Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/04—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbonitrides

Definitions

• a method for fabricating improved cast refractory tooling materials comprises preparing a melt of titanium-tungsten-carbon-base alloy compositions (Ti W JC or titanium-tungsten-nitrogen-carbon base alloy compositions (Ti W (N C under a nitrogen-containing atmosphere, in which the mole fraction x is variable between the limits 0.25 and 0.70, the mole fraction y is less than 0.50, the stoichiometry parameter 5, which measures the combined gramatoms of nitrogenand carbon present per gramatom metal in the alloy, is vari able between 0.25 and 0.45, and rapidly cooling the melt to form a carbonitride-metal alloy composite having a finegr'ained microstructure consisting of a refractory, hard carbonitride phase and a metal phase, with the metal phase being rich in'tungsten and contributing toughness to the composite and the carbonitride phase having titanium as
• the present invention relates to carbonitride alloys and more particularly to a method of making carbonitride alloys which, due to their physical characteristics, are particularly useful as machine tools.
• sintered carbide of one form or another.
• Commercial sintered carbide tooling material usually consists of a hard carbide alloy, usually tungsten and titanium carbide, dispersed in a matrix or binder of an iron group metal, usually cobalt or nickel.
• the binder provides toughness to the brittle carbide and also serves as a sintering aid during fabrication.
• the iron group metals have relatively low melting temperatures and the loss of strength of the binder alloys based on these metals at relatively low temperatures can cause thermal deformation and thermal wear to become the predominate wear mechanism at high cutting speeds and can cause premature failure of the tools.
• -It is accordingly an object .of the present invention to provide an improved method for making material for use as machine tooling material.
• improved cast refractory tooling materials are fabricated by a method comprising preparing a melt of titanium-tungsten-carbonbase alloy compositions (Ti W )C or titanium-tungsten-nirtogen-carbon-base alloy compositions under a nitrogen-containing atmosphere, in which the mole fraction x is variable between the limits 0.25 and 0.70, the mole fraction y is less than 0.50, the stiochiometry parameter z, which measures the combined gramatoms of nitrogen and carbon present per gramatom metal in the alloy is variable between 0.25 and 0.45, and rapidly cooling the melt to form a carbonitride-metal alloy composite having a fine-grained microstructure consisting of a refractory, hard carbonitride phase and a. metal phase, with the metal phase being rich in tungsten and contributing toughness to the composite and the carbonitride phase having titanium as its base metal.
• the alloys of the invention are based on Group -IV metal (titanium, zirconium and hafnium)-rich carbonitride alloys (relative Group IV metal content in excess of 60 atomic percent) bonded by Group V-I metal (molybdenum and tungsten)-rich refractory metal alloys (relative Group VI metal content in excess of atomic percent).
• the desired microstructure of the composition which consists of a fine-grained aggregate of carbonitride and metal phase, is obtained through rapid solidification of eutectic or near-eutectic alloys formed between the metal and the carbonitride phase.
• the lamellar, eutectic-type structure consists of the carbonitride phase, which is responsible for the cutting action, and the metal alloy, which contributes toughness and strength to the composite.
• a hypereutectic composition of the carbonitride metal is provided in which grains of primary carbonitride are dispersed throughout the lame'llar eutectic structure. The presence of the primary carbonitride phase significantly improves the performance of the composite when employed as a machine tool.
• the carbonitr-ide metal composite comprises a fine-grained lamell ar structure consisting of a tungstenrich metal binder alloy and a carbonitride phase having titanium as its base metal.
• the carbonitride phase is a solid solution between isomorphous monocarbides and mononitrides.
• the molar ratio of nitrogen to carbon in the carbonitride phase can be varied at will but as is discussed below, for reasons related to fabricability and performance of the alloys, is usually kept below 0.40.
• carbonitride alloys are made possible by the existence of pseudobinary eutectic equilibria between the metal and the mononitride phases in the boundary systems titanium-tongstem-nitrogen, zirconium-tungsten-nitrogen and hafnium-tungsten-nitrogen, and the existence of nearly isothermally solidifying, eutectic-type equilibria between the carbonitride land the metal solid solutions in the systems titauium-tungsten-carhon-nitrogen, zirconiumtung stemcarbon-nitrogen and hafnium-tungsten-carbonnitrogen.
