Microstructure and phase composition of an Fe-Al-Ce alloy

Application of high temperature intermetallic compounds as structural materials is an important problem of modern materials science. The unique properties of iron aluminides (FeAl, Fe3Al) lend them development potential in this context. This is based on their ability to form a protective aluminum oxide (Al2O3) scale in oxidizing environments at elevated temperatures. In addition to excellent corrosion resistance, iron aluminides offer low density and low material cost. In the present research, the influence of cerium and other lanthanides (La, Pr, Nd) on the structure and phase composition of iron aluminides based on the FeAl intermetallic was investigated. The alloy in question contained 37 at% Al, 0.4 at% Ce, and Fe balance. (For simplicity, Ce denotes all lanthanides collectively.) A series of hot extruded specimens were prepared and examined using optical and S.E. microscopy, EDS, TEM, and X-ray diffractometry. The matrix was found to be the FeAl intermetallic compound; lanthanides were not detected in it. Equiaxed precipitates (maximum size 7--8 microm) uniformly distributed in the matrix were identified as the Fe3Al intermetallic of stoichiometric composition. The following lanthanide-containing phases were also detected: the binary Al4Ce (oI30) and two ternaries -- (Fe,Al)17Ce2, having hexagonal structure (hR19), and CeFe4Al8 (it26)