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

100%

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.

Decomposition Processes in the Anomalous Supersaturated Solid Solution of Binary and Ternary Aluminium Alloys Alloyed with~Sc and~Zr

88%

Berezina A., Monastyrska T., Molebny O., Nosenko V., Kotko A.

Acta Physica Polonica A

2012

vol. 122

issue 3

539-543

Decomposition of supersaturated solid solution of aluminium alloys alloyed with Sc and Zr have been studied in the work. The binary hypereutectic Al-Sc alloys, hyperperitectic Al-Zr alloys and ternary Al-Sc-Zr alloys were chosen. Alloys were obtained by the melt-spinning. Melts were quenched from temperatures of T = 1000C and T = 1400°C. The crystallization of anomalously supersaturated solid solution (T_{quen.} = 1400°C) or the crystallization with the formation of "fan" structure (T_{quen.} = 1000°C) are possible. The decomposition of anomalously supersaturated solid solution is continuous, with the precipitation of nanosized spherical Al_3X (X = Sc, Zr) particles. The loss of thermal stability of Al-Sc alloys is due to the loss of coherence of the strengthening Al_3Sc phase. In Al-Zr alloys the loss of strength is due to the formation of a stable tetragonal DO_{23}-ordered Al_3Zr phase. After co-alloying of Al by Sc and Zr a bimodal grained structure was observed for the hypereutectic ternary alloy (T_{quen.} = 1400°C). Nanosized grains of 50-60 nm were present on the boundaries of 1-2 μm large-sized grains. Transmission electron microscopy shows the formation of nanocomposite Al_3Zr/Al_3Sc particles. The formation of Al_3Zr shell changes the nature of the interfacial fit of the particle with the matrix and slows down the decomposition during the coalescence.

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2 Acta Physica Polonica A

1 2015

1 2012

2 Berezina A.

2 Kotko A.

1 Molebny O.

1 Molebnyi O.

1 Monastyrska T.

1 Nosenko V.

Search results

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

Decomposition Processes in the Anomalous Supersaturated Solid Solution of Binary and Ternary Aluminium Alloys Alloyed with~Sc and~Zr