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Title:Nanoindentation of copper covetics and the mechanical testing and microstructural imaging of additive manufactured Inconel 718
Author(s):Valdez, Mario A
Advisor(s):Jasiuk, Iwona M.
Department / Program:Mechanical Science & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Additive Manufacturing
Inconel 718 (IN718)
metal matrix composites
Abstract:There have been large developments in metallic material systems over the past century. The mechanical properties of metals have been manipulated by varying the composition of alloys. In this thesis we characterize two metal-based metallic systems: novel metal carbon materials (covetics) and additive manufactured Inconel. Recent efforts have led to the discovery of a new class of material called covetics, in which metal and carbon are combined in a new way via a hybrid of metallic and covalent bonds. First, nanoindentation is used to evaluate the mechanical properties of copper-carbon covetics with varying compositions. Test specimens are as cast and have compositions of 0, 3, 5, and 9 weight percent activated carbon. Additionally, this study investigates the mechanical properties of some W-series copper-carbon composites. Four different compositions were compared: 0.83 weight percent activated carbon, 2 weight percent activated carbon, 0.167 weight percent carbon nanotubes, and 0.67 percent graphene nanoplatelets. Base metal, standard copper 10200 was also tested for comparison. Results of nanoindentation showed that there was no distinct trend in hardness or modulus values for the covetic samples tested. However, the specimen with 9 weight percent carbon had the largest hardness and modulus values. It was found that the covetic specimens had lower hardness and modulus values than the base metal, suggesting the copper 10200 specimen had some plasticity. The W-series specimens showed no significant differences in hardness or modulus values, regardless of composition. Along with investigating a new class of material systems, this thesis also investigates the mechanical properties of additive manufactured alloys. Inconel 718 test specimens with varying degrees of porosity were fabricated via direct metal laser sintering. Drop-weight impact tests, uniaxial compression tests, and hardness tests were used to compare mechanical properties across various densities. Additionally, the external and internal structures of the specimens were analyzed through the use of micro-computed tomography and scanning electron microscopy. The results of drop-weight impact tests showed that there was a significant drop in energy absorption once porosity is introduced into specimens. Uniaxial compressions showed similar results with modulus and yield strength values decreasing as more porosity is introduced. Stress-strain curves of porous specimens possessed two linear regions, which is often found in foams. Scanning electron microscopy and micro-computed tomography showed an open-cell foam-like structure throughout the specimens. It was found that the specimens with the two lowest densities had large voids corresponding to unsintered regions.
Issue Date:2015-12-09
Rights Information:Copyright 2015 Mario Valdez
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12

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