Enhancing fatigue performance by tuning of residual stresses in welded joints through nanometallic multilayer

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.