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L12 ordering and δ' precipitation in Al-Cu-Li
Pascal Neibecker1,2,3, Michael Leitner4, Muna Kushaim5,6
1Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstr. 1, 85748, Garching, Germany. pascal.neibecker@frm2.tum.de.
This study clarifies the precipitation mechanism of the delta prime (Al3Li) phase in Al-Li alloys. Ternary alloys reveal evidence of congruent ordering and L12 microstructure, resolving long-standing scientific debate.
Area of Science:
- Materials Science
- Metallurgy
- Physical Chemistry
Background:
- The precipitation mechanism of the delta prime (Al3Li) phase in aluminum-lithium (Al-Li) alloys is a subject of ongoing scientific debate.
- Previous research has been limited by the rapid kinetics in binary Al-Li systems, hindering experimental clarification of the congruent ordering process.
Purpose of the Study:
- To investigate the precipitation mechanism of the delta prime (Al3Li) phase in ternary Al-Cu-Li alloys.
- To experimentally clarify the conjectured congruent ordering process by utilizing alloys with slower precipitation kinetics.
Main Methods:
- Transmission Electron Microscopy (TEM)
- High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM)
- Differential Scanning Calorimetry (DSC)
- Atom Probe Tomography (APT)
Main Results:
- Clear evidence for congruent ordering in a specific compositional range of Al-Cu-Li alloys.
- Observation of a strongly L12 ordered microstructure after natural aging, with a chemically homogeneous lithium distribution.
- Demonstration of alloy decomposition upon annealing at elevated temperatures.
Conclusions:
- The study provides experimental validation for congruent ordering in Al-Li systems.
- The findings offer insights into the reaction pathway of delta prime precipitation.
- Results are compared with the Bragg-Williams-Gorsky model predictions for decomposition and ordering.
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