US20150030494A1

Movatterモバイル変換

Info

Publication number: US20150030494A1
Application number: US14/380,112
Authority: US
Inventors: Charles Malcolm Ward-Close
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-02-24
Filing date: 2013-02-20
Publication date: 2015-01-29
Also published as: CN104136148B; JP2015516299A; IN2014DN07557A; CA2864297A1; GB2519190A; GB201203359D0; CA2864295A1; GB2499669B; US20150017475A1; GB201412653D0; GB2519190B; GB2523857A; AU2013223879B2; GB201412652D0; CN104136148A; WO2013124649A1; NZ628379A; EP2817116A1; AU2013223879A1; GB2499669A

Abstract

Methods and apparatus for producing an object, the method comprising: performing an Additive Manufacturing process to produce an intermediate object from provided metal or alloy, whereby the intermediate object comprises regions having a contaminant concentration level above a threshold level; based upon one or more parameters, determining a temperature and a duration; and performing, on the intermediate object, a contaminant dispersion process by, for a duration that is greater than or equal to the determined duration, heating the intermediate object to a temperature that is greater than or equal to the determined temperature and less than the melting point of the metal or alloy, the contaminant dispersion process being performed so as to disperse, within the intermediate object, a contaminant from regions of high contaminant concentration to regions of low contaminant concentration until the intermediate object comprises no regions having a contaminant concentration level above the threshold level.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is the National Stage of International Application No. PCT/GB2013/050410, filed 20 Feb. 2013, which claims the benefit of and priority to GB 1203359.3, filed 24 Feb. 2012, and GB1301173.9, filed 23 Jan. 2013, the contents of all of which are incorporated by reference as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to the production of objects.

BACKGROUND

Additive Manufacturing (AM) (also known as Additive Layer Manufacturing (ALM), 3D printing, etc.) refers to processes that may be used to produce functional, complex objects, layer by layer, without moulds or dies. Typically, AM processes include providing material (e.g. metal, ceramic or plastic) in the form of a powder or a wire, and, using a powerful heat source (such as a laser beam, electron beam or an electric, or plasma welding arc), an amount of that material is melted and deposited upon a base work piece. Subsequent layers are then built up upon each preceding layer so as to form the object.

Example AM processes include, but are not limited to, Laser Blown Powder, Laser Powder Bed, and Wire and Arc technologies.

However, objects produced using AM processes, particularly those made using powder material, may comprise one or more contaminated regions, i.e. regions in which the material that forms the object has been contaminated by a contaminant (e.g. oxygen). Also, objects produced using AM processes, particularly those made using powder material, may comprise micro-pores and other imperfections at or proximate to the surface of the object. The presence of such contaminated regions and other imperfections tend to adversely affect the fatigue performance of an object, especially in high-cycle fatigue situations. For example, the imperfections may act as crack initiators.

SUMMARY OF THE INVENTION

The contaminant dispersion process may be performed such that the contaminant is substantially uniformly distributed within the bulk of the object.

The contaminant dispersion process may comprise performing, on the intermediate object, a hot isostatic pressing process at a temperature that is greater than or equal to the threshold temperature and for a duration that is greater than or equal to the threshold duration.

The determined temperature may be between 1100° C. and the melting point of the provided metal or alloy.

The determined temperature may be between 1300° C. and the melting point of the provided metal or alloy.

The determined duration may be greater than or equal to one hour.

The determined duration may be greater than or equal to two hours.

The Additive Manufacturing (AM) process may be a process selected from the group of AM processes consisting of: a powder bed fusion AM process, a blown powder AM process, a sheet lamination AM process, a laser blown powder AM process, a laser powder bed AM process, and an AM process that implements wire and arc technology.

The metal or alloy from which the object is made may be selected from a group of metals or alloys consisting of: titanium alloys, steel, nickel superalloys and aluminium alloys.

The metal or alloy may be Ti-6Al-4V.

The metal or alloy may be provided in powder form.

The Additive Manufacturing process may be a powder bed Additive Manufacturing process.

The contaminant may comprise oxygen.

