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Main Title: Thickening of T1 Precipitates during Aging of a High Purity Al−4Cu−1Li−0.25Mn Alloy
Author(s): Häusler, Ines
Kamachali, Reza Darvishi
Hetaba, Walid
Skrotzki, Birgit
Type: Article
Language Code: en
Abstract: 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.
Issue Date: 21-Dec-2018
Date Available: 2-Aug-2019
DDC Class: 500 Naturwissenschaften und Mathematik
Subject(s): Al-Cu-Li-alloy
T1 precipitate
microstructure evolution
volume fraction
number density
strain difference
Sponsor/Funder: DFG, 237105621, SPP 1713: Stark gekoppelte thermo-chemische und thermo-mechanische Zustände in Angewandten Materialien
Journal Title: Materials
Publisher: MDPI
Publisher Place: Basel
Volume: 12
Issue: 1
Article Number: 30
Publisher DOI: 10.3390/ma12010030
EISSN: 1996-1944
Appears in Collections:FG Elektronenmikroskopie und -holographie » Publications

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