Microstructure-Property Correlations

Heterogeneity is present in materials at various length scales and in different forms.  For example, polycrystalline materials are heterogeneous in that they are composed of crystals of different orientations and that they contain defects of various dimensions, e.g., dislocations and grain boundaries.  Another type of heterogeneity is the variation in compositions, such as in composites and porous media.  These structural heterogeneities result in a distribution of local materials properties.  From this known distribution we can evaluate the apparent or effective properties of heterogeneous materials.  Our goal is to quantitatively correlate the effective properties with the connectivity among various microstructural elements, which is the object of percolation theory.  Combining homogenization schemes with percolation concepts offers a robust approach to understanding microstructure-property relationships.  We study discrete network problems and also more common continuum problems using both theoretical modeling and computer simulations.  For example, the figure below shows the effective diffusivity of a ternary grain boundary network calculated from our model (color surface plot) and from a simulation (gray dots).  We also experimentally seek to improve the mechanical properties of metallic materials by manipulating the connectivity of the heterogeneous interfacial networks.

Macroscopic effective diffusivity of ternary grain boundary networks with diffusivity contrast ratio D1:D2:D3 = 1:104:108.  Each axis of the horizontal triangle maps to the fraction of boundaries of each type.  The sudden increase in the effective diffusivity reflects the percolation of fast-diffusing components in the network.

Published Articles:

Coble creep in heterogeneous materials: The role of grain boundary engineering
Chen Y, Schuh CA; PHYSICAL REVIEW B 76 (6): Art. No. 064111 AUG 2007 (PDF)

Contribution of triple junctions to the diffusion anomaly in nanocrystalline materials 
Chen Y, Schuh CA; SCRIPTA MATERIALIA 57 (3): 253-256 AUG 2007 (PDF)

Geometric considerations for diffusion in polycrystalline solids
Chen Y, Schuh CA; JOURNAL OF APPLIED PHYSICS 101 (6): Art. No. 063524 MAR 2007 (PDF)

Percolation of diffusional creep: A new universality class
Chen Y, Schuh CA; PHYSICAL REVIEW LETTERS 98 (3): Art. No. 035701 JAN 2007 (PDF)

Diffusion on grain boundary networks: Percolation theory and effective medium approximations
Chen Y, Schuh CA; ACTA MATERIALIA 54 (18): 4709-4720 OCT 2006 (PDF)