EP0732415A1 - Verfahren zur Herstellung einer intermetallischen Verbindung - Google Patents

Verfahren zur Herstellung einer intermetallischen Verbindung Download PDF

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Publication number
EP0732415A1
EP0732415A1 EP96301717A EP96301717A EP0732415A1 EP 0732415 A1 EP0732415 A1 EP 0732415A1 EP 96301717 A EP96301717 A EP 96301717A EP 96301717 A EP96301717 A EP 96301717A EP 0732415 A1 EP0732415 A1 EP 0732415A1
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EP
European Patent Office
Prior art keywords
metal component
liquid metal
mould
mould cavity
powder
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96301717A
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English (en)
French (fr)
Inventor
Zhu Zhang
Robert Edward Emmett
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Deritend Advanced Technology Ltd
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Deritend Advanced Technology Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9505094.4A external-priority patent/GB9505094D0/en
Priority claimed from GBGB9526166.5A external-priority patent/GB9526166D0/en
Priority claimed from GBGB9601331.3A external-priority patent/GB9601331D0/en
Application filed by Deritend Advanced Technology Ltd filed Critical Deritend Advanced Technology Ltd
Publication of EP0732415A1 publication Critical patent/EP0732415A1/de
Withdrawn legal-status Critical Current

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    • 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
    • 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
    • C22C1/047—Making non-ferrous alloys by powder metallurgy comprising intermetallic 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
    • 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
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

  • This invention relates to a method of making a product comprising an intermetallic compound.
  • Intermetallic compounds for example titanium aluminides, have good high temperature mechanical properties, a relatively low density and good oxidation resistance. This renders them potential replacements for super alloys and other high temperature materials in, for example, aerospace, industrial gas turbines, electronic and automotive applications.
  • Intermetallic compound ingots may be produced by electroslag or vacuum induction melting for further processing and shaping using hot forging techniques.
  • problems with shape deformation and resulting microstructure and mechanical properties have restricted the use of this method from widespread use in manufacturing industry.
  • Another alternative method hitherto proposed is to carry out a powder metallurgical process to produce a initially porous structure which is then hot isostatically pressed to allow the reaction required to produce an intermetallic compound to take place and to fully densify the structure. Complexity and limitations on the size and accuracy of products have restricted the application of this method.
  • Objects of the present invention are to provide a method of and apparatus for making a product comprising an intermetallic compound whereby the above mentioned disadvantages are overcome or are reduced.
  • a method of making a product comprising an intermetallic compound including the steps of permeating a powder metal component, having a first melting point, with a liquid metal component, having a second melting point which is lower than the first melting point, to produce a product comprising an intermetallic compound of said powder and liquid metal components.
  • the method may be performed in a mould cavity.
  • the mould cavity may define the net shape of the product or near net shape of the product.
  • Said step of permeating a powder metal component with a liquid metal component may be performed to produce an intermediate form and the method may include the step of heat treating the intermediate form to produce said product.
  • the powder metal component comprises titanium or may comprise iron and the liquid metal component aluminium.
  • Said step of permeating a powder metal component with a liquid metal component may be performed under specific conditions to produce said product without a discrete step of heat treating an intermediate form.
  • the powder metal component comprises nickel or may comprise iron and the liquid metal component aluminium.
  • the method may include the step of subjecting the liquid metal component to a pressure which is greater than a pressure to which the powder metal component is subjected.
  • the subjection of the components to such a pressure difference may cause or assist said permeating of the powder metal component with the liquid metal component.
  • the powder metal component and the liquid metal component may be subjected to pressure to cause or assist permeation of the powder metal component with the liquid metal component.
  • the components may be subject to pressure by the application of fluid pressure such as gas, or by the application of mechanical pressure, such as by a mechanical ram.
  • the powder metal component may comprise a rigid preform.
  • the powder metal component may be in flowable form.
  • the powder metal component may be introduced into the mould cavity and then the liquid metal component may be introduced into the mould cavity.
  • the powder metal component may be degassed. That is, the powder metal component may be treated to remove gaseous and/or volatile material, for example by heating and evacuation.
  • the powder metal component may be degassed after being introduced into the mould cavity and before introduction of the liquid metal component.
  • the liquid metal component may be allowed to solidify and the solidified intermediate form may then be subjected to said heat treatment to effect a solid state phase transformation to provide said product comprising an intermetallic compound.
  • a predetermined atomic fraction of said powder metal component and said liquid metal component may be introduced into said mould cavity.
  • the mould cavity may have a wall which is impermeable as hereindefined.
  • the liquid metal component may be introduced into the mould cavity via an ingate from a reservoir.
