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In the present study, powder metallurgy processed unmilled AlMg5 (AlMg5-UM), milled AlMg5 (AlMg5-M), and milled AlMg5–0.4 vol.% Al2O3 (AlMg5–0.4Al2O3) nanocomposite were successfully spark plasma sintered at 550 °C. The microstructural analysis of spark plasma sintered AlMg5-UM revealed equi-axed grains with average size of 20 ± 5 μm. The microstructural analysis of spark plasma sintered AlMg5-M and AlMg5–0.4Al2O3 revealed a bimodal grain structure with both fine-coarse grains of size 700 nm–8 μm and 300 nm–8 μm, respectively. The spark plasma sintered AlMg5-UM exhibited a yield strength (YS) of 132 ± 3 MPa, ultimate tensile strength (UTS) of 296 ± 2 MPa and % elongation (% El) of 22 ± 2 comparable to the conventional Al 5083 alloy — O temper (YS of 145 MPa, UTS of 281 MPa and % El of 16). The spark plasma sintered AlMg5-M and AlMg5–0.4Al2O3 exhibited YS of 242 ± 9 MPa and 274 ± 5 MPa, UTS of 376 ± 4 MPa and 417 ± 8 MPa and % El of 19 ± 1 and 10 ± 1, respectively. The lower strength (YS and UTS) of AlMg5-UM can be ascribed to its coarse grains. Among the milled samples, the AlMg5–0.4Al2O3 composite exhibited high strength and it can be ascribed to its fine grain size (Hall–Petch effect), higher dislocation density and Orowan strengthening effect due to Al2O3 reinforcements. Keywords: Spark plasma sintering, Nano-composites, Microstructure, Hardness, Mechanical properties

The potential hazard posed by nanomaterials can be significantly influenced by transformations which these materials undergo during their lifecycle, from manufacturing through to disposal. The transformations may depend on the nanomaterials’ own physicochemical properties as well as the environment they are exposed to. This study focuses on the mechanisms of transformation of cerium oxide nanoparticles (CeO2 NPs) in laboratory experiments which simulate potential scenarios in which the NPs are exposed to phosphatebearing media. We have experimented with the transformation of four different kinds of CeO2 NPs, in order to investigate the effects of nanoparticle size, capping agent (three were uncapped and one was PVP capped) and oxidation state (two consisted mostly of Ce4+ and two were a mix of Ce3+/Ce4+). They were exposed to a reaction solution containing KH2PO4, citric acid and ascorbic acid at pH values of 2.3, 5.5 and 12.3, and concentrations of 1mM and 5mM. The transformations were followed by UV-vis, zeta potential and XRD measurements, which were taken after 7 and 21 days, and by transmission electron microscopy after 21 days. X-ray photoelectron spectroscopy was measured at 5mM concentration after 21 days for some samples. Results show that for pH 5 and 5mM phosphate concentration, CePO4 NPs were formed. Nanoparticles that were mostly Ce4+ did not dissolve at 1mM reagent concentration, and did not produce CePO4 NPs. When PVP was present as a capping agent it proved to be an extra reducing agent, and CePO4 was found under all conditions used. This is the first paper where the transformation of CeO2 NPs in the presence of phosphate has been studied for particles with different size, shapes and capping agents, in a range of different conditions and using many different characterisation methods., peer-reviewed

We present a detailed experimental and theoretical analysis of the epitaxial stress relaxation process in micro-structured compositionally graded alloys. We focus on the pivotal SiGe/Si(001) system employing patterned Si substrates at the micrometre-size scale to address the distribution of threading and misfit dislocations within the heterostructures. SiGe alloys with linearly increasing Ge content were deposited by low energy plasma enhanced chemical vapour deposition resulting in isolated, tens of micrometre tall 3D crystals. We demonstrate that complete elastic relaxation is achieved by appropriate choice of the Ge compositional grading rate and Si pillar width. We investigate the nature and distribution of dislocations along the [001] growth direction in SiGe crystals by transmission electron microscopy, chemical defect etching and etch pit counting. We show that for 3 μm wide Si pillars and a Ge grading rate of 1.5% μm−1, only misfit dislocations are present while their fraction is reduced for higher Ge grading rates and larger structures due to dislocation interactions. The experimental results are interpreted with the help of theoretical calculations based on linear elasticity theory describing the competition between purely elastic and plastic stress relaxation with increasing crystal width and Ge compositional grading rate.

International audience; Semipolar (1122 ) GaN layers grown by metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) are studied by transmission electron microscopy (TEM). The layers exhibit numerous defects with different geometries in comparison to the growth along the c-axis, they are identified as mostly partial dislocations, basal and prismatic stacking faults. The dislocations density is in the order of 5x109 cm-2, the corresponding Burger vectors are b = 1/6 < 2023 >, b = 1/3 < 1010 > and a small fraction of perfect a type dislocations with b = 1/3 < 1120 > has been observed. The basal stacking fault density is in the order of 1x106 cm-1. In an attempt to reduce the defect density, SixNy interlayers have been used as nanomasks for epitaxial lateral overgrowth, our analysis shows that this leads to a quite small reduction of the defects as compared to the starting layer.

International audience; InAlN/GaN layers grown by metalorganic vapor phase epitaxy have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). It is shown that the surface morphology and the crystallinity of the InAlN layers critically depend on the In composition. AFM analysis points out that step flow growth may not be easily attained in this system: when the InAlN or AlN interlayer thickness is increased, the growth mode becomes three dimensional. However, the formed islands are hundred of nanometers apart, and were not observed in the transmission electron microscope. From the TEM investigation, it is pointed out that v-shaped defects are present at the surface of some layers and they may be as deep as the whole ternary alloy, they are connected to threading dislocations originated from the underlying template layers. As expected the measured residual strain is minimum when the ternary layer composition is close to 16-17% In.