Mechanical testing was performed to determine the influence of compositional changes on the Young’s modulus and hardness of half-Heusler compounds of the base composition Zr0.5Hf0.5CoSb0.99Sn0.01. In the efforts to decrease the thermal conductivity of the composition toward the development of thermoelectric materials with high thermal conversion efficiencies, specimens were fabricated with varying amounts of rhodium and iridium at the cobalt site. In addition to the general Zr0.5Hf0.5CoSb0.99Sn0.01 composition, six hot-pressed samples of the Zr0.5Hf0.5CoxRh1−xSb0.99Sn0.01 (0.0≤x≤1.0) composition and four hot-pressed samples of the Zr0.5Hf0.5CoxIr1−xSb0.99Sn0.01 (0.0≤x≤0.7) composition were synthesized. Indentation measurements were obtained using both microhardness testing and depth-sensing nanoindentation. The general Zr0.5Hf0.5CoSb0.99Sn0.01 composition was observed to have a hardness and elastic modulus around 896HV0.2 and 247GPa, respectively. For all of the compositions tested the hardness range was observed to lie between 347HV0.2 and 951HV0.2. The elastic moduli for these compositions were found to range between 97GPa and 247GPa. The effects of the rhodium substitution and iridium substitution at the cobalt site on the elastic stiffness and hardness are examined.

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