Fracture Toughness of Fe-Zn Intermetallic Compound Layer

The Fe-Zn intermetallic compounds (IMC) layers composed of delta(p), delta(k), and Gamma phases were fabricated using two different kinds of Fe/Zn diffusion couple (DC), and the fracture toughness of the constituent phases was estimated from the toughness of the IMC layers. In the DCs with sufficient Zn supply, the IMC layers were mainly composed of delta(p) phase after isothermal holding at 450-600 degrees C for 60 s, while in the DCs with limited Zn supply, the IMC layers were composed of delta(p), delta(k), and Gamma phases at the early stage of isothermal holding, which was later dominated by Gamma phase with further isothermal holding. The average grain size of the IMC phases was found to increase with increased holding temperature. From the comparisons between the MC layers composed mainly by either delta(p) or Gamma phases, toughness of Gamma phase was found inferior to that of delta(p) phase. In addition, it was demonstrated that the toughness of delta(p), and Gamma was found to increase with decreased average grain size. Whereas, from the results using the multi-phase IMC layers, the toughness of delta(k) phase was found almost equivalent to that of Gamma phase.