Title: Three Dimensional Printed Hot Isostatic Pressing Containers and Processes for Making Same.

Inventors: Rick Lucas, Howard Kuhn, Michael Orange, and Thomas Lizzi Background

[0001] Field of the Invention: The invention relates to methods of preparing powder containers for use in hot isostatically pressing, to the containers themselves, and to the use of the containers to produce hot isostatically pressed parts.

[0002] Background of the Invention: Hot isostatic pressing ("HIP") involves the application of an isostatic pressure to an object that is at a temperature at which the pressure is sufficient to cause the object to plastically deform. HIP is commonly used for densify parts made by casting, powder metallurgical, and ceramic processes by closing or diminishing the size residual porosity in the parts.

[0003] HIP is also used as a means for consolidating metal powders directly into a dense object. The metal powders are placed into a container which is malleable at the HIP temperature. The container is attached to a vacuum pump to evacuate gases. Often, the container is heated while it is attached to the vacuum pump as an aid in removing adsorbed gases from the surfaces of the powder particles and of the container. The container is then hermetically sealed, e.g. by hot crimping, and then hot isostatically pressed at a time, temperature, pressure combination selected based upon the type of powder, the size of the container, and the objective of the HIP process. After HIP, the container is removed from the part by machining and/or chemical dissolution.

[0004] Over the years, variations have been developed for performing HIP on powder encapsulated in a container. Some variations were directed at improving the throughput efficiency through the use of auxiliary furnaces in combination with the vessels in which the high pressure is applied. Other variations were directed at increasing the complexity of the resultant part geometry. Some of these shape-related variations were directed at increasing the complexity of the container, e.g. the use of spin formed containers. Others employed a deformable mold, e.g. a ceramic mold made by the lost-wax process, placed within the container and surrounded by a secondary pressing media. These variations, though, have their limitations and their drawbacks. Spin formed containers are useful only for parts which have axial symmetry. Containers made by welding sections together give rise to problems with gas- leakage at welds, disparity in strength and deformation at welds, and limitations on weld placement. The use of a secondary pressing media distorts the hydrostatic pressure field and the use of internal molds present difficulties in mold design, preparation, and uniformity of filling.

[0005] Additional information about hot isostatic pressing can be found in the book "Hot Consolidation of Powders and Particulates" by Animesh Bose and William B. Eisen, published by the Metal Powders Industry Federation, 2003, ISBN 1-878954 495-4.

Summary of the Invention

[0006] The present invention provides methods for preparing containers for use in HIP. In accordance with the present invention, a container is formed by three dimensional printing a build powder in the shape the container is to have and then the container is consolidated by heat treating the printed part to densify and strengthen the build powder. In some embodiments of the present invention, the container is printed with internal features which will produce passageways in the HIP part. Since these internal features are analogous to cores that are used in the foundry industry, they will be referred to herein as cores.

[0007] Three dimensional printing was developed in the 1990's at the Massachusetts Institute of Technology and is described in several United States patents, including the following United States patents: 5,490,882 to Sachs et al, 5,490,962 to Cima et al, 5,518,680 to Cima et al, 5,660,621 to Bredt et al, 5,775,402 to Sachs et al, 5,807,437 to Sachs et al, 5,814,161 to Sachs et al, 5,851,465 to Bredt, 5,869,170 to Cima et al, 5,940,674 to Sachs et al, 6,036,777 to Sachs et al, 6,070,973 to Sachs et al, 6,109,332 to Sachs et al, 6,112,804 to Sachs et al, 6,139,574 to Vacanti et al, 6,146,567 to Sachs et al, 6,176,874 to Vacanti et al, 6,197,575 to Griffith et al, 6,280,771 to Monkhouse et al, 6,354,361 to Sachs et al, 6,397,722 to Sachs et al, 6,454,811 to Sherwood et al, 6,471,992 to Yoo et al, 6,508,980 to Sachs et al, 6,514,518 to Monkhouse et al, 6,530,958 to Cima et al, 6,596,224 to Sachs et al, 6,629,559 to Sachs et al, 6,945,638 to Teung et al, 7,077,334 to Sachs et al, 7,250,134 to Sachs et al, 7,276,252 to Payumo et al, 7,300,668 to Pryce et al, 7,815,826 to Serdy et al, 7,820,201 to Pryce et al, 7,875,290 to Payumo et al, 7,931,914 to Pryce et al, 8,088,415 to Wang et al, 8,211,226 to Bredt et al, and 8,465,777 to Wang et al. In essence, three-dimensional printing involves the spreading of a layer of particulate material and then selectively jet-printing a fluid onto that layer to cause selected portions of the particulate layer to bind together. This sequence is repeated for additional layers until the desired part has been constructed. The material making up the particulate layer is often referred as the "build material" and the jetted fluid is often referred to as a "binder", or in some cases, an "activator". Post-processing of the three- dimensionally printed part is often required in order to strengthen and/or densify the part.

