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
  • C22C1/053—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor with in situ formation of hard compounds
• • 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
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

• the invention comprises a process for producing composite cermet materials comprising titanium carbide, titanium nitride or tungsten carbide and metal or metal alloy, suitable for the production of iron, steel or general metal or metal alloy components having high levels of hardness and wear resistance.
• cermet is used to refer to materials that comprise both a ceramic and a metal or metal alloy, which are also known as metal matrix composites. Introducing a ceramic phase into a metal matrix provides characteristic features of each in the resultant product. The ceramic increases hardness and wear resistance but is often brittle, while the metal or metal alloy contributes toughness and ductility. However, "wetting " ' of the ceramic component by the metal to obtain cohesive bonding between the metal or metal alloy and the ceramic component is a major challenge in the preparation of such materials.
• New Zealand patent 229777 describes a process for the manufacture of cermets by the synthesis of titanium carbides and/or nitrides by carbothermal reduction of ilmenite.
• the invention comprises a process for producing a composite material of titanium carbide, titanium nitride, or tungsten carbide and a metal or metal alloy, comprising blending together precursor materials including a titanium or a tungsten source, a source of carbon, and a metal or metal alloy and heating the precursor materials in a vacuum or an inert atmosphere or a nitrogen containing atmosphere to a temperature effective to form TiC, TiN or WC, to thereby form a material comprising particles of TiC, TiN or WC substantially encapsulated in a matrix of iron.
• the metal or metal alloy is iron or steel or an iron or steel alloy, but alternatively composites based on other metals such as copper or aluminium or magnesium and TiC, TiN or WC could be formed.
• the titanium source includes titanium dioxide.
• the iron source includes ilmenite, magnetite, or hematite, preferably of average particle size less than 10 microns.
• the precursor materials are heated to a temperature sufficient to form TiC. TiN or WC but at which the metal phase may soften but does not become molten (liquid) so that the TiC, TiN or WC is formed in situ without melting the metal phase.
• cermets we have found that by the process of blending the precursor materials and then reacting at such a temperature cermets may be formed, in which the iron encapsulates the fine particles of titanium carbide, titanium nitride, or tungsten carbide which are formed, to hinder their surface oxidation on removal of the synthesised cermet bodies from the controlled atmosphere furnace. Further, the iron encapsulation assists wetting and dispersion of the ceramic component.
• the process may include as a subsequent step adding the product produced to a melt of metal or a metal alloy to distribute the TiC, TiN or WC particles throughout the metal or metal alloy.
• the product produced typically has a porous structure and the process may include as a subsequent step contacting the porous cermet with a molten metal or metal alloy so that the metal or metal alloy infuses into and fills voids within the porous cermet material.
• the resulting material formed by the process of the invention may be useful as TiC, TiN or WC-rich intermediate billets or pellets for further processing into useful components, by hot metal forging for example.
• These TiC, TiN or WC-rich billets may also be added to molten iron, steel or iron alloy which is preferably under vacuum or an inert atmosphere to enable particulates of TiC, TiN or WC to be incorporated and distributed throughout the iron or steel or iron alloy.
• another process for producing end components may comprise synthesising the TiC- Fe, TiN-Fe or WC-Fe porous intermediate cermets as shapes or shaping same to the required component or product end shape, and then infilling or infusing the component as referred to, with metal or a metal alloy such as iron, steel or an iron alloy or alternatively aluminium or magnesium or their alloys, to form the final product or component.
• metal or a metal alloy such as iron, steel or an iron alloy or alternatively aluminium or magnesium or their alloys
• Figure 1 is the x-ray diffractogram of titanium carbide synthesised using the process of this invention and based on equation 5 showing the carbothermal reduction of titanium dioxide and ilmenite;
• Figure 2 is a diffractogram of titanium nitride synthesised using the process of the invention and based on equation 7 showing the nitridation of titanium dioxide and ilmenite:
• Figure 3 is a micrograph of a cross-section of a material produced as in the following example 5:
• Figures 4 and 5 are micrographs of cross-sections of a material produced as in the following example 7;
• Figure 6 is a micrograph of a material produced as in the following example 8.
• Figures 7 and 8 are micrographs of cross-sections of materials produced as in the following example 10.
• cermets rich in titanium carbide or tungsten carbide are produced by intimately blending together a titanium or tungsten source and a source of carbon and a metal or metal alloy, and heating the precursor materials in a vacuum or inert atmosphere to carbothermally reduce the titanium or tungsten source in situ, to thereby produce a porous cermet material rich in titanium carbide or tungsten carbide, bonded to and surrounded by a matrix of the metal or metal alloy.
