Molecular Dynamics Simulations of Cluster-assembled Metallic Glasses

Metallic glasses are an exciting class of amorphous materials, primarily known for their interesting properties such as high resilience and superior strength. Tailoring the local structure of these glasses is a step towards an increased control of their properties in a manner similar to how microstructures of crystalline materials are already being altered to suit various applications today. Recently, films prepared via an intricate assembly of amorphous clusters by energetic deposition were reported to demonstrate a remarkable change in properties depending on the deposition energy. The properties of the so-prepared cluster-assembled metallic glasses are currently believed to arise from the deposition process, and the formation of cluster-cluster interfaces—creating novel microstructures otherwise absent in traditionally prepared glasses. Being in the nascent stages of conception, the nature of the cluster-assembled glasses remains largely unexplored. In the present thesis, molecular dynamics simulations of the cluster-assembled metallic glasses are studied in a model CuZr system. The development and implementation of new simulation protocols uncover the mechanisms of the formation routes to these novel cluster-assembled glassy films, the morphologies adopted by the clusters, and the local topological order in the materials. ... mehrTwo amorphous phases are identified in these glasses: one in the cores of the clusters, and the other in the continuous network of interfaces formed amongst the clusters. The amorphous short- and medium-range orders of cluster-assembled glasses are demonstrated to not only differ considerably from the traditional metallic glasses prepared by rapid quenching, but also to vary with cluster-impact energies in both the core and interface regions. In cluster-assembled glasses the interface regions are more densely packed than the cores, while the core atoms occupy lower energy states—a surprising outcome when contrasted with the traditional glasses where denser packing and lower energetic states occur together. Such an interesting occurrence is found to be a consequence of the core and interface regions having distinct chemical compositions. The inherent chemical heterogeneity of the precursor clusters also plays a role in the variation of local order and energetic states of cluster-assembled glasses made from varying cluster sizes. However, the local short-range order and the thermal evolution of the enthalpy is found to be invariant with cluster size in these materials. These investigations provide a computer-aided understanding of amorphous cluster assembly and the synthesis of tailorable non-crystalline architectures in the quest to harness the properties of amorphous materials in the future.