  • the liquid metal component may be introduced into the mould cavity from the reservoir through a passage which communicates with the ingate.
  • the liquid metal component may be introduced into the mould cavity via an ingate from a reservoir.
  • the or each ingate may comprise an aperture or a plurality of apertures or a porous material such as a porous ceramic material which may also function as a filter.
  • the reservoir may be disposed above the mould cavity and the liquid metal component being fed downwardly into the mould cavity through the passage.
  • the liquid metal component may be fed downwardly into the mould cavity from the reservoir by virtue of flow under gravity.
  • a valve means may be provided to control the flow of molten metal from the reservoir to the mould cavity.
  • the valve means may comprise a stopper rod or other valve member moveable relative to a valve seat.
  • the mould and the reservoir may be mounted for movement relative to a horizontal axis so that in a first position the mould may be disposed above the reservoir and in a second position the mould may be disposed below the reservoir so that metal can flow from the reservoir into the mould cavity under gravity.
  • the reservoir and mould may be mounted for rotation about said axis or may be mounted for orbital or any other desired movement in which said change of orientation may take place.
  • the reservoir may be disposed below the mould cavity and the liquid metal may be fed upwardly into the mould cavity through the passage.
  • the liquid metal component may be introduced into the mould cavity via an ingate by immersing the ingate in a bath of said liquid metal component held in a reservoir.
  • the whole of the mould is immersed in the bath.
  • the ingate may be at the top of the mould cavity or may be at any other desired position.
  • the ingate is not at the top of the mould cavity only a part of the mould may be immersed in the bath of liquid metal component and the mould cavity being filled by applying pressure to the liquid metal bath to force it into the mould cavity.
  • the introduction operation may be performed so that the temperature of the metal in the bath is above the melting point of the liquid metal component but below the melting point of the intermetallic compound so that the intermetallic compound will solidify within the mould cavity whilst the mould cavity is immersed or partly immersed in the bath, and the mould containing the solidified intermetallic compound can be removed from the bath.
  • the mould cavity may be provided with a plurality of ingates.
  • the or each ingate may be positioned at any desired location in a wall of the mould.
  • At least one ingate may be provided in the part of the wall of the mould which defines the internal surface of the tubular mould cavity.
  • the liquid metal component in the reservoir may be subject to pressure.
  • the pressure may be mechanical pressure, for example, by advancing a piston in said reservoir to apply pressure to a surface of the liquid metal.
  • the pressure may be applied by subjecting a surface of the metal in the reservoir to fluid pressure, for example, gaseous pressure.
  • Said application of pressure may feed or aid the feed of metal from the reservoir into the mould cavity and/or subject the metal in the mould cavity to pressure.
  • the mould cavity may be disposed in an enclosure, the interior of which may be placed in communication with the reservoir, for example through the ingate and the interior of the enclosure may be subject to said fluid pressure.
  • the mould cavity may be connected in communication with a degassing means through the ingate or, alternatively, through a conduit separate from the ingate.
  • conduit means which may comprise a passage, are provided continuously to connect the interior of the enclosure to the source of fluid pressure. Flow of fluid pressure through the passage may be controlled by suitable valve means.
  • the conduit means may comprise a passage extending lengthwise of a pivot member by which the mould and reservoir are mounted for rotation about said axis.
  • the pressure may be maintained for a predetermined time, for example, until the liquid metal in the mould cavity has solidified, or, alternatively, for a time which is predetermined so as to ensure complete or substantially complete permeation of the liquid metal component into the powder metal component.
  • the powder metal component may comprise titanium, iron or nickel.
  • the liquid metal component may comprise aluminium.
  • the intermetallic compound may comprise titanium aluminide, which may be TiAl 3 , TiAl or Ti 3 Al, nickel aluminide which may be NiAl 3 , Ni 2 Al 3 ,NiAl, Ni 3 Al or iron aluminide which may be Fe Al 3 Fe 2 Al 5 , FeAl or Fe 3 Al.
  • the intermetallic compound may comprise (expressed in Atomic %): Powder Al Others When present TI + usual impurities Optionally ) TiAl 3 Balance 75 ) 1 - 4 ) 1 - 25 TiAl Balance 47 - 56 ) 1 - 4 ) Ti 3 Al Balance 20 - 38 ) 7 - 25 Ni + usual impurities Optionally NiAl 3 Balance 75 ) 1 - 2 ) Ni 2 Al 3 Balance 58 - 63 ) 1 - 2 ) 1 - 15 NiAl Balance 45 - 59 ) 1 - 2 ) Ni 3 Al Balance 25 - 28 ) 7 - 14 Fe + usual impurities Optionally FeAl 3 Balance 75 ) 1 - 4 ) Fe 2 Al 5 Balance 71 - 73 ) 1 - 4 ) 1 - 15 FeAl Balance 36 - 55 ) 1 - 4 ) Fe 3 Al Balance 22 - 36 ) 5 - 6
  • the "other" components may comprise chromium, manganese or niobium and may be present in the range specified above.
