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Phase transformations in the Al-Li-Hf and Al-Li-Ti systems

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Abstract

Phase transformations in Al-1, 9Li-1.6Hf and Al-1.5Li-0.7Ti (wt pct) alloys have been analyzed thoroughly using various electron microscopy techniques. An Ll2-ordered ternary Al3 (Li,X) phase, orά (X), forms in both alloys during heat treatment. Theά forms as spherical precipitates by normal nucleation and growth and in the Hf alloy as filaments by discontinuous precipitation. The X:Li ratio in these precipitates is found to be a function of the precipitation mode in the Hf alloy.ά is coherent with the Al matrix and serves as a preferred nucleation site for the precipitation of the Al3Li orδ' phase when the alloy is aged at 190°C. Theδ', also Ll2-ordered, grows as continous envelopes which completely enclose theα' phase. An altered morphology predominates forα'(Ti) after extended heat treatment. The major feature of the altered morphology is the incorporation of spiraled dislocations at theα'/matrix interface, which act to ease the misfit between theα' (Ti) and the matrix.δ' forms as caps on the alteredα'(Ti) in areas away from the dislocations. Disruption of theα' envelopes is attributed to the strain fields and loss of coherency associated with the presence of interfacial dislocations and a possible local shift from Ll2 to DO22 ordering in theα'(Ti) precipitates.

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Authors and Affiliations

  1. Chemicals and Pigments Department, Jackson Laboratory, E.I. DuPont de Nemours, Inc., 08023, Deepwater, NJ

    Nancy F. Levoy (Development Chemist)

  2. Department of Materials Science and Engineneering, Massachusetts Institute of Technology, 02139, Cambridge, MA

    John B. Vandersande (Professor)

Authors
  1. Nancy F. Levoy
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  2. John B. Vandersande
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Levoy, N.F., Vandersande, J.B. Phase transformations in the Al-Li-Hf and Al-Li-Ti systems. Metall Trans A 20, 999–1019 (1989). https://doi.org/10.1007/BF02650137

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  • DOI: https://doi.org/10.1007/BF02650137

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