Copper is a material of interest to Additive Manufacturing (AM) owing to its outstanding material properties, which finds use in enhanced heat transfer and electronics applications. Its high thermal conductivity and reflectivity cause challenges in the use of Powder Bed Fusion AM systems that involve supplying high-energy lasers or electron beams. This makes Binder Jetting a better alternative as it separates part creation (binding together of powders) from energy supply (post-process sintering). However, it is challenging to fabricate parts of high density using this method due to low packing density of powder while printing. This work aims to investigate the effects of Hot Isostatic Pressing (HIP) as a secondary post-processing step on the densification of Binder Jet copper parts. By understanding the effects of HIP, the author attempts to create parts of near-full density, and subsequently to quantify the effects of the developed process chain on the material properties of resultant copper parts. The goal is to be able to print parts of desired properties suited to particular applications through control of the processing conditions, and hence the porosity. First, 99.47% dense copper was fabricated using optimized powder configurations and process parameters. Further, the HIP of parts sintered to three densities using different powder configurations was shown to result in an improvement in strength and ductility with porosity in spite of grain coarsening. The strength, ductility, thermal and electrical conductivity were then compared to various physical and empirical models in the literature to develop an understanding of the process-property-performance relationship. / Master of Science / Additive Manufacturing (AM) is a technique of fabricating an object in a layer-wise fashion. The layer-based approach provides opportunity for the manufacture of highly complex shapes. Binder Jetting is an AM technology that creates parts by the selective jetting of a polymeric binder onto successive layers of powdered material. In the case of metals, the printing process is followed by sintering in an oven, which burns out the binder and densifies the part. However, this is typically not enough to remove all the porosity in a specimen. While this enables the fabrication of a variety of materials, the porosity in sintered parts can be a detriment to their properties. This work aims to investigate the use of post-process Hot Isostatic Pressing (HIP) to eliminate the remaining porosity. HIP is a technique of applying high pressures at high temperatures in an inert gas medium. The goal of this research is to scientifically understand and quantify the effect of HIP on sintered parts made via Binder Jetting. The research is carried out in the context of copper, which has unique mechanical, thermal and electrical conductance properties that could be influenced by the presence of pores. In this work, the effects of the Binder Jetting-Sintering-HIP process chain on the porosity, and consequently the material properties, of copper parts are quantified. Resolving the issue of porosity can enable the printing of copper parts for specialized applications from electronic components to rocket engines. Developing a quantitative understanding can pave the way to design specific processing conditions to fabricate not only fully dense copper parts with superior properties, but also parts of a designed level of porosity that have specific target material properties.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/82833 |
| Date | 13 April 2018 |
| Creators | Yegyan Kumar, Ashwath |
| Contributors | Mechanical Engineering, Williams, Christopher B., Yu, Hang, Huxtable, Scott T. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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