Here, melt-extracted Ni- and Fe-based amorphous metallic fibers (AMFs) were annealed below their glass transition temperatures. The tensile behaviors and microstructures of the melt-extracted and the annealed AMF samples were studied. For melt-extracted Ni- and Fe-based samples, the difference of fracture angles can be attributed to their difference of parameter α in the unified tensile fracture criterion. The revolution in the microstructure and mechanical properties induced by annealing treatment has been interpreted in detail. Prolonging the annealing time or increasing the annealing temperature can lead to an increase in fracture stresses of both Ni- and Fe-based AMFs. It was demonstrated that the increase in the fracture stresses of annealed AMFs is caused by the free volume annihilation in annealing processing.
