Microscopic hardness and dynamic mechanical analysis of rapidly solidified Fe-based amorphous alloys

A systematic work was conducted to investigate the nanoindentation, dynamic relaxation, high-temperature rheological behavior, and structural relaxation after high-temperature deformation of Fe_52-xCo₂₀Ni_xB₁₉Si₅Nb₄ (x = 7,12,17, labeled as S₁, S₂ and S₃) metallic glass. The results of nanoindentation indicate that the hardness of amorphous alloy reduces first and then enhances with the increase of Ni content. S₁ alloy exhibits the highest hardness of 13–16 GPa, while relatively excellent compression plasticity is reached in S₂ alloy. Besides, the glass transition temperature (T_g), initial crystallization temperature (T_x), α relaxation temperature (T_α) and internal friction change at different temperatures were determined and compared. The critical temperature, strain rate during non-Newton to Newtonian rheology and Newtonian viscosity at T_g temperature were discussed. Moreover, it was found that the activation volume improved and then decreased due to structural relaxation. At last, combined with the width of the supercooled liquid region, relaxation behavior and rheological viscosity at high temperature, the microstructure evolution of the three kinds of metallic glass under T_g temperature deformation was explained.