Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/05—Mixtures of metal powder with non-metallic powder
  • C22C1/051—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
  • B22F3/26—Impregnating
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/4981—Utilizing transitory attached element or associated separate material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12007—Component of composite having metal continuous phase interengaged with nonmetal continuous phase

Definitions

• Cemented carbide compositions are prepared by the production of a sintered cemented carbide compact by conventional liquid-phase sintering techniques, followed by chemical removal of the metallic binder and replacement by infiltration with a second metallic binder different than the original binder. The resulting compositions are fully dense, have a fine-grained, homogeneous structure and possess the high hardness normally associated with cemented carbide alloys.
• This invention relates to a process for the production of cemented carbide compositions having an ususual combination of desirable properties and to the cemented carbide compositions so produced.
• Cemented carbides are well known for their unique combination of hardness, strength and abrasion resistance and are, accordingly, extensively used for such industrial applications as cutting tools, drawing dies and wear parts. They are produced by powder metallurgy techniques involving the liquid-phase sintering of one or more refractory carbides of Groups IV, V and VI of the Periodic Table with one or more of the iron-group metals.
• the iron-group metals exist as a matrix or binder in the sintered alloy and act to bond or cement the refractory carbides.
• the matrix alloy is almost always an iron-group (Fe, Co, Ni) metal or alloy because the latter possesses a number of critical properties necessary to the sintering process and to the metallurgical structure upon which the unique properties of the sintered alloy depend.
• the binder metal must have the ability to produce a reasonably low melting point with the carbide through eutectic formation. It must also possess the ability to dissolve a fairly large amount of the carbide while in the liquid state and it must adequately wet the carbide such that densification is accomplished completely and within a reasonable period of time. In addition, the binder should not enter into an irreversible reaction with the carbide to any great extent.
• the binder should contribute to the high strength of the cemented carbide alloy, preferably at elevated temperatures as Well as at room temperatures.
• binder metals commercially used. Cobalt is by far the most extensively used binder for tungsten carbide, and nickel is the most extensively used for titanium carbides.
• binder metals or alloys have been suggested, particularly as a substitute for cobalt in WC-Co alloy systems. However, many are unsuitable for reasons set forth above. In other cases, such metals or alloys may be used as binders but only in volume percentages greater than about 15 or 20%.
• US. Pat. 3,215,510 discloses the use of nickel-chromium alloys as a substitute for cobalt in WC alloys, with resulting improved corrosion resistance without sacrifice of strength or hardness. Satisfactory densification and other properties in the sintered compact are obtained, however, only with binder contents greater than about 15 volume percent 10 weight percent).
• the inherent advantages of the cobalt or nickel matrix are utilized to prepare a cemented carbide of the desired density, structural uniformity and homogeneity, after which the original binder is then removed and replaced with the selected matrix containing the properties desirable in the final cemented carbide composition.
• the cobalt or nickel binder is used as a processing aid because of its uniquely suitable prop erties for this purpose.
• the products of this invention are fully dense-greater than 99% and usually greater than 99.5% by volume of theoretical density, have a hardness greater than about and usually greater than Rockwell A, are strong and are characterized by a fine grained, homogeneous metallurgical structure.
• cemented carbide alloys which contain binder metals or alloys which do not themselves satisfy the stringent metallurgical requirements for liquid-phase sintering.
• the only metallurgical requirements that the binder phase must possess for this method are (1) the ability to wet the carbide skeleton well enough to infiltrate the skeleton, and (2) freedom from detrimental irreversible reactions with the carbide.
• WC, TiC, or WC-TiC-TaC-based composites having fine (1 to 3 micron) uniformly dispersed carbide grains at a level of greater than 80 volume percent with a matrix phase of elements such as copper, silver or gold, or of alloys such as nickel-chromium, nickel-aluminum, cobalt-aluminum, copper-silicon, alloys of nickel or cobalt and refractory metals such as niobium, tantalum, chromium, molybdenum or tungsten.
• elements such as copper, silver or gold, or of alloys such as nickel-chromium, nickel-aluminum, cobalt-aluminum, copper-silicon, alloys of nickel or cobalt and refractory metals such as niobium, tantalum, chromium, molybdenum or tungsten.
• the invention also makes possible the preparation of fully dense cemented tungsten carbide compositions of high corrosion resistance containing less than 15% by volume of a nickel-chromium binder alloy. As set forth above, this has not been previously possible with a volume of binder less than 15%.