• cermets rich in titanium nitride may be produced by blending together a titanium source and a metal or a metal alloy and heating the precursor materials and carbon in a nitrogen containing atmosphere to produce a cermet material rich in titanium nitride. The reaction is carried out at a temperature which may soften the metal or metal alloy in the precursor material but does not cause the metal or metal alloy to become molten (liquid).
• the precursor materials would typically be blended in a powdered or granular form, and by any suitable blending technique which will achieve intimate mixing of the precursor materials.
• the precursor materials may be mixed in a liquid medium and then dried (by which is meant removal of liquid by any means including oven drying or filtering for example) to form a substantially dry cake or body of the precursor materials, which is then heated to carry out the reaction.
• the precursor materials may be mixed by being milled or ground together for example.
• titanium dioxide may be blended in an organic or aqueous medium with carbon preferably in powdered or particulate form, such as carbon lampblack, coal, charcoal or graphite or a material that decomposes to form carbon at an elevated temperature, with either clean fine particulate iron compounds such as ilmenite (FeTiO ), magnetite (Fe 3 O 4 ), hematite (Fe O 3 ) or metallic iron (Fe) produced by milling or a suitable alternative method.
• the carbon source is lampblack.
• ilmenite is used as a raw resource material because it contains titanium but any combination of iron compounds may be used.
• the molar quantities of titanium dioxide may vary widely but useful proportions are about three moles of titanium dioxide to about one of ilmenite.
• the precursor materials may then be shaped by being pressed or extruded for example, or by any other shaping operation(s) or form intermediate billets or pellets or to the final shape of a component or product.
• the precursor materials are then heated and reacted in a controlled temperature furnace under either vacuum or an inert atmosphere such as argon gas to synthesise titanium carbide. Alternatively heating under a nitrogen atmosphere will enable the synthesis of titanium nitride.
• the heating schedule comprises heating the shaped blended material in a non oxidising atmosphere to a temperature of at least substantially 1000°C and most preferably 1180 - 1450°C. Typical heating schedules for either the synthesis of titanium carbide or titanium nitride are 1180°C for 7 hours followed by 1250°C for 2 hours.
• Equations 1 to 5 show carbothermal reactions of titanium dioxide with iron, ilmemte and hematite to synthesise titanium carbide.
• Equations 6 and 7 show the reaction for the synthesis of titanium nitride from ilmenite with and without the addition of titanium dioxide as a raw material.
• FeTiO 3 + 4C TiC + Fe + 3 CO 3
• Figure 1 is an x-ray diffractogram of the products of reaction equation 5.
• Figure 1 shows phase pure x-ray patterns characteristic of TiC and Fe.
• Figure 2 is an x-ray diffractogram of the products of reaction equation 7.
• Figure 2 shows phase pure x-ray patterns characteristic of TiN and Fe.
• the resulting carbothermally reduced porous cermet materials synthesised by the process of the invention are generally strong and readily handled without damage.
• the synthesised material exhibits about 35-50% apparent porosity and there is a tendency for the outer boundary of the material to exhibit an enrichment of metallic iron.
• the material is porous the encapsulation of the titanium carbide, titanium nitride, or tungsten carbide, by the metallic iron matrix provides a protective barrier for these phases against surface oxidation. The exclusion of air by the metallic iron matrix hinders the oxidation at the surface of the TiC, TiN or WC particulates.
• Titanium carbide, titanium nitride, or tungsten carbide in the enriched cermet intermediate material may be incorporated into metal or metal alloys such as iron or steel or iron or steel alloys by many methods including incorporating for example pellets of the material into molten metal and allowing the titanium carbide, titanium nitride, or tungsten carbide phase to disperse throughout the molten material.
• the encapsulation of the ceramic particulates of TiC, TiN and WC in the cermet intermediate by metallic iron prevents oxidation at the surface and enables ready wetting and cohesive bonding by the metal or metal alloy.
• a vacuum induction furnace with provision for supply of a protective atmosphere such as argon is the preferred production method and such heating is often accompanied by significant stirring and therefore rapid mixing of the solid TiC, TiN or WC particulates could be expected.
• titanium carbide, titanium nitride, or tungsten carbide enriched billets is by allowing molten metal such as iron or steel or iron or steel alloys, or aluminium or magnesium or their alloys, to infill the porous titanium carbide, titanium nitride or tungsten carbide enriched material by capillary attraction.
