Advanced Materials Research Vol. 829

Abstract: Processing through the application of severe plastic deformation (SPD) provides an opportunity for achieving significant grain refinement, typically to the submicrometer or even the nanometer level. If these small grains are reasonably stable at elevated temperatures, it is possible to achieve excellent superplastic capabilities at very rapid strain rates. Recent developments on the flow properties of ultrafine-grained materials are examined and it is shown that the flow mechanisms can be readily depicted using deformation mechanism maps. Examples of maps are presented for materials processed by SPD techniques.

Abstract: In the present study, compression tests were performed at a strain rate of 0.001 to 0.1 sˉ1 and in the range of 600°C to 900°C to investigate the high temperature deformation behavior and flow stress model of commercially pure titanium after severe plastic deformation (SPD). It was found that the effects of temperature and strain rate are significant in dictating the steady state flow stress levels. Flow accompanied by thermal softening was observed due to a combination of dynamic recovery and recrystallization for deformation at or above 600°C. Furthermore, microstructural evolutions of the as processed and hot deformed material were investigated. Based on constitutive equations, the flow stress was modeled for this light ultra-fine grained (UFG) material. The validity of the model was demonstrated with satisfactory agreement in light of the experimental mechanical behavior.

Abstract: A novel experimental technique called "Multi-Axial Incremental Shearing" (MAIS) is proposed to impose plastic shear strain to the bulk metallic materials. The evolution of strain during MAIS processing of AA1100 alloy has been studied by employing 3D finite element modeling. The commercial code DEFORM was used to analyze the deformation and evolution of the working load with rams displacement as the material passes through the die. Simulation results showed that a large amount of accumulative strain can be applied to the sample without change of its dimensions. In order to verify the metal flow and microstructure characteristics, Sn-1wt.% Bi alloy specimens as the representative of the soft metals have been deformed by MAIS process.

Abstract: Primary crystallization of amorphous Al₈₆Ni₆Y₆Ce₂ (at.%) alloy was investigated through differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction. Moreover, nanoindentation analysis was performed to relate the hardness to the structure of the alloy. The kinetic parameters of the first crystallization process were determined by Kissinger method. The average amount of Avrami exponent (n=1.7±0.21) was concluded the primary crystallization occurred through three dimensional diffusion-controlled growth with decreasing rate. The α-Al nanoparticles 58 nm in size homogeneously embedded in the glassy matrix were formed during primary crystallization. Significant changes in the hardness occurred due to the change of the crystalline structures. The hardness of 7.30±0.58 GPa was obtained by annealing at 618 K with a microstructure of Al nanoparticles and Al₃Ni intermetallic compound in an amorphous matrix.

Abstract: Fe-10Ni-7Mn (wt. %) steel is a member of ultrahigh strength steels which shows good ductility in the solution annealed condition and excellent age hardenability. In the current research, this alloy was subjected to heavy cold rolling in which the reverse transformation of martensitic to austenite was brought about. From the XRD, DSC and dilatometric analyses, it is resulted that after 60 % cold rolling the austenite phase may be formed by displacive mechanism. Stability of austenite at room temperature is referred to the ultrafine/nanograin size of austenite after deformation which prevents the austenite to martensite transformation. The presence of ultrafine/nanoaustenite formed by displacive mechanism leads to the observation of new mechanical properties during cyclic tensile test. This behavior is known as pseudoelastic phenomenon. In this behavior, during loading-unloading tensile cycle, the shape of the specimen return to its original configuration with a hysteresis loop in its path to the zero strain point.

Abstract: In this research the composition of polyurethane open cell (PUOC) with two concentrations of SiO₂ nanoparticles (1 and 2wt. %) have been prepared. Optical microscopy imaging, watering uptake, FTIR and Raman spectroscopy of the synthesized samples were measured. The optical microscopy imaging of samples showed differences in the appearance of matrix by applying of different amount of SiO₂ nanoparticles. Variations of the water uptake of specimens were related to the function of SiO₂ nanoparticles (NPs) and their concentrations. The degree of phase separation and the hydrogen bonding index in samples were evaluated in terms of their FTIR spectroscopy data. The apparent and real densities of foams were measured and then total porosity, open porosity and close porosity of samples were calculated. According to creating voids in polyurethane, the apparent and real density has different behavior by adding of SiO₂ nanoparticles (NPs). The open porosity of samples is increased by adding the amount of nanoparticles but the close and total porosity are decreased.

Abstract: The bead on plate welding specimens with the 1mm thickness was fabricated by Nd:YAG pulsed laser SW-1 . The effects of laser process parameters on the weld dimensions, metallurgical and mechanical properties of weld metal were investigated. The results showed that both weld depth and weld width increase with voltage. Unlike base metal that has coaxial grain structure, weld metal is composed of a dendritic structure. Grain growth in the heat affected zone did not occur. However, ultrafine precipitations were deposited at the HAZ which their size was approximately between 500 nm to microns. All tensile specimens failed in the fusion zone.

Abstract: Nanostructured organic materials have received considerable attention over the past decade. This nanostructure is responsible for their unusual acoustic, thermal, and mechanical properties. One of the most studying of this field is sol-gel polymerization of resorcinol-formaldehyde, followed by organic solvent exchange, supercritical drying. However, the conventional process involves long gelation time, expensive monomer of resorcinol, high cost of supercritical drying device and so on, which makes it some distance away from being promoted to commercial production. In this work, to reduce cost and time, the reaction of novolac resin and hexamine and ambient pressure drying method was used for preparation and drying of organic gel. To reduce time, the polymerization in saturated atmosphere of solvent vapor instead of conventional sol-gel polymerization presented. These nanostructure materials have a nanoporous structure that constructed by colloidal like particles gathered up in filament-shaped. Because of this nanoporosity and structure, these materials have very low fracture energy and could including them as brittle materials. The goal of this research produces these nanostructure materials using novel method and enhances fractural resistance. To gain this proposes, the feasibility of using acrylonitrilebutadiene rubbers (NBR) has been investigated. For studying of morphology and properties of this structure, we used SEM, FTIR and porosimetry analysis. The results shows that the addition of 0.5, 1 and 2 wt% NBR to Novolac nanostructure increased density and decrease the pore volume and pore size.

Abstract: Porous structures of carbon nanotube (CNT) composites with highly accessible surface areas have numerous potential applications such as heterogeneous catalysts and adsorbents. In this study sodium alginate was added to CNTs dispersions as gelling agent. Before being dried, the hydrogels were shaped into bead, disk, and sheet forms. The alginate in the composites was then decomposed by heating up the samples under an inert gas. The morphology of the as-prepared composite was studied by scanning and transmission electron microscopy and the pore size distribution was measured by BJH method. The MWCNT composite showed a density of around 0.08 g/cm³ and a specific surface area of 164 m²/g. The as-synthesized porous composite was examined as an adsorbent to remove methylene blue (MB) from aqueous solutions. Complete removal of MB was observed. The adsorption isotherm and kinetics were also evaluated.