Microstructure Evolution and Some Properties of Hard Magnetic FeCr30Co8 Alloy Subjected to Torsion Combined with Tension

The hard magnetic alloy FeCr30Co8 alloy was subjected to severe plastic deformation (SPD) by torsion combined with tension in the temperature range of 750 °C to 850 °C. This range of deformation temperatures corresponds to the α solid solution on the Fe–Cr–Co phase diagram. The study of the alloy after SPD by means of X-ray diffraction (XRD) and scanning and transmission electron microscopy techniques showed the formation of a gradient microstructure with fine grain size in the surface layer and precipitation of the hard intermetallic σ-phase. Next, the magnetic and mechanical properties of the deformed alloy after short annealing at 1000 °C and magnetic treatment were studied. A slight decrease in coercive force was found, along with a significant gain in plasticity and strength. The effective deformation temperature was determined to obtain the optimal magnetic and mechanical characteristics of the alloy. This method of deformation can be applied for the improvement of the mechanical properties of some magnets (high-speed rotors) which should have good magnetic properties within their volume while maintaining good mechanical properties on the surface.