Patent Publication Number: US-2016228991-A1

Title: Acoustic manipulation and laser processing of particles for repair and manufacture of metallic components

Description:
This application claims benefit of the 5 Feb. 2015 filing date of U.S. provisional patent application No. 62/112,398. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of materials technology, and specifically to laser processing of particles being manipulated with acoustic energy, and more specifically to methods and apparatuses that enable the fabrication and repair of multi-material components through laser processing of metallic and ceramic particles being manipulated with acoustic energy. 
     BACKGROUND OF THE INVENTION 
     Selective laser additive manufacturing includes selective laser melting (SLM) and selective laser sintering (SLS) of powder beds to build a component layer by layer to achieve a net shape or a near net shape. In such processes a powder bed of the component final material or precursor material is deposited on a working surface. Laser energy is selectively directed onto the powder bed following a cross-sectional area shape of the component, thus creating a layer or slice of the component, which then becomes a new working surface for the next layer. The powder bed is conventionally spread over the working surface in a first step, and then a laser defines or “paints” the component sectional area on the bed in the following step. The component is then indexed vertically down with respect to the processing plane in a third step. The three steps are repeated to build a part in a layer-like fashion. 
     Use of mixed bed approaches does not allow for selective placement of different materials to form integrated systems containing multiple materials. Such integrated systems may include, for example, an inner superalloy substrate coated with a diffusion bonded MCrAlY coating which is further bonded to an outer ceramic thermal barrier coating (TBC). Selective placement of different materials would be necessary in order to employ laser additive manufacturing (LAM) techniques to efficiently produce multi-material components containing integrated systems such as the gas turbine airfoil  300  illustrated in  FIG. 17 . 
       FIG. 17  is a cross-sectional view of an exemplary gas turbine airfoil  300  containing a leading edge  302 , a trailing edge  304 , a pressure side  306 , a suction side  308 , a metal substrate  310 , cooling channels  312 , partition walls  314 , turbulators  316 , film cooling exit holes  318 , cooling pins  320 , and trailing edge exit holes  322 . In this example, whereas the metal substrate  310 , partition walls  314 , turbulators  316  and cooling pins  320  are fabricated of a superalloy material, the exterior surfaces of the airfoil substrate  310  are coated with a porous ceramic thermal barrier coating  324 . A metallic bond coat  326  such as an MCrAlY may also be applied between the superalloy substrate  310  and the thermal barrier coating  324  to enhance bonding between the superalloy and ceramic layers and to further protect the superalloy material from external oxidants. 
     The use of LAM techniques to produce a multi-material component such as the airfoil of  FIG. 17  would require not only the selective placement of different materials, but it would also require an ability to selectively apply different processing conditions (i.e., placement and intensity of laser heating) to these different components. This is because selective melting of a superalloy powder to form the metal substrate  310  would generally require different heating conditions than selective sintering of a ceramic powder to form the thermal barrier coating  324 . Another serious complication arises from the need to protect the superalloy powder and resulting metal substrate  310  from reacting with atmospheric oxidants such as oxygen and nitrogen. Especially for a large airfoil  300 , the use of LAM techniques could also require an ability to perform SLM and SLS under atmospheric conditions without jeopardizing the chemical and/or physical properties of the resulting component. 
     Although selective powder placement can be achieved using a plurality of nozzles adapted to deliver powder sprays to a focal point, such techniques using gas-fed filler powder often experience a high percentage of waste of valuable filler material due to scattering of the powder during processing. Powder scattering can also occur when using open powder beds due to pressure generated by plasmas that form during laser processing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  illustrates the use of mutually-opposed ultrasonic transducers to generate an ultrasonic standing wave in which particles can be trapped and steered to nodes separated by a fixed distance; 
         FIG. 2  illustrates the use of two orthogonal sets of mutually-opposed ultrasonic phased-array transducers to generate overlapping ultrasonic standing waves in which particles can be trapped and steered in a three-dimensional space defined in part by the arrangement of the transducers; 
         FIGS. 3A and 3B  illustrate one embodiment of how a separation distance of particles trapped within an ultrasonic standing wave can be altered by simultaneously adjusting the separation distance of mutually-opposed ultrasonic transducers and the wavelength of an ultrasonic standing wave generated between the transducers; 
         FIG. 4  illustrates one embodiment of an apparatus for laser processing of particles being held and manipulated with acoustic energy in which two orthogonal sets of mutually-opposed ultrasonic transducers are situated horizontally; 
         FIG. 5  illustrates one embodiment of an apparatus for laser processing of particles being held and manipulated with acoustic energy in which two orthogonal sets of mutually-opposed ultrasonic transducers are situated vertically; 
         FIG. 6  is a schematic diagram of one embodiment of a method for laser processing of particles being held and manipulated with acoustic energy; 
         FIGS. 7A-7D  illustrate embodiments of a method for laser processing of particles being held and manipulated with acoustic energy; 
         FIGS. 8A-8C  illustrate embodiments of a method for removing a slag layer covering a deposited metal layer; 
         FIG. 9  illustrates one embodiment of a method for laser processing of different sets of particles being independently held and manipulated with acoustic energy to form a multi-material deposit; 
         FIG. 10  illustrates a sectional view of one embodiment of a composite particle containing a metallic outer layer surrounding an inner flux-containing core; 
         FIG. 11  illustrates a sectional view of one embodiment of a composite particle containing a metal alloy and a flux composition and having a glass-like, crystalline, or semi-crystalline structure; 
         FIGS. 12A and 12B  illustrate the use of acoustic energy to separate particles having different sizes and different densities; 
         FIG. 13  illustrates the use of an ultrasonic phased-array transducer to generate and move a single focal point; 
         FIG. 14  illustrates one embodiment of a method for separating particles on a flat surface using acoustic energy; 
         FIG. 15A  illustrates the use of acoustic energy to selectively excite a particle having a natural frequency f n   A , 
         FIG. 15B  illustrates the use of acoustic energy to selectively excite particles having a natural frequency f n   A , causing a selective fluidization of particles in a mixed bed; 
         FIG. 16  illustrates an apparatus capable of both selective particle excitation and particle trapping and steering, according to one embodiment; and 
         FIG. 17  illustrates a sectional view of a gas turbine airfoil. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present inventors recognized that a need exists for methods and apparatuses allowing the manufacture and repair of intricate multi-material components in an automated (additive) fashion through the efficient use of powdered materials. Such methods and apparatuses would ideally enable selective handling, placement, and processing of different powdered materials—while at the same time minimizing the inefficient use of expensive materials that can result from scattering of powdered materials and degradation of sensitive metals through exposure to air. Ideal methods and apparatuses would also avoid the use of powder beds in which an excess amount of expensive and/or air-sensitive powder is used to envelop the working surface. 
     The present inventors propose solving the problems described above by using acoustic trapping and manipulation (steering) of particles to enable the efficient and automated repair and fabrication of three-dimensional components through methods such as selective laser additive manufacturing. 
     It is known that particles and other acoustic discontinuities are subjected to certain forces when exposed to ultrasonic energy. These so-called acoustic forces are generally larger in an ultrasonic standing wave (USW) than in a progressive wave. Furthermore, the physical location of particles may be predictably altered by exposing the particles to an ultrasonic standing wave having a defined resonant frequency. 
       FIG. 1  illustrates a system in which particles  18  within a fluid are bounded by two mutually-opposed ultrasonic transducers  2 , or by a transducer  2  and a mutually-opposed reflector  4 . When the transducer  2  (or set of transducers) is driven so as to excite a resonance frequency of the cavity, a standing wave  6  can be created in the cavity with associated pressure maxima and minima. In order to match the resonance frequency of the cavity, the separation length (L)  12  between the mutually-opposed transducers  2  (or between the transducer  2  and the reflector  4 ) must equal a whole number multiple (N) of either a full wavelength (λ)  8  or half-a-wavelength (λ/2)  10 , as expressed in Equation (1): 
     
       
         
           
             
               
                 