• phase equilibria in the metal-rich regions of the nitride and carbonitride systems are such, that over a wide range of metal-exchanges and temperatures, Group IV metal-rich carbonitride, or-nitride, solid Solutions are in equilibrium with tungsten-rich metal alloys.
• the products of the eutectic crystallization consist of tungsten-rich binder alloys (relative tungsten content in excess of 80 atomic percent) and a Group IV metal-rich carbonitride alloy (relative Group IV metal content in excess of 60 atomic percent).
• the nitrogen dissociation pressures of only nitride-containing alloys located within the range where suitable binder alloys are formed, are too high at melting temperatures to be of practical use.
• the nitrogen partial pressures as well as the eutectic temperatures are substantially lowered by alloying the nitrides with carbides.
• eutectic solidification occurs at approximately 2750 C. along the join metal+carbonitride, at which the metal phase consists of a 94 atomic percent tungsten, 6 atomic percent titanium-alloy, and the interstitial alloy of almost pure titanium carbonitride.
• TiN in contact with a 10 atomic percent titanium-90 atomic percent tungsten metal alloy melts at 2970 C. and the mixture has at this temperature a decomposition pressure of approximately 6 atmospheres.
• the behavior of the other Group IV metal nitrides (ZrN, HfN) in systems with tungsten are generally similar to the titanium systems, except that the nitrogen decomposition pressures at equivalent temperatures and pressures are somewhat lower than in the titanium-based alloys.
• the eutectic temperatures in these systems are higher than in the titanium systems (3070 C. at the join ZrN-tungsten and 3100 C. at the join HEN-tungsten) and remain practically unchanged by alloying with carbon; additionally, the nitride or oarbonitride content of the eutectic structure is lower than in the titanium systems, which results in substantially higher wear rates of zirconium and hafnium-based alloys in application as machine tools.
• phase equilibria in the corresponding systems of Group IV metals with molybdenum, nitrogen, and carbon are generally similar to the tungsten systems, although the eutectic temperatures, and hence the nitrogen decomposition pressures, of the alloys in the melting range are substantially lower.
• the hard alloy content of the eutectics in the molybdenum-containing alloys and the strengths of molybdenum-rich alloy binders are too low, however, in order to be competitive with the tungstenbased alloys as machine tools.
• the preferred embodiment of the carbonitride-metal composite in applications as a machine tool is therefore based on the titanium-tungsten-carbon-nitrogen system.
• certain improvements can be achieved by alloying with other elements, notably by partial substitution of titanium by zirconium or hafnium, and by small additions of Group V metals (vanadium, niobium and tantalum). Partial substitution of tungsten by molybdenum and rhenium is also possible.
• the stoichiometry parameter 2 measures the combined number of moles of interstitial atoms of carbon and nitrogen per gramatom of metal titanium+tungsten.
• the latter method of defining the overall composition of the alloys is especially useful in defining concentration spaces of interstitial alloys of the type discussed here.
• the relationships between the two sets of concentration parameters, which of the alloys of the invention, are as follows: V V V
• Ti W (C ;,N of the base alloys extend between limits of 2: between 0.28 and 0.60, of y less than 0.50, and of z between 0.28 and 0.37. Alloys located outside the preferred range, but inside the boundaries defined by limits of x between 0.25 and 0.70, of y less than 0.50, and of z between 0.25 and 0.45, are less suitable for machine tools but are acceptable for some applications.
• carbonitrideametal composites with low interstitial element contents consist of eutectic only and exhibit somewhat higher wear rates than hypereutectic alloys which contain excess primary carbonitride. Castability, however, becomes poor it the carbon plus nitrogen content of the alloys exceeds about 28 atomic percent (z 0.39). Machine tools fabricated from such alloys are also more prone to edge-chipping than tools fabricated from the tougher eutectic, or slightly hypereutectic, alloys.
• the alloys may, for example, be prepared by are (skull) meltingin a nonconsumable electrode arc furnace, or by plasma arc melting, and casting of the melt in water cooled molds, or moldsmade of refractory materials, preferably graphite.
• the nitrogen in the compositing may be furnished either by providing it directly in the melts, such as by adding TiN to the melt, or it may be furnished from a nitrogencontaining atmosphere above the melt.
