Patent Publication Number: US-2023143154-A1

Title: Piston crank agitation mechanism for physical vapor deposition conformal coatings on powder

Description:
STATEMENT OF GOVERNMENT INTEREST 
     This invention was made with government support under Grant No. 80NSSC18K0255 awarded by the National Aeronautics and Space Administration. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     Applying a thin film coating to powder under vacuum conditions requires mechanical agitation of the powder to achieve a uniform film. Previous efforts have successfully produced thin film coatings on powder but did not make provision for scalability. Furthermore, current systems are not able to uniformly and efficiently coat the powder. 
     Some current devices include rotating vessel designs that serve to mix the powder during sputter deposition, as shown schematically in  FIG.  1 A . Such systems do not completely use the container for coating, and the powder collects at the bottom of the (tilted) vessel. Thus, even with uniform sputtered coating, the reduced coating on the powder from these devices is non-uniform, often to the point of forming separate platinum agglomerates. 
     Other current devices employ a rapidly oscillating vessel to induce agitation in the powders contained therein, as shown schematically in  FIG.  1 B . The motion is produced by small angle, oscillating rotations of a shaft with a cantilever beam (at the end of which the powder container is affixed), producing near-linear displacements at the end of the beam. Although these systems are able to uniformly coat powders, they did not address scalability. In other words, these designs make no provision to expand the design of their system for processing large quantities of powder. 
     Another design of current devices utilizes a shuttle constrained by linear bearings and guides and driven by an eccentric rotating mass attached thereto and held against gravity by springs, as shown schematically in  FIG.  1 C . This design appears to be of simple mechanical design and yields linear motion. However, the requirements for the motor are stringent, as it must withstand the oscillations of the shuttle as well as be compatible with vacuum. Because of these motor requirements, the mechanical design is not as simple as it appears. Further, the use of springs complicate scalability, as their presence introduces the possibility of resonance. Again, because the system dynamics must be accounted for in each scenario, the mechanical design is not simple. 
     Thus, a need exists for a scalable mechanism for mechanical powder agitation that is of simple mechanical design, maximizes powder area exposed to the sputtering gun, and provide uniform agitation. 
     SUMMARY 
     Various implementations include a device for deposition of conformal coatings. The device includes a powder container, a connecting rod, and a crankshaft. The powder container has a first side and a second side opposite and spaced apart from the first side. The first side is configured to contain a powder. The connecting rod has a first end and a second end opposite and spaced apart from the first end. The first end is directly hingedly coupled to the second side of the powder container. The crankshaft has a crankshaft longitudinal axis, a main shaft portion extending along the crankshaft longitudinal axis, and a cam portion radially offset from and rotatable about the crankshaft longitudinal axis. The second end of the connecting rod is directly rotatably coupled to the cam portion. Rotation of the crankshaft about the crankshaft longitudinal axis causes the second end of the connecting rod to rotate about the crankshaft longitudinal axis such that the connecting rod causes the powder container to linearly oscillate between a first position and a second position. The powder container is closer in the first position than in the second position to the crankshaft longitudinal axis. 
     In some implementations, the device further includes a base having a first surface and a second surface. In some implementations, the crankshaft is rotatably coupled to the first surface of the base, and the powder container oscillates in a direction perpendicular to the second surface of the base. 
     In some implementations, the device further includes one or more linear bearings coupled to the powder container for guiding the powder container between the first position and the second position. 
     In some implementations, the crankshaft includes tool steel. 
     In some implementations, the device further includes one or more rotational bearings. In some implementations, the crankshaft extends through and rotates relative to the one or more rotational bearings. In some implementations, the one or more rotational bearings include Vespel Polyimide. 
     In some implementations, the device further includes a housing defining a vacuum chamber. In some implementations, the powder container is at least partially disposed within the vacuum chamber. 
     In some implementations, the device further includes a vacuum source in fluid communication with the housing. In some implementations, the vacuum source is configured to cause a lower pressure within the vacuum chamber than in an ambient environment. 
     In some implementations, the device further includes a physical vapor deposition source for depositing a coating material toward the first side of the powder container. In some implementations, the physical vapor deposition source includes a magnetron sputtering device. In some implementations, the physical vapor deposition source includes a pulsed-laser physical vapor deposition source. In some implementations, the physical vapor deposition source includes an electron-beam physical vapor deposition source. 
     In some implementations, the device further includes a motor for causing rotation of the crankshaft about the crankshaft longitudinal axis. 
     In some implementations, the powder container oscillates at a frequency equal to a rotational speed of the crankshaft about the crankshaft longitudinal axis. 
     In some implementations, the powder container includes aluminum. 