                   L 
                   = 
                   
                     N 
                     × 
                     
                       ( 
                       
                         λ 
                         2 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     where ‘N’ represents a whole number greater than zero. 
     Particles  18  exposed to the standing wave  6  will generally be transported towards pressure nodes  14  within the field by axial forces. Theory predicts that particles will move towards either the nodes  18  or the antinodes  16  of the standing wave depending upon the relative density factor (ratio of the fluid and particle densities), see, e.g., Hill, M. et al., “Ultrasonic Particle Manipulation,” Microfluidic Technologies for Miniaturized Analysis Systems (2007), Chapter 9, pp. 357-83. When the ratio of the particle density to the fluid density is less than 0.4 (and the particle is incompressible) the acoustic force will act towards the pressure antinodes  16 . For density ratios above 0.4, which will be the case for real near-rigid particles, the acoustic radiation force will act towards the pressure node of the standing wave. 
     This basic concept has recently been improved to allow acoustic trapping and manipulation of particles capable of being levitated in a three dimensional space.  FIG. 2  depicts an ultrasonic levitation apparatus  19  employing two sets of mutually-opposed phased-array ultrasonic transducers  20 A- 20 D, which was recently described by Ochiai, Y. et al.,  PLOS One,  2014, 9(5), pp. 1-5, the entire contents of which are incorporated herein by reference. This manipulation system  19  includes two mutually-opposed arrays  20 A- 20 B and  20 C- 20 D that are used to generate standing waves having a common focal point. The position of the focal point may then be digitally controlled with a resolution of 1/16 of the wavelength to alter the position of particles trapped in standing wave nodes to allow manipulation of the particles within the three-dimensional space. 
     For example, as illustrated in  FIG. 2 , three separate sets of levitated particles  22 ,  24  and  26  having a fixed separation distance  28  may be moved from one focal point  30  to another focal point  32  in the three-dimensional space by digitally retuning the phase-array transducers  20 A- 20 D. Importantly, because the wavelengths (and frequencies) of the perpendicular standing waves are fixed, the separation distance  28  for the particles  22 ,  24  and  26  remains constant from one focal point  30  to another  32 . 
     Embodiments of the present disclosure, on the other hand, will allow manipulation of not only the focal point of levitated particles in a three-dimensional space, but will also allow adjustment of the separation distance  28  between the different sets of particles  22 ,  24  and  26 . Such an ability to control the separation distance  28  can be important in some embodiments involving the selective placement and processing of different materials (e.g., metal versus ceramic materials) forming different portions of intricate three-dimensional components. Furthermore, embodiments of the present disclosure will enable an ability to reliably levitate and manipulate metal-containing particles which are generally considered to be difficult, if not impossible, to levitate using acoustic energy. 
       FIGS. 3A and 3B  illustrate one embodiment enabling the separation distance  40  between different sets particles  22 ,  24  and  26  trapped in nodes of an ultrasonic standing wave to be altered.  FIG. 3A  depicts an initial state in which the three sets of particles  22 ,  24  and  26  are trapped/levitated within different nodes  14  of an initial ultrasonic standing wave  6 ′ generated from two mutually-opposed transducers  20 A and  20 B. Unlike the levitation system  19  of  FIG. 2 , the transducers  20 A and  20 B of  FIG. 3A  are moveable transducers connected to a pair of transducer movement actuators  42 A and  42 B. The initial separation distance (d 1 )  40  of the levitated particles  22 ,  24  and  26  may be altered by simultaneously reducing both the separation distance (L 1 )  34  and wavelength  38 A and  38 B of the ultrasound emitted from the transducers  20 A and  20 B—such that at any given moment during the transition the separation distance  40  satisfies Equation (1) above. Wavelength (and frequency) modulation is accomplished by simultaneously controlling the ultrasound generators  36 A and  36 B to maintain a standing wave within the transitioning separation distance (L 1 )  34 . 
       FIG. 3B  depicts the final state in the which the three sets of particles  22 ,  24  and  26  are still trapped/levitated within the corresponding nodes, but because the separation distance (L 2 )  44  and the wavelengths  46 A and  46 B are lower than the corresponding distance (L 1 )  34  and frequencies  38 A,  38 B in  FIG. 3A , the final particle separation distance (d 2 )  47  is now smaller than the initial particle separation distance (d 1 )  40 . In the non-limiting illustration of  FIGS. 3A and 3B , the position of the transducers  20 A and  20 B is altered to maintain a common focal point  30  such that the set of particles  24  maintains its original position while the sets  22  and  26  move inward  41 A,  41 B to reduce the separation distance. In other embodiments an initial focal point may be altered such that the separation distance and position of all levitated particles may be changed. 
       FIG. 4  illustrates one embodiment of an acoustic levitation laser processing apparatus  50  having a horizontal orientation.  FIG. 5  illustrates a related embodiment of an acoustic levitation laser processing apparatus  86  having a vertical orientation. 
     The non-limiting apparatus  50  of  FIG. 4  includes two sets of mutually-opposed phased-array ultrasonic transducers  20 A- 20 B and  20 C- 20 D arranged in a horizontally-oriented square-shaped work area further containing a moveable support structure  51  comprising a working surface  54  attached to a support plate  56  connected to a platen  58  that is in acoustic communication with an additional transducer  60 . In the non-limiting embodiment of  FIG. 4  the transducer  60  is connected to a component movement actuator  64  via a moveable piston  62 . The ultrasonic phased-array transducers  20 A,  20 B,  20 C and  20 D are each connected to independently-operable transducer movement actuators  42 A,  42 B,  52 A and  52 B respectively which, as explained above, allow respective distances (L) between the mutually-opposed transducers to be adjusted. Although not shown in  FIG. 4 , each ultrasonic phase-array transducer  20 A,  20 B,  20 C and  20 D is further controlled by an ultrasonic generator (e.g.,  36 A or  36 B in  FIG. 3A ) allowing synchronized modulation of standing wave wavelengths (frequencies). 
     The size, dimensions, placement and number of ultrasonic transducers are not confined to the illustrations in  FIGS. 4 and 5 . In other embodiments these parameters may be altered significantly. In some embodiments, for example, the ultrasonic phased array transducers may be curved to form concave transducers, or may be arranged into a continuously circular or spherical array that surrounds the working object being fabricated or repaired. Acoustic transducers of the present disclosure may be fabricated using materials and techniques well known in the art for producing acoustic energy. 
     The apparatus  50  of  FIG. 4  also contains additional components enabling particle handling and laser processing. These components include a particle handling device  66  adapted to dispense particles into any node located within an ultrasonic standing wave generated between the mutually-opposed transducers, and/or to withdraw particles from any node located within a standing wave. In some embodiments the apparatus may include at least one particle delivery device  66  and optionally at least one particle withdrawal device  66 . In some embodiments the particle delivery device  66  may be in the form of an acoustically-reflective or non-reflective pipette device capable of precisely dispensing particles into individual nodes at a sufficiently low velocity to allow capture (trapping) and levitation of the particles within the nodes. In some embodiments the particle withdrawal device  66  may be in the form of an acoustically-reflective or non-reflective pipette device capable of precisely withdrawing particles from individual nodes at sufficiently low velocity to allow selective withdrawal of sets of levitated particles without disrupting particles trapped in nearby nodes. In some embodiments the particle withdrawal device  66  precisely withdraws particles by drawing a slight vacuum on levitated particles located in a particular node. 
     The particle handling device  66  is also adapted to be independently moveable such that particles may be delivered and/or withdrawn to or from any location within the work area of the apparatus  50 . To enable movement the particle handling device  66  is attached to a handling device movement actuator  68 . 
     The non-limiting apparatus  50  of  FIG. 4  also contains a first and second energy beam source  70 ,  74  adapted to be independently movable such that a trajectory of an energy beam transmitted by the energy beam source can be directed to a target surface on the working surface  54 . The term “energy beam” is used herein in a general sense to describe a narrow, propagating stream of particles or packets of energy. An energy beam as used in this disclosure may include a light beam, a laser beam, a particle beam, a charged-particle beam, a molecular beam, etc., which upon contact with a material imparts kinetic (thermal) energy to the material. 
     To enable movement, the first and second energy beam sources  70  and  74  are attached to energy beam source movement actuators  72  and  76 . The first and second energy beam sources  70 ,  74  may be a laser beam, an electron beam, a plasma beam, one or more circular laser beams, a scanned laser beam (scanned one, two or three dimensionally), an integrated laser beam, a pulsed (versus continuous wave) laser beam, etc. The use of a rectangular shaped beam may be advantageous for embodiments having a relatively large volume of particles to be heated. In such cases the first and/or second energy beam source  70 ,  74  may be a diode laser beam having a generally rectangular cross-sectional shape, although other known types of energy beams may also be used. 
