Sintering of Nano-Particle Powders: Simulations and Experiments

Abstract

The sintering and consolidation of nano-particle powders were investigated using both computer simulation and direct experimentation. Molecular dynamics was employed to investigate the sintering of Cu nano-particles. Both spherical and cylindrical particles were employed in these simulations. The work demonstrates that sintering of these systems can take place on a time scale of tens of picoseconds, owing to the high shear stresses that develop at small particle contacts. For two and three particle sintering, it was observed that mass transport occurs by plastic flow. It was also found that crystallographically misaligned particles rotate to form low energy boundaries. The influence of the initial packing configuration was also investigated. Full densification occurs during pressureless sintering at room temperature only if the nano-particle assembly is close-packed. The effect of both isostauc and uniaxial stress on densification of Cu was also studied. Grain boundary sliding and grain boundary relaxation were also investigated. Experimental measurements of densification of bulk specimens undergoing shear deformation provide information on the macroscopic sintering behavior of large assemblies of nano-crystals. The constitutive law for densification of nano-crystalline TiO₂ has been obtained. Attempts are made to relate the observed macroscopic sintering behavior of this system to the microscopic processes elucidated by the simulations.