breaks, indicating the strength of this bond.

In FIG. 5 the areas indicated by reference numeral 80 are the diamond crystals and the regions indicated at 82 are the matrix metal. It will be noted that the diamond crystals have various shapes and that they are intertwined. In the normal procedure for recovering diamonds from a cell of the type disclosed, and wherein the diamond crystals are completely separated from all of the metal in the cell, the diamond crystals will break at the smaller sections thereof and the result will be rather small diamond crystals having absolutely clean surfaces to which it is difficult to cause any sort of binding or bonding material to adhere.

It the converted charge, when removed from the cell, is not subjected to treatment to remove the matrix metal from the diamonds, the diamonds remain imbedded in the matrix metal so that the metal forms a supporting and enclosing and tightly adherent matrix. The diamond crystals retain their integrity and are supported by the matrix metal and do not break or fracture at the small cross sectional portions thereof. The result seems to be that, while the article removed from the cell can relatively easily be formed as by grinding with a silicon carbide or diamond grit wheel, for example, the articles nevertheless are extremely resistant to wear when used as turning tools or the like. The diamonds have more or less random orientation and no particular care need be taken in locating the cutting edge on the article as in the case with large natural diamond crystals that are presently employed for turning tools. Such natural diamond crystals must be carefully oriented in a certain manner to obtain the best results.

Furthermore, the random orientation of the diamond crystals in the matrix metal insures a strong cutting edge on any part of the insert so finished. The inserts can, therefore, be indexed and inverted and will always present a good edge to the work.

It will be seen in FIG. 5 that the matrix metal completely fills the space between adjacent diamond crystals and some is embodied within the limits of diamond crystals so that the diamond crystals are completely supported by the matrix metal in all directions.

FIG. 6 is a view similar to FIG. 5 but is enlarged to 500 times normal and has been etched so as better to develop the contrast between the diamond crystals and the matrix metal. In FIG. 6 the regions marked 84 are the diamond crystals and the regions marked 86 are the metal regions. Due to the etching carried out on the sample, FIG. 6 more clearly illustrates the great preponderance of diamonds in the material than does FIG. 5. Substantially 83 per cent by volume of the sample is diamond and the remainder is matrix metal.

The tool shown in FIG. 3 is a simple tool using a circular cutting element taken from a conventional cylindrical cell. FIGS. 7, 8, 9, and 10 show certain other types of turning tools that can be made according to the present invention. FIG. 7, for example, shows a holder 90 having a pocket 92 formed therein in which is disposed an insert 94, according to the present invention, which is substantially rectangular. Insert 94 can be made in a rectangular cell and thereafter finished by grinding on the top and bottom and the four edges, as it can be cut from any other shape of connected charge. An insert finished in this manner has four indexed positions and can be inverted and thus has eight effective cutting regions thereon. Furthermore, the insert can be sharpened when it becomes dull and restored to original cutting condition. Insert 94 in FIG. 7 is loosely disposed in the recess and is clamped therein by clamp member 96 which may also hold a chip breaker 98 in place on top of the insert. A shim 100 may be disposed in the pocket beneath the insert if so desired according to conventional practices followed with cutting inserts.

In FIG. 8 the holder 102 is formed with a slot 104 and disposed in the slot in end to end relation are cutting inserts 106 according to the present invention. These inserts may be brazed or cemented in position in the slot. Brazing of the inserts in position is a relatively simple matter because the matrix metal easily fuses with the brazing material. For cementing, an epoxy cement is an ideal material. The tool of FIG. 8 could be used for boring operations, for example.

FIG. 9 shows a tool similar to that illustrated in FIG. 3 except that the insert 108 brazed on the holder 110 is triangular and may be made in a triangular cell.

FIG. 10 shows a fragment of a saw, a cement saw, for example, having teeth 214 and tips 216 made according to the present invention and brazed to the teeth.

The tools illustrated in FIGS. 3 and 7 to 9 utilize relatively large cutting inserts but it will be understood that cutting inserts substantially smaller in cross sectional area than the charge in the cell could be made and brazed or clamped on holders according to the present invention.

