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Despite the large number of studies on the development of multilayered composites using accumulative roll bonding method (ARB), there are not enough available details concerning the effect of the temperature variation on the constituent layer microstructure and the nature and kinetics of the developed intermetallic compounds. The present work aims to process an Al/IF steel multilayered composite using ARB and to understand the effect of non-isothermal heating on its structural evolution. The elaborated material is characterized by using thermal Differential Dilatometry (DD), Scanning Electronic Microscopy (SEM) and x-ray Diffraction (XRD). The progress of the ARB leads to the dispersion of the Fe layers between the Al layers and does not lead to the formation of diffusion layer. The continuous heating leads, for temperature lower than 330 °C, to the occurrence of the recovery reaction in the Al layers, which produces a big contraction and causes a partial softening of the material. The formation of the intermetallic compound Al5Fe2 seems to occur at higher temperatures and leads to a significant expansion of the material. This effect is explained by the increase in the atomic specific volume. [ABSTRACT FROM AUTHOR]

Glass and melt structures are inherently complex and disordered with significant changes expected to occur with temperature. In the present paper, a comparison of the structure of glasses and liquids along the MgSiO3-CaSiO3 join is carried out using neutron and X-ray diffraction (XRD). Empirical Potential Structure Refinement (EPSR) simulations were used to fit the experimental data. The average coordination number (CN) and site distribution is obtained for Mg and Ca showing distinct sites between the two cations and higher coordinated sites in the liquids. The major glass to melt modifications is observed at the scale of intermediate range order (IRO) by rearrangement of the (Ca,Mg)-Si and (Ca,Mg)-(Ca,Mg) connections. The structural evolution with temperature, especially concerning the cationic environments, illustrates the differences between glass and melt organization. These changes highlight the important contribution of cations to thermodynamical properties, diffusion and glass forming ability. [ABSTRACT FROM AUTHOR]

Abstract: The atomic structures of liquid Si metal and SiGe alloy in the normal and supercooled liquid states have been measured by X-ray diffraction from aerodynamically levitated and laser heated liquid droplets. The measurements covered a wide range of scattering vector Q (0.8–20A−1) and a wide temperature range that extended into the supercooled region. The present results on liquid Si confirm earlier measurements that showed a decrease in first-shell coordination with increased supercooling. For liquid SiGe, the shoulder on the high-Q side of the first peak in the structure factor S(Q) sharpens with increased supercooling, suggesting an increase in covalent bonding and development of chemical short-range order. [Copyright &y& Elsevier]

The sequence and kinetics of pre-precipitation in an Mg-1.43Nd (wt.%) alloy was investigated after severe plastic deformation by high-pressure torsion (HPT) at room temperature using in situ synchrotron X-ray diffraction and differential scanning calorimetry (DSC). In situ aging at 250 °C up to 5 h led to precipitation of the β 1 -Mg 3 Nd and β-Mg 12 Nd phases but without any evidence for the metastable β ‴ (undifferentiated β ’’ -DO19 and β′-Mg 7 Nd) or equilibrium β e -Mg 41 Nd 5 phases. The β 1 -Mg 3 Nd and β-Mg 12 Nd phases appeared rapidly after HPT processing and their amounts were relatively large compared to the non-deformed sample. The Avrami time exponent of the β-Mg 12 Nd phase had a value near unity indicating a mechanism of nucleation after saturation and growth of the particles in 2 dimensions. DSC analysis revealed all metastable phases as well as the equilibrium phase. The activation energies associated with the pre-precipitation phases ranged between ∼126 and ∼235 kJ mol −1 . [ABSTRACT FROM AUTHOR]

To understand the behavior of rare earth elements (REE) in magmatic systems it is important to characterize in a systematic way their incorporation into silicate melts and glasses. Here, we study the structural environment of the REE Y and La in four aluminosilicate glasses and melts with varying REE content, using a combined simulation and diffraction approach. Glasses are investigated by X-ray and neutron diffraction as well as classical molecular dynamics simulations using two different polarizable ion potentials. Structure models of the corresponding melts are derived from classical and first-principles molecular dynamics simulations. We discuss the effect of temperature on coordination numbers and rationalize the structural changes in response to variations in melt/glass composition in terms of cation field strengths. We find robust evidence that REE and Al coordination numbers decrease with increasing REE content in the investigated melts and glasses. Comparing the two classical potentials, one of them is able to reproduce features of the experimental structure factors with a mixture of corner- and edge-sharing Al-O/REE-O polyhedra, whereas the other potential predicts corner-sharing Al-O/REE-O polyhedra only. [ABSTRACT FROM AUTHOR]

The existence of liquid–liquid phase transitions has been suggested for liquid Fe and some of its alloys. In order to shed light on this phenomenon in-situ cooling of the Fe 80 B 20 and Fe melts was performed under a synchrotron beam radiation. It allowed for the continuous acquisition of X-ray diffraction spectra in the supercooled liquid region below the liquidus temperature. The procedure allowed monitoring of the structural changes in the supercooled liquid state using real-space atomic pair PDF(R) and radial RDF(R) distribution functions. The results are discussed in comparison with those of molecular dynamics simulation for liquid Fe. [ABSTRACT FROM AUTHOR]

The thermal expansion of α-Fe (ferrite) and γ-Fe (austenite) nanocrystals confined inside multiwalled carbon nanotubes (MWCNTs) is studied in situ, using synchrotron x-ray diffraction, as a function of temperature. While the thermal expansion of ferrite is similar to that of bulk material, a peculiar behavior is evidenced for austenite: The thermal expansion becomes abnormally high above 500 °C. A scenario involving progressive carbon uptake in γ-Fe nanocrystals gives a satisfactory understanding of the phenomenon, and allows one to propose a value of the carbon solubilization rate in γ-Fe particles confined inside MWCNTs. [ABSTRACT FROM AUTHOR]

Iron-bearing nanocrystals (i.e. nanolites) are enigmatic particles recently found1 in volcanicglasses produced during explosive eruptions of magmas. The formation of these smallcrystals during magma transport towards Earth’s surface changes the melt structure, increasesviscosity2 and the likelihood of hazardous explosive eruptions. Despite decades of research,few direct measurements have been made of the structure of magmas in situ undervolcanic conditions. We have performed in situ high temperature synchrotron X-ray diffraction measurementsof volcanic melts during cooling to monitor nanolite precipitation from magmas at eruptivetemperature. This allowed the characterization, over a timescale in the order of seconds,of the transient evolution of the melt structure during cooling under controlledconditions of oxygen fugacity. The results reveal the formation of nanolites duringcontrolled cooling. The XRD data presented here is the first in situ high-temperatureobservation of the formation of nanolites in volcanic melts. This finding allows us toexplore the mechanisms acting during nanolite formation and explosive eruption ofmagmas. 1. Mujin, M., Nakamura, M. & Miyake, A. Eruption style and crystal size distributions:Crystallization of groundmass nanolites in the 2011 Shinmoedake eruption. Am. Mineral.102, 2367–2380 (2017). 2. Di Genova, D. et al. A chemical tipping point governing mobilization and eruptionstyle of rhyolitic magma. Nature 552, 235–238 (2017). [ABSTRACT FROM AUTHOR]