Volume 102, Issue 12

The effect of annealing on the mechanical anisotropy of hot pack rolled Ti-6Al-4V thin sheets was studied. Partial recrystallization/globularization of the deformed microstructure was observed during high temperature annealing of rolled sheets. The room temperature tensile properties obtained along different orientations from rolling direction to transverse direction are used to evaluate the % In Plane Anisotropy (% IPA ), and Anisotropic Index ( δ ). A significant decrease in anisotropy with the increase in annealing temperature was observed. The Knoop hardness based plane stress yield loci were evaluated for the sheets in as-rolled and annealed conditions and the variation in the shape and size of yield loci divulged the decrease in mechanical anisotropy with annealing. The X-ray diffraction scans also revealed the weakening of basal texture qualitatively.

Mechanical spectroscopy, differential scanning calorimetry measurements and light microscopy studies were performed on homogenised and plastically deformed samples of commercial WE43 magnesium alloy. Plastic deformation was performed both at 300 K and 643 K, and at 1 % and 10 % of uniform plastic deformation. Samples 1 % deformed at 300 K did not show recrystallisation, but recovery at about 633 K was detected. Samples 1 % deformed at 643 K recovered dynamically, during hot working. Samples 10 % deformed at 300 K began to recrystallise at about 730 K, meanwhile samples 10 % deformed at 643 K dynamically recrystallised during hot working.

The weld metal microstructures and the weldability of a tantalum-containing cast cobalt-based superalloy were investigated using gas tungsten arc welding. It was found that the tantalum carbides in the base metal have remained stable up to the fusion line. The results showed that the formation of Ta-rich carbides (TaC) is very sensitive to time and temperature; so the as-weld microstructure is unstable from a metallurgical aspect. The formation of fine precipitates due to the high cooling rate of the welding process resulted in a weld metal with an undesirable hardness and microstructure after autogenous welding, especially after post weld heat treatment. Further results revealed that using a filler metal containing significantly less carbon and tantalum has solved the mentioned problems and made acceptable welds after post weld heat treatment.

The 3D shape of X-ray reflections from the γ/γ′-microstructure of a nickel-base superalloy was investigated using synchrotron X-ray radiation and a position sensitive area detector. The measurements were performed on the 4 th generation single-crystal nickel-base superalloy TMS138. The results show that X-ray reflections from non-cubic crystallographic planes have a complex 3D shape which changes during rafting. The 3D intensity distributions contain information about the spacing of the planes and their orientation as well. Whereas h 00 reflections show the usual splitting into a γ′ and one γ-subreflection, the hh 0 and hhh reflections show two and three γ-peaks respectively, resulting from the different types of {100} matrix channels. Therefore, these 3D diffraction measurements supply additional information about the spatial distribution of microstrains.

Microstructural evolution during partial remelting of AM60B alloy refined by 0.2 wt.% SiC particles at 615 °C has been investigated. The effect of as-cast microstructure on the resulting semisolid microstructure has also been discussed. The results indicate that the evolution process includes five stages, initial rapid coarsening, structure separation, spheroidization and coarsening, partial melting and final coarsening. The finer the as-cast microstructure is, the smaller and more spheroidal the primary particles of the resulting semisolid microstructure are. There is a threshold for the grain size of the as-cast microstructure. When the grain size is about 100 μm, one dendrite frequently evolves into one primary particle after being partially remelted. But when the grain size is larger than 100 μm, one dendrite often separates into several particles, and when it is smaller than 100 μm, one primary particle always originates from several dendrites.

The viscosity of eutectic PdSi alloys has been measured using different techniques. Conventional oscillating cup viscosimetry was used in the ground-based laboratory, while the oscillating drop technique was applied in a microgravity experiment. Different working equations were utilised to derive the viscosity from the damping of the oscillations, and the results thus obtained were compared to each other and available literature data. An overall satisfactory agreement was found, while, at lower temperatures, an increasing difference between the viscosities obtained using the two models was observed.

In the presence of polyethylene glycol, bimodal mesoporous nanorod γ-alumina was successfully synthesized via the thermal decomposition of ammonium aluminium carbonate hydroxide precursor which was prepared via hydrothermal processing with inorganic aluminium salt. The alumina exhibits high surface area (494 m 2 g –1 ), large porosity (1.1 m 3 g –1 ) and a particular double-pore structure after calcination at 500 °C. The smaller pore diameter is concentrated on about 3 nm and the larger one is exhibited in the range of 10 – 38 nm. The scaffold-like aggregation of γ-alumina nanorods endows this novel material with excellent thermal stability. A possible formation mechanism of bimodal mesoporous structure is also proposed in this study.

The aim of this study was to investigate the effect of fuel/oxidizer ratio on the combustion synthesis of nano-crystalline Zn – CoO green pigment. The fuel and oxidizer used in this study were glycine and nitrate respectively. Products were characterized by means of X-ray diffraction, Fourier transformation infra red spectroscopy, scanning electron microscopy and diffuse reflectance spectroscopy. X-ray diffraction patterns (XRD) showed that the formation of pure hexagonal ZnO phase was insensitive to fuel/oxidizer ratio variations. Well-crystalline single-phase ZnO was observed for low and stoichiometric fuel/oxidizer ratios. Average crystallite size determined from the Scherrer formula varied from 18 to 75 nm. The morphology of the obtained samples changed from hexagonal pyramidal to irregular porous sponge-like particles. The colorimetric results showed a broad reflectance band around 530 nm (green region) for all samples. The observation of green appearance of different samples synthesized using different fuel/oxidizer ratios was related to fade of Co 3 O 4 X-ray diffraction patterns and entrance of Co into ZnO structure.