• the partial pressure of the nitrogen in thenitrogen-containing atmosphere is preferably maintained at a value less than four atmospheres. For reasons not well understood at the present time, cracking of the cast parts during cooling also appeared substantially reduced for the alloys which were melted under nitrogen. Induction melting of the composites in a lower frequency inductionfurnace, (1000fto 2000 Hz.), using graphite as container material, plasma arc melting, and direct resistance melting is also possible. I
• Centrifugal casting-of the melt is preferable to casting techniques employing stationary molds, because the former technique minimizes the problems associated with the formation of shrinkage pipes, allows higher casting speeds, and also permits the development of processes by which multiple dies can be usedjto cast parts closely to shape.
• Dense bodies can also be prepared by powdermetallurgical techniques, using premelted and then comminuted alloy stock. The performance of sintered alloys as machine tools, however, is inferior to the performance of the cast alloys.
• the eutectic or near-eutectic melts of the alloys of the invention be solidified under a high temperature gradient (preferably above 20 C./se c.) in order to assure the formation of the fine-grained structure necessary to obtain composites with optimum mechanical properties and performance as machine tools. It has been observed that solidification under higher temperature gradients causes Auser-grained structure and, conversely, solidification under lower temperature gradients causes a coarser-grained structure.
• the quaternary alloys of the base alloy system can be extensively modified by alloying additions of other metals or interstitials without changing their principal characteristics.
• a correlation between amount and type of alloying additions, and performance of the resulting composites as machine tools, indicates that noticeable improvements can be achieved by certain low level alloying additions to the base alloys, but that higher level (above 5 atomic percent) alloying is generally unnecessary or even undesirable; addition of selected elements up to certain concentrations proved inert While others resulted, even at low concentrations, in a substantial drop of the cutting performance.
• the summary of the effect of alloying additions to titanium-tungsten-carbon-nitrogen-based alloys given below is based on the performance of the carbonitride-metal composites in cutting annealed 4340 steel.
• Molybdenum substituted in amounts up to 10 atomic percent of tungsten in the base alloy system, resulted in no noticeable change in performance, although castability appeared impaired at concentrations higher than 5 atomic percent. Exchanges of 50 atomic percent resulted in nose breakdown and chip welding under the chosen test conditions.
• Rhenium in amounts up to 15 atomic percent in replacement for tungsten improves the cracking resistance of the composites, but had no measurable effect on cutting performance.
• Oxygen in amounts up to 4 atomic percent in replacement for carbon or nitrogen results in reduced friction and welding tendency, at some sacrifice in strength and cracking resistance.
• Example IV A metal-carbide alloy with the initial composition Ti Zr W C was arc melted in a graphite skull and nitrided in the melted state by a 2 minute exposure to nitrogen at atmospheric pressure prior to casting. The nitrogen content of the alloys was atomic percent, resulting in an approximate overall composition of the cast part corresponding to Ti Zr W C N
• a method of forming a carbonitride-metal alloy composition comprising the steps of:
• preparing a melt comprising a Group IV metal-Group VI metal-nitrogen-carbon base alloy composition in which said Group IV metal is comprised of at least 85 atomic percent titanium, said Group VI metal is comprised of at least 90 atomic percent tungsten, and in which the mole fraction x is variable between the limits 0.25 and 0.70, the mole fraction y is less than 0.50, and the stoichiometry parameterz, which measured the combined number of moles of nitrogen and carbon per'gramatom metal alloy, is variable between the limits 0.25 and 0.45; and cooling said melt at a rate faster than 20 C.
• said Group VI metal comprises at'least 97 atomic percent tungsten and up to 3 atomic percent chromium.
• Group VI 5 metal comprises at least 90 atomic percent tungsten and up to 10 atomic percent 'rhenium
• said Group IV metal comprisesat least 85 atomic percent titanium and up to atomic percent selected from the group consisting of zirconium and hafnium.
• said melt comprises a Group V metal-titanium-tungsten-carbon-nitrogen base alloy composition (M Ti ,,W (N C in which M is a Group V metal selected from the group consisting of vanadium, niobium and tantalum, the mole fraction 12- is less'than 0.05, the mole fraction x is variable between the .limits 0.25 and 0.70, the mole fraction y is less than-0.50, and the stoichiometry parameter '2, which measures the combined number of moles of nitrogen and carbon per gramatornmetal alloy, is variabl between the limits 0.25 and 0.45.