  • the intermetallic compound alternatively may comprise molybdenum silicide or niobium beryllides or chromides.
  • At least one additional component may be introduced into the mould cavity prior to permeating the powder metal component with the liquid metal component.
  • the non-metallic reinforcement may be added to the intermetallic compound to create a metal matrix composite (MMC) having modified thermophysical properties.
  • MMC metal matrix composite
  • the additional component may comprise ceramic particles such as silicon carbide or alumina particles, fibres such as silicon carbide or alumina fibres, whiskers such as silicon carbide whiskers or monofilament, multifilament or random fibres.
  • Said step of permeating a powder metal component with a liquid metal component may be performed to provide a product having a first portion which has a melting point which is higher than the melting point of a second portion of the product.
  • Said step of permeating a powder metal component with a liquid metal component may be performed with different atomic proportions by atomic weight of powder metal component and liquid metal component in at least one pre-determined part of the mould.
  • the method may comprise a step of introducing said powder metal component into a first part of the mould cavity and permeating the powder metal component in said first part with said liquid metal component and introducing another component, selected from a powder metal component and a liquid metal component, in a second part of the mould cavity not occupied by the powder metal component.
  • the other component may be a liquid metal component.
  • the other component may be at least one powder metal component the or each of which provides a different atomic proportion of powder metal component to liquid metal component to the proportion provided in the first part of the cavity and the method including a further step of permeating the or each other powder metal component with a liquid metal component.
  • the mould cavity may comprise a third part unoccupied by a powder metal component and into which a liquid metal component is introduced.
  • compositions and proportions by atomic weight in each part may be in accordance with the values tabulated in Table 1 hereof.
  • a product in accordance with the further more specific aspect of the invention, may be provided with different physical properties such as melting points, in different regions of the product.
  • a part of the product adjacent a surface which, in use, is subjected to high temperature such as the crown of an automotive piston may be provided with a higher melting point than the remainder of the product.
  • the powder metal component comprises a surface part having an atomic proportion to provide a surface part of NiAl
  • a mould cavity 10 of a desired net shape that is to say, a shape which is the same as, or similar to, a desired final shape of a product, and having an ingate I is provided in a mould or die 11 by suitable means such a shaped mould can be distinguished from, for example, an ingot mould by virtue of the product having a desired three dimensional shape and generally being not formed to a final shape by further forming .
  • the cavity is made using a lost wax disposable pattern in a refractory material which in the present example is silica, but which may be zirconia and/or alumina.
  • the refractory material of the mould in the present example comprises silica bonded with silicate formulated so as to make the mould impervious, or substantially impervious, to liquid or gas.
  • the mould is then fired in conventional manner to a temperature sufficient to remove volatile material and to stabilise the mould.
  • the cavity may be made in any other suitable manner and need not be made to net shape, although such is preferred.
  • the mould may be made in one of said refractory materials, or in plaster or any suitable moulding material using removable patterns.
  • the mould is made of alumina it may be made, for example, of alumina silicate which renders the mould, in itself, impermeable.
  • the mould may be made by machining a suitable mould material and where, for example, the mould material is metal, then the cavity is generally referred to as being made in a die.
  • the mould is made in such a way as to be impermeable.
  • impermeable we mean herein that the mould is at least sufficiently impermeable a) for liquid metal to be cast into the mould so as to prevent penetration of the mould surface by the liquid metal surface, and b) to prevent passage of gas from the interior of the wall of the mould to prevent ingress of gas into the interstices between the powder particles, of the powder metal component, from within the interior of the mould wall prior to being permeated with the liquid metal component.
  • internal of the mould wall we mean gas which has either permeated into the mould wall and been held there within the mould wall or gas which has passed through the interior of the mould wall from the exterior of the mould wall into the mould cavity.
  • degree of "prevention" can vary with the desired application and/or manufacturing technique including the mould material of the product concerned. For example, for some applications a relatively rough surface is desirable.
  • the mould may be made of material which is itself impermeable as well as a mould which is coated or otherwise treated so as to be impermeable.
  • the porosity for example the pore size of the mould, may vary with temperature within the above-mentioned limits.
  • An important requirement is that the mould is, in practice, sufficiently impermeable to liquid metal to be cast into the mould as well as to passage of gas from the interior of the wall of the mould to produce satisfactory results.
  • the mould cavity then has a powder metal component introduced thereinto, through the ingate I as shown at 12 in Figure 2.
