US20190091768A1

US20190091768A1 - Rapid additive sintering of materials using electric fields

Info

Publication number: US20190091768A1
Application number: US15/716,664
Authority: US
Inventors: Brandon A. McWilliams; Jian H. Yu; Jeffrey Zabinski
Original assignee: US Army Research Laboratory; United States Department of the Army
Current assignee: US Army Research Laboratory; United States Department of the Army
Priority date: 2017-09-27
Filing date: 2017-09-27
Publication date: 2019-03-28

Abstract

Rapid additive sintering of materials using electric fields includes a pair of electrodes including a first and second electrode, a power supply operatively connected to the pair of electrodes, and an area in between the pair of electrodes that holds a material. The first electrode is configured for flash sintering the material. The first electrode may be movable and may include a stylus. The material may include powder and may include any of metallic and ceramic material. Multiple layers of materials may be flash sintered by the first electrode. The first electrode may generate an electric field between the first electrode and the material causes the flash sintering. A nozzle may supply the material at variable speeds. The first electrode may be configured to move at variable speeds and in variable directions. The flash sintering may occur at an electric field between 10-50000 V/cm and an electric current between 0-30A.

Description

GOVERNMENT INTEREST

The embodiments herein may be manufactured, used, and/or licensed by or for the United States Government without the payment of royalties thereon.

BACKGROUND

Technical Field

The embodiments herein generally relate to manufacturing processes, and more particularly to three-dimensional/additive manufacturing (3D/AM) processing.

Description of the Related Art

There are several critical technology gaps that must be addressed to enable 3D/AM to accelerate away from prototypes and mold/die production toward production of finished parts. For example, finished parts production is an enabler for providing the defense industry with a threat responsive capability to deal with unknowns and surprises on the battlefield, and to reduce logistics burdens. Highlighted are two critical gaps: one is the ability to realize in-line certification of finished parts and the other is to control the processing-structure-property-performance relationships from 3D/AM machines. Controlling the final properties will enable 3D/AM to produce structural components.
Laser based 3D printing systems are designed specifically for processing of metals. These processes rely on local melting and re-solidification of the powder bed which typically results in non-ideal microstructure and properties and may also introduce defects such as porosity and non-equilibrium inclusions or precipitates. The high temperatures associated with laser based AM methods also results in high residual stresses and distortions which may render the part unusable or require additional post processing and associated time and costs.

SUMMARY

In view of the foregoing, an embodiment herein provides an apparatus comprising a pair of electrodes comprising a first electrode and a second electrode; a power supply operatively connected to the pair of electrodes; and an area in between the pair of electrodes that holds a material, wherein the first electrode is configured for flash sintering the material. The first electrode may be movable. The first electrode may comprise a stylus. The material may comprise powder. The material may comprise any of metallic and ceramic material. The apparatus may further comprise multiple layers of materials flash sintered by the first electrode. The first electrode may generate an electric field between the first electrode and the material causes the flash sintering. The apparatus may further comprise a nozzle that supplies the material, wherein the nozzle is configured to supply the material at variable speeds. The first electrode may be configured to move at variable speeds and in variable directions. The flash sintering may occur at an electric field between 10-50000 V/cm and an electric current between 0-30 A.
Another embodiment provides a method comprising positioning a pair of electrodes comprising a first electrode and a second electrode; positioning material in between the pair of electrodes; and applying an electric field between the first electrode and the material causing flash sintering of the material. The method may further comprise moving the first electrode over the material. The material may comprise powder. The material may comprise any of metallic and ceramic material. The method may further comprise applying additional material after the flash sintering; and performing another flash sintering process. The method may further comprise forming multiple layers of sintered material. The method may further comprise shaping the multiple layers into a 3D structure. The method may further comprise supplying the material at variable speeds. The method may further comprise moving the first electrode at variable speeds and in variable directions. The flash sintering may occur at an electric field between 10-50000 V/cm and an electric current between 0-30 A.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:

FIG. 1 illustrates a schematic diagram of an apparatus according to an embodiment herein;

FIG. 2 illustrates a schematic diagram of the encircled portion A of the apparatus of FIG. 1 according to an embodiment herein;

FIG. 3A illustrates a scanning electron microscope (SEM) image of several layers of aluminum additively built on a copper substrate according to an embodiment herein;

FIG. 3B illustrates another SEM image of several layers of aluminum additively built on a copper substrate according to an embodiment herein; and

FIG. 4 is a flow diagram illustrating a method according to an embodiment herein.

