Influence of thermal treatment on microstructure of Fe75Ni2Si8B13C2 amorphous alloy

DSC and thermomagnetic measurements of Fe75Ni2Si8B13C2 amorphous alloy investigated in 298–973 K temperature range show that alloy remains amorphous up to around 773 K, when it undergoes multi-step structural transformation. As thermomagnetic measurements provided more complete information, the alloy ribbon was successively annealed at temperatures chosen on the basis of these measurements and its microstructure was investigated after each annealing cycle using X-ray diffraction and SEM. XRD and microstructural analysis of the as-prepared and the annealed sample showed there is no difference between shiny and matte side of the ribbon. Two stable, α-Fe(Si) and Fe2B, and one metastable, Fe3B, crystalline phases were identified after annealing. Microstructural analysis showed that Fe3B probably acts as an intermediate in the formation of Fe2B, which formed later than the other two phases. Si and B in the alloy show a tendency to separate into different phases, exhibiting complementary fluctuations in concentration in chemical depth profile. Analysis of microstructure, combined with chemical composition, showed that after the final annealing at 973 K, alloy ribbon is composed of interdispersed nanocrystals of α-Fe(Si) and Fe2B less than 90 nm in size, with no observable larger domains of either phase.