A method of consolidating a powder

Abstract

 A method of consolidating a powder (10) comprises the steps of filling an electrically conductive container (12) with the powder (10). Any air is evacuated out of the filled container (12), which is then sealed. The sealed container (12) is placed in a die (20) and a force is applied to consolidate the powder (10). Simultaneously an electric pulse and an ultrasonic pulse are applied to the container (12) as the powder (10) is consolidated. The electric and ultrasound pulses are applied during consolidation to disrupt the grain boundaries and assist in the fragmentation of any oxides.
The container (12) is then removed from the die (20) and from the consolidated powder (10).

Description

[0001] The present invention relates to a method of consolidating a powder to produce a component, join components or coat a component. In particular it relates to a method of consolidating a powder to produce new components, join components or coat components suitable for aerospace applications.

[0002] Aerospace components require the use of high strength, high temperature resistant alloys, which are notoriously difficult to process. As it is not possible to weld or use other fabrication techniques on these alloys, components are machined from billets. Machining the components from billets is time consuming, expensive and wasteful.

[0003] Powder metallurgy has been used to produce billets of these high performance alloys from which components having complex geometries are machined. Current powder processing routes for these alloys require expensive and wasteful processes, such as extrusion, to eliminate traces of prior particle grain boundaries and produce low specification components.

[0004] The present invention seeks to provide a powder processing route which overcomes the problems of prior particle grain boundaries and provides a low cost manufacturing route for components from these high specification alloys.

[0005] According to one aspect of the present invention a method of consolidating a powder comprises the steps of filling an electrically conductive container with powder, evacuating air out of the filled container and sealing the filled container after evacuation, placing the sealed container in a die and applying a force sufficient to consolidate the powder whilst simultaneously applying a electric pulse and an ultrasound pulse thereto, removing the container from the die and removing the container from the consolidated powder.

[0006] According to a second aspect of the present invention a method of consolidating a powder to join preforms comprising the steps of placing at least two preforms in abutting relationship in an electrically conductive container, coating the abutting surfaces of the preforms with powder, evacuating any air out of the container and sealing the container after evacuation, placing the sealed container in a die and applying a force sufficient to consolidate the powder and join the preforms whilst simultaneously applying an electric pulse and an ultrasound pulse to the container, removing the container from the die and removing the container from the joined preforms.

[0007] According to a third aspect of the present invention a method of consolidating a powder comprises the steps of placing a preform in an electrically conductive container, coating the surfaces of the preform with powder, evacuating any air out of the container and sealing the container after evacuation, placing the sealed container in a die and applying a force sufficient to consolidate a coating of the powder onto the preform whilst simultaneously applying an electric pulse and an ultrasound pulse to the container, removing the container from the die and removing the container from the coated preform.

[0008] The powder coating may have a different composition to the preforms and the composition of each of the preforms may be different.

[0009] The electric and ultrasound pulses are applied during consolidation to disrupt the grain boundaries and assist in the fragmentation of any oxides.

[0010] Preferably a high amplitude, high frequency electrical pulse is applied to the container. The electrical pulse heats the surface of the powder, increasing the plasticity at the surface. Electrical energy in the range of 1-20KHz is applied with a frequency of the order of 20KHz.

[0011] The force used to compress the powder may be a mechanically induced shock wave in the range of 5-20 GPa. The shock wave assists in the disruption of the grain boundaries and helps destroy any oxides.

[0012] The ultrasound pulse, is of the order of 20KHz, and is applied simultaneously with the shock wave to further disrupt the grain boundaries and to assist in the fragmentation of oxides.

[0013] Preferably the container is vibrated as it is filled with the powder. The powder may be a nickel alloy and the container may be made from nickel, mild steel or stainless steel.

[0014] The consolidated powder may then be sintered or hot isostatically pressed.

[0015] The present invention will now be described with reference to the accompanying drawings in which;

[0016] Figure 1 shows apparatus suitable for consolidating a powder in accordance with present invention.