In this study, a good combination of electrospun poly(caprolactone) nanofibers incorporated with high purity titanium nanoparticles is introduced for hard tissue engineering applications. A simple approach to utilize the colloidal properties of poly(caprolactone) and titanium nanoparticles are exploited to form nanofibers by the simple electrospinning process. The prepared colloidal solutions were characterized using dynamic light scattering and electrophoratic light scattering which indicated unimodal size distribution and negative zeta potential. To investigate the bioactivity of the resultant nanofiber mats, they were incubated in simulated body fluid at 37 °C for 10 days. Field emission scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy indicated that incorporation of titanium strongly activates precipitation of the apatite-like materials from the utilized simulated body fluid. Moreover, in-vivo experiments using experimental dogs revealed that nanofibers can yield good tissue regeneration on the surfaces of nanofibers.

The influence of ammonia concentration on the formation of hollow silica microspheres via polystyrene beads templating was investigated. Hollow silica microspheres could only be templated in water – ethanol – ammonia – tetraethyl orthosilicate media with low concentrations of ammonia. It is shown that in template-free media, the aggregation of silica particles decreases with ammonia concentrations. Thus, the aggregation degree of formed silica particles may imply whether a silica forming media is suitable for preparing hollow silica microspheres via polystyrene beads templating. The increase in ammonia promotes spontaneous nucleation and condensation of silica oligomers to form silica particles. The repulsive forces between the particles as well as those between them and templates are relatively large, hindering the assembly of silica primary particles on the templates to form silica shells.

A series of MSU- x wormlike mesoporous silica samples were synthesized using a new type of gemini surfactants [C n H 2 n +1 N + (CH 3 ) 2 –CO 2 –(CH 2 ) 4 –CO 2 –N + (CH 3 ) 2 C n H 2 n +1 ] ·2 Br ( n = 12, 14, 16) at circumneutral pH and characterized using Fourier transform infrared spectroscopy, thermo gravimetric analysis, X-ray diffraction, N 2 adsorption-desorption and scanning electron microscopy. The MSU- x samples have high surface area and thick pore walls. The pore structure remained after treatment in boiling water for 72 h, which has hardly been reported among mesoporous materials synthesized under mild conditions. The effects of synthesis temperature, aging time and concentration of surfactant on the mesoporous structure were investigated. Based on these, a formation mechanism of mesoporous silica using the new gemini surfactant was proposed.

The aim of this study was to use ground silica sand, ground granulated blast furnace slag and ground basaltic pumice in the production of adhesives for tiles. The main purpose was to improve the durability of adhesives. Furthermore, an investigation was carried out to determine adhesive resistance to aggressive conditions. The study examines the effects of acids, shrinkage and freezing thawing cycles. The results showed that the adhesives were prepared and applied easily due to improved initial adhesion. The durability improvement can be explained by the low water absorption and high permeability. All specimens were observed to fulfill the shear and tensile adhesion strength requirements of both European and Turkish Standards.

ZnSe nanowires have been successfully synthesized through chemical vapor deposition assisted by laser ablation in a tube furnace on a silicon substrate coated with a gold film of 2 nm thickness. X-ray powder diffraction measurements reveal that the synthesized products had pure hexagonal wurtzite structure. The microstructures and chemical composition of the as-grown nanowires have been investigated by means of electron microscopy, energy dispersive spectroscopy, photoluminescence and Raman spectroscopy. The results reveal that the as-grown material consists of ZnSe nanowires with diameters ranging from 60 – 100 nm and with lengths up to several tens of micrometers. High resolution transmission electron microscopy and selected area electron diffraction indicated that as-synthesized nanowires were single crystalline in nature. Micro-photoluminescence studies on ZnSe nanowire reveal strong emission at 460 nm. The Raman peak at 251 cm −1 is attributed to the longitudinal optic phonon mode of ZnSe.

Dielectrophoresis was used to align single-walled carbon nanotubes between microelectrodes in deionized water. The influences of solvent concentration, alternating current voltage amplitude and frequency, and direct current electric field on the alignment of nanotube were studied. The results show that the number of deposited carbon nanotubes could be adjusted via the solution concentration and voltage amplitude. Alternating current frequency affects the orientation of the nanotubes. At higher frequency, nanotubes are well assembled between the electrodes. When applying a composite electric field, the direct current component would generate vortex flux at the vicinity of nanotubes, which changes the nanotube alignment.

The composition, morphology and the long-term corrosion resistance in sodium chloride solution of zinc phosphate coating on AZ31B magnesium alloy were investigated using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, hydrogen evolution and potentiodynamic polarization curve experiments. The results indicate that the phosphate coating consists mainly of Zn 3 (PO 4 ) 2 · 4 H 2 O, Zn 2 Mg(PO 4 ) 2 and metallic Zn. The variations of the hydrogen evolution, i corr and corrosion morphologies indicate that the corrosion process of zinc phosphate has three stages. At the first stage, the corrosion resistance of the phosphate sample is higher than that of the uncoated sample. At the second stage, the corrosion rate basically remains constant. At the third stage, a Zn – Mg galvanic cell and galvanic corrosion are formed between zinc and the AZ31B substrate, and the corrosion resistance of the phosphate sample is lower than that of the uncoated sample.