A study of tensile properties in Al–Si–Cu and Al–Si–Mg alloys: Effect of β-iron intermetallics and porosity

The effect of β-iron intermetallics and porosity on the tensile properties in cast Al–Si–Cu and Al–Si–Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of β-iron intermetallics, most noticeable up to β-iron intermetallic lengths of 100 μm in 319.2 alloys, or 70 μm in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate–high Fe and high cooling rate–low Fe. The results are explained in terms of the β-Al₅FeSi platelet size and porosity values obtained.     

Effect of pores and acicular eutectic silicon particles on the performance of Al–Si–Mg (AS7G03) casting

Excellent castability, corrosion resistance and high specific strength has made cast Al–Si–Mg alloys a suitable candidate material for various aerospace application. Aluminium alloy casting AS7G03, belonging to Al–Si–Mg series of cast alloy in Y23 condition, is being used as outlet adaptor of liquid propellant tank for Indian space programme. During developmental stage, one of the castings namely oxidizer tank outlet adaptor failed and parted in to two pieces during the proof pressure test (PPT) at 22 bar.This paper brings out the details of investigation and correlates the effect of pores and acicular unmodified silicon particle on the performance of the material.     

Microstructure and XRD analysis of brazing joint for duplex stainless steel using a Ni–Si–B filler metal

Brazing of a nitrogen-containing duplex stainless steel was preformed using a nickel-based filler metal (Ni-4.5wt.%, Si-3.2wt.%, B). The microstructure of the brazed joint was investigated using scanning electron microscopy, energy dispersive spectrometry, electron probe microanalyzer, and layer-by-layer X-ray diffraction analysis. The results indicated that before completion of isothermal solidification, BN, Ni₃B and Ni₃Si precipitates formed at the interface, in the athermally solidified zone and isothermally solidified zone, respectively. After isothermal solidification, only γ-Ni phase appeared in the brazed interlayer. The appearance of hardness peak values in the athermally solidified zone and the interface most probably corresponded to the formation of Ni₃B and BN, respectively.     

Effect of rapid solidification on the microstructure and mechanical properties of hot-pressed Al–20Si–5Fe alloys

The aim of this work is to study the effect of cooling rate and subsequent hot consolidation on the microstructural features and mechanical strength of Al–20Si–5Fe–2X (X = Cu, Ni and Cr) alloys. Powder and ribbons were produced by gas atomization and melt spinning processes at two different cooling rates of 1 × 10⁵ K/s and 5 × 10⁷ K/s. The microstructure of the products was examined using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The particles were consolidated by hot pressing at 400 °C/250 MPa/1 h under a high purity argon atmosphere and the microstructure, hardness and compressive strength of the compacts were evaluated. Results showed a profound effect of the cooling rate, consolidation stage, and transition metals on the microstructure and mechanical strength of Al–20Si–5Fe alloys. While microstructural refining was obtained at both cooling rates, the microstructure of the atomized powder exhibited the formation of fine primary silicon (~ 1 μm), eutectic Al–Si phase with eutectic spacing of ~ 300 nm, and δ-iron intermetallic. Supersaturated Al matrix containing 5–7 at.% silicon and nanometric Si precipitates (20–40 nm) were determined in the microstructure of the melt-spun ribbons. The hot consolidation resulted in coarsening of Si particles in the atomized particles, and precipitation of Si and Fe-containing intermetallics from the supersaturated Al matrix in the ribbons. The consolidated ribbons exhibited higher mechanical strength compared to the atomized powders, particularly at elevated temperatures. The positive influence of the transition metals on the thermal stability of the Al–20Si–5Fe alloy was noticed, particularly in the Ni-containing alloy.     

Mesoporous Metal–Metalloid Amorphous Alloys: The First Synthesis of Open 3D Mesoporous Ni‐B Amorphous Alloy Spheres via a Dual Chemical Reduction Method

Selective hydrogenation of nitriles is an industrially relevant synthetic route for the preparation of primary amines. Amorphous metal–boron alloys have a tunable, glass‐like structure that generates a high concentration of unsaturated metal surface atoms that serve as active sites in hydrogenation reactions. Here, a method to create nanoparticles composed of mesoporous 3D networks of amorphous nickel–boron (Ni‐B) alloy is reported. The hydrogenation of benzyl cyanide to β‐phenylethylamine is used as a model reaction to assess catalytic performance. The mesoporous Ni‐B alloy spheres have a turnover frequency value of 11.6 h^?1, which outperforms non‐porous Ni‐B spheres with the same composition. The bottom‐up synthesis of mesoporous transition metal–metalloid alloys expands the possible reactions that these metal architectures can perform while simultaneously incorporating more Earth‐abundant catalysts.     

Experimental Study on the Effect of Cooling Rate on the Secondary Phase in As‐Cast Mg–Gd–Y–Zr Alloy

The effect of cooling rate on the composition, morphology, size, and volume fraction of the secondary phase in as‐cast Mg–Gd–Y–Zr alloy is investigated. In the study, a casting containing five steps with thickness of 10–50 mm is produced, in which cooling rate ranging from 2.6 to 11.0 K s^?1 is created. The secondary phase is characterized using optical microscope (OM), scanning electron microscope (SEM), and electron probe micro‐analyzer (EPMA). The volume fraction of the secondary phase is determined using OM and quantitative metallographic analysis, and Vickers hardness test is conducted to verify the analysis results. The effect of the cooling rate on the volume fraction of the secondary phase is discussed in detail. The result shows that with the increase of the cooling rate, the size of the secondary phase decreases. The effect of the cooling rate on the volume fraction of the secondary phase is complicated somewhat. A comprehensive analysis on the experimental data shows that a critical cooling rate may exist, over which the volume fraction of the secondary phase decreases with the increase of the cooling rate, however under which the volume fraction increases with the increase of the cooling rate.

