Selective dissolution-induced mechanical damage in Cu/Nb laminated composites revealed by in-situ acoustic emission monitoring

Cu/Nb laminated composites combine high electrical conductivity with mechanical strength, but their environmental reliability under selective phase dissolution remains insufficiently understood. In this study, corrosion-induced damage in Cu/Nb laminated composites was investigated in 3.5 wt% NaCl solution using potentiodynamic anodic polarization, in-situ optical microscopy, acoustic emission (AE) monitoring, and post-corrosion microstructural characterization. Pure Cu was examined as a reference to separate Cu-dominated electrochemical behavior from damage specific to the laminated architecture. The Cu/Nb laminates exhibited polarization behavior similar to pure Cu, indicating that the electrochemical response was mainly governed by Cu dissolution and CuCl-based passivation. However, after passivation-film breakdown, short-duration high-frequency AE events appeared only in the Cu/Nb laminates. Cross-sectional observations revealed that selective dissolution of Cu produced subsurface cavities beneath the Nb layers, leading to local Nb-layer deformation, collapse, and crack initiation. Time-frequency analysis confirmed that these transient signals were distinct from low-frequency periodic signals associated with the electrochemical measurement system. These results demonstrate that selective Cu dissolution can mechanically destabilize corrosion-resistant Nb layers and that AE monitoring can detect such transient corrosion-deformation coupling in laminated metallic composites.