• the practice of this invention also makes possible the preparation of cemented carbide alloys containing nickel-aluminum alloy binders with from 1 to by weight aluminum. Such binders are well known for their high temperature strength and would, accordingly, enhance the high temperature deformation resistance of a cemented carbide. Again, they have been unsuitable because of their inability to participate satisfactorily in the liquid-phase sintering process to obtain the required densification and fine-grained, homogeneous structure.
• the high temperature strength of cobalt is also enhanced with from 1 to 10% aluminum.
• carbide alloys with aluminum alloy binders of less than 20 volume percent This has been extremely clifficult because a substantial portion of the aluminum in the binder alloy irreversibly oxidizes during normal cold-pressing and liquid-phase sintering processing.
• the result has been the formation of numerous oxide inclusions in the cemented carbide, which is detrimental to the properties of the resulting cemented carbide composition.
• the present process avoids substantially all aluminum oxide formation because the aluminum need not be present as a powder at any stage of the process.
• Additional binder alloy systems made possible by the practice of this invention are nickelor cobalt-based binder alloys having higher aluminum contents, such as the nickel-aluminum compounds Ni Al, NiAl and the cobalt compound CoAl. These nickel and cobalt intermetallic compounds are attractive as binders for both tungsten carbide and mixed tungsten carbide alloys as a means to obtain exceptionally high deformation resistance temperatures--up to 1350-1600 C. It is not possible to make fully dense cemented carbides having less than 20 volume percent of such binders by liquid-phase sintering since the solubility of WC in these compounds is very I low, preventing the redistribution of the carbide phase which is so necessary in the liquid-phase sintering process.
• the cemented carbide composition should contain sufficient volume percent of refractory carbide metal to leave an intact skeleton after removal of the binder.
• the carbide skeleton will usually break into several pieces or disintegrate into powder during the leaching process when the carbide content is less than about 80 volume percent. It is possible to prepare carbide skeletons by other means, such as hot-pressing, which would not disintegrate at a volume percent of less than 80%. Hot-pressing can also be employed to obtain carbide skeletons which have greater than 80% volume density. However, hot-pressing has a number of disadvantages.
• the cobalt binder may only be necessary to remove the cobalt binder from the surface regions of the initial cemented carbide body.
• a different or second binder metal can be infiltrated into the carbide to any desired depth, in order to provide the desired properties in this critical surface region, while the cobalt binder remains in the bulk of the carbide body.
• time and temperature of infiltration By varying the time and temperature of infiltration, varying degrees of alloying can be obtained between the infiltrated metal and the bulk cobalt binder.
• the infiltrant is restricted to those metals and alloys having a melting point lower than that of the WC-Co or WC-TiC-TaC-Co eutectic.
• Infiltrant alloys which dissolve the carbide should be presaturated with the carbide in order to prevent dissolution of the skeleton.
• nickel-chromium alloys should normally be saturated with tungsten carbide when infiltrating a tungsten carbide skeleton.
• liquid-phase sintering comprises coldpressing an intimate powder mixture of refractory metal carbide and binder metal to the desired shape.
• the pressed part is then heated, normally in an inert or reducing atmosphere, to an elevated temperature, normally from l300-l500 C., to sinter the alloy.
• an elevated temperature normally from l300-l500 C.
• a liquid phase of the binder metal and a small amount of the refractory carbide forms, permitting complete and rapid densification.
• the binder metal is removed. We have found this may be conveniently and economically accomplished by leaching with an acid. To accelerate the leaching process, the acid should be heated, most conveniently to boiling temperature. Acids which are particularly useful are hydrochloric and sulfuric, preferably at dilute constantboiling concentrations. Leaching will normally occur over a period of days or weeks for complete removal of binder, depending of course on the size of the product, or lesser time if only the surface is to be leached.
• the carbide skeleton is oxidized to some extent during leaching, the net result of which is a loss of carbon from the skeleton.
• the carbon can be replaced by firing the skeleton in a carburizing atmosphere and/or by adding the desired carbon to the infiltrant.
• Infiltration is carried out in a reducing or slightly carburizing atmosphere, depending on the specific composition of the carbide skeleton structure.
• the infiltrating binder in such forms as a powder, solid body, or foil, is raised to slightly above its melting point while in contact with the skeleton and then infiltrates by capillary action.
