Band 103, Heft 7

Via solid–solid diffusion couples, electron probe microanalysis and the Whittle and Green method, interdiffusivities in fcc Al–Cu–Mn alloys at 1123 K were measured. The reliability of the obtained diffusivities is validated by comparing the computed diffusivities with literature data plus constraints among the diffusivities. Through assessments of experimentally determined diffusion coefficients by means of a diffusion-controlled transformations simulation package, the atomic mobilities of Al, Cu, and Mn in fcc Al–Cu–Mn alloys are obtained. Comprehensive comparisons between the model-predicted and the experimental data indicate that the presently obtained atomic mobilities can reproduce most of the diffusivities, concentration profiles, and diffusion paths reasonably.

The effect of Mn addition on the microstructure, thermal and mechanical properties in as-cast and cold-rolled Al–Sc–Zr alloys was studied. Electrical resistometry, differential scanning calorimetry and microhardness measurements were used. Transmission electron microscopy, electron backscatter diffraction and X-ray diffraction of specimens quenched from temperatures of pronounced changes in resistivity helped to identify the microstructural processes responsible for resistivity changes. The distinct microhardness increase observed after annealing above ∼320°C is caused by precipitation of the Al 3 Sc particles. The cold-rolling prior to a heat treatment has no substantial effect on temperature position of the Al 3 Sc-phase precipitation. The formation of Al 6 Mn and/or Al 6 (Mn,Fe) particles is responsible for the intensive resistivity decrease of the cold-rolled materials compared to the as-cast materials. Precipitation of these particles has an insignificant effect on microhardness. The apparent activation energy for the precipitation of the Al 3 Sc particles was determined.

High temperature deformation behavior of a Ni30Co17Fe53 alloy has been investigated by carrying out hot compression tests at temperatures ranging from 600°C to 1150°C under strain rates between 10 −5 and 1 s −1 . Both the temperature and strain-rate dependence of the flow stress were found to be described by a hyperbolic sine function. Hot formability of this alloy was also estimated by constructing an empirical processing map based on a dynamic materials model, from which the region with high power dissipation efficiency was exhibited as a feasible combination of processing condition at around 1150°C and 10 −2 s −1 . Three different thermo-mechanical treatment processes were adopted for hot-forging to investigate its influence on microstructure and subsequent thermal expansion and thermal conductivity.

The aim of this study is to demonstrate the transformation of grade-A steel into dual-phase steel by heat treatment, and the joint performance of dual-phase steels welded by means of the gas metal arc welding process using both solid and flux-cored welding wires. Dual-phase steels with different contents of martensite were obtained by intercritical annealing in different temperature ranges of a grade-A shipbuilding steel, followed by water quenching. The experimental results revealed that the tensile strength of the dual-phase steels joined by solid wire is higher than that of the flux-cored wire joints. The microstructure of grade-A steel consists of ferrite and pearlite, while the dual-phase steels consist of ferrite and martensite. On the other hand, while the martensitic phase is especially encountered in the weld metal of the dual-phase steels joined with the solid wire, the ferrite phase is more common in the weld metal of the flux-cored wire joints.

This research studies the effect of dynamic solidification, niobium addition, and their combined action on the as-cast structure and mechanical properties of hypoeutectic 15% Cr-2% Mo white cast irons containing 2.5% C. The effect of heat treatment at different tempering temperatures was also studied. Investigations were performed by means of image analysis, scanning electron microscopy, and X-ray diffraction. Abrasion resistance and impact toughness tests were performed. Fracture and worn surfaces were studied. Results show that optimized abrasion resistance and impact toughness can be achieved in a homogeneous microstructure consisting of hard, fine, and non-interconnected carbides in a matrix that has a high fraction of metastable austenite.

In the present study, squeeze-cast A356 matrix composites reinforced with B 4 C particles were prepared and different volume fractions of B 4 C particles of various sizes were incorporated into the aluminum alloy by a mechanical stirrer. Wear properties of the unreinforced alloy and composites with different vol.% of boron carbide particles were measured and compared. It is noted that composites exhibit better wear resistance compared to the unreinforced alloy. According to the differences in wear rates of the composites, two separate wear-rate regimes were identified as low- and high-wear-rate regimes. It is observed that all the composite samples reinforced with 1 μm B 4 C particles show high wear-rate, regardless of the particle volume fraction. However, none of the samples containing 50 μm particles display this type of wear regime. Microscopic examination using a scanning electron microscope equipped with an energy-dispersive spectrometer, was carried out on the worn surfaces, subsurfaces, and debris. Rough and smooth regions are distinguished on the worn surface of the composites similar to the unreinforced alloy.

