Showing papers on "Alloy published in 2007"

Solid solution alloys of AlCoCrFeNiTix with excellent room-temperature mechanical properties

Abstract: Alloys with composition of AlCoCrFeNiTix (x: molar ratio; x=0,0.5,1,1.5) were designed by using the strategy of equiatomic ratio and high entropy of mixing. The alloy system is composed mainly of body centered cubic solid solution and possesses excellent room-temperature compressive mechanical properties. Particularly for AlCoCrFeNiTi0.5 alloy, the yield stress, fracture strength, and plastic strain are as high as 2.26GPa, 3.14GPa, and 23.3%, respectively, which are superior to most of the high-strength alloys such as bulk metallic glasses.

Alloy Design for Lithium-Ion Battery Anodes

Abstract: A set of guidelines is proposed for designing high-energy-density alloy anode materials It is first shown that the molar volume of lithium is about 9 mL/mol in a wide variety of lithium alloys and is independent of lithium content Using this property of lithium alloys, simple relationships between the volumetric energy density and the volumetric expansion of an alloy are derived These relationships are extremely powerful for designing alloys with the maximum possible energy density for a given electrode-coating performance

Microstructure and compressive properties of multicomponent Alx(TiVCrMnFeCoNiCu)100−x high-entropy alloys

Abstract: The microstructure and compressive properties of Al x (TiVCrMnFeCoNiCu) 100− x ( x = 0, 11.1, 20 and 40 at.%) high-entropy alloys were studied. With the increase of Al content, the number of phases in the alloys gradually decreases. When Al content is 20 at.%, only bcc solid-solution structure is found in the alloy. The effect of high mixing entropy does facilitate the formation of simple solid solutions, making the total number of phases well below the maximum equilibrium number allowed by the Gibbs phase rule. The solid-solution strengthening mechanism and the structure transformation from fcc to bcc make the alloys have fairly high compressive strength; among them the compressive strength of Al 11.1 (TiVCrMnFeCoNiCu) 88.9 alloy reaches 2.431 GPa.

Enhanced mechanical behavior of a nanocrystallised stainless steel and its thermal stability

Abstract: This paper discusses the mechanical properties of a nanocrystallised stainless steel obtained using surface mechanical attrition treatment (SMAT) and the underlying grain refinement mechanism using transmission electron microscopy (TEM). It was shown that grain refinement down to the nanometer range has the potential to significantly improve the mechanical properties of a 316L stainless steel which becomes comparable in strength to titanium alloys. Hence, promising structural applications could be considered for such a material. At the same time, the thermal stability of this nanocrystallised material was studied in the temperature range from 100 to 800 °C. The results show that the nanometer scaled microstructure is retained up to 600 °C and that a controlled annealing treatment could even lead to enhancement of both strength and ductility of this material. All these results are explained in terms of microstructural investigations, X-ray diffraction measurements, tensile and bending tests as well as microhardness measurements.

Corrosion behavior of biomedical AZ91 magnesium alloy in simulated body fluids

Abstract: Fast degradation rates in the physiological environment constitute the main limitation for magnesium alloys used in biodegradable hard tissue implants. In this work, the corrosion behavior of AZ91 magnesium alloy in simulated body fluids (SBF) was systematically investigated to determine its performance in a physiological environment. The influence of the main constituent phases on the corrosion behavior was studied by in situ visual observation and scanning electron microscopy. Energy dispersive x-ray spectrometry and Fourier transfer infrared spectroscopy revealed that both calcium and magnesium phosphates are present in the corroded products besides magnesium oxide. Electrochemical methods including open circuit potential evolution and electrochemical impedance spectroscopy were used to investigate the mechanism. The corresponding electrode controlled processes and evolution of the corrosion products layer were discussed. The degradation rate after immersion in SBF for seven days was calculated from both the weight loss and hydrogen evolution methods.

Body-centered cubic iron-nickel alloy in Earth's core.

