Deformation and fracture behavior of rapidly solidified and annealed iron-silicon alloys

Abstract

In this study, the mechanical properties, deformation behavior, and fracture modes of iron-silicon melt-spun ribbons are related to changes in silicon composition from 4.5 to 6.5 wt pct and the influence of ordering phase transformations. The as-solidified melt-spun ribbons, which exhibit plasticity even for the Fe-6.5 wt pct Si composition, provide the opportunity to characterize dislocation glide. Tensile deformation with a plastic strain of ∼2 pct produced planar slip of pure edge and pure screw mainly on {112} slip planes although slip on {011} and {123} planes was also observed. The extended dislocations became qualitatively more planar as silicon concentration increased owing to reduced cross-slip. For the Fe-6.5 wt pct Si material, pairs of dislocations with the same Burgers vector were observed. As ribbon thickness increased, the material's ductility decreased. Thinner ribbons provide a reduced mean free path of gliding dislocations and fewer impediments to glide before they reach the ribbon surface, which removes strain hardening effects. In the as-solidified state, the B2 and DO3 order has been suppressed. Heat treating the 6.5 wt pct silicon ribbons induces the ordering phase transformations and reduces the ductility. The most embrittled condition occurs for the coexistence of B2 and D03 ordered domains after annealing at 400 °C to 500 °C. © The Minerals, Metals & Materials Society and ASM International 2008.