Evolution of the Mechanical, Magnetic and Anti-Corrosion Behavior of Fe-Co-B-Si-Nb Bulk Metallic Glass during Thermally-Induced Devitrification

Fe36Co36B19.2Si4.8Nb4 bulk glassy rods with 2 mm in diameter were manufactured by copper mould casting. The effects of annealing treatments on the microstructure, mechanical, magnetic and anticorrosion properties of this alloy are investigated. Annealing below the glass transition temperature causes the formation of small atomic clusters showing a pseudo-tenfold symmetry quasicrystal-like structure with close relationship to the Fe23B6 phase. This phase is actually the first to crystallize upon annealing, although two further crystallization events occur at higher temperatures. The as-cast alloy exhibits ultra-high hardness (> 14 GPa), high Young’s modulus (> 200 GPa) and good wear resistance. These properties are further enhanced after thermal treatments. In turn, the coercivity of the as-cast alloy also increases after thermally induced devitrification. Electrochemical measurements show that both the as-cast and annealed specimens exhibit good corrosion resistance. The possible mechanisms responsible for these annealing-induced changes in the behavior of the Fe-based metallic glass are discussed.