Indentation Testing of Bulk Zr 0.5 Hf 0.5 Co 1-x Ir x Sb 0.99 Sn 0.01 Half-Heusler Alloys
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1267-DD05-23
Indentation Testing of Bulk Zr0.5Hf0.5Co1-xIrxSb0.99Sn0.01 Half-Heusler Alloys Melody A. Verges1,3, Paul J. Schilling1,3, Jeffrey D. Germond1,3, Puja Upadhyay1,3, William K. Miller1,3, Nathan J. Takas2,3, and Pierre F. P. Poudeu2,3 1 Department of Mechanical Engineering, University of New Orleans, New Orleans, LA 70148, U.S.A. 2 Department of Chemistry, University of New Orleans, New Orleans, LA 70148, U.S.A. 3 Advance Materials Research Institute, University of New Orleans, New Orleans, LA 70148, U.S.A. ABSTRACT Indentation tests were performed to assess the influence of compositional changes on the mechanical properties of several half-Heusler compounds with the general composition Zr0.5Hf0.5Co1-xIrxSb0.99Sn0.01 (x=0.0,0.1,0.3,0.5,0.7). These samples were synthesized by high temperature solid-state reactions and were consolidated by hot-pressing. Indentation measurements were obtained using both microhardness testing (Vickers) and depth-sensing nanoindentation. These measurements were used to determine the microhardness and the elastic modulus of each half-Heusler compound. The Vickers hardness values were found to range between 876 and 964. A slight increase in hardness was observed with the addition of iridium. The elastic stiffness values ranged from 229 GPa to 246 GPa. Here, a slight decrease in stiffness was observed with the addition of iridium. INTRODUCTION While studies engaged in optimizing transport properties are being utilized to maximize thermal efficiencies of thermoelectric materials, research aimed at studying mechanical properties of these materials serve to characterize the mechanical behavior of these materials in thermoelectric devices. The elastic stiffness, for example, determines the mechanical response of the thermoelectric module and becomes an important property to consider in its design. For a thermoelectric couple it is advantageous to have similar stiffness values for both the n-type and p-type legs. The hardness of the material is linked to the fracture toughness [1] as well as the machinability and wear resistance of brittle materials [2,3]. Furthermore, the hardness of a material is directly related to its strength. The compressive strength of a fine-grained, brittle material with minimal manufacturing defects roughly approaches one-third of its hardness [4]. Higher hardness values indicate a thermoelectric material’s ability to withstand higher loadings. Hardness and stiffness studies as a function of composition for bulk materials have been performed on a variety of semiconducting materials including the LAST (AgPbSbTe) compounds, half-Heusler compounds of the NiZrSn1-xSbx composition, sodium cobalt oxides, and polycrystalline zinc-antimony alloys [5-11]. In a number of these studies the mechanical properties are significantly affected as a result of doping. For example, the study conducted by Kawaharada et al [5] on the NiZrSn1-xSbx (x=0.01-0.28) half-Heusler compounds concluded that increasing the antimony content from 0.01 to 0.28 resulted in a decrease of the ela
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