The intermediate object may comprise a plurality of open cavities. The method may further comprise performing a sealing process on the intermediate object to seal the openings of the open cavities, thereby forming a plurality of closed cavities, and reducing the sizes of the closed cavities by performing a consolidation process on the intermediate object having the closed cavities.

The produced object may comprise a plurality of open cavities. The method may further comprise performing a sealing process on the object to seal the openings of the open cavities, thereby forming a plurality of closed cavities, and reducing the sizes of the closed cavities by performing a consolidation process on the object having the closed cavities.

The step of reducing the sizes of the closed cavities may be performed at least until the closed cavities are no longer present.

The step of performing a consolidation process may comprise performing a hot isostatic pressing process.

The step of performing a sealing process may comprise plastically deforming the surface of the object.

Plastically deforming the surface of the object may comprise shot peening the surface of the object.

The step of performing a sealing process may further comprise sintering the object after the surface of the object has been plastically deformed.

The method may further comprise determining a contaminant concentration level of a region of the intermediate object.

The determined temperature and duration may be based upon the determined contaminant concentration level.

The determining of a contaminant concentration level of a region of the intermediate object may comprise determining the maximum contaminant concentration level within the intermediate object.

In a further aspect, the present invention provides an object that has been produced using a method according to any of the above aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration (not to scale) showing example Additive Manufacturing apparatus;

FIG. 2 is a process flow chart of an embodiment of a process of producing an object;

FIG. 3 is a schematic illustration (not to scale) showing a stage of an Additive Manufacturing process performed by the Additive Manufacturing apparatus; and

FIG. 4 is a schematic illustration (not to scale) of a cross section of the object at a certain stage of the process ofFIG. 2.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration (not to scale) showing exampleAdditive Manufacturing apparatus2 that is to be used, in an embodiment, to perform an Additive Manufacturing process so as to create anobject4.

The terminology “Additive Manufacturing” is used herein to refer to all additive processes that may be used to produce functional, complex objects, layer by layer, without moulds or dies e.g. by providing material (e.g. metal or plastic) in the form of a powder or a wire, and, using a powerful heat source such as a laser beam, electron beam or an electric, or plasma welding arc, melting an amount of that material and depositing the melted material (e.g. on a base plate/work piece6), and subsequently building layers of material upon each preceding layer.

Additive Manufacture (AM) may also be known inter alia as 3D printing, Direct Digital Manufacturing (DDM), Digital Manufacturing (DM), Additive Layer Manufacturing (ALM), Rapid Manufacturing (RM), Laser Engineering Net Shaping (LENS), Direct Metal Deposition, Direct Manufacturing, Electron Beam Melting, Laser Melting, Freeform Fabrication, Laser Cladding, Direct Metal Laser Sintering.

In this embodiment, theAM apparatus2 is apparatus for performing a powder bed AM processes. Further information on powder bed AM apparatus and processes may be found, for example in Gibson, I. Rosen, D. W. and Stucker, B. (2010) “Additive Manufacturing Technologies: Rapid Prototyping Direct Digital Manufacturing” New York, Heidelberg, Dordrecht, London: Springer, which is included herein by reference. However, in other embodiments, a different type of AM apparatus is used produce theobject4, e.g. by performing a different type of AM process. Examples of other appropriate AM processes that may be used to produce theobject4 include, but are not limited, blown powder AM processes, sheet lamination AM processes, vat photopolymerisation AM processes, laser blown powder AM processes, laser powder bed AM processes, and AM processes that implement wire and arc technology.

In this embodiment, theAM apparatus2 comprises a heat source in the form of alaser source8 configured to produce a high poweredlaser beam10. Thelaser source8 may be any appropriate type of laser source, e.g. a laser source that is configured to have a continuous wave power output of 500 W.

TheAM apparatus2 further comprises a source of metallic material (hereinafter referred to as “metallic powder12) in the form of a powder repository14 (or powder bed). In this embodiment, the metallic material is titanium alloy powder (e.g. Ti-6Al-4V). Titanium alloy powder typically has spherical grains with a diameter in the range 0-45 μm.

In other embodiments, a different type of material (e.g. a different type of metallic power, a plastic powder, or a ceramic powder) may be used.

