Welded joints suffer from reduced fatigue life due to geometric stress concentrations and metallurgical changes in the heat-affected zone that promote crack initiation under cyclic loading. This study investigates a novel postweld treatment, utilizing a Cu/Ni nanometallic multilayer thin film deposited onto the welded butt joint. Deposition current densities and individual Cu/Ni layer thicknesses are systematically varied to optimize fatigue performance. A multiscale residual stress (RS) analysis characterizes stress states within individual multilayers and in the steel substrate, indicating all substrate RS are compressive in nature after thin film deposition. Results demonstrate a direct correlation between compressive RS magnitude and fatigue strength improvement. Tested at ΔσR = 0.75 × fy, a more than a 300% increase in cycles to failure is seen compared to the as-welded condition. This postweld treatment offers a promising approach for extending the operational life of welded structures across industrial applications.
Spalek et al. (Wed,) studied this question.