Phase transformations and magnetic properties of ball-milled Fe–6P–1.7C powders

• Nanocrystalline Fe–6P–1.7C powders were obtained by mechanical alloying method.
• The crystallite size reduction is accompanied by the introduction of internal strains.
• Thermal annealing leads to the strain relaxation and grain growth.
• The magnetic properties depend on the particle size and the chemical composition.
• Porosity and microhardness of the powders increase with microstructural refinement.

Nanocrystalline Fe–6P–1.7C powders were prepared by mechanical alloying from elemental Fe, P and C powders in a high energy planetary ball-mill P7 under argon atmosphere. Phase transformations, morphological changes, thermal stability, magnetic properties and microhardness evolution were studied by X-ray diffraction, scanning electron microscope, differential scanning calorimetry, vibrating sample magnetometer and Vickers microhardness. The Rietveld refinement of the X-ray diffraction pattern reveals the formation of disordered Fe(P) and Fe(C) solid solutions and Fe2P phosphide after 9 h of milling. On further milling (50 h), Fe3P, Fe3C and Fe(P, C) phases are formed when the total mixing of the elemental powders is achieved at the atomic level. The crystallite size reduction down the nanometer scale (∼9 nm) is accompanied by the introduction of internal strains up to 1.8% (root-mean square strain, rms). The mixing kinetics of the elemental powders can be described by an Avrami parameter n = 1.5. The saturation magnetization and coercivity values are of about 157.3 emu/g and 80 Oe, respectively, after 24 h of milling.

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