DETAILED DESCRIPTION

The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The embodiments herein provide a flash sintering process to enable 3D printing or AM. The embodiments herein use electric field effects to rapidly sinter materials additively to form bulk solid components. Referring now to the drawings, and more particularly to FIGS. 1 through 4, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.
The embodiments herein provide an AM technique for fabrication of 3D metallic and ceramic components of complex geometry on demand. The technique provided by the embodiments herein uses electric fields to exploit flash sintering phenomena and to rapidly sinter powder feedstocks. The process uses a low current, high voltage flash sintering process to fuse powders into dense structures at significantly lower temperatures and faster rates than conventional processes.
FIG. 1 illustrates an apparatus 10 comprising of a conductive build plate/electrode 15, a movable electrode 25, and a power supply (AC or DC) 30 comprising wiring 50 connected to the movable electrode 25. Supplying materials (e.g., powders) 35 are provided on the conductive build plate/electrode 15 and near the movable electrode 25, and may be supplied using an off-axis or in-line nozzle 55 (shown as an off-axis nozzle 55 in FIGS. 1 and 2, for example). The powder material 35 is sintered in between the electrodes 15, 25 by the flash sintering effect, which limits the spatial extent of deposition onto the build plate or support structure 15. The powder 35 may be pre-compacted to improve initial density. The energized movable electrode 25, which may be configured as a stylus, is then passed over the powder 35 to consolidate by sintering or melting a single layer of the powder 35. To additively build a component, the powder 35 is deposited and sintered repeatedly to build layers 40, 45 until the net shape of the desired final geometry is obtained. The geometry of the deposited layers 40, 45 can be regulated by controlling the: (a) electrical field strength between the electrode 25 and the growing material interface of the powder 35; (b) powder feed rate; and (c) speed and direction of the movable electrode 25. Accordingly, in FIG. 1, layers 40, 45 depict previously sintered material and material 35 is currently undergoing flash sintering.
The embodiments herein exploit flash processing, which enables material consolidation at significantly lower temperatures (on the order of hundreds of degrees Centigrade below traditional sintering) and at significantly higher rates (from several hours in conventional processing to tens of seconds using the embodiments herein). Low temperature sintering within a narrow spatial extent enables incorporating flash technology into an additive processing system to deposit material in complex geometries and create valuable components and finished products. The flash sintering process typically uses electric fields on the order of 10-50000 V/cm and electric currents between 0-30 A. The electric field enhances the thermodynamics and kinetics of consolidation. The flash phenomenon describes the point at which the material 35 rapidly densifies and is associated with a change in electrical conductivity of the material from insulating to conducting. The flash phenomenon is ideally suited for exploitation in an additive manufacturing tool. The tip 20 of the movable electrode 25 is brought into close proximity to the powder 35, as further shown in FIG. 2. This permits both a high electric field (field strength divided by distance) and limits the spatial extent of the deposition for creation of fine features. FIGS. 3A and 3B illustrate SEM images of several layers of aluminum alloy 5083 additively built on a copper substrate according to an embodiment herein. The images confirm the validity of the techniques provided by the embodiments herein.
FIG. 4, with reference to FIGS. 1 through 3B, is a flow diagram illustrating a method according to an embodiment herein. The method comprises positioning (60) a pair of electrodes 15, 25 comprising a first electrode 25 and a second electrode 15; positioning (62) material 35 in between the pair of electrodes 15, 25; and applying (64) an electric field between the first electrode 25 and the material 35 causing flash sintering of the material 35. The method may further comprise moving the first electrode 25 over the material 35. The material 35 may comprise powder. Additionally, the material 35 may comprise any of metallic and ceramic material. The method may further comprise applying additional material 35 after the flash sintering, and performing another flash sintering process. The method may further comprise forming multiple layers 40, 45 of sintered material. The method may further comprise shaping the multiple layers 40, 45 into a 3D structure. The method may further comprise supplying the material 35 at variable speeds. The method may further comprise moving the first electrode 25 at variable speeds and in variable directions.
The embodiments herein address the gap of micro-structural control, which the conventional solutions have not been able to provide. One aspect of the embodiments herein create microstructures with desirable properties/performance) at lower temperatures. The reduction in processing temperature may be greater than 800° C., which is quite substantial for reduction of costs, and enables manufacture of materials with unique microstructures and properties not obtainable through conventional techniques. In addition, the techniques of exploiting “flash technology” in 3D/AM as provided by the embodiments herein permits very short manufacturing times (e.g., hours) to produce complex components. Lower temperatures and shorter manufacturing times reduce cost and provide a means to produce parts from ceramics with new microstructures compared to conventional techniques. The embodiments therein, therefore lower costs, enables new finished or near net shape components, and increases availability. Polymers and metals dominate the 3D/AM space. Accordingly, the technique provided by the embodiments herein opens new markets in ceramics. The embodiments herein also apply to metal 3D/AM processing, and again offers reduced temperature processing and access to new properties through control of the microstructure.
The embodiments herein provide on-demand manufacturing in support of agile expeditionary forces, on-demand manufacturing of complex geometry components for light weighting efforts and rapid prototyping, and allow for rapid production of 3D printed components and for the repair of damaged components. The flash processing techniques utilized by the embodiments herein enables densifying materials that cannot be utilized in traditional AM or sintering processes. The embodiments herein are able to fuse powders into dense structures at significantly lower temperatures and faster rates than conventional processes such as Direct Metal Laser Sintering (DMLS), Laser Engineered Net Shaping (LENS), and arc welding. The process provided by the embodiments herein involves solid state processing which has advantages of preserving microstructures of starting feedstocks, including nanocrystalline structures. The process provided by the embodiments herein is not limited to metals, and enables much lower temperature sintering and processing of wide range of materials, including AM of ceramics, and multi-material processing with a single apparatus 10. Accordingly, the embodiments herein may be utilized in several types of diverse applications including the rapid prototyping of a wide range of materials, complex geometry components, agile expeditionary manufacturing, reduce logistic burden of soldiers in field, repair and sustainment of existing systems/components, 3D printed ceramics, 3D printed composite structures, 3D printed metallic structures, 3D printed nanomaterials, and 3D printed biomaterials.
The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.

