Fabrication of ultra-fine grained Hf-based materials with superior hardness and temperature-independent electrical conductivity by a combination of high-energy ball milling and spark plasma sintering

Ultra-fine grained (UFG) hexagonal-close-packed (HCP) hafnium (Hf) and Hf-5 wt%Y2O3 (HYO) were pre-pared by a combination of high-energy ball milling and spark plasma sintering (SPS), and both possess high relative density (95-99%), high hardness, and low electrical conductivity. The HYO sample shows superior hardness of 12.11 GPa, which is about 6-7 times of that of coarse-grained Hf, and electrical conductivity of 2 x 10(5) S/m, which keeps constant and is almost independent of temperature. It is very possible for HYO with these good properties to become an excellent plasma torch cathode. The analysis of the microstructure under transmission electron microscope (TEM) and scanning electron microscope (SEM) shows that the superior hardness of the samples originates from the grain boundary (GB) strengthening and the pinning effects of the Y2O3 particles, while their almost temperature-independent electrical conductivity originates from the combining effects of the dispersion of large electrical resistivity particles Y2O3 and the dense high -angle grain boundaries (GBs). (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

Ultra-fine grained hafnium and Hf-5 wt%Y2O3 samples with high relative density, high hardness, and low electrical conductivity were prepared using a combination of high-energy ball milling and spark plasma sintering. The analysis of the microstructure revealed that the superior hardness of the samples is due to grain boundary strengthening and the pinning effects of the Y2O3 particles, while their almost temperature-independent electrical conductivity is attributed to the dispersion of Y2O3 particles and the dense high-angle grain boundaries.