• M Ti ,,W N C in which M is a Group V metal selected from the group consisting of vanadium, niobium and tantalum, the mole fraction 12- is less'than 0.05, the mole fraction x is variable between the .limits 0.25 and 0.70, the mole fraction y is less than-0.50, and the stoichiometry parameter '2, which
• melt comprises atitanium-tungsten-carbon-nitrogen-boron base alloy composition I (Ti W (B N C in which theli'nole fraction x is variable between the limits 0.25 arr d070, the 'mole fraction 11 is less than 0.03, the mole fraction y is less than 0.50, and the stoichiometry parame'ter z, which measures the combined number of moles of boron, nitrogen and carbon pergramatom metal alloy, is variable between the limits 025 and 0.45.
• said melt comprises a titanium-tungsten-carbon-nitrogen-oxygen base alloy composition (Ti W )(O N C in which the mole fraction x is variable between the limits 0.25 and 0.70, the mole fraction t is less than 0.04, the mole fraction y is less than 0.50, and the stoichiometry parameter z, which measures the combined number of mfolesof oxygen, nitrogen and carbon per gramatom metal alloy, is variable between the limits 0.25 and 0.45 I I I L '1 9.
• said melt is pre pared under ⁇ nitrogen-containing atmosphere.
• a method of forming a carbonitride-metalalloy composition comprising the steps of: I preparing a melt comprising a Group IV metal-Group VI' metal c'arbon base alloy composition I under a nitrogen containing atmosphere, in which said group IV metal is comprised of at least 85 atomic percent titanium, said Group VI metal 'is comprised of at least 90 atomic percent tungsten, and in which the mole fraction x is variable between the limits 0.25 and 0.70, and the stoichiometry pa rameter z, which measured the number of moles of carbon per gramatom metal alloy, is variable between the limits 0.25 and 0.45; and cooling said melt at a rate faster than 20 C. per
• acarbonitride-inetal alloy composite having'a'fine-"grained, lamellar microstructure consisting of a refractory, hard carbonitride phase and a metal phase, with the metal phase being rich in said Group VI metal and contributing toughness "'tothe composite and said carbonitride phase having said Group IV metal as its base metal.
• said Group VI metal comprises at least 90 atomic percenttungsten and up to 10 atomic percentmolybdenum.
• -'said'Group VI metal comprises at least 97 atomic percent tungsten and up to 3 atomic percent chromium.
• said Group IV metal comprises at least 85 atomic percent titanium and up to 15 atomic percent selected from the group consisting of zirconium and hafnium.
• said melt comprises a Group V metal-titanium-tungsten-carbon base alloy composition (M Ti, W ,)C, in which M is a Group V metal selected from the group consisting of vanadium, niobium and tantalum, the mole fraction v is less than 0.05, the mole fraction x is variable between the limits 0.25 and 0.70, and the stoichiometry parameter 2, which measures the number of moles of carbon per gramatom metal alloy, is variable between the limits 0.25 and 0.45.
• M Ti, W ,)C Group V metal-titanium-tungsten-carbon base alloy composition
• melt comprises titanium-tungsten-carbon-boron base alloy composition (Ti W (B C in which the mole fraction x is variable between the limits 0.25 and 0.70, the mole fraction u is less than 0.03, and the stoichiometry parameter z, which measures the combined number of moles of boron and carbon per gramatom metal alloy, is variable between the limits 0.25 and 0.45.
• said melt comprises a titanium-tungsten-carbon-oxygen base alloy composition (Ti W )'(0 C in which the mole fraction References Cited UNITED STATES PATENTS 3,124,452 3/1964 Kraft -135 3,169,828 2/1965 Muta 23-191 3,492,100 1/1970 Roubin 23-315 3,528,808 9/1970 Lemkey 75135 X 3,554,737 1/ 1971 Foster 75-434 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R. 75--134 F, 135, 176

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cutting Tools, Boring Holders, And Turrets (AREA)
• Manufacture And Refinement Of Metals (AREA)

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Cited By (16)

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• 1970
  • 1970-11-03 US US89222A patent/US3703368A/en not_active Expired - Lifetime
• 1971
  • 1971-07-02 GB GB3122571A patent/GB1356301A/en not_active Expired
  • 1971-09-28 FR FR7134804A patent/FR2112988A5/fr not_active Expired
  • 1971-10-26 CA CA126,082A patent/CA948889A/en not_active Expired
  • 1971-11-02 JP JP46086864A patent/JPS5229241B1/ja active Pending

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