Method of manufacturing a porous material

Abstract

There is provided a method (300) of manufacturing a porous material. The method (300) comprises the steps (301, 302) of: a) forming a powder layer (170), the powder layer (170) comprising a first precursor powder (123), and b) applying a laser beam (134) to modify the powder layer (170) in selected regions of the powder layer to form a porous material layer. The step (302) of applying a laser beam (134) comprises controlling one or more parameters of the laser beam (134) to control the pore structure of the porous material layer. The one or more parameters of the laser beam (134) comprises the shape and / or size of a laser beam spot on the powder layer (170).

Description

[0001] P / 90593.W001 1

[0002] METHOD OF MANUFACTURING A POROUS MATERIAL

[0003] Field of the Invention

[0004] The present invention relates to a method of manufacturing a porous material. In particular, the invention relates to a method of forming a porous material from a first precursor powder and applying a laser to modify the powder layer in selected regions of the powder layer to form a porous material layer. There is also provided a porous material formed by such a method.

[0005] Backaround to the Invention

[0006] Porous materials may be used in a variety of applications. For example, conventional passive and active (fan assisted) heat sink thermal management devices are commonly used to maintain electronic systems. Such heat sink devices are predominantly manufactured from highly conductive metals such as copper, aluminium, or a combination of the two.

[0007] In particular, heat pipes are becoming increasingly utilised as thermal management solutions in many applications. Heat pipes are highly effective two-phase heat transfer devices that consist of a sealed receptacle with inner channel, a porous wick structure and hermetically sealed working fluid. Heat applied at the end of the heat pipe causes the working fluid to evaporate from liquid to vapour. The increased pressure created at the evaporator section causes the vapour to travel to the condenser end of the heat pipe. The vapour then condenses back to the liquid phase and releases the heat absorbed in the evaporator section. The liquid may then be transferred back to the evaporator section via a porous wick through capillary action.

[0008] During heat pipe design it is usually the manufacturability of the porous wick structure that will be the heat pipes performance limiting factor. The capability of the porous wick to generate capillary pressure and the permeability of the selected working fluid in the porous wick are the key indicators of the performance of the porous wick. Currently, due to manufacturing constraints common heat pipe capillary designs include sintered wick structures which cannot be fully optimised for both capillary pressure and permeability.

[0009] Other applications of porous materials include an acoustic control structures, and biomedical materials for use in a human or animal body.

[0010] However, it often difficult to control the pore structure of such porous materials. Control of the pore structure of such porous materials would allow for the properties of said material to be better tailored to the application.

[0011] It would therefore be beneficial to provide a method of manufacturing a porous material which overcomes the above drawbacks.

[0012] Summary of Invention P / 90593.W001 2

[0013] According to the present disclosure, there is provided a method of manufacturing a porous material, wherein the method comprises the steps of: a) forming a powder layer, the powder layer comprising a first precursor powder, and b) applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer, wherein the step of applying a laser beam comprises controlling one or more parameters of the laser beam to control the pore structure of the porous material layer, and wherein the one or more parameters of the laser beam comprises the shape and / or size of a laser beam spot on the powder layer.

[0014] Such a method may therefore utilise Laser powder bed fusion (L-PBF) additive manufacturing (AM) to manufacture the porous material. L-PBF utilises laser energy to selectively melt material in a layer-by-layer process dictated by the systems sliced data and selected laser parameter scan paths. This layer-by-layer L-PBF process enables the manufacturing of complex metal parts that are not feasible with more traditional machining, forming, and casting technologies and therefore offers much potential for complex manufacturing of metal components. L-PBF offers the potential for significantly enhanced properties of products, such as heat sinks, heat exchangers, pin fin plates and wick heat pipes. However, laser processing parameters and manufacturing methodology can require significant optimisation for specific materials and geometries. Using standard parameters to manufacture porous wick structures has been found to result in a non- homogenous porous structure. By developing a new laser manufacturing methodology the laser can be controlled to apply the laser energy density optimised for a controlled porous structure. Advantageously, it has been found that the pore structure of the porous material layer may be controlled by controlling the shape and / or size of a laser beam spot on the powder layer. This therefore allows for a desired pore structure to be determined, and subsequently selecting a predetermined shape and / or size parameter to achieve the desired pore structure for a specified precursor powder.

[0015] Optionally, the step of controlling one or more parameters of the laser beam comprises varying the one or more parameters of the laser beam to vary the pore structure of the porous material layer.

[0016] This may be particularly advantageous when the product being built up from the precursor powder requires a non-uniform porosity for optimum performance. For example, in heat pipe, the viscosity of liquid within the porous wick may be dependent on temperature. The pore structure of the porous material layer may therefore be varied dependent on the anticipated temperatures at different regions of the porous wick when building up the porous wick from the precursor powder. This enables pore structures and porosity to easily be adjusted throughout the porous material layer enabling optimisation of the capillary pressure and permeability for the working fluid at the specific phase and viscosity at the temperature related to that section of the heat transfer device. P / 90593.W001 3

[0017] The porous material layer may comprise a non-uniform porosity across the porous material layer. In other words, the method may comprise the step of varying the one or more parameters of the laser beam to vary the pore structure of the porous material layer across the porous material layer. This may be particularly advantageous dependent on the orientation in which the product is built up from the precursor powder, and whether variations in the pore structure are required as outlined above in a direction in the plane of the porous material layer.

[0018] As used herein a “porous material” or “porous material layer” may refer to a material or a material layer having a porosity of at least 10%, preferably at least 20%, preferably still at least 30%, preferably still at least 40%, preferably still at least 80%, preferably still at least 90%.

[0019] Optionally, the shape and / or size of a laser beam spot on the powder layer is controlled by manipulating a shaped laser beam prior to the laser beam reaching the powder layer. Optionally, the shape and / or size of a laser beam spot on the powder layer is controlled by splitting the laser beam prior to the laser beam reaching the powder layer. Once the laser leaves the resonator it can be either guided in its current shape to the materials processing zone via fibre optics and optical mirrors or further split and / or focused with beam deflection mirrors and / or transmissive elements to enable beam forming material processing. For example, manipulating the shaped laser beam prior to the laser beam reaching the powder layer may comprise manipulating the shaped laser beam using one or more of fibre optics, optical mirrors, beam deflection mirrors and / or transmissive elements. For example, splitting the laser beam prior to the laser beam reaching the powder layer may comprise splitting the laser beam using one or more of fibre optics, optical mirrors, beam deflection mirrors and / or transmissive elements. In particular, manipulating a shaped laser beam prior to the laser beam reaching the powder layer may comprise manipulating the shape of the laser beam after the laser beam has exited a fibre optic component. Manipulating the shape of the laser beam after the laser beam has exited a fibre optic component may comprise using beam deflection mirrors and / or transmissive elements.

