Microstructure evolution and magnetic properties of hard magnetic FeCr22Co15 alloy subjected to tension combined with torsion

Axially symmetric magnets with good mechanical properties in the surface layer and good magnetic properties in the volume of material are essential in the production of increasing number of modern electrical devices. In order to obtain this type of gradient structure, two phase (α + γ) hard magnetic FeCr22Co15 alloy was subjected to tension and torsion in temperature range 725-850 °C. The microstructure observations of deformed samples showed the formation of gradient microstructure with minimum grain size (about 1 μm) in the surface layer of material. On the basis of TEM observations, it was found that the deformation resulted in the martensitic transformation of γ into αγ phase. The microstructure observations also showed the presence of intermetallic σ phase (Fe-Cr) with the maximum precipitates amount in the surface layer of material. The measurements of magnetic properties showed decreasing coercive force of FeCr22Co15 alloy after deformation due to preservation of αγ phase (about of 35%) in the microstructure after magnetic treatment. On the other hand, αγ phase might have appeared as a plastic constituent among brittle grains of α phase, which had a positive influence on mechanical properties of the material.