Precipitation Sequence in the Mg&amp;ndash;Gd&amp;ndash;Y System Investigated by HRTEM and HAADF-STEM

Matsuoka, Y.; Matsuda, Kenji; Watanabe, Kenji; Nakamura, Junya; Lefebvre, W.; Nakagawa, Daisuke; Saikawa, Seiji; Ikeno, Susumu

doi:10.2320/matertrans.l-m2014824

Cited by 27 publications

(4 citation statements)

References 16 publications

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“…In addition to age hardenable Al alloys, examples of alloy systems exhibiting this mechanism are various Fe alloys [1,2], Cu-Co [3], Cu-Ni-Si [4], Mg-Y/Gd [5,6], and even doped non-metallic compounds such as the ferroelectric BiFeO3-Nd-Ti [7]. There typically exists a precipitation sequence, where a phase with a lower bulk enthalpy nucleates in connection to another precipitate in the host lattice.…”

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confidence: 99%

A hybrid aluminium alloy and its zoo of interacting nano-precipitates

Wenner

Marioara

Andersen

et al. 2015

Materials Characterization

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An alloy with aluminium as its base element is heat treated to form a multitude of precipitate phases known from different classes of industrial alloys: Al-Cu(-Mg), Al-Mg-Si-Cu, and Al-Zn-Mg. Nanometer-sized needle-shaped particles define the starting point of the phase nucleation, after which there is a split in the precipitation sequence into six phases of highly diverse compositions and morphologies. There are several unique effects of phases from different alloy systems being present in the same host lattice, of which we concentrate on two: the replacement of Ag by Zn on the Ω interface and the formation of combined plates of the θ' and C phases. Using atomically resolved scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy, we investigate the formation mechanisms, crystal structures and compositions of the precipitates.

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confidence: 99%

A hybrid aluminium alloy and its zoo of interacting nano-precipitates

Wenner

Marioara

Andersen

et al. 2015

Materials Characterization

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“…Here, it is worth mentioning that many β″ particles in Mg–La alloys can reach a thickness of 2–3 nm (about five times the c -length of the β″ unit cell) along the [0001] α direction. Therefore, compared to the other precipitation products reported previously, such as the zigzag monolayer structure and some occasionally occurred D0 19 structural unit cells, − the captured β″ in this study can be deemed as a real precipitation phase with the obvious three-dimensional periodic structure.…”

Section: Resultsmentioning

confidence: 61%

On Shapes and Orientations of Precipitation Strengthening Phases in an Aged Mg–La Alloy

Sun

Ren

Wang

et al. 2023

Crystal Growth & Design

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The shapes and orientations of precipitates have important influences on the mechanical properties of precipitation-strengthened magnesium alloys. In this work, the microstructure and precipitation behaviors of an aged Mg-3.0 wt % La alloy are investigated by atomic resolution scanning transmission electron microscopy. The main precipitate product at the peak-aged stage is a category of La-enriched solid solution with a face-centered cubic (FCC) lattice, which will subsequently evolve into another precipitation strengthening phase with a tetragonal (T) lattice at the over-aged stage. The crystallographic orientations and shapes of FCC and T precipitates are elaborated on. Distinctively, La-rich FCC structures can maintain three types of orientation relationships (ORs) with the α-Mg matrix, which are defined as type-A OR (⟨001⟩FCC //[0001]α), type-B OR (⟨110⟩FCC //[0001]α), and type-C OR (⟨111⟩FCC //[0001]α). It is concluded that the T phase always nucleates at the {100}FCC crystallographic planes of La-rich FCC structures and gradually grows up by consuming La-rich solid solution. Based on the conversion from FCC to T lattices, the occurred T precipitates can be divided into four classifications whose fourfold rotational axes are parallel to the c-axis, basal plane, ⟨202̅3⟩α, and ⟨101̅2⟩α zone axes of the α-Mg matrix, respectively. At the same time, there exist six sets of crystallographic ORs (type-A1, type-A2, type-A3, type-B1, type-B2, and type-C1) between the T phase and α-Mg matrix. In view of the interfacial matching, the shapes of the existing T phase involve the sphere, prismatic, and basal plates, whose effects on the mechanical properties are also predicted theoretically.

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“…However, the structures and compositions of precipitate phases, GP zones and clusters that form in the early stage of decomposition are still poorly understood [11,12]. It remains to be firmly established whether solute clusters form and, if so, how they interact with lattice defects such as dislocations and twins.…”

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confidence: 99%

Solute Segregation and Aggregation in Mg Alloys

Nie

Zhu

Wilson

2015

Magnesium Technology 2015

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Extended AbstractThe addition of adequate amounts of rare-earth (RE) alloying elements can produce appreciable effects on microstructures, formability and mechanical properties of magnesium alloys. At low concentrations, it can weaken the basal texture in the asdeformed and the recrystallized conditions in wrought alloys and improve the creep resistance of casting alloys at elevated temperatures; at high concentrations, it can bring significant age hardening effects and thus improve the alloy strength. While this knowledge has been known for some years, the precise roles of RE solutes in texture weakening and the early stage of precipitation remain unclear.It has been demonstrated in recent years that the application of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) can reveal the distribution of RE solutes and the structure of precipitate phases at the atomic scale. The use of this Z-contrast imaging technique, combined with atom probe tomography or other characterization techniques such as energy dispersive X-ray spectroscopy and electron energy loss spectroscopy, has revealed the occurrence of solute segregation in high-angle grain boundaries even in solid solution single phase alloys based on the Mg-Gd system [1-4]. The segregation of RE atoms in the grain boundaries will no doubt impede the boundary migration [5] and thus change the recrystallization behaviours and perhaps even the recrystallization texture. In addition to the wellestablished solute segregation in the partially-coherent high-angle grain boundaries, a very recent study using HAADF-STEM [6] has revealed the occurrence of a periodic segregation of solute atoms in fully-coherent twin boundaries of { } D , { } D and { } D . This segregation results from the minimization of elastic strain energies associated with twin boundaries and the over-sized individual solute atoms, and it provides a strong pinning of the twin boundaries and a concomitant annealing hardening effect when the alloy is deformed under certain circumstances. Subsequent studies using first-principles density functional theory computations indicate that solute atoms of most commonly used alloying elements have a strong tendency to segregate to { } D twin boundaries [7,8], and that solute segregation can also occur in a symmetrical tilt boundary [9].

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Precipitation Sequence in the Mg–Gd–Y System Investigated by HRTEM and HAADF-STEM

Cited by 27 publications

References 16 publications

A hybrid aluminium alloy and its zoo of interacting nano-precipitates

A hybrid aluminium alloy and its zoo of interacting nano-precipitates

On Shapes and Orientations of Precipitation Strengthening Phases in an Aged Mg–La Alloy

Solute Segregation and Aggregation in Mg Alloys

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