In operation, a first piston16 (that is located at the bottom of the first repository) is raised (in the direction indicated by an arrow inFIG. 1 and the reference numeral18) so as to raise an amount of thepowder12 above a top level of therepository14.

In this embodiment, aroller20 is rolled (in the direction indicated by an arrow inFIG. 1 and the reference numeral22) over the upper surface of therepository14 and across an upper surface of afurther repository24. This is performed so that themetallic powder12 that was raised above the level of therepository14 by the raising of thefirst piston16 is spread over an upper surface of thefurther repository24. Thus, a top surface of the contents of thefurther repository24 is covered by a layer ofmetallic power12. In other embodiments, a different means of spreading themetallic powder12 across a top surface of the contents of thefurther repository24, such as a wiper, may be used instead of or in addition to theroller20.

After a layer ofmetallic power12 has been spread across a top surface of the contents of thefurther repository24, thelaser source8 is controlled by acomputer26 to deliver thelaser beam10 via anoptical fibre28 to focussingoptics30 which focus thelaser beam10 to thefocal point32 on the layer ofmetallic power12 has been spread across a top surface of the contents of thefurther repository24.

Thelaser beam10 produced by thelaser source8 is focused upon the layer ofmetallic powder12 has been spread across the top surface of the contents of thefurther repository24 so as to melt a portion of the layer ofmetallic powder12.

In this embodiment, a portion of themetallic powder12 on the top surface of thefurther repository24 is fully melted, and subsequently allowed to cool so as to form a layer of solid material.

Asecond piston34, located at the bottom of thefurther repository24 is then lowered (i.e. moved in a direction indicated inFIG. 1 by a solid arrow and the reference numeral36) to allow for a further layer ofmetallic powder12 to be spread by the roller20 (and subsequently melted and allowed to solidify) across the top surface of the contents of thefurther repository24.

Many layers of material are laid on top of one another (in accordance with adigital design model38 for theobject4 stored by the computer26) to produce theobject4.

In this embodiment, thelaser source8 and focussingoptics30 are moveable under the control of thecomputer26 in an X-Y plane that is parallel to the top surface of the contents of the further repository24 (i.e. a top surface of the object4). Thus, the laserfocal point14 may be directed to any point in a working envelope in the X-Y plane so that layers of material of a desired shape may be deposited.

Thus,AM apparatus2 for performing a process of producing, in accordance with an embodiment, theobject4 is provided.

FIG. 2 is a process flow chart of an embodiment of a process of producing (i.e. manufacturing, building, constructing, etc.) theobject4 using the above describedexample AM apparatus2.

Theobject4 that is to be produced by the method ofFIG. 2 may be any appropriate type of object having any appropriate size and shape. In this embodiment, the producedobject4 is made of titanium or a titanium alloy. However, in other embodiments, the producedobject4 is made of a different material to theobject2 in this embodiment.

At step s2, a three dimensionaldigital model38 of the object4 (that is to be produced) is provided. Thedigital model38 of theobject4 is a digital design model for theobject4.

In this embodiment, thedigital model38 is stored by thecomputer26. In this embodiment, thedigital model38 can be viewed, manipulated and analysed using thecomputer26 e.g. by implementing a suitable software package or tool.

At step s4, a base plate is provided. The base plate provides a parent structure upon which layers of material are to be added (by theAM apparatus2 performing the AM process) so as to form theobject4. In this embodiment, the base plate may, for example, be secured to thesecond piston34 e.g. using any appropriate means.

At step s6, the AM apparatus is calibrated. This calibration process may, for example, include accurately measuring thebase plate6 and/or providing or creating a three dimensional digital model of thebase plate6. These data and thedigital model38 of theobject4 may be used to generate a “tool path” that, during the AM process, will be followed by theAM apparatus2 so as to produce theobject4.

At step s8, using theAM apparatus2, an AM process is performed to add layers of material to thebase plate6, and thereby form theobject4. In this embodiment, theAM apparatus2 is for performing a powder bed AM process and is described in more detail above with reference toFIG. 1. In this embodiment, the AM process is the powder bed AM process described in more detail above with reference toFIG. 1. Further information on powder bed AM apparatus and the powder bed AM process can be found, for example in the above mentioned “Additive Manufacturing Technologies: Rapid Prototyping Direct Digital Manufacturing”, which is incorporated herein by reference. However, in other embodiments, a different type of AM apparatus and/or process is used produce theobject4.