  • the powder is titanium metal powder, but may comprise other suitable material for producing intermetallic compounds, such as nickel or iron.
  • the powder metal component instead of comprising metal powder in flowable form, may comprise a rigid preform made by conventional powder metallurgical techniques to produce a preform with interstices between the powder metal particles.
  • the titanium powder had an average particle size of 70 ⁇ m and a purity of about 99.75%.
  • the particle size may lie in the range, for example 10 - 150 ⁇ m or, for example, 30 - 250 ⁇ m.
  • the volume fraction introduced in the present example was about 50% but the volume fraction may lie in the range 35% to 75%.
  • the preform may be pressed as necessary to achieve the desired volume fraction and the mould cavity is configured so as to provide a predetermined clearance with the preform.
  • the clearance may, for example, be the minimum necessary to allow introduction of the preform into the cavity.
  • the mould 11 is disposed in the chamber 13.
  • the chamber 13, in the present example, comprises a lower part 14 in which the mould 11 is disposed and an upper part 15 in which a crucible 16 for receiving liquid metal component is received.
  • the mould 11 may be introduced into a lower part 14 of the chamber either before or after filling the mould 11 with the powder metal component.
  • the crucible 16 is filled with the desired amount of liquid metal 17 which in the present example comprises aluminium, but which, if desired, may comprise other suitable material for any of the alternative powder metal components.
  • Suitable means are provided to maintain the metal in the crucible 16.
  • Such means may comprise a magnetic field, a mechanical plug or other means as described hereinafter with reference to Figures 9 - 15.
  • the chamber 13 is then sealed from atmosphere and is evacuated to remove air from the interior of the chamber and consequently from the interstices between the powder particles 12 in the mould 11.
  • the inside of the chamber 13 and or the mould 11 may be heated to facilitate the above described degassing process and the removal of volatile materials from the mould and the chamber.
  • the liquid metal component 17 is poured from the bottom of the crucible 16 through a tap hole 18 into a feeder system 19 of the mould 11 and, hence, via the ingate I, into the mould 11. Initially the molten metal 17 rests temporarily in the feeder system 19 on top of the powder component 12 so as to seal the evacuated interstices inside the impermeable mould 11.
  • the powder and liquid components within the mould 11 are and then subjected to pressure to ensure that the powder metal component is permeated with the liquid metal component so that all, or substantially all, of the interstices between the particles of the powder metal components are filled with liquid metal.
  • This pressure overcomes flow resistance and surface tension effects and ensures complete permeation.
  • the pressure may be applied using any one of the casting apparatus described hereinafter and illustrated with reference to Figures 9 - 15.
  • the intermediate product 22 contains the correct ratio of finely distributed components necessary to produce the intermetallic compound.
  • the thus produced intermediate product is then subject to a solid state phase transformation heat treatment to create an intermetallic compound.
  • the heat treatment to produce a titanium aluminide intermetallic compound of desired microstructure and mechanical properties comprises a two stage solid state phase transformation in the range 520 - 600°C, typically 570°C and in the range 1200°C up to the limit of stability, typically 1350°C.
  • the powder metal component may comprise titanium, iron or nickel.
  • the liquid metal component may comprise aluminium.
  • the intermetallic compound may comprise titanium aluminide, which may be TiAl 3 , TiAl or Ti 3 Al, nickel aluminide which may be NiAl 3 , Ni 2 Al 3 , NiAl, Ni 3 Al or iron aluminide which may be FeAl 3 Fe 2 Al 5 , FeAl or Fe 3 Al.
  • the liquid metal and powder metal components may comprise compositions selected from the ranges set out below (expressed in Atomic %): TABLE 1 Powder Al Others When present Ti + usual impurities Optionally ) TiAl 3 Balance 75 ) 1 - 4 ) 1 - 25 TiAl Balance 47 - 56 ) 1 - 4 ) Ti 3 Al Balance 20 - 38 ) 7 - 25 Ni + usual impurities Optionally NiAl 3 Balance 75 ) 1 - 2 ) Ni 2 Al 3 Balance 58 - 63 ) 1 - 2 ) 1 - 15 NiAl Balance 45 - 59 ) 1 - 2 ) Ni 3 Al Balance 25 - 28 ) 7 - 14 Fe + usual impurities Optionally FeAl 3 Balance 75 ) 1 - 4 ) Fe 2 Al 5 Balance 71 - 73 ) 1 - 4 ) 1 - 15 FeAl Balance 36 - 55 ) 1 - 4 ) Fe 3 Al Balance 22 - 36 ) 5 - 6
  • the resultant intermetallic components may be as set out in Table 2.