[0020] Optionally, the shape and / or size of a laser beam spot on the powder layer is controlled by generating a shaped laser in a laser beam source prior to the laser beam exiting the laser beam source. Lasers (Light Amplification by Stimulated Emission of Radiation (LASER)) are an amplified form of energy carrying light transmission created within a resonator through the stimulation of a laser active medium (LAM). The resonator guides photons through the LAM amplifying the laser light while enabling laser beam formed photons to exit the resonator at predetermined points directing the laser beam. Resonators are designed to allow the stream of photons and therefore the LASER energy to exit at predefined sections and therefore the beam shape can be controlled through resonator design. For example, generating a shaped laser in a laser beam source prior to the laser beam exiting the laser beam source may comprise generating a shaped laser in a resonator. P / 90593.W001 4

[0021] Optionally, the laser beam spot comprises a shape different to a gaussian shape. Optionally, the laser beam spot comprises a doughnut or ring shape. As used herein, the ‘shape’ of the laser beam spot may refer to the shape formed from the highest intensity areas of the laser beam spot. In other words, the doughnut or ring shape may comprise a doughnut or ring of greatest intensity, with reducing intensity away from the doughnut or ring shape.

[0022] Optionally, the laser beam spot further comprises a central gaussian shape. In other words, the central gaussian shape may comprise a central spot of greatest intensity, with reducing intensity away from the central spot. The intensity may reduce away from the central spot in a generally gaussian fashion.

[0023] The laser beam spot may comprise both the central gaussian shape and the doughnut or ring shape.

[0024] Optionally, controlling one or more parameters of the laser beam comprises controlling the ratio of power applied to the powder layer by the doughnut or ring shape and the power applied to the powder layer by the central gaussian shape. For example, varying one or more parameters of the laser beam may comprise varying the ratio of power applied to the powder layer by the doughnut or ring shape and the power applied to the powder layer by the central gaussian shape.

[0025] Advantageously, it has been found that by controlling the ratio of power applied to the powder layer by the doughnut or ring shape and the power applied to the powder layer by the central gaussian shape, the porosity of the porous material layer may be varied. This therefore provides a method of controlling and varying porosity in across the porous material layer. Optionally, the method further comprises the steps of: c) subsequently re-forming a further powder layer above the porous material layer, the further powder layer comprising the first precursor powder, and d) repeating steps b) and c) to form a porous material structure. Similarly to as outlined above, such a method may therefore utilise Laser powder bed fusion (L-PBF) additive manufacturing (AM) to manufacture a three-dimensional porous material structure.

[0026] Optionally, the step of repeating steps b) and c) to form a porous material further comprises varying the one or more parameters of the laser beam to vary the pore structure of the porous material structure between at least two different regions of the porous material structure.

[0027] For example, each porous material layer may comprise a uniform porosity across each porous material layer, but the porous material structure may comprise non-uniform porosity between at least two consecutive porous material layers.

[0028] In other words, the method may comprise the step of varying the one or more parameters of the laser beam to vary the pore structure of the porous material layer between porous material layers. This may be particularly advantageous dependent on the orientation in which the product is built up from the precursor powder, and whether variations in the pore structure are required as outlined above in a direction perpendicular to the plane of the porous material layer. P / 90593.W001 5

[0029] Optionally, the pore structure is varied such that the porous material structure comprises a first pore structure at a first region at a first end of the porous material structure, and a second pore structure different to the first pore structure at a second region at a second end of the porous material structure. As outlined above, this may be particularly beneficial for heat pipes, in which the anticipated temperature at a first end of the heat pipe is different to the anticipated temperature at a second end of the heat pipe. Optionally, the first end is at an opposite end of the porous material structure to the second end.

[0030] Optionally, the first precursor powder is a first metal precursor powder. Optionally, the first precursor powder comprises aluminium or an aluminium alloy. For example, the first precursor powder may comprise AISil OMg. Optionally, the first precursor powder comprises copper or a copper alloy. Aluminium and copper may be an attractive choice for heat pipe manufacture due to high thermal conductivity properties. Optionally, the first precursor powder comprises zinc and copper. Optionally, the first precursor powder comprises brass.

[0031] Optionally, the first precursor powder is a first composite precursor powder. The first composite precursor powder may comprise at least a first component and a second component different to the first component. The first composite precursor powder may comprise a metal. The first composite precursor powder may comprise a further material. The first composite precursor powder may comprise coated particles. Each coated particle may comprise a core material coated by an outer shell layer. The core material may comprise a non-metal. The core material may have lower boiling point than the material of the outer shell layer. Each coated particle may comprise a diamond coated by an outer shell layer. The outer shell layer may comprise a highly thermally conductive metal or alloy thereof. The conductive metal or alloy thereof may comprise at least one of copper, silver, gold, or aluminium. Preferably, the highly thermally conductive metal or alloy thereof may comprise at least one of copper, silver, or aluminium. For example, the highly thermally conductive metal or alloy thereof may comprise aluminium alloy 7075. As used herein, aluminium alloy 7075 may comprise 5 to 7 % zinc, 2 to 3% magnesium, and 1 to 2 % copper by weight. The average diameter of the coated particles may be between 5 micrometres and 200 micrometres. The average thickness of the outer shell layer may be between 5 nanometres and 100 micrometres. The mass fraction of diamond in the coated particles may be between 5 % and 60 %.

[0032] Optionally, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer comprises applying a laser beam to melt or sinter at least one component of the powder layer in selected regions of the powder layer to form a porous material layer. Optionally, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer comprises applying a laser beam to melt or sinter the powder layer in selected regions of the powder layer to form a porous material layer. P / 90593.W001 6

[0033] This may be particularly applicable to embodiments in which the powder layer comprises a first metal precursor powder.

