US3147542A

US3147542A - Shaping cemented hard metal carbide compositions

Info

Publication number: US3147542A
Authority: US
Inventors: Benjamin C Boeckeler
Original assignee: Kennametal Inc
Current assignee: Kennametal Inc
Priority date: 1962-12-13
Filing date: 1962-12-13
Publication date: 1964-09-08
Anticipated expiration: 1981-09-08
Also published as: GB1069975A

Description

P 8, 1964 B. c. BOECKELER 3,147,542

SHAPING CEMENTED HARD METAL CARBIDE COMPOSITIONS Filed Dec. 13, 1962 INVENT OR.

BEAU/MIN C. 8060 62 5Q Arron/V5345.

United States Patent 3,147,542 SHAPING CEMENTED HARD METAL CARBIDE COMPOSITIONS Benjamin C. Boeckeler, Greenshurg, Pa., assignor to Kennametal, Inc., Latrobe, Pa., a corporation of Pennsylvania Filed Dec. 13, 1062, Ser. No. 244,452 8 Claims. (Ql. 29-18237) This invention relates to a method whereby sintered shapes of, for example, cemented hard metal carbide compositions can be readily formed, as well as to novel structures comprising shapable cemented hard metal carbide compositions and the products thereby obtained.

It is a primary object of the present invention to provide a method whereby sintered cemented hard metal carbide bodies can be shaped to close dimensions relatively inexpensively which method is easily practiced with techniques presently available in the art of hard metal carbide products.

It is another object of the invention to provide shapes of cemented hard metal carbides characterized by at least a surface area of uncemented skeletal hard metal carbide.

Another object of the invention is to provide tools made from shapes of cemented hard metal carbides in accordance with the foregoing object.

Still another object of the invention is to provide shapes of cemented hard metal carbide compositions having at least a surface zone of a lower cement content, as compared with the central portion thereof, which zone of lowered cement composition is of a higher hardness than the main body.

Other objects will be apparent from the following detailed description and drawings in which:

FIG. 1 represents a side sectional view of a sintered cemented hard metal carbide body;

FIG. 2 shows, schematically, the body of FIG. 1 after a leaching treatment of the invention;

FIG. 3 shows the body of FIG. 2 after a shaping step; and

FIG. 4 schematically represents the body of FIG. 3 subsequent to cement reinfiltration.

Prior to the present invention, it has been conventional, in producing tools such, for example, as files of cemented hard metal carbides, to use machining processes in which the desired shape is machined into the surface of a sintered body of the cemented hard metal carbide composition by use of diamond tools. The costs in tools and labor of such machining practices are exceedingly high. Other attempts to attain this object have been made in which green shapes of cemented hard metal carbide compositions have been preshaped while in the green or presintered state and thereafter are sintered to produce the final product. However, shrinkage of major proportions occurs in the sintering of green or presintered shapes, and suitable final dimensions are obtained only with a final grinding, usually diamond grinding or grinding with silicon carbide, boron carbide, or boron nitride.

These and other problems are overcome in accordance with the present invention in which shapes such as files, clamping jaws, plungers and the like can be made by a process including the step of removing cement from at least-a surface zone of a sintered cemented hard metal carbide body to result in a skeletal formation of the hard metal carbide in that zone. The skeletal zone is then formed by conventional techniques, such as wet diamond machining, wet lapping with boron nitride, boron carbide or silicon carbide or dry machining with diamond or a carbide tool, to a tolerance even within about one percent of the desired dimensions. Since the skeletal layer is relatively soft, diamond wear is negligible. Thereafter, the

shaped body is sintered again and during this sintering operation, the cement from the main body reinfiltrates the shaped skeletal zone resulting, if desired, in a higher hardness than that of the main body. This second sintering generally 1s accompanied by minimal shrinkage that may be on the order of as low as 0.6 percent; this makes it possible to predict the final size with good accuracy. Consequently, any final grinding that need be accomplished is of a minor order. Indeed, where extreme tolerances are not required, final grinding may be dispensed with and thus tools are produced at considerable saving over that heretofore possible.

