CROSS REFERENCE TO RELATED APPLICATIONS

This application represents the first application for a patent directed towards the invention and the subject matter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming a composite component, in which a plurality of feed materials are initially in a powdered state and a solid component is formed by the application of heat.

The present invention also relates to an apparatus for forming a composite component, of the type in which a plurality of feed materials are initially in a powdered state and a solid component is formed by the application of heat.

2. Description of the Related Art

Composite components are component parts made from two or more dissimilar materials that are consolidated to produce a single structure with characteristics different from the individual constituent materials. The composite structure may be preferred for a number of reasons for example in creating a multi-layer component having a hard exterior surface but a low density, light-weight interior.

A variety of methods are known for producing a multi-layer component comprising one or more dissimilar materials, such as hard facing or laser cladding.

However these known methods incur a number of problems. Firstly, a disadvantage is experienced in the number of separate processes required to create the finished component. Secondly, such techniques of applying a layer of material to the exterior of a solid object result in a non-discreet join of the two materials, leading to a structural weakness at the interface.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method of forming a composite component from a plurality of dissimilar powdered feed materials comprising the steps of; obtaining a negative ceramic mould of a component defining a first aperture associated with a first region of the mould and a second aperture associated with a second region of the mould; deploying a first powdered feed material into said first region of the negative mould via the first aperture and a second powdered feed material into said second region of the negative mould via the second aperture; and increasing the temperature within said negative mould to a first temperature causing said first feed material to melt during a heating stage.

According to a second aspect of the present invention there is provided an apparatus for forming a composite component from a plurality of dissimilar powdered feed materials comprising; a negative ceramic mould defining a first aperture associated with a first region of the mould and a second aperture associated with a second region of the mould; wherein said first aperture is configured for insertion of a first powdered feed material into said first region of the mould and said second aperture is configured for insertion of a second powdered feed material into a second region of the mould; and said negative ceramic mould is suitable for heating to a first temperature during a heating stage.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a method of forming a composite component from powdered feed materials;

Figure 2 shows a procedure for the creation of a negative mould;

Figure 3 shows the deployment of feed materials together in the mould of Figure 2;

Figure 4 shows a feeder section of a negative mould; Figure 5 shows the negative mould of Figure 4 after solidification; Figure 6 shows a mould with two regions and two feed materials being inserted separately;

Figure 7 shows the mould of Figure 6 after heating to join the feed materials;

Figure 8 shows a cross section view of a first mould with a partition; Figure 9 shows in cross section a second mould with a partition;

Figure 10 shows a processing apparatus;

Figure 11 shows a temperature-time graph for the process of Figure 8; Figure 12 shows a temperature-time graph for the process of Figure 9.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Figure 1

A method of forming a composite component from powdered feed materials is illustrated in Figure 1 , in which a solid component is formed from a plurality of dissimilar powdered feed materials by the application of heat.

At step 101 , a negative mould 102 is obtained that defines the profile of a component to be produced. At step 103, the powdered feed materials, first feed material 104 and second feed material 105 are deployed into the negative mould. At step 106, heat is applied to the mould increasing the temperature and causing the powdered feed materials to melt during a heating stage. At step 107 the temperature is maintained where necessary to allow diffusion of first feed material 104 with second feed material 105. At step 108 the temperature is decreased, causing the molten feed materials to solidify during a cooling stage. Figure 2

As discussed with reference to step 101, a negative mould is obtained from a positive model of a component.

A method of obtaining a negative mould is illustrated in Figure 2. A positive model 201 is created from an appropriate medium such as a rapid prototyping material, polystyrene or wax, defining the geometry of the desired component.

Negative mould 102 is then formed around the positive model to define a negative profile of the component. In a first embodiment, the negative mould comprises a layer of material having a melting point higher than that of first feed material 104 and second feed material 105, such as a very high temperature ceramic material. The ceramic shell is created by applying a plurality of layers of ceramic slurry to the exterior of the positive model, until the required wall thickness is achieved.

The sacrificial positive model material 201 is then evacuated from the negative mould 102 via aperture 202 using an appropriate removal technique, such as the application of heat and/or a solvent. This leaves a cavity 203 defining the exterior surface of the component.

