Application of magnetic field to the control of grain boundary segregation in iron

摘要

Magnetic annealing was carried out to examine the effect of a magnetic field on impurity segregation to grain boundaries in an Fe-0.8 at.% Sn alloy at 973 K for 6 h with a superconducting magnetic field up to 6 T. After magnetic annealing, atomic force microscopy was applied to evaluate grain boundary energy, and FEG-TEM/EDS analyses were performed across the grain boundaries whose character was previously determined by orientation imaging microscopy. Of particular interest is the finding that grain boundary energy increased with increase in the strength of a magnetic field applied during annealing. Furthermore, FEG-TEM/EDS analyses revealed that the tin concentration at random boundaries in magnetically (H = 3 T) annealed sample was almost the same as the grain interior, whereas the content in ordinarily (H = 0) annealed sample was approximately 1.5 times higher than that in the grain interior. These findings are the first demonstration that magnetic annealing has a great potential for the control of grain boundary segregation and improvement in grain boundary segregation-induced embrittlement in ferromagnetic polycrystalline materials.