Structure and Failure of fcc/bcc Heterophase Boundaries in Metals

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Heterophase Interface between fcc and bcc metals exist in many microelectronic devices and in composite materials. Compared to other interphase boundaries, for example metal/ceramic interfaces, the failure processes at fcc/bcc heterophase boundaries are poorly understood. The purpose of the proposed project is to study the structure, the mechanical properties and the resistance to damage formnation of different fcc/bcc interfaces in the Cu-Ta model system. The interfacial structure will be studied in close collaboration with the group of Prof. Yuri Mishin at George Mason University, Fairfax, USA, who is also developing the angularly dependent interatomic Potentials used to model the atomic interaction in the Cu-Ta system. The group of Prof. Mishin will then focus on the study of diffusion at the fcc/bcc interface, whereas we will focus on the determination of the initial failure modes as a function of loading mode and orientation of the interface and of the two adjacent crystals. Particular emphasis will be put on defects at the fcc/bcc interfaces and on pore formation. The transition of vacancy clusters to a macroscopic pore, as well as the actual decohesion process will both be studied. The dynamics of crack propagation and energy dissipation mechanisms at high temperatures shall also be investigated. The correlation between structure, mechanical properties, defect formation, diffusion coefficients and fracture at these heterophase boundaries will significantly advance our understanding of the behavior of heterophase boundaries in such material systems. It will also lay the foundations for further studies towards electromigration failure and reliability of fcc/bcc composites.