Figure 3

Step 103 for the deployment of feed materials is illustrated in Figure 3. The positive sacrificial model 201 has been removed as shown previously with reference to Figure 2, leaving negative mould 02 ready to receive feed material, such as first feed material 104 and second feed material 10S contained within feed device 301. In an embodiment the filling of negative mould 102 is facilitated by vibration of the mould to encourage the powdered feed materials to settle. Negative mould 102 is placed upon vibrating table 302, itself supported by stable base member 303. In this way, as powdered feed materials are introduced to the mould they tend to compact under gravity.

In the embodiment illustrated in Figure 3 first feed material 104 and second feed material 105 have been combined in powder form in feed device 301 , prior to introduction to the mould. This type of powder preparation is advantageous as it allows for very precise material compositions and uniform dispersions of particles before agglomeration. First feed material 104 comprises a metallic melt powder with a first melting point and second feed material 105 comprises a ceramics substance with a much higher melting point than that of first feed material 104.

Thus, in the illustrated embodiment first feed material 104 and second feed material 105 are deployed into the mould together via aperture 202 so as to fill cavity 203 within negative mould 102, and then heated as in step 106 during a heating stage. The temperature is increased by heating the negative mould 102 to a first temperature, approximately equal to the melting point of first feed material 104, thereby causing first feed material 104 to melt. However second feed material 105, having a melting point much higher than that of the first temperature is not melted and remains in its solid particulate form.

In alternative embodiments the heating stage described above is performed in a pressure controlled environment at a pressure other than atmospheric pressure of 1 bar. In a first embodiment the pressure is reduced to below atmospheric pressure by removing air from the pressure controlled environment. In a second embodiment the applied pressure is increased to a level above atmospheric pressure. Equally the heating stage may be performed under time-evolving pressure conditions.

Figure 4

A negative mould 401 , substantially similar to negative mould 102, of Figure 3 is shown in partial cross section in Figure 4 after deploying step 103 and heating step 106. As previously described with reference to Figure 3, negative mould 401 has been heated to a first temperature thereby melting first feed material 104 whilst second feed material 105 is not melted but remains uniformly distributed throughout the casting. In this embodiment mould 401 includes a component section 402 and a feeder section 403. The feeder section 403 defines a generally cylindrical passageway 404, extending from a first open end 405 and entering the component section 402 at a second end 406 via aperture 407.

Feeder section 403 feeds additional liquefied material into negative mould 401 during cooling stage 108 as the molten material contained within negative mould 401 contracts in volume. When materials cool from their molten liquid phase, their volume reduces as the temperature decreases to the point at which they become solid. Therefore feeders are used to provide liquefied material to compensate for the shrinkage cavities that would otherwise form at one or more thermal centres in the interior of the casting. Therefore the volume of the liquefied material in feeder section 403 is determined by the requirement for sufficient liquid material to be provided in order to compensate for the volume reduction of the material as it cools. During solidification the material contracts typically by about 7% by volume and consequently an equal volume of liquefied material enters the component section from the feeder section.

The efficiency of the feeder section 403 is influenced by the static pressure in the feeder, resulting from the amount of liquefied material it holds and its vertical height. The static pressure head assists in forcing the liquefied material into the casting as it cools. Moulds in accordance with this preferred embodiment have one or more feeders that are sufficiently tall such that during production of the composite component, the height of liquefied material within the feeder remains above the tallest part of the component section of the mould. This allows sufficient pressure to be exerted on the molten material within the mould as to ensure that any fine features defined by the mould are reproduced.

Figure 5

As previously discussed with reference to Figure 4, in an embodiment only first feed material 104 is melted whilst second feed material 105 remains in its solid form. Figure 5 shows negative mould 401 after cooling stage 108 whereby the temperature within the mould has decreased to below the first temperature causing said first feed material to solidify and the volume of liquefied material within the feeder section has reduced to level 501. Therefore after cooling step 108, the molten first feed material 104 solidifies consolidating said second feed material particles 105 within the bulk casting providing structural locking. In this way composite components may be produced that exhibit improved tensile and impact strengths, compared to those components with a uniform composition.

Unlike negative mould apparatus of the prior art, in the illustrated embodiment negative mould 401 is not hermetically sealed during heating stage 106 and cooling stage 108. Moulds of the prior art compensate for a reduction in volume of feed materials during temperature changes by plastically deforming. In an embodiment negative mould 401 is substantially rigid and is configured to be incompressible so as not to deform during heating stage 106 and cooling stage 108. In order to account for fluctuations in volume of the material within the negative mould during temperature changes, negative mould 401 is configured to be pervious to the atmosphere during use. Therefore negative mould 401 exchanges volume with the atmosphere via aperture 407 and feeder section 403. However, in an alternative embodiment negative mould 401 is hermetically sealed after deploying stage 103 and prior to heating stage 106, by capping feeder section 403 to prevent interaction with the atmosphere.

