Positron lifetime measurements were used for studying decomposition during post-quench in situ annealing of binary Al-7.35 at.% Li and ternary Al-7.3 at.% Li-X (X=1.1 at.% Cu, 5.2 at.% Mg or 0.18 at.% Sc) alloys. A typical lifetime of 185+or-5 ps observed in Al-Li is attributed to coherent delta '(Al3Li) particles. In ternary alloys positrons show a strong response to the formation of semicoherent and incoherent phases such as T1(Al2LiCu) and Al2LiMg. Positron trapping in Al-Li-Sc is attributed to composite delta ' (Al3Li)/Al3Sc particles associated with vacancies. Quenched-in vacancies were detected in Al-Li-Sc and Al-Li-Mg but not in Al-Li-Cu and Al-Li.

Positron lifetime τ measurements are performed to study defect annealing and decomposition in Al–(0.003 to 0.36 at%) Sc alloys during isochronal and isothermal heat treatment of water‐quenched samples. A two‐stage behaviour of the positron lifetime observed below 200°C is explained as migration and clustering of quenched‐in vacancy‐Sc atom complexes followed by the annealing of vacancy clusters. In alloys containing 0.18 and 0.36 at% Sc an extra peak appears in the average positron lifetime around 300°C which is attributed to the precipitation of coherent Al3Sc particles. Although the volume fraction of Al3Sc is very small, f ≈ 0.5%, the precipitates are detected by positrons due to their fine‐disperse distribution (diameter ≈ 10 nm). A vacancy‐type lifetime component which appears simultaneously with the precipitate formation is attributed to structural vacancies of the Al3Sc phase or to vacancies associated with the Al3Sc particle‐matrix interface.

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Abstract. The structure formation in hypereutectic Al-Sc and hyperperitectic Al-Zr, Al-Hf alloys with concentration of alloying element up to 1.3 at.% have been studied under conditions far from thermodynamical equilibrium depending on cooling rate and quenching temperature. The co-operative growth structures are solidified with cooling rate of 10 2 -10 3 K/s regardless of overheating and under cooling rate of 10 5 -10 6 K/s at small overheating. The phase compound of these structures is -solid solutions and phase with L1 2 -ordered structure or two solid solutions with different concentrations of alloying element. The large overheating leads to formation of -solid solution anomalously supersaturated under cooling rate of 10 5 -10 6 K/s.

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