[0034] Applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer comprises applying a laser beam to boil, vaporise and / or carbonise at least one component of the powder layer in selected regions of the powder layer to form a porous material layer. For example, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer comprises applying a laser beam to boil or carbonise at least one component of the powder layer in selected regions of the powder layer to form a porous material layer. For example, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer comprises applying a laser beam to boil or vaporise at least one component of the powder layer in selected regions of the powder layer to form a porous material layer. For example, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer comprises applying a laser beam to carbonise or vaporise at least one component of the powder layer in selected regions of the powder layer to form a porous material layer.

[0035] This may be particularly applicable to embodiments in which the powder layer comprises a first composite precursor powder. For example, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer may comprise applying a laser beam to boil, vaporise and / or carbonise the core material of the coated particles of the powder layer in selected regions of the powder layer to form a porous material layer. For example, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer may comprise applying a laser beam to boil, vaporise and / or carbonise the diamonds of the coated particles of the powder layer in selected regions of the powder layer to form a porous material layer. The porous material layer may therefore comprise a material from the outer shell layer of the coated particles of the powder layer.

[0036] This may also be particularly applicable to embodiments in which the powder layer comprises a first metal precursor powder. For example, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer may comprise applying a laser beam to boil, vaporise and / or carbonise a first component of the first metal precursor powder of the powder layer in selected regions of the powder layer to form a porous material layer. When the first metal precursor powder comprises an alloy, the alloy may comprise a first component and a second component. The first component may have a boiling point at a first temperature and the second component may have a melting point at a second temperature. The first temperature may be less than the first temperature. In this example, upon application of a laser, the first component may boil, vaporise and / or carbonise, and the second component may melt and / or sinter. This may create a porous material formed from the second component. When the first metal precursor powder comprises brass, the first component may be zinc, and the P / 90593.W001 7 second component may be copper. The first component may therefore be referred to as a sacrificial component.

[0037] This may also be particularly applicable to embodiments in which the powder layer comprises at least one sacrificial precursor powder and at least one further precursor powder. For example, applying a laser beam to modify the powder layer in selected regions of the powder layer to form a porous material layer may comprise applying a laser beam to boil, vaporise and / or carbonise the at least one sacrificial precursor powder of the powder layer in selected regions of the powder layer to form a porous material layer. The porous material layer may be formed from the at least one further precursor powder. The at least one sacrificial precursor powder may have a boiling point at a first temperature and at least one further precursor powder may have a melting point at a second temperature. The first temperature may be less than the first temperature. In this example, upon application of a laser, the comprises at least one sacrificial precursor powder may boil, vaporise and / or carbonise, and the at least one further precursor powder may melt and / or sinter. This may create a porous material formed from the at least one further precursor powder. For example, the at least one sacrificial precursor powder may comprise zinc powder, and the at least one further precursor powder may comprise copper powder.

[0038] According to a second aspect of the present disclosure, there is also provided a method of manufacturing a porous material, wherein the method comprises the steps of: a) forming a powder layer the powder layer comprising a first precursor powder, and b) applying a laser beam to boil, vaporise and / or carbonise at least one component of the powder layer in selected regions of the powder layer to form a porous material layer.

[0039] The method according to the second aspect of the present disclosure may include any feature mentioned herein with respect to the first aspect of the present disclosure.

[0040] Optionally, the porous material is a wicking material for a heat transfer device.

[0041] According to a third aspect of the present disclosure, there is also provided a porous material formed by the method according to the first or second aspect for use in a heat transfer device.

[0042] According to a fourth aspect of the present disclosure, there is also provided a porous material formed by the method according to the first or second aspect for use as an acoustic control material. The acoustic control material may be for use in industries such as automotive and aerospace where automotive floor panels and aerospace bulkheads are examples of mechanical structures where the secondary function extends to providing adequate acoustic comfort. An acoustic control material may refer to a material in which the energy of an incident sound wave that is neither reflected nor transmitted by the material. Instead, the soundwave may be absorbed within the material through energy conversion. This mechanism of acoustic absorption within the material can be due to some or all of the following five mechanisms: viscous losses, thermal-elastic damping, resonance within the pore cavities, vortex shedding at sharp edges, and P / 90593.W001 8 direct mechanical damping in the material itself. In particular, an acoustic control material may refer to a material which exhibits a sound reflectivity of greater than 85 % at frequencies above 500 Hz.

[0043] According to a fifth aspect of the present disclosure, there is also provided a porous material formed by the method according to the first or second aspect for use as a biomedical material in a human or animal body. The biomedical material may be for use in orthopaedic implants and substitute bone structures. For example, under favourable conditions, bone tissue has the ability to heal itself. However, to do this the tissue has to undergo dynamic remodelling, maturation, differentiation, and controlled resorption requiring a scaffold and / or supporting structure. A porous material with permeability closer to (or the same as) that of actual bone improves osteoblasts attachment and significantly enhances the biological compatibility of bone scaffolds.

[0044] According to a sixth aspect of the present disclosure, there is also provided a method of manufacturing a heat transfer device, wherein the method comprises the steps of: a) depositing a first precursor powder from a first container in a first pattern and depositing a second precursor powder from a second container in a second pattern to form a powder layer, and b) applying the laser or electron beam to modify the powder layer in selected regions of the powder layer to form a heat transfer device layer, the heat transfer device layer comprising a porous material portion formed from the first precursor powder and a wall portion formed from the second precursor powder, wherein the step of applying a laser beam comprises controlling one or more parameters of the laser beam to control the pore structure of the porous material portion, and wherein the one or more parameters of the laser beam comprises the shape and / or size of the laser beam spot on the powder layer.

[0045] The advantages of such a method are similar to those outlined above with respect to the first aspect. It has been found that the pore structure of the porous material layer may be controlled by controlling the shape and / or size of a laser beam spot on the powder layer. This therefore allows for a desired pore structure to be determined, and subsequently selecting a predetermined shape and / or size parameter to achieve the desired pore structure for a specified precursor powder. The first and second precursor powders being used to form a porous material portion and a wall portion directly means that more complex heat transfer device geometries may be produced when compared to conventional heat transfer device manufacturing methods.

