Abstract:
Improved methods and containers for forming billets using hot isostatic pressing are provided. The methods and containers have features that control the deformations of the container during the high temperatures and pressures experienced in such processing so that the loss or removal of material from the resulting billet can be optimized.

Description:
FIELD OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to an improved method and container for forming billets using hot isostatic pressing and, more specifically, to a method and container having features that control the deformations of the container during the high temperatures and pressures experienced in such processing. 
       BACKGROUND OF THE INVENTION 
       [0002]    Metallurgical techniques have been developed for the manufacture of a metal billet or other object from metal powders created in a predetermined particle size by e.g., microcasting or atomization. Usually highly alloyed with Ni, Cr, Co, and Fe, these powders are consolidated into a dense mass approaching 100 percent theoretical density. The resulting billets have a uniform composition and dense microstructure providing for the manufacture of components having improved toughness, strength, fracture resistance, and thermal expansion coefficients. Such improved properties can be particularly valuable in the fabrication of e.g., rotary components for a turbine where high temperatures and/or high stress conditions exist. 
         [0003]    The consolidation of these metal powders into a dense mass typically occurs under high pressures and temperatures in a process referred to as hot isostatic pressing (HIP). Typically, the powders are placed into a container (sometimes referred to as a “can”) that has been sealed and its contents placed under a vacuum. The container is also subjected to an elevated temperature and pressurized on the outside using an inert gas such as e.g., argon to avoid chemical reaction. For example, temperatures as high as 480° C. to 1315° C. and pressures from 51 MPa to 310 MPa or even higher may be applied to process the metal powder. By pressurizing the container that is enclosing the powder, the selected fluid medium (e.g., an inert gas) applies pressure to the powder at all sides and in all directions. 
         [0004]    The equipment required for HIP treatment is typically very costly and requires special construction. Due to the extreme temperatures and pressures, the container is substantially deformed or crushed as the volume of the powder decreases during the HIP process and the container becomes joined to the surface of the billet created by the compacted powder. Depending upon the desired shape for the resulting billet, all or portions of the surface of the container may be cut away i.e., by machining after the HIP process. In addition, portions of the billet may also be cut away depending upon the shape desired and the nature of deformations that occurred during the HIP process. Given that the powder used to manufacture the billet is typically very expensive, removal of portions of the billet is undesirable. A process that allows for shape control during compaction while optimizing the removal of material from the billet is needed. 
         [0005]      FIGS. 1A and 1B  provide an exemplary illustration of the problems confronted using conventional containers in the HIP process.  FIG. 1A  provides a schematic illustration of a portion of a container  101  before being subjected to the extreme temperature and pressure of the HIP process. Container  101  encloses the powder mixture  105  intended for compaction and provides a seal to prevent the ingress of the fluid used for pressurization e.g., argon during the HIP process. Before pressurization, the walls  110  between top  100  and bottom  135  are basically straight and/or without deformation. Top  100  and bottom  135  are also undeformed before the HIP process. 
         [0006]    In general, the thickness, type, and structure of material used for container  101  is determined in part by the weight of powder to be held within container  101 . More particularly, in addition to providing a pressure seal, container  101  is also used to transport the powder to a pressure vessel for the HIP process and, therefore, must be constructed to bear the weight of the powder e.g., several tons in some applications. For example, container  101  might be constructed from mild steel of approximately ½″ in thickness. However, other materials and thicknesses may be used. If the container is intended to remain on the billet for inclusion on the ultimate article of manufacture, additional considerations may determine the choice of material for container  101 . 
         [0007]      FIG. 1B  illustrates the same portion of container  101  after being subject to the HIP process. The conditions of the HIP process have now converted the powder into a metal billet  106 . However, the change in density from powder to a solid metal has also resulted in a rather dramatic change in volume. As the volume decreased, container  101  also deformed with the change from powder  105  to billet  106 .  FIG. 1B  illustrates that wall  110  has now taken on an arcuate shape, and top  100  and bottom  135  may undergo deformations as well. 
         [0008]    Unfortunately, depending upon the shape desired for billet  106  (or the shape of the ultimate component to be constructed from billet  106 ), the deformations shown in  FIG. 1B  may be undesirable because the resulting shape for billet  106  may require the removal of valuable material from its surface. For example, assuming a cylindrical outer surface is needed along wall  110  of billet  106 , container  101  and billet  106  may need to be cut i.e., machined along line  130  in order to obtain the desired outer surface. However, in addition to the destruction of container  101 , significant amounts of the billet  106  will be lost at portions  115  along the top and bottom of container  101 . Because of the substantial costs of the original powder, this loss is undesirable. In addition, although less significant than the powder costs, portions of container  101  are also lost as a result of the machining process. 
