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A6: Characterization

Mechanical properties of tetrahedrite composite materials, including slow crack growth and fracture toughness

C. Y. Liu1, E. D. Case1, A. D. Facci1, R. D. Schmidt1, X. Lu2, D. T. Morelli1, I. B. Perez1, B. P. Rook1,and L. T. Drzal1
1Chemical Engineering and Materials Science Department, Michigan State University, East Lansing, MI2Physics and Astronomy Department, Michigan State University, East Lansing, MI

As a low-cost, earth-abundant and natural mineral-based thermoelectric material with dimensionless figure of merit near 1 at 700 K, tetrahedrite is a promising material for energy harvesting applications. However, as is the case with most thermoelectric materials, enhancing the fracture toughness of tetrahedrite could greatly enhance its mechanical integrity under the thermal fatigue conditions that characterize waste heat harvesting applications.

In this study, we attempt to enhance the fracture toughness of tetrahedrite by adding either (i) silicon carbide nanoparticles or (ii) graphene nanoplatelets into tetrahedrite powders prior to densification, with the volume fraction of added nanophases ranging from about 0.5 to 3 percent. In addition to characterizing the fracture toughness and hardness by Vickers indentation, the elastic moduli were measured using resonant ultrasound spectroscopy (RUS) analysis. Environmentally-assisted slow crack growth (SCG) behavior is also investigated to determine if the flaws introduced by cutting and grinding procedures during fabrication are subject to growth in the presence of water vapor, since such growth can degrade mechanical properties.