2014 Volume 100 Issue 3 Pages 390-396
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 δp, δk, and Γ phases were formed first, and it was later replaced by an IMC layer composed only of Γ phase by the growth of δk and Γ phases. The addition of Si in steel suppresses the formation of Γ phase as well as the growth rate of δk phase, and IMC layers composed mainly of either δp or δk phases were successfully fabricated. Si was found to accumulate in α-Fe at the α-Fe/δk interface, which indicates that Si partitioning at the α-Fe/δk 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 δk phase were demonstrated inferior to those of δp phase.