[0046] The method according to the sixth aspect of the present disclosure may comprise any feature outlined above with respect to the first or second aspect of the present disclosure. Similarly, method according to the first or second aspect of the present disclosure may comprise any feature outlined with respect to the sixth aspect of the present disclosure.

[0047] Optionally, the first precursor powder is a first metal precursor powder. Optionally, the first precursor powder comprises aluminium or an aluminium alloy. For example, the first precursor P / 90593.W001 9 powder may comprise AISil OMg. Optionally, the first precursor powder comprises copper or a copper alloy. Optionally, the second precursor powder is a second metal precursor powder. Optionally, the second precursor powder comprises aluminium or an aluminium alloy. For example, the second precursor powder may comprise AISil OMg. Optionally, the second precursor powder comprises copper or a copper alloy. Aluminium and copper may be an attractive choice for heat pipe manufacture due to high thermal conductivity properties.

[0048] Optionally, the second precursor powder comprises a different material to the first precursor powder. Optionally, the second precursor powder comprises a different metal to the first precursor powder. For example, optionally, the second precursor powder comprises aluminium or an aluminium alloy and the first precursor powder comprises copper or a copper alloy. This may be particularly advantageous, as aluminium may provide lighter weight and less expensive wall portions. Furthermore, aluminium provides better properties for welding or connecting the heat transfer device to other components. However, the silicon content in some aluminium alloys is not compatible with the preferred ammonia working fluid due to chemical reactions between ammonia and silicon which can lead to the creation of non-condensable gases. Therefore copper may provide better chemical properties when in contact with working fluids used within the heat transfer device, such as ammonia.

[0049] Optionally, the porous material portion is integrally formed with the wall portion. This may eliminate the need for a separate step to join the porous material portion with the wall portion.

[0050] Optionally, the step of controlling one or more parameters of the laser beam comprises varying the one or more parameters to vary the pore structure of the porous material portion. This may be particularly advantageous when the heat transfer device being built up from the precursor powders requires a non-uniform porosity for optimum performance. For example, in heat pipe, the viscosity of liquid within the porous wick may be dependent on temperature.

[0051] The pore structure of the heat transfer device may therefore be varied dependent on the anticipated temperatures at different regions of the porous wick when building up the porous wick from the precursor powder.

[0052] The heat transfer device layer may comprise a non-uniform porosity across the porous material portion of the heat transfer device layer. In other words, the method may comprise the step of varying the one or more parameters of the laser beam to vary the pore structure of the porous material portion of the heat transfer device layer across the porous material portion of the heat transfer device layer. This may be particularly advantageous dependent on the orientation in which the heat transfer device is built up from the precursor powders, and whether variations in the pore structure are required as outlined above in a direction in the plane of the heat transfer device layer.

[0053] Optionally, the porous material portion is a wicking material portion. P / 90593.W001 10

[0054] Optionally, the method further comprises the steps of: c) subsequently re-forming a further powder layer above the heat transfer device layer, the further powder layer comprising the first precursor powder and the second precursor powder, and d) repeating steps b) and c) to form a heat transfer device comprising a wall structure and a porous material structure.

[0055] Optionally, the step of repeating steps b) and c) to form a heat transfer device further comprises varying the one or more parameters of the laser beam to vary the pore structure of the porous material structure between at least two different regions of the porous material structure.

[0056] For example, each heat transfer device layer may comprise a uniform porosity across the porous material portion of each heat transfer device layer, but the heat transfer device may comprise non-uniform porosity between the porous material portions of at least two consecutive heat transfer device layers.

[0057] In other words, the method may comprise the step of varying the one or more parameters of the laser beam to vary the pore structure of the porous material portion of the heat transfer device layer between heat transfer device layers. This may be particularly advantageous dependent on the orientation in which the heat transfer device is built up from the precursor powders, and whether variations in the pore structure are required as outlined above in a direction perpendicular to the plane of the heat transfer device layer.

[0058] Optionally, the pore structure is varied such that the porous material structure comprises a first pore structure at a first region at a first end of the porous material structure, and a second pore structure different to the first pore structure at a second region at a second end of the porous material structure. As outlined above, this may be particularly beneficial for heat pipes, in which the anticipated temperature at a first end of the heat pipe is different to the anticipated temperature at a second end of the heat pipe. Optionally, the first end is at an opposite end of the porous material structure to the second end.

[0059] Optionally, the porous material structure is a wicking material structure.

[0060] As used herein, the ‘shape’ of the laser beam spot may refer to the shape formed from the highest intensity areas of the laser beam spot. In other words, the doughnut or ring shape may comprise a doughnut or ring of greatest intensity, with reducing intensity away from the doughnut or ring shape.

[0061] Optionally, the laser beam spot further comprises a central gaussian shape. The laser beam spot may comprise both the central gaussian shape and the doughnut or ring shape.

[0062] Optionally, controlling one or more parameters of the laser beam comprises controlling the ratio of power applied to the powder layer by the doughnut or ring shape and the power applied to the powder layer by the central gaussian shape. For example, varying one or more parameters of the laser beam may comprise varying the ratio of power applied to the powder layer by the doughnut P / 90593.W001 11 or ring shape and the power applied to the powder layer by the central gaussian shape. Advantageously, it has been found that by controlling the ratio of power applied to the powder layer by the doughnut or ring shape and the power applied to the powder layer by the central gaussian shape, the porosity of the porous material layer may be varied. This therefore provides a method of controlling and varying porosity in across the porous material layer.

[0063] According to a seventh aspect of the present disclosure, there is also provided a heat transfer device formed by the method according to the sixth aspect of the present disclosure.

[0064] Brief Description of the Drawings

[0065] Figures 1 A and 1 B are schematics of a cross-section of a laser powder layer fusion apparatus for use with a method according to the present disclosure.

[0066] Figure 1 C shows a cross-section of an exemplary powder layer being formed on top of a partially formed heat transfer device.

[0067] Figure 1 D shows a schematic of a laser source.

[0068] Figure 2 is a photograph of a cross-section of a heat transfer device manufactured using a method according to the present disclosure.

[0069] Figure 3 illustrates a series of different laser beam power distributions and cross sections, corresponding perspective views of the laser beam power distributions, and corresponding resultant porous structures formed using the different laser beam power distributions.