In this embodiment, the AM process is performed in a substantially inert atmosphere (e.g. a chamber that is back-filled with an inert gas e.g. argon).

In this embodiment, the AM process comprises using alaser beam10 to meltmetallic powder12 at the laserfocal point14. Typically, as this is performed, small droplets of molten material, or powder grains that have been heated by thelaser beam10, are ejected or sprayed (e.g. by the forces created by the heating process) away from thefocal point14 of thelaser beam10.

FIG. 3 is a schematic illustration (not to scale) showing small droplets of molten material (hereinafter referred to as the “droplets” and indicated inFIG. 3 by the reference numeral40) being ejected, expelled or sprayed away from thefocal point14 of thelaser beam10 during the AM process. In some embodiments, instead of or in addition toliquid droplets40 of molten material being ejected, expelled or sprayed away from thefocal point14 of thelaser beam10 during the AM process, heated solid particles of metallic material may be ejected and may also become contaminated by gasses or vapours present in the chamber atmosphere.

In this embodiment, the droplets40 (and solid heated particles) have been heated by thelaser beam10. Due to their elevated temperature and high surface area relative to their volume, the droplets40 (and solid heated particles) tend to be highly reactive. Thus, the droplets40 (and solid heated particles) tend to react with any contaminants that are present in thechamber atmosphere42 in which the AM process is being performed. For example, thedroplets40 may absorb oxygen gas that has contaminated thechamber atmosphere42 and is present in the chamber in which the AM process is being performed. Also for example, thedroplets40 may react with any water vapour that has contaminated thechamber atmosphere34 and is present in the chamber in which the AM process is being performed.

In this embodiment, a proportion of the droplets40 (and solid heated particles), that have reacted with the contaminant within thechamber atmosphere42 and that have been sprayed, or expelled away from the laserfocal point14, land on the surface of theobject4 being formed. Such a droplet40 (or solid heated particle) of contaminated material may be “welded” into the structure of theobject4 when thelaser beam10 is focused at the location on the surface at which that contaminated material landed.

Also in this embodiment, a proportion of thedroplets40, that have reacted with the contaminant within thechamber atmosphere42 and that have been sprayed, or expelled away from the laserfocal point14, land in a bed ofun-melted titanium powder12 contained within thefurther repository24 and surrounding theobject4 being formed. The unusedmetallic powder12 contained within thefurther repository24 is recycled (i.e., reused in the AM process that is performed to produce theobject4, or in future AM processes). Thus, recycled powder that has absorbed a contaminant may be bonded, or welded, into the structure of theobject4.

Thus, theobject4 produced using the AM process of step s8 may comprise one or more contaminated regions. In other words, theobject4 may comprise regions in which the material of theobject4 is contaminated (by a contaminant such as oxygen).

At step s10, after theobject4 has been produced by the AM process, theobject4 is allowed to cool and, in this embodiment, theobject4 is removed from thefurther repository24. Excess (i.e. unused or unmelted)metallic power12 may be removed from the object, e.g. using an air jet, or by washing the object.

Thus, theobject4 is formed. The remaining steps of the process ofFIG. 2 describe the processing of theobject4 formed at step s10 that is performed, in this embodiment to produce thefinished object4.

FIG. 4 is a schematic illustration (not to scale) of a cross section of a portion of theobject4 produced by performing steps s2 to s10 as described above.

Thesurface44 of theobject4 is relatively uneven, i.e. rough.

In this embodiment, proximate to itssurface44, theobject4 comprises a plurality of open cavities46 (i.e. open pores or voids in the material body). Theseopen cavities46 are cavities or hollows that are open to the atmosphere, i.e. cavities or hollows that are connected to thesurface44 of theobject4 such that gas can flow from outside theobject4 into the thoseopen cavities46.

