PNNL

Abstract

In this study we investigated the effects of Bi addition on the microstructure and mechanical properties of electrodeposited nanocrystalline Ag coatings. Microstructural features were investigated with transmission electron microscopy (TEM). The results indicate that the addition of Bi introduced nanometer scale Ag-Bi solid solution particles and more internal defects to the initial Ag microstructures. The anisotropic elastoplastic properties of Ag nanocrystalline coatings with and without Bi addition were examined with nanoindentation experiments in conjunction with the recently developed inverse calculation. The results indicate that the as-deposited nanocrystalline Ag coating contained high mechanical anisotropy. With the addition of 1 atomic percent (at.%) Bi, the anisotropy within Ag-Bi coating was very small, and yield strength of nanocrystalline Ag-Bi alloy in both longitudinal and transverse directions were improved by over 100% compared to that of Ag. On the other hand, the strain hardening exponent of Ag-Bi was reduced to 0.055 from the original 0.16 of Ag coating. Furthermore, the addition of Bi only slightly increased the electrical resistivity of the Ag-Bi coating in comparison to Ag. Results of our study indicate that Bi addition is a promising method for improving the physical and mechanical performances of Ag coating for electrical contact.