[0070] Figure 4 is a schematic illustrating a method of manufacturing a heat transfer device according to the present disclosure.

[0071] Figure 5 is a schematic illustrating a method of manufacturing a porous material according to the present disclosure.

[0072] Figures 6A and 6B are micrographs illustrating a porous microstructure formed from a precursor powder comprising copper-coated diamonds.

[0073] Detailed Description

[0074] Figures 1A and 1 B are schematics of a cross-section of a laser powder layer fusion (L-PBF) apparatus for use with the method according to the present disclosure.

[0075] The present invention will be described with respect to the method of manufacturing a heat transfer device. However, it can be understood that the present invention encompasses more generally a method of manufacturing a porous material. Such porous materials may be used for other purposes outside of heat transfer devices, such as in acoustic or biomedical materials. P / 90593.W001 12

[0076] The apparatus 100 comprises a fabrication compartment 114. The fabrication compartment 114 is defined by four walls 116 and a fabrication compartment floor portion.

[0077] The fabrication compartment floor portion is movable up and down relative to the rest of the apparatus 100 using a fabrication piston 124.

[0078] The apparatus 100 further comprises a recoater 118. An example of a suitable recoater is the Aerosint recoater obtainable from Aerosint SA.

[0079] The recoater 118 comprises two separate containers: a first container 122, and a second container 124. Each container is configured to hold a separate precursor powder.

[0080] The recoater 118 is configured to move horizontally relative to the rest of the apparatus 100. The recoater 118 is configured to move from a first position as illustrated in Figure 1A, over one of the four walls 116 defining the fabrication compartment 114, and over the top of the fabrication compartment 114. This movement is illustrated in Figure 1 B.

[0081] The apparatus 100 further comprises laser apparatus, the laser apparatus comprising a laser source 130 and a scanning mirror 132 positioned above the powder reservoir 112 and the fabrication compartment 114. The laser source 130 is configured to provide a laser beam 134 from the laser source 130 to the scanning mirror 132. The scanning mirror 132 is configured to reflect the laser beam 134 from the laser source 130 on to the top of the fabrication compartment 114. The scanning mirror 132 is adjustable and controllable, such that the scanning mirror 132 can reflect the laser beam 134 from the laser source 130 on to any part of the top of the fabrication compartment 114. The laser apparatus is further configured to vary the cross-sectional power distribution of the laser beam 134 normal to the beam direction. For example, the laser beam 134 may comprise a Gaussian power distribution normal to the beam direction, or a doughnut or ring shape cross-sectional power distribution normal to the beam direction.

[0082] Light (including lasers) is an electromagnetic wave consisting of bundles of wave energy called photons. Photons have (almost) no mass, no charge but are capable of energy transportation and therefore a light beam can be considered a stream (beam) of photons or stream (beam) of energy. Photons can interact with particles such as atomic shell electrons where photon energy is either absorbed (transfer of energy), reflected (change of energy direction), or transmitted (energy passes through the medium). Light energy transportation is characterised in Joule (J), power in Watt (W) and energy density in joule or watt per square meter. The amount of energy that can be transported is dependent on the wave frequency. A shorter wavelength has a higher frequency and therefore more energy as higher frequency wavelength photons carry more energy. The apparatus 100 is contained within a sealed container (not shown), such that the apparatus may be in a vacuum, or such that the sealed container can be filled with an inert gas such as argon, nitrogen, helium, or any mixture thereof. P / 90593.W001 13

[0083] In use, the first container 122 of the recoater 118 is filled with a first metal precursor powder 123.

[0084] The second container 124 of the recoater 118 is filled with a second metal precursor powder 125.

[0085] In the present example, the first metal precursor powder 123 and the second metal precursor powder 125 comprise the aluminium alloy AISil OMg. However, it can be understood that the first metal precursor powder 123 and the second metal precursor powder 125 may comprise different metals, such as aluminium, copper, and alloys thereof.

[0086] The sealed container is evacuated such that the apparatus 100 is under vacuum, or alternatively the sealed container is filled with inert gas such as argon, nitrogen, helium, or any mixture thereof, such that the apparatus 100 is held in an inert atmosphere.

[0087] At the start of manufacturing, the fabrication piston 124 is fully extended, such that the volume of the fabrication compartment 114 is zero, and the floor of the fabrication compartment 114 is aligned with the flat top portion of the four walls 116.

[0088] Upon starting the laser powder layer fusion process, the fabrication piston 124 retracts by a set distance.

[0089] The recoater 118 then passes over the top of the fabrication compartment 114, as illustrated in Figure 1 B, and deposits the first and second metal precursor powders 123, 125 from the first and second containers 122, 124 respectively in a predetermined pattern to form a first powder layer for the first layer of the heat transfer device 160.

[0090] This is illustrated in more detail in Figure 1 C, which shows a cross-section of an exemplary powder layer 170 being formed on top of a partially formed heat transfer device 160. The first and second metal precursor powders 123, 125 are deposited to form a first region 171 consisting of the first metal precursor powder 123 and a second region 171 consisting of the second metal precursor powder 125. The two regions form the predetermined pattern. The remaining powder layer 170 is excess powder.

[0091] The apparatus 100 is connected to a computer (not shown) comprising a memory on which a computer programme is stored. The computer programme comprises a set of instructions for the predetermined pattern. The computer controls the operation of the recoater 118 and the first and second containers 122, 124 based on said set of instructions. The predetermined pattern corresponds to a layer of the heat transfer device 160.

[0092] Once the recoater 118 is retracted from the top of the fabrication compartment 114, the laser source 130 is subsequently powered, and the scanning mirror 132 directs the laser beam 134 across the powder layer in the fabrication compartment 114 in a predetermined laser pattern corresponding to the layer of the of the heat transfer device 160. P / 90593.W001 14

[0093] Similarly, the computer programme comprises a set of instructions for the predetermined laser pattern. The computer controls the operation of the laser source 130 and scanning mirror 132 based on said set of instructions. The set of instructions for the laser source 130 and scanning mirror 132 include the predetermined laser pattern and shape of each layer of the heat transfer device 160. The set of instructions for the laser source 130 and scanning mirror 132 also include parameters for the laser source 130 and scanning mirror 132. These include for example laser beam power, the scanning speed of the laser beam 134 across the powder layer, the hatch distance of the laser beam 134 between successive passes across the powder layer, and laser beam 134 cross-sectional power distribution normal to the beam direction. The set of instructions for the predetermined laser pattern are dependent on the instructions for the predetermined pattern for the powder deposition, as all of the laser parameters may vary dependent on the composition of the powder at the location which the laser is directed at.