In alternative embodiments the cooling stage may be conducted under pressure conditions other than atmospheric pressure, or applied pressure may be varied as a function of time. Altering the pressure under which the material solidifies can influence the crystal structure of the casting. Solidifying during the cooling stage under increased pressure conditions is likely to result in a denser and more structurally uniform casting, enhancing the impact properties of the component.

Figure 6

The negative moulds 02 and 401 described with reference to Figures 1 to 5 have only a first aperture and corresponding feeder section to allow deployment of feed materials into the mould. However in an alternative embodiment a mould is provided which has more than one aperture for deployment of feed materials separately into different regions of the mould.

An example of such a mould is shown in cross section in Figure 6. The mould 601 has a first region 602 and a first aperture 603 associated with said first region 602, and a second aperture 604 associated with a second region 605. Similar to mould 102, mould 601 also includes feeder sections 606 and 607 extending from respective apertures.

First feed material 608 is deployed into first region 602, via first aperture 603 and feeder section 606. Second feed material 609 is deployed separately to said first feed material 608 into second region 605, via second aperture 604 and feeder section 607. This results in a casting with different materials localised to different regions of the component. The feed materials are deployed into their respective regions at roughly the same rate therefore they meet at an interface 610 that is approximately equidistant between first aperture 603 and second aperture 604.

Figure 7

Negative mould 601 previously discussed with reference to Figure 6 is shown in Figure 7 during the application of heat. In this embodiment first feed material 608 and second feed material 609 are both metallic melt powders, therefore are melted when the temperature of mould 601 is increased to their respective melting points.

First feed material 608 is a metal powder with a melting temperature of 700°C and second feed material 609 is a different metal powder with a melting temperature of 1000°C.

Heat is applied to negative mould 601 as indicated by the arrows, so as to raise its temperature to a first temperature, approximately equal to the melting point of the first feed material. Therefore first feed material 608 is melted within first region 602. The temperature is further increased to a second temperature approximately equal to the melting point of second feed material 609, thereby melting second feed material 609.

In an embodiment said first feed material 608 is joined to said second feed material 609 by selective alloying through solid state diffusion of the particles.

At this point both first feed material 608 and second feed material 609 are in their molten liquid states and thus diffusion occurs resultant of the Brownian motion of the particles. At the interface 610 some of the particles of first feed material 608 deployed in first region 602 drift rightwards into second region 605. Similarly particles of second feed material 609 drift leftwards from second region 605 into first region 602, thereby alloying said first feed material 608 to said second feed material 609 across an alloyed region 701 about the interface 610.

The extent to which said first feed material 608 is alloyed to said second feed material 609 is controlled by the diameter d of the alloyed region 701. The diameter d of alloyed region 701 is dictated by the distance to which the particles are allowed to diffuse into the adjacent region. This is dependent on the energy of the particles, itself a function of the temperature, and the time period for which the feed materials are in their molten state.

In the illustrated embodiment the second temperature is maintained during step 107, for a time period of 10 seconds, so as to allow diffusion of particles over an alloyed region of diameter d. When the desired degree of alloying is achieved the temperature of negative mould 601 is decreased to below the melting points of the feed materials thereby preventing excessive diffusion of the molten materials.

Therefore once solidified a component is produced with a non-uniform metallurgy along its length, with a discreet interface between the different regions of material. In this way the component enjoys the functional benefits of both first feed material 608 and second feed material 609, whilst maintaining the structural properties of a single casting. Figure 8

An example of a component produced by a process embodying the present invention is illustrated in cross section in Figure 8. Figure 8 shows a negative mould 801 , similar in construction to negative mould 601 of Figures 6 & 7, in that the moulding defines a component comprising a first region 802 and a second region 803, accessed by apertures 804 and 805 respectively. First region 802 is filled with first feed material 806 which is a titanium powder and second region 803 is filled with second feed material 807 which is a titanium carbide powder.

Additionally negative mould 801 comprises a partition 808 thereby dividing first region 802 and second region 803. Partition 808 is a titanium sheath that is approximately 2mm in thickness and completely separates first region 802 from second region 803.

