An experimental investigation of phase transformations in the Al-rich corner of the Al–Cr–Fe system

Abstract

This paper presents a comprehensive investigation of the aluminium-rich corner of the Al–Cr–Fe phase diagram within the solidification interval, using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and electron probe microanalysis (EPMA). Liquidus and solidus surfaces were constructed. The nature of the phase equilibria and invariant reactions observed between the phases were different from those recently reported in the literature. It was determined that over the composition range ∼80–100 at.% Al, the liquidus surface is characterized by primary solidification fields of two ternary compounds Al76Cr16Fe8 (O) and Al82.5Cr11.5Fe6 (H), four solid solutions based on binary phases Al4Cr, Al11Cr2, Al13Cr2 and Al13Fe4 and one solid solution based on aluminium. The solidus surface over the composition range ∼75–100 at.% Al is characterized by three three-phase fields (Al) + Al13Fe4 + Al13Cr2, Al13Fe4 + Al13Cr2 + H and Al13Fe4 + Al11Cr2 + H, which result from invariant four-phase equilibria of transition type at 770, 680 and 654 °C respectively. It was also found that only Al13Cr2 and Al13Fe4 phases coexist in equilibrium with the aluminium solid solution.