FIG. 11 shows in vertical cross section a cell for the formation of articles of a predetermined shape whereby machining time required for reducing the articles to a useable condition is greatly reduced. The cell arrangement is shown in transverse cross section in FIG. 12 and a typical work member as removed from the cell is shown at FIG. 13. Referring more particularly to FIGS. 11 and 12, the outermost sleeve 200 of the cell is in the form of an aluminum oxide member cylindrical on the outside and having a substantially square hole 202 extending axially therethrough. Closely fitted in hole 202 is a square graphite sleeve 204 and within graphite sleeve 204 is a thinner aluminum oxide sleeve 206. The inner and outer alumina sleeves and the intervening graphite sleeve are assembled as shown in FIGS. 11 and 12 and the innermost sleeve 206 receives the charge which is in the form of individual bodies 208 consisting of nondiamond carbon and metal. Disposed between the individual bodies 208 are high density aluminum oxide divider members 210. When the cell illustrated in FIGS. 11 and 12 is subjected to heat and pressure in the diamond stable range of the pressure-temperature equilibrium diagram for carbon, the carbon goes into solution in the metal and substantially immediately precipitates therefrom in the form of diamond crystals so that each body 208 forms, in effect, an individual charge which is converted in the aforesaid manner.

After conversion, the cell is broken open and the converted bodies 208 are removed therefrom. One such body is indicated at 212 in FIG. 13 and it will be seen to comprise a slightly irregular block which is a solid mass of matrix metal and diamonds of the nature which has been described previously. Block 212 in FIG. 13 required only a small amount of machining to finish off the several faces thereof whereupon it can be used as a cutting insert by attaching it to suitable holder therefor. The blocks 212 can be made to any desired shape and need not be square as shown in FIG. 13. Any dimensional size can be made within the limits of cross sectional area on which the necessary pressure can be developed.

The blocks 212 can be used as cutting inserts or, if made to relatively small sizes could be brazed on the tips of teeth 214 of a saw as indicated at 216 in FIG. 10. Other uses for the diamond products as disclosed herein will suggest themselves to those skilled in the art.

When the diamond products according to the present invention are to be employed as cutting inserts, it is important for the metal forming the matrix in which the diamond crystals are imbedded to be a tough high melting point material of the nature of Inconels previously referred to, or other alloys possessing high strength.

Another characteristic of the diamond product manufactured according to the present invention is that it has an extremely high coefficient of heat conductivity. Natural diamonds, for the reason that they have such an extremely high coefficient of heat conductivity, are employed for heat sinks and the like where it might be necessary, for example, to maintain an electrical component such as a transistor within relatively close temperature limits. The high heat conductivity of a natural diamond enables it to be employed to stabilize the temperature of a transistor more efficiently than other materials.

The material of the present invention, consisting principally of diamond crystals intimately bonded to a solid metal matrix has a coefficient of heat conductivity which, while somewhat less than that of solid natural diamond, is nevertheless substantially greater than that of metal. Thus the diamond product according to the present invention can also find a use as a heat sink or the like.

In cases where the diamond product is employed for purposes where its heat conductivity is the important characteristic, the matrix metal would not, of course, be required to be a tough heat resistant material such as Inconel. Conversion of the nondiamond carbon to diamond form in the presence of metal or alloy, even where the metal, or alloy, is not required to be tough or high melting point, or both, still requires, of course, that the metal or alloy include a carbon solvent. For example, when the diamond product is manufactured for use as a heat sink, copper, which is not a carbon solvent, might be included with the metal or alloy with which the carbon is converted for the reason that copper itself has a high heat conductivity.

In the specification and claims, the term "metal" includes a carbon solvent metal and alloys or mixtures thereof with other metals which may or may not be carbon solvents.

The invention includes modifications and adaptations within the scope of the appended claims.

Claims

What is claimed is:

1. In the manufacture of sharp edge cutting elements, a method for simultaneously making a plurality of said elements comprising: confining in a cell a plurality of charges on non-diamond carbon and matrix metal and a carbon solvent metal in alignment and separating individual charges into discrete bodies separated by alumnia oxide divider members, developing conditions of pressure and temperature on said charges which are in the thermodynamically diamond stable region of the carbon equilibrium diagram when in the presence of said solvent metal thereby to cause conversion of the carbon to diamond, removing the converted charge from the cell, separating said discrete bodies at said divider members, and shaping at least a part of each body so separated to the form of a cutting element having at least one cutting edge thereon, said elements being adapted for mounting on holders to permit said cutting edges of the elements to be presented to work to be cut thereby.