Cold compaction of metal-ceramic (ferromagnetic-antiferromagnetic) composites using high pressure torsion

摘要

Metal-ceramic powder mixtures consisting of Co (ferromagnetic) and NiO (antiferromagnetic), at the 1:1 weight ratio, have been compacted by high pressure torsion (HPT) both with and without a prior ball milling (BM) process. The compaction causes a strong reduction of the crystallite sizes, introduces large amounts of stacking faults in the metal and induces a phase transformation from the fcc to the hcp Co allotropes. An enhancement of the coercivity is observed, which is ascribed to the Co particle size refinement, the increase of stacking faults and the magnetic coupling between Co and NiO. Furthermore, ball milled Co-NiO powders compacted by HPT exhibit values of the Vickers microhardness almost twice the value obtained for pure Co subjected to HPT.