Interrelation of cell spacing, intermetallic compounds and hardness on a directionally solidified Al–1.0Fe–1.0Ni alloy

Al–Fe–Ni alloys show very promising properties for applications in industrial furnaces and petrochemical plants. Mechanical strength and corrosion resistance are obvious requirements concerning such applications. As-cast Al–Fe–Ni alloys allow the development of some intermetallic compounds (IMCs), which depend on both the alloy composition and solidification conditions, i.e., growth rate and cooling rate. Some typical phases are Al3Fe, Al6Fe, Al3Ni and Al9FeNi. The isolated or simultaneous occurrence of these IMCs is expected to affect the mechanical properties. In the present investigation, an Al–1.0 wt%Fe–1.0 wt%Ni alloy was directionally solidified under transient heat flow conditions, allowing a wide spectrum of cooling rates to be examined (from 36.5 to 0.8 K/s). A comprehensive characterization was performed including Thermo-Calc computations, experimental cooling rates, scanning electron microscopy (SEM), cellular spacing, XRD spectra and Vickers microhardness. It was found that rod-like Al9FeNi IMC in the boundaries of Al-rich cells prevailed along the entire Al–Fe–Ni alloy casting. A Hall–Petch equation relating hardness to the cell spacing is proposed.