Volume 102, Issue 10

A comparative study of some of the most important effects of the diverse microalloying elements on austenite and ferrite microstructure of hot rolled microalloyed steels is carried out. The values of different aspects such as pinning and driving forces, size of precipitates, activation energies or diffusion coefficients are discussed. Titanium is the most effective element to control grain growth at high reheating temperatures and a weight Ti/N ratio close to 2 is recommended. Aluminum can help to control grain growth at medium temperatures, but its addition to Ti steels can promote abnormal grain growth. Niobium is the most effective element to inhibit static recrystallization of austenite, due to the adequate precipitation temperature range at deformation temperatures and the strong pinning effect of Nb carbonitrides. Finally, the preferential nucleation of intragranular ferrite on particles such as vanadium carbonitrides enhances the ferrite grain refinement.

Experimental studies have been conducted to determine the primary phases and liquidus temperatures in the “SnO 2 ” – CaO – SiO 2 system in air between 1693 and 1898 K, using high temperature equilibration and quenching followed by electron probe X-ray microanalysis. The following primary phase fields were identified: CaSiSnO 5 (malayaite), Ca 3 Si 2 SnO 9 (tricalcium tin silicate), CaSiO 3 (pseudo-wollastonite), Ca 2 SiO 4 (dicalcium silicate), SiO 2 (tridymite and cristobalite), SnO 2 (cassiterite) and CaSnO 3 (calcium stannate).

All known phases of the chromium – sulfur binary system have been taken into consideration within a thorough thermodynamic analysis of phase equilibria and thermodynamic data at 1 bar total pressure over the entire composition range between 25 °C and temperatures above the liquidus. Gibbs energy modeling for ten phases has been performed. A limited set of model quantities were optimized by which the experimental data can be reproduced simultaneously within experimental limits of error. New interpretations of complex phase relations are obtained. The extended modified quasichemical model is applied for the liquid chromium – sulfur phase. The Gibbs energy of high-temperature chromium pyrrhotite solution is described by a two-sublattice model within the framework of the compound energy formalism. The sulfur solubility of solid chromium is modeled using a substitutional approach. The Gibbs energies of six stoichiometric compounds are also modeled. The first internally consistent description of all thermodynamically stable phases known in the literature for the chromium – sulfur system is presented.

Homogeneous Al-3.7 wt.% Cu samples (Al solid solution) were (partially) melted by rapid heating in a steep temperature gradient and quenched immediately after the onset of melting. Traces of melting, particularly intragranular eutectic and θ-phase particles as well as intergranular eutectic and θ-phase layers, were observed in the quenched microstructure. The intragranular particles (mean diameter locally < 200 nm) represent former liquid droplets that nucleated as a consequence of some supersaturation of the Al solid solution. The intergranular layers represent former liquid films that nucleated at the grain boundaries. At temperatures slightly above the solidus temperature, segmentation of the film was observed. Concentration distributions measured using energy dispersive X-ray analysis indicate the migration direction of the film and the supersaturation as the driving force for migration.

The vaporisation of Al – Co alloys has been investigated in the temperature range of 1 201 to 1 552 K using Knudsen effusion mass spectrometry. Nine different compositions have been examined in the composition range x (Co) = 0.62 to 0.47. Al(g) and Co(g) were the vapour species observed over all the alloy samples excepting x (Co) = 0.47 over which only Al(g) could be identified. Partial pressure – temperature relations and thermodynamic activities of Co and Al were derived. The enthalpies and Gibbs free energies of formation of Al 0.5 Co 0.5 (s) at 298.15 K were obtained as Δ f H o m =− 54.9 ± 4.8 kJ mol −1 and Δ f G o m =− 51.4 ± 1.4 kJ mol −1 . This is the first time activities of Co have been determined experimentally across the B2-AlCo(s) single phase region.

