Abstract:
A system for treatment of atomized powder including a fluidized bed operable to treat feedstock alloy powders. A method of treating atomized powder including communicating an inert gas into a fluidized bed; communicating an atomized powder into the fluidized bed; and heating the atomized powder in the fluidized bed, eject the treated powders out of the fluidized bed to quench the powders.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This disclosure was made with Government support under contract W911NF-14-2-0011 awarded by the U.S. Army. The Government has certain rights in this disclosure. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to additive manufacturing and, more particularly, to processing additive manufacturing feedstock powder. 
         [0003]    Precision engineered parts such as gas turbine components may be manufactured by an additive manufacturing operation such that features associated with conventional manufacturing processes, e.g., machining, forging, welding, casting, etc. can be eliminated to facilitate savings in cost, material, and time. 
         [0004]    Metal alloy powders are often produced by a gas, centrifugal atomization process. Powder in this state is then supplied as feedstock for additive manufacturing, solid state consolidation, and other powder metallurgy processes. An issue with atomized powder may be that the microstructure of the individual powder particles can differ and be nonhomogeneous. 
       SUMMARY 
       [0005]    A system for treatment of atomized powder according to one disclosed non-limiting embodiment of the present disclosure can include a fluidized bed operable to heat treat feedstock alloy powders, the feedstock alloy powders heat treated for microstructure control to hereby condition the feedstock alloy powders into a state to facilitate solid-state consolidation. 
         [0006]    A further embodiment of the present disclosure may include wherein the feedstock alloy powders are degassed. 
         [0007]    A further embodiment of the present disclosure may include an inert gas in communication with the fluidized bed. 
         [0008]    A further embodiment of the present disclosure may include a quenching reservoir in communication with the fluidized bed. 
         [0009]    A further embodiment of the present disclosure may include a three-way valve in communication with the quenching reservoir. 
         [0010]    A further embodiment of the present disclosure may include a water bubbler, a fine powder collector and a quenching powder collector in communication with the three-way valve. 
         [0011]    A further embodiment of the present disclosure may include a vibrator in communication with the fluidized bed and the line to a quenched powder collector to facilitate to eject the atomized powder. 
         [0012]    A method of treating atomized powder according to one disclosed non-limiting embodiment of the present disclosure can include communicating an inert gas into a fluidized bed; communicating an atomized powder into the a fluidized bed; and heating the atomized powder in the fluidized bed, the feedstock alloy powders heat treated for microstructure control. 
         [0013]    A further embodiment of the present disclosure may include communicating the atomized powder into a quenching reservoir. 
         [0014]    A further embodiment of the present disclosure may include communicating the atomized powder from the quenching reservoir to a three way valve. 
         [0015]    A further embodiment of the present disclosure may include communicating the atomized powder from the three way valve to a fine powder collector. 
         [0016]    A further embodiment of the present disclosure may include communicating the atomized powder to the fine powder collector through a water bubbler. 
         [0017]    A further embodiment of the present disclosure may include quenching the atomized powder. 
         [0018]    A further embodiment of the present disclosure may include degassing the atomized powder. 
         [0019]    A further embodiment of the present disclosure may include communicating the atomized powder from the three way valve to a quenched powder collector. 
         [0020]    The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. The drawings that accompany the detailed description can be briefly described as follows: 
           [0022]      FIG. 1  is a micrograph of a powder particle of aluminum alloy 7075 (AA7075) in the as-atomized state with some alloy additions (bright), segregated to the boundaries; 
           [0023]      FIG. 2  is a system for treatment of atomized powders for an additive manufacturing process according to one disclosed non-limiting embodiment; 
           [0024]      FIG. 3  is a micrograph of a heat treated as-atomized powder particle heat treated by the system of  FIG. 2  to eliminate segregation and condition the powder into a state more ideal for solid state consolidation; and 
           [0025]      FIG. 4  is a process for treatment of atomized powders for an additive manufacturing process according to one disclosed non-limiting embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    With reference to  FIG. 1 , an issue with atomized powder may be that the microstructure of the individual powder particles can noticeably differ from the structure. For example, alloys can derive strength from additions that go into solid solution or precipitate out as well dispersed second phase particles can exhibit significant chemical segregation. For example, segregation is evident in powder particle  12  of aluminum alloy 7075 (AA7075) in the as-atomized state as some of the alloy additions (bright colored areas; 10) show clearly segregated boundaries. 