X-ray powder diffractometry, scanning electron microscopy, optical microscopy and differential thermal analysis were used for constructing the isothermal section of the Al–Dy–Zr system in the whole compositional range at 773 K. The existence of 13 binary compounds and 1 ternary compound, i.e. Al 3 Zr, Al 2 Zr, Al 3 Zr 2 , AlZr, Al 3 Zr 4 , Al 2 Zr 3 , AlZr 2 , AlZr 3 , α - Al 3 Dy, Al 2 Dy, AlDy, Al 2 Dy 3 , AlDy 2 , and Al 30 Dy 7 Zr 3 were confirmed. The ternary compound Al 30 Dy 7 Zr 3 has AuCu 3 structure (space group Pm3m) with lattice parameter of a = 0.4206 nm. The isothermal section consists of 17 single-phase regions, 32 binary-phase regions and 16 ternary-phase regions. The homogeneity of Dy in the binary compounds Al 3 Zr, Al 2 Zr, Al 3 Zr 2 , and AlZr 2 is determined to be 2 at.%, 3 at.%, 4 at.%, and 2 at.% Dy, respectively. The homogeneity range of Dy in Zr is up to v7 at.% Zr. The solid solubility of Zr in the binary compounds Al 3 Dy, Al 2 Dy, and AlDy is determined to be 2 at.%, 26 at.%, and 3 at.% Zr, respectively.

Calorimetric investigations have been done on the Au–Sb–Sn system with a Calvet-type micro-calorimeter. The partial and integral enthalpies of mixing in the ternary system were determined at six cross-sections at 873 K. Three additional cross-sections were measured at 1073 K to check if there are any temperature dependencies. No temperature dependence could be found. The substitutional solution model of Redlich–Kister–Muggianu was used for a least-square fit of the experimental data in order to get an analytical expression for the integral enthalpy of mixing. The isoenthalpy curves for the Au–Sb–Sn system were constructed at 873 K. The Chou model was used to calculate the enthalpies of mixing for the ternary system. The calculated values were then compared with the experimental data. The calculated data are in very good agreement with the experimentally determined values.

A bulk nanostructured Ni 50 Al 17 Fe 33 alloy was produced by combustion synthesis associated with rapid solidification. The microstructure and mechanical properties of the as-fabricated material were investigated by means of scanning electron microscopy, X-ray diffraction, and mechanical tests. The Ni 50 Al 17 Fe 33 alloy was composed of eutectic matrix and precipitated phase. The eutectic matrix consisted of 30–50 nm globular γ′-(Ni,Fe) 3 Al and 5–10 nm γ-Ni(Fe) boundary. The precipitate was comprised of 100–150 nm γ′-(Ni,Fe) 3 Al, γ-Fe, and α-Fe solid solution phases. The nanostructured Ni 50 Al 17 Fe 33 alloy exhibited simultaneously high yield stress (about 900 MPa), high fracture strength (over 3860 MPa), and good ductility (over 75%) in compression.

In the present work sand-blasting-induced structural, thermal, and mechanical effects were studied in Zr 58.3 Cu 18.8 Al 14.6 Ni 8.3 bulk metallic glass. It was observed that sand blasting favors disordering of the atomic configuration, formation of free volume and evolution of multiple intersecting shear bands. As a result, considerable compressive plasticity was achieved in sand-blasted samples. It was also observed that in order to superimpose the effect of pre-straining and extra free volume for improving compressive plasticity, there exists a limit to both parameters.

The dynamics of oxygen transport along the slag–metal interface of pure iron and alumina-saturated CaO–Al 2 O 3 –SiO 2 slag was studied using high-temperature X-ray image analysis. The oscillations of the metal drop occurring due to the interfacial movement of oxygen atoms driven by Marangoni forces were studied in detail. The change in interfacial area during the oscillations was measured using a digitizing software and MATLAB. It was observed that the interfacial velocity as a function of oxygen exhibits insignificant variation with temperature. Further, the values obtained for the interfacial velocity using oxygen concentration difference at the interface were slightly lower in comparison to those using sulfur. The possible reason for this lower velocity could be that, although oxygen is a smaller atom compared to that of sulfur, the energy barrier at the free iron surface is higher for oxygen, thus hindering its motion along the interface.

We present a polymer complex solution method using a modified combustion synthesis procedure, for the production of well crystalline, sub-micron gadolinia-doped ceria powders of Ce 0.9 Gd 0.1 O 1.95 composition. Polyethylene glycol of two different molecular weights (200 and 20000) was used as both fuel for the combustion and nucleating agent for the crystallization process. The synthesized materials were characterized using X-ray diffraction, thermal analysis, scanning electron microscopy, and optical and photoluminescence spectroscopy. The powders are quite similar, fully crystallized in a cubic fluorite-type phase with average crystallite size of about 70 nm and average particle size in the range 220–240 nm. UV-vis absorption spectra show the absorption edge at 3.26 eV. The presence of oxygen vacancies, confirmed indirectly by clear violet emission observed at 428 nm, originated from the 5 D 1 → 4 F 1 transition of Ce 3+ ions.