Also, theobject4 further comprises a plurality of closed cavities48 (i.e. closed pores or voids in the material body). Theseclosed cavities48 are hollow spaces or pits in the body of theobject4. Furthermore, theclosed cavities48 are not open to the atmosphere, i.e. they are not connected to thesurface44. In other words, gas cannot flow from outside theobject8 into theclosed cavities48 and vice versa.

Also, theobject4 further comprises a plurality of contaminated regions50 (i.e. regions in which material that has previously absorbed or reacted with a contaminant, such as oxygen, has been incorporated, i.e. bonded or welded). In some embodiments, a contaminatedregions50 may be the result of the titanium powder raw material being contaminated e.g. by an undesired metal such as tungsten, copper or iron or a ceramic material such as an oxide, nitride or carbide. The contaminatedregions50 within the object may have a different chemical structure to the material that forms the rest of the object matrix (i.e. to the uncontaminated titanium object4). Also, the contaminatedregions50 within theobject4 may have different material properties (e.g. they may be harder, or softer, and may cause degradation of fatigue performance) than the material that forms the rest of the object matrix (i.e. to the uncontaminated titanium object4).

The presence of micro-pores (i.e. the open andclosed cavities46,48) and the other imperfections (i.e. the contaminated regions50) in theobject4 tend to adversely affect the fatigue performance of theobject4, especially in high-cycle fatigue situations. For example, the

cavities

46,48 and contaminatedregions50 may act as crack initiators. Also, the

cavities

46,48 and the contaminatedregions50 tend to adversely affect the load-bearing characteristics of theobject4.

In conventional methods, after theobject4 has been formed at step s8, the object may be further processed so as to smooth therough surface44. For example, a machining or polishing process may be performed. However, such processes tend to be inappropriate when attempting to fully remove theopen cavities46. Furthermore, such processes tend not to shrink, or remove, theclosed cavities48 or the contaminatedregions50 from theobject4. Machining thesurface44 of theobject4 to a sufficient depth may be performed to remove surface roughness and cavities connected to thesurface44. Machining may expose internal closed cavities that were originally isolated and machining tends to be relatively expensive and, depending on the complexity of the shape of theobject4, would at least partly negate the cost advantage of using a net-shape-process to form theobject4. Polishing processes also remove material from an object and so, if continued to a sufficient depth, may be performed to remove surface roughness and surface connected cavities. Polishing processes also tend to be relatively expensive to perform. Also, processes such as Hot Isostatic Pressing (HIPing), that may be employed to remove internal pores, tend not to have any effect on surface connected cavities.

Deficiencies of conventional methods of producing objects/parts may be overcome by performing steps s12 to s16 on theobject4, as opposed to just performing a machining/polishing process. Thus, the object formed at step s10 may be thought of as an “intermediate object” that is to be further processed (in accordance with steps s12 to s16) to produce a “final object”.

At step s12, theobject4 produced at step s10 is peened.

A conventional shot peening process may be used. For example, a process in which thesurface44 of theobject4 is impacting with shot (e.g. substantially round particles made of metal, glass or ceramic) with sufficient force such that theobject4 is plastically deformed at itssurface44 may be implemented. Also for example, laser, or ultra-sonic, peening may be performed.

In embodiments in which thesurface44 of theobject4 is impacted with shot, any appropriate shot medium may be used, e.g. S330 (cast steel with an average diameter of 0.8 mm). Also, any appropriate shot peening pressure may be used, e.g. 0.5 bar, 0.75 bar, 1.25 bar, 2 bar and 4 bar. Also, any appropriate Almen intensities may be used, e.g. 0.15 mmA, 0.20 mmA, 0.30 mmA, 0.38 mmA and 0.52 mmA.

After peening, thesurface44 of the peened object is relatively smooth (compared to thesurface44 prior to peening).

Furthermore, the process of shot peening tends to plastically deform theobject4 at itssurface44 such that the openings of theopen cavities46 are either closed such that gas cannot flow from outside theobject4 into anopen cavity46 and vice versa (i.e. such that, in effect, anopen cavity46 becomes a closed cavity48), or are closed such that the opening of anopen cavity46 to thesurface44 is very small but that gas may still flow from outside theobject4 into anopen cavity46 and vice versa.