     In some implementations, the first side of the powder container defines a concave surface that at least partially defines a powder chamber. 
     In some implementations, the first side of the powder container defines at least one wall extending in a direction from the first position to the second position. In some implementations, the at least one wall at least partially defines a powder chamber. 
     In some implementations, the first side of the powder container defines at least one inclined side wall that at least partially defines a powder chamber. 
     In some implementations, the first side of the powder container defines at least one concave side wall that at least partially defines a powder chamber. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Example features and implementations are disclosed in the accompanying drawings. However, the present disclosure is not limited to the precise arrangements and instrumentalities shown. 
         FIG.  1 A  shows a schematic view of a prior art system including a rotating vessel design that serves to mix the powder during sputter deposition of conformal coatings. 
         FIG.  1 B  shows a schematic view of a prior art system including a rapidly oscillating vessel to induce agitation in the powders during sputter deposition of conformal coatings. 
         FIG.  1 C  shows a schematic view of a prior art system including a shuttle constrained by linear bearings and guides and driven by an eccentric rotating mass attached thereto and held against gravity by springs to introduce agitation during sputter deposition of conformal coatings. 
         FIG.  1 D  shows a schematic view of a device for deposition of conformal coatings, according to one implementation. 
         FIG.  2    is a perspective view of a device for deposition of conformal coatings, according to another implementation. 
         FIG.  3    is a perspective view of the crankshaft of the device of  FIG.  2   . 
         FIG.  4 A  is a perspective view of the powder container of the device of  FIG.  2   . 
         FIG.  4 B  is a side view of the powder container of the device of  FIG.  2   . 
     
    
    
     DETAILED DESCRIPTION 
     The devices, systems, and methods described herein include a piston-crank mechanism used to agitate powder by applying an oscillation to a powder container containing that powder, as shown schematically in  FIG.  1 D . This powder container is open to a physical vapor deposition source, which applies conformal coatings to the powder. The devices, systems, and methods described herein use of the piston-crank mechanism to provide agitation, rather than alternate means. 
     The piston-crank agitation system applies an oscillation of fixed amplitude in a linear manner. This characteristic allows the powder container to be as large as the vacuum chamber will permit and/or for powder to be dispersed across the entire base of the powder container. This maximizes coating efficacy in comparison to other systems. 
     The devices, systems, and methods described herein may be used to produce conformal coatings on powders (e.g., core-shell structures) with minimal exposure of the powders or coatings to contaminants, which have applications in the energy, aerospace, and nuclear industries. Such applications are particularly useful for additive manufacturing where precise tailoring of powder properties (composition, surface morphology/characteristics) is required. 
     Great flexibility in the process is inherent, as most metals may be readily deposited. Potential applications include: nuclear thermal propulsion, high temperature composites, thermite propellants/explosives, and nanocrystalline materials. The devices, systems, and methods described herein are scalable (there are no geometric limitations inherent to the concept) and applies coatings with approximately four times the “deposition efficacy” (volume of coating/energy input) in comparison to alternate systems published in the literature. 
     The piston-crank design of the devices, systems, and methods described herein, like an automobile piston engine, trades some mechanical complexity for reliable dynamic behavior. The system produces linear motion of the powder container, which may be as large as desired, so long as the mechanical components may safely handle the stresses imposed during operation. While the mathematical equations describing the dynamic motion of the system are complex, the motion is not. The powder container has a fixed mechanical amplitude that is unaffected by mechanical frequency or mass of the powder in the container. Thus, once the system is constructed, a user may fill the container with powder and run the system without needing to make any adjustments to avoid undesirable system behavior, such as resonance. 
       FIG.  2    shows a device  100  for deposition of conformal coatings, according to aspects of a first implementation. The device  100  includes a base  110 , a crankshaft  130 , a connecting rod  140 , a powder container  150 , a vacuum chamber  172 , and a physical vapor deposition source  180 . 
     The base  110  has a first surface  112  and a second surface  114  opposite and spaced apart from the first surface  112 . Two rotational bearings  116  are coupled to the first surface  112  of the base  110  such that the openings of the rotational bearings  116  are axially aligned with each other. 
     The rotational bearings  116  shown in  FIG.  2    include Vespel Polyimide plain bearings, but in other implementations, the rotational bearings include ball bearings (e.g., Si 3 N 4  ball bearings), any other type of plain bearing (e.g., Rulon J plain bearings), or bearing made of any material such as Frelon, Rulon 641, Rulon LR, or any material capable of withstanding the rotational and radial loads of the system. In some implementations, the device can include any number of one or more rotational bearings. 