Claims

What is claimed is:

1. An apparatus comprising:

a pair of electrodes comprising a first electrode and a second electrode;

a power supply operatively connected to said pair of electrodes; and

an area in between said pair of electrodes that holds a material,

wherein said first electrode is configured for flash sintering said material.

2. The apparatus of claim 1, wherein said first electrode is movable.

3. The apparatus of claim 1, wherein said first electrode comprises a stylus.

4. The apparatus of claim 1, wherein said material comprises powder.

5. The apparatus of claim 1, wherein said material comprises any of metallic and ceramic material.

6. The apparatus of claim 1, further comprising multiple layers of materials flash sintered by said first electrode.

7. The apparatus of claim 1, wherein said first electrode generates an electric field between said first electrode and said material causes said flash sintering.

8. The apparatus of claim 1, further comprising a nozzle that supplies said material, wherein said nozzle is configured to supply said material at variable speeds.

9. The apparatus of claim 2, wherein said first electrode is configured to move at variable speeds and in variable directions.

10. The apparatus of claim 7, wherein said flash sintering occurs at an electric field between 10-50000 V/cm and an electric current between 0-30 A.

11. A method comprising:

positioning a pair of electrodes comprising a first electrode and a second electrode;

positioning material in between said pair of electrodes; and

applying an electric field between said first electrode and said material causing flash sintering of said material.

12. The method of claim 11, further comprising moving said first electrode over said material.

13. The method of claim 11, wherein said material comprises powder.

14. The method of claim 11, wherein said material comprises any of metallic and ceramic material.

15. The method of claim 11, further comprising:

applying additional material after said flash sintering; and

performing another flash sintering process.

16. The method of claim 15, further comprising forming multiple layers of sintered material.

17. The method of claim 16, further comprising shaping said multiple layers into a three-dimensional (3D) structure.

18. The method of claim 11, further comprising supplying said material at variable speeds.

19. The method of claim 12, further comprising moving said first electrode at variable speeds and in variable directions.

20. The method of claim 12, wherein said flash sintering occurs at an electric field between 10-50000 V/cm and an electric current between 0-30 A.