APPLICATION OF AN ACOUSTIC-EMISSION TECHNIQUE TO THE HIGH-TEMPERATUREOXIDATION OF FE-CR-AL ALLOYS

Acoustic-emission analysis combined with thermogravimetry has been use d to investigate the oxidation behavior of undoped and doped Fe-Cr-Al alloys. It was demonstrated that acoustic-emission signals which were detected upon isothermal oxidation of undoped Fe-20Cr-5Al arise from b uckling of the fine-grain alpha-Al2O3 layer. The acoustic-emission sig nals which were detected upon isothermal oxidation of Fe-18Cr-12Al are attributed to repeated cracking of the coarse-grain alpha-Al2O3 layer . The mass-gain curve results from superimposed diffusion-controlled o xide growth and accelerated oxide growth after cracking of the oxide l ayer. The present study shows that acoustic-emission analysis is very useful as it complements thermogravimetric results. The advantage of a coustic-emission analysis is that it reveals cracking and spalling of the oxide layer, which is not recorded by thermogravimetry.