     In some embodiments the first and second energy beam source  70 ,  74  may be in the form of lower power lasers (e.g., 503 nm and 1.06 μm Nd:YAG lasers) and/or higher power lasers (e.g., 1.06 μm ytterbium fiber, 5.4 μm CO and 10.6 μm CO 2  lasers). In some embodiments the intensity and shape of an energy beam may be precisely controlled by employing laser scanning (rastering) optics to form a heated area having a precisely defined size and shape to accommodate the shape of the sets of levitated particles being laser processed. 
     The components of the apparatus  50  are independently operable and may be directed by a controller  80  based in part upon optical signals inputted  82  from an optical instrument  78  to produce output  84  to the components. 
       FIG. 5  illustrates a related embodiment of an acoustic levitation laser processing apparatus  86  have a vertical orientation. This apparatus  86  contains all of the same components as the apparatus  50  of  FIG. 4 , but the orientation of the working area defined by the mutually-opposed phased-array ultrasonic transducers  20 A- 20 B and  20 C- 20 D (transducer  20 D is not shown) are reversed such that the transducers  20 A and  20 B are arranged vertically and the particle handling device  66  is arranged horizontally. The embodiment of  FIG. 5  can be useful in certain manufacturing and repair scenarios in which it is advantageous to dispose a component being fabricated or repaired in a horizontal orientation. 
       FIG. 6  is a schematic diagram of one embodiment of a method  100  for laser processing of particles being held and manipulated with acoustic energy using an apparatus such as those illustrated in  FIGS. 4 and 5 . In this method, step  105  involves generating at least one ultrasonic standing wave between mutually-opposed ultrasonic phased-array transducers having an adjustable separation distance. Step  110  involves dispensing metal-containing particles into a first node located in the ultrasonic standing wave. Optional step  115  involves dispensing ceramic-containing particles into a second node located adjacent to the first node holding the metal-containing particles. Step  120  involves positioning a working surface below or adjacent to the first node holding the metal-containing particles and optionally below or adjacent to the second node holding the optional ceramic-containing particles. Optional step  125  involves adjusting a distance between the first node holding the metal-containing particles and the second node holding the ceramic-containing particles to match a corresponding distance in a component being fabricated. 
     Step  130  involves irradiating the metal-containing particles with a first energy source such that the metal-containing particles form a melt pool in contact with the working surface, and optionally irradiating the optional ceramic-containing particles with a second energy source such that the ceramic-containing particles are heated in contact with the working surface. Step  135  involves allowing the melt pool to cool and solidify into a metallic deposit bonded to the working surface. Optional step  140  involves breaking up and removing an optional slag layer covering the metallic deposit to produce a deposited metal layer bonded to the working surface. 
       FIGS. 7A-7D and 8A-8C  illustrate the processing steps of  FIG. 6 . As shown in  FIG. 7A , steps  105 ,  110 ,  115  and  120  involve generating an ultrasonic standing wave  6  between mutually-opposed ultrasonic phased-array transducers  20 A and  20 B, dispensing metal-containing particles  154  into a first node  155  located in the ultrasonic standing wave, optionally dispensing ceramic-containing particles  156  into a second node  157  located adjacent to the first node  155  holding the metal-containing particles, and positioning  120  a working surface  159  below the first and second nodes  155 ,  157 .  FIG. 7A  also shows an additional step of dispensing different metal-containing particles  152  into a third node  153  of the ultrasonic standing wave. 
     In some embodiments involving the dispensing of three different types of particles, for example, the metal-containing particles  152  may contain a superalloy metal, or elements of a superalloy metal, which ultimately form a superalloy substrate  160  of a component  158  being fabricated by the method  100 —while the metal-containing particles  154  may contain a bond coat metal such as a MCrAlY, and the ceramic-containing particles  156  may contain a yttrium-stabilized zirconia (YSZ) which ultimately form a bond coat layer  162  and thermal barrier coating (TBC)  164  respectively of the component being fabricated. 
     The term “superalloy” is used herein as it is commonly used in the art, i.e., a highly corrosion and oxidation resistant alloy that exhibits excellent mechanical strength and resistance to creep at high temperatures. Superalloys typically include a high nickel or cobalt content. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g. IN 100, IN 700, IN 713, IN 738, IN 792, IN 939), Rene alloys (e.g. Rene N5, Rene 41, Rene 80, Rene 108, Rene 142, Rene 220), Haynes alloys (282), Mar M, CM 247, CM 247 LC, C263, 718, X-750, ECY 768, 282, X45, PWA 1480, PWA 1483, PWA 1484, CMSX single crystal alloys (e.g., CMSX-4, CMSX-8, CMSX-10), GTD 111, GTD 222, MGA 1400, MGA 2400, PSM 116, Mar-M-200, Udimet 600, Udimet 500 and titanium aluminide. The terms “metal,” “metallic material,” “alloy,” and “metal alloy” are used herein in a general sense to describe pure metals, semi-pure metals and metal alloys. 
       FIG. 7B  illustrates the optional step  125  of adjusting a distance between the first node  155  holding the metal-containing particles  154  and the second node  157  holding the ceramic-containing particles to match a corresponding distance of or in a component  158  being fabricated.  FIGS. 7B and 7C  also illustrate the step  130  of irradiating the metal-containing particles  152 ,  154  with a first energy beam  166  to form a melt pool  170 ,  172  in contact with the working surface  159 , and irradiating the ceramic-containing particles  156  with a second energy beam  168  such that the ceramic-containing particles are heated (sintered)  174  in contact with the working surface  159 . 
       FIG. 7D  illustrates the result of step  135  in which the melt pools  170 ,  172  are allowed to cool and solidify into metallic deposits  176 ,  182  bonded to the working surface  159 . Cooling of the melt pools  170 ,  172  may also result in the formation of a slag layer  178  covering the metallic deposits  176 ,  182 , and cooling of the heating ceramic material  174  results in the formation of a deposited TBC layer  180  bonded to the working surface  159 . 
       FIG. 8A  illustrates the step  140  of breaking up  186  the slag layer  178 . In some embodiments, such as the illustration of  FIG. 8A , the slag layer  178  is broken up  186  by applying ultrasonic energy to the component  158  via a transducer  60  in acoustic communication with the component  158 . The breaking up  186  process may be further enhanced by positioning the breaking up slag layer  178  in contact with the ultrasonic standing wave  6  and/or by applying an energy beam  167  to the slag layer  178 . The breaking up  186  process may be directed using a controller  80 , based upon input from an optical instrument  78 , in which a wavelength (frequency) and/or intensity of ultrasonic energy transmitted from the transducer  60  may be altered through an ultrasonic wave generator  184 . 
     In some embodiments the transducer  60  may used to create an ultrasonic standing wave between the working surface  159  and an ultrasonic phased-array transducer positioned opposite the working surface  159 . Some such embodiments, for example, employ a modified version of the apparatus of  FIG. 5  in which the working surface  54  (attached to the horizontally-disposed moveable support structure  51 ) and an ultrasonic phase-array transducer  20  are mutually opposed such that an ultrasonic standing wave may be created allowing particles trapped with nodes to be shifted towards the working surface  54  by modulating the phase of the ultrasonic standing wave. In other similar embodiments the working surface may serve as a reflector to maintain an ultrasonic standing wave generated by an opposed ultrasonic phased-array transducer, wherein the phase of the standing wave may be modulated to shift trapped particles towards the working surface  54 . 
       FIG. 8B  illustrates the removal step  140  in which broken up slag layer  188  present on the deposited surface  196  may be dislodged using gas emitted from a gas-flushing device  194  (depicted in  FIG. 8B  as a pipette). Slag particles  190  that become levitated in nodes of the ultrasonic standing wave may also be withdrawn from the standing wave using a particle withdrawal device  192  (employing, e.g., a vacuum) capable of precisely withdrawing particles from individual nodes. In some embodiments the particle withdrawal device  192  may be in the form of an acoustically-reflective or non-reflective pipette device. 
       FIG. 8C  illustrates a resulting component  158  including a newly deposited slice  196  containing a superalloy substrate layer  160 , a bond coat layer  162  and a thermal barrier coating layer  164  whose separation and placement was controlled by the separation and placement of the levitated particles  152 ,  154  and  156  in relation to the positioning of the working surface  159 . 
       FIG. 9  illustrates one embodiment of a method for continuous laser processing of different sets of particles being independently held and manipulated with acoustic energy to form a multi-material deposit. In this non-limiting illustration, a series of powder deliver devices  198 A- 198 F are used to dispense three sets of superalloy-containing particle sets  152 ′,  152 ″ and  152 ′″, one set of bond contain metal-containing particles  154 , and two sets of TBC ceramic-containing particle sets  156 ′ and  156 ″ into multiple groups of linearly-situated situated nodes defined by ultrasonic standing waves  6  and  7 . Laser processing using at least two different laser sources  166  (other sources not shown) leads to the formation of a superalloy-containing melt pool  170 , a bond coat metal-containing melt pool  172 , and a sintering ceramic deposit  174 —all in contact with a working surface  54  which is continuously moved  199  such that a continuous layer of deposited superalloy  176 , bond coat  182 , and TBC  180  is bonded to the working surface  54 . In some embodiments a slag layer  178  is also formed and covers the metallic deposits  176  and  182 . After depositing a new slice  196  of component  158  under fabrication or repair, the slag layer  178  may be removed as explained above. 
