Young's Modulus and Hardness of Zr_(0.5)Hf_(0.5)Ni_xPd_(1-x)Sn_(0.99)Sb_(0.01) Half-Heusler Compounds

摘要

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 Zr_(0.5)Hf_(0.5)NiSn_(0.99)Sb_(0.01). In the efforts to decrease the thermal conductivity of the compound toward the development of thermoelectric materials with high thermal conversion efficiencies, specimens were fabricated with varying amounts of palladium at the nickel site. In addition to the general Zr_(0.5)Hf_(0.5)NiSn_(0.99)Sb_(0.01) composition, nine hot-pressed samples of the Zr_(0.5)Hf_(0.5)Ni_(1_x)Pd_xSn_(0.99)Sb_(0.01) (0.0 ≤ x ≤ 1.0) composition were synthesized. Indentation measurements were obtained using both microhardness testing and depth-sensing nanoindentation. The general Zr_(0.5)Hf_(0.5)NiSn_(0.99)Sb_(0.01) composition was observed to have a mean hardness and mean elastic modulus of 939(42)HV0.2 and 238.5(3.8)GPa, respectively. (The numbers in parentheses represent ± one standard deviation in data; an HV of 0.2 implies that the Vickers hardness attained corresponds to an indentation loading of 0.2 kg.) For all of the compositions tested the hardness range was observed to lie between 654HV0.2 and 979HV0.2. The elastic moduli for these compositions were found to range between 194.0 GPa and 238.5 GPa. The effects of the palladium substitution at the nickel site on the elastic stiffness and hardness are discussed. The hardness and stiffness of these compositions are compared to other selected half-Heuslers, skutterudites, LAST materials, and oxides in the literature that are being explored for thermoelectric applications.