Microstructural stability in rapidly solidified ternary iron aluminides

Abstract

Iron aluminides containing ternary additions of Cr, Si and other alloying elements offer good oxidation and sulphidation resistance at a relatively low cost but these alloys have only moderate strength at elevated temperatures and are of limited ductility. The generation of a distribution of fine dispersoids throughout the matrix of these alloys can provide increased strength and also improve ductility by reducing grain size. We report a study of the microstructural stability of rapidly solidified strip of iron aluminides containing chromium and minor additions of both titanium and boron. As cast strip thickness was in the range 80-120μm. Figure 1 shows the grain structure near the centre of the as cast strip of a 66.5Fe-28.5Al-5.0Cr (at.%) alloy. The grain size in this view of the strip is quite small (2-5μm) although optical metallography of the longitudinal and transverse cross sections show that the grain structure is columnar through much of the strip thickness.