     In some embodiments the working surface  54  in a process of  FIG. 9  may be an upper surface of a multi-material component  158 , such that the resulting deposited layer constitutes a slice  196  of a component being fabricated in an additive fashion. In other embodiments involving bulk production of metals, or involving the repair of hollow components, the working surface  54  may be in the form of fugitive support material. “Fugitive” means removable after formation of the cladding layer, for example, by direct (physical removal), by a mechanical process, by draining, by fluid flushing, by chemical leaching and/or by any other known process capable of removing the fugitive support material from its position. Examples of fugitive support materials include powders (e.g., metal, glass, ceramic, fiber powders), solid objects (e.g., metal, glass, ceramic, composite, plastic, resinous structures, graphite, dry ice), woolen materials (e.g., steel wool, aluminum oxide wool, zirconia wool) and foamed materials (e.g., polymer foams, high-temperature spray foams) to name a few. Any material or structure capable of providing support and then being removable after the formation of a metal and/or ceramic deposit may serve as the fugitive support material. 
     Another aspect of the present disclosure relates to embodiments which will enable the levitation and manipulation of metal-containing particles which are generally considered to be difficult, if not impossible, to levitate using acoustic energy. Whereas it is generally known that levitation of metal particles (such as traditionally-employed filler materials) can be very challenging due to the high density of such particles, the present invention will address this limitation by employing composite particles containing a metal alloy and a flux composition. 
       FIG. 10  illustrates a cross section of one embodiment of a composite material  88  in the form of coated particles comprising a flux-containing core  90  surrounded (coated) by a metallic layer  91 . In this non-limiting illustration, the metallic layer  91  acts as a physical barrier that resists adsorption and permeation by atmospheric agents such as oxygen, nitrogen and moisture. In some embodiments the metallic layer  91  may also contain at least one metal (such as nickel) that is chemically resistant to atmospheric agents including oxygen and nitrogen. 
     The metallic layer  91  may contain a pure metal such as nickel, a metal alloy such as a superalloy, or combinations of different metals and alloys. Superalloys may contain mixtures of base metals (e.g., Ni, Fe and Co) along with other metals, metalloids and nonmetals such as chromium, molybdenum, tungsten, tantalum, aluminum, titanium, zirconium, niobium, rhenium, yttrium, vanadium, carbon, boron, and hafnium, to name a few. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g. IN 100, IN 700, IN 713, IN 738, IN 792, IN 939), Rene alloys (e.g. Rene N5, Rene 41, Rene 80, Rene 108, Rene 142, Rene 220), Haynes alloys (282), Mar M, CM 247, CM 247 LC, C263, 718, X-750, ECY 768, 282, X45, PWA 1480, PWA 1483, PWA 1484, CMSX single crystal alloys (e.g., CMSX-4, CMSX-8, CMSX-10), GTD 111, GTD 222, MGA 1400, MGA 2400, PSM 116, Mar-M-200, Udimet 600, Udimet 500 and titanium aluminide. 
     The metallic layer  91  may contain a metal content that matches the composition of a metallic deposit to be formed through melt processing, or it may contain a single metal or a subset of metals contained in the metallic deposit. Thus, as explained below in greater detail, a laser powder deposition using the composite particle  88  of  FIG. 10  may be used to form a melt pool having a metal composition identical to the metallic layer  176 ,  182 , or to form a melt pool whose metal composition is supplemented using at least one additional metal filler or metal-containing flux material. 
     The metallic layer  91  may be formed of a single metal layer having a homogeneous composition or may be formed of a single metal layer that is compositionally graded. In some embodiments, for instance, the metallic layer  91  of  FIG. 10  may be graded such that the outer surface contains a higher proportion of nickel than the inner surface of the metallic layer  91 —providing greater protection for reactive metals (e.g., Al, Ti and Fe) contained in the metallic layer  91 . Upon melting, the metallic components of a compositionally-graded metallic layer  91  may then undergo mixing such that a resulting metal deposit is a homogeneous composition having a desired alloy content. The metallic layer  91  may also be formed of more than one metal layer having the same or different metallic compositions. By illustration, in some embodiments the composite particle  88  of  FIG. 10  comprises a flux-containing core  90  surrounded (coated) by an intermediate superalloy layer which is surrounded (coated) by an outer layer of nickel. 
     As explained below in greater detail, the flux-containing core  90  comprises a flux composition providing at least one protective function during melt processing of composite particles. Flux compositions may include one or more inorganic compound such as a metal oxide, a metal halide, a metal oxometallate, a metal carbonate, or mixtures thereof, and may also include one or more organic compound such as a high-molecular weight hydrocarbon, a carbohydrate, a natural or synthetic oil, an organic reducing agent, a carboxylic acid or polyacid, a carboxylic acid salt or derivative, an amine, an alcohol, a natural or synthetic resin, or mixtures of such compounds, to name a few. 
     In some embodiments the composite particle  88  may also include an additional outer-protective layer (not shown) containing an inorganic protective material, which surrounds (coats) the metallic layer  91 . Such inorganic protective materials may include metal oxides like alumina (Al 2 O 3 ) and silica (SiO 2 ) that can protect the metallic layer  91  during storage and may also act as protective flux materials during laser processing. It is most useful if such inorganic outer protective layer is introduced as a smooth (e.g. glass-like) coating on the particles such that the surfaces are not hygroscopic. 
     Composite materials, such as the composite material  88  of  FIG. 10 , are expected to reduce physical and chemical defects in the corresponding melt processed materials—because the metallic layer  91  can contain chemically-resistant metals such as nickel which are inert to atmospheric reactants, and can also be surface processed to resist adsorption of atmospheric moisture. 
     Metal-coated composite materials such as the embodiment of  FIG. 10  may be prepared using a variety of different methods depending upon the desired composition, size and geometry. Such methods include hydrometallurgical processing, physical and chemical vapor deposition, electroless plating, and gas-phase coating. 
     In some non-limiting processes a flux-containing particulate may be initially produced by agglomerating individual particles containing a flux composition using organic or inorganic binders, and then milling the resulting agglomerates to form a flux-binder mixture which is then cured to form flux-containing particles. The flux-containing particles may then be screened to a desired particle size, size range, or geometry required for a particular application. After the flux-containing particles are sized, a metal composition is deposited thereon to form coated composite materials such as the composite particle  88  of  FIG. 10 . 
     For example, the flux-containing particles may be clad with nickel using hydrometallurgical processing—in which a dissolved nickel complex is precipitated onto the flux-containing particles by reduction with hydrogen optionally at elevated temperature and pressure. After the nickel is precipitated onto the flux-containing particles, the resulting metal-coated composite particles may be washed and dried. Additional metal coating and/or alloying may also occur in order to produce multi-layered or graded coatings, or to modify the composition of the metallic layer, using processes such as chemical vapor deposition (CVD). 
     Physical vapor deposition (PVD) may also be used to form metal-coated composite materials such as the composite particle  88  of  FIG. 10 . In such processes a metallic material is vaporized and transported in the form of a vapor through a vacuum or low pressure gaseous environment (or plasma) to previously-sized flux-containing particles where the metallic material condenses. PVD processes may be used to deposit films of metal elements or alloys. For example, PVD may be used to coat flux-containing particles that are suspended in a fluidized bed by a fluidization gas. The PVD may be non-directed or directed which can provide metal-coated composite materials having defined and repeatable coatings. Directed vapor deposition (DVD) may also be used in combination with electron beam-based (or ion beam-based aka sputter deposition) evaporation techniques to improve the yield and/or quality of metal-coated composite materials suitable for melt processing. PVD can be used to generate single-layer metallic coatings as well as multi-layer and compositionally-graded coatings. 
     Electroless plating may also be used to produce metal-coated composite materials such as the composite particle  88  of  FIG. 10 . For example, an electroless plating solution containing a metal ion (such as nickel ion) and a soluble reducing agent (such as a hypophosphorate salt) may be mixed with flux-containing particles to form a metallic layer covering the flux-containing particles. Gas-phase coating may also be used by preparing a mixture of flux-containing particles in a flowable medium which is converted into an aerosol containing droplets of the flux-containing particles suspended in a carrier gas. The liquid contained in the aerosol may optionally be removed and the resulting gas-dispersed particles may optionally be dried by heating. The resulting gas-phase flux-containing particles may then be coated using, for example, physical vapor deposition (PVD) or chemical vapor deposition (CVD) with a reactive gas containing a metal such as nickel or a metal alloy. 
     Metal-coated composite materials, such as the composite particle  88  of  FIG. 10 , can be produced in various sizes ranging, for example, from about 1 to about 1000 micrometers in average diameter. In some embodiments the sizes range from about 5 to about 500 micrometers, or from about 20 to about 100 micrometers, in average diameter. Optimum ranges of size may vary according to application. 
