Electronic structure characteristics of Fe-6.5 wt%Si alloy doped with rare earth elements and its effect on mechanical properties

Effects of rare earth RE (Y, La, Ce) element doping on electronic structure of Fe-6.5 wt%Si alloy and the influence mechanisms of RE doping on mechanical properties of the alloy were studied via first-principles calculation based on density functional theory (DFT). The results show that there exists significant electron transfer between solid solution RE atom and Fe, Si atoms, which leads to a significant change on the gain/loss quantity of electrons and the bonding properties of atoms, thus changing the covalent interaction of Fe–Fe bonds and Si–Fe bonds, reducing the ordered degree and improving the deformability of Fe-6.5 wt%Si alloy. With an increase of RE content, the tensile deformability at 400 °C of as-cast alloy specimens presented a change rule of first increasing and then decreasing, and the elongation to failure increased from about 7% of non-RE-doped specimens to a maximum of about 22–23% of RE doped specimens. The content of Y, La, and Ce is about 59 ppm, 38 ppm, and 75 ppm respectively (atom fraction, called reasonable content) when the deformability improvement effect of RE is better, the RE exceeding reasonable content tended to enrich near grain boundaries and caused inter-granular brittleness. Through a comparative study between non-RE-doped alloy and RE (Ce) doped alloy, it was found that there was no significant difference in microstructure and crystal structure between the warm-rolled samples of two alloys, but Ce doping reduced tensile yield strength σ0.2 from 1618.5 MPa to 1515.3 MPa and increased elongation to failure from 0.67% to 0.80% at room temperature of warm-rolled samples by weakening covalent interaction of some bonds, which helps to improve cold rolling deformability of samples, and Ce doping caused no obvious damage to magnetic properties of the thin sheet after cold rolled.