Fabrication of open-pore titanium foam for use in load-bearing applications using the spaceholder process

Abstract

A sodium chloride space-holder process involving two heat treatments is used to create open-pore metal foams (e.g., titanium foams) with high porosity (approximately 70-90 percent) for use in load-bearing applications. Mechanically reliable titanium foams are produced using the space-holder method, which involves first sieving sodium chloride powder to a desired pore size range, mixing it with titanium powder, and compressing it at high temperature under pressure. After removing the sodium chloride in water to create pores, an additional heat treatment is applied to further strengthen the chemical bonds between the titanium particles. This process uses a combination of a pneumatic press and a furnace under argon gas to apply pressure and temperature in parallel. The resulting titanium foam is well chemically bonded and has increased durability for suitable use in structural applications.

Description

[Technical Field]

[0001] explanation CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Application No. 63 / 011,944, filed April 17, 2020.

[0002] Background of the Invention The present invention relates to the field of materials, and more particularly to metal foams for use in load-bearing applications. Summary of the Invention [Problem to be solved by the invention]

[0003] There is a need for complex shaped metal foam formations, microscale, large area, thin metal foams with porosities greater than 80 percent, and techniques for making such foams. [Means for solving the problem]

[0004] Brief Summary of the Invention A sodium chloride space-holder process involving two heat treatments is used to create open-pore metal foams (e.g., titanium foams) with high porosity (approximately 70-90 percent) for use in load-bearing applications. Mechanically reliable titanium foams are produced using the space-holder method, which involves first sieving sodium chloride powder to a desired powder size range (i.e., a desired pore size range), mixing it with titanium powder, and compressing them together at high temperatures. After removing the sodium chloride in water to create pores, an additional heat treatment is applied to further strengthen the chemical bonds between the titanium particles. This process involves applying pressure and temperature in parallel using a combination of a pneumatic press and a furnace under argon gas. The process involves two heat treatments: the first heat treatment is performed under pressure before removing the sodium chloride powder, and the second heat treatment is performed after removing the sodium chloride. The resulting titanium foam is well chemically bonded and has increased durability for suitable use in structural applications.

[0005] The space holder process is used to produce open-pore metal foams (e.g., titanium foams) for use in load-bearing applications. Titanium foams can be produced using the space holder method, where sodium chloride powder is subsequently removed in water to create pores. Here, the combined application of high temperature and pressure allows for more effective sintering of the titanium particles (creating a higher degree of chemical bonding) than either heat or pressure alone. The process uses a furnace and a flow of argon gas (or other noble gas). To further strengthen the open-pore metal foam for use in load-bearing applications, a further heat treatment is required. Therefore, the sintering process involves two heat treatments: the first heat treatment is performed before removing the sodium chloride powder, and the second heat treatment is performed after removing the sodium chloride. The resulting titanium foam is sufficiently chemically bonded and has increased durability for most load-bearing applications.

[0006] In one implementation, the titanium foam has a porosity ranging from about 70 percent to about 90 percent and a pore size distribution ranging anywhere between about 30 microns and about 300 microns. The pore size distribution can range from about 50 microns to about 100 microns. The pore size distribution can range from about 100 microns to about 300 microns.

[0007] In various implementations, the structural elements are made from titanium foam, where the titanium foam is milled or machined using water jet, wire cutting, or saw cutting methods.

[0008] A manufacturing process for creating porous titanium foam comprises a sodium chloride space holder method, which may include: sieving sodium chloride space holder powder to a suitable size range of about 30 microns to about 300 microns by applying a sieving process; mixing the sieved sodium chloride powder and titanium powder in an automatic mixer for about 5 minutes to about 30 minutes; heating the sieved sodium chloride powder and titanium powder mixture in a furnace under argon gas and pressing it using a pneumatic press at about 200°C to about 800°C for about 10 minutes to about 12 hours under a pressure of about 10 megapascals to about 200 megapascals; immersing the pressed sodium chloride and titanium composite in water for about 30 minutes to about 24 hours, and dissolving and removing the sodium chloride from the titanium foam using ultrasonic treatment or agitation. Further high temperature sintering is carried out at about 700°C to about 1200°C under argon gas for about 0.5 hours to about 10 hours.The titanium foam is then filled with crystal bond or polymer resin, followed by grinding, cutting, and machining to produce complex shaped elements or components with smooth cut surfaces.