     Importantly, both the size and the composition of composite materials suitable for acoustic handling and laser processing will be optimized to reduce density relative to traditional filler materials, while maintaining a large enough cross section (e.g., diameter) to maximize the acoustic forces applied to composite materials in contact with a standing ultrasonic wave. Such composite materials are formed such that a flux-to-metal volume ratio ranges from about 2:98 to about 98:2. Because flux compositions are generally less dense than metal alloys, higher flux-to-metal volume ratios tend to produce composite materials having lower overall density—which in some embodiments may be advantageous to ensure adequate acoustic trapping and manipulation. In some embodiments the flux-to-metal volume ratio ranges from about 40:60 to about 95:5, or from about 50:50 to about 85:15. In other embodiments the flux-to-metal volume ratio ranges from about 55:45 to about 90:10, or is about 65:35. 
       FIG. 11  illustrates another embodiment of a composite material  92  in the form of fused particles comprising a metal alloy  93  and a flux composition  94 , wherein the metal alloy  93  and the flux composition  94  may be randomly distributed and randomly oriented within a fused composite lattice  95 , or may be in a crystalline or semi-crystalline form. In the non-limiting illustration of  FIG. 11 , the fused structure of the composite material  92  acts as a physical or chemical barrier that resists adsorption and permeation by atmospheric agents such as oxygen, nitrogen and moisture. For example, the fused structure may be in the form of conglomerate flux/metal glass particles which exhibit high resistance to moisture adsorption and low reactivity with atmospheric reactants—unlike merely agglomerated flux/metal materials which are often very prone to moisture adsorption and air reactivity due to their relatively high surface area and porosity. 
     The metal or alloy  93  in the fused composite material  92  of  FIG. 11  may be a pure metal such as nickel or may be metal alloys such as superalloys based on nickel, iron and cobalt, optionally containing other metals, metalloids and nonmetals as described above. The metallic portion of the composite material  92  may be in the form of equivalent metallic particles having the same composition, which are evenly distributed throughout the fused particles, or may in the form of non-equivalent metallic particles having different compositions. In one example of the later embodiments, the fused composite material  92  may contain non-equivalent metallic particles having different compositions which, when melted and mixed together into a melt pool, can form a superalloy metal deposit. 
     As explained below in greater detail, the flux composition  94  comprises a flux material providing at least one protective function during melt processing of the composite material  92 . Flux compositions may include one or more inorganic compound such as a metal oxide, a metal halide, a metal oxometallate, a metal carbonate, or mixtures thereof, and may also include one or more organic compound such as a high-molecular weight hydrocarbon, a carbohydrate, a natural or synthetic oil, an organic reducing agent, a carboxylic acid or polyacid, a carboxylic acid salt or derivative, an amine, an alcohol, a natural or synthetic resin, or mixtures of such compounds, to name a few. 
     Fused composite materials, such as the composite material  92  of  FIG. 11 , are expected to reduce physical and chemical defects in the corresponding melt-processed materials—because the fused structure is in the form of a glass-like, crystalline, or semi-crystalline composite lattice that is highly resistant to both moisture adsorption and reactivity with atmospheric agents such as oxygen and nitrogen. 
     Fused composite materials such as the embodiment of  FIG. 11  may be prepared by dry mixing the metal alloy  93  and the flux composition  94  together and then fusing or melting the resulting conglomerate mixture into a liquid state using, for example, a high-temperature furnace. The resulting molten material is then allowed to cool and solidify into a fused conglomerate glass, crystalline or non-crystalline form which may then be crushed or ground into different particle sizes and shapes. 
     Fused composite materials, such as the composite particle  92  of  FIG. 11 , can be produced in various sizes ranging, for example, from about 1 to about 1000 micrometers in average diameter. In some embodiments the sizes range from about 5 to about 500 micrometers, or from about 20 to about 100 micrometers, in average diameter. 
     Importantly, both the size and the composition of fused composite materials suitable for acoustic handling and laser processing will be optimized to reduce density relative to traditional filler materials while maintaining a large enough cross section (i.e., diameter) to maximize the acoustic forces applied to composite materials in contact with a standing ultrasonic wave. Such fused composite materials are formed such that a flux-to-metal volume ratio ranges from about 2:98 to about 98:2. Because flux compositions are generally less dense than metal alloys, higher flux-to-metal volume ratios tend to produce composite materials having lower overall density—which in some embodiments may be advantageous to ensure adequate acoustic trapping and manipulation. In some embodiments the flux-to-metal volume ratio ranges from about 40:60 to about 95:5, or from about 50:50 to about 85:15. In other embodiments the flux-to-metal volume ratio ranges from about 55:45 to about 90:10, or is about 65:35. 
     As explained and illustrated above, composite materials of the present disclosure (e.g., particles  88  and  92 ) contain both a metal portion and a flux composition which provides at least one protective function during melt processing. The flux composition and the resulting slag layer  178  (see  FIGS. 7D and 9 ) can provide a number of beneficial functions that can improve the chemical and/or mechanical properties of deposited metals formed by melt processing of the composite materials described herein. 
     First, the flux composition and the resulting slag layer  178  can both function to shield both the region of the melt pool  170 ,  172  and the solidified (but still hot) melt-processed layer  176 ,  182  from the atmosphere. The slag floats to the surface to separate the molten or hot metal from the atmosphere, and the flux composition may be formulated to produce at least one shielding agent which generates at least one shielding gas upon exposure to laser photons or heating. In some embodiments shielding gases may coalesce into a gaseous envelope covering the melt pool  170 ,  172 . Shielding agents include metal carbonates such as calcium carbonate (CaCO 3 ), aluminum carbonate (Al 2 (CO 3 ) 3 ), dawsonite (NaAl(CO 3 )(OH) 2 ), dolomite (CaMg(CO 3 ) 2 ), magnesium carbonate (MgCO 3 ), manganese carbonate (MnCO 3 ), cobalt carbonate (CoCO 3 ), nickel carbonate (NiCO 3 ), lanthanum carbonate (La 2 (CO 3 ) 3 ) and other agents known to form shielding and/or reducing gases (e.g., CO, CO 2 , H 2 ). The presence of the slag layer  178  and the optional shielding gas can avoid or minimize the need to conduct melt processing in the presence of inert gases (such as helium and argon) or within a sealed chamber (e.g., vacuum chamber or inert gas chamber) or using other specialized devices for excluding air. 
     Second, the slag layer  178  can act as an insulation layer that allows the resulting melt-processed layer  176 ,  182  to cool slowly and evenly, thereby reducing residual stresses that can contribute to post weld cracking, reheat or strain age cracking, and secondary reaction zone formation. Such slag blanketing over and adjacent to the deposited metal layer  176 ,  182  can further enhance heat conduction towards an underlying component, which in some embodiments can promote directional solidification to form elongated (uniaxial) grains in the melt-processed layer  176 ,  182 . 
     Third, the slag layer  178  can help to shape and support the melt pool  170 ,  172  to keep them close to a desired height/width ratio (e.g., a ⅓ height/width ratio). This shape control and support further reduces solidification stresses that could otherwise be imparted to the melt-processed layer  176 ,  182 . Along with shape and support, the slag layer  178  can also be produced from a flux composition that is formulated to enhance surface smoothness of the melt-processed layer  176 ,  182 . 
     Fourth, the flux composition and the slag layer  178  can provide a cleansing effect for removing trace impurities that contribute to inferior properties. Such cleaning may include deoxidation of the melt pool  170 ,  172 . Some flux compositions may also be formulated to contain at least one scavenging agent capable of removing unwanted impurities from the melt pool. Scavenging agents include metal oxides and fluorides [such as calcium oxide (CaO), calcium fluoride (CaF 2 ), iron oxide (FeO), magnesium oxide (MgO), manganese oxides (MnO, MnO 2 ), niobium oxides (NbO, NbO 2 , Nb 2 O 5 ), titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ), and other agents known to react with detrimental elements such as sulfur and phosphorous and elements known to produce low melting point eutectics] to form low-density byproducts expected to “float” into a resulting slag layer  178 . 
     Fifth, the flux composition and the slag layer  178  can increase the proportion of thermal energy delivered to the working surface  54 ,  159  (see  FIGS. 4-5, 7A and 9 ). This increase in heat absorption may occur due to the composition and/or form of the flux composition. In terms of composition the flux may be formulated to contain at least one compound capable of absorbing laser energy at the wavelength of a laser energy beam used as the energy beam  166 . Increasing the proportion of a laser absorptive compound causes a corresponding increase in the amount of laser energy (as heat) applied to the particles. This increase in heat absorption can provide greater versatility by allowing the use of smaller and/or lower power laser sources that may be capable of producing a relatively shallower melt pool  170 ,  172 . In some cases the laser absorptive compound could also be an exothermic compound that decomposes upon laser irradiation to release additional heat. An example of such composite exothermic particulate would be particles with a CO 2  generating core (e.g. including a carbonate) surrounded by aluminum and finally coated with nickel. Nickel coated aluminum powder is in fact proposed as a fuel for propulsion on Mars where CO 2  is plentiful and which provides for such exothermic reaction. 
