The effects of cell spacing and distribution of intermetallic fibers on the mechanical properties of hypoeutectic Al–Fe alloys

The aim of the present investigation was to contribute to provide a basis for understanding how to control solidification parameters, microstructure and mechanical strength of Al–Fe alloys. Upward directional solidification experiments have been carried-out with commercially pure Al and Al–0.5 wt.% Fe, Al–1.0 wt.% Fe and Al–1.5 wt.% Fe alloys. The tensile tests results have been correlated to cell spacing (λ₁), since cellular growth has prevailed along all obtained Al–Fe castings. The used casting assembly was designed in such way that the heat was extracted only through the water-cooled system at the bottom of the casting. In order to investigate the nature of Al–Fe intermetallic fibers, they were extracted from the aluminum-rich matrix by using a dissolution technique. These fibers were then investigated by SEM-EDAX microscopy. It was found that the ultimate tensile strength, yield tensile strength and elongation increase with decreasing cell spacing. The highest ultimate tensile strength was that obtained for the most refined microstructure, i.e. for the Al–1.5 wt.% Fe alloy sample, where a higher density of eutectic fibers was found distributed in a more homogeneous way along the casting section due to lower cell spacings. In contrast, the elongation was found to decrease with increasing solute content.     

Influence of neutron irradiation on the characteristics of Cu–13%wt.Al–4%wt.Ni shape memory alloy

Unirradiated and neutron irradiated Cu–13%wt.Al–4%wt.Ni shape memory alloy, SMA, were investigated by differential scanning calorimetry, DSC, and electrical resistivity changes, ERC, measurements, X-ray diffraction, XRD and optical microscopy methods. The forward and reverse temperatures of martensite⇔austenite phase transformation decreased and transformation enthalpies increased after the neutron irradiation of samples. Some changes in the lattice parameters and surface morphologies of sample were also seen after neutron irradiation.     

Effects of F− on the optical and spectroscopic properties of Yb3+/Al3+-co-doped silica glass

Yb³⁺/Al³⁺-co-doped silica glasses with different F⁻ content were prepared in this work by sol–gel method combined with high temperature sintering. XRF, FTIR and XPS methods were used to confirm the presence of F⁻. The effects of F⁻ on the optical and spectroscopic properties of these glasses have been investigated. It is worth to notice that the F⁻/Si⁴⁺ mass ratio equal to 9% is a significant value showing a real change in the variation trends of numerous following parameters: refractive index, UV absorption edge, absorption and emission cross sections, scalar crystal-field N_J and fluorescent lifetimes. Furthermore, introduction of F⁻ can adjust the refractive index of Yb³⁺/Al³⁺-co-doped silica glass and it is useful for large mode area (LMA) fibers.     

Influence of the Extra Layer on the Transport Properties of NdFeAsO1?0.14F0.14 and FeSe0.88 Superconductors from Magneto Dynamic Analysis

In this letter, the electromagnetic response of the NdFeAsO_1?0.14F_0.14 (T _c =49?K) superconductor system, characterized by FeAs and NdO alternating layers, has been compared with that of FeSe_0.88. We have studied the flux dynamics of these two systems by means of ac multi-harmonic magnetic susceptibility. The analysis shows that although characterized by larger thermal fluctuations due to its higher T _c , NdFeAsO_1?0.14F_0.14 exhibits a stronger pinning force relative to FeSe_0.88. The further Irreversibility Line (IL) analysis also points out that both superconductors have a 3D flux pinning behavior. We associate the stronger pinning force in the NdFeAsO_1?0.14F_0.14 structure to the presence of the extra NdO layer. Different pinning contributions can be associated to the structural stress associated to FeAs superconducting layers and/or to the Nd³⁺ ions magnetic moment (????3.6???_B) contribution on the flux cores. We will also show that these pinning are over imposed to a weak collective contribution due to the dopant F atoms.     

Effect of hollow sphere size and size distribution on the quasi-static and high strain rate compressive properties of Al-A380–Al2O3 syntactic foams

Metal matrix syntactic foams are promising materials for energy absorption; however, few studies have examined the effects of hollow sphere dimensions and foam microstructure on the quasi-static and high strain rate properties of the resulting foam. Aluminum alloy A380 syntactic foams containing Al₂O₃ hollow spheres sorted by size and size range were synthesized by a sub-atmospheric pressure infiltration technique. The resulting samples were tested in compression at strain rates ranging from 10^?3 s^?1 using a conventional load frame to 1720 s^?1 using a Split Hopkinson Pressure-bar test apparatus. It is shown that the quasi-static compressive stress–strain curves exhibit distinct deformation events corresponding to initial failure of the foam at the critical resolved shear stress and subsequent failures and densification events until the foam is deformed to full density. The peak strength, plateau strength, and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance. The compressive properties did not show measurable strain rate dependence.     

