Influence of Stress on Precipitation and Coarsening in Alloys.
UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES ELECTRONIC SCIENCES LAB
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Scanning and transmission electron microscopy of precipitate morphologies of normalized and stress-aged Udimet 700 and Ni9 Al wt pct alloys were studied. In both alloys, rods and plates are formed by a coarsening process involving shape change and agglomeration. All experimental observations, the stress aging behavior of Mar-M200, the NiAl-Cr eutectic and the various omega containing titanium-base alloys can be understood on the basis that the morphology forms, and minimizes a free energy including interfacial energy, residual strain energy and interaction energy terms. A method of estimating the residual strain energy and interaction energy of an infinite plate, infinite rod and cuboidal composite has been developed. A theory of diffusional creep has been developed for binary metallic solid-solutions subjected to a uniform uniaxial state of stress. Several predictions of the theory have been confirmed in NiCr and NiW solid solutions.
- Metallurgy and Metallography