In consequence of these discoveries, several unique shapes result and are represented in the drawing. For example, upon leaching cement from the surface zone 10 of the body 12 of a sintered, cemented hard metal (FIGS. 1 and 2) being treated there results a skeletal formation 14 of the hard metal that remains integral with the main body of material. By way of example, if body 12 con tamed about 10 weight percent cement, the skeletal zone 14 could have a cement content on the order of about 0.03 weight percent. This product, which is readily shapable in the skeletal zone, can be supplied to tool makers or users who can easily finish the tool in any fashion they desire. Upon shaping, as by grinding ridges 16 (FIG. 3) into a surface of the skeletal zone 14, and then sintering the body, another unique product results in that there is a cement gradient from the untreated to treated portions as well as a hardness gradient with the shaped zone having a higher hardness than that of the main body. Thus, referring to FIG. 4 and considering it as made in accordance with the example given hereinafter, central portion 20 will have essentially the original composition and physical properties while zone 14 will have a lower cement content. It should be noted that reinfiltration can, if desired, be carried out for a period sumciently long that cement distribution becomes largely uniform and in that instance aurgace hardness will be essentially that of the untreated The invention is applicable generally to sintered, cemented hard metal carbide bodies. By way of example, it can be practiced with bodies composed of tungsten carbide, tantalum carbide, columbium carbide, titanium carbide, zirconium carbide or molybdenum carbide, as well as mixtures of two or more carbides, cemented with any desired cement such, for example, as cobalt, nickel, molybdenum, iron, chromium tungsten manganese and mixtures of the foregoing. As will be evident to those skilled in the art the particular carbide and cement as well as their concentrations in any given practice will be determined by the end product to be obtained, and do not constitute limitations on the invention. Similarly, the sintered cemented hard metal carbide bodies can be prepared by any of the processes presently available, and the details of suitable processes are known to the art in the published technical and patent literature, and usually involve pressing and sintering homogenized mixtures of powdered cement and hard metal carbides. It is to be noted that these carbide compositions can be referred to as hard metal compositions as Well as cermets.

The workable or locally shapable zone is developed in a sintered cemented hard metal body in accordance with the present invention by leaching in which the cement in that zone is selectively dissolved away leaving a skeletal formation of crystals of the metal carbide. Leaching is accomplished by exposing the zone to be treated to a solvent, which is selective for the cement at the conditions of treatment, for a period of time, e.g. 0.5 to 72 or more hours, suificient to remove cement to the depth desired. A practice that has been found convenient for this purpose is the masking of the parts that are not to be attacked followed by immersion of a substantial part or all of the workpiece in the leaching solution. Any practice that prevents attack by the leachant constitutes suitable masking. For treating periods up to about 24 hours with ferric chloride, a vinyl plastic electrical insulating tape (such as Tuck-Tape No. 330 of Technical Tape Co.) is satisfactory. Masking for periods up to about 72 hours in an aqueous solution of ferric chloride is achieved with a dipped or sprayed coating of 851K808, a proprietary product of Rinshed-Mason Company of Anaheim, California.

The solvent used for selectively removing cement depends on such factors as, for example, the hard metal carbide and cement involved. The preferred leaching solvent for all binders is an aqueous ferric chloride solution that contains up to about 25 weight percent of ferric chloride. Acids such as the common mineral acids, e.g. hydrochloric acid, can also be used but may release hydrogen gas that interferes with the process by blanketing the cement to be dissolved. By way of example, the preferred leaching solvent for sintered cobalt cemented tungsten carbide with a cobalt concentration of 5 to 15 weight percent is an aqueous ferric chloride solution of about 8 to 25 weight percent ferric chloride, suitably also containing small amounts of hydrochloric acid to provide a pH of 2.0 to 4.0. The presence of acid helps prevent the deposition of oxide-hydrates of iron. It is believed that the action of ferric chloride is to cause an oxidation-reduction reaction in which the ferric ion is reduced to ferrous ion and the cobalt metal is oxidized to cobaltous ion.

