Materials Science Forum Vol. 978

Abstract: Currently, porous SiC ceramics have been a focus of interesting research in the field of porous materials due to their excellent structural properties, high strength, high hardness, and superb mechanical and chemical stabilities even at high temperatures and hostile atmospheres. Porous SiC ceramics have been considered as suitable candidate materials for catalyst supports [1-2], hot gas or molten metal filters [3], high temperature membrane reactors [4], thermal insulating materials [5], gas sensors [6] etc. Porous SiC ceramics are fabricated by various methods including partial sintering [7], carbothermal reduction [8-9], replication or pyrolysis of polymeric sponge [10-12], reaction bonding [13] etc. In all these methods SiC needs to be sintered which requires a very high temperature due to the strong covalent nature of the Si-C bond, selective sintering additives, expensive atmosphere, costly and delicate instrumentation. Processing of porous SiC ceramics at low temperature using a simple technique thus becomes necessary. Bonding of SiC can be done at low temperatures by use of different oxide and non-oxide secondary phases. They include silica, mullite, cordierite, silicon nitride, etc. Various sintering additives are used for the formation of variety of secondary oxide bond phases for formations for porous SiC [14-19] Choice of mullite as a bond for SiC has many advantages. Mullite possesses a high melting point (T_m= 1850°C) and a low oxygen diffusion coefficient (5.6 x 10^-14 m²/sec at 50°C). It has a matching thermal expansion coefficient with SiC (CTE_mullite= 5.3 ×10^-6/K; CTE_SiC = 4.7 ×10^-6/K at RT-1000 °C) and a high strength that can be retained up to a very high temperature. Different sources of aluminum, such as Al₂O₃, Al, AlN, and Al (OH)₃ powders were used for the formation of mullite bonded porous SiC ceramics (MBSC) [20-21]. However, the mullitization temperature of 1550^o C is still necessary. In this work, mullite bonded porous SiC ceramics were fabricated by an in situ reaction-bonding process; the mixture of clay and CaCO₃ were chosen as sintering additives to lower the mullitization reaction between Al₂O₃ and oxidation-derived SiO_2. The effect amount of alumina, sintering temperature and other sintering aids on material property such as porosity/pore size distribution mechanical and micro structural properties of porous oxide bonded SiC ceramics were studied.

Abstract: Energy crisis poses a major challenge in the modern industrial scenario. A critical aspect of the shop floor work includes the welding of dissimilar metal sheets which require the right amount of energy. In order to tackle these challenges, a conservative and energy efficient method are necessary. Recently, automotive industries have been widely adopted the ultrasonic metal welding process for assembling lithium-ion battery packs and its modules. The joining of these dissimilar metals using any other conventional welding process is extremely challenging due to varying physical, chemical, thermal properties, the formation of the heat affected zone and lesser bond strength. However, ultrasonic metal welding yields better quality welds under the influence of optimal parametric conditions. In this research, the weld quality of two dissimilar materials, namely, aluminum (AA1060) with cupronickel (C71500) sheets investigated at different welding time, vibration amplitudes and welding pressures with a fixed ultrasonic frequency of 20 kHz. Experimental results show the tensile shear strength of the weld is maximum at the highest vibration amplitude with a moderate amount of weld pressure and weld time. Additionally, the joint quality and its associated microstructure at the weld region are analyzed by scanning electron microscopy (SEM) to reveal the bond strength with the interlocking feature.

Abstract: Functionally graded materials are prevalent among industries for its low weight compared to alloys. Depending upon the applications ceramic-ceramic materials can be graded to obtain novel functional combination. In a disk, yielding mainly occurs at the root, hence to overcome the yielding problem, Al₂O₃ material was used at the root and graded with different ceramics; as ceramics possess high yield strength. In composites, many methods are available to calculate effective mechanical properties and modified rule of mixture (MROM) is one of these. In MROM only single parameter, stress to strain transfer ratio needs to be identified which in present case was calculated using inverse approach i.e. by comparing Halpin-Tsai model with MROM. Variational formulation method was employed taking radial displacement field as unknown variable. The effective Young’s modulus calculated was then verified with experimental data and good agreement was seen. Further effective yield stress distribution was quantified and plotted to compare with von-Mises stress. Limit elastic speed then obtained was used to rank different ceramic-ceramic graded combinations. Limit speed defines the performance of disk and thus it was chosen as a selection parameter.

Abstract: In this present study, molecular dynamics simulation of creep for ultrafine grain NC Ni specimens with different grain sizes have been carried out under a constant 1 GPa applied load for various creep temperatures to study the dependence of grain growth on creep temperature and grain size during creep process and its influence on creep properties. It is observed that the extent of grain growth in ultrafine grain NC Ni during creep deformation process is more if creep in creep temperature is higher. A noteworthy anomaly, that is NC Ni with smaller grain exhibits better creep property compared to NC Ni with larger grain, is observed in case of higher creep temperatures (i.e. around or greater than 1400K).

Abstract: In this article, molecular dynamics simulations have been performed to study the effect of crack on the tensile strength of a bicrystal of Zr. Bicrystal with a symmetric tilt grain boundary, with crack and without crack, are generated along [0001] tilt axis. This is further subjected to tensile loading and the stress strain response of the bicrystals with and without crack is studied. The strength of the bicrystal with crack is lower than the one without crack.

