Mechanically alloyed Fe-Zr-(B,Cu) alloys: effect of composition and heat treatment on the microstructure and the magnetic properties

Abstract

Nanocrystalline Fe 86Zr 7(B,Cu) 7 alloys were prepared by mechanical alloying of elemental powders, and investigated by X-ray diffraction, differential scanning calorimetry and electron microscopy. The as-milled powders consist of supersaturated bcc solid solutions with grain sizes of typically 5–10 nm and a small amount of amorphous phase, which depends on the overall composition of the alloy. The refinement of the crystal size to the nanometer range is accompanied by an increase in atomic-level strain. Heat treatment at elevated temperatures leads to chemical redistribution, strain release and grain growth for the bcc solid solutions prior to the crystallization of the amorphous phase. Both grain growth and strain release depend on the volume fraction of amorphous phase and the particular annealing treatment of the powders. The magnetic properties of the material are discussed with respect to the composition of the material, the deformation and recovery processes during milling, and the strain release and the phase transitions upon subsequent heating. The results are compared with data for rapidly quenched materials.