S. Nilufar, I. Jasiuk
University of Illinois at Urbana-Champaign,
Keywords: copper, carbon, covetics, mechanical properties, structure, composition
Summary:It is known that solubility of carbon in copper is very small. Covetics are novel materials in which carbon is infused into a metal in a new way far beyond the solubility limit. We studied the structure, composition, and properties of 10200 copper-carbon covetics, with 0, 3, 5 and 9 weight percent (wt%) of carbon. These materials were in as cast T0 condition. Scanning electron microscopy (SEM) was used to visualize grain size and fracture surfaces. X-Ray Diffraction was employed to measure lattice parameter and crystalline size. The crystallite size of copper covetics decreased for 3 wt% C covetics but then the value increased with addition of more carbon. SEM-Energy Dispersive Spectroscopy (EDS) and combustion infrared detection were used to measure carbon content. Amount of carbon detected in SEM–EDS analysis was less than the target amount of C used during the manufacturing process. Smaller grain size and crystalline size and larger lattice constant were found in the 3 wt% C covetic. Mechanical properties were obtained using hardness, impact and tensile tests. Covetic materials with 3 wt% C showed highest Vickers and Rockwell hardness, Charpy impact energy, and yield and ultimate tensile strengths. More specifically, for the 3 wt% C covetic the Vickers and Rockwell hardnesses increased by 71% and 92% respectively as compared to the 0 wt% C. The maximum energy increased almost three times for the samples which had 3 wt% C as compared with the material with 0 wt% C. Under tensile loading, copper covetics also exhibited higher yield strength, ultimate strength, and at the same time higher deformations. The ultimate tensile strength increased by 31% (from 0 to 3 wt% C) from about 170 MPa to nearly 223 MPa. Similarly, 0.2% yield strength increased by 33% for the same material. Elastic modulus remained unchanged and the value was 115-117 GPa for all studied covetics. Ultimate tensile strain also increased for 3 wt% C covetics. Finally, density decreased with increasing carbon content. In summary, the Cu-C covetics showed improved mechanical properties over base copper material and new deformation mechanisms, which make them promising new metal-based structural materials. Further fundamental studies are needed to study these materials so they can be safely used in variety of engineering applications.