Sharif Digital Repository

In this paper, an introduction of the finite element approach to microstructure based modelling is provided, and the primary and secondary dendrite arm spacings of A356 alloy in the solidification process are simulated. The simulated results of dendrite morphology and the experimental measurements are presented and compared with the investigations of other researchers, which confirmed the accuracy of this model in its ability to predict the dendrite arm spacing. Each of the length scales, including silicon rod diameter and spacing, is discussed in detail. Analytical equations are generated for the length scales and incorporated in the Sharif University Technology academic software for the... 

The process through which neurons are labeled is a key methodological choice in measuring neuron morphology. However, little is known about how this choice may bias measurements. To quantify this bias we compare the extracted morphology of neurons collected from the same rodent species, experimental condition, gender distribution, age distribution, brain region and putative cell type, but obtained with 19 distinct staining methods. We found strong biases on measured features of morphology. These were largest in features related to the coverage of the dendritic tree (e.g., the total dendritic tree length). Understanding measurement biases is crucial for interpreting morphological data  

In this study, the permeability for interdendritic liquid flow through equiaxial mushy zone has been modeled and experimentally measured. In the present work, by applying a virtual dendrite in a micro-domain and solving Navier-Stokes equation, flow pattern around the dendrite has been obtained and then by applying Darcy's law to this 3D domain the permeability has been determined. In this micro-model the influence of solid fraction and geometry of dendrites have been assessed. Numerically determined values of permeabilities have been analyzed by the use of SPSS statistical software. Then an experimental method is used to measure the permeability for flow through equiaxial mushy zone of Pb-Sn... 

In this work, effective parameters of SIMA process to obtain non dendritic microstructure in A356 alloy were investigated. In addition, the effect of SIMA process on the evolution of morphology of silicon and intermetallic phases in this alloy was studied. Microstructure images obtained from optical microscopy and SEM observation showed that increase in plastic work up to 40% and then holding of samples in the semi solid state at temperature of 580°C, causes that primary dendritic structure changes to non dendritic, fine and globular structure, but optimum reheating time completely depended on initial thickness of samples. If all parameters of SIMA process are the same, the grain boundaries... 

In this investigation, the permeability of interdendritic liquid flow through the equiaxial mushy zone has been modelled for Pb-Sn alloys based on experimental measurements. In the present work by solving Navier-Stokes equation, the flow pattern around the equiaxed dendrite has been obtained and then permeability has been determined by applying Darcy's law. Numerical determined values of permeabilities have been analysed by the use of Statistical Package for the Social Sciences (SPSS) statistical software. Then an experimental method has been used to measure the permeability for flow through equiaxial mushy zone of Pb-Sn alloys. Results show that increasing the solid fraction and... 

In this research the effects of cold deformation and heating to the semi-solid temperature on microstructure and mechanical properties of cast dendritic and non-dendritic structures of A356 alloy were investigated. To produce the non-dendritic samples, the semi-solid slurry was obtained by electromagnetic stirring and rheoforged and then the samples were heated to semi-solid temperature. In order to impose the deformation to the dendritic and non-dendritic samples, multidirectional forging process was used. Non-dendritic samples were deformed with applying one to three passes of the multidirectional forging and then were kept at the semi-solid range of temperature again. Microstructural and... 

To improve the efficiency of electrochemical processes for environmental remediation, we present a new type of hybrid nanomaterials based on leaf-like copper-based quaternary transition metals and spongy monolayer graphene. To demonstrate the functionality of the hybrid electrocatalyst, fast and competent electrooxidation of water and glucose is shown. The mechanism of improved catalysis is ascribed to the synergetic catalytic effect of quaternary Cu-Ni-Fe-Co alloy with dendritic morphology along with the highly conductive and spongy structure of the graphene monolayer. It is shown that water oxidation can be performed at a low overpotential of 315 mV to reach a current denisty of 100 mA... 

