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Abstract: One of the most effective ways to increase the current-carrying ability of Nb3Sn superconductor is doping of the superconducting phase by Ti, since it leads to Hc2 increase due to the rise of Nb3Sn phase electrical conductivity in normal state, and also to acceleration of the Nb3Sn layer growing during reaction and to critical current density increasing. The investigations of structure and composition of Nb3+xSn superconducting strands by SEM, TEM and EDXS microanalysis have been carried out. The structure and composition of Nb3Sn superconducting phase of the strands after reaction at 575°C 150 h+650°C 200h have been studied. The dependence of Ti content in Nb3Sn phase from the amount of Ti introduced in Nb filaments or in bronze matrix has been also studied. It was found, that the lowest Ti content corresponds to introduction of it through the matrix doping. It has been established that Nb content in Nb3Sn essentially exceeds the stoichiometric one (3:1). The Nb3Sn lattice parameters have been defined by XRD. It was found, that the lattice parameters in the samples with Ti doped matrix were the closest to the stoichiometric Nb3Sn. The correspondence between grain morphology and composition of superconducting phase and critical current density of studied strands has been established. [Copyright &y& Elsevier]

The interaction between dislocations and nano-precipitates during deformation directly influences hardening response of precipitation-strengthening metals such as Al-Mg-Si alloys. However, how coherent and semi-coherent nano-precipitates accommodate external deformation applied to an Al alloy remains to be elucidated. In-situ tensile experiments in a transmission electron microscope (TEM) were conducted to study the dynamic process of dislocations cutting through coherent needle-like β″ precipitates with diameters of 3∼8 nm. Comprehensive investigations using in-situ, ex-situ TEM and atom probe tomography uncovered that β″ precipitates were firstly sheared into small fragments, and then the rotation of the fragments, via sliding along precipitate/matrix interfaces, destroyed their initially coherent interface with the Al matrix. In contrast, semi-coherent βʹ precipitates with sizes similar to β″ were more difficult to be fragmented and accumulation of dislocations at the interface increased interface misfit between βʹ and the Al matrix. Consequently, βʹ precipitates could basically maintain their needle-like shape after the tensile deformation. This research gains new insights into the interaction between nano-precipitates and dislocations. [Display omitted] [ABSTRACT FROM AUTHOR]

The rheological properties of amorphous olivine thin films deposited by pulsed laser deposition have been studied based on ambient temperature nanoindentation under constant strain-rate as well as relaxation conditions. The amorphous olivine films exhibit a viscoelastic-viscoplastic behavior with a significant rate dependency. The strain-rate sensitivity m is equal to ∼ 0.05 which is very high for silicates, indicating a complex out-of-equilibrium structure. The minimum apparent activation volume determined from nanoindentation experiments corresponds to Mg and Fe atomic metallic sites in the (Mg,Fe) 2 SiO 4 crystalline lattice. The ambient temperature creep behavior of the amorphous olivine films differs very much from the one of single crystal olivine. This behavior directly connects to the recent demonstration of the activation of grain boundary sliding in polycrystalline olivine following grain boundary amorphization under high-stress. [Display omitted] [ABSTRACT FROM AUTHOR]

Recent observations made by the authors revealed the activation of stress induced amorphization and sliding at grain boundary in olivine [1] , a mechanism which is expected to play a pivotal role in the viscosity drop at the lithosphere-asthenosphere boundary and the brittle-ductile transition in the lithospheric mantle. However, there is a lack of information in the literature regarding the intrinsic mechanical properties and the elementary deformation mechanisms of this material, especially at time scales relevant for geodynamics. In the present work, amorphous olivine films were obtained by pulsed laser deposition (PLD). The mechanical response including the rate dependent behavior are investigated using a tension-on-chip (TOC) method developed at UCLouvain allowing to perform creep/relaxation tests on thin films at extremely low strain rates. In the present work, strain rate down to 10−12 s−1 was reached which is unique. High strain rate sensitivity of 0.054 is observed together with the activation of relaxation at the very early stage of deformation. Furthermore, digital image correlation (DIC), used for the first time on films deformed by TOC, reveals local strain heterogeneities. The relationship between such heterogeneities, the high strain rate sensitivity and the effect of the electron beam in the scanning electron microscope is discussed and compared to the literature. [Display omitted] [ABSTRACT FROM AUTHOR]