  • Table 2 Intermetallic Density, g/cm 3 Aluminium, wt% Melting point, °C Ni 3 Al 7.293 13.28 1395 NiAl 5.91 31.49 1639 Ni 2 Al 3 4.787 40.81 1133 NiAl 3 3.957 57.96 854 Fe 3 Al 6.648 13.87 1502 FeAl 5.585 32.57 1215 Fe 2 Al 5 3.963 54.70 1171 Ti 3 Al 4.216 15.81 1600 TiAl 3.63 36.03 1460 TiAl 3 3.371 62.82 1340
  • the respective intermetallic component may be formed during the permeation operation without the need for a subsequent heat treatment to cause a solid state transformation to the respective intermetallic component.
  • the powder metal component comprises iron or titanium a combination of intermetallic formation during permeation and during a subsequent solid state heat treatment occurs. This condition is possible but it is not necessarily always like this.
  • Ni, Ti and Fe have an essentially similar nature, that is, during infiltration of an aluminium melt a more or less partial reaction may occur depending upon the powder volume fraction, the melt temperature, the applied pressure, the particle morphology and hence, generally, the velocity of infiltration.
  • the "other" component if and when present may comprise chromium, manganese or niobium, or any desired combination of two or more of the above.
  • the intermetallic compound alternatively may comprise molybdenum silicide or niobium beryllides or chromides depending on the powder and liquid metal components.
  • At least one additional component may be introduced into the mould cavity prior to permeating the powder metal component with the liquid metal component.
  • the non-metallic reinforcement may be added to the intermetallic compound to create a metal matrix composite (MMC) having modified thermophysical properties.
  • MMC metal matrix composite
  • the additional component may comprise ceramic particles such as silicon carbide or alumina particles, fibres such as silicon carbide or alumina fibres, or whiskers such as silicon carbide whiskers.
  • Random fibres are usually about 3 ⁇ m and over in diameter and have a typical fibre length of about 50 ⁇ m. Whiskers are single crystals, so rarely grow larger than 0.5 ⁇ m in diameter. Said additional component does not form an intermetallic compound with the liquid metal component.
  • the resultant net shape product comprising titanium aluminide intermetallic compound is illustrated at 23 in Figure 8 and may comprise a single product or may comprise a plurality of products depending on the configuration of the mould cavity 10.
  • the mould cavity 10 is defined in a die 25, having an ingate I, and which in the present example is made by machining in a suitable die steel.
  • the wall of the mould cavity is impermeable since the steel is impermeable itself and split lines in the die are provided with suitable seals.
  • a melting chamber 26 in which a crucible 27 is positioned, surrounded by a heating coil 28 such as an induction or resistance heating coil.
  • the crucible 27 is made of a suitable material to withstand the temperature and mechanical stresses and has a generally cylindrical interior 30.
  • a generally cylindrical ram 29 is positioned above the crucible 27.
  • the ram 29 is adapted to be advanced into the interior 30 of the crucible 27 by a suitable mechanical means such as a hydraulic piston, illustrated diagrammatically at 31.
  • the ram 29 in the present case is of generally cylindrical configuration and closely conforms to an internal surface 32 of the interior 30 of the crucible 27.
  • the cavity 10 is connected by a conduit 33 and a valve 34 to a vacuum system 35.
  • a clamp 38 is provided to hold the die 25 in engagement with the melting chamber 26.
  • the cavity 10 is filled with powder metal component as described hereinbefore, and the crucible 27 is filled with a desired amount of liquid metal component.
  • liquid metal is, substantially, retained in the crucible 30 simply by virtue of the liquid metal flowing through the opening 18 until it rests on the upper surface of the powder metal component in the cavity 10. If desired, however, liquid metal may be retained wholly within the crucible 27 by any other suitable means such as those described hereinbefore.
  • a degassing operation is carried out as described previously using the vacuum system 35 and then liquid metal is permitted to leave the crucible through the tap hole 18.
  • the hydraulic piston 31 is operated to advance the ram 29 into the interior 30 of the crucible 27 and thus apply mechanical pressure to the molten metal in the crucible 27 and maintain this pressure in the range 10 - 30 bar as the molten metal is caused to permeate the powder metal component.
  • the pressure may be maintained until the liquid metal component has solidified, or may be removed or reduced prior to complete solidification of the liquid metal component.
  • the die 25 is then separated from the melting chamber 26 and is opened and the method continued as described hereinbefore.
  • the apparatus comprises a mould chamber 50 in which is housed an impermeable disposable ceramic mould 11 having an ingate I and made from plaster or refractory material such as silica, zirconia and/or alumina as described hereinbefore and defining a mould cavity 10.
  • the mould cavity 10 in this embodiment has a feeder portion 19 similar to that described previously and illustrated in Figure 3.
