Experimental determination of phase diagram in the Zn-Fe binary system

A critical determination of a phase diagram of the Zn-Fe binary system was carried out by EPMA analysis for skillfully prepared and equilibrated two-phase alloys for solid phases and by EDS areal analysis for the Fe solubility in the heterogeneously solidified liquid phase instead of the conventional diffusion couple method. It was newly confirmed that equilibrium compositions of intermetallic compounds tend to shift toward the Fe side compared to the previous phase diagram on the whole and that the solubility ranges of the Γ-Fe3Zn10 and Γ1-Fe11Zn40 phases are much narrower than those in the literature. The critical composition of the second-order order-disorder transition between δ1k-FeZn7 and δ1p-FeZn10 at high temperature was estimated by Vickers hardness measurement. Furthermore, the phase separation, i.e., the first-order transition, between the δ1k and δ1p phases in the low temperature region was directly found out and its equilibrium compositions were confirmed by EPMA analysis for the two-phase microstructures. The width of the δ1k + δ1p two-phase region at 500 °C is only 0.5 at.% and the δ1p decomposes into the δ1k and ζ-FeZn13 phases via a eutectoid reaction at a temperature between 455 °C and 445 °C. While being mostly coincident with those in the previous literature at temperatures between 1000 °C and 600 °C, the solubility of Fe in the liquid (L) Zn phase is about twenty times larger than the assessed value in the literature at temperatures below 500 °C. A eutectic reaction, L → ζ + (ηZn), was confirmed to occur by precise EPMA analysis and DSC measurement.