Effects of the wheel rotation speed during the melt-spinning process on the structural morphology and the thermoelectric properties of Ti0.5Zr0.5NiSn alloy

Half-Heusler alloys based on (Ti, Hf, Zr)NiSn possess excellent mechanical and chemical properties as well as high thermal stability, making them promising materials for high-performance thermoelectric (TE) power generators. However, the high cost of Hf limits its use in these alloys. Therefore, Hf-free (Ti, Zr)NiSn alloys synthesised using a rapid process offer a cost-effective approach to reducing product costs. In this study, we employed the fast synthesis melt-spinning (MS) method to prepare an Hf-free Ti0.5Zr0.5NiSn alloy while systematically optimising MS conditions. We found that by varying the rotation speed of the copper wheel in the MS system from 1000 to 4000 rpm, a marked change in the structural morphology of the melt-spun ribbons occurred. Grain growth during the spark plasma sintering process significantly affected TE properties of the bulk Ti0.5Zr0.5NiSn alloy depending on the structural morphology. As a result, a maximum ZT of ~1.1 at 823 K was achieved for a wheel rotation speed of 3000 rpm, which is comparable to ZT values obtained from the (Ti, Hf, Zr)NiSn-based half-Heusler alloys prepared by other methods.