Consolidation of Al/Fe₃O₄ composites using high-pressure torsion and their magnetic properties

Severe plastic deformation using high-pressure torsion was applied for consolidation of Al/Fe₃O₄ composites. The consolidation was achieved with the Vickers microhardness saturated to -240 HV for Al-10 vol%Fe₃O₄ and to ∼300 HV for Al-20 vol%Fe ₃O₄ after processing for 5 revolutions under a pressure of 6 GPa. The density increased with straining and reached the highest after 5-7 revolutions but decreased for further revolutions. The coercive force had the same trend as the density but the saturation magnetization is almost invariable with straining. No appreciable difference was observed between the magnetic fields applied in the directions perpendicular and parallel to the ring plane. Electrical conductivity decreased with straining and this was attributed to generation of a large amount of lattice defects such as grain boundaries.