純亜鉛融液／鋼界面におけるFe-Zn系金属間化合物形成に及ぼす鋼中Siの影響

抄録

The effect of Si additions to the steel on the microstructure and growth kinetics of the Fe-Zn intermetallic compound (IMC) in the Fe/Zn diffusion couple with limited Zn supply was experimentally investigated. Three different steels with Si contents of less than 0.01 wt%, 0.44 wt%, and 1.85 wt% were machined in cylindrical shape of 8 mmφ×6 mmh, and their bottom surfaces were polished chemically and mechanically to remove oxide and Si depletion layer. Pure Zn (99.99%) film was inserted between two steel cylinders, and enclosed in the steels in vacuum. The samples were heated at 450 °C for various holding time. Without Si, an IMC layer composed of δ_p, δ_k, and Γ phases were formed first, and it was later replaced by an IMC layer composed only of Γ phase by the growth of δ_k and Γ phases. The addition of Si in steel suppresses the formation of Γ phase as well as the growth rate of δ_k phase, and IMC layers composed mainly of either δ_p or δ_k phases were successfully fabricated. Si was found to accumulate in α-Fe at the α-Fe/δ_k interface, which indicates that Si partitioning at the α-Fe/δ_k interface is responsible for the instability of Γ phase and slow supply of Fe from steel substrates. Finally, the fracture toughness and adhesion of IMC layer composed mainly of δ_k phase were demonstrated inferior to those of δ_p phase.