In this embodiment, the plastic deformation of thesurface44 of theobject4 is performed by peening. However, in other embodiments a different plastic deformation process is used, for example, a process of burnishing e.g. using a roller. Such finishing methods (e.g. tumbling, burnishing, shot peening etc.) tend not to remove material from an object.

At step s14, the peenedobject4 is sintered.

In this embodiment, a temperature at which, and duration for which, the object is sintered is selected or determined.

The value for the sintering temperature is determined based upon any appropriate parameters, such that, when the object is heated to or above that temperature, contaminant is diffused within the object4 (from region having high contaminant concentration to regions having low contaminant concentration) at or above a desired rate.

The value for the sintering duration is determined based upon any appropriate parameters, such that, when the object is heated to or above the determined sintering temperature for that duration, the maximum contaminant concentration level within theobject4 is below a threshold value. In some embodiments, the sintering duration is determined such that, when the object is heated to or above the determined sintering temperature for that duration, the contaminant concentration level within theobject4 is substantially uniform.

Examples of appropriate parameters that may be used to determine the sintering temperature or duration include, but are not limited to, the type of metal or alloy from which the object has been produced, the shape and/or size of the object, a contaminant concentration level of a region of the object (e.g. a maximum contaminant concentration level within the object4), and a threshold contaminant concentration level below which the maximum contaminant concentration level within theobject4 is to be reduced.

In this embodiment, theobject4 is sintered at relatively high temperate. For example, the sintering of the peened object may comprise sintering at a temperature in the range 900° C. to the melting point of the object. In this embodiment, theobject4 is made of Ti-6Al-4V, the melting point of which is approximately 1600° C. Preferably, theobject4 is sintered at or above a temperature of 1100° C. More preferably, the object is sintered at or above a temperature of 1300° C.

In this embodiment, the object is sintered for a relatively long period of time, e.g. 1 hour, or 2 hours, or longer. The length of time sintering is to be performed for may depend upon the type of material from which theobject4 is made, or any other appropriate parameter.

In this embodiment, the sintering process is performed for a time period, and at a temperature, that provide the following:

- the openings of the open cavities46 (that were either closed or almost closed by the peening process of step s10) are diffusion bonded such that, in effect, theopen cavities46 becomeclosed cavities48. In other words, the openings of theopen cavities46 are fully sealed by sintering theobject4;
- the contaminant(s) within the contaminatedregions50 of theobject4 are diffused within theobject4, e.g. throughout the bulk of the object. Preferably, this is performed such that the contaminant is dispersed substantially uniformly throughout the bulk of theobject4, i.e. such that no one region of theobject4 has a substantially higher concentration of contaminant than a different region of theobject4.

In this embodiment, the peenedobject4 is sintered at a temperature that is below the melting point of the material from which theobject4 is made.

One advantage of plastically deforming the surface prior to sintering is that recrystallisation and diffusion bonding during high temperature sintering tends to be faster and more effective at smoothing the surface and closing open cavities when compared to an undeformed surface. This may, for example, be due to stored dislocation energy and residual stress within theobject4.

At step s16, a hot isostatic pressing (HIP) process is performed on thesintered object4.

A conventional HIP process is used to reduce the porosity, and increase the density, of thesintered object4. In this embodiment, thesintered object4 is subjected to elevated temperature and elevated isostatic gas pressure by subjecting thesintered object4 to heated and pressurised argon. A HIP cycle having a duration of approximately 2 hours, a temperature of 920° C., and a pressure of 102 MPa may be used.

The HIP process produces a relatively high pressure at thesurface44 of thesintered object4, whilst the pressures in the closed cavities48 (including theopen cavities46 that have been formed intoclosed cavities48 as described above) are relatively low. This is due to theclosed cavities48 not being open to thesurface44, i.e. being gas-tight. As a result of plastic deformation, creep, and/or diffusion bonding caused by the elevated temperature and pressure, theclosed cavities48 in thesintered object4 shrink or vanish completely.