         [0009]    Therefore, an improved device that provides for the reduction or elimination of powder loss in connection with HIP treatment would be useful. An improved device that also allows for more variation in the construction of containers associated with HIP treatment would also be useful. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0010]    Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
         [0011]    The present invention provides for an improved method and container for use in HIP processing. More specifically, the present invention provides a method and container having one or more features that control deformation of the container during HIP processing so that material loss and be eliminated or reduced. The present invention can also allow for additional efficiencies in that containers constructed from different materials and structures are also provided. 
         [0012]    For example, in one exemplary embodiment, the present invention provides a container for use during hot isostatic pressing of a powder into a billet. The container includes at least one wall contacting the powder. A plurality of shape-control elements are positioned along such wall. The shape-control elements are configured for controlling the deformation of the container during the hot isostatic processing such that the resulting billet has at least one surface that is convex, concave, or both after the hot-isostatic processing. 
         [0013]    In another exemplary embodiment, a container for compaction processing of a powder is provided. The container includes a cylindrically-shaped outer wall that defines axial and circumferential directions. The outer wall has a plurality of shape-control elements spaced along the circumferential direction of the outer wall. The shape-control elements are configured for determining the deformation of the outer wall as the volume of the powder is reduced under pressure. A container top and a container bottom are connected to the outer wall. The outer wall extends between the container top and the container bottom so as to define an interior of the container for receipt of the powder. 
         [0014]    In another exemplary aspect of the present invention, a method for optimizing the use of material during hot isostatic pressing is provided. The method includes the steps of providing a container for the receipt of a powder intended for compaction, determining the position of shape-control elements along at least one wall of the container, the shape-control elements configured for controlling the deformation of the container during hot isostatic pressing; positioning the shape-control elements along at least one wall of the container; and deforming the container while compacting the powder during hot isostatic pressing so as to provide a billet. 
         [0015]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A full and enabling disclosure of exemplary embodiments of the present invention, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
           [0017]      FIG. 1A  is a schematic cross-section along one side of a container before subjection to a HIP process. 
           [0018]      FIG. 1B  is a schematic cross-section along one side of the container of  FIG. 1A  after undergoing the pressure and temperature of a HIP process. 
           [0019]      FIG. 2  is perspective view of an exemplary embodiment of a container according to the present invention. 
           [0020]      FIG. 3  is a top view of the exemplary embodiment of the container shown in  FIG. 2 . 
           [0021]      FIG. 4  is a side view of the exemplary embodiment of  FIG. 2  after being subjected to a HIP process. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    For purposes of describing the invention, reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0023]      FIGS. 2 and 3  provide an exemplary embodiment of a container  201  constructed according to the present invention. In particular, container  201  contains shape-control elements  220  positioned along the circumferential direction C ( FIG. 3 ) of cylindrically-shaped wall  210  and along the outside surface  250  thereof. Each shape-control element  220  extends longitudinally along the axial direction A ( FIG. 2 ) of wall  210 . As best seen from  FIG. 3  and  FIG. 5A , each shape-control element  220  has a triangular cross-section. 
         [0024]    Shape-control elements  220  provide reinforcements to control the deformation of contain  201  during the HIP process. More particularly, for the exemplary embodiment of container  201 , shape-control elements  220  prevent or minimize arcuate deformation of wall  210  during the HIP process as occurred with wall  110  in  FIG. 1B .  FIG. 4  depicts container  201  after being subjected to the HIP process. The volume of container  101  has decreased as illustrated by phantom lines and the closer spacing of shape control elements  220 . However, while wall  210  has experienced deformation, wall  210  remains substantially straight as part of a controlled deformation. Accordingly, the shape of billet  206  retains the desired cylindrical shape as shown in the cut-way portion of  FIG. 4 . As such, whether container  201  is to be left on billet  206  or removed by machining, the use of powder in creating billet  206  has been optimized with little or no loss of valuable material. 
         [0025]    Features for shape control can be added to other surfaces of container  201  as well. For example, container top  200  and bottom  235  each have shape-control elements  225 . These shape-control elements  225  are configured so that as the powder volume decreases by compaction to become billet  206 , the deformation results in a flat surface. More specifically, as shown in  FIG. 2 , top  200  and bottom  235  each have a slightly arcuate shape. During the HIP process, shape-control elements  225  allow top  200  and bottom  235  to deform in a controlled manner such that the resulting shape provides a flat surface as shown in the cutaway portion of  FIG. 4 . It should be understood that the resulting cylindrically-shaped billet  206  is provided by way of example only. Other shapes for billet  206  may be desired and container  201  and its associated shape control elements can be modified accordingly. 
