Indentation into an Al/Si composite: enhanced dislocation mobility at interface

Using molecular dynamics simulation, we study the indentation of a metal–ceramics (Al/Si) composite and compare it to that of the pure elements. An Al/Si interface running perpendicular to the surface is indented centrally. We find that—due to its higher stiffness and yield strength—Si expands into the Al side. As a consequence, the plasticity on the Al side is enhanced, leading to the formation of complex dislocation networks. On the Si side, the phase transformation from cubic diamond to bct5 structure, and subsequent amorphization near the indenter are accelerated, while the number of dislocations formed in the surviving cubic diamond phase is reduced. In both materials, the mobility of the dislocations is enhanced, in particular because the dislocations glide easily on the interface; as a consequence the composite is softer than the average of its constituents.