Application of an acoustic-emission technique to the high-temperature oxidation of Fe-Cr-Al alloys

Acoustic-emission analysis combined with thermogravimetry has been used 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 buckling of the finegrain α-Al2O3 layer. The acoustic-emission signals which were detected upon isothermal oxidation of Fe-18Cr-12Al are attributed to repeated cracking of the coarse-grain α-Al2O3 layer. The mass-gain curve results from superimposed diffusion-controlled oxide growth and accelerated oxide growth after cracking of the oxide layer. The present study shows that acoustic-emission analysis is very useful as it complements thermogravimetric results. The advantage of acoustic-emission analysis is that it reveals cracking and spalling of the oxide layer, which is not recorded by thermogravimetry.