       FIG.  3    shows the crankshaft  130  of the device  100  shown in  FIG.  2   . The crankshaft  130  has a crankshaft longitudinal axis  132 , a main shaft portion  134  extending along the crankshaft longitudinal axis  132 , and a cam portion  136  radially offset from and rotatable about the crankshaft longitudinal axis  132 . The main shaft portion  134  of the crankshaft  130  extends through the openings of the two rotational bearings  116  and rotates relative to the two rotational bearings  116  such that the crankshaft  130  is rotatably coupled to the first surface  112  of the base  110 . 
     The crankshaft  130  shown in  FIGS.  2  and  3    includes tool steel, but in other implementations, the crankshaft includes stainless steel (e.g. 316 or 17-4 PH stainless steel), aluminum (e.g., 6061 aluminum), titanium or a titanium alloy, a nickel-based alloy, or any other material capable of withstanding the rotational and radial loads of the system. 
     The connecting rod  140  has a first end  142  and a second end  144  opposite and spaced apart from the first end  142 . The second end  144  of the connecting rod  140  is directly rotatably coupled to the cam portion  136  of the crankshaft  130 . 
     The connecting rod  140  shown in  FIG.  2    includes aluminum (6061), but in other implementations, the connecting rod includes stainless steel, tool steel, titanium or a titanium alloy, a nickel-based alloy, or any other material capable of withstanding the oscillating loads of the system. 
       FIGS.  4 A and  4 B  show the powder container  150  of the device  100  shown in  FIG.  2   . The powder container  150  has a first side  152  and a second side  154  opposite and spaced apart from the first side  152 . The first end  142  of the connecting rod  140  is directly hingedly coupled to the second side  154  of the powder container  150 . The first side  152  of the powder container  150  defines a concave bottom surface  156  and a side wall  158  extending from the bottom surface  156  to form a cylindrical wall. The concave bottom surface  156  and cylindrical side wall  158  define a powder chamber  159  for containing powder  190 . 
     The powder container  150  shown in  FIGS.  2 ,  4 A, and  4 B  includes aluminum, but in other implementations, the powder container includes stainless steel, tool steel, titanium or a titanium alloy, a nickel-based alloy, or any other material capable of withstanding the oscillating loads of the system and containing powder. 
     Although the first side  152  of the powder container  150  shown in  FIGS.  2 ,  4 A, and  4 B  includes a concave bottom surface  156 , in other implementations, the bottom surface of the first side of the powder container is flat or includes any other concave and/or convex contours. Although the first side  152  of the powder container  150  shown in  FIGS.  2 ,  4 A, and  4 B  includes a cylindrical side wall  158  extending from the bottom surface  156 , in other implementations, the first side of the powder container has any other cross-sectional shape, such as ovate, triangular, rectangular, or any other shape. In some implementations, the first side of the powder container defines at least one inclined side wall, at least one concave side wall, and/or any other side walls and/or bottom surfaces capable of defining a powder chamber. 
     The base  110  further includes two guide tracks  120  and four linear bearings  122 . The two guide tracks  120  extend perpendicularly to the first surface  112  of the base  110 . Two linear bearings  122  are slidingly coupled to each of the guide tracks  120 , and the linear bearings  122  are coupled to the powder container  150  for guiding the powder container  150  between the first position and the second position, as discussed below. 
     An output shaft  162  of a motor  160  is coupled to the main shaft portion  134  of the crankshaft  130  for causing rotation of the crankshaft  130  about the crankshaft longitudinal axis  132 . 
     In use, a powder  190  is disposed within the powder chamber  159  of the powder container  150 . The motor  160  is activated to cause rotation of the main shaft portion  134  of the crankshaft  130  about the crankshaft longitudinal axis  132 . The rotation of the main shaft portion  134  of the crankshaft  130  about the crankshaft longitudinal axis  132  causes the cam portion  136  of the crankshaft  130  and the second end  144  of the connecting rod  140  that is rotatably coupled to the cam portion  136  to rotate about the crankshaft longitudinal axis  132 , as shown in  FIG.  1 D . As the second end  144  of the connecting rod  140  rotates about the crankshaft longitudinal axis  132 , the powder container  150  that is hingedly coupled to the first end  142  of the connecting rod  140  and constrained to a linear path by the linear bearings  122  is caused to linearly oscillate between a first position and a second position, wherein the powder container  150  is closer in the first position than in the second position to the crankshaft longitudinal axis  132 . Because the guide tracks  120  to which the linear bearings  122  are slidingly coupled extend perpendicularly to the first surface  112  of the base  110 , the powder container  150  oscillates in a direction perpendicular to the first  112  and second surfaces  114  of the base  110 . 
