Processing of FeCo Nanosized Soft-Magnetic Material by Powder Metallurgy Technique

Abstract

A nanosized cobalt-based alloy containing 20 wt % Fe was synthesis by electroless chemical reduction method using alkaline tartarate bath and sodium hypophosphite as a reducing agent . The powder was investigated by optical microscope, SEM and XRD to identify the powder shape, size and the chemical composition. The prepared powder has a spherical shape with a particle size of about 200 nm. The investigated powder was cold compacted at 600 MPa and then sintered in hydrogen atmosphere at 1050 0C. Metallographic, physical, magnetic and electrical properties investigations were carried out for the prepared powder and its sintered compacts. The prepared powder has 2.5% phosphorus content which was liberated by heating the compacts to the sintering temperature in hydrogen atmosphere. From the results of the density measurements we can observe that the prepared sintered FeCo material had a relative density about 96% to the theoretical. But the results of the electrical properties measurements give an indication of the decreasing in the electrical resistivity than the materials produced by the traditional methods. On the other hand the magnetic measurements, of the FeCo powder has a lower specific saturation induction, Bs, than the sintered one which was due to the presence of the paramagnetic metal phosphides in the powder but after rising the temperature to sintering the, Bs, values is increased due to the conversion of the phosphides to the metallic state and the phosphorus was liberated, but the coercive force was decreased by sintering of the powder compacts by lowering the porosity of the materials with sintering and the formation of the soft magnetic materials Fe-Co solid solution which was investigated by XRD having the highest specific saturation induction value. Also the magnetic permeability of the prepared sintered material was increase with increasing the applied field until 50 Oe which has the highest value and decreased with increasing the field more than 50Oe. From the magneto-resistance measurements, it was shown that the sintered material has a positive magneto-resistance in the field direction but a negative one in the direction perpendicular to the current and the field.