Grain boundaries in rapidly solidified and annealed Fe-6.5 mass% Si polycrystalline ribbons with high ductility

The type and frequency of grain boundaries in rapidly solidified and subsequently annealed ribbons of Fe-6.5 mass% Si alloy have been determined to discuss the origin of high ductility of the annealed ribbons. The electron channelling pattern (ECP) technique for crystallographic orientation determination was applied. Ribbons subjected to slight annealing after the solidification have a random grain orientation distribution and contain higher frequencies (86–87%) of high-energy boundaries or so called random boundaries. On the other hand, rapidly solidified and fully annealed ribbons with a large grain size of 600 μm and {100} texture contain low-energy boundaries such as low-angle and low Σ, coincidence boundaries in high frequencies. Nearly one half of the boundaries are of low-energy type. Some coincidence boundaries such as Σ5, Σ13 and S 25 occur 3–8 times more frequently than those predicted for a polycrystal with randomly oriented grains. Similarly, low-angle boundaries compose 25% of the total boundaries in the fully annealed ribbon. The inverse cubic root Σ dependence of the frequency for the coincidence boundaries has been discussed. The high ductility of fully annealed Fe-6.5 mass% Si alloy polycrystalline ribbons is attributed to a high frequency of the low-energy boundaries with strong resistance to intergranular fracture.