[0094] In the present example, the heat transfer device 160 is formed using a laser with a power between 10 W and 3000 W, a scanning speed across the powder layer between 100 millimetres per second and 3000 millimetres per second, and a hatch distance across the powder layer between 0.1 millimetres and 2 millimetres. The laser beam 134 cross-sectional power distribution normal to the beam direction can be varied by the laser source 130, and may comprise for example a Gaussian power distribution normal to the beam direction or a doughnut or ring shape cross-sectional power distribution normal to the beam direction.

[0095] The laser beam 134 modifies the powder layer to generate a porous material layer. In the present example, the laser beam 134 melts each particle of the powders, such that the powder layer 170 is densified in the predetermined pattern into a first layer of a heat transfer device 160. Excess precursor power 110 remains in regions of the fabrication compartment 114 which were not selectively targeted with the laser beam 134. In the present example, the thickness of the first layer of a heat transfer device 160 is less than or equal to 1 millimetre. Although as described herein, the laser beam 134 melts each particle of the powders, it can be understood that the laser beam 134 may instead only heat up each particle of the powders such that the powder layer 170 is densified through sintering of each particle of the powders.

[0096] In this particular example, the first region 171 forms the porous material portion of the layer of the heat transfer device 160. The second region 172 forms the wall portion of the layer of the heat transfer device 160. Once built up with multiple layers, the porous material portions together form a porous material structure 161 of the heat transfer device 160, and the wall portions together form a wall structure 162 of the heat transfer device 160.

[0097] In the present example, to form the porous material portion of each layer, a laser is applied with a power between 80 W, a scanning speed across the powder layer of 500 millimetres per second, and layer thickness of 0.03 millimetres. P / 90593.W001 15

[0098] Once the first layer of the heat transfer device 160 is formed, the process is repeated, with the fabrication piston 124 again retracting by the set distance. The recoater 118 again passes over the top of the fabrication compartment 114. The recoater 118 deposits the first and second metal precursor powders 122, 124 respectively in a further predetermined pattern to form a further powder layer for the subsequent layer of the heat transfer device 160. The set of instructions stored on a memory on the computer (not shown) comprises instructions for each of the further predetermined patterns. Each further predetermined pattern corresponds to a subsequent layer of the heat transfer device 160. Each predetermined pattern for each layer of the heat transfer device 160 may be different from the previous layer, or the same as the previous layer. Each predetermined pattern is dependent on the desired structure of the final heat transfer device 160.

[0099] The laser source 130 is again powered, and the scanning mirror 132 directs the laser beam 134 across the powder layer 170 in the fabrication compartment 114 in a further predetermined laser pattern corresponding to the subsequent layer of the heat transfer device 160. The further predetermined laser pattern corresponding to the subsequent layer of the heat transfer device 160 can be different to the predetermined laser pattern corresponding to the first layer of the heat transfer device 160, such that a heat transfer device 160 can be formed with a varying cross- sectional shape.

[0100] When the laser beam 134 is directed across the powder layer 170 in the fabrication compartment 114 to form the subsequent layer of the heat transfer device 160, the laser source 130 may produce a laser beam 134 with sufficient power to remelt a portion of the previous layer of the heat transfer device 160 to ensure sufficient bonding between the previous and subsequent layers of the heat transfer device 160.

[0101] Figure 1 D shows a schematic of a laser source 130. The laser source comprises a laser active medium 194 into which pumping energy input 192 is provided. The pumping energy input 192 excites some atoms or molecules 193, which subsequently emit photons 196. A resonator 191 guides the photons 196 through the laser active medium amplifying the laser light, while enabling laser beam formed photons to exit the resonator at predetermined points, hence forming the laser beam 134. The resonator 191 can be designed to allow the stream of photons 196 and therefore the laser beam 134 to exit at predefined sections and therefore the laser beam 134 shape can be controlled through resonator design.

[0102] Once the laser beam 134 leaves the laser beam source 130 it can be either guided in its current shape to the powder layer zone via fibre optics and optical mirrors or further split and / or focused with beam deflection mirrors and transmissive elements to control the shape and / or size of the laser beam spot on the powder layer.

[0103] An example cross-section of the heat transfer device 160 formed by the above method is illustrated in Figure 2. P / 90593.W001 16

[0104] The heat transfer device 160 comprises a wall structure 162 at the outer surfaces of the heat transfer device 160. A porous material structure 161 is contained within the wall structures 162 and contacts the inner surfaces of the wall structure 162. A void 163 is formed at the centre of the heat transfer device 160, between opposite sides of the porous material structure 161. The porous material structure 161 comprises pores in the region of 140pm for optimum working fluid capillary action. The porous material structure 161 further comprises porous material struts 164, spanning the void 163 between opposite sides of the porous material structure 161. The porous material struts 164 provide greater mechanical strength to the heat transfer device 160.

[0105] Figure 3 illustrates a series of different laser or electron beam power distributions and cross sections. These shapes are formed by a resonator within the laser source 130. The laser beam cross sectional shapes illustrated in Figure 3 all correspond to the laser beam cross sectional shapes at the surface of the powder layer 170 in the fabrication compartment 114 during fabrication of the porous material structure of the heat transfer device 160.

