Plastic Deformation of Sendust Single Crystals

Abstract

Magnetic heads made of Sendust alloy head cores (standard chemical composition: Fe-9.6 wt%Si-5.4 wt%Al) are known to have superior magnetic properties and wear resistance. The cores are usually made by mechanical working, such as slicing and grinding since the alloy is so hard and brittle that it has been believed to be difficult to make head cores by plastic deformation. In the present work, plastic deformability of the alloys was investigated by compressive tests on Sendust single crystals at temperatures between room temperature and 1173 K and various strain rates. Main results are summarized as follows.
The operative slip systems are {110}⟨111⟩ and {112}⟨111⟩ depending on compressive axis. Therefore, the von Mises criterion for a polycrystalline material to deform plastically by slip within grains is satisfied, indicating that the brittleness of Sendust alloys cannot be explained by the number of independent slip modes available. At room temperature the stress-strain curve exhibits three stages in a similar manner to Fe₃Al and Fe₃Si with DO₃ structure.
Above the temperature where yield stress decreases abruptly, the steady state deformation takes place. Under the condition of the steady state deformation, the strain rate is represented by the relationship of \dotε=Bσⁿexp(−Q⁄kT), where n=4.6 and Q=540 kJ/mol. These results suggest that even a polycrystalline material of Sendust alloy may be deformable under the suitable conditions.