     Because one rotation of the cam portion  136  of the crankshaft  130  causes the powder container  150  to move from the first position, to the second position, and back to the first position, the powder container  150  oscillates at a frequency equal to a rotational speed of the crankshaft  130  about the crankshaft longitudinal axis  132 . Thus, the frequency of the oscillation of the powder container  150  can be selected by selecting a specific rotational speed of the output shaft  162  of the motor  160 . Furthermore, because the powder container  150  and output shaft  162  of the motor  160  are distantly coupled to each other through rigid components and is not meaningfully affected by any flexing or slipping of components, the oscillation frequency of the powder container  150  is as consistent as the rotational speed of the motor  160 . 
     The powder  190  shown in  FIG.  2    is a spherical-type powder (e.g., particles), but in other implementations, the powder used can be any other shape, such as linear powder (e.g., nanotubes, nanorods) or planar (e.g., nanosheets, nanoplates). 
     The device  100  can further include a housing  170  defining a vacuum chamber  172 , as shown in  FIG.  1 D . Only a portion of the powder container  150  in  FIG.  1 D  is disposed within the vacuum chamber  172 , but in other implementations, any number of components can be disposed within the vacuum chamber as long as the powder container is at least partially disposed within the vacuum chamber. The device  100  also includes a vacuum source  174  in fluid communication with the housing  170 . The vacuum source  174  is configured to cause the vacuum chamber  172  to be a lower pressure than the ambient environment. In some implementations, the vacuum source is capable of causing the vacuum chamber to be a complete vacuum. 
     As shown in  FIG.  1 D , the device  100  can further include a physical vapor deposition source  180  for depositing a coating material  192  toward the first side  152  of the powder container  150  such that the coating material  192  is directed down onto the powder  190  within the powder container  150 . The physical vapor deposition source  180  is disposed within the vacuum chamber  172  of the housing  170  such that the coating material  192  exiting the physical vapor deposition source  180  is not subjected to external factors such as air movement. This allows the coating material  192  to be deposited onto the powder  192  more uniformly. The physical vapor deposition source  180  shown in  FIG.  1 D  is a magnetron sputtering device, but in other implementations, the physical vapor deposition source is a pulsed-laser physical vapor deposition source, an electron-beam physical vapor deposition source, or any other physical vapor deposition source known in the art. The physical vapor deposition source  180  provides the benefits of being able to easily deposit most metals and alloys, avoiding exposure to secondary substances (e.g., hydrogen), and good adherence of coating material onto the powder. However, in other implementations, the device can include any other deposition source known in the art. 
     As the powder container  150  of the device  100  linearly oscillates between the first position and the second position, the powder  190  disposed within the powder container  150  is tossed in a direction from the first position toward the second position. As discussed above, the structure of the device  100  disclosed herein allows for consistent linear oscillation of the powder container  150 , which creates consistent movement of the powder  190  within the powder container  150 . The even deposition of the coating material  192  from the physical vapor deposition source  180  onto the moving powder  190  creates a more uniform coating of the coating material  192  on the powder  190 . 
     The devices and methods disclosed herein can be modified to move at different fixed amplitudes and at different frequencies by making changes to the dimensions of various components and to the rotational speed of the crankshaft. The devices also allow for scaling of the system. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the claims. Accordingly, other implementations are within the scope of the following claims. 
     Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present claims. In the drawings, the same reference numbers are employed for designating the same elements throughout the several figures. A number of examples are provided, nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the disclosure herein. As used in the specification, and in the appended claims, the singular forms “a,” “an,” “the” include plural referents unless the context clearly dictates otherwise. The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. Although the terms “comprising” and “including” have been used herein to describe various implementations, the terms “consisting essentially of” and “consisting of” can be used in place of “comprising” and “including” to provide for more specific implementations and are also disclosed. 
     Disclosed are materials, systems, devices, methods, compositions, and components that can be used for, can be used in conjunction with, can be used in preparation for, or are products of the disclosed methods, systems, and devices. These and other components are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these components are disclosed that while specific reference of each various individual and collective combinations and permutations of these components may not be explicitly disclosed, each is specifically contemplated and described herein. For example, if a device is disclosed and discussed each and every combination and permutation of the device, and the modifications that are possible are specifically contemplated unless specifically indicated to the contrary. Likewise, any subset or combination of these is also specifically contemplated and disclosed. This concept applies to all aspects of this disclosure including, but not limited to, steps in methods using the disclosed systems or devices. Thus, if there are a variety of additional steps that can be performed, it is understood that each of these additional steps can be performed with any specific method steps or combination of method steps of the disclosed methods, and that each such combination or subset of combinations is specifically contemplated and should be considered disclosed.