High-Temperature Microstructure Evolution of Copper-BCC Metallic Composites
Abstract
Nanocomposite metals have a high interface area per unit volume, resulting in high interface energy per unit volume. This elevated energy density drives microstructure changes, especially at elevated temperatures. However, the mechanisms governing these changes are not well understood.
We examine the microstructure changes that occur following the discontinuity of a Cu-terminated layer within a Nb matrix. Our experimental findings reveal a transformation where Cu fragments into a series of distinct Cu particles within a layered composite after the layer pinch-off event. We compare our observations to a previous numerical study utilizing the Chan-Hillard equitation in the phase field model. In this context, we refer to the Cu-Nb mobility at 800℃ in the Chan-Hillard equation as M(c)=(M_0=7.3±3.6 〖nm〗^5/s∙eV)|1-c^2 | , where the order parameter, c, is 1 for Cu and -1 for Nb.
Moreover, we also observed the mass transport occurring across grain boundaries in a phase-separating metallic composite. Remarkably, despite the immiscibility of Nb and Cu, we discover the Nb transport through Cu grain boundaries in a Mo/Cu/Nb layered composite, especially the non-coherent twin boundaries of Cu. Our observations indicate that Nb exhibits solubility within Cu grain boundaries, effectively acting as a short-circuit path for mass transport. This phenomenon has also been discovered in other phase-separating layered composites, which infer the grain boundary is a short circuit path for mass transport, discarding the solubility of the two materials.
Collections
Citation
Sheu, Emmeline (2023). High-Temperature Microstructure Evolution of Copper-BCC Metallic Composites. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /202946.