Structural Materials: Understanding Atomic-Scale Microstructures
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Emmanuelle A. Marquis, Michael K. Miller, Didier Blavette, Simon P. Ringer, Chantal K. Sudbrack, and George D.W. Smith Abstract With the ability to locate and identify atoms in three dimensions, atom-probe tomography (APT) has revolutionized our understanding of structure-property relationships in materials used for structural applications. The atomic-scale details of clusters, second phases, and microstructural defects that control alloy properties have been investigated, providing an unprecedented level of detail on the origins of aging behavior, strength, creep, fracture toughness, corrosion, and irradiation resistance. Moreover, atomic-scale microscopy combined with atomistic simulation and theoretical modeling of material behavior can guide new alloy design. In this article, selected examples highlight how APT has led to a deeper understanding of materials structures and therefore properties, starting with the phase transformations controlling the aging and strengthening behavior of complex Al-, Fe-, and Ni-based alloys systems. The chemistry of interfaces and structural defects that play a crucial role in high-temperature strengthening, fracture, and corrosion resistance are also discussed, with particular reference to Zr- and Al-alloys and FeAl intermetallics.
Introduction The increasing economic and environmental costs of energy are driving the design and development of new and improved structural alloys with remarkable combinations of physical properties. The notion of new structural alloys that are merely stronger or harder than contemporary systems may well be a significant basis for new alloy development but, increasingly, it is a novelty in the balance of various structural properties that is presenting the greatest opportunities. New combinations of properties that are usually in conflict with each other, such as strength and ductility, or enhanced static and dynamic mechanical properties in combination with enhanced recyclability, corrosion resistance, and thermal properties are of great interest. The capacity of materials scientists and engineers to understand and control phase transforma-
tions and related phenomena at the nanoscale is a key enabler of these technologies, and thus the challenges in materials characterization are acute. As demonstrated in the following selected examples, atom-probe tomography (APT) is providing unparalleled insights into the three-dimensional nanoscale structure, which is creating new ideas in alloy design and development.
Phase Transformations The following three examples illustrate how APT provided unique insights into atomistic phenomena of stages of phase transformation that could not be studied otherwise: clustering as the precursor to precipitation in Al, accelerated precipitation during irradiation of Cu-containing steels, and kinetic pathways in phase decomposition of Ni alloys. Other exam-
MRS BULLETIN • VOLUME 34 • OCTOBER 2009 • www.mrs.org/bulletin
ples include the unique contribution of APT to the 3D imaging and analysis of spinodal decomposition i
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