Microstructure and mechanical properties of laser-deposited Cu-based alloy coatings on Al substrate

This study investigates the microstructure, mechanical properties, and tribological behavior of Cu-Ag-Al alloy coatings with varying Ag/Al ratios. The coatings exhibit a dual-layer structure comprising a Cu-Ag-Al ternary surface layer and an Ag interlayer, where increasing Ag interlayer thickness (210–610 μm) directly enhances the eutectic phase fraction (27–73%). Phase evolution is composition-dependent: high-Al Cu-19Ag-20Al forms β’ phases via β→β’ ordering, while lower-Al alloys (Cu-34Ag-15Al, Cu-45Ag-12Al) stabilize Cu solid solutions (Cu S.S.) with nanotwins due to suitable stacking fault energy (SFE). Mechanical performance is governed by dual-phase interactions: the β’ phase in Cu-19Ag-20Al achieves high hardness (4.71 GPa) and work-hardening rates (2699 MPa) via coherent (128)-plane interfaces, whereas nanotwin-strengthened Cu S.S. phases dominate in low-Al alloys. Tribological analysis reveals that increasing Ag content reduces friction coefficients (0.72→0.33) through the formation of Ag-rich nanocrystalline tribolayers. However, wear resistance peaks in Cu-34Ag-15Al (397 μm scar width), balancing 42 vol.% hard Cu S.S. phases with 58 vol.% friction-reducing eutectic structures. Excessive eutectic content in Cu-45Ag-12Al compromises wear resistance despite low friction, underscoring the necessity of optimizing phase hardness and tribolayer efficacy. These findings highlight the critical role of Ag/Al ratio in tailoring phase selection, strengthening mechanisms, and wear performance in Cu-based coatings.