[0106] A first setting 180 corresponds to 100% of the power of the laser beam 134 being concentrated at the centre of the laser beam 134. The power of the laser beam 134 at the centre of the laser beam 134 follows a Gaussian power distribution normal to the beam direction, such that the power of the laser beam reduces following a Gaussian, or normal, distribution in a direction normal to the beam direction. A second setting 181 corresponds to 70% of the power of the laser beam 134 being concentrated at the centre of the laser beam 134, and 30% of the power of the laser beam 134 being concentrated in a doughnut or ring shape surrounding the centre of the laser beam 134. A third setting 182 corresponds to 60% of the power of the laser beam 134 being concentrated at the centre of the laser beam 134, and 40% of the power of the laser beam 134 being concentrated in a doughnut or ring shape surrounding the centre of the laser beam 134. A fourth setting 183 corresponds to 50% of the power of the laser beam 134 being concentrated at the centre of the laser beam 134, and 50% of the power of the laser beam 134 being concentrated in a doughnut or ring shape surrounding the centre of the laser beam 134. A fifth setting 184 corresponds to 30% of the power of the laser beam 134 being concentrated at the centre of the laser beam 134, and 70% of the power of the laser beam 134 being concentrated in a doughnut or ring shape surrounding the centre of the laser beam 134. A sixth setting 185 corresponds to 20% of the power of the laser beam 134 being concentrated at the centre of the laser beam 134, and 80% of the power of the laser beam 134 being concentrated in a doughnut or ring shape surrounding the centre of the laser beam 134. A seventh setting 186 corresponds to 10% of the power of the laser beam 134 being concentrated at the centre of the laser beam 134, and 90% of the power of the laser beam 134 being concentrated in a doughnut or ring shape surrounding the centre of the laser beam 134. P / 90593.W001 17

[0107] Also illustrated in Figure 3 are corresponding perspective views of the laser beam power distributions, for each of the first 180, second 181 , third 182, fourth 183, fifth 184, sixth 185 and seventh 187 settings.

[0108] The laser beam 134 cross-sectional power distribution normal to the beam direction can be varied using any of the above settings by the laser source 130 during additive manufacturing of the porous material structure of the heat transfer device 160.

[0109] In particular, the laser beam 134 cross-sectional power distribution normal to the beam direction can be varied depending on the porosity desired at that particular location of the porous material structure.

[0110] The effect of the laser beam power distributions on the porosity of the pore structure of the porous material structure is also illustrated in Figure 3. The first setting 180 results in a first pore structure 161 A. The second setting 180 results in a second pore structure 161 B. The third setting 180 results in a third pore structure 161 C. The fourth setting 180 results in a fourth pore structure 161 D. The fifth setting 180 results in a fifth pore structure 161 E. The sixth setting 180 results in a sixth pore structure 161 F. The seventh setting 180 results in a seventh pore structure 161 G. As above, these resultant pore structures were formed from a first precursor powder AISi1 OMg. As the ratio of power applied to the powder layer by the doughnut or ring shape to the power applied to the powder layer by the central gaussian shape increases, such that more power is applied to the powder layer by the doughnut or ring shape, and less power is applied to the powder layer by the central gaussian shape, the pore size of the porous material structure increases.

[0111] For example, the laser beam 134 may comprise a different cross-section shape as outlined above depending on whether the laser beam is modifying a portion of the powder layer 170 which comprises the first metal precursor powder or the second metal precursor powder. For example, the beam 134 may comprise a different cross-section shape to reduce to porosity of the wall structure 162 of the heat transfer device 160.

[0112] Additionally, the laser beam 134 cross-sectional power distribution normal to the beam direction can be varied depending on whether the laser beam is modifying a portion of the powder layer 170 which comprises a boundary between a section of the first metal precursor powder and a section of the second metal precursor powder.

[0113] This method of forming a heat transfer device 160 is illustrated by the schematic shown in Figure 4.

[0114] The method 200 includes the step of forming the powder layer 201 , the powder layer comprising the first metal precursor powder and the second precursor powder deposited in first and second predetermined patterns respectively. P / 90593.W001 18

[0115] The method 200 then comprises the step 202 of applying a laser beam 134 to modify the powder layer in selected regions of the powder layer to form a heat transfer device layer. The resulting heat transfer device layer comprises a porous material portion formed from the first metal precursor powder and a wall portion formed from the second metal precursor powder. This step 202 of modifying the powder layer in selected regions of the powder layer includes controlling one or more parameters of the laser beam to control the pore structure of the porous material portion. The one or more parameters of the laser beam comprises the shape and / or size of a laser beam spot on the powder layer, as described above.

[0116] As described above, the method further comprises subsequently the step 203 of re-forming a further powder layer above the heat transfer device layer, the further powder layer comprising the first metal precursor powder and the second metal precursor powder. Again, the first metal precursor powder and the second metal precursor powder are arranged in predetermined patterns corresponding to the particular layer being built up.

[0117] The method then comprises repeating steps 202 and 203 to form the heat transfer device 160. The wall portions are built up to form a wall structure, and the porous material portions are built up to form a porous material portion. Once the heat transfer device 160 is formed, the heat transfer device 160 is removed 204 from the fabrication compartment 114 and the excess precursor powder 110.

[0118] More, generally, the present disclosure also encompasses a method 300 of forming a porous material. The method 300 of forming a porous material is illustrated by the schematic shown in Figure 5.

[0119] The method 300 includes the step 301 of forming the powder layer 170, the powder layer 170 comprising the first metal precursor powder 123.

[0120] The method 300 then comprises the step 302 of applying a laser beam 134 to modify the powder layer in selected regions of the powder layer to form a porous material layer. This step 303 of modifying the powder layer in selected regions of the powder layer includes controlling one or more parameters of the laser beam to control the pore structure of the porous material layer. The one or more parameters of the laser beam comprises the shape and / or size of a laser beam spot on the powder layer, as described above.

[0121] Similarly to as described above, the method further comprises the step 303 of subsequently reforming a further powder layer above the heat transfer device layer, the further powder layer comprising the first metal precursor powder. Again, the first metal precursor powder is arranged in predetermined pattern and / or shape corresponding to the particular layer of the porous material structure being built up. P / 90593.W001 19

[0122] The method then comprises repeating steps 302 and 303 to form the porous material structure. Once the porous material structure is formed, the porous material structure is removed 304 from the fabrication compartment 114 and the excess precursor powder 110.

[0123] Although the method of forming a porous material has been described above with respect to the laser beam melting or sintering at least one component of the precursor powders, in can be understood that the present disclosure also includes methods of forming a porous material in which a laser beam boils, vaporises or carbonises at least one component of the powder layer in selected regions of the powder layer to form a porous material layer.

[0124] Figures 6A and 6B are micrographs at two different scales illustrating a porous microstructure 400 formed from a precursor powder comprising copper-coated diamonds. In particular, the first precursor powder comprises coated particles having an average diameter between 5 micrometres and 500 micrometres. The average thickness of an outer shell layer of copper surrounding each diamond particle is between 5 nanometres and 200 micrometres.

