TEM Studies of Cross Sections of Oxidized Fe-25Cr-6Al-La Alloy

摘要

The oxidation behavior of the alloy Fe-25%Cr-6%Al-RE (rich in lanthanum) was investigated by means of TEM analysis. The results show that after 2 hr oxidation of the alloy in pure oxygen at 1200℃, La precipitated in the oxide scale at the top of α-Al_2O_3 grains and at the grain-boundary regions in the form of tiny particles of hexagonal La_2O_3. These tiny particles prevented aluminum from diffusing toward the surface and suppressed lateral growth of the oxide scale. The rare-earth constituents accelerated the internal oxidation of the alloy during thermal cycling between 1200℃ and room temperature. They appeared as particles of aluminum oxide and lanthanum oxide. Particles of cubic La_2O_3 precipitated in the alloy matrix near the oxide scale-metal interface in a direction parallel to grain boundaries.