Reaction kinetics study of hydrogen reduction of high energy milled CoCrFeNi high-entropy alloy (HEA)

In this study, an equimolar CoCrFeNi high-entropy alloy (HEA) was fabricated via ball milling and hydrogen reduction to assess the feasibility of hydrogen reduction of chromium oxide in chromium based HEAs. High-energy milling of metal oxide powders (Co 3 O 4, Cr 2 O 3 , NiO and α-Fe 2 O 3 ) at 2400 rpm produced a homogeneous solid solution, with particle sizes reduced from 60.74 nm at 5 h and 39.84 nm at 30 h milling time. Thermogravimetric analysis (TGA) at varying heating rates was employed, and the Kissinger–Akahira–Sunose (KAS) method was used to compare the reaction kinetics between 5 h and 30 h milled HEA. The 5 h milled HEA reached a conversion fraction of reaction up to 0.71 at 996 °C, while the 30 h milled HEA achieved a conversion of approximately 0.75 at 881 °C. TGA analysis of 30 h milled HEA revealed a 17.3% degree of Cr 2 O 3 reduction without holding time and 52.7 % degree of Cr 2 O 3 reduction after 3 h hold at 1000 °C. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) confirmed nano-sizing, homogeneity, and phase transformation with increased milling time. The results demonstrate that extended milling enhances microstructural development and hydrogen reduction, potentially making this process a viable alternative to gas atomization for creating CoCrFeNi HEA nanopowder agglomerates for specialized applications. • CoCrFeNi high-entropy alloy fabricated via ball milling and hydrogen reduction. • Reaction kinetics assessed hydrogen reduction feasibility for chromium oxide. • TGA and KAS method determined apparent activation energy of reduction process. • Eco-friendly fabrication of high-entropy alloys was proven to be possible.