Microstructural evolution and analysis of Zr–Co/Cu–Al glassy composites and crystallized alloys via indentation and MD simulations

Abstract

B2-containing bulk metallic glass (BMG) composites are still attractive due to their unique deformation mechanism and positive effect on work-hardening and ductility. As stated in review [1], the competition between B2 phase formation, retention of amorphous matrix and intermetallic compounds depends on several parameters, such as alloy composition and cooling rate. For a given BMG composite containing B2 phase, the glass matrix, B2 phase, and brittle compounds generally coexist. As a result, the relationship between microstructures such as atomic diffusion and micro-indentations must be investigated. In this work, nano-indentation, micro-hardness, and molecular dynamics (MD) simulations were performed on two Zr–Co/Cu–Al BMG composites with certain differences in amorphous matrix and crystalline phases such as their distribution, volume fraction, or types. The results indicated that the (1) formation of B2 phase, and precipitation of brittle compounds substantially differed; (2) the atomic transfer in these indented positions can be observed in simulated experiments and line scanning images (energy dispersive spectroscopy) for alloy compositions; (3) the degree of atomic diffusion in BMG composites functioned as the depth of nano-indentation via MD simulations; (4) the differences in nano-deformation via MD simulations can be observed for Zr–Cu alloys with various crystals; (5) the micro-indentation may stimulate transformation or B2 phase formation in localized regions upon indented stress; (6) the simulated results and experimental outcomes were mutually corroborated. These results also give a hint that atomic diffusion and phase formation in multiple mingled microstructures really existed, but they were very complicated and different in localized areas. This research is important and provides a clue for further exploration of the relationship between deformation and atomic diffusion.