     Additionally, the flux composition may be formulated to compensate for loss of volatilized or reacted elements during processing or to actively contribute elements to the melt-processed layer  176 ,  182  that are not otherwise contained in metal alloy  91 ,  93 . Such vectoring agents include titanium, zirconium, boron and aluminum containing compounds and materials such as titanium alloys (Ti), titanium oxide (TiO 2 ), titanite (CaTiSiO 5 ), aluminum alloys (Al), aluminum carbonate (Al 2 (CO 3 ) 3 ), dawsonite (NaAl(CO 3 )(OH) 2 ), borate minerals (e.g., kernite, borax, ulexite, colemanite), nickel titanium alloys (e.g., Nitinol), niobium oxides (NbO, NbO 2 , Nb 2 O 5 ) and other metal-containing compounds and materials used to supplement molten alloys with elements. Certain oxometallates as described below can also be useful as vectoring agents. 
     In some embodiments the metal-containing particles  152 ,  154  may not be composite particles but may instead be typical metallic filler materials known in the relevant art. Furthermore, in some embodiments the ceramic-containing particles  156  may also contain a flux composition. 
     Flux compositions contained in particles of the present disclosure may include one or more inorganic compound selected from metal oxides, metal halides, metal oxometallates and metal carbonates. Such compounds may function as (i) optically transmissive vehicles; (ii) viscosity/fluidity enhancers; (iii) shielding agents; (iv) scavenging agents; and/or (v) vectoring agents. 
     Suitable metal oxides include compounds such as Li 2 O, BeO, B 2 O 3 , B 5 O, MgO, Al 2 O 3 , SiO 2 , CaO, Sc 2 O 3 , TiO, TiO 2 , Ti 2 O 3 , VO, V 2 O 3 , V 2 O 4 , V 2 O 5 , Cr 2 O 3 , CrO 3 , MnO, MnO 2 , Mn 2 O 3 , Mn 3 O 4 , FeO, Fe 2 O 3 , Fe 3 O 4 , CoO, Co 3 O 4 , NiO, Ni 2 O 3 , Cu 2 O, CuO, ZnO, Ga 2 O 3 , GeO 2 , As 2 O 3 , Rb 2 O, SrO, Y 2 O 3 , ZrO 2 , NiO, NiO 2 , Ni 2 O 5 , MoO 3 , MoO 2 , RuO 2 , Rh 2 O 3 , RhO 2 , PdO, Ag 2 O, CdO, In 2 O 3 , SnO, SnO 2 , Sb 2 O 3 , TeO 2 , TeO 3 , Cs 2 O, BaO, HfO 2 , Ta 2 O 5 , WO 2 , WO 3 , ReO 3 , Re 2 O 7 , PtO 2 , Au 2 O 3 , La 2 O 3 , CeO 2 , Ce 2 O 3 , and mixtures thereof, to name a few. 
     Suitable metal halides include compounds such as LiF, LiCl, LiBr, LiI, Li 2 NiBr 4 , Li 2 CuCl 4 , LiAsF 6 , LiPF 6 , LiAlCl 4 , LiGaCl 4 , Li 2 PdCl 4 , NaF, NaCl, NaBr, Na 3 AlF 6 , NaSbF 6 , NaAsF 6 , NaAuBr 4 , NaAICl 4 , Na 2 PdCl 4 , Na 2 PtCl 4 , MgF 2 , MgCl 2 , MgBr 2 , AlF 3 , KCl, KF, KBr, K 2 RuCl 5 , K 2 IrCl 6 , K 2 PtCl 6 , K 2 PtCl 6 , K 2 ReCl 6 , K 3 RhCl 6 , KSbF 6 , KAsF 6 , K 2 NiF 6 , K 2 TiF 6 , K 2 ZrF 6 , K 2 PtI 6 , KAuBr 4 , K 2 PdBr 4 , K 2 PdCl 4 , CaF 2 , CaF, CaBr 2 , CaCl 2 , CaI 2 , ScBr 3 , ScCl 3 , ScF 3 , ScI 3 , TiF 3 , VCl 2 , VCl 3 , CrCl 3 , CrBr 3 , CrCl 2 , CrF 2 , MnCl 2 , MnBr 2 , MnF 2 , MnF 3 , MnI 2 , FeBr 2 , FeBr 3 , FeCl 2 , FeCl 3 , FeI 2 , CoBr 2 , CoCl 2 , CoF 3 , CoF 2 , CoI 2 , NiBr 2 , NiCl 2 , NiF 2 , NiI 2 , CuBr, CuBr 2 , CuCl, CuCl 2 , CuF 2 , CuI, ZnF 2 , ZnBr 2 , ZnCl 2 , ZnI 2 , GaBr 3 , Ga 2 Cl 4 , GaCl 3 , GaF 3 , GaI 3 , GaBr 2 , GeBr 2 , GeI 2 , GeI 4 , RbBr, RbCl, RbF, RbI, SrBr 2 , SrCl 2 , SrF 2 , SrI 2 , YCl 3 , YF 3 , YI 3 , YBr 3 , ZrBr 4 , ZrCl 4 , ZrI 2 , YBr, ZrBr 4 , ZrCl 4 , ZrF 4 , ZrI 4 , NbCl 5 , NbF 5 , MoCl 3 , MoCl 5 , RuI 3 , RhCl 3 , PdBr 2 , PdCl 2 , PdI 2 , AgCl, AgF, AgF 2 , AgSbF 6 , AgI, CdBr 2 , CdCl 2 , CdI 2 , InBr, InBr 3 , InCl, InCl 2 , InCl 3 , InF 3 , InI, InI 3 , SnBr 2 , SnCl 2 , SnI 2 , SnI 4 , SnCl 3 , SbF 3 , SbI 3 , CsBr, CsCl, CsF, CsI, BaCl 2 , BaF 2 , BaI 2 , BaCoF 4 , BaNiF 4 , HfCl 4 , HfF 4 , TaCl 6 , TaF 5 , WCl 4 , WCl 6 , ReCl 3 , ReCl 6 , IrCl 3 , PtBr 2 , PtCl 2 , AuBr 3 , AuCl, AuCl 3 , AuI, KAuCl 4 , LaBr 3 , LaCl 3 , LaF 3 , LaI a , CeBr 3 , CeCl 3 , CeF 3 , CeF 4 , CeI 3 , and mixtures thereof, to name a few. 
     Suitable oxometallates include compounds such as LiIO 3 , LiBO 2 , Li 2 SiO 3 , LiClO 4 , Na 2 B 4 O 7 , NaBO 3 , Na 2 SiO 3 , NaVO 3 , Na 2 MoO 4 , Na 2 SeO 4 , Na 2 SeO 3 , Na 2 TeO 3 , K 2 SiO 3 , K 2 CrO 4 , K 2 Cr2O 7 , CaSiO 3 , BaMnO 4 , and mixtures thereof, to name a few. 
     Suitable metal carbonates include compounds such as Li 2 CO 3 , Na 2 CO 3 , NaHCO 3 , MgCO 3 , K 2 CO 3 , CaCO 3 , Cr 2 (CO 3 ) 3 , MnCO 3 , CoCO 3 , NiCO 3 , CuCO 3 , Rb 2 CO 3 , SrCO 3 , Y 2 (CO3) 3 , Ag 2 CO 3 , CdCO 3 , In 2 (CO 3 ) 3 , Sb 2 (CO 3 ) 3 , O 2 CO 3 , BaCO 3 , La 2 (CO 3 ) 3 , Ce 2 (CO 3 ) 3 , NaAl(CO 3 ) (OH) 2 , and mixtures thereof, to name a few. 
     Optically transmissive vehicles include metal oxides, metal salts and metal silicates such as alumina (Al 2 O 3 ), silica (SiO 2 ), zirconium oxide (ZrO 2 ), sodium silicate (Na 2 SiO 3 ), potassium silicate (K 2 SiO 3 ), and other compounds capable of optically transmitting laser energy (e.g., as generated from NdYAG, CO 2  and Yt fiber lasers). 
     Viscosity/fluidity enhancers include metal fluorides such as calcium fluoride (CaF 2 ), cryolite (Na 3 AlF 6 ) and other agents known to enhance viscosity and/or fluidity (e.g., reduced viscosity with CaO, MgO, Na 2 O, K 2 O and increasing viscosity with Al 2 O 3  and TiO 2 ) in welding applications. 
     Shielding agents include metal carbonates such as calcium carbonate (CaCO 3 ), aluminum carbonate (Al 2 (CO 3 ) 3 ), dawsonite (NaAl(CO 3 )(OH) 2 ), dolomite (CaMg(CO 3 ) 2 ), magnesium carbonate (MgCO 3 ), manganese carbonate (MnCO 3 ), cobalt carbonate (CoCO 3 ), nickel carbonate (NiCO 3 ), lanthanum carbonate (La 2 (CO3) 3 ) and other agents known to form shielding and/or reducing gases (e.g., CO, CO 2 , H 2 ). 
     Scavenging agents include metal oxides and fluorides such as calcium oxide (CaO), calcium fluoride (CaF 2 ), iron oxide (FeO), magnesium oxide (MgO), manganese oxides (MnO, MnO 2 ), niobium oxides (NbO, NbO 2 , Nb 2 O 5 ), titanium oxide (TiO 2 ), zirconium oxide (ZrO 2 ) and other agents known to react with detrimental elements such as sulfur and phosphorous to form low-density byproducts expected to “float” into a resulting slag layer  34 . 
     Vectoring agents include titanium, zirconium, boron and aluminum containing compounds and materials such as titanium alloys (Ti), titanium oxide (TiO 2 ), titanite (CaTiSiO 5 ), aluminum alloys (Al), aluminum carbonate (Al 2 (CO 3 ) 3 ), dawsonite (NaAl(CO 3 )(OH) 2 ), borate minerals (e.g., kernite, borax, ulexite, colemanite), nickel titanium alloys (e.g., Nitinol), niobium oxides (NbO, NbO 2 , Nb 2 O 5 ) and other metal-containing compounds and materials used to supplement molten alloys with elements. 
     In some embodiments the flux composition may also contain certain organic fluxing agents. Examples of organic compounds exhibiting flux characteristics include high-molecular weight hydrocarbons (e.g., beeswax, paraffin), carbohydrates (e.g., cellulose), natural and synthetic oils (e.g., palm oil), organic reducing agents (e.g., charcoal, coke), carboxylic acids and dicarboxylic acids (e.g., abietic acid, isopimaric acid, neoabietic acid, dehydroabietic acid, rosins), carboxylic acid salts (e.g., rosin salts), carboxylic acid derivatives (e.g., dehydro-abietylamine), amines (e.g., triethanolamine), alcohols (e.g., high polyglycols, glycerols), natural and synthetic resins (e.g., polyol esters of fatty acids), mixtures of such compounds, and other organic compounds. 
     In some embodiments flux compositions include: 
     5-60% by weight of metal oxide(s); 
     10-70% by weight of metal fluoride(s); 
     5-40% by weight of metal silicate(s); and 
     0-40% by weight of metal carbonate(s), 
     based on a total weight of the flux composition. 
     In some embodiments flux compositions include: 
     5-40% by weight of Al 2 O 3 , SiO 2 , and/or ZrO 2 ; 
     10-50% by weight of metal fluoride(s); 
     5-40% by weight of metal silicate(s); 
     0-40% by weight of metal carbonate(s); and 
     15-30% by weight of other metal oxide(s), 
     based on a total weight of the flux composition. 
     In some embodiments flux compositions include: 
     5-60% by weight of at least one of Al 2 O 3 , SiO 2 , Na 2 SiO 3  and K 2 SiO 3 ; 
     10-50% by weight of at least one of CaF 2 , Na 3 AlF 6 , Na 2 O and K 2 O; 
     1-30% by weight of at least one of CaCO 3 , Al 2 (CO 3 ) 3 , NaAl(CO 3 )(OH) 2 , CaMg(CO 3 ) 2 , MgCO 3 , MnCO 3 , CoCO 3 , NiCO 3  and La 2 (CO 3 ) 3 ; 
     15-30% by weight of at least one of CaO, MgO, MnO, ZrO 2  and TiO 2 ; and 
     0-5% by weight of at least one of a Ti metal, an Al metal and CaTiSiO 5 , based on a total weight of the flux composition. 
     In some embodiments the flux compositions include: 
     5-40% by weight of Al 2 O 3 ; 
     10-50% by weight of CaF 2 , 
     5-30% by weight of SiO 2 ; 
     1-30% by weight of at least one of CaCO 3 , MgCO 3  and MnCO 3 ; 
     15-30% by weight of at least two of CaO, MgO, MnO, ZrO 2  and TiO 2 ; and 
     0-5% by weight of at least one of Ti, Al, CaTiSiO 5 , Al 2 (CO 3 ) 3  and NaAl(CO 3 )(OH) 2 , 
     based on a total weight of the flux composition. 
     In some embodiments the flux composition contains at least two compounds selected from a metal oxide, a metal halide, an oxometallate and a metal carbonate. In other embodiments the flux composition contains at least three of a metal oxide, a metal halide, an oxometallate and a metal carbonate. In still other embodiments the flux composition may contain a metal oxide, a metal halide, an oxometallate and a metal carbonate. Viscosity of the molten slag may be increased by including at least one high melting-point metal oxide which can act as thickening agent. Thus, in some embodiments the flux composition is formulated to include at least one high melting-point metal oxide. Examples of high melting-point metal oxides include metal oxides having a melting point exceeding 2000° C.—such as Sc 2 O 3 , Cr 2 O 3 , Y 2 O 3 , ZrO 2 , HfO 2 , La 2 O 3 , Ce 2 O 3 , Al 2 O 3  and CeO 2 . 
     In some embodiments the flux compositions of the present disclosure include zirconia (ZrO 2 ) and at least one metal silicate, metal fluoride, metal carbonate, metal oxide (other than zirconia), or mixtures thereof. In such cases the content of zirconia is often greater than about 7.5 percent by weight, and often less than about 25 percent by weight. In other cases the content of zirconia is greater than about 10 percent by weight and less than 20 percent by weight. In still other cases the content of zirconia is greater than about 3.5 percent by weight, and less than about 15 percent by weight. In still other cases the content of zirconia is between about 8 percent by weight and about 12 percent by weight. 
     In some embodiments the flux compositions of the present disclosure include a metal carbide and at least one metal oxide, metal silicate, metal fluoride, metal carbonate, or mixtures thereof. In such cases the content of the metal carbide is less than about 10 percent by weight. In other cases the content of the metal carbide is equal to or greater than about 0.001 percent by weight and less than about 5 percent by weight. In still other cases the content of the metal carbide is greater than about 0.01 percent by weight and less than about 2 percent by weight. In still other cases the content of the metal carbide is between about 0.1 percent and about 3 percent by weight. 