In spite of the excellent machinability and wear resistance of graphitic steels, they exhibit low hardness and mechanical properties due to the presence of a ferritic matrix, soft graphite phase and need for prolonged annealing time. So the matrix evolution of graphitic steel from ferritic to pearlitic, bainitic, martensitic and tempered martensite can overcome to this shortcoming. To achieve this purpose, reaustenitizing graphitic steel has been done at two temperatures (820 °C and 850 °C) and followed by different cooling rates. During this treatment, the ferritic matrix in graphitic steel was replaced by other phases such as pearlitic, bainitic etc. which also contain graphite particles. These transformed microstructures can improve the hardness and mechanical properties of graphitic steel.

One distinct concentration of copper was embedded into a silica matrix to form xerogel using the copper source Cu(NO 3 ) 2 · 3H 2 O. The xerogel samples were prepared by hydrolysis and condensation of tetraethyl orthosilicate by the sol-gel method. In this investigation, the new molar ratio of H 2 O/TEOS (tetraethyl orthosilicate) was determined as 11.7. Also, the necessary amount of trihydrated copper nitrate was added to the solution in such a manner that the concentration of copper oxide in the final solution reached to 10 wt.%. After ambient drying, the xerogel samples were heated from 60 to 1 000 °C at a slow heating rate (323 K h – 1 ). Their structural properties were characterized by thermal gravimetric analysis, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, surface analysis and thermal-program reduction methods at different temperatures.

Electrospray deposition is fast finding application in the field of thin film device manufacturing processes. The ease and cost efficiency attached to electrospray deposition with possible integration with roll-to-roll fabrication lines is the potential future of thin film device manufacturing. In this study thin films composed of copper-indium-diselenide, more commonly known as CIS, have been made using the electrospray deposition of nano-particle based inks for the ultimate manufacture of CIS-based solar cells. It is the first time that a complete CIS layer has been deposited through electrospray in a single step without involving any other process. Deposited layers are thoroughly characterized using techniques such as scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. Moderate voltage requirements, dense, large grained, ∼1 μm thick layers and reasonable sintering temperatures involved in the electrospray deposition process promise the possible applicability of electrospray deposition in the manufacturing of cheap and easy to build solar cells.

Silk fibers produced by the orb spiders Argiope amoena and Nephila clavata were examined using scanning electron microscopy. The fibers were produced on a horizontal surface by unanesthetized spiders. The fibers have different morphologies, physical structures, and fibrous compositions broadly consisting of one to four filaments and numerous fibrilliform filaments with varying diameters. The fibers are composed of a wide range of different silk fibrils (e. g. major and minor ampullate or other gland silk). We examined a range of silks produced by orb spiders. The spiders produce different silks for purposes such as web mooring, web radial threads, scaffolding anchoring silk of egg cases. In addition fiber deposited when moving towards prey enmeshed in the web, fiber deposited when returning to the web center, and fiber used to hang vertically downwards from a branch are all different. The studies indicate that these two species of orb spider can spin fibers of diverse complex structures constructed from fibrils from different glands that vary in number, diameter, morphology, and conformation depending on application. We interpret the variation in the silk produced by relating it to the required tensile properties, a biological cost–benefit principle, and the functional requirements for different natural environments and applications.

In the present article, nickel cobalt ferrite (Co 0.5 Zn 0.5 Fe 2 O 4 ) nanoparticles were synthesized using a template-assisted hydrothermal method. Carboxymethyl cellulose was used as the templating agent for controlling the morphology of the Co 0.5 Zn 0.5 Fe 2 O 4 nanoparticles. The synthesized nanoparticles were characterized using X-ray diffraction, scanning electron microscopy, and a vibrating sample magnetometer. The results indicated that the morphology of the nanoparticles changed from granular and superparamagnetic to platelike and ferromagnetic with the addition of the template. The Co 0.5 Zn 0.5 Fe 2 O 4 nanoparticles synthesized without the template exhibited a saturation magnetization and coercivity 2.81 T and 0.2 kA · m – 1 , while when the template was used, the saturation magnetization and coercivity increased to 3.13 T and 76.6 kA · m – 1 as the template proportion increased to 0.3.