Solution of the cement is generally expedited by maintaining the leaching solvent at an elevated temperature of about 160 to 200 F. or higher. Penetration into the cemented hard metal by the solution is relatively rapid at the beginning of the leaching process and, of course, slows down as the cement near the surface is removed. For example, it has been found that immersion of a workpiece of sintered cobalt cemented tungsten carbide in ferric chloride for periods of 2 to 36 hours results in generally satisfactory penetration with a larger percentage of the cobalt being removed in the first few hours. In this fashion and with the ferric chloride at a 1.0 gram formula weight per liter concentration, penetrations on the order of up to about 0.080 inch have been obtained in about 32 hours. The penetration achieved, and cement removed in any given practice, is dependent on a variety of factors. For example, the higher the cement concentration, the higher the penetration. On the other hand, the finer the crystals of hard metal present, the more limited the rate of penetration. It will be appreciated that by inter-adjustment of the variables, any given penetration desired can be achieved. There results, upon removal of the cement, a skeletal layer of interconnected hard metal crystals held together by the bonding forces among those crystals developed during the first sintering operation. At the end of the leaching treatment, it is desirable to wash the workpiece to remove residual leaching solution if it can have any adverse effect during resintering.

Another of the important steps in the process is the final sintering operation in which cement from the central or main portion of the body being worked upon is caused to migrate and reinfiltrate the skeletal zone. Reinfiltration is effected by sintering in a vacuum, or a neutral or reducing (hydrogen) atmosphere at a temperature of about 2300 to 2800 F. for about A to 15 hours. For cobalt cemented tungsten carbide shapes of the usual cobalt concentration of about 5 to 15 weight percent, it has been found that adequate reinfiltration occurs upon sintering in a vacuum for at least one-half hour at a temperature on the order of 2300 to 2800 F. Reinfiltration preferably occurs by solid state diffusion of the cement and one of its objects is to produce a gradient in cement concentration from the main body through the skeletal hard metal. It is preferred to use the lower temperatures within this range, thereby avoiding possible eutectic temperatures at t which reinfiltration possibly would no longer be by solid state diffusion. It will be appreciated that the specific conditions used for cement reinfiltration will vary depending upon the actual composition involved, and that suitable sintering conditions to accomplish this for a particular practice can readily be chosen by the artisan.

The invention will be described further in conjunction with the following specific examples in which the details are given by way of illustration and are not to be construed as limiting.

Example I A body of sintered cobalt cemented tungsten carbide measuring inch thick by A inch wide by 1 inch long Was used in this example. Its original hardness was 88.2 Rockwell A, and its composition, by weight, was 12 percent cobalt and 88 percent of tungsten carbide. This was immersed in an aqueous ferric chloride solution of a concentration of 1.0 gram formula weight per liter of solution for a period of 8 hours. The ferric chloride solution was maintained at 194 F. The piece was then removed from the solution and examined, and it was found that cobalt had been removed to a depth of of an inch on all exposed surfaces. Nevertheless, the overall dimensions corresponded, within a few thousandths of an inch, to the original dimensions.

The piece was then machined using a hand-held carborundum rod and grooves were cut to the interface of unleached cobalt. After washing the machined workpiece to remove leachant, it was placed in a vacuum sintering furnace, heated to 2740 F. and maintained at that temperature for /2 hour at an absolute pressure of microns. Upon removal from the furnace, it was noted that the cobalt had redistributed itself, moving from the unattacked central core out into the skeletal layer of crystalline tungsten carbide. Measurement on the thus treated surfaces showed that the hardness had risen uniformly to 90.1 Rockwell A. The dimensions after this final sintering operation were still substantially the same as the starting dimensions.

Example II A body of sintered nickel and molybdenum cemented titanium carbide that also contained a mixed carbide of niobium, tantalum and titanium was used. Its dimensions were inch long x 0.250 inch thick x 0.184 inch wide. Its actual composition, by weight, was 64 percent titanium carbide, 6 percent of the mixed carbide of niobium, tantalum and titanium, 25 percent nickel and 5 percent molybdenum. This piece was immersed in a solution containing 0.575 gram formula weight of ferric chloride per liter for a period of four hours. The ferric chloride solution was maintained at a temperature of 187 F. The piece was then removed from the solution and examined, and it was found that the nickel binder phase had been extracted to a depth of 0.026 inch and that a porous skeletal layer of titanium carbide of that thickness had been left behind.