[0009] Additionally, in various implementations, at least one of a polymer, carbamide (CO(NH2)2), sucrose crystals, urea, or calcium chloride powder is used as a space holder in place of sodium chloride powder.

[0010] Other objects, features, and advantages of the present invention will become apparent from a consideration of the following detailed description and the accompanying drawings, in which like reference characters represent like features throughout the drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows a schematic diagram of the processing of titanium foam using two-stage heat treatment sintering for load-bearing applications. [Figure 2A] This shows a photograph of a sieve that can control the particle size of sodium chloride to a desired particle size. [Figure 2B] 1 shows a scanning electron micrograph of the resulting sodium chloride particles having the desired size range. [Figure 3] 1 shows a hot air press for preparing sintered titanium-sodium chloride composites. [Figure 4] 1 shows the X-ray diffraction pattern of a hot pressed titanium foam-sodium chloride composite after sintering and before the sodium chloride particles are removed by dissolving in water. [Figure 5] Figure 1 shows the X-ray diffraction pattern of the final pure titanium foam after the sodium chloride particles have been removed by dissolving in water. [Figure 6] 1 shows an optical micrograph of the glossy surface of titanium foam processed by one-stage heat treatment sintering. [Figure 7A] 1 shows a scanning electron micrograph of the fissured surface of a titanium foam exhibiting loosely bonded titanium particles after a single heat treatment process. [Figure 7B] 1 shows a scanning electron micrograph of the fissured surface of a titanium foam exhibiting loosely bonded titanium particles after a single heat treatment process. [Figure 8A]1 shows an optical micrograph of the glossy surface of titanium foam processed by a two-stage heat treatment sintering process. [Figure 8B] 1 shows an optical micrograph of the glossy surface of titanium foam processed by a two-stage heat treatment sintering process. [Figure 9A] 1 shows a scanning electron micrograph of the fissured surface of titanium foam (exhibiting closely bonded titanium particles after a two-stage heat treatment process). [Figure 9B] 1 shows a scanning electron micrograph of the fissured surface of titanium foam (exhibiting closely bonded titanium particles after a two-stage heat treatment process). [Figure 9C] 1 shows a scanning electron micrograph of the fissured surface of titanium foam (exhibiting closely bonded titanium particles after a two-stage heat treatment process). [Figure 9D] 1 shows a scanning electron micrograph of the fissured surface of titanium foam (exhibiting closely bonded titanium particles after a two-stage heat treatment process). [Figure 10A] 1 shows a scanning electron micrograph of the fissured surface of a titanium foam exhibiting tightly chemically bonded titanium particles after a two-stage heat treatment process. [Figure 10B] 1 shows a scanning electron micrograph of the fissured surface of a titanium foam exhibiting tightly chemically bonded titanium particles after a two-stage heat treatment process. [Figure 11] 1 shows a photograph of a titanium foam square bar with a smooth surface, demonstrating excellent machinability for structural element applications. DETAILED DESCRIPTION OF THE INVENTION

[0012] Detailed Description of the Invention Figure 1 shows a schematic diagram of the processing of titanium (Ti) foams using a two-stage heat treatment sintering for load-bearing applications. This salt (sodium chloride)-based space holder method, which can be implemented in various ways, involves mixing sodium chloride (NaCl) and metal powder (e.g., titanium powder) together (steps 1, 2, and 3) and finally removing the space holder to leave pore spaces of controlled size and shape (steps 4, 5, and 6). It is important to sieve the space holder powder to obtain a suitable size range, preferably tens to hundreds of microns (Figure 2).