When producing more complex components using powder pressing techniques a problem is experienced in terms of maintaining the positioning of the feed materials, to prevent gravitational sedimentation or incidental dispersion in the powder phase prior to melting. By including partition 808 first feed material 806 in first region 802 is prevented from migrating into second region 803 and diffusing with second feed material 807 until partition 808 is melted.

In this embodiment the object to be produced is a rack component corresponding to a rack and pinion arrangement, used for transforming the rotational motion of a toothed pinion gear into linear motion of the splined rack. The splined surface of the rack component is repeatedly subjected to a torque exerted by the pinion gear; therefore must be extremely hard so as to be resistant to material degradation. However, additionally the component must be relatively lightweight.

Thus, it is desirable to have a first region of the component composed of a substance that is sufficiently lightweight, such as titanium, but wherein the driving splines have an increased surface hardness for example by using a titanium carbide powder.

In the illustrated embodiment first feed material 806 second feed material 807 and partition 808 each have a melting point corresponding to a first temperature. Therefore upon application of heat to a first temperature, as in step 106 and described with reference to figure 7, first feed material 806, second feed material 807 and partition 808 are melted, thereby allowing interaction of the molten feed materials in the opposing regions.

As in step 07 the temperature is maintained for a period of time to allow a diffusion layer of sufficient diameter as to create a discreet interface between first feed material 806 and second feed material 808 to form.

When the diffusion layer forming the alloyed region is the desired diameter the temperature is decreased to below said first temperature, causing the casting to solidify during a cooling stage.

Although cooling at a natural rate may be suitable for some materials, others may require accelerated cooling. In an embodiment the temperature of the mould is decreased rapidly by forcing an inert gas such as argon or helium to flow over the negative mould 801.

Figure 9

A fifth example of a mould embodying the present invention is shown in Figure 9. Mould 901 for producing a gas turbine blade component is illustrated comprising a first region 902 innermost, contained within partition 903 and a second region 904 outermost.

Similarly to Figure 8, first region 902 is fed via first feeder section 905 through first aperture 906, and second region 904 is fed through second feeder section 907 and second aperture 908.

In an embodiment of the invention partition 903 is invested within the positive wax model of the component, as shown with reference to Figure 2 during construction of mould 901. Therefore when the sacrificial material forming the positive model is removed partition 903 remains inside negative mould 901 supported by feeder section 90S.

In the illustrated embodiment first feed material 909 in first region 902 and second feed material 910 in second region 904 are metallic powders. First feed material 909 is a low density metal powder such as aluminium with superior thermal conductivity characteristics, whilst second feed material 910 is a high density metal such as steel with increased surface hardness. First feed material 909 and second feed material 910 both have a melting point corresponding to a first temperature.

Partition 903 comprises a third material such as nickel which is beneficial to the alloying process, and having a melting point corresponding to a second temperature, higher than the first temperature.

Therefore when the temperature of mould 901 is increased to the first temperature, both first feed material 909 and second feed material 910 are melted, however they are separated by partition 903 which remains in solid form. Further increasing the temperature of the negative mould 901 to the second temperature causes the partition 903 to be melted, thereby allowing diffusion of first feed material 909 with second feed material 910, creating an alloyed region comprising both first feed material aluminium particles, second feed material steel particles and partition material nickel particles.

By altering the composition of the material used to create partition 903 it is possible to influence the melting point and therefore alloying temperature of the various feed materials.

In an embodiment the partition 903 is formed of a ceramic material having a melting point far greater than the melting points of the feed materials. Therefore the alloying process is conducted at a greatly increased temperature, resulting in a more uniform crystalline structure of the alloyed region.

Although the invention has been described by embodiments present using only two powdered feed materials, it will be appreciated that in alternative embodiments any number of dissimilar feed powders may be used.

Equally components may be created with any number of different localised regions of dissimilar materials, accessed by any number of apertures for insertion of feed materials. Indeed in a yet further alternative embodiment of the present invention a multi-core rod component is formed, comprising ten regions separated by nine partitions into which ten dissimilar feed materials are deployed.

Figure 10

Apparatus for performing the processing method embodying the present invention in which moulds such as negative mould 901 , containing powdered feed materials are processed to form a composite component, is illustrated in Figure 10.