The workpiece was then placed in a vacuum furnace and resintered at a temperature of 2400 F. for /2 hour. Upon removal from the furnace, it was noted that the nickel binder had reinfiltrated the external skeletal layer of mixed carbides of titanium, niobium and tantalum. The hardness of the reinfiltrated surface was determined and ranged from 88.1 to 88.8 Rockwell A, and was substantially unchanged from the original hardness. Micro photographs made across a polished cross section were uniform throughout and indicated that reinfiltration of the titanium carbide skeletal layer by the nickel binder phase was complete.

Example III A standard tool blank was used in this example, its major surfaces were /2 inch squares and it was /s inch thick. This body of sintered material contained, by weight, 5.75 percent of cobalt, 2.25 percent of tantalum carbide and 92 percent of tungsten carbide. The tool blank was leached in a solution containing 1.0 gram formula weight of ferric chloride per liter at a temperature of 176 F. for a period of four hours. Thereafter, penetration was measured and it was determined that the cobalt binder phase had been extracted to a depth of 0.014 inch and that a porous skeletal layer of tungsten and tantalum carbide of that thickness had been left. The piece was then rough lapped on one of the /2 inch square surfaces using 3280 Norbide (a proprietary of the Norton Company) as the lapping compound and a machine lapper operating at 61 r.p.m. In about five minutes time, an average of 0.0074 inch was removed. All the lapping took place in the skeletal layer and did not reach the cobalt interface.

After rough lapping, the piece was finish lapped using No. 3 diamond dust and a finish of 1.5 to 2.0 microinches was obtained after 0.0005 inch was removed.

The piece was then thoroughly cleaned using boiling acetone followed by treatment in dilute hydrochloric acid and ammonium hydroxide to remove traces of oil and lapping material from interstices of the skeletal layer. The cleaned piece was then placed in a vacuum furnace and resintered at a temperature of 2350 F. for /2 hour during which the cobalt binder reinfiltrated the external skeletal layer of tungsten and tantalum carbide. Shrinkage due to extraction and reinfiltration was 0.25 percent. Hardness measurements showed no loss in hardness.

Surface hardening tests as noted above have been made on sintered cobalt cemented carbide bodies. The results show generally that surface hardness can be increased /2 Rockwell A and occasionally as much as 2 /2 Rockwell A with cement concentrations up to about 11 weight percent. In analogous tests in which test pieces were leached and reinfiltrated, and thereafter ground to remove all of the treated surfaces, measurements were made to determine theeffect on the core properties, due to the cobalt loss attending its migration from the core on reinfiltration. It has been determined that appreciable weakening does not occur.

From the foregoing discussion and description, it is apparent that the present invention is a marked advance in the refractory carbide arts. With the processes disclosed, it is now possible to make intricate shapes, such as files, clamping jaws, undercuts, holes and the like in sintered cemented hard metal shapes without the need to practice tedious and expensive grinding. Moreover, many shapes thereby produced are uniquely improved for many practices in that the finished surfaces are at a higher hardness than that of the main body.

It is to be further noted that when a bar or other shape of sintered cemented hard metal carbide is treated on but one surface in accordance with the present invention, there is a tendency for it to curve, after reinfiltration, since the practice results in at least a tendency to shrink thereby placing the shrinking side in tension and the untreated side in compression. By attaching such a bar with its reinfiltrated side next to a backing, such as a steel surface, and drawing it close as by clamping or brazing, the bar tends to straighten; this increases the compression on the exposed (untreated) side of the bar. This increases the strength of the exposed side and therefore increases its ability to withstand the breaking forces of load or impact to which it may be subjected in use.

The foregoing can be used to particular advantage in parts that are to be used under extreme compression, for example, Bridgman anvils such as used or which are used in the field of ultra-high pressure research and manufacture. Cemented tungsten carbide normally is the material used for such applications. By applying the present invention to all the external surfaces of such anvils, there is produced a reinfiltrated zone that, in view of the application of the invention, places the entire central portion of the anvil under compression. The anvil, being normally mounted within an alloy steel support ring, will thus have on it the compressive forces exerted by the support ring as well as the extra compressive forces added by application of this invention. Accordingly, anvils made in this general fashion will be able to increase still further the upper pressure limit attainable by use of such structures. Other applications of the invention in which these forces can be used, will be apparent to those skilled in the art.