[0013] When the prepared mixture of sodium chloride powder and metal powder is hot-pressed (step 3), the sodium chloride powder acts only as a pore space holder and can be rinsed away in a later stage. After the salt powder is removed (step 4), a further high-temperature heat treatment (step 5) is applied to the metal foam (e.g., Figure 1) to increase the strength and ductility of the metal foam for load-bearing applications. In addition, polymer particles, low-melting-point metals such as tin, magnesium, or zinc, carbamide (CO(NH2)2), sucrose crystals, urea, or calcium chloride (CaCl2) can also be used as space holders because they can be removed by melting or washing.

[0014] 1. Referring to FIG. 1, in step 1, powders are prepared: titanium powder and sodium chloride powder.

[0015] 2. In step 2, the powders are mixed. The pore size range is determined by the size range of the sieved sodium chloride powder desired for the particular application.

[0016] 3. In step 3, the powder mixture is heated and pressed. The result is a composite of titanium foam and sodium chloride.

[0017] 4. In step 4, sodium chloride particles are selectively removed in water. 5. In step 5, further processing is carried out to further sinter the titanium particles. In particular, the titanium foam is heat treated under a controlled atmosphere (e.g., argon gas) to improve sintering of the metal powder.

[0018] 6. In step 6, the titanium foam formation is machined to the desired specifications for the load-bearing application.

[0019] 1 may have additional steps (not necessarily those described in this patent), some of the steps shown may be replaced with other steps, fewer steps or only some of the steps shown, the steps may be in a different order than shown, or any combination thereof. Furthermore, the steps in other implementations may not be exactly the same as the steps shown, but may be modified or changed as appropriate for a particular application or based on the circumstances.

[0020] Figure 2A shows a photograph of sieves (e.g., 50 micron, 100 micron, and 300 micron sieves) that can control the range of sodium chloride particle sizes to achieve a desired range. Figure 2B shows a scanning electron micrograph of the resulting sodium chloride particles having a desired size range after the sieving process. Here, it is important to achieve a targeted, desired range of pore sizes by applying a controlled sieving process for a specific application (e.g., battery electrodes, supercapacitor electrodes, structural elements, or many other applications).

[0021] Figure 3 shows a hot air press for preparing a sintered titanium-sodium chloride composite. Upper and lower press dies and the compressed composite (titanium and sodium chloride composite) are enclosed in a furnace containing heating elements. While applying pressure at room temperature may be sufficient in some cases, when making titanium foams with higher porosity, applying pressure at elevated temperatures is desirable to achieve stronger titanium particle bonding during sintering and, consequently, improved mechanical properties of the resulting titanium foam.

[0022] The pneumatic press has a steel die, a heating element, and a pressure reader. The titanium and sodium chloride powder mixture is placed into the steel die of the press. Adjacent to the steel die is a heating element, which heats the powder within the die. The pneumatic press presses, or applies pressure to, the powder within the die, compacting it together.

[0023] Figure 4 shows the X-ray diffraction pattern of a hot-pressed titanium foam-sodium chloride composite after sintering at about 650°C for about 2 hours, but before removing the sodium chloride particles by dissolving them in water. Notably, only titanium and sodium chloride are detected; no undesired impurities or new phases are present. The preferred range for applied pressure is about 10 MPa to 200 MPa, and the preferred range for applied temperature is about 200°C to 800°C, for a period of about 10 minutes to about 12 hours under argon gas.

[0024] Figure 5 shows the X-ray diffraction pattern of the final pure titanium foam after the sodium chloride particles have been removed by dissolving them in water, demonstrating successful processing of the titanium foam with no compositional changes and no impurities. The cleaning time in water ranges from about 30 minutes to about 24 hours, depending on the size of the foam. The cleaning process can be expedited by using a stirring or sonication device in the water.