Abstract: Oil-water separation has become the prime concern for fossil fuel exploration industries. In the present study, superhydrophobic coating on filter paper was prepared to repellent water while allowing oil to flow freely from its porous structures. Coating was generated by solution-casting technique on cellulosic filter paper using silica nanoparticles (SiO₂) along with silane coupler hexadecyltrimethoxysilane (HDTMS). The contact angle was measured, and it has shown 175.1° ± 1.5°, and the tilting angle is 1.5° ± 0.2°. The surface topography of coated and treated samples was also examined. Furthermore, thermal stability of fabricated filter papers was evaluated by annealing at a different range of temperatures (20 °C-220 °C). The pH resistance of the coatings were inspected by immersing the specimens in acidic and alkali solutions (pH 2-13). The mechanical durability was examined by tape-peeling and abrasion tests. Moreover, these samples have shown waterjet impact resistance. Filtration study was performed on coated filter papers using various oil-water mixtures of kerosene-water and petroleum ether-water and results have shown the separation efficiency of 99% and 98.5%, respectively. Thus these filter papers can have potential practical and industrial applications.

Abstract: In this report, graphene sheets used as reinforcements for improvement of anti-corrosion properties have been synthesized by electrochemical intercalation and exfoliation process. The (001) and (002) plane of graphene sheets at a 2θ angle of 13.2 and 26.13 confirmed by X-ray diffraction pattern. High-resolution TEM confirms 8-12 layers of graphene present in the final products. The as-received graphene sheets have been used as reinforcement with copper matrix to synthesize Cu-Gr nanocomposite by electrodeposition method. The results and investigations of Cu-Gr composite thin films deposited from the bath containing 0.1g/L and 0.5g/L graphene concentrations with acidic copper sulfate solution have been compared. The surface morphology and roughness of composites were studied by SEM, AFM and surface profiler. The presence of graphene in Cu-Gr nanocomposite confirmed by EDS analysis. It was observed that the reinforcement particle has increased the mechanical properties of Cu-Gr composite (by 30%) with the addition to the copper matrix. The corrosion resistance of sample was studied by Tafel extrapolation method in standard borate buffer solution. For nanocomposites of 0.5g/L graphene, the values of Tafel constants are, βa=177.37 mv, βc=138.51 mv, Icorr = 9.3165×10-7Amp/cm², Ecorr = -0.051 volts and corrosion rate 0.01028 mm/a as comparison to the corrosion rate of pure electroplated copper of a value of 0.029 mm/a. The corrosion rate of 0.5g/L Cu-Gr composite was found to be decreased by 2.7 times as compared to pure copper thin films. The structure of the films before and after corrosion was also analyzed to co-relate the electrochemical and structural relationship.

Abstract: One of the most important and widely visualized process taking place in nature is condensation. Superhydrophobic surfaces, which facilitates dropwise condensation has been the principal area of research in the last decade or so. Fabrication of superhydrophobic surface can be achieved by either surface modification using mechanical process, surface treatment like coating or by the combination of both. But, the major drawback of coating is its durability and vulnerability. So, in this work we have fabricated a robust surface by means of picosecond laser machining. Apart from being a simple process, this method has an advantage of cutting down the surface fabrication time by several hours as compared to other methods like one-step immersion, electro-deposition, top-down fabrication method, etc. In our work three different work specimens irradiated with different laser power were studied for its surface morphologies by scanning electron microscope (SEM) images and its wettability was measured using contact angle meter. It is found that the wettability of surface changes with different laser power and hence it is possible to control the wettability by adjusting the laser parameters. Condensation experiment was carried out on these different surfaces and its performance was compared with plain surface.

Abstract: Coatings are implemented on engineering metals and alloys to augment the surface properties such as hardness as well as resistance to wear and corrosion. Heat treatments of coated metals/alloys are performed to aid in the progress of the bonding of the coatings to the substrate. During the air cooling process, the difference in the compositions of the coating and the substrate materials causes them to cool at different rates, which leads to straining in them. The paper presents the research on the mathematical investigation to evaluate the residual stresses in coatings caused due to heat treatments and subsequent air cooling. The mathematical modelling is executed to formulate the equations to represent the residual stresses retained in the coatings due to the heat treatments and subsequent air cooling. Air cooling undergoes two stages namely the initial quenching phase and the final cooling phase. During the quenching phase, the strain was expressed by considering the elastic, plastic and thermal strain components. Poisson’s ratio, deviatoric stress differential of the modulus of plasticity, coefficient of thermal expansion and change in temperature are used to express the elastic, plastic and thermal strain components. During the final cooling phase, the strain was expressed by considering only the elastic and thermal stain components, as the plastic staining the coating material generally does not occur during the final cooling phase and occurs only during the initial quenching phase. From the strain components, the residual stresses for the coatings in the x, y and z axis were formulated. Thus, the total residual stress is the sum total of stresses caused during the initial quenching phase and the final cooling phase.

Abstract: The present study deals with impact of gangue amount (Al₂O₃, SiO₂) in iron ores on reduction of its pellets for production of sponge iron. Iron ore pellets were reduced isothermally with noncoking coal fines in the range of 1123 - 1273 K with a time interval of 15, 30,45,60,90 and 120 min. As the temperature rose from 1123 to 1223 K, the reducibility index of iron ore pellets increased and then decreased at temperature 1273 K. All iron ore pellets shows complete reduction at temperatures of 1173 and 1223 K within 120 minutes. The reduction results clearly show that the reducibility of the pellets depends on the initial mineralogy of the ore. It was also observed that the reducibility decreased as gangue content (Al₂O₃ + SiO₂) increases. The activation energy of the pellets decreased from 46.54 and 49.13 kJ/mol when the gangue content increased. The pellets were metallographically characterized before and after reduction to identify phase transformations. Examination of the SEM microphotographs revealed that Whisker shape of iron grains were formed during the reduction process and clear porous structure was observed.