The Coulomb blockade effect is commonly used in solid state electronics for the control of electron flow at the single-particle level. Potentially, it allows the creation of single-electron point sources demanded for prospective electron microscopy instruments and other vacuum electronics devices. Here we realize this potential via creation of a stable point electron source composed of a carbon nanowire electrically coupled to a diamond nanotip by a tunnel junction. Using energy spectroscopy analysis, we characterize the electrons liberated from the nanometer scale carbon heterostructures in time and energy domains. Our experimental results demonstrate perfect agreement with theory prediction of Coulomb oscillations of the Fermi level in the nanowire and allow to determine the mechanisms of their suppression. Persistence of the oscillations at room temperature, high intensity field emission with currents up to 1 μA, and other characteristics of our emitters are very promising for practical realization of coherent single-electron guns. Image 1 [ABSTRACT FROM AUTHOR]

Phase formation and transitions in platinum silicide films on polycrystalline Si in the process of Pt magnetron sputtering and heat treatments at different temperatures are studied using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and X-ray diffractometry. Phases of amorphous and polycrystalline Pt 3 Si and Pt 2 Si are shown to form during the room-temperature Pt deposition on poly-Si beneath the Pt layer. The relaxation of the interfacial film and partial transformation of Pt 3 Si into Pt 2 Si occurs as a result of the thermal treatment for 30 min in the temperature range from 125°C to 300°С. The Pt 3 Si and Pt 2 Si phases crystallize to PtSi due to annealing at the temperatures from 320°C to 480°С for the same time period. Image 1 • Interface domain in magnetron sputtered and annealed Pt/poly-Si film is studied. • Pt 3 Si and Pt 2 Si phases form at room temperature during Pt deposition on poly-Si. • Interfacial film relaxation turns Pt 3 Si to Pt 2 Si due to annealing at 100 < T < 200 °C. • Pt 3 Si and Pt 2 Si transit to PtSi due to annealing at temperatures from 320 to 480 °C. • Pt 3 Si phase is detected up to the annealing temperature of 350 °C. [ABSTRACT FROM AUTHOR]

A detailed microstructural examination endeavoring to understand the interfacial phenomena yielding to cohesion in solid-state assembling processes was performed. This study focuses on the transition zone of a dissimilar titanium alloy joint obtained by Linear Friction Welding (LFW) the β-metastable Ti17 to the near-α Ti6242. The transition zone delimitating both alloys is characterized by a sharp microstructure change from acicular HCP (Hexagonal Close-Packed) α′ martensitic laths in the Ti6242 to equiaxed BCC β (Body-Centered Cubic) subgrains in the Ti17; these α′ plates were shown to precipitate within prior-β subgrains remarkably more rotated than the ones formed in the Ti17. Both α′ and β microstructures were found to be intermingled within transitional subgrains demarcating a limited gradient from one chemical composition to the other. These peculiar interfacial grains revealed that the cohesive mechanisms between the rubbing surfaces occurred in the single-phase β domain under severe strain and high-temperature conditions. During the hot deformation process, the mutual migration of the crystalline interfaces from one material to another assisted by a continuous dynamic recrystallization process was identified as the main adhesive mechanism at the junction zone. The latter led to successful cohesion between the rubbing surfaces. Once the reciprocating motion stopped, fast cooling caused both materials to experience either a β lean →α′ or β lean →β metastable transformation in the interfacial zone depending on their local chemical composition. The limited process time and the subsequent hindered chemical homogenization at the transition zone led to retaining the so-called intermingled α'/β m subgrains constituting the border between both Ti-alloys. Image 1 • The β-metastable Ti17 & quasi-α Ti6242 alloy grades were successfully joined by LFW. • Thermomechanical processing conditions led to a β-fragmentation process in the joint. • Mutual crystalline interfaces migration between the materials induced by β-CDRX. • Cohesion obtained above β-transus resulting in a β-microstructural continuity. • High cooling rates resulted in a sharp α'/β phase contrast in the junction zone. [ABSTRACT FROM AUTHOR]