NSF Young Investigator

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9457964 Hemker Dislocation motion in intermetallic alloys is known to be governed by the dislocation core geometry, but attempts to capitalize on this knowledge have been inhibited by the small number of experimental observations currently available. This study, which is unique in that it provides a very quantitative measure of dislocation core geometries by combining transmission electron microscopy with computer generated image simulations, provides a way of experimentally observing and characterizing dislocation core structures in intermetallic alloys. These quantitative observations are used to link the atomic structure of dislocation cores with the macroscopic mechanical properties in several different intermetallic alloys. It is known that the addition of iron to nickel-germanium reduces the anomalous flow strength behavior and eventually results in alloys in which the flow strength decreases "normally" with increasing temperature. Deforming a series of specimens that vary systematically in iron content and relating the measured fault energies with the yielding behavior of the individual alloys will provide valuable information about the sources of the flow strength anomaly in all L12 alloys. %%% A fundamental understanding of the processes that control dislocation motion in intermetallic alloys will allow alloy designers to modify alloy stoichiometry to maximize both ductility and high temperature strength. ***