Thermal stability, dynamic mechanical analysis and nanoindentation behavior of FeSiB(Cu) amorphous alloys

The aim of the present study is to investigate the crystallization behavior, microstructural evolution and mechanical behavior of the Fe-based amorphous alloy with three various compositions (at%): Fe80.75Si8B11.25 (Cu-free and Silicon-rich alloys), Fe85.2Si0.9B12.62Cu1.28 and Fe78.6Si1.8B17.75Cu1.85 (Cu-containing and Si-poor alloys). The presence of Cu decreased the activation energy of the first crystallization peak and glass transition temperature. Furthermore, anomalous behavior was observed in Avrami exponent at the final stage of the crystallization of the Cu-containing alloys. Absence of Cu resulted in a coarse dendritic structure while finer and equiaxed grains were achieved by Cu addition. Nanoindentation size effect (the decrease of hardness with the increase of indentation depth) was observed in amorphous ribbons (regardless of composition) from 10 to 70 mN load and further increase of load did not change the hardness and Young׳s modulus noticeably. Isothermal annealing effectively increased the hardness (H) and Young׳s modulus (Er) of the alloys. In addition, it was found that the plastic work of nanoindentation decreased after annealing in Cu-free alloy whereas it increased in Cu-containing one which could be due to the refined microstructure. Besides, shear bands around the indents in amorphous ribbons were disappeared after 1 h annealing which could be due to the change in plastic deformation mechanism from shear banding to strain-hardening.