The apparatus 1001 comprises a vacuum furnace 1002, creating a vacuum-tight chamber 003 and having a door 1004 to allow loading and unloading of the chamber 1003.

In an embodiment vacuum furnace 1002 includes means for varying the temperature and pressure within. Vacuum furnace 1002 has a heat source for producing radiant heat such as resistance heating element 1005, which is connected to power supply 1006.

The apparatus 1001 also includes a vacuum pump 1007 connected to chamber 1003 for evacuating air from the chamber 1003 such that the pressure in the chamber may be reduced to below atmospheric pressure. Additionally a compressor 1008 is also provided so as to allow the pressure inside the chamber 1003 to be increased above atmospheric pressure.

Electronic controller 1009 is provided comprising temperature sensor 1010 and pressure sensor 1011 and associated wiring. Temperature sensor 1010 is located within chamber 1003 and is configured to provide signals indicative of the actual temperature within chamber 1003. Similarly pressure sensor 1011 is configured to provide an indication of the air pressure within the chamber 1003.

Electronic controller 1009 is configured to receive signals from temperature sensor 1010 and pressure sensor 1011 , and modulate the power supply 1006 for the resistance heating element 1005, vacuum pump 1007 and compressor 1008 accordingly. In an embodiment, controller 1009 is a programmed computer system or microcontroller.

In an embodiment of the invention it is desirable that the cooling stage is accelerated to cause the molten feed materials to decrease in temperature and solidify more rapidly. Therefore compressor 1008 is used to force an inert gas, such as nitrogen into vacuum chamber 1003 whilst vacuum 1007 evacuates the spent gas, thereby creating a cooling convection current over negative mould 901.

Figure 11

An example of process steps 106-108 embodying an aspect of the present invention as illustrated in Figure 8 is depicted by the graph of Figure 11. The graph 1101 shows a plot of temperature (T) as a function of time (t).

Initially at time 1102 the chamber of vacuum furnace 1002 is at ambient temperature 1103. Electrical power is then supplied to the resistance heating coils, at time 1104 until time 1105 to raise the temperature within the chamber to a first temperature 1106, above the melting point of first feed material 806, second feed material 807 and partition 808, thereby establishing molten liquid within mould 801.

The increased temperature 1106 is stably maintained between times 1105 and 1 07, thereby maintaining the feed materials in their molten state and enabling a degree of diffusion at the interface.

When the period of time that has elapsed is sufficiently long to allow a suitable amount of diffusion between first feed material 806 and second feed material 807, creating an alloyed region of desired diameter, power to the resistance coils is interrupted and heating stops.

At time 1107 the power is cut-off and the chamber is allowed to cool naturally, until at time 1108 the temperature has returned to ambient temperature 1103, the casting has solidified and may now be removed from the chamber.

Figure 12

A second example of process steps 106-108 embodying the aspect of the invention as illustrated in Figure 9, is shown by graph 1201 in Figure 12.

Again at time 1 02 the vacuum furnace chamber is at ambient temperature 1103. At time 1104 the heating stage begins and the temperature of the chamber increases until the first temperature 1106 at time 1105. At this stage first feed material 909 and second feed material 910, both having melting temperatures below first temperature 1106, have been melted and are in their molten state.

However as discussed with reference to Figure 9, partition 903 has a higher melting point than either first feed material 909 or second feed material 910, therefore remains in its solid phase. Therefore in this embodiment heating continues for a further period of time, until time 1202 when the temperature has increased to second temperature 1203 and the partition is melted. At this stage both first feed material 909, second feed material 910 and partition 903 are in molten states and begin to diffuse at the interface. In this embodiment it is desirable that the alloyed region created by the diffusion of particles is relatively larger in diameter than the alloyed region created in the process shown in Figure 11. Therefore the increased temperature is maintained for a longer period of time, from time 1202 until time 1203, thereby allowing a greater degree of particle diffusion. At time 1203 the alloyed region is of adequate diameter and therefore power to the heating coil is interrupted and cooling begins.

In this embodiment it is desirable that the cooling stage is accelerated. Therefore at time 1203 compressor 008 and vacuum 1007 are configured to force a convection current over the negative mould 901 , as described with reference to Figure 10 during the cooling step of 108. This results in a rapid decrease in temperature of negative mould 901 and consequently solidification of the molten feed materials occurs quickly. At time 1204 the temperature in the chamber has returned to ambient temperature 1003 and the mould may be removed from the chamber and further processed if necessary.