Molecular dynamics study on the coalescence kinetics and mechanical behavior of nanoporous structure formed by thermal sintering of Cu nanoparticles

A molecular dynamics (MD) simulation is performed on the coalescence kinetics and mechanical behavior of a thermally sintered nanoporous copper (Cu) nanoparticulate system. To investigate the effect of particle size and sintering temperature on the coalescence of the nanoparticulate system, particles with sizes of 4, 5, and 6 nm are sintered at temperatures of 300, 500, and 700 K. To determine the thermal sintering process at elevated temperatures and ambient pressure, bulk periodic nanoparticle unit cells consisting of a finite number of nanoparticles are equilibrated through isothermal-isobaric ensemble simulations. In thermally sintered configurations, uniaxial tension/compression and shearing simulations are applied at a constant strain rate to derive stress-strain curves. It is found that stacking faults are actively generated in smaller nanoparticles even at a low sintering temperature, while local amorphization and surface and grain boundary diffusion are rather prominent in larger nanoparticles. Even at the same sintering temperature, the density of the sintered nanoparticle increases as the size of the nanoparticle decreases. In elastic moduli, the same particle size dependency is observed, while no obvious difference is observed in tension and compression. On the other hand, the yield strengths of the sintered nanoparticles in tension are larger than those in compression. The asymmetric yield strength of the sintered systems is clarified by addressing the surface stress and surface equilibrium strain of atoms on the surface of nanopores by the evolution of atomic virial stress in tension and compression.