[0025] Figure 6 shows an optical micrograph of the glossy surface of titanium foam processed by one-stage heat treatment sintering. Although two-stage heat treatment is preferred, one-stage heat treatment may be sufficient for some applications, such as energy electrodes, that do not require a certain level of load-bearing capacity. However, it is generally difficult to achieve porosity greater than about 80 percent without further heat treatment.

[0026] 7A and 7B show scanning electron micrographs of the fractured surface of a titanium foam (77 percent porosity) exhibiting loosely bonded titanium particles after a single heat treatment process. The scanning electron micrographs in FIGS. 7A and 7B are at different magnification levels. This titanium foam may not have sufficient strength and ductility for load-bearing applications. Also, this single heat treatment process is not suitable for producing titanium foams with porosities greater than about 80 percent.

[0027] 8A and 8B show optical micrographs of the glossy surface of titanium foam processed by a two-stage heat treatment sintering process: Fig. 8A shows an 80 percent titanium foam that underwent two-stage heat treatment, and Fig. 8B shows an 85 percent titanium foam that underwent two-stage heat treatment.

[0028] The arrows point to the white areas, where strong chemical bonds between the titanium metal particles can be seen. The two-stage sintering process allows for the production of titanium foams with relatively high porosity (over 80 percent, up to 90 percent).

[0029] Additionally, Figures 9A, 9B, 9C, and 9D show scanning electron micrographs of the fissured surface of titanium foam (about 80 to about 85 percent porosity) exhibiting densely bonded titanium particles after a two-stage heat treatment process. The applied pressure and temperature were about 100 MPa and about 650°C, respectively, and removal of the sodium chloride was followed by a further heat treatment at about 1000°C. Such titanium foams are expected to have sufficient strength and ductility for a variety of load-bearing applications.

[0030] The effect of further heat treatment on the final titanium foam microstructure is evident from Figures 10A and 10B, which show scanning electron micrographs of the fissured surface of a titanium foam (approximately 80 percent porosity) demonstrating the strong chemical bonds (arrows) between the titanium particles after the two-step heat treatment process. Further heat treatment is important to achieve a mechanically reliable titanium foam for use in load-bearing structural applications. Figures 10A and 10B show two scanning electron micrographs taken at two different magnification levels.

[0031] Figure 11 shows a titanium foam square bar (left) with a smooth surface that exhibits excellent machinability for structural element applications. The close-up (right) shows a typical microstructure of a machined titanium foam cross section. With further heat treatment, titanium foam can be machined to form complex shapes and parts that can be used in structural applications.

[0032] While example embodiments have been described in some detail, such description and such embodiments are not intended to limit the scope of the claimed invention. For example, the two-stage space holder technique described in Figure 1 can also be applied to the production of aluminum foam, copper foam, or nickel foam.

[0033] This patent describes several example implementations with specific dimensions, measurements, temperatures, and values. These examples are not intended to be exhaustive or to limit the invention to the precise form described. Such values, percentages, times, and temperatures are approximate. These values ​​may vary due to, for example, measurement or manufacturing variations or tolerances or other factors. For example, temperature and time values ​​may vary within ±5 percent, ±10 percent, ±15 percent, ±20 percent, or ±25 percent, depending on the strictness of manufacturing and measurement tolerances.

[0034] Furthermore, such values ​​are for one particular implementation, and other implementations may have different values; for example, a particular value may be larger for a large-scale process or formation and smaller for a small-scale formation. A device, apparatus, or process may be made proportionally larger or smaller by proportionally adjusting relative measurements (e.g., by maintaining the ratio between different measurements the same or approximately the same). In various implementations, the values ​​may be the same as the given value, approximately the same as the given value, greater than the given minimum value, less than the given maximum value, or any combination thereof.