         [0026]    Using the teachings disclosed herein, one of ordinary skill in the art will understand that multiple variations for the shape-control elements can be used to control the deformation to the container that occurs during the HIP process in order to achieve the shape desired for the resulting billet. Returning to the embodiment of  FIG. 2 , for example, the length and orientation of shape-control elements  220  along the axial direction A can be modified depending upon the deformation desired, the compaction behavior of the powder, the process conditions of the HIP, and other variables. By way of example, shape-control elements  220  could be oriented diagonally, horizontally, and at different spacings and thickness than shown in  FIG. 2 . Similarly, for top  200  as shown in  FIG. 3 , the spacing, shape, thickness, and orientation of shape control elements  225  can be varied to control deformation as desired. 
         [0027]    Additionally, the cross-section of the shape-control elements can also varied. As previously described, shape-control element  220  has a triangular cross-section as shown in  FIG. 5A . However, many other shapes can be applied, and  FIG. 5B  provides an example of a hemispherical cross-section for shape-control element  260 . 
         [0028]    The shape-control elements of  FIGS. 4 ,  5 A, and  5 B are depicted as being located along the outside surface  250  of the wall of container  201 . Using the teachings disclosed herein, it should be understood that shape-control features can also be located along the inside surface  245  of container  201 . For example,  FIG. 5C  depicts a shape-control element  270  have dimple-like cross-section located along the inside surface  245 . This shape-control element  270  could be constructed as an indentation extending longitudinally in the axial direction A over some predetermined portion of the length of wall  210 . Alternatively, shape-control element  270  could be constructed as a series of dimples (i.e., indentations) arranged in various orientations along wall  210  depending upon the resulting deformation that is desired. Rather than only reinforcing wall  210 , the dimple shape-control elements  270  help control deformation by initiating the points at which buckling occurs as container  201  is compressed during the HIP process. 
         [0029]    The shape-control elements in  FIGS. 2 ,  3 ,  4 , and  5 A- 5 C are illustrated as being an integral part of wall  210 . However, shape-control elements can also be welded or otherwise attached to the inner surface  245  or outer surface  250  of wall  210 . For example, in lieu of the shape-control elements  220  on container  201 , a serious of plates could welded to wall  210  at locations spaced about the circumferential direction C. As previously indicated, the width, length, and location of such plates are determined according to the deformation desired for container  201  during the HIP process. 
         [0030]    In addition to providing for control of the deformation that occurs during compaction in the HIP process, the use of shape-control elements allows for container  201  to be constructed with thinner walls made from a variety of materials such as e.g., stronger, higher alloy materials that used for container  101 . This results in part because shape-control elements are being used to control the deformation rather than relying upon the thickness of the container to determine the shape of the resulting billet. Also, by using shape-control elements to optimize the deformation of the powder and using a support frame or carriage device (not shown) to support the container, less material can be used in the construction of container as it is not being relied upon to support the weight of the powder or billet during transport. 
         [0031]    Examples of the present invention have been described with reference to a cylindrically-shaped container  201  for which arcuate deformation of wall  210  was not desired. However, the present invention applies to other desired shapes for both the container and billet—before and after the HIP process. For example, it may be desirable to have concave surfaces, convex surfaces, or both in the resulting billet. As such, the shape of the container before the HIP process and the desired shape for the billet after the HIP process may be non-cylindrical depending upon the intended application for the resulting billet. Regardless, in each case, the present invention provides for the application of shape-control elements that are located and configured to control deformation during the HIP process in order to achieve a predetermined shape for the resulting billet. By way of example, before submitting to the HIP process, the container might have one or more concave walls to which shape-control elements have been added so that the concave shape is maintained or even further accentuated after the HIP process. Alternatively, the shape-control elements may be configured to provide deformation control of the container from e.g., one or more straight surfaces to one or more convex or concave surfaces after the HIP process. Accordingly, the present invention is not limited to any particular shapes for the container or resulting billet and, instead, provides apparatus and methods for controlling deformation during the HIP process so as to achieve a predetermined shape for the resulting billet. As a result, savings in both material costs and manufacturing time are achieved. 
         [0032]    While the present subject matter has been described in detail with respect to specific exemplary embodiments and methods thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.