Mechanical and Electrical Responses of Magnetron-Sputtered AgNi Coatings Under Radial Fretting: A Contact Model Incorporating Residual Stress

Stable electrical contacts must maintain mechanical integrity and low electrical resistance under fretting conditions, but the influence of deposition-induced residual stress on coated rough interfaces remains unclear. In this paper, 2.8 μm AgNi coatings containing 1–8 at.% Ni were deposited by magnetron sputtering. Their microstructure, mechanical properties, residual stress, resistivity, and coupled force–resistance responses were examined over 20 displacement-controlled radial-fretting cycles to resolve the early-cycle evolution from initial asperity accommodation to electromechanical stabilization. A residual-stress-aware multiasperity model was developed to interpret the stabilized high- and low-load electrical responses by coupling elastic–plastic asperity contact with finite-thickness constriction resistance and conducting-spot interactions. Increasing Ni content increased the magnitude of the compressive residual stress from 35.3 to 312.3 MPa. The stabilized Rmin increased from 0.464 ± 0.028 to 0.575 ± 0.029 mΩ, whereas Rmax decreased from 3.064 ± 0.151 to 1.797 ± 0.083 mΩ across the composition series. The cycle-resolved histories showed that Rmin was weakly cycle-dependent, whereas Rmax increased markedly in the low-Ni coatings as the return-point preload progressively relaxed. At the stabilized cycle, the multiasperity model reproduced the contrasting composition-dependent resistance trends at the high- and low-load endpoints. A paired sensitivity analysis showed that residual stress had a minor influence on Rmin but reduced Rmax by up to 20.3% by suppressing accumulated plastic settlement and preserving the return-point conducting network. These results reveal a mechanical–electrical design trade-off in which Ni enrichment increases high-load resistance but is associated with improved preload retention and early cycle-to-cycle electrical stability.