Improvement in the Oxidation Resistance of Al-deposited Fe-Cr-Al Foil by Pre-oxidation

摘要

The oxidation kinetics of conventional Fe-Cr-Al foil, Al-deposited foil, and Al-deposited and pre-oxidised foil was studied at 1373 K in air. All the foils were 50 μm thick and contained minor additions of rare earth elements. The oxide scales were observed with SEM and TEM combined with EDS, and were examined with X-ray diffractometry. The deposition of Al onto the foil from vapour phase improves the oxidation resistance. Details regarding this matter were reported elsewhere. The combination of the Al deposition and the subsequent pre-oxidation at 1173 K for 90 ks in air further increases the oxidation resistance, i.e. the smallest parabolic rate constant among the three kinds of specimens and excellent scale adherence. The pre-oxidation enhances the growth of θ-Al_2O_3, which transforms to α-Al_2O_3 during the subsequent oxidation. However, such α-Al_2O_3 grains are much larger than those formed on the conventional foils of similar chemical compositions. Small closed voids and small spinel type oxide particles appear in α-Al_2O_3 grains with the progress of oxidation. The former is explained in terms of the volume decrease accompanying the phase transformation and the latter by small solubility of Fe in α-Al_2O_3.