     

Synergistic Effects of B4C and Sn on the Coupled Growth Pattern and Mechanical Properties of Mg–Y–Zn–Mn Alloy Containing LPSO and W Phases

The effect of boron carbide (B₄C) particles and Sn on the microstructure and mechanical properties of Mg₉₄Y_2.5Zn_2.5Mn₁ alloy is mainly studied in this work. The results show that separated addition of B₄C and Sn could not achieve very good results. The separated addition of Sn significantly promotes the formation of LPSO phase, but it cannot change the growth pattern of LPSO phase and W phase. Adding B₄C changes the growth pattern of LPSO phase, but cannot effectively promote the formation of LPSO phase. The addition of B₄C and Sn in combination achieves the growth pattern transformation of α‐Mg from irregular dendrite to equiaxed dendrite and refines the grain size, which makes LPSO phase and W phase no longer grow by coupled growth. When 0.02 wt% B₄C and 0.35 wt% Sn is added, the Mg₉₄Y_2.5Zn_2.5Mn₁ alloy's growth pattern is changed and grains are refined, and thus exhibit superior mechanical properties. (Ultimate tensile strength of 255 MPa and elongation of 8.8%).

     

Influence of Ingot and Powder Metallurgy Production Route on the Tensile Creep Behavior of Mo–9Si–8B Alloys with Additions of Al and Ge

Refractory metals and their alloys show potential for high temperature applications, due to the elevated melting points often paired with very good creep resistance. Spark plasma sintering (SPS) as well as arc‐melting is used here to prepare quaternary and quinternary Mo–9Si–8B–xAl–yGe (x is 0 or 2; y is 0 or 2, all numbers in at%) samples. All samples consist of a Mo solid solution (Mo_ss) and two intermetallic phases: Mo₃Si (A15) and Mo₅SiB₂ (T2). Aluminum and germanium reduce the melting point and slightly decrease the density of the material. The specimens are homogenized and coarsened by a subsequent heat‐treatment in vacuum at 1850 °C for 24 h. The resulting microstructure is investigated using scanning electron microscope (SEM), energy‐dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), X‐ray fluorescence spectroscopy (XRF), and inductively coupled plasma optical emission spectrometry (ICP‐OES) analysis. A vacuum creep testing device for small tensile creep specimens is presented. It is heated by graphite radiation heaters usable up to 1500 °C in vacuum of 2 · 10^‐4 Pa with an oil diffusion pump. Tensile creep tests are performed at 1250 °C and stresses from 50 MPa up to 250 MPa. Specimens produced by ingot metallurgy feature superior creep properties compared to powder metallurgy samples.     

Insight into the flow‐condition‐based interpolation finite element approach: solution of steady‐state advection–diffusion problems

The flow‐condition‐based interpolation (FCBI) finite element approach is studied in the solution of advection–diffusion problems. Two FCBI procedures are developed and tested with the original FCBI method: in the first scheme, a general solution of the advection–diffusion equation is embedded into the interpolation, and in the second scheme, the link‐cutting bubbles approach is used in the interpolation. In both procedures, as in the original FCBI method, no artificial parameters are included to reach stability for high Péclet number flows. The procedures have been implemented for two‐dimensional analysis and the results of some test problems are presented. These results indicate good stability and accuracy characteristics and the potential of the FCBI solution approach. Copyright © 2005 John Wiley & Sons, Ltd.     

A reduced‐order representation of the Poincaré–Steklov operator: an application to coupled multi‐physics problems

This work investigates a model reduction method applied to coupled multi‐physics systems. The case in which a system of interest interacts with an external system is considered. An approximation of the Poincaré–Steklov operator is computed by simulating, in an offline phase, the external problem when the inputs are the Laplace–Beltrami eigenfunctions defined at the interface. In the online phase, only the reduced representation of the operator is needed to account for the influence of the external problem on the main system. An online basis enrichment is proposed in order to guarantee a precise reduced‐order computation. Several test cases are proposed on different fluid–structure couplings. Copyright © 2016 John Wiley & Sons, Ltd.     

High‐Energy Efficiency Membraneless Flowless Zn–Br Battery: Utilizing the Electrochemical–Chemical Growth of Polybromides

Aqueous Zn–Br batteries (ZBBs) offer promising next‐generation high‐density energy storage for energy storage systems, along with distinctive cost effectiveness particularly in membraneless and flowless (MLFL) form. Unfortunately, they generally suffer from uncontrolled diffusion of corrosive bromine components, which cause serious self‐discharge and capacity fade. An MLFL‐ZBB is presented that fundamentally tackles the problem of bromine crossover by converting bromine to the polybromide anion using protonated pyridinic nitrogen doped microporous carbon decorated on graphite felt (NGF). The NGF electrodes efficiently capture bromine and polybromide anions at the abundant protonated nitrogen dopant sites within micropores and facilitate effective conversion of bromine into polybromides through electrochemical–chemical growth mechanism. The MLFL‐ZBBs with NGF exhibit an extraordinary stability over 1000 charge/discharge cycles, with an energy efficiency over 80%, the highest value ever reported among membraneless Zn–Br batteries. Judicious engineering of an atomistically designed nanostructured electrode offers a novel design platform for low cost, high voltage, long‐life cycle aqueous hybrid Zn–Br batteries.