[0035] Embodiment 1 In one implementation, the production of highly porous open-pore titanium foams using a spaceholder process involving a two-stage heat treatment is described for use in load-bearing applications. Some examples of load-bearing applications include relatively large or three-dimensional battery or supercapacitor electrodes, or casings or structural members for information technology (IT) devices, components or panels for replacing any metal alloys used in construction and infrastructure (e.g., building structural components), housings for devices and components (e.g., television or display panel housings, computer and laptop computer housings, etc.), land or land-based vehicles (e.g., wagons, bicycles, scooters, motorcycles, automobiles, trucks, buses, and tanks), trains and trams, watercraft (e.g., ships, boats, and hovercraft), aircraft (e.g., airplanes, helicopters), submarines and other underwater vehicles, spacecraft (e.g., satellites, space stations), defense and military and related components and systems (e.g., missiles, rockets, guns, cannons, and ammunition), robots, machines, and many other applications for reducing the weight of load-bearing or structural components.

[0036] Titanium foam can be manufactured using a space holder method with a two-stage heat treatment (e.g., sodium chloride powder is subsequently removed in water to create pores). In one implementation, a vacuum furnace with extremely high purity (greater than 10^-4 torr) is used. The cullet symbol (^) is used to indicate that the number following this symbol is an exponent. In another implementation, the process uses a common furnace with flowing argon gas, which can be relatively inexpensive and simple to use in mass production.

[0037] The process for producing titanium foam involves two heat treatments. The first heat treatment is performed before removing the sodium chloride powder. The second heat treatment is performed after removing the sodium chloride. The effect of the second heat treatment is to dramatically improve the mechanical properties of the titanium foam for use in load-bearing applications. Scanning electron microscope analysis (and images) clearly show that after the second heat treatment, the titanium powder particles in the titanium foam are well chemically bonded together, increasing the durability of the titanium foam.

[0038] In one specific implementation, the procedure includes the following: 1. In one implementation, sieves with specific pore sizes can be used herein to control the pore size to achieve a desired range. For example, the size of the sodium chloride powder is controlled to be in the range of about 50 microns to about 100 microns by sieving the sodium chloride powder through two different sieves with pore sizes of about 50 microns to about 100 microns.

[0039] 2. Mix titanium powder (about 1 micron to about 40 microns) with sieved sodium chloride powder in a mixer for about 5 minutes to about 30 minutes, where the weight or volume ratio of titanium powder to sodium chloride powder depends on the desired target porosity to be achieved in the final titanium foam.

[0040] 3. Using a hydraulic press, compress the mixture under a pressure of about 10 to 200 megapascals for about 10 minutes to about 12 hours, while simultaneously compressing the mixture in a heated furnace at 200°C to 800°C under argon gas.

[0041] In a press, a load or stress (load per unit area) is typically applied to a workpiece (e.g., a mixture of titanium powder and sieved sodium chloride powder), causing the workpiece to distort. In one implementation, an upper column descends and presses the mold and powder mixture against a lower plate, resulting in equal force on both sides (e.g., from above and below).

[0042] 4. Dissolve the spacer (eg, NaCl) in the heat-treated compact using water (about 20° C. to about 100° C.) by magnetic stirring or ultrasonication.

[0043] 5. The titanium foam can be further heat treated (or sintered) at a higher temperature (e.g., to further sinter the loosely bonded titanium particles in the titanium foam) in flowing argon at about 700°C to about 1200°C for about 0.5 hours to about 10 hours to form a stronger microstructure by further forming chemical bonds between the loosely bonded titanium powder particles. In this process flow, the first heating step is performed inside the press (step 3 described above) and the second heating step is performed outside the press.

[0044] 6. Titanium foam can be filled with crystal bond or polymer resin, then milled, cut and machined into complex shaped elements or components with smooth cut surfaces.