The HIP process performed on the sintered object may cause diffusion of the contaminants within theobjects4. However, at a typical HIP temperature of 920° C., in titanium, the diffusion rates of most contaminants e.g. oxygen, nitrogen, carbon, etc. tend to be relatively low and sufficient to disperse contamination over only small distances, e.g. a few microns. In contrast, at a typical sintering temperature of 1300° C., the diffusion rate of contaminants tends to be several orders of magnitude faster than it is at 920° C., and therefore diffusion distances are correspondingly much greater. The sintering process described above may be thought of as a “contaminant homogenisation process”, i.e. a process of homogenising a concentration of a contaminant within an object produced using an AM process.

The hot isostatic pressing of thesintered object4 produces thefinished object4. Thus, a process of producing theobject4 is provided.

In the above embodiments, the process of producing the object comprises peening, sintering and subsequently HIPing an object. This process of peening, sintering and subsequently HIPing an object may be performed in accordance with any of the methods described in patent application GB1203359.3, “Processing of Metal or Alloy Objects”, filed at the United Kingdom Intellectual Property Office (UKIPO) on 24 Feb. 2012, and incorporated herein, in its entirety, by reference.

An advantage provided by the above described methods is that pores, pits, or other (e.g. minute) openings, orifices, or interstices in the surface of the object tend to be removed. In other words, defects and/or discontinuities at or proximate to the surface of the object may, in effect, be repaired. These open cavities may act as crack initiators. Thus, removal of these open cavities from the object tends to result in improved fatigue performance, especially in high-cycle fatigue situations. The improved surface finish and microstructure of the object tend to improve its fatigue performance.

The above described methods also tend to remove (or shrink) the closed cavities (or other voids or hollows that are closed to the surface) in the body of the object. This also tends to improve the microstructure of the object, which tends to lead to improved fatigue performance.

A further advantage provided by the above described methods is that regions with relatively high concentrations of contaminants within an object produced using an AM process tends to be removed. Regions with relatively high levels or concentrations of a contaminant within an object (i.e. the contaminated regions50) tend to have different material properties than the material that forms the rest of the object matrix, and may act as crack initiators or adversely affect the properties of the object. Thus, removal of these relatively contaminated regions (i.e. by more evenly distributing the contaminant throughout the object4) tends to result in improved fatigue performance and material properties of theobject4.

Conventionally, objects produced using AM processes are not typically treated by sintering those objects at high temperatures. This is partly for cost reasons and partly because high temperature sintering of such an object tends to increase the grain size within the object, thereby reducing the strength of the object. However, the present inventors have realised that, surprisingly, the benefits gained by sintering the object so as to more evenly (e.g. uniformly) distribute contaminants within the object outweigh the disadvantages of performing the sintering process (i.e. the increased grain size).

Objects produced using an above described process tend to be able to withstand a greater maximum stress, and/or withstand a greater number of fatigue load cycles to failure, when compared to objects produced using a conventional AM process.

A further advantage provided by the above described methods is that the surface finish of the object tends to be improved. The object tends to be smoother and shinier than those that are produced using conventional techniques. This increased reflectivity is important in certain applications. For example, if the object is for decorative purposes, the improved aesthetic appearance of the object tends to be important. Also for example, the object tends to be less likely to retain dirt or surface contamination, and be easier to clean and less abrasive.

A further advantage provided by the above described processes is that an object is produced by an AM process. This tends to provide that the object is produced with very little wastage. Furthermore, it tends to be relatively easy to make relatively complex shapes that may be prohibitively expensive to machine.

The above described processes are advantageously applicable to objects of any size. The treatment process (e.g. a process of shot peening, sintering, and hot isostatic pressing) is performed after the formation of the object (i.e. after the performance of the AM process).

A further advantage provided by the above described processes is that the some of them may be performed on a large number of objects simultaneously. Thus, a cost of performing any or all of these operations (per component) may be significantly reduced.

A further advantage provided by the above described method is that a metallic powder that is known to contain contaminants may be used, by performing an AM process, to create an object that has substantially the same or better material/fatigue properties as a different object that has been produced, using the same AM process, from a metallic powder that contains fewer impurities or contaminants. This is because the object created from the relatively more contaminated powder may be treated (using the treatment processes described herein) so as to improve the material/fatigue properties of the object to be the same or better than those of the object formed from the relatively less contaminated powder. Thus, costs of producing an object having given material/fatigue properties may be reduced.

