Near–atomic-scale observation of grain boundaries in a layer-stacked two-dimensional polymer

Two-dimensional (2D) polymers hold great promise in the rational materials design tailored for next-generation applications. However, little is known about the grain boundaries in 2D polymers, not to mention their formation mechanisms and potential influences on the material’s functionalities. Using aberration-corrected high-resolution transmission electron microscopy, we present a direct observation of the grain boundaries in a layer-stacked 2D polyimine with a resolution of 2.3 Å, shedding light on their formation mechanisms. We found that the polyimine growth followed a “birth-and-spread” mechanism. Antiphase boundaries implemented a self-correction to the missing-linker and missing-node defects, and tilt boundaries were formed via grain coalescence. Notably, we identified grain boundary reconstructions featuring closed rings at tilt boundaries. Quantum mechanical calculations revealed that boundary reconstruction is energetically allowed and can be generalized into different 2D polymer systems. We envisage that these results may open up the opportunity for future investigations on defect-property correlations in 2D polymers.

Molecular dynamics studies on the grain growth of nanocrystalline Ni and Ni3Al

With molecular dynamics simulations, the growth of face-centered-cubic nanocrystalline materials Ni and Ni3Al has been studied. It is found that grain-rotation induced grain coalescence and curvature-driven grain-boundary migration are dominant mechanisms in the nanograin growth. A detailed comparison of the nanograin growth between the two systems is discussed in terms of grain rotation and grain sliding. We also study the temperature effect and the size effect in the nanograin growth. The tendency of twinning in the nanograin growth is discussed. It is found that in Ni3Al, it seems more possible for nanograins to grow into twin-like structures than single crystal unless at very high temperatures.

Effects of Extrusion Ratio on Microstructures and Properties of Al-Cu-Mg-Ag-Ce-Er Alloy Wires

The Al-Cu-Mg-Ag-Ce-Er alloy wires with different extrusion ratio (λ=12, 25, 50, 100) were produced by hot extrusion at 450oC. The effects of extrusion ratio on the microstructures, tensile strength and elongation of Al-Cu-Mg-Ag-Ce-Er alloy wires were researched by means of OM, SEM, TEM and mechanical test.The results show that with the extrusion ratio increasing, the average grain size decreased from 83μm to 42μm, the Al2Cu, Al8Cu4Ce and Al8Cu4Er phases was broken gradually, and the homogeneousdistribution about these second-phases in the alloy wires increased. The tensile strength increased from 366MPa to 459MPa with extrusion ratio, and the elongation initially decreased and then increased with the increase of extrusion ratio. Dynamic recrystallization for Al-Cu-Mg-Ag-Ce-Er alloy occurred at different extrusion ratios. Withincreasing of extrusion ratio, the main nucleation mechanism of dynamic recrystallization changed from the sub-grain coalescence at lower extrusion ratioto the acceleration of second-phases for nucleation at higher extrusion ratio.

Part II - Microstructural and Physical of Calcium Phosphate Biomaterials Obtained from Natural Raw Materials

Calcium phosphate bioceramics obtained from raw materials are potential bone substitutes in orthopedic and dental applications. Calcium phosphates attained from calcareous shells using wet methods provide an interconnected microporous framework, shown to be promising and contribute to cell adhesion and proliferation. This study aimed to characterize three different calcium phosphate ratio compositions: (i)1.4, (ii)1.6 and (iii)1.7 molar, sintered for 2 hours at 1100°C and 1200°C. Scanning electron microscopy field effect [FEG] and confocal were used to assess microstructural characterization and Arthur method to determine open porosity. FEG and confocal analyses showed good grain coalescence, sinterability and well defined interfaces for all Ca/P molar at 1100°C and 1200°C. Open porosity and hydrostatic density exhibit better results when using Ca/P molar ratio (iii)1.7 at 1100°C. The results showed that open porosity is related to Ca/P ratio and by temperature. As the Ca/P increases so does the open porosity. Inversely occurs for temperature. As the temperature increases the porosity decreases and in parallel, the grain size increases.

HRTEM Analysis of Magnetron Sputtered Ni4Al Thin Films

The nanostructural characteristics of direct-current magnetron sputter-deposited Ni4Al alloy films were studied during in situ isothermal annealing in a transmission electron microscope (TEM). An expansion of the lattice by nearly 5% was observed for the synthesized films in their low-thickness and as-deposited state. The lattice size approaches the bulk value when the film thickness increases or after vacuum annealing heat-treatment. The Ni4Al films have a nanocrystalline structure in which the ordered L12 phase appears upon annealing at above 500°C. A grain coalescence trend was found for the Ni4Al films during the in situ annealing above 500°C. This can be the main reason for the abnormal grain growth of these films at these high temperatures.

Microstructural Evolution of 7050 Aluminum Alloy Semisolid Billets Fabricated by RAP Process

In the present study, 7050 supplied in extruded state was heated to different temperatures below solidus or the semisolid state and microstructural evolution and coarsening were investigated. The results showed that complete recrystallisation only occurs after soaking for 5 minutes at 545°C, which is characterised by formation of a lot of fine equiaxed grains. RAP is suitable for fabricating high-quality semisolid billet of 7050 aluminum alloy with an average grain size ranging from 47.4 um to 70.5 um and a roundness ranging from 1.3 to 1.7. Grain growth occurs as the samples were soaked at 610°C and 615°Cfor prolonged soaking time. When the isothermal temperatures were 610°C and 615°C, the coarsening rate constants were 359.5μm3s-1 and 470.5μm3s-1, respectively, indicating an increase of coarsening rate constant (K) with the increasing isothermal temperature. Coarsening tends to occur via Ostwald ripening and coalescence. Ostwald ripening plays an important role during the whole coarsening process, but the grain coalescence only contributes to coarsening after soaking for 12 minutes. 625°C is an optimal temperature to keep cylinder shape of the sample due to collapse of the sample above this temperature, leading to difficult clamping.