Thermal transformations in mechanically alloyed Fe-Zn-Si materials

Abstract

The ball milling of elemental powders corresponding to Γ (Fe₃Zn₁₀)+0.12 wt pct Si; Γ₁ (Fe₅Zn₂₁) + 0.12 wt pct Si; δ (FeZn₇)+0.12 wt pct Si; and ζ (FeZn₁₃)+0.12 wt pct Si composition ratios yields crystalline, mechanically alloyed phases. Differential scanning calorimetry (DSC) measurements of these materials show that they evolve differently, with well-defined characteristic stages. The activation energies for processes corresponding to these stages, based on kinetic analyses, are determined and correlated to microstructural evolvements. The processes occurring during the first stage below 250 °C, for all of the materials studied using X-ray diffraction (XRD) analysis, are associated with release of strain, recovery, and limited atomic diffusion. The activation energies for recovery processes are 120 kJ/mole for the Γ+0.12 wt pct Si, 131 kJ/mole for δ+0.12 wt pct Si, and 96 kJ/mole for ζ+0.12 wt pct Si alloys. At higher temperatures, recrystallization and other structural transformations occur with activation energies of 130 and 278 kJ/mole for Γ+0.12 wt % Si; of 161 kJ/mole for Γ₁+0.12 wt pct Si; of 167 and 244 kJ/mole for δ+0.12 wt pct Si; and of 641 kJ/mole for the ζ+0.12 wt pct Si. In addition, a eutectic reaction at 420 °C±3 °C, corresponding to the Zn-Si system, and a melting of Zn in Fe-Zn systems are observed for the ζ+0.12 wt pct Si material. The relation of FeSi formation in the Sandelin process is discussed.