Understanding materials microstructure and behavior at the mesoscale
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Introduction The mesoscale is a crucial realm in materials science, especially for polycrystalline materials. Put as succinctly as possible, a mesoscale property is an attribute of a material that cannot be straightforwardly constructed from properties at the atomic scale.1 The prefix “meso-” implies being between the atomic and macroscopic scales, but the precise length or time scale where the break in understanding develops depends on the property. Figure 1 illustrates the difference between traditional, reductionist approaches to science that attempt to deduce specific aspects of the underlying length or time scale from the larger scale behavior of systems, versus the constructionist approach, which is typical of mesoscale science, of seeking to build up properties by moving up the time and length scales. This article attempts to explain where a few mesoscale challenges exist for structural materials and their properties. As pointed out in Table I, the properties of perfect crystal lattices can be calculated, although there are significant exceptions. Linear elastic deformation, even of composite materials, can be computed quantitatively with good accuracy, for example. Many of the useful materials properties for engineering depend, however, on the properties of lattice defects, such as interstitials, dislocations, and interfaces.
Dislocations, in particular, are well understood as individual defects where an example of a well-established method is the calculation of the Peierls stress required to move them through a lattice.2 Plastic deformation presents challenges because it generates large dislocation densities on multiple slip systems. Through the formation of various junctions,3 the dislocations interact in complex ways that lead to heterogeneous densities and patterning that continue to be the subject of active research. Anisotropic interactions of defects within grain neighborhoods further complicate determination of emergent mesoscale properties. Given the importance of defect populations and their spatial heterogeneity, it is evident that multimodal, multiscale characterizations of materials are crucial to improving our understanding. Equally important is the use of models to quantify understanding, but these models must be tested against detailed experimental data. Accordingly, this article attempts to explain where a few mesoscale challenges exist for structural materials and their properties.
Mesoscale characterization and modeling of deformation Plastic deformation of metals and alloys has been studied for decades. From the perspective of materials science, plastic deformation is dominated at low temperatures by dislocation
A.D. Rollett, Department of Materials Science and Engineering, Carnegie Mellon University, USA; [email protected] G.S. Rohrer, Department of Materials Science and Engineering, Carnegie Mellon University, USA; [email protected] R.M. Suter, Department of Physics, Carnegie Mellon University, USA; [email protected] DOI: 10.1557/mrs.2015.262
© 2015 Materials Research Society
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