• EXAMPLE 1 Rectangular-shaped pieces of cemented carbide having dimensions .750" x .375" x .200" and composition volume percent WC1O volume percent Co (6 weight percent Co) were prepared by conventional cold-pressing and liquid-phase sintering techniques. The pieces were then leached for seven days in boiling 20% hydrochloric acid to remove the cobalt. At the end of this period a chemical analysis showed the residual cobalt content to be 0.16 weight percent. The resulting tungsten carbide skeletons were then fired one hour at 1100 C. in a carburizing hydrogen-base atmosphere to remove residual acid and to help restore carbon that was lost due to oxidation during leaching.
• the tungsten carbide skeletons were then infiltrated with nickel-chromium alloys containing additionally 20% WC and 2% carbon by weight.
• the WC was added to presaturate the infiltrant with WC so as to prevent erosion of the WC skeleton during infiltration.
• the carbon was added to restore the carbon content of the WC skeleton and thus prevent the formation of eta phase type ternary carbides.
• the amount of infiltrant used was by weight in excess of the amount needed to fill the voids in the carbide skeleton.
• the temperature used ranged from 1450 C. for the 5 to aluminum-containing alloys to 1700 C. for the 30% aluminum alloy.
• corrematrix compositions was seen to rise from a value somesponding properties of a WG-10 volume percent Co comwhat lower than the original at 0% Al to a value submercial alloy (Composition 1) from which the WC-Ni, stantially higher at 2.5% A1 and then steadily decline Cr alloys (Compositions 2, 3 and 4) were prepared: 15 with increasing aluminum content.
• the hardness was rela- TABLE I Transverse rupture Corrosion Density, strength, Hardsuscepti- Composition gm./cc. p.s.i. ness, RA bility '1.
• the density, hardness and strength of the WC-Ni-Cr alloys are nearly the same as the WC-Co tively low at 0% Al and then rose steadily with increasing aluminum content.
• WC skeletons having 10 volume percent porosity were prepared by acid-leaching the cobalt from WC-10 volume percent Co cemented carbide composites and were subsequently hydrogen-fired as in Example 1 above. These were then infiltrated with a series of nickel-aluminum alloys containing from 2.5 to 30 weight percent aluminum. Suificient WC and carbon were added to each infiltrant to prevent erosion and to prevent the formation of eta phase type ternary carbides. This amounted to 5% WC when the aluminum content was from 2.5 to 10% and no WC when the aluminum content was greater than 10%. Two percent carbon was added to all compositions.
• the lower aluminum-containing alloys displayed excellent wear resistance in metal turning tests.
• tool inserts of Composition 4 in Table II were used to machine the nickel-base alloy, Ren 41. It was found that the wear rate of the WC-Ni-Al tool was about 40% less than that of the WC-10 volume percent Co tool material used commercially for this purpose.
• EXAMPLE 3 WC skeletons having 10 volume percent porosity were prepared by acid-leaching the cobalt from WG-10 volume percent Co composites and subsequently hydrogen-firing, as in Example 1. They were then infiltrated with a series of cobalt-aluminum alloys containing 2.5 to 30% aluminum. About 5% WC was included in the infiltrant when the Al content was less than 15% and 2% carbon was added to all infiltrants. Infiltration was accomplished at various temperatures, depending upon the Al content, as in Example 2. The resulting physical properties are shown in Table III.
• the WC10 volume percent Co-Al alloys were found to possess the same improved high temperature deformation resistance and machining properties that were described in Example 2 for WC-lO volume percent Ni-Al alloys.
• EXAMPLE 4 A WC-lO volume percent cobalt composition was acidleached such that the cobalt was removed to a depth of .010 inch below the surface. The porosity network thus generated was then infiltrated with gold by placing the required amount of gold foil over the compact and heating to 1150 C. in a hydrogen atmosphere.
• Cutting inserts /2" x /2" x A of initial composition 72% WC, 8% TiC, 11.5% Tac, 8.5% Co were leached for one week in boiling HCl as in Example 1 above, forming carbide skeletons that were 88% dense. These were subsequently infiltrated at 1600 C. with Co-% Al alloy containing additionally 5% WC and 2% carbon. They were then used to machine SAE 1045 teel under conditions which produce significant nose deformation of the original cobalt matrix composition (measured bulge of .005"). Under these conditions the Co-Al matrix material was significantly less deformed (measured bulge of .001").
• a process for producing a cemented carbide composition comprising sintering a pressed mixture of a refractory metal carbide and an iron group binder metal,
• the refractory carbide is one or more carbides of tungsten, titanium, or tantalum.
• a process for producing a cemented tungsten carbide composition comprising sintering a pressed mixture containing tungsten carbide and less than 20 volume percent of a cobalt binder, chemically removing the cobalt binder from the sintered composition, and

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Cited By (16)

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• 1969
  • 1969-04-16 US US816778A patent/US3551991A/en not_active Expired - Lifetime
• 1970
  • 1970-04-07 GB GB1641870A patent/GB1310381A/en not_active Expired
  • 1970-04-15 DE DE2018032A patent/DE2018032C3/de not_active Expired
  • 1970-04-16 FR FR7013834A patent/FR2045357A5/fr not_active Expired

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