Jonathan E. Spowart

Multi-scale characterization of spatially heterogeneous systems: implications for discontinuously reinforced metal–matrix composite microstructures

Abstract A new multi-scale technique is presented for characterizing the spatial distribution of second-phase particles in two-dimensional distributed multi-phase systems. The implications for the characterization of reinforcement distributions in discontinuously reinforced metallic matrix composite microstructures are discussed, along with results of the analysis both for simulated and experimental discontinuously reinforced aluminum (DRA) materials. A systematic variation in the degree of spatial heterogeneity is observed with increasing length scale. This result leads to the definition of the parameter LH or homogeneous length scale. The relevance of LH measured for a real DRA microstructure is then discussed in the context of statistical variations in mechanical properties such as tensile strength, ductility, and fracture toughness.

The 3-D analysis of discontinuously reinforced aluminum composite microstructures

Automated serial sectioning is presented as an attractive experimental technique for producing an accurate, large-scale three-dimensional (3-D) digital microstructural model of an extruded discontinuously reinforced aluminum composite material. The model is used as input for an elastic-plastic 3-D finite-element analysis that simulates tensile loading of the microstructure. The 3-D visualization and characterization of the resultant deformation structures within the composite microstructure has allowed some of the critical microstructural features that control the tensile response to be identified.

Effects of Disorder State and Interfacial Layer on Thermal Transport in Copper/Diamond System

The characterization of Cu/diamond interface thermal conductance (hc) along with an improved understanding of factors affecting it are becoming increasingly important, as Cu-diamond composites are being considered for electronic packaging applications. In this study, ∼90u2009nm thick Cu layers were deposited on synthetic and natural single crystal diamond substrates. In several specimens, a Ti-interface layer of thickness ≤3.5u2009nm was sputtered between the diamond substrate and the Cu top layer. The hc across Cu/diamond interfaces for specimens with and without a Ti-interface layer was determined using time-domain thermoreflectance. The hc is ∼2× higher for similar interfacial layers on synthetic versus natural diamond substrate. The nitrogen concentration of synthetic diamond substrate is four orders of magnitude lower than natural diamond. The difference in nitrogen concentration can lead to variations in disorder state, with a higher nitrogen content resulting in a higher level of disorder. This difference ...

Multiscale Characterization of Spatial Heterogeneity in Multiphase Composite Microstructures

A computational characterization technique is presented for assessing the spatial heterogeneity of two reactant phases in a three-phase chemically reactive composite. This technique estimates the reaction yield on multiple microstructure length scales based on the segregation of the two reactant phases and the expected reaction stoichiometry. The result of this technique is a metric, quantifying the effectiveness of phase mixing in a particular microstructure as a function of length scale. Assuming that the proportionate mixing of reactant phases on multiple length scales will enhance reaction kinetics and the overall level of reaction completion, this tool can subsequently be used as a figure-of-merit for optimizing microstructure via appropriate processing. To illustrate this point, an example is shown where a bimodal three-phase microstructure has a higher reaction yield at every length scale when compared with a monomodal three-phase microstructure with the same constituent loading.