Outstanding corrosion resistance of an Fe-based crystalline-amorphous nano-composite alloy

Superior corrosion resistance is always obtained in Fe-based alloys by major Cr alloying via a stable passive film or a uniform amorphous structure without boundaries. It is of great importance to explore new strategies for developing environmentally friendly Cr-free materials and further improving the corrosion resistance. In this study, we found an evolutionary route for unparalleled corrosion resistance by constructing a unique crystalline-amorphous nano-composite (CANC) structure in a commercial Fe_73.3Si_15.5B₇Nb₃Cu₁Ni_0.2 alloy via a facile heat treatment. The ribbon samples with a nanoscale α-Fe(Si) grain and amorphous matrix composite structure exhibit a super-low corrosion rate of about 0.022, 0.054 and 0.005 mm·year⁻¹ in 0.1 M NaCl, HCl and NaOH solutions, respectively, which are much lower than crystalline and amorphous counterparts. The improvement of corrosion resistance can be attributed to the precipitation of nanoscale α-Fe(Si) grains in the amorphous matrix and the formation of a dense oxide layer on the surface. The enrichments of Si in α-Fe(Si) grains and Nb in the amorphous matrix are critical for the positive effect of the nanocrystallization. These results provide a new paradigm for the design of advanced alloys with high corrosion resistance.