[0008] In some embodiments of the present invention, the consolidation of the printed container includes the infiltrating of the printed container with a liquid metal. In some embodiments of the present invention, the consolidated printed container is plated with a metal to seal its external surface.

Brief Description of the Drawings

[0009] The criticality of the features and merits of the present invention will be better understood by reference to the attached drawings. It is to be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the present invention.

[0010] FIG. 1 is a schematic perspective view of a valve body that is to be made according to an embodiment showing the internal passages in dashed lines.

[0011] FIG. 2 is an elevation cross-sectional view taken along a vertical midplane of a container according to an embodiment for making the valve body of FIG. 1.

Detailed Description of Preferred Embodiments

[0012] The criticality of the features and merits of the present invention will be better understood by reference to the attached drawings. It is to be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the present invention. It is to be understood that whenever a range of values is described herein or in the appended claims that the range includes the end points and every point therebetween as if each and every such point had been expressly described. Unless otherwise stated, the word "about" as used herein and in the appended claims is to be construed as meaning the normal measuring and/or fabrication limitations related to the value which the word "about" modifies. Unless otherwise specified, the term "embodiment" is used herein to refer to embodiments of the present invention.

[0013] The present invention provides novel and useful methods for making HIP containers as well as the parts resulting from the use of those HIP containers. FIG. 1 shows an example of a valve body 2 that is to be made by HIP consolidation of a metal powder. The valve body 2 has a top flange 4 and a bottom flange 6 with a passage 8 extending therebetween. The valve body 2 also has a neck 10, for accommodating a handle stem, having internal threads 12.

[0014] FIG. 2 shows a cross-sectional elevation view of a first HIP container 20 for making the valve body 2 according the present invention. The first HIP container 20 includes an outer section 22 and an inner core 24 with a cavity 26 being situated therebetween. The cavity 26 is shaped and sized so that use of the first HIP container 20 would result in the production of the valve body 2. As shown, the first HIP container 20 has two ports, first and second ports 28, 30 through which the metal powder, which after being consolidated by HIP is to constitute the valve body 2, may be loaded into the cavity 26 and gas extracted from the cavity 26. It is within the scope of the present invention for the first HIP container 20 to include a single port or any number of ports, the design features of which are selected to permit the powder filling and/or the gas evacuation of the cavity 26. The first and second ports 28, 30 have been chosen to have different designs in this exemplary embodiment in order so illustrate some of the port design variations encompassed by the present invention. The first port 28 has a collar 32 protruding from the outer section 22. The collar 32 is adapted to receive a crimpable tube 36 (shown in phantom) which is fastened to collar 32 by weld 38 (shown in phantom) which is of a length and size so as to be adapted to be attached to a vacuum hose. The second port 30 includes a crimpable, pipe-like protrusion 40 that is of a length and size so as to be adapted to vacuum hose. The first HIP container 20 also has an optional gas-impervious coating 42 which is best seen in the expanded view of section A. The coating 42 covers the exterior of first HIP container 20 and is designed to prevent gas leakage into the cavity 30 during the gas evacuation of the cavity 30 and during the hot isostatic pressing of the first HIP container 20. A coating such as coating 42 is necessary only in cases in which the first HIP container 20 has interconnected porosity which would cause a vacuum leak in cavity 26 or would permit gas to enter the cavity 26 during the hot isostatic pressing of first HIP container 20. [0015] The first HIP container 20 is made according to the present invention by three dimensional printing followed by post-printing processing. The build powder used for three dimensional printing the first HIP container 20 is selected to be compatible with the three dimensional printing process, the post-printing processing of the printed container, the metal powder that is to be contained within the cavity 26 of the first HIP container 20, and the HIP condition. For example, the build powder may be chosen to be a low carbon steel powder of a powder size and distribution that allows it be readily spread in a three dimensional printer and then sintered into a strong monolithic body or sintered and infiltrated with a bronze into a strong composite body. The low carbon steel is also amenable to being hot crimped to form a vacuum-tight seal after powder has been filled into the cavity 26 and the gases have been evacuated out of cavity 26. Though strong at room temperature, the low carbon steel flows easily under common HIP temperature and pressure conditions to allow a metal powder contained within the cavity 26 to consolidate into a dense part. Low carbon steel is also easily machined and/or chemically removed from the valve body 2 that was formed as a result of the hot isostatic pressing of the metal powder in the cavity 26.