  • the mould 11 is rendered impervious by virtue of a silicate coating, as described hereinbefore.
  • the interior of the mould chamber 50 is connected by a manifold 52 and valves 53, 54 to a vacuum system 55 or a pressure source 56 respectively.
  • a melting chamber 57 which houses a crucible 58 surrounded by a heating coil 51.
  • the crucible 58 has a hollow interior 59 into which molten metal is fed via a gate valve 61.
  • a stopper rod 62 is provided to close a pouring hole 63 of the crucible 58.
  • a metal loading port 60 above the crucible 58 is connectable by a manifold 64 and valves 65, 66 to a pressure source 56 or a vacuum system 55 respectively.
  • valves 53, 66 are closed and the valves 54, 65 opened so as to apply gaseous pressure to the top of the metal in the feeder portion 19 and thus pressuring the interior of the cavity 10.
  • a mould chamber 70 is releasably mounted on and sealed to a melting chamber 71 which is mounted for rotation about a horizontal axis 72, by virtue of a stub axle 73 received in a bearing 74 and a hollow stub axle 75 being received in a bearing 76.
  • the bearings 74, 76 are supported by bearing frames 77.
  • the hollow interior of the stub axle 75 is connected at one end by an annular aperture 78 to the interior of the mould chamber 70 and by virtue of a transverse aperture 79 at the other end and a valve 80 to a pressure source 81 and by a second, diametrically opposite transverse aperture 82 and a valve 83 to a vacuum system 84.
  • a crucible 85 is disposed within the melting chamber 71 and surrounded by a heating coil 86.
  • the liquid metal component 17 is introduced into the crucible 85 and then the mould chamber 70 is sealingly mounted on the melting chamber 71.
  • a degassing operation is then performed using the vacuum system 84 with the valve 83 open and the valve 80 closed.
  • the assembly of melting chamber and mould chamber 71, 70 is rotated through 180° about the axis 72 so that liquid metal from the crucible 85 is poured into the feeder portion 19 and through the ingate I into the mould 11 and then the interior of the assembly 70, 71 is pressurised from the source 81 through the valve 80, the valve 83 being closed, and so gaseous pressure is applied to the surface of metal in the feeder portion 19 via the passage 89.
  • the remainder of the process is performed as described hereinbefore.
  • the powder material is either in the form of a rigid or semi-rigid preform, or is introduced into the mould cavity in flowable form held in place by a filter or is subsequently compacted to sufficient extent so as to retain its shape and position in the mould 11 whilst in an inverted position.
  • the mould cavity 10 having an ingate I is defined in an impermeable permanent die 90 which in the present example is made by machining in a suitable die steel.
  • a melting chamber 91 in which a crucible 92 is positioned, surrounded by a heating coil 93.
  • the lower end of a generally cylindrical feed tube 94 is immersed in the liquid metal component contained in the crucible 92.
  • the upper end of the feed tube 94 is removably sealed to the inlet to the die 90.
  • the cavity 10 is connected by a conduit 95 and a valve 96 to a vacuum system 97.
  • a valve 99 similarly connects the melting chamber 91 to the vacuum system 97.
  • the cavity 10 is filled with powder metal component as described hereinbefore, and the crucible 92 is filled with a desired amount of liquid metal component.
  • a degassing operation is carried out as described previously using the vacuum system 97. Simultaneously vacuum valves 96 and 99 are closed and pressure valve 101 is opened applying pressure to the molten metal in the crucible. The molten metal is caused to rise up feed tube 94 and permeate the powder metal component. The pressure may be maintained until the liquid metal component has solidified whereupon the die 90 separated from the melting chamber 91 is opened and the method continued as described hereinbefore.
  • the mould cavity 10 is defined in an impermeable disposable ceramic mould 11 made from plaster or refractory material and which is rendered impervious by virtue of a silicate coating as described hereinbefore.
  • the mould cavity is provided with an ingate I at the entrance to which is provided a filter 103 and the filter 103 also retains the powder metal component within the mould cavity.
  • the mould cavity may be provided with a plurality of ingates at desired positions to ensure proper filling of the mould cavity depending upon the mould cavity configuration.
  • a filter or a plurality of filters 103 being provided for each ingate.
  • the or each filter may comprise a porous ceramic material.
  • a crucible 106 provides a reservoir which is charged with liquid metal component to a level L and the temperature of the liquid metal component is controlled by an electrical heating coil 107.
  • the mould 11 containing the powder metal component is mounted on a rod 104 which can be moved vertically through an opening 104 a in a lid 105 of an enclosure or melting chamber 102.
  • the lid 105 is removably sealed to the chamber 102 so as to provide a fluid tight enclosure.
