Degeneration of thermal insulation property for Fe-based amorphous coating during long-term heat exposure

Fe-based amorphous coatings have been proposed to perform a promising thermal barrier application, however, the uncertain degeneration of properties induced by thermal stimulation is significantly concerned owing to their metastable nature. Herein, Fe₅₇Cr₁₅Nb₄B₂₀Si₄ amorphous coating with a low thermal conductivity was employed to investigate the degeneration of thermal insulation property and related mechanisms during long-term heat exposure. Excellent stability can be defined for the amorphous coating when annealed below glass transition temperature, despite a slight increase of thermal conductivity induced by structural relaxation. Extraordinary increase of thermal conductivity is found when prolonged annealing time at a critical temperature of 600 °C. The sluggish structural sintering dominates thermal conductivity to increase, whereas the effect of precipitated ultrafine nanocrystals is little. The cooperation of grain coarsening and structural sintering leads to a dramatical increase of thermal conductivity at the initial stage of 850 °C annealing, while the relatively low increase of thermal conductivity with prolonged duration is ascribed to the further grain growth. The obtained results demonstrate a comprehensive understanding on the thermal evolution of Fe-based amorphous coatings and form a basis for future works aiming to shed further light on the degeneration of related metallic coatings at high temperatures.