Abstract: Cosmochemical, geochemical, and geophysical studies provide evidence that Earth's core contains iron with substantial (5 to 15%) amounts of nickel. The iron-nickel alloy Fe0.9Ni0.1 has been studied in situ by means of angle-dispersive x-ray diffraction in internally heated diamond anvil cells (DACs), and its resistance has been measured as a function of pressure and temperature. At pressures above 225 gigapascals and temperatures over 3400 kelvin, Fe0.9Ni0.1 adopts a body-centered cubic structure. Our experimental and theoretical results not only support the interpretation of shockwave data on pure iron as showing a solid-solid phase transition above about 200 gigapascals, but also suggest that iron alloys with geochemically reasonable compositions (that is, with substantial nickel, sulfur, or silicon content) adopt the bcc structure in Earth's inner core.

Intermetallic FexAly-phases in a steel/Al-alloy fusion weld

Abstract: The microstructure of joints between an Al-alloy and a zinc coated ferritic steel sheet manufactured by the so-called CMT joining method is investigated. The joint consists of a weld between the Al-alloy and Al 99.8 filler and a brazing of the filler to the zinc coated steel. The morphology, the structure and the defects of the intermetallic phases that developed at the interface between the steel and the Al 99.8 filler are characterised using scanning and transmission electron microscopy. The intermetallic phase seam is only about 2.3 μm thick and consists of trapezoidal nearly equiaxial Fe2Al5 grains surrounded by finger-like remains of the steel and mostly elliptical FeAl3 grains extending into the Al 99.8 filler material. Both the Fe2Al5 and the FeAl3 grains contain crystal defects.

Structure-activity-stability relationships of Pt-Co alloy electrocatalysts in gas-diffusion electrode layers

Abstract: We establish relationships between the atomic structure, composition, electrocatalytic activity, and electrochemical corrosion stability of carbon-supported Pt−Co alloy nanoparticles in electrode catalyst layers. These Pt−Co catalysts have received much attention for use as cathode layers in polymer electrolyte membrane fuel cells (PEMFCs) because of their favorable oxygen-reduction-reaction (ORR) activity and suspected corrosion stability. We reported an enhancement of activity of low-temperature Pt50Co50 of 3 times that of pure carbon supported Pt catalysts. The use of synchrotron X-ray diffraction has enabled structural characterization of the alloy nanoparticles both before and, importantly, after electrocatalysis under fuel cell like conditions. From this, a detailed picture of the relative activity and stability of Pt−Co alloy phases as a function of synthesis conditions has emerged. We have investigated the structure, composition, chemical ordering, and concentration of Pt−Co alloy phases in (i) a ...

The effect of boron on the corrosion resistance of the high entropy alloys Al0.5CoCrCuFeNiBx

Abstract: High entropy alloys are a newly developed family of multicomponent alloys that consist of various major alloying elements, including copper, nickel, aluminum, cobalt, chromium, iron, and others. Each element in the alloy system is present at between 5 and 35 atom %. A high entropy alloy has numerous beneficial mechanical, magnetic, and electrochemical characteristics. This investigation discusses the corrosion resistance of the Al 0.5 CoCrCuFeNiB x alloys with various amounts of added boron. Surface morphological and chemical analyses verified that the addition of boron produced Cr, Fe, and Co borides. Therefore, the fraction of Cr outside borides precipitates was scant. The anodic polarization curves and electrochemical impedance spectra of the Al 0.5 CoCrCUFeNiB x alloys, obtained in 1 N H 2 SO 4 aqueous solution, clearly reveal that the general corrosion resistance decreases as the concentration of boron increases.