  • the chamber 102 is provided with a degassing system 108 connectable with the interior of the chamber 102 by a valve 109 and with a gaseous pressure system 110 connectable to the interior of the chamber 102 by a valve 111.
  • a degassing operation is then performed as described previously using the vacuum 108 with the 109 open and the valve 111 closed.
  • the mould 11 When the degassing operation has been completed the mould 11 is immersed in the liquid metal in the crucible 106 by operation of the hydraulic piston 112 to lower the rod 104.
  • the valve 109 is closed and the valve 111 is open so as to apply gaseous pressure from the pressure system 110 to the liquid metal contained in the crucible 106.
  • the liquid metal is thus caused to enter the mould cavity via the or each ingate and associated filter or filters 103 and thus permeates the powder metal component.
  • a plurality of moulds may be immersed in the crucible 106 by a suitable mounting on the rod 104 or by providing a plurality of rods 104 moveable simultaneously or independently by appropriate hydraulic pistons similar to the piston 112.
  • the temperature of the metal in the crucible 106 is maintained above its melting point but below the melting point of the intermetallic compound.
  • the intermetallic compound comprises y titanium aluminide, melting point 1450°C, and the liquid metal component is aluminium, melting point 660°C, the aluminium may be maintained at a temperature lying in the range 700°C to 900°C.
  • a similar temperature differential lying in the range 400°C to 1000°C, may be provided between the melting point of the liquid metal component and of the intermetallic compound where these differ from the particular example described hereinbefore.
  • FIG 14 there is shown apparatus for use in a method similar to that described with reference to Figure 13 but Figure 14 shows an impermeable disposable ceramic mould 11 which defines a tubular or part tubular product from which it will be seen that a plurality of ingates I are provided disposed at desired positions over the whole of the wall of the mould 11 which defines the internal surface of the tubular product, or tubular part of the product, to be made.
  • each ingate could comprise a single aperture or comprise a porous material or indeed a single ingate covering the whole internal surface could be provided.
  • the ingate may have a plurality of discrete apertures or comprise a porous ceramic body.
  • Such a disposition of ingates on the internal surface facilitates the casting of products incorporating a tubular configuration.
  • the cavity 10 is again defined in an impermeable permanent die and, in the present example, is configured to produce an automotive engine piston.
  • the cavity instead of the cavity 10 being filled with powder metal component as was the case of the embodiment previously described with reference to Figure 9, the cavity has the powder metal component introduced into a first part P1 of the mould cavity adjacent the bottom end thereof.
  • the powder metal component may comprise, for example, a layer of nickel powder in flowable form, or alternately, if desired, nickel powder in the form of a rigid preform.
  • the powder metal component may be, for example, approximately 1-2mm thick and may be of shallow cup shape as shown in Figure 15 or of any other desired configuration to provide a desired part of the final product with desired properties.
  • Liquid metal component such as aluminium or a suitable aluminium alloy is then introduced into the mould cavity as described in connection with the previous embodiment described with reference to Figure 9 so that the powder metal component disposed in the first part P1 of the mould cavity is permeated with the liquid metal component and a second part P2 of the mould cavity, which does not contain a powder metal component is occupied with the desired amount of liquid metal component.
  • the first part of the mould cavity may have a powder metal component of a volume fraction introduced thereinto and a second part of the mould cavity adjacent the first part may have another powder metal component introduced thereinto of different volume fraction to the powder metal component in the first part.
  • Liquid metal component is introduced into the mould cavity to permeate the powder metal components disposed in the first and second parts of the mould cavity and to occupy to a desired extent a third part of the mould cavity, not occupied by the powder metal components, with liquid metal component.
  • the resultant product may have a region such as a surface part which comprises Ni Al, then a region comprising Ni 2 Al 3 and then a region comprising Ni Al 3 all as integral regions of the product, as the composition approaches that of aluminium or an aluminium alloy, the remainder of which comprises aluminium or aluminium alloy.
  • the intermetallic compound for example NiAl, Ni 2 Al 3 , or NiAl 3 may be of constant composition throughout the respective region.
  • the composition of the intermetallic may vary in accordance with the phase diagram, according to the range of volume fraction provided in the region and/or according to the range of volume fraction which results from introduction of the liquid metal component into the region.
  • transition regions between these parts where the composition comprises a mixture of the intermetallic components of the adjacent regions.
  • the transition region between the NiAl region and the Ni 2 Al 3 region may comprise a mixture of the two intermetallic compounds which varies from 100% NiAl progressively to 100% Ni 2 Al 3 . Similarly for other transition regions.