     In some embodiments the flux compositions of the present disclosure include at least two metal carbonates and at least one metal oxide, metal silicate, metal fluoride, or mixtures thereof. For example, in some instances the flux compositions include calcium carbonate (for phosphorous control) and at least one of magnesium carbonate and manganese carbonate (for sulfur control). In other cases the flux compositions include calcium carbonate, magnesium carbonate and manganese carbonate. Some flux compositions comprise a ternary mixture of calcium carbonate, magnesium carbonate and manganese carbonate such that a proportion of the ternary mixture is equal to or less than 30% by weight relative to a total weight of the flux material. A combination of such carbonates (binary or ternary) is beneficial in most effectively scavenging multiple tramp elements. 
     Flux compositions of the present disclosure may be formulated to react chemically with the constituents of the melt pool  170 ,  172  in order to affect the mechanical properties of the resulting layer of slag  178  which can facilitate its removal. For example, it may be desirable to incorporate particularly brittle oxides into the slag layer  178 . Slag detachability is a function of both the physical properties of the coating materials and the flux materials, as well as chemical reactions that can occur in the transitory melt. For example, large differences in coefficients of thermal expansion between the layer of slag  178  and underlying materials can promote effective detachment of the slag. The thickness of the resulting layer of slag  178  can also affect cooling rates and slag detachability as explained above. High cooling rates promote slags that are generally more difficult to remove. 
     Flux compositions rich in zirconia (ZrO 2 ) and/or alumina (Al 2 O 3 ) may provide good slag detachability in processes of the present disclosure. In some embodiments described below, zirconia and/or alumina are contained as the majority component(s) in both the flux compositions and the resulting layers of slag  178 . Rutile (TiO 2 ) containing fluxes can also produce slag layers  178  having good detachability. Similar benefits may also occur using titanium-containing oxometallates such as Cr 2 TiO 5  and FeTiO 5 . In some embodiments the flux composition contains an amount of rutile (TiO 2 ) ranging from about 2 percent by weight to about 10 percent by weight. In other embodiments flux compositions contains an amount of a titanium-containing oxometallate (e.g., Cr 2 TiO 5 , FeTiO 5 , etc.) ranging from about 2 percent by weight to about 10 percent by weight. 
     For some alloy systems the presence of belite ((CaO) 2 (SiO 2 ) or Ca 2 SiO 4 ) in the flux composition can be beneficial to promote detachment of the slag layer  178 ; however, interactions with other compounds should also be considered. For example, the present inventors have found that the presence of CaF 2  in some flux compositions may be important in promoting fluidity of the molten slag and in reducing oxygen—but the presence of CaF 2  in flux compositions containing significant quantities of silica (or silica-type compounds) may produce a slag layer  178  that is difficult to remove. Consequently, flux compositions high in CaF 2  (e.g., at least 30 weight percent) and low in silica (SiO 2 ) (e.g., less than 10 weight percent) are found to be useful to form a more readily-detachable slag layer  178 . Also, flux compositions containing lower CaF 2  contents (e.g., less than 25 weight percent) can tolerate higher levels of silica (SiO 2 ) (e.g., more than 15 weight percent) and still form a detachable slag layer  178 . It is also recognized (as disclosed in U.S. Pat. No. 4,750,948 for submerged arc welding of nickel based alloys) that careful balancing of calcium fluoride, alumina, zirconia and cryolite (Na 3 AlF 6 ) may be beneficial in producing good slag characteristics in embodiments of the present disclosure. Flux compositions of the present disclosure may contain modest amounts of CaO and MgO (esp., to provide cleansing action) but these compounds should be limited to avoid the formation of perovskite (CaTiO 3 ) and chromium spinel (MgAlCrO 4 ) that tend to adhere slag layers  178  to metal deposits  176 ,  182 . Flux compositions of the present disclosure may include less than 20 percent by weight of CaO and MgO combined to provide some benefit without exhibiting an adverse effect on detachability. In some embodiments the flux compositions may include less than 10 percent by weight of CaO and MgO combined. 
     All of the percentages (%) by weight enumerated above are based upon a total weight of the flux material being 100%. 
     Commercially availed fluxes may also be used to form composite materials of the present disclosure. Examples includes flux materials sold under the names Lincolnweld P2007, Bohler Soudokay NiCrW-412, ESAB OK 10.16 and 10.90, Special Metals NT100, Oerlikon OP76, Bavaria WP 380, Sandvik 50SW, 59S or SAS1, and Avesta 805. Such commercial fluxes may be ground to a smaller particle size range before use. Such commercial fluxes may also be combined with other fluxing constituents mentioned above for enhanced purposes of fluidity control, scavenging, detachability, etc. 
     Other embodiments will enable the separation and laser processing of different particles using acoustic energy based on differences in particle size, shape and density.  FIGS. 12A and 12B  illustrate the use of acoustic energy to separate particles having different sizes and different densities. Focusing on  FIG. 12A , it is known that particles exposed to acoustic energy may be subjected to different acoustic forces based on the cross section presented by the particles. In the illustration of  FIG. 12A , a mixture  200  of two different kinds of particles having the same density—small particles  201  and large particles  203 —may be subject to different forces. In most circumstances it is expected that the small particles  201  will experience a smaller acoustic force (F a   S )  206  when exposed to ultrasound  202 , and the larger particles  203  will experience a larger acoustic force (F a   L )  210 . Consequently, when directed to an ultrasonic focal point under the influence of the ultrasound  202 , the small particles  201  will move at a lower velocity and the large particles  203  will move at a higher velocity—such that the small and large particles will separate to form separate groups of particles  204  (small particles) and  208  (large particles). 
     Particles may also be separated using acoustic energy based on differences in particle density. Focusing on  FIG. 12B , it is known that particles exposed to acoustic energy may move at different velocities due to differences in particle density—leading to differences in particle acceleration. In the illustration of  FIG. 12B , a mixture  212  of two different kinds of particles having the same cross section (size) but different densities—particles of lower density  211  and particles of higher density  213 —may experience different accelerations. In most circumstances it is expected that particles having the same cross section (size) will experience the same acoustic force when exposed to ultrasound  202 . Therefore, the resulting acoustic acceleration for each type of particle will be indirectly proportional to the density (and mass) of the particle—such that the higher density particles  213  will experience a lower acceleration and velocity (v 1 )  216  and the lower density particles  211  will experience a higher acceleration and velocity (v 2 )  220 . Consequently, when directed to an ultrasonic focal point under the influence of the ultrasound  202 , the lower density particles  211  and the higher density particles  213  will separate to form separate groups of particles  218  (lower density particles) and  214  (higher density particles). 
     Embodiments of the present disclosure can utilize these acoustic phenomena to separate different types of particles on a working surface.  FIG. 13  illustrates the use of an ultrasonic phase-array transducer to generate and move a single focal point from one location on a working surface  54  to another location. It is known to use ultrasonic phased-array transducers that can be tuned to steer particles to a certain focal point in a two or three-dimensional space.  FIG. 13  illustrates one embodiment in which a linear ultrasonic phased-array transducer  221  is used to generate an initial focal point  222 , which is then shifted  224  continuously from the initial focal point  222  to a final focal point  226  located some distance away on a working surface  54 . 
       FIG. 14  illustrates one embodiment of a method for separating particles on a working surface  54  using acoustic energy. This non-limiting illustration employs a two-dimensional ultrasonic phase-array transducer  230  adapted to create an initial focal line  232  on the working surface  54 . A mixture  234  of two different particle types arranged into a line (distinguished by cross section (size) or density) is then steered into the initial focal line  232  using ultrasonic irradiation. The mixture of particles may originate from an adjacent powder bed, or may originate from a particle delivery device as illustrated in  FIGS. 4-5 and 7A  and described above. The separation process occurs by continuously shifting  236  the focal line from the initial focal line  232  to a final focal line  238 . As the particle mixture moves from the initial focal line  232  to the final focal line  238  the different types of particles can be separated based upon differences in cross section (size) or density as explained above to form two separate lines  240  and  242  containing the respective particle types. Laser processing may then be carried out to selectively heat or melt the respective particles lines to form metal deposits and ceramics, as illustrated in  FIGS. 7A-D . 
     Other embodiments will enable the separation and laser processing of different particles using acoustic energy based on differences in the natural vibrational frequencies of the different particles. Both metallic and non-metallic particles held together by intra-particle bonds (e.g., covalent and non-covalent bonds) may be vibrated by exposure to radiation at one or more frequencies corresponding to resonance frequencies of the particles. These resonance frequencies (also commonly referred to as “natural” frequencies) depend upon both the strength (stiffness) of the intra-bonds and the mass of the intra-particle bodies (elements) held together by the intra-bonds, as expressed in Equation (2): 
     