High-temperature corrosion of electric-arc coatings sprayed from powder core wires based on the Fe–Cr–B–Al system

We study the kinetics of oxidation of electric-arc dispersion-hardened coatings of the Fe–Cr–B–Al system alloyed with 6% Ni, 3% W, 1% Mo, and 1% V by spraying from powder-core wires at 700 °C. The coatings 0.5 mm in thickness were applied to plates of low-carbon steel by using powder-core wires with a diameter of 1.8 mm developed at the Karpenko Physicomechanical Institute for the coefficient of filling of the charge equal to 20–27%. The specimens were tested for heat resistance at 700°C for 100 h. The variations of the structure of the coating in the course of its long-term high-temperature oxidation were studied in an EDX metallographic microscope with EVO-4XVP microanalytic system and by using the X-ray diffraction analysis. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 93–97, September–October, 2008.     

Effects of temperature and ferromagnetism on the γ-Ni/γ′-Ni3Al interfacial free energy from first principles calculations

The temperature dependencies of the γ(f.c.c.)-Ni/γ′-Ni₃Al(L1₂) interfacial free energy for the {100}, {110}, and {111} interfaces are calculated using first-principles calculations, including both coherency strain energy and phonon vibrational entropy. Calculations performed including ferromagnetic effects predict that the {100}-type interface has the smallest free energy at different elevated temperatures, while alternatively the {111}-type interface has the smallest free energy when ferromagnetism is absent; the latter result is inconsistent with experimental observations of γ′-Ni₃Al-precipitates in Ni–Al alloys faceted strongly on {100}-type planes. The γ(f.c.c.)-Ni/γ′-Ni₃Al interfacial free energies for the {100}, {110}, and {111} interfaces decrease with increasing temperature due to vibrational entropy. The predicted morphology of γ′-Ni₃Al(L1₂) precipitates, based on a Wulff construction, is a Great Rhombicuboctahedron (or Truncated Cuboctahedron), which is one of the 13 Archimedean solids, with 6-{100}, 12-{110}, and 8-{111} facets. The first-principles calculated morphology of a γ′-Ni₃Al(L1₂) precipitate is in agreement with experimental three-dimensional atom-probe tomographic observations of cuboidal L1₂ precipitates with large {100}-type facets in a Ni-13.0 at.% Al alloy aged at 823 K for 4096 h. At 823 K this alloy has a lattice parameter mismatch of 0.004 ± 0.001 between the γ(f.c.c.)-Ni-matrix and the γ′-Ni₃Al-precipitates.     

Effect of load and reciprocating velocity on the transition from mild to severe wear behavior of Al–Si–SiCp composites in reciprocating conditions

In the present paper, the effect of normal load and reciprocating velocity on transition from mild to severe wear of A319/15%SiC_p, A336/15%SiC_p, and A390/15%SiC_p composites have been reported. Composites were produced through liquid metal metallurgy route. Adhesive wear behavior of composites was studied under dry reciprocating conditions using indigenously developed reciprocating friction wear test rig conforming to ASTM Standard G133-05. It was found that increase in normal load increases wear rate and depending upon the reciprocating velocity and type of composites, mode of wear changes from mild oxidative to severe metallic wear was noticed. The load corresponding to the transition from mild to severe wear usually termed as transition load was found to decrease with increase in reciprocating velocity and reduction in silicon content in the alloys used for the development of Al–Si–SiC_p composites. At 1 m/s reciprocating velocity, the transition load for A319/15%SiC_p, A336/15%SiC_p and A390/15%SiC_p composites were found to be in the range of 60–90 N, 60–105 N and 60–120 N respectively. Scanning electron microscope (SEM) study of wear surface and wear debris were conducted to analyze the mode of wear and operating wear mechanism. Severe wear was characterized by massive plastic deformation and gross material removal while the mild wear was found to be associated with delamination and scoring as main wear mechanisms responsible for material loss. Wear mechanism maps for different Al–(6–18)%Si–15%SiC_p composites were proposed in reciprocating contacts.