Surface aluminization for enhancing oxidation resistance of Nb 0.86 Hf 0.14 FeSb thermoelectric element

NbFeSb-based half-Heuslers (HHs) exhibit exceptional high-temperature thermoelectric (TE) performance, but their practical deployment is hindered by insufficient oxidation resistance. Here, a surface aluminization technology is introduced to improve oxidation resistance by forming in-situ intermetallic compounds on the material surface. During this process, a dense coating with a thickness of 40-80 μm is formed through a solid/gas reaction between Al and the main constituents of HHs, exhibiting a lamellar structure composed of Al 13 Fe 4 , Al 3 Nb and AlSb in sequence. The coating and substrate exhibit a robust metallurgical bond. Benefiting from the intrinsic oxidation resistance of aluminides, the coating serves as an effective diffusion barrier against oxygen penetration. Diffusion kinetics analysis reveals that the coating/substrate interface maintains an ultra-low diffusion rate in air, extending the predicted service life to over 10 years. The coated elements demonstrate negligible degradation in TE properties during prolonged aging at 973 K. The surface aluminization method effectively improves the feasibility and thermal stability of NbFeSb-based HHs in air, thus advancing their practical applications.