It should be noted that certain of the process steps depicted in the flowcharts ofFIG. 2 and described above may be omitted or such process steps may be performed in differing order to that presented above and shown inFIG. 2. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally.

Apparatus, including the computer, may be provided by configuring or adapting any suitable apparatus, for example one or more computers or other processing apparatus or processors, and/or providing additional modules. The apparatus may comprise a computer, a network of computers, or one or more processors, for implementing instructions and using data, including instructions and data in the form of a computer program or plurality of computer programs stored in or on a machine readable storage medium such as computer memory, a computer disk, ROM, PROM etc., or any combination of these or other storage media.

In the above embodiments, the object is formed using a powder bed AM process. However, in other embodiments the object is formed using a different type of AM process, for example, a blown powder process, a sheet lamination process, a vat photo-polymerisation process, a Laser Powder Bed process, or an ALM process that implements Wire and Arc technologies.

In other embodiments, the treatment process performed on the object produced using an AM process comprises peening, sintering, and hot isostatic pressing.

However, in other embodiments, the treatment process comprises the sintering process, and not the peening or HIPing processes. The high temperature sintering process advantageously tends to provide that the contaminant(s) within the contaminated regions of the object diffuse within the object, e.g. throughout the bulk of the object e.g. such that no one region of the object has a substantially higher concentration of contaminant than a different region of the object. This advantageously tends to result in improved fatigue performance and material properties of the object.

Also, in other embodiments, the treatment process comprises the hot isostatic pressing process, and not the sintering or peening processes. The hot isostatic pressing process advantageously tends to provide that the closed cavities in the object shrink or vanish completely. This advantageously tends to result in improved fatigue performance and material properties of the object. Also, if performed at a suitably high temperature (i.e. >900° C.), and for a suitably long duration, the hot isostatic pressing process advantageously tends to provide that the contaminant(s) within the contaminated regions of the object diffuse within the object, e.g. throughout the bulk of the object e.g. such that no one region of the object has a substantially higher concentration of contaminant than a different region of the object. This advantageously tends to result in improved fatigue performance and material properties of the object.

In some embodiments, the peening process is omitted.

In the above embodiments, the object is formed from a titanium alloy (e.g. an alloy comprising titanium with 6% aluminium and 4% vanadium which is also known as Ti-6Al-4V, or 6-4, 6/4, ASTM B348 Grade 5). However, in other embodiments, the object is formed from a different material. For example, in other embodiments, the object is formed from a pure (i.e. unalloyed) metal or a different type of alloy to that used in the above embodiments, or a ceramic.

In the above embodiments, the treatment process (i.e. a process of peening, sintering, and hot isostatic pressing) is performed on a single object. However, in other embodiments, a treatment process, or part of a treatment process, may be performed on any number of (different or the same) objects. This advantageously tends to reduce the cost of the process per component.

In the above embodiments, the sintering of the object is performed at the above specified temperatures, and for the above specified time-periods. However, in other embodiments sintering of an object is performed at a different appropriate temperature and/or for a different appropriate time period.

In the above embodiments, the HIP process is performed at the above specified temperatures and pressures, and for the above specified time-periods. However, in other embodiments a HIP process is performed at a different appropriate temperature and/or pressure, and/or for a different appropriate time period.

In the above embodiments, the sealing process performed on the object to seal the openings of the open cavities (i.e. the process of shot peening and sintering, or the process of coating and heating) is performed once before the HIP process is performed on the object. However, in other embodiments, before the HIP process is performed, one or both of the sealing processes may be performed multiple times. For example, the sealing process of peening and sintering may be performed more than once. In such an example, the sintering process that follows a shot peening process, tends to soften the work hardened surface formed during shot peening and tends to disperse any surface contamination into the bulk of the object, making the surface of the object more amenable to another shot peening process. Furthermore, the second, and any subsequent, shot peening processes may be performed at a lower intensity than the first shot peening process. This tends to result in a better surface appearance.