  • a powder metal component or components may be disposed in any desired part or parts of the mould cavity and powder metal components of different volume fraction may be provided at different parts of the mould cavity.
  • volume fraction can be varied by powder metallurgical techniques for example by virtue of using different particle morphology, and/or size and/or by putting a different amount of powder in the or a desired region.
  • the reaction of the powder metal component and the liquid metal component to produce the intermetallic compound may occur either as the liquid metal part advances through the powder metal component or generally within the product, for example, after a short delay.
  • the reaction occurs in an intermediate body the reaction may again occur as described above.
  • the composition of the intermetallic compound may vary without falling outside the scope of this patent application for example by a few percent although those stated are preferred compositions.
  • the pressure applied to the liquid component lies in the range 10 - 30 bar and is typically 20 bar.
  • higher pressures may be used, for example, up to 100-500 bar or even higher pressures eg 1000 bar may be used where, for example, conventional squeeze casting is used to apply a mechanical pressure directly to the liquid metal.
  • a pressure below atmospheric pressure may be applied to the powder component and atmospheric pressure applied to the liquid metal component to cause or assist the permeation.
  • any suitable means of providing a pressure difference between the liquid and powder components in which the pressure acting on the liquid component is relatively greater than that acting on the powder component may be provided.
  • powder metal we mean discrete particles of metal with a maximum dimension of less than 1mm (1,000 ⁇ m). Generally, the particles of the powder metal component are dry prior to introduction of the liquid metal component.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Manufacture Of Alloys Or Alloy Compounds (AREA)
EP96301717A 1995-03-14 1996-03-13 Verfahren zur Herstellung einer intermetallischen Verbindung Withdrawn EP0732415A1 (de)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
GB9505094 1995-03-14
GBGB9505094.4A GB9505094D0 (en) 1995-03-14 1995-03-14 Method of and apparatus for making a product comprising an intermetallic compound
GBGB9526166.5A GB9526166D0 (en) 1995-12-21 1995-12-21 Method of and apparatus for making a product comprising an intermetallic compound
GB9526166 1995-12-21
GBGB9601331.3A GB9601331D0 (en) 1996-01-23 1996-01-23 Method of and apparatus for making a product comprising an intermetallic compound
GB9601331 1996-01-23

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EP0732415A1 true EP0732415A1 (de) 1996-09-18

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DE102010061960A1 (de) * 2010-11-25 2012-05-31 Rolls-Royce Deutschland Ltd & Co Kg Verfahren zur endkonturnahen Fertigung von hochtemperaturbeständigen Triebwerksbauteilen

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3809550A1 (de) * 1988-03-22 1989-10-19 Vaw Ver Aluminium Werke Ag Verfahren zur pulvermetallurgischen herstellung eines leichten und warmfesten bauteiles
US5015440A (en) * 1989-09-01 1991-05-14 Mcdonnell Douglas Corporation Refractory aluminides
WO1992017297A1 (en) * 1991-04-08 1992-10-15 Aluminum Company Of America Fabrication of metal matrix composites by vacuum die casting
WO1994021407A1 (en) * 1993-03-19 1994-09-29 Massachusetts Institute Of Technology Method for producing articles by reactive infiltration

Family Cites Families (5)

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Publication number Priority date Publication date Assignee Title
US3553806A (en) * 1968-01-04 1971-01-12 Clevite Corp Bearing and method of making same
JPS6029431A (ja) * 1983-07-28 1985-02-14 Toyota Motor Corp 合金の製造方法
US4915908A (en) * 1984-10-19 1990-04-10 Martin Marietta Corporation Metal-second phase composites by direct addition
AU626435B2 (en) * 1989-07-10 1992-07-30 Toyota Jidosha Kabushiki Kaisha Method of manufacture of metal matrix composite material including intermetallic compounds with no micropores
GB2259308A (en) * 1991-09-09 1993-03-10 London Scandinavian Metall Metal matrix alloys

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3809550A1 (de) * 1988-03-22 1989-10-19 Vaw Ver Aluminium Werke Ag Verfahren zur pulvermetallurgischen herstellung eines leichten und warmfesten bauteiles
US5015440A (en) * 1989-09-01 1991-05-14 Mcdonnell Douglas Corporation Refractory aluminides
WO1992017297A1 (en) * 1991-04-08 1992-10-15 Aluminum Company Of America Fabrication of metal matrix composites by vacuum die casting
WO1994021407A1 (en) * 1993-03-19 1994-09-29 Massachusetts Institute Of Technology Method for producing articles by reactive infiltration

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CA2171701A1 (en) 1996-09-15
GB9605405D0 (en) 1996-05-15
JPH09104932A (ja) 1997-04-22
GB2298872A (en) 1996-09-18

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