[0017] Figure 2 shows apparatus suitable for joining preforms of consolidated powder.

[0018] Figure 3 shows apparatus suitable for consolidating a powder coating onto a preform.

[0019] Referring to figure 1, a nickel alloy powder 10 is encapsulated in a container 12. The container 12 is made from a ductile material, which is electrically conductive and which will not contaminate the powder by diffusion. In the preferred embodiment of the present invention the container 12 is made from pure nickel, mild steel or stainless steel sheet. Electrically insulting connectors 14 are provided on either end of the container 12.

[0020] The container 12 is vibrated to pack the powder 10 down. A vacuum pump (not shown) is attached to a tube 16 on the container 12 and is used to evacuate the gas atmosphere surrounding the powder 10. Once the gas has been evacuated from the container 12 the tube 16 is crimped and welded shut.

[0021] The sealed container 12 is then placed into a die 20 having two electrically insulated connectors 22. The electrical connecters 22 are attached to a source of electrical energy, such as a capacitor bank (not shown).

[0022] The die 20 is closed and motor-driven hydraulic actuators (not shown) apply a force in the direction of arrows A to the die 20. A hydrostatic medium 18, such as a fluid or elastomer, produces a shock wave that is transmitted to the powder filled container 10. The shock wave applies a force, in the range of 5-20 GPa. The force necessary will depend upon the type of powder and the size of the component. For a nickel alloy powder a shock wave of the order of 10 GPa is applied for a few tenths of a microsecond to effect full consolidation.

[0023] As the force is applied to the die 20 the capacitor bank simultaneously delivers a high amplitude, high frequency pulse of electrical energy to the connectors 22 on the die 20. For a nickel alloy powder a 1-20KJ pulse of electrical energy is delivered at a frequency of approximately 20KHz and an amplitude as high as the frequency switch system will allow. The electrical energy is transmitted to the connectors 14 on the container 12. The electric energy is transmitted through the powder 10 for of the order of 10 milliseconds. The electrical pulse has a waveform and amplitude that are tailored to disrupt grain boundaries and oxides. The electrical pulse is applied for of the order of 10 milliseconds such that it heats the surface of the powder 10 to increase the plasticity but does not allow substantial heat conduction into the powder 10, which could cause micro structural alteration.

[0024] An ultrasound pulse of the order of 20kHz is also superimposed onto the shock wave to further disrupt the grain boundaries and to assist in the fragmentation of any oxides.

[0025] Once the powder 10 has been consolidated the container 12 is removed from the die 20. The preform is then removed from the container 12, either by machining or by electrolysis. Boron nitride could be used as a release agent to assist in the removal of the preform from the container.

[0026] It is possible to fabricate complex components through the repeated use of the process. In figure 2 preforms 10a, 10b and 10c, are placed in the container 12. Mechanical compaction is aided by coating the abutting surfaces 11 of the preforms 10a, 10b, and 10c with powder 10. The powder coated onto abutting faces 11 of the preforms 10a, 10b and 10c may be of a different composition. This is particularly beneficial when the preforms 10a, 10b and 10c are formed from powders of dissimilar materials, which cannot be joined by conventional techniques such as welding.

[0027] The container 12 is evacuated, sealed and placed into the die 20. A shock wave is generated in the hydrostatic medium 18 whilst an electrical pulse and ultrasound pulse is applied simultaneously to the container 12 to join the preforms 10a, 10b and 10c together.

[0028] The ultrasound pulse has a frequency of the order of 20kHz and is superimposed onto the shock wave to further disrupt the grain boundaries and to assist in the fragmentation of any oxides.

[0029] The container 12 is then removed from the die 20 and from the joined preforms.

[0030] The method can also be used to apply a powder coating to a preform. Referring to figure 3 a preform 10d is placed in the container 12. Powder 10 is placed around the surfaces of the perform 10d. The powder coating 10 may be of a different composition to the perform 10d.