The deformation behavior under uni-axial tensile loading is investigated and reported in the case of cold rolled Nimonic C-263 alloy sheet products of different thicknesses (0.5 mm and 1 mm) in the solution treated and aged conditions. The studies conducted include (i) Microstructure, (ii) X-ray diffraction, (iii) Texture and (iv) Tensile properties and in-plane anisotropy in the yield behavior (both tensile yield strength and ultimate tensile strength as well as ductility). The results of the present study showed that despite the presence of weak crystallographic texture in this crystal symmetric material, the degrees of in-plane anisotropy in strength as well as plastic deformation properties are found to be significant in both solution treated and aged conditions, thus having significant technological relevance for both further processing and design purposes. Further, the influence of aging and sheet thickness on the tensile deformation behaviour is also found to be considerable. A brief discussion on the technological implications of these results is also included.

As-cast 7 xxx series aluminum alloys experience a severe loss in ductility upon cooling and become brittle below 300 °C. In order to simulate the thermal stresses arising during casting, a thorough understanding of the thermal contraction behavior during solidification and cooling is required. In this study, some thermal properties of the AA7050 alloy are determined experimentally in the “as-cast” condition. Solidification contraction tests were performed to determine the onset of thermal contraction in the grain refined alloy and dilatometry tests were conducted to estimate the coefficient of thermal expansion/contraction of the alloy. Our simulation results showed that although the temperature dependence of the coefficients of thermal expansion/contraction obtained from the tests differ from the predictions of thermodynamic data-base, these differences are not crucial to the results of the thermomechanical simulations.

Tailor welded blanks are complex component designs tailor-made through welding of multiple metal sheets with different thicknesses, shapes and/or strengths prior to forming. Making tailor welded blanks out of interstitial free galvanized steels not only provides the general advantages of tailor blanks including the weight and manufacturing cost reductions per part, but also considering the properties of the parent sheet, could guarantee exceptional corrosion resistance as well as favorable formability characteristics. The quality of the weld joint in these blanks and their formability is directly influenced by the parameters of the welding process. In this research, the use of CO 2 laser for welding thin interstitial free galvanized steel sheets with different thicknesses (0.8 and 1.2 mm) was optimized using the Taguchi analytical methodology. The welding parameters including the shielding gas pressure, laser power and travel speed of the laser beam were evaluated by measuring the dome height value after forming and the optimal welding parameters values were obtained. The optimal result was equated with the highest dome height value and consequently highest formability. Results showed that the welding parameters have a great effect on achievable properties of tailor welded blanks and entrapment of zinc vapor due to evaporation of zinc has a significant role in determining the weld quality of the studied blanks. Microstructure, hardness and mechanical properties of different welds were also investigated. Formation of voids and porosity as well as lack of diffusion were some of the results of welding with non-optimized parameters. An equation based on a regression model is presented to predict the minimum dome height value of tailor welded blank consisted of interstitial free galvanized steels with a thickness ratio of 1.5.

Properties such as density, porosity, shrinkage and compressive strength of bauxite refractories were investigated by selecting different bauxite grain size, water content, molding pressure and firing temperature. The stress – strain data were modeled using parameters such as maximum stress, maximum strain, elasticity and non linearity. Simple mathematical models were used to correlate the examined properties with production conditions and materials’ characteristics, through regression analysis. Thus, it was found that firing at 1 400 °C led to shrinkage, while low porosity and high maximum stress refractories are produced when increasing all production conditions. Maximum strain and the non-linearity parameter increase with temperature, while molding pressure increases only maximum strain. Finally, the elasticity parameter decreases with grain size and molding pressure.

In this study, the effect of limewater on the flexural strength and water permeability of concrete containing Fe 2 O 3 nanoparticles has been investigated. Portland cement was partially replaced by Fe 2 O 3 nanoparticles as nano-fillers with 0.5, 1.0, 1.5 and 2.0 wt.%. Curing of the specimens was carried out in water and saturated limewater for 7, 28 and 90 days. The results indicate that replacement of cement by Fe 2 O 3 nanoparticles up to 2.0 wt.% produces concrete with improved flexural strength and water permeability when the specimens are cured in saturated limewater. The level of replacement for the specimens cured in water is 1.0 wt.%. Fe 2 O 3 nanoparticles can improve the filler effect and the high reactivity of fine particles also substantially increases the quantity of strengthening gel.