This paper presents the results obtained and the deductions made from a series of microstructural studies and mechanical tests involving gray cast iron which was sand cast using a variety of modules. The effect of cooling rate on the primary dendrite arm spacing (DAS), secondary dendrite arm spacing (SDAS), thickness of ferrite-cementite layer (λe) and the hardness (HB) were evaluated. Results show that the both DAS and SDAS and also λe are highly dependent on the cooling rate, and they decreases as the cooling rate increases. More attempts were also done to correlate the HB with DAS, SDAS and λe. It was found that HB increases as DAS, SDAS and λe decreases  

A method for joining metals in the semisolid state is presented. A model alloy Sn-15%Pb was used to demonstrate the concept. By presented process, dendritic microstructure of the weld zone can be avoided. Moreover, near-weld zone of the cold worked substrates which is affected by heat would have a globular structure due to a thermomechanical treatment. The two substrates were heated up locally in the joint line to the semisolid temperature range. At this point a stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Localized mechanical properties of different zones were examined using Shear Punch Test (SPT), showing a good strength in the weld... 

A numerical model has been developed for the determination of liquid flow permeability through columnar dendrite during growth and segregation in Al-Si mushy alloys. The model is inclusive of two stages, first numerical evolution of the dendrite shape during growth, and second numerical determination of the permeability. Simulation results shown which Si concentration by transform of dendrite shape dendrite could reduce of the interdendritic liquid permeability. © 2005 Elsevier Ltd. All rights reserved  

The dendritic structure of a cast ZA27 alloy can be transformed into a globular structure, if it is cold worked prior to being held in a semi-solid condition. The globular or the equiaxed particles are surrounded by the lower melting matrix. The dendritic structure was swaged and recrystallised prior to holding in a semi-solid state in this investigation. The semi-solid holding of the alloy at temperatures above and below that of peritectic reaction was carried out for various lengths of time. It was shown that the liquid fraction is decreased to below the peritectic temperature which leads to a reduction of lubrication between the solid globules and an increasing deformation force. Holding... 

A novel electrode consisting of 3D porous nickel‒cobalt‒copper sulfide dendritic structures is synthesized, in which, for the first time ternary Ni–Co–Cu foam is constructed through hydrogen bubble template and followed by sulfidization via a hydrothermal reaction in thiourea. The 3D, porous Ni–Co–Cu dendritic sulfide electrode exhibits a high specific capacitance of 1203.75 F g−1 (0.963 F cm−2) at current of 1.0 mA and excellent cycling stability, excellent ratability along with high cycle stability. An asymmetric supercapacitor (ASC) using dendritic sulfide structures and reduced electro-etched carbon fiber paper (RECF) as the positive and negative electrodes, respectively is developed.... 

In this study, in order to compare effect of unidirectional compression and rolling on final microstructure of strain induced melt activated (SIMA) A356 aluminum alloy, rectangular samples with dimensions of 3cm×5cm in area and 1cm in thickness and cylindrical specimens with 2.5cm in diameter and 1cm in length, have been prepared for rolling and compressing processes, respectively. Then, these samples were plastically deformed at a same strain in ambient temperature. Afterward, the strained samples were cut into equal quarters. In the next stage, to produce globular microstructure, these specimens were partially remelted in 580°C for different times. Results obtained from light microscopy... 

In the present work, a mathematical model was developed based on finite difference method to predict the microporosity distribution in A356 aluminum alloy casting. Heat, mass, and gas conservation equations were solved in this model. Moreover, Darcy's equation was considered in the mushy zone. Results show that the distribution and concentration of microporosities in cast parts vary with both cooling rate and initial gas content. Simulation results were compared with experimental data where proportionally good agreement with experimental results was found. Finally, a complex cast part was simulated presenting the ability of the model to predict the porosities in industrial cast parts  

This paper addresses the factors affecting the mechanical properties of dissimilar resistance spot welds between Nimonic 263 and Hastelloy X nickel-based superalloys. The fusion zone (FZ) of the dissimilar weld displayed higher hardness values compared to the base metals which can be attributed to (i) the formation of Mo-rich carbide in the interdendritic zone due to positive segregation behavior of Mo and C during non-equilibrium solidification of the weld, (ii) the enhanced solid solution strengthening due to mixing of the base metals, and (iii) the formation of ultra-fine dendritic structure in the FZ due to ultra-fast cooling rate of the resistance spot welding. Formation of...