[0031] The container 12 is evacuated, sealed and placed into the die 20. A shock wave is generated in the hydrostatic medium 18 whilst an electrical pulse and ultrasound pulse is applied simultaneously to the container 12.

[0032] Once the powder 10 has been consolidated the container 12 is then removed from the die 20 and from the coated preform 10d.

[0033] The process described simultaneously compacts and disrupts grain boundaries and oxides in the powder 10. As the heat is not conducted into the powder 10 this comparatively cold processing route allows fine-grained preforms of consolidated powder to be produced. A fine grain structure is required to produce tough, fatigue resistant components. The process thus enables the use of low cost manufacturing route to produce high specification preforms of material from powder, join dissimilar performs together or apply powder coatings to the preforms.

[0034] On completion of the process the consolidated preforms may be further processed depending on the material properties required for a particular application. For example the preforms of consolidated powder may be subsequently sintered or hot isotropically pressed.

Claims

1. A method of consolidating a powder (10)^- comprising the steps of filling an electrically conductive container (12) with powder (10), evacuating any air out of the filled container (12) and sealing the filled container (12) after evacuation, placing the sealed container (12) in a die (20) and applying a force sufficient to consolidate the powder (10), removing the container (10) from the die and removing the container (10) from the consolidated powder (12) characterised in that an electric pulse and an ultrasonic pulse are simultaneously applied to the container (12) during consolidation.

2. A method of consolidating a powder (10) to join preforms (10a, 10b, 10c) comprising the steps of placing at least two performs (10a, 10b) in abutting relationship in an electrically conductive container (12), coating the abutting surfaces (11) of the preforms (10a, 10b) with powder (10), evacuating any air out of the container (12) and sealing the container (12) after evacuation, placing the sealed container (12) in a die (20) and applying a force sufficient to consolidate the powder (10) and join the preforms (10a, 10b), removing the container from the die (20) and removing the container (12) from the joined performs (10a, 10b) characterised in that an electric pulse and an ultrasonic pulse are simultaneously applied to the container (12) during consolidation.

3. A method of consolidating a powder (10) to coat a preform (10d) comprising the steps of placing at least one preform (10d) in an electrically conductive container (12), coating the surfaces of the perform (10d) with powder (10), evacuating any air out of the container (12) and sealing the container (12) after evacuation, placing the sealed container (12) in a die (20) and applying a force sufficient to consolidate the powder (10) into a coating on the preform (10d) and subsequently removing the container (12) from the die (20) and the container (12) from the coated preform (10d) characterised in that an electric and an ultrasonic pulse are simultaneously applied to the container (12) during consolidation.

4. A method as claimed in claim 2 characterised in that that the composition of each of the preforms (10a, 10b, 10c) is different.

5. A method as claimed in claims 2-4 characterised in that the powder (10) coating has a different composition to the performs (10a, 10b, 10c, 10d).

6. A method as claimed in any of claims 1-5 characterised in that high amplitude, high frequency electrical energy is applied to the container (12).

7. A method as claimed in claim 6 characterised in that electrical energy in the range of 1-20 KJ is applied to the container (12).

8. A method as claimed in claim 6 characterised in that the frequency of the electrical energy is of the order of 20KHz.

9. A method claimed in any of claims 1-8 characterised in that the force used to compress the powder (10) is a mechanically induced shock wave.

10. A method as claimed in claim 9 characterised in that the shock wave applies a force in the range of 5-20 GPa.

11. A method as claimed in any of claims 1-10 characterised in that in which the ultrasound pulse has a frequency of 20KHz.

12. A method as claimed in any preceding claim characterised in that the container (12) is vibrated as it is filled with powder (10).

13. A method as claimed in any preceding claim characterised in that the powder is a nickel alloy.

14. A method as claimed in any preceding claim characterised in that the container (12) is made from nickel.

15. A method as claimed in any preceding claim characterised in that consolidated powder (10) is sintered after removal of the container (12).

16. A method as claimed in any preceding claim characterised in that the consolidated powder (10) is hot isostatically pressed after removal of the container (12).

Drawing