[0125] The porous microstructure 400 is formed following the method outlined in Figure 5 above. The step 302 of applying a laser beam 134 to modify the powder layer in selected regions of the powder layer to form a porous material layer in particular comprises applying the laser beam 134 to vaporise or carbonise the diamond particles in the first precursor powder of the powder layer in selected regions of the powder layer to form a porous material layer comprising copper. The diamond particles are vaporised or carbonised into a gas, leaving behind a porous copper microstructure 400.

[0126] This concept may also be applied to other precursor powder materials, such as brass. Brass comprises zinc, having boiling temperature is 907 degrees Celsius, and copper, having a melting temperature of 1084 degrees Celsius. Therefore, boiling and vaporisation of the zinc can cause gas entrapment porosity in the resultant porous material layer. Therefore, in this particular embodiment, the step 302 of applying a laser beam 134 to modify the powder layer in selected regions of the powder layer to form a porous material layer in particular comprises applying the laser beam 134 to boil the zinc in the first precursor powder of the powder layer in selected regions of the powder layer to form a porous material layer comprising copper. The zinc is boiled into a gas, leaving behind a porous copper microstructure.

Claims

P / 90593.W001 20Claims1 . A method (300) of manufacturing a porous material, wherein the method (300) comprises the steps (301 , 302) of: a) forming a powder layer (170), the powder layer (170) comprising a first precursor powder (123), and b) applying a laser beam (134) to modify the powder layer (170) in selected regions of the powder layer to form a porous material layer, wherein the step (302) of applying a laser beam (134) comprises controlling one or more parameters of the laser beam (134) to control the pore structure of the porous material layer, and wherein the one or more parameters of the laser beam (134) comprises the shape and / or size of a laser beam spot on the powder layer (170), and wherein the step (302) of applying a laser beam (134) to modify the powder layer (170) in selected regions of the powder layer (170) to form a porous material layer comprises applying a laser beam (134) to boil, vaporise and / or carbonise at least one component of the powder layer (170) in selected regions of the powder layer (170) to form a porous material layer.

2. A method (300) of manufacturing a porous material according to claim 1 , wherein the step of controlling one or more parameters of the laser beam (134) comprises varying the one or more parameters of the laser beam (134) to vary the pore structure of the porous material layer.

3. A method (300) of manufacturing a porous material according to claim 2, wherein the shape and / or size of a laser beam spot on the powder layer is controlled by manipulating a shaped laser beam prior to the laser beam reaching the powder layer.

4. A method (300) of manufacturing a porous material according to claim 3, wherein the shape and / or size of a laser beam spot on the powder layer (170) is controlled by splitting the laser beam (134) prior to the laser beam reaching the powder layer (170).

5. A method (300) of manufacturing a porous material according to claim 2, wherein the shape and / or size of a laser beam spot on the powder layer (170) is controlled by generating a shaped laser in a laser beam source prior to the laser beam (134) exiting the laser beam source.P / 90593.W001 216. A method (300) of manufacturing a porous material according to any preceding claim, wherein the laser beam spot comprises a doughnut or ring shape, the doughnut or ring shape comprising a doughnut or ring of greatest intensity, with reducing intensity away from the doughnut or ring shape.

7. A method (300) of manufacturing a porous material according to claim 6, wherein the laser beam spot further comprises a central gaussian shape, the central gaussian shape comprising a central spot of greatest intensity, with reducing intensity away from the central spot.

8. A method (300) of manufacturing a porous material according to claim 7, wherein controlling one or more parameters of the laser beam (134) comprises controlling the ratio of power applied to the powder layer (170) by the doughnut or ring shape and the power applied to the powder layer by the central gaussian shape.

9. A method (300) of manufacturing a porous material according to any preceding claim, wherein the method further comprises the steps (303, 304) of: c) subsequently re-forming a further powder layer (170) above the porous material layer, the further powder layer (170) comprising the first precursor powder (123), and d) repeating steps b) and c) to form a porous material structure.

10. A method (300) of manufacturing a porous material according to claim 9, wherein the step (304) of repeating steps b) and c) to form a porous material further comprises varying the one or more parameters of the laser beam (134) to vary the pore structure of the porous material structure between at least two different regions of the porous material structure.11 . A method (300) of manufacturing a porous material according to claim 10, wherein the pore structure is varied such that the porous material structure comprises a first pore structure at a first region at a first end of the porous material structure, and a second pore structure different to the first pore structure at a second region at a second end of the porous material structure.

12. A method (300) of manufacturing a porous material according to claim 11 , wherein the first end is at an opposite end of the porous material structure to the second end.

13. A method (300) of manufacturing a porous material according to any preceding claim, wherein the first precursor powder (123) is a first metal precursor powder.

14. A method (300) of manufacturing a porous material according to any preceding claim, wherein the first precursor powder (123) comprises aluminium or an aluminium alloy.P / 90593.W001 2215. A method (300) of manufacturing a porous material according to any preceding claim, wherein the first precursor powder (123) comprises copper or a copper alloy.

16. A method (300) of manufacturing a porous material according to any preceding claim, wherein the first precursor powder (123) comprises brass.

17. A method (300) of manufacturing a porous material according to any one of claims 1 to 12, wherein the first precursor powder (123) is a first composite precursor powder, the first composite precursor powder comprising at least a first component and a second component different to the first component.

18. A method (300) of manufacturing a porous material according to claim 17, wherein the first precursor powder (123) comprises coated particles.

19. A method (300) of manufacturing a porous material according to claim 18, wherein each coated particle comprises a diamond coated by an outer shell layer, the outer shell layer comprising at least one of copper, silver, gold, or aluminium.

20. A method (300) of manufacturing a porous material according to any preceding claim, wherein the step (302) of applying a laser beam (134) to modify the powder layer (170) in selected regions of the powder layer (170) to form a porous material layer comprises applying a laser beam (134) to melt or sinter at least one component of the powder layer (170) in selected regions of the powder layer (170) to form a porous material layer.21 . A method (300) of manufacturing a porous material according to any preceding claim, wherein the porous material is a wicking material for a heat transfer device (160).

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