Abstract: Half-Heusler (HH) compounds have emerged as promising candidates for high-temperature thermoelectric power generation; however, their mechanical properties in service environments have been scarcely reported. In this study, the temperature dependences of the mechanical responses and failure mechanisms of an n-type ZrNiSn-based HH compound (Zr_0.5Hf_0.5NiSn_0.985Sb_0.015) were systematically evaluated through high-temperature compression tests and microfractographic characterization. The test results indicated that the elastic modulus and ultimate compressive strength of Zr_0.5Hf_0.5NiSn_0.985Sb_0.015 decreased with increasing temperature. The stress-strain behavior of the material changed from linear (300, 500, and 700 K) to nonlinear (900 and 1100 K). Microfractography observations revealed that increasing the temperature reduced the strength of the grain boundary as well as aggravated oxidation and segregation on the fracture surface, which significantly impacted the macro-compressive behavior of Zr_0.5Hf_0.5NiSn_0.985Sb_0.015 at elevated temperatures. Finally, a stress-strain relationship for the ZrNiSn-based HH was proposed to describe the change in the compressive response from linear to nonlinear with increasing temperature. The present study elucidates the load-carrying and failure mechanisms of Zr_0.5Hf_0.5NiSn_0.985Sb_0.015 within its operational temperature range, providing valuable guidance for the mechanical design of HH thermoelectric devices over their entire service temperature range.

Key words: Half-Heusler compounds, Temperature dependence, Mechanical response, Failure mechanism