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Browsing by Author "Fraser, HL"

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    Predicting pseudomorphic phases in multilayers: Hexagonal-closed-packed Nb in Nb/Zr
    (American Institute of Physics, 2003-12-17) Thompson, GB; Banerjee, R; Fraser, HL; University of Alabama Tuscaloosa; University System of Ohio; Ohio State University
    As the dimensions of materials are reduced to the nanometer scale, changes in phase stability, referred to as pseudomorphism, are being reported. Such changes in phase stability are often serendipitously discovered in multilayered thin films. In this letter, we use a classical thermodynamic treatment to model and predict phase stability in Nb/Zr multilayers. An outcome of this letter is the development of a biphase stability diagram that represents the interrelationship of phase stability to volume fraction and length scale. Using this methodology, an hcp Nb phase stability field was empirically postulated and subsequently confirmed by x-ray and electron diffraction. The successful prediction of this phase, based upon classical thermodynamics quantities, suggests that other types of phase stabilities in other multilayers could be proposed using the biphase diagram. (C) 2004 American Institute of Physics.
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    Tuning phase stability in nanocomposite multilayers
    (American Institute of Physics, 2003-08-26) Thompson, GB; Banerjee, R; Fraser, HL; University System of Ohio; Ohio State University; University of Alabama Tuscaloosa
    As thin-film layers in a multilayered stack are reduced in thickness, changes in phase stability can result within the individual layers. These changes in phase are expected to have a significant influence upon the functional properties of the nanostructured composite. The ability to engineer, or tune, phase stability at this nanometer length scale is of significant importance in order to maximize the functional properties of these materials. We report the prediction and experimental conformation of tuning the hcp to bcc phase stability in Ti for Ti/Nb multilayered nanocomposites. The prediction was based upon selective alloying of Ti with a bcc beta stabilizing element using a new form of a thermodynamic phase diagram for predicting phase stability in thin-film multilayers. (C) 2003 American Institute of Physics.