Effect of Y for enhanced age hardening response and mechanical properties of Mg–Gd–Y–Zr alloys

Abstract: In this study, compositional dependence of age hardening response and tensile properties were investigated for Mg–10Gd–xY–0.4Zr (x = 1, 3, 5 wt.%) alloys. With increasing Y content, the age hardening response of the alloys enhanced and tensile properties increased. The Mg–10Gd–5Y–0.4Zr alloy exhibited maximum tensile strength and yield strength at aged-peak hardness, and the values were 302 MPa and 289 MPa at room temperature, and 340 MPa and 267 MPa at 250 °C, respectively. The strong peak age hardening was attributed to the precipitation of prismatic β′ plates in a triangular arrangement. The cubic shaped β phase was also observed at grain boundaries. The remarkable improvement in strength is associated with a uniform and high dense distribution of β′ and cubic shaped β precipitate phases in Mg matrix. Elongation of Mg–10Gd–0.4Zr alloys decreased with increasing Y content, and the elongation of Mg–10Gd–5Y–0.4Zr alloy was less than 3% below 250 °C, whereas the alloys containing 1 wt.% and 3 wt.% Y exhibited higher elongation than 5% at room temperature.

Suppression of intermetallic reaction layer formation by controlling heat flow in dissimilar joining of steel and aluminum alloy

Abstract: In order to suppress the formation of intermetallic reaction layer during laser welding of steel and aluminum alloy dissimilar materials, effect of backing block (heat sink) was investigated. FEM analysis as well as welding experiments with various backing blocks for controlling heat flow were performed. It was found that thickness of intermetallic reaction layer was reduced by increasing welding speed and by applying a backing block with higher thermal conductivity. FEM analysis also showed that when increasing welding speed or applying a backing block with higher thermal conductivity, molten time of aluminum alloy became shorter and predicted thickness of intermetallic reaction layer became thinner. It could be concluded that the thickness of intermetallic reaction layer could be suppressed by using a backing block (as a heat sink) for controlling heat flow in welding region. The joining strength was strongly dependent on the thickness of intermetallic reaction layer. Therefore the backing block was significantly effective for controlling heat flow and consequently for attaining good joining strength.

Ductile titanium alloy with low Poisson's ratio.

Abstract: We report a ductile beta-type titanium alloy with body-centered cubic (bcc) crystal structure having a low Poisson's ratio of 0.14. The almost identical ultralow bulk and shear moduli of similar to 24 GPa combined with an ultrahigh strength of similar to 0.9 GPa contribute to easy crystal distortion due to much-weakened chemical bonding of atoms in the crystal, leading to significant elastic softening in tension and elastic hardening in compression. The peculiar elastic and plastic deformation behaviors of the alloy are interpreted as a result of approaching the elastic limit of the bcc crystal under applied stress.

A new Ti-based bulk glassy alloy with potential for biomedical application

Abstract: The thermal properties, glass forming ability (GFA) and mechanical properties of a series of Ti 40 Zr 10 Cu 40− x Pd 10+ x ( x = 0, 2, 4, 6, 8, 10) bulk glassy alloys were examined by differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffractometry (XRD) and compressive test. The series of bulk glassy alloys are expected to be used as biomedical materials because of the absence of toxic elements such as Ni, Al and Be. The Ti 40 Zr 10 Cu 36 Pd 14 alloy exhibits the highest GFA, resulting in a maximum diameter of 6 mm, and high thermal stability with a supercooled liquid region (Δ T x ) of 49 K. The bulk glassy alloy has higher specific strength of 2.7 × 10 5 Nm/kg and lower Young's modulus of 82 GPa than those of conventional biomedical Ti alloys. These are favorable for application to biomaterials.

Development of Ti-Mo alloys for biomedical applications: Microstructure and electrochemical characterization

Abstract: Ti–Mo alloys from 4 to 20 Mo wt.% were arc-melted. Their compositions and surfaces were analyzed by EDX, XRF and SEM. The Mo mapping shows a homogeneous distribution for all alloys. The XRD analysis showed that the crystal structure of the alloys is sensitive to the Mo concentration; a mixture of the hexagonal α′ and orthorhombic α″ phases was observed for the Ti–4Mo alloy, and the α″ phase is observed almost exclusively when the concentration of Mo added to the Ti reaches 6%. A significant retention of the β phase is observed for the alloy containing 10% Mo, while at higher Mo concentrations (15% and 20%), retention of phase β is only verified. Preliminary electrochemical studies have indicated a valve-metal behavior and good corrosion resistance in aerated Ringer solution for all alloys.