       
         
           
             
               
                 
                   
                     f 
                     n 
                   
                   = 
                   
                     
                       1 
                       
                         2 
                          
                         π 
                       
                     
                      
                     
                       
                         k 
                         m 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where “k” represents the stiffness (strength) (N/m) of the intra-particle bond and “m” represents the mass (kg) of the intra-particle bodies (elements). 
     Because different particles will generally possess different natural vibrational frequencies, it is possible to selectively vibrate and translate particles by applying acoustic energy at a natural frequency of a certain type of particle.  FIG. 15A  illustrates the use of acoustic energy to selectively excite a particle A  400  having a natural frequency f n   A .  FIG. 15A  shows a group of particles  401  including particles A  400  having a certain natural frequency (f n   A ) and particles B  402  having a different natural frequency (f n   B ). Upon exposure of the group of particles  401  to acoustic energy  404  having the same frequency (f n   A ) as the particles A  400 , the particles A become vibrationally excited particles  406 —whereas the particles B  302  remain in a non-excited (non-vibrating) state. Using this ability to selective excite and vibrate particles will enable these particles to be selectively manipulated as further explained below. 
     One type of selective particle manipulation using natural vibrational frequencies is illustrated in  FIG. 15B .  FIG. 15B  shows the use of acoustic energy to selectively excite particles having a natural vibrational frequency (f n   A ), causing a selective fluidization of particles in a mixed bed  410 . The mixed bed  410  in this case includes particles A  412  having a certain natural frequency (f n   A ) and particles B  414  having a different natural frequency (f n   B ). Upon exposure of the mixed bed  410  to acoustic energy  416  having the same frequency (f n   A ) as the particles A  412 , the particles  412  become vibrationally excited particles  422 —whereas the particles B  414  remain in a non-excited (non-vibrating) state. This selective excitation of the particles  422  causes a selective fluidization of the particles  422 , allowing them to move in a certain direction (shown in this case moving in an upward direction) based on properties such as particle density—such that an initially uniform mixed bed  411  is transformed into a non-uniform mixed bed  424 . In the resulting non-uniform mixed bed  424 , the excited particles A  422  congregate primarily in an upper layer  420 ; whereas the non-excited particles  414  remain primarily in a lower layer  418 . In this manner, by non-limiting example, particles having different natural vibrational frequencies may be selectively moved in a vertical direction. 
     Different particles may also be selectively excited and moved in a horizontal direction as illustrated in  FIG. 16 .  FIG. 16  shows an apparatus capable of selectively exciting particles having a certain natural vibrational frequency (f n ), and then using acoustic trapping and steering to further translate the excited particles along a horizontal working surface  54 . This apparatus includes the working surface  54  upon which a mixture  432  of particles A  406  and particles B  402  is placed in acoustic communication with a transducer  436  adapted to apply acoustic energy a different (electronically-tunable) frequencies. The particles A  406  have a natural vibrational frequency (f n   A ) that is different than the natural vibrational frequency (f n   B ) of the particles B  402 . Upon exposure of the mixture  432  to acoustic energy  404  having the same frequency as the natural vibrational frequency (f n   A ) of the particles A  406 , these particles become vibrationally excited and can move (spread) along the horizontal working surface. 
     The apparatus of  FIG. 16  also includes an ultrasonic phased-array transducer  221  adapted to produce tunable acoustic focal points at various locations along the working surface  54 . In the illustration of  FIG. 16  the ultrasonic phased-array transducer  221  is initially tuned to create an initial focal point  410 —causing some of the excited particles A  406  to move  412  into the focal point  410  and become acoustically trapped. Meanwhile, the non-excited particles B  402  remain largely unaffected in the mixture  432 . Additional translation of the trapped particles  414  may then be accomplished by altering the tuning of the ultrasonic phased-array transducer  221  such that the focal point moves  416  from the initial focal point  410  to a final focal point  418 . Such movement  416  of the focal point thereby selectively translates the trapped particles  414  to a new location on the working surface  54 . 
     Embodiments such as the apparatus and method of  FIG. 16  are expected to enable the selective manipulation and laser processing of both metallic and non-metallic particles, to produce multi-material articles through additive manufacturing. 
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.