Abstract
Ni-Fe alloys with varying nickel contents (5%, 10%, 20%, and 30%) were successfully synthesized through a novel simultaneous reduction-sintering of nano-sized NiO-Fe(2)O(3) precursors. Non-isothermal reduction was performed in hydrogen gas up to 1000 °C at varying heating rates (10-25 °C/min), followed by sintering in pure argon atmosphere at temperatures between 1000 °C and 1300 °C. Thermal analyses (TG-DTA), X-ray diffraction, and scanning electron microscopy with energy dispersive X-ray analysis identified complex, multi-step reduction reactions and phase transformations influenced by reduction temperature, heating rate and precursor composition. Kinetic analyses indicated a dual control mechanism dominated initially by combined gaseous diffusion and interfacial reactions, transitioning to interfacial chemical reactions at higher temperatures. Sintering characteristics of compacts derived from precursors containing 5-30% NiO-Fe(2)O(3) were examined at temperatures from 1000 to 1300°C for 60 min in pure argon. Increased Ni content promoted the formation of intermetallic phases (Fe(7)Ni(3) and Fe(3)Ni), enhancing compositional homogeneity and reducing grain boundary visibility. Higher sintering temperatures notably improved grain growth, densification, intermetallic formation, reduced porosity, and increased micro-hardness. It was found that the combination of 20-30 wt% NiO with reduction at 900 °C followed by sintering at 1300 °C for 60 min yielded the best overall performance of synthesis Ni-Fe alloys. This optimization is making these materials more suitable for structural and functional applications where high strength and density are required.