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

摘要

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 Al_3Fe, Al_6Fe, Al_3Ni and AlgFeNi. 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 AlgFeNi 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.