In accordance with the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A method comprising leaching metal from a portion of a sintered, metal cemented hard metal carbide body, shaping the resulting skeletal zone of hard metal in said body, then heating the shaped product to infiltrate metal from the main portion of the hard metal carbide body to the shaped skeletal zone, and recovering the resulting product.

2. A method in accordance with claim 1 in which the metal cement in said sintered, metal cemented hard metal carbide body is at least one member selected from the group consisting of cobalt, molybdenum, nickel, iron, chromium, tungsten, manganese and mixtures thereof.

3. A method in accordance with claim 2 in which said metal cement is removed from a portion of said sintered, metal cemented hard metal carbide body by treating said body with an aqueous ferric chloride solution.

4. A method comprising leaching metal cement from a surface portion of a sintered, metal cemented hard metal carbide body to produce a skeletal formation of hard metal substantially free from metal cement, shaping the skeletal formation, then infiltrating metal cement into the skeletal formation by heating the shaped body for a period sufficient for metal cement to migrate into the skeletal formation.

5. A method comprising treating a sintered body composed of at least one carbide selected from the group consisting of titanium carbide, tungsten carbide, molybdenum carbide, tantalum carbide, columbium carbide, and zirconium carbide and at least one metal cement selected from the group consisting of cobalt, nickel, molybdenum, iron, chromium, tungsten and manganese and mixtures thereof, in a selected portion of a surface of the body with an aqueous solution comprising ferric chloride to remove metal cement from said surface portion and produce a skeletal formation of carbide substantially free from metal cement therein, shaping the skeletal formation to a desired shape, then heating the shaped body by subjecting it to a temperature of at least 2300 F. to infiltrate metal cement. from the body to the shaped skeletal zone.

6. As a new article of manufacture a sintered, metal cemented hard metal carbide body having a shapable surface area comprising skeletal hard metal carbide relatively free of metal cement and integral with the remainder of the body.

7. As a new article of manufacture a hard metal carbide body composed of at least one carbide selected from the group consisting of tungsten carbide, tantalum carbide, columbium carbide, titanium carbide, zirconium carbide and molybdenum carbide and at least one metal cement selected from the group consisting of cobalt, nickel, molybdenum, iron, chromium, tungsten and manganese and mixtures thereof, having a shapable surface comprising skeletal hard metal carbide relatively free of metal cement and integral with the remainder of the body, the skeletal hard metal carbide being the same carbide as the main body.

7 8 8. A shape comprising a sintered, metal cemented hard References Cited in the file of this patent metal carbide body having a first metal cement concen- UNITED STATES PATENTS tration therein, a surface portlon on said shape of skeletal hard metal carbide infiltrated With metal cement from the 1,842,103 Lalse Jan 1932 remainder of the carbide body and having a metal cement 5 2,244,052 Corns/cock June 1941 concentration that is lower than that in the remainder of 2,244,053 comstock June 1941 the body, the surface portion being of a higher hardness 2,313,227 D6 Bats M r- 194 2,888,247 Haglund May 26, 1959 than the remainder of the body.

Claims

7. AS A NEW ARTICLE OF MANUFACTURE A HARD METAL CARBIDE BODY COMPOSED OF AT LEAST ONE CARBIDE SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN CARBIDE, TANTALUM CARBIDE, COLUMBIUM CARBIDE, TITANIUM CARBIDE, ZIRCONIUM CARBIDE AND MOLYBDENUM CARBIDE AND AT LEAT ONE METAL CEMENT SELECTED FROM THE GROUP CONSISTING OF COBALT, NICKEL, MOLYBDENUM, IRON, CHROMIUM, TUNGSTEN AND MANGANESE AND MIXTURES THEREOF, HAVING A SHAPABLE SURFACE COMPRISING SKELETAL HARD METAL CARBIDE RELATIVELY FREE OF METAL CEMENT AND INTEGRAL WITH THE REMAINDER OF THE BODY, THE SKELETAL HARD METAL CARBIDE BEING THE SAME CARBIDE AS THE MAIN BODY.