Acoustic emission studies towards better understanding of high temperature oxidation in Cr---Mo steels

Application of acoustic emission (AE) for the study of the oxidation behaviour of Cr---Mo steels in a wide range of temperatures is described. AE parameters, i.e. events, ring down counts (RDC), rise time (R<SUB>t</SUB>), event duration (E<SUB>d</SUB>) and root mean square voltage (RMS) have been applied successfully to detect the initiation of breakaway oxidation and in-situ spalling of the oxide scales formed on 2&#183;25Cr---1Mo and 9Cr---1Mo steels at high temperatures. Time domain, frequency domain and amplitude distribution analyses were used to study these phenomena. Attempts have also been made to characterise the isothermal scale growth by measuring selective AE parameters. AE results have been corroborated with the corresponding thermogravimetric results