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Open AccessArticle

Thickening of T1 Precipitates during Aging of a High Purity Al–4Cu–1Li–0.25Mn Alloy

1
Federal Institute for Materials Research and Testing (BAM), Department 5: Materials Engineering, 12205 Berlin, Germany
2
Institute of Optics and Atomic Physics, Technical University of Berlin, 10623 Berlin, Germany
3
Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany
4
Department of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Gesellschaft, 14195 Berlin, Germany
5
Department of Heterogeneous Reactions, Max-Planck-Institute for Chemical Energy Conversion, 45470 Mülheim an der Ruhr, Germany
*
Author to whom correspondence should be addressed.
Materials 2019, 12(1), 30; https://doi.org/10.3390/ma12010030
Received: 2 December 2018 / Revised: 16 December 2018 / Accepted: 16 December 2018 / Published: 21 December 2018
(This article belongs to the Section Structure Analysis and Characterization)
The age hardening response of a high-purity Al–4Cu–1Li–0.25Mn alloy (wt. %) during isothermal aging without and with an applied external load was investigated. Plate shaped nanometer size T1 (Al2CuLi) and θ′ (Al2Cu) hardening phases were formed. The precipitates were analyzed with respect to the development of their structure, size, number density, volume fraction and associated transformation strains by conducting transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) studies in combination with geometrical phase analysis (GPA). Special attention was paid to the thickening of T1 phase. Two elementary types of single-layer T1 precipitate, one with a Li-rich (Type 1) and another with an Al-rich (Defect Type 1) central layer, were identified. The results show that the Defect Type 1 structure can act as a precursor for the Type 1 structure. The thickening of T1 precipitates occurs by alternative stacking of these two elementary structures. The thickening mechanism was analyzed based on the magnitude of strain associated with the precipitation transformation normal to its habit plane. Long-term aging and aging under load resulted in thicker and structurally defected T1 precipitates. Several types of defected precipitates were characterized and discussed. For θ′ precipitates, a ledge mechanism of thickening was observed. Compared to the normal aging, an external load applied to the peak aged state leads to small variations in the average sizes and volume fractions of the precipitates. View Full-Text
Keywords: Al-Cu-Li-alloy; precipitation; T1 precipitate; microstructure evolution; thickening; creep; volume fraction; number density; strain difference Al-Cu-Li-alloy; precipitation; T1 precipitate; microstructure evolution; thickening; creep; volume fraction; number density; strain difference
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MDPI and ACS Style

Häusler, I.; Kamachali, R.D.; Hetaba, W.; Skrotzki, B. Thickening of T1 Precipitates during Aging of a High Purity Al–4Cu–1Li–0.25Mn Alloy. Materials 2019, 12, 30.

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