A combined single crystal X-ray diffraction and electron diffraction study of the T2phase in Al-Li-Cu alloys

Both single crystal X-ray diffraction techniques and convergent beam electron diffraction have been employed to examine the structure of theT ₂ (Al₆CuLi₃) phase in three particular Al-Li-Cu alloys. It is shown thatT ₂ displays icosahedral symmetry both in a high purity laboratory melt and in two impure alloys which had been processed industrially. Possible reasons for the five-fold symmetry ofT ₂ are discussed.     

The aging characteristics of an AI-2 Pct Li-3 Pct Cu-0.12 Pct Zr alloy at 190 °C

The aging characteristics of an Al-2 pct Li-3 pct Cu-0.12 pct Zr alloy at 190 °C have been examined using transmission electron microscopy. Specifically, the development of intragranular microstructures, and the interactions among the various precipitate species have been documented. Theδ′ phase (Al₃Li) is shown to be present, not only as small spherical particles, but also as a shell aroundβ′ (Al₃Zr) and as a film on the broad coherent faces of the θ′ (Al₂Cu). At peakage (18 hours), theδ′ is associated predominantly with theθ′. However, overaging leads to dissolution of theθ′ and a concomitant increase in the volume fraction of theT ₁. This latter phase can cut/grow through the δ’ and plays an increasing role in determining theδ′ distribution after prolonged aging. Finally, T₂ is found to precipitate within the matrix in the overaged condition. TheT ₂ precipitates display icosahedral symmetry. No evidence for the presence of theδ phase has been obtained.     

On the nucleation ofθ′ and T1 on Al3Zr precipitates in Al-Li-Cu-Zr alloys

Two quaternary Al-Li-Cu-Zr alloys have been investigated using electron microscopy. Ageing at 190° C resulted in the nucleation of precipitates on the Al₃Zr/matrix interface in addition to heterogeneous nucleation on matrix dislocations. In the majority of cases, the broad, coherent face of the plans ms in contact with the Al₃Zr precipitates. Similar evidence showed that nucleation of T₁ precipitates occurred on the Al₃Zr, but to a lesser extent than. Solid-solid nucleation theory has been used to account for the Al₃Zr acting as a nucleation substrate.     

Analysis of Zinc 65 Contamination After Vacuum Thermal Process

Radioactive contamination with a gamma energy emission consistent with ⁶⁵Zn was detected in a glovebox following a vacuum thermal process. The contaminated components were removed from the glovebox and subjected to examination. Selected analytical techniques were used to determine the nature of the precursor material, i.e., oxide or metallic, the relative transferability of the deposit and its nature. The deposit was determined to be borne from natural zinc and was further determined to be deposited as a metallic material from vapor.