• TiC enriched material produced as in example 4 was placed in an alumina crucible with 9.91 grams of NiHard alloy (BSS 4844 Grade 2D) and these materials were heated under a protective argon atmosphere to 1450°C for two hours (without stirring). After cooling the material was found to have taken the form of the crucible and the cross section of the body showed that TiC had dispersed throughout the whole body.
• Figure 3 shows a micrograph of a cross section of the material. Initial hardness of the NiHard alloy used in the process was 450 HV 2 o and the hardness of the resultant material with the incorporation of TiC was 808 HV 20 .
• TiC enriched material produced as in example 4 was placed in an alumina crucible with 9.11 grams of NiHard alloy (BSS 4844 Grade 2D) and these materials were heated under a protective argon atmosphere to 1450°C for two hours (without stirring). After cooling the material was found to have partially taken the form of the crucible and the cross section of the body showed that the TiC had dispersed throughout the whole material.
• Initial hardness of the NiHard alloy used was 450 HV 20 and the hardness of the resultant material with the incorporation of TiC was 850 HV 20 .
• TiC enriched material produced as in example 4 was placed in an alumina crucible with 50.23 grams of NiHard alloy (BSS 4844 Grade 2D) and these materials were heated under a protective argon atmosphere to 1500°C for two hours without stirring. After cooling the molten material was found to have taken the form of the crucible and the cross section of the body showed that the TiC had dispersed throughout 73% of the body of the material.
• the initial hardness of the NiHard alloy used was 450 HV 2 Q and the portion of the final material containing TiC had a mean hardness measurement of 708 HV 2 o. Percentage area measurement of the TiC particulates on a cross section of this sample was 38.9 as determined using SEM back scatter imaging.
• Figures 4 and 5 are micrographs of the sample portion containing TiC.
• TiC enriched material produced as in example 4 was placed in a fireclay crucible with 353.4 grams of NiHard alloy (BSS 4844 Grade 2D) and these materials were heated under vacuum to 1400°C for a 3 hour soak period. After cooling, the molten material was found to have taken the form of the crucible and formed a non-porous body by infilling the previously porous TiC material with
• This non porous TiC containing billet of 515 grams was placed together with 1905 grams of NiHard alloy (BSS 48444 Grade 2D) into a crucible of a 10 kg capacity induction furnace.
• a small quantity of slag 40wt%CaO/40wt%Al 2 O 3 /20wt %SiO 2 ) was added.
• These materials under a vacuum of 1.5 Torr, were electrically heated initially at 8kW power input which was increased stepwise to 17 kW over 21 minutes. After 31 minutes when the material was molten and at 1550 C. the chamber was opened and the melt stirred.
• the melt was manually stirred for a further five occasions over the following 15 minutes and after the last stirring 46 minutes from commencement of the heating, the melt was poured into a sand mould. There were risers of 7, 10. and 13 mm diameter within the sand mould. Microscopic examination of these cross sections showed distribution of TiC throughout the metal matrix. Micrographs of two such examples are shown in figures 7 and 8.
• Samples of grey cast iron with and without various portions of TiC enriched material prepared as in example 9 were heated initially to 1440°C under vacuum and then to 1500°C under an argon atmosphere.
• One part by weight of enriched TiC was added to 20, 10 and 5 parts by weight of the cast iron.
• the cast iron specimen heated without the presence of TiC showed significant grain growth but such grain growth was inhibited on all three specimens with added TiC.
• TiC enriched material as in example 9 (first part) was placed in a graphite crucible together with aluminium alloy and heated under vacuum to a soak temperature of 900°C for 1 hour. After cooling the aluminium was found to have infilled the body to the complete length by capillary attraction producing a dense and light weight cermet. X-ray diffraction patterns of the reacted product showed titanium carbide, aluminium and iron aluminide phases The initial hardness of the aluminium alloy used was 35 HV 20 and the infilled material containing 45 volume percent of TiC gave a mean hardness measurement of 110 HV 20 .

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• 2001
  • 2001-02-22 AU AU2001236246A patent/AU2001236246A1/en not_active Abandoned
  • 2001-02-22 CA CA002400632A patent/CA2400632A1/en not_active Abandoned
  • 2001-02-22 EP EP01908504A patent/EP1268106A4/de not_active Withdrawn
  • 2001-02-22 WO PCT/NZ2001/000024 patent/WO2001062420A1/en not_active Application Discontinuation
  • 2001-02-22 US US10/204,082 patent/US20030145685A1/en not_active Abandoned

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