Hydrogen-induced degradation behavior of nickel alloy studied using acoustic emission technique

Abstract

Hydrogen embrittlement susceptibility of nickel alloy (Inconel 625) is examined by a conventional strain rate tensile test (10−3 s−1) equipped with an acoustic emission (AE) setup. From the spectral analysis of AE signals coupled with the clustering procedure followed by the electron microscopic characterization, we have demonstrated the capability of the AE technique in identifying the hydrogen-dislocation interactions, crack initiation and propagation in various hydrogen-charged samples. The enhanced hardening behavior of hydrogen-charged samples is investigated from the viewpoint on the elementary dislocation theory, using a phenomenological relationship between the acoustic emission power and the experimentally measurable strain hardening parameters derived from the monotonic tensile test. In this way, we have shown that the mobile dislocation density increases with hydrogen content. In addition, the average velocity of dislocations is assessed from the AE data, and it is found to be reduced with the hydrogen concentration. The statistical crack analysis reveals the crack transition from the transgranular to intergranular mode in the samples failed under the hydrogen environment. The competition between these two fracture modes is explained by relating the hydrogen concentration profile with loading conditions.