Mass Transport of Metallic Nanostructures during Sintering Process: A Molecular Dynamics Perspective

Sintering of nanomaterials has been broadly utilized as a joining technique in various applications for achieving excellent mechanical, thermal, and electronic properties. However, the joining of the nanomaterial will facilitate the growth of the nanograin, which deteriorate the performance of the mechanical properties. Also, different defects developed during the sintering process deteriorate the thermal and electronic properties. Therefore, how to prevent the growth of the nanograin and the development of the defects during sintering have become an extremely important issue for improving the properties of sintered joints. This research employs molecular dynamics approach to reveal the atomic-scale sintering dynamics and study the properties of the sintered products of Cu-Ag core-shell nanoparticles (NPs) and nanowires (NWs), over a wide range of temperatures and on three different sintering models: (1) two core-shell NP model; (2) two core-shell NW model; (3) multiple core-shell NP model. Two new sintering mechanisms are found: (1) crystallization-amorphization-recrystallization during solid-phase sintering process and (2) wetting in the sintering of two unequally sized NPs induced by its own small size of existence of Cu core. A three-stage sintering is found for both NPs and NWs. The rupture strength of the sintered joint in the NW is found even higher than the CS NW itself. The effect of porosity and NP agglomeration effect on sintering of multiple core-shell NP model is unravled and the properties of the sintered structure at different temperatures are analyzed in terms of the porosity, grain size, and crystallinity. Through these researches, size and temperature effects on the sintering dynamics of the Cu-Ag core shell NPs/NWs are unraveled, enhanced understanding in defects formation and grain growth are achieved. Those results are expected to contribute to the development of various applications such as electronic packaging, wearable electronics, and energy devices.