Controlling the Critical Temperature in Mg1−x Al x B2

Here we report synthesis and characterization of high quality samples of the superconducting system Mg_1−x Al _x B₂, with a novel optimized preparation method, in a wide range of Al concentration. All the physical properties of the samples can be tuned continuously with increasing Al content. We have characterized the samples for their structural, morphological and magnetic properties with high resolution XRD, SEM-EDS and susceptibility measurements. We have prepared a large number of Al doped MgB₂ in the range 0<x<0.57. All the samples are bulk superconductors and the critical temperature show a smooth and regular behavior as a function of x. This work was supported by European project 517039 “Controlling Mesoscopic Phase Separation” (COMEPHS) (2005). An erratum to this article can be found at     

Hybrid prediction-optimization approaches for maximizing parts density in SLM of Ti6Al4V titanium alloy

Journal of Intelligent Manufacturing - It is well known that the processing parameters of selective laser melting (SLM) highly influence mechanical and physical properties of the manufactured...     

Using a neural network for predicting the average grain size in friction stir welding processes

In the paper the microstructural phenomena in terms of average grain size occurring in friction stir welding (FSW) processes are focused. A neural network was linked to a finite element model (FEM) of the process to predict the average grain size values. The utilized net was trained starting from experimental data and numerical results of butt joints and then tested on further butt, lap and T-joints. The obtained results show the capability of the AI technique in conjunction with the FE tool to predict the final microstructure in the FSW joints.     

Activation Energy of the Photo Induced Q2 Oxygen Ordered Phase in the La2CuO4.08 Superconductor

The interstitial oxygen ordering in a La₂CuO_{4+ y} (y = 0.08) single crystal with a T _c = 38 K has been investigated. We have studied the growth dynamics of the three dimensional (3D) ordered phase, called Q2, at different temperatures under X-ray illumination. The critical temperature T ₀～334 K of the order-disorder transition for the Q2 phase has been determined. We have found that the illumination of the sample with a continuous polarized synchrotron radiation X-ray flux stimulates the oxygen ordering kinetics. The photoinduced ordering process shows a threshold characteristic of cooperative phenomena and its kinetics shows a temperature dependence that is controlled by the activation energy E _A = 100 meV.     

Anomalous Thermal Expansion in Superconducting Mg1− x Al x B2 System

The thermal lattice expansion in the superconducting Mg_{1? x} Al _x B₂ system (x = 0, 0.13, and 0.59) has been measured using high-resolution X-ray powder diffraction. An unusual large negative thermal expansion (NTE) appears for temperatures below T ^* = 60 K in the MgB₂. The NTE effect increases in Mg_0.87Al_0.13B₂ and disappears at high Al content in the Mg_0.59Al_0.41B₂ where the temperature dependence of volume follows a standard Einstein model in the whole temperature range. The anomalous behavior of the thermal expansion provides a direct evidence in the physics of diborides for the relevance of the proximity to the 2.5 Lifshitz electronic topological transition where the Fermi surface of the σband changes from a two-dimensional (2D) to a three-dimensional (3D) topology.     

AZ31 magnesium alloy recycling through friction stir extrusion process

Friction Stir Extrusion is a novel technique for direct recycling of metal scrap. In the process, a dedicated tool produces both the heat and the pressure to compact and extrude the original raw material, i.e., machining chip, as a consolidated component. A proper fixture was used to carry out an experimental campaign on Friction Stir Extrusion of AZ31 magnesium alloy. Variable tool rotation and extrusion ratio were considered. Appearance of defects and fractures was related to either too high or too low power input. The extruded rods were investigated both from the metallurgical and mechanical points of view. Tensile strength up to 80 % of the parent material was found for the best combination of process parameters. A peculiar 3D helical material flow was highlighted through metallurgical observation of the specimens.     

Computer aided engineering of the sheet bending process

The effects of the punch nose radius and sheet thickness on the elastic springback and residual stresses in the 90° V-punch and U-die bending process of AA 5083 aluminium alloy have been extensively studied by numerical simulations based on the finite element method. The results show that, irrespective of the sheet thickness and punch stroke, the springback ratio is not affected by the punch nose radius. Such results are in excellent agreement with the experimental ones obtained in similar conditions. As far as punch nose radius effects on the residual stresses are considered, significant differences were observed between residual stresses predicted with different nose radii. In particular, the shifting of the neutral layer and increase in the magnitude of the residual stresses predicted by the FEM code were found with decreasing punch nose radius.     

A Model for Liquid-Striped Liquid Phase Separation in Liquids of Anisotropic Polarons

The phase separation between a striped polaron liquid at the particular density and a high density polaron liquid is described by a modified Van der Waals scheme. The striped polaron liquid represents the pseudo gap matter or Wigner-like polaron phase at 1/8 doping in cuprate superconductors. The model includes the tendency of pseudo-Jahn-Teller polarons to form anisotropic directional bonds at a preferential volume with the formation of different “liquid phases”. The model gives the coexistence of a first low density polaron striped liquid and a second high density liquid that appears in cuprate superconductors for doping larger than 1/8. We discuss how the strength of anisotropic bonds controls the variation the phase separation scenarios for complex systems in the presence of a quantum critical point where the phase separation vanishes.     

A universal fluid cell for the imaging of biological specimens in the atomic force microscope

Recently, atomic force microscope (AFM) manufacturers have begun producing instruments specifically designed to image biological specimens. In most instances, they are integrated with an inverted optical microscope, which permits concurrent optical and AFM imaging. An important component of the set‐up is the imaging chamber, whose design determines the nature of the experiments that can be conducted. Many different imaging chamber designs are available, usually designed to optimize a single parameter, such as the dimensions of the substrate or the volume of fluid that can be used throughout the experiment. In this report, we present a universal fluid cell, which simultaneously optimizes all of the parameters that are important for the imaging of biological specimens in the AFM. This novel imaging chamber has been successfully tested using mammalian, plant, and microbial cells. Microsc. Res. Tech. 76:357–363, 2013. © 2013 Wiley Periodicals, Inc.     

Self-piercing riveting for aluminium alloys-composites hybrid joints

In the paper, the growing interest on hybrid joints developed between composite panels and aluminium alloys blanks is focused. The self-piercing riveting operation is considered and its feasibility for the proposed joints verified. The most relevant process parameters were investigated in order to determine a suitable process window and, what is more, the mechanical performances of the developed joints were investigated in order to determine process parameters aimed to maximise them. Finally, the failure mechanics of the obtained joints were considered in order to highlight the mechanisms which occur and determine the lost of the load carrying capability of the joints. The developed experiments demonstrated that self-piercing riveting can be effectively used to join fibreglass composite panels and aluminium blanks.