Titanium dioxide nanotube arrays on titanium were fabricated via anodic oxidation and heat treatment. The diameters of nanotubes ranged from 20 to 200 nm, and the lengths were 500 and 1000 nm. The adsorption behavior of bovine serum albumin onto the nanotube arrays was investigated. Surface characterization for samples was carried out using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Adsorbance of bovine serum albumin was detected with an ultraviolet spectrophotometer. The results showed that the nanotube arrays on titanium surfaces significantly enhanced bovine serum albumin adsorption. The nanotube arrays with larger diameter could adsorb more bovine serum albumin, but longer nanotubes showed less adsorbance than shorter nanotubes. In the present work, the nanotube arrays with 160–200 nm diameter, the largest diameter, showed the highest adsorption ability, and the maximum adsorption capacity q m was 31.40 mg · cm −2 . In addition, the adsorbance of bovine serum albumin increased with increase of initial bovine serum albumin concentrations, and a saturation value was achieved at the initial bovine serum albumin concentration of 2.0 mg · ml −1 .

In this study, carbon-nanotubes-based Al/CNT/Al displacement sensors were designed, fabricated by deposition of the carbon nanotubes on an adhesive elastic polymer tape, and placed in the elastic casing, and investigated. The diameter of multiwalled nanotubes varied between 10–30 nm. The thickness of the carbon nanotube layers in the samples was 300–430 μm. The interelectrode distance (length) and width of the surface-type samples were in the range of 4–6 mm and 3–4 mm, respectively. The DC resistance of the sensors from different batches was decreased on average by 3 times as the displacement was increased up to 900 μm. The resistance–displacement relationships were supported by simulation.

Hybrid nanostructures were prepared by mixing gold and palladium nanoparticles with multi- and single-walled carbon nanotubes. The approach to prepare these nanohybrid implies the interaction of long hydrocarbon chains chemisorbed at the nanoparticles surface and the graphitic walls of nanotubes. Transmission electron microscopy results show the efficiency of this simple method to assemble these nanostructures. The electron microscopy images show that nanoparticles are effectively absorbed on the nanotube surfaces homogeneously but without any particular order. These nanostructures have proven to be stable after a moderate ultrasonic treatment.

The effect of solid content of conductive silver paste on the film thickness, microstructure of screen-printed front contact, and electrical performance of crystalline silicon solar cells was investigated. Three different solid content pastes were tested. It is found that the solid content of silver paste strongly affects the film thickness, microstructure of the thick film, and electrical performance of the cells. The paste with 84 wt.% solid content has higher viscosity and density than the ones with 82 wt.% and 83 wt.%. After sintering, the front Ag electrode thick film prepared using the paste with 84 wt.% solid content has a larger film thickness and the corresponding cell exhibits higher photoelectric conversion efficiency than the ones with 82 wt.% and 83 wt.% under the same conditions. This indicates that increasing film thickness can improve the conversion efficiency.

In-plane electrical conductivity higher than 100 S cm −1 for composite bipolar plates is required in fuel cells. The effect of the conductive filler size and shape, as one important factor, on the conductivity of polypropylene/graphite/carbon black (PP/G/CB) composites is investigated in this study. The “as-received” G particles were sieved to different sizes; melt compounded with PP and CB, then compression moulded to plates for conductivity measurements. G particles have different size distributions and their morphology appear with irregular shapes. The intermediate G size and relatively narrow distribution (40–150 μm) shows the highest conductivity at 80 wt.% filler loading of about 88.6 S cm −1 . The presence of small G particles between larger ones and the particle's point-to-point and surface-to-surface contacts are found to be important factors in determining the conductivity values. The flexural properties are still below the target and need to be improved.

This study investigates the durability of fired brick produced with additives of textile factories' waste ash and basaltic pumice. The effects of incorporating waste ash and basaltic pumice on durability and mechanical properties of the clay bricks were studied. Samples were produced with different ratios of the textile factories' waste ash and basaltic pumice added and at different fire temperatures of 700, 900, and 1050°C for 8 h. The bricks with additives were produced by adding equal amounts of textile factories' waste ash and basaltic pumice, separately and together, with rates of 5, 10 and 20 wt.%. The produced samples were kept one year in sodium sulphate and sodium nitrate and tested under freezing–unfreezing and drying–wetting conditions. Then compression strength and mass loss of the samples with and without additives were investigated. The test results were compared with standards and results obtained from control specimens. The results showed that incorporations up to 10 wt.% of textile factories' waste ash and basaltic pumice is beneficial to the fired brick. Both textile factories' waste ash and basaltic pumice were suitable additives and could be used for more durable clay brick production at 900°C fire temperature.