Acoustic emission(AE) response of Inconel 600 alloy during intergranular stress corrosion Cracking(IGSCC) has been evaluated to compare the crack behavior with AE signals generated during IGSCC and to obtain the minimum crack length detectable with AE.
Piezoelectric AE transducers were mounted on the both end of the plate tension specimen of thickness 1.6mm and the gauge section was confined in the corrosion cell. Measurements were made for test specimens with use of a constant extension rate tester(CERT) in $Na_2S_4O_6$ solution at room temperature. Differently heat treated specimens were tested under various test conditions, namely, different strain rate and different concentration of electrolytic solution.
Results of these experiments consisted of ; The procedure used for the initial crack detection tests was to loading the samples in air to the 1.1 times yield strength and monitoring continuously the AE activity from elastic/plastic deformation until the AE activity was nearly zero. The solution was then added to the cell and the electrochemical potential was adjusted to the 200mV level. It was demonstrated by this study that AE was capable of detecting early stage of crack generation in Inconel 600 alloy.
Results were different for samples with a high and low degree of sensitization in $10^{-2}$M and $10^{-4}$M $Na_2S_4O_6$ solution and at $2.5\times10^{-5}s^{-1}$ and $5\times10^{-6}s^{-1}$ strain rate. Whereas in $10^{-4}$M $Na_2S_4O_6$ solution, stress corrosion cracking was not observed, and in $10^{-2}$M $Na_2S_4O_6$ solution and $5\times10^{-6}s^{-1}$ strain rate, IGSCC initiation was observed after a delay time of 6h and rapid crack propagation occurred.
Following the detection of 3∼4 valid hits, the sample was removed from the test cell and evaluated initial crack size in a scanning electron microscope. Intergranular stress corrosion cracks of about 300㎛ in length were detectable with AE.
