Effect of Zr on the Oxidation Properties of Fe3Al Intermetallic Compound

摘要

This review is concerned with the effect of the addition of zirconium as a third element on the heat-resisting properties of Fe_3Al intermetallic compounds and explains their high-temperature oxidation mechanism.The Fe_3Al and Fe_3Al-0.05Zr specimens were isothermally oxidized in the temperature range of 1173～1473 K in synthetic air for 100 h.The formation of the alumina layer approximately obeyed the parabolic rate law,with the exception of short initial stage.The parabolic rate constant values for the Zr-doped Fe_3Al decreased at all tested temperatures.Fe_3Al revealed massive spallation,whereas Fe_3AlZr produced a flat,adherent oxide layer.The microstructure investigations of the alumina scales grown thermally on the Fe_3Al-Zr alloy by means of SEM-EDS showed that they were 1.5～2μm thick and consisted of a small inner columnar layer and an equiaxed outer grain layer.Additionally,very fine(50～150 nm) oxide particles rich in Zr were found across the alumina scales.The addition of Zr significantly affected the oxidation behavior of Fe_3Al by improving the adherence of theα-Al_2O_3 scale.TEM-SAD investigations of the alumina scales on samples prepared using the FIB(Focused Ion Beam) method confirmed the presence of small tetragonal zirconia grains near the scale/gas and alloy/scale interfaces,most of which were formed along alumina grain boundaries(gbs).Zr gb-segregation was found using HRTEM.The role of preferential formation of zirconium oxide along the alumina scale grain boundaries and the effect of Zr gb-segregation on oxidation and scale growth mechanisms were analyzed by means of two-stage oxidation experiments using ^(16)O_2/^(18)O_2.The SIMS oxygen isotope profiles for the Fe_3Al-Zr alloy oxidized at 1373 K, after two-stage oxidation experiments,revealed that oxygen anion diffusion is predominant compared to that of aluminum cation diffusion.