Synthesis and microstructural characterization of nanostructured Fe50Ni50 alloy prepared by mechanical alloying

Abstract

In this comprehensive study, the synthesis, phase evolution, and microstructural characteristics of nanostructured Fe50Ni50 alloy powders produced via high-energy mechanical alloying (MA) were systematically investigated. Elemental iron and nickel powders were processed in a high-energy planetary ball mill under a controlled argon protective atmosphere to prevent oxidation, utilizing a constant ball-to-powder weight ratio (BPR) of 20:1 and a rotational speed of 350 rpm across cumulative milling durations of 0, 4, 8, 32, 48, and 96 hours. The structural transformations, crystallite size refinement, internal lattice strain accumulation, and lattice parameter expansion were evaluated using X-ray diffraction (XRD) data interpreted through Scherrer and Williamson–Hall analytical approaches. Furthermore, morphological alterations, particle size distributions, and microstructural transitions were examined using scanning electron microscopy (SEM) equipped with secondary electron detectors and Image Tool software. The XRD results indicate that continuous high-energy mechanical deformation up to 96 hours induces complete mechanical alloying, resulting in the formation of a random (Ni,Fe) solid solution with a face-centered cubic (fcc) crystal structure, as evidenced by the disappearance of the individual bcc iron diffraction peaks and significant broadening of the nickel-related peaks. The crystallite size exhibited a sharp initial decline followed by a relatively stable trend, decreasing from an initial value of 65 nm to a minimum of 12 nm after 96 hours. Simultaneously, the internal lattice strain increased progressively, reaching a maximum value of 0.58%. Morphological analyses revealed that initial microforging, cold welding, and particle flattening predominated during the early milling stages, whereas extended milling induced severe work hardening and fracture, ultimately achieving a dynamic steady-state balance at 96 hours, with refined, relatively uniform, and spherical particles possessing an average size of 10 μm.