         [0027]    For powder metallurgy techniques that require elevated temperatures i.e., melting or partial melting of the powder, the as-atomized feedstock condition may not be as much of a concern. However, for solid-state consolidation processes, such as cold spray that rely on plastic deformation of the powder particles, the feedstock microstructure may be relatively more critical. Excessive segregation in the as-atomized powder can be detrimental as clustering of alloy additions at the boundary/interface regions can result in a weakening or embrittling effect. The consequence may result in poor particle-particle bonding; in other words, the as-atomized powder microstructure inhibits the formation of robust bonds between particles. 
         [0028]    With reference to  FIG. 2 , a system  20  for treatment, e.g., heat treatment, degassing, etc., have atomized powders for an additive manufacturing process is schematically illustrated. The additive manufacturing process sequentially builds-up layers of atomized alloy material that include but are not limited to, steel alloys, stainless steel alloys, titanium alloys, nickel alloys, aluminum alloys and others in atomized powder material form. Nickel alloys may have specific benefit for parts that operate in high temperature environments, such as, for example, environments typically encountered by aerospace and gas turbine engine components. 
         [0029]    In one embodiment, the system  20  is operable to heat treat as-atomized powder to eliminate the segregations ( FIG. 1 ) and thereby condition the powder into a state that is more ideal for solid-state consolidation ( FIG. 3 ). The approach described herein begins with as-atomized feedstock and allows the powder to be subjected to a heat treatment to include but not limited to homogenization, solutionizing, quenching, and aging. Specifically, the process  100  ( FIG. 4 ) provides for a powder treatment that utilized a fluidized bed that feeds into a quench reservoir connected to a powder collector. 
         [0030]    The powder  30  to be processed is loaded into a fluidized bed  32  via a valve  50  (Step  102 ;  FIG. 4 ). An inert gas  36  such a nitrogen or argon from a tank  38  is introduced through a bleed line  40  with a relatively small flow rate while a valve  42  is open and valve  44  remains closed to avoid an initial gas burst in the fluidized bed  32 . The inert gas  36  may be preheated or otherwise communicated into the fluidized bed  32 . 
         [0031]    The inert gas  36  is then directed into the fluidized bed  32  by opening valve  44  and closing valve  42  (Step  104 ;  FIG. 4 ). A mass flow controller  46  and pressure sensor  48  may be utilized to control the inert gas. The inert gas flow rate is determined, for example, to fluidize the powder based on the properties of the powder and the gas, the treatment conditions (temperature and pressure), and the internal diameter of the fluidized bed. The fluidized bed  32  is then heated to a desired temperature for a desired time to achieve the desired treatment of the atomized powders, e.g., heat treatment, degassing, etc. (Step  106 ;  FIG. 4 ). That is, the powder particles in the fluidized bed  32  are in full fluidization while being heated to avoid conglomeration of the particles. 
         [0032]    When the powder has had sufficient time at temperatures within the fluidized bed  32 , the powder is ejected by increasing the gas flow rate to the value  44 . The particles leave the fluidized bed  32  through cooling coils  60  of a quench reservoir  62 . The quench reservoir  62  can be filled with a variety of mediums such as, but not limited to, water, ice water, oil, dry ice, liquid nitrogen, liquid argon, liquid helium, etc., to provide right quenching medium temperatures, coupled with powder ejecting rates to control the quenching rate of the powder particles (Step  108 ;  FIG. 4 ). 
         [0033]    A valve  50  directs the inert gas exiting from the fluidized bed  32  to the fine powder collector  52  via the quenched powder collector  58  through a three-way valve  54 , then vented through a water bubbler  56  (Step  110 ;  FIG. 4 ). That is, the powder particles collected in the fine powder collector  52  and residual therefrom is collected in the water bubbler  56  to avoid ejection into the environment. 
         [0034]    The system  20  enables the heat treatment of atomized powders to control powder particle microstructure for solid state consolidation applications. By controlling time, temperature, and cooling rate, the necessary regimen can be applied to the powder to influence chemical homogeneity, grain size, secondary phase growth, secondary phase distribution, etc. to attain the microstructural condition most favorable for desired solid-state consolidation. This process allows the powder particles to be subject to the same heat treat steps experienced by a conventional alloy ingot to include solutionizing, quenching, and aging. In addition, the process addresses key challenges of heat treating powder particles by working in an inert environment to limit oxidation and minimizing particle sintering, caking, and/or agglomeration. 
         [0035]    The use of the terms “a,” “an,” “the,” and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. It should be appreciated that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to normal operational attitude and should not be considered otherwise limiting. 
         [0036]    Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
         [0037]    It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
         [0038]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
         [0039]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.