[0045] In one implementation, a method for forming a titanium foam includes the steps of: sieving unsorted sodium chloride spacer powder to obtain a sorted sodium chloride spacer powder having a particle size of about 30 microns to about 300 microns; mixing the sorted sodium chloride powder and titanium powder in an automatic mixer for about 5 minutes to about 30 minutes; and heating the mixture of the sorted sodium chloride powder and titanium powder in a furnace under argon gas and heating it at 200°C to 80°C using a pneumatic press for about 10 minutes to about 12 hours. pressing the composite at 0°C under a pressure of about 10 to 200 megapascals to obtain a compressed sodium chloride and titanium composite (e.g., heating and pressing may be performed in parallel or simultaneously), immersing the compressed sodium chloride and titanium composite in water for about 30 minutes to about 24 hours and using ultrasonic treatment or agitation to dissolve and remove the sodium chloride from the composite to obtain a titanium foam, and sintering the titanium foam at about 700°C to about 1200°C under argon gas for about 0.5 to about 10 hours. The resulting titanium foam may have a porosity ranging from about 70 percent to about 90 percent and a pore size distribution ranging anywhere between about 30 microns to about 300 microns.

[0046] Additionally, the method may include filling the titanium foam with crystal bond or polymer resin followed by grinding, cutting, and machining into complex shaped elements or parts with smooth cut surfaces. The method may include water jet, wire cutting, or saw This may include using cutting to machine the titanium foam into structural elements.

[0047] The pore size distribution of the titanium foam may range from about 50 microns to about 100 microns.The pore size distribution of the titanium foam may range from about 100 microns to about 300 microns.

[0048] In various implementations, at least one of a polymer, carbamide, sucrose crystals, urea, or calcium chloride powder is used as the space holder in place of unscreened sodium chloride space holder powder.

[0049] While the present invention has been described above for purposes of illustration and description, it is not intended to be exhaustive or to limit the invention to the precise form described, as many modifications and variations are possible in light of the above teachings. Certain embodiments have been selected and described in order to best explain the principles of the invention and its practical application. It is believed that this description will enable those skilled in the art to optimally utilize and practice the invention in various embodiments and with various modifications suited to particular applications. The scope of the invention is defined by the following claims.

Claims

1. 1. A method for forming a titanium foam, the method comprising: A step of sorting the unsorted space holder sodium chloride powder with a sieve to obtain sorted space holder sodium chloride powder having a particle size of 30 microns to 300 microns; mixing the selected sodium chloride powder and titanium powder in an automatic mixer for 5 to 30 minutes; heating the mixture of the selected sodium chloride powder and the titanium powder in a furnace under argon gas and pressing it using a pneumatic press at 200°C to 800°C for 10 minutes to 12 hours under a pressure of 10 to 200 megapascals to obtain a compacted sodium chloride and titanium composite, wherein heating and pressing are carried out simultaneously; immersing the compressed sodium chloride and titanium composite in water for 30 minutes to 24 hours and using ultrasonic treatment or agitation to dissolve and remove the sodium chloride from the composite to obtain a titanium foam; sintering the titanium foam at 700°C to 1200°C under argon gas for 0.5 hours to 10 hours; The titanium foam has a porosity ranging from 70 percent to 90 percent and a pore size distribution ranging anywhere between 30 microns and 300 microns.

2. 10. The method of claim 1, comprising filling the titanium foam with Crystalbond and then machining it into a complex shaped element or part with smooth cut surfaces.

3. 10. The method of claim 1, comprising filling the titanium foam with a polymer resin and then machining it into a complex shaped element or part with smooth cut surfaces.

4. 10. The method of claim 1, wherein the pore size distribution of the titanium foam ranges from 50 microns to 100 microns.

5. 10. The method of claim 1, wherein the pore size distribution of the titanium foam ranges from 100 microns to 300 microns.

6. The method of claim 1 , comprising using a water jet to machine the titanium foam into structural elements.

7. The method of claim 1 , comprising machining the titanium foam into structural elements using wire cutting.

8. The method of claim 1 , comprising machining the titanium foam into structural elements using sawing.

9. 2. The method of claim 1, wherein at least one of polymer, carbamide, sucrose crystals, urea, or calcium chloride powder is used as a space holder instead of the unsorted sodium chloride powder as a space holder.

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