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Composite Particles Formation and Behaviour in Al-Li Alloys Alloyed by Sc (Zr) under Heat Treatment and Severe Plastic Deformation

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Molebnyi O., Berezina A., Kotko A.

Acta Physica Polonica A

2015

vol. 128

issue 4

564-569

The mechanism and kinetics of Al₃Li/Al₃Sc composite particles formation during aging of triple Al-Li-Sc alloys were studied. The particles of such type consist of two isomorphic phases, ordered by L1₂ type. Composite particles in Al-Li-Sc are formed by epitaxial nucleation of δ' (Al₃Li) phase on pre-existing Al₃Sc precipitates at low temperature aging in the area of existence of Al₃Li phase, and form uniform shell around them. The motive force of such heterostructure formation is the minimization of total surface, elastic and chemical energy of the alloy. Dark-field transmission electron microscopy images of such composite particles taken from superlattice reflex 100 are composed of a dark core surrounded by a bright shell. The mutual diffusion of Li and Sc during the aging of Al-Li-Sc alloys is observed. The dark-field transmission electron microscopy image of the composite particle obtained from superlattice reflection became transparent after continuous natural aging of Al-Li-Sc alloys. The presence of the particle in Al matrix can be only seen due to decoration by secondary precipitations of δ' (Al₃Li) phase. Composition analysis of such transparent particles was carried out using two-beam kinematical theory of electron diffraction. Such composite particles with transparent cores remain in Al matrix even after severe plastic deformation of Al-Li-Sc alloy.

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1 Acta Physica Polonica A

1 2015

1 Berezina A.

1 Kotko A.

1 Molebnyi O.

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Composite Particles Formation and Behaviour in Al-Li Alloys Alloyed by Sc (Zr) under Heat Treatment and Severe Plastic Deformation