[0016] The compatibility of the build powder with the metal powder that is to be consolidated within cavity 26 may be enhanced by adjusting the character of the portion of the surface of the cavity 26 that comes into contact with the build powder. The character may be adjusted by chemically altering that surface by chemical means to make the surface relatively inert. This may be done by contacting the surface with chemical solutions or suspensions, by exposing the surface to an appropriate gas or combination of gases at an appropriate temperature, or a combination of these methods. The character of the surface also be adjusted by coating the surface with a relatively inert material, e.g., alumina, boron nitride, etc. The coating may be applied by exposing the surface to a suspension of the inert material in an appropriate carrier fluid. The surface character may also be adjusted through a combination of the use of a chemical means and the application of a coating material.

[0017] The optional gas-impervious coating 42, when used, must adhere well to the underlying surface of the first HIP container 20. It must also be capable of extending over and sealing any porosity on that underlying surface and to maintain a gas-tight seal even during the pressure and temperatures applied during the HIP. Thus, both the thickness and the material properties of coating 42 must be chosen with care. It is within the scope of the present invention that the coating 42 consist of a single layer or of multiple layers. When coating 42 consists of multiple layers, the layers may be of the same material or they may be of different materials each of which is chosen so that the overall coating 42 has the aforementioned adherence and performance characteristics. The coating 42 may be applied by a number of different methods and by a combination of methods. One method is to apply the coating 42 by electroplating or electroless plating or a combination thereof. An example of such a coating may be a nickel plated coating having a thickness about 60 to 100 microns. Another method is to apply the coating 42 by dipping the first HIP container 20 into a molten metal bath of the coating material or a succession of baths of one or more coating materials, using whatever preheating and atmospheric protections against undesirable chemical reactions as are necessary. Another method is to apply the coating by plasma spray deposition. Two or more of these methods may be combined to form the coating 42. Appropriate cleaning and other surface preparations, e.g., surface roughness adjustments, the application of transient interfacial layers, etc., are to be used during the application of coating 42. Precautions are to be taken during the formation of the coating 42 to achieve the desired amount of cleanliness of the cavity 26 and its surfaces. In some embodiments, the coating 42 may cover a portion or all of the surface of cavity 26. Additional information concerning the means for the application of coating 42 can be found in ASM "Handbook Volume 5 : Surface Engineering" published by ASM International in 1994 as ISBN 978-0-87170-384-2.

[0018] The present invention may employed to make any desired part by means of HIP. The container is provided with a cavity that is configured and dimensioned to result in the desired hot isostatically pressed part. The outer surface of the container is designed to conform to the cavity so as to subject the cavity to an isostatic pressure that is undistorted. The thickness of the container wall between the cavity and the outer surface is preferably chosen to be as thin as is practicable taking into regard the material from which the container is constructed, the container's design, and the need to maintain the structural integrity of the container during construction and processing. Preferably, the wall thickness is in the range of between about 0.01 inches (0.25 millimeters) and 0.5 inches (12.7 millimeters).

[0019] The sintering of the build powder may be by solid state sintering, reactive sintering, transient liquid phase sintering, or liquid phase sintering. Additional information about sintering may be found in "Sintering Theory and Practice" by Randal M. German, which was published by John Wiley & Sons, Inc. in 1996 with ISPB 0-471-05785-X. [0020] All United States patents and patent applications, all foreign patents and patent applications, and all other documents identified herein are incorporated herein by reference as if set forth in full herein to the full extent permitted under the law.