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This study aims to clarify the growth process of the β-phase in Al-Mg-Si alloys from the point of view of morphological evolution. The orientation relationship, shape, growth process, misfit value, and interfacial condition between the β-phase and Al matrix were investigated using high-resolution transmission electron microscopy (HR-TEM), focused ion beam (FIB), and optical microscope (OM). In a previous study, the growth process and shape of the β-phase were determined using scanning electron microscopy (SEM). It was proposed that the truncated octahedron (8{111}, 6{100} facets) transforms into a hexahedron (6{100} facets). This study proposes that two new three-dimensional shapes of the β-phase exist between the truncated octahedron and hexahedron, and we identified the {111} β facets at the edges of the β-phase. We proposed the morphology evolution during the growth process of Mg 2 Si crystals and calculated the misfit to understand that the unstable {111} β facet has a higher misfit value compared to the {001} β and {011} β facets. Our observations provide insight into how they influence the behavior of Mg 2 Si crystals, which is crucial for predicting the microstructural evolution of Al-Mg-Si alloys and for designing materials with desired properties. • Investigated the morphology evolution of the β-phase in Al-Mg-Si alloys. • Explored β-phase orientation relationship, shape, and growth process using HR-TEM, FIB, and OM. • Discovered {111} β facets and proposed new three-dimensional shapes for the β-phase. • Calculated misfit values, revealing the instability of the (111) β facet compared to (001) β and (011) β facets. • Contributed to understanding microstructural evolution in Al-Mg-Si alloys and material design. [ABSTRACT FROM AUTHOR]

• The structural transformation of Y 2 O 3 during high-energy ball milling is investigated. • Complete phase transformation from cubic to monoclinic is achieved after 30 h of milling. • XRD and Rietveld refinement analysis for the quantification of phase fraction, crystallite size and strain. • Transformation mechanism confirmed by HRTEM and EELS analysis. • Transformation sequence is: Yc → Yc + Ym → Ym. • Monoclinic Y 2 O 3 is found to be much finer than its cubic allotrope. [Display omitted] In-depth understanding of the structural transformation mechanism in nanocrystalline yttria (Y 2 O 3) is crucial to design advanced materials satisfying a wide range of technical demands. Present study investigates the structural modification in cubic Y 2 O 3 nanopowders induced by high energy ball-milling as a function of milling duration. Y 2 O 3 nanopowder with an initial crystallite size of 25–50 nm was subjected to high energy ball milling (1000 rpm) for incremental time periods up to 30 h. X-ray diffraction (XRD) and Rietveld analysis were employed to study the phase evolution, crystallite size, and strain at every stages of milling. High Resolution Transmission Electron Microscopy (HR TEM) and Electron Energy Loss Spectroscopy (EELS) is utilized to realize the mechanisms involved in phase transformation. It is observed that as milling duration progresses, the cubic Y 2 O 3 gets refined and gradually transforms to the monoclinic phase. It is also apparent that at finer sizes, the monoclinic phase is preferred over the cubic one. The critical crystallite size for the monoclinic phase to stabilize is observed to be ~ 13 nm. Results show the complete structural modification after 30 h of milling duration. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution electron microscopy (HREM) images of the overlap structures in TiAl have been studied by the comparisons of experimental techniques and theoretic simulations. Several misunderstandings about TiAl microstructures were corrected. First, studies revealed that the reported 9R structures in TiAl must result from the overlap of two twin-related γ laths. They were not the true 9R structure. Second, the fringes (FR) between the γ and α2 phases have once been misconsidered as the stacking faults fringes which promoted the α2 ↔γ phase transformations. This work proved them to be the fringes caused by the overlap of the α2 and γ phases. Through study of the imaging of the overlap structures, a new formation mechanism of the fringes has been proposed. [Copyright &y& Elsevier]

The γ" phase and the γ′ phase are metastable precipitates in Cu-2.0 wt%Be alloy, which play a key role in strengthening the alloy. This paper mainly discusses the formation process, microstructure and strengthening mechanism of these two precipitates. The structure, quantity and size of precipitates in the alloy treated at different aging temperatures were analyzed by transmission electron microscopy (TEM). The strengthening mechanism of the γ" phase and the γ′ phase was analyzed by theoretical calculation. The results show that with the increase of aging temperature, the size of γ" phase changes slightly, but the density decreases significantly, while the size and density of γ′ phase increase with the increase of aging temperature. High resolution transmission electron microscopy (HRTEM) analysis shows that the γ" phase is semi coherent with the matrix, so it will be cut off by dislocations. The atoms in the γ′ phase are arranged perfectly, they can't shear with dislocations, so they can be strengthened by the Orowan dislocation bypass mechanism. The strength mechanism of γ" phase is location shear mechanism and the strengthening mechanism of γ′ phase is Orowan bypass mechanism. • The evolution of metastable precipitates in Cu-2.0 wt%Be alloy was studied. • Both dislocation shear mechanism and dislocation bypass mechanism exist in Cu be alloy. • γ" phase strengthen alloy mainly through the shear mechanism, γ′ phase strengthen alloy mainly through the Orowan mechanism. [ABSTRACT FROM AUTHOR]