Sharif Digital Repository

Modeling of the static recrystallization in deformed copper specimens with different initial grain sizes is carried out based on a previous dislocation-grain size interaction model and a Monte Carlo simulation. From the dislocation-grain size interaction model, the stored energy of the deformed copper is calculated considering the interaction of the dislocations due to the different initial grain sizes. Then, utilizing the stored energy and Monte Carlo simulation the kinetic of recrystallization and recrystallized grain sizes are obtained. The JMAK plots of the modeling results show that, in conditions of 2D modeling and site-saturated nucleation, the Avrami exponent is 2 ± 0.1. The time for... 

The prediction of material microstructure is of great interest to the material designers since the property and performance of materials depend strongly on their microstructures. In this research the Monte Carlo method and grain growth phenomenon have been used to predict the limiting grain size in the presence of second phase particles. The results showed a good agreement with the previous published results predicted by the analytical models. It was found that the lattice orientation parameter, Q, strongly affects the kinetic of the grain growth. The experimental and theoretical results of limiting grain size predicted by Monte Carlo method showed that by decreasing the value of Q the... 

The high temperature superconductor thin films Cu1-xTl xBa2Ca3Cu4O12-δ (Cu1-xTlx- 1234) are post-annealed in a nitrogen atmosphere. The zero-resistivity critical temperature (Tc(R ≤ 0)) of these thin films is increased from 92.3 to 104K. The grain size is enhanced and their morphology is improved with the post-annealing. The enlargement of grain size is linked to fluctuation-induced conductivity (FIC) in the light of Aslamazov-Larkin (AL) theory. The FIC measurements have shown that the cross-over of three-dimensional (3D) to two-dimensional (2D) behaviour of fluctuations is shifted to higher temperature values with an increase of post-annealing temperature. These results have shown that the... 

Some mechanical and metallurgical properties of hollow and solid long forged products are compared. The metallurgical properties include such micro- and macro-structural characteristics as the grain size and grain flow patterns. Mechanical evaluation was performed by means of hardness testing. Some theoretical analyses were also carried out. The results indicate that the hollow or mandrel forged products possess better properties. Both the mechanical and metallurgical properties are more uniform and homogeneous through the thickness direction in such products. By contrast, in the solid forged parts, there is a gradient in the micro- and macro-structural properties from the surface to the... 

Kinetics of oxidation of MgO-C refractory bricks containing 14.3% graphite, 80.9% magnesia, and 4.8% phenolic resin is investigated comprehensively. Effect of temperature and grain size distribution on the rate of oxidation of graphite is evaluated by application of a mathematical model developed on the basis of shrinking core/progressive conversion regime to the gas-solid processes involved. Incorporation of the experimental data into the mathematical model indicates that a mixed controlling mechanism governs the oxidation rate. Three activation energies were recognized: (a) 68 kJ/mol for chemical adsorption of gas on the surface of the graphite flakes, (b) 22 kJ/mol for pore diffusion of... 

Although, the optical flow sensors which are used in optical mouse have high resolution in measuring displacement, their error refrain us from a precise and reliable measurement. Besides, these sensors require calibration based on the surface. Their error has different sources and the most important is surface texture in micro level. In this research, we have worked to find surface conditions on which sensor measurement is more precise. For this aim, we used an 800 DPI low cost optical flow sensor. For making different surface textures and grains, we printed different textures with 600 and 1200DPI resolution on white paper with certain length. Then we used optical flow sensor for measuring... 

The effect of combined electromagnetic-ultrasonic fields evaluated on grain refinement. Cavitation induced by the combination of technologies suggested as major mechanism for grain refinement. A numerical simulation performed predicting the cavitation regions in the molten AA5754 aluminum alloy. It was concluded that the cavitation phenomenon occurs near the electromagnetic and ultrasonic sources. The observed acoustic streaming induced by ultrasonic horn is more intensive than the electromagnetic one. The ultrasonic streaming could transport small bubbles into the bulk rapidly. These micro-bubbles collapsed due to acoustic vibrations where the resulting micro-jets were strong enough to... 

Crystal-size distribution (CSD) is one of the most important parameters in sugar production. The objective is to grow crystals of uniform sizes or narrow CSD. CSD appears to be determined by the growth-rate history of the crystals and the relative supersaturation (SS) of the solution from which crystals growth takes place. Three methods for preparation of nucleation seeds were described and used for industrial crystallization of raw and white sugars; these are wet milling filtered sugar (ML), agitating saturated solution (AS) and powdered sugars (PD). Rosin-Rammler (RR) and mathematical models were adopted to investigate CSD and the uniformity of the produced crystals. Higher uniformity... 

Effects of cooling slope angle and the temperature of molten metal on the globular structure of M2 high speed steel after holding at the semisolid state have been investigated. The globular structure was achieved by pouring the molten metal at 1595 °C on the ceramic cooling slope with the length of 200 mm and the angle of 25°. The globular structure of M2 high speed steel in the form of rolled-annealed and as cast condition after holding at semisolid state has been achieved. The size of globular grains of cooling slope sample was smaller than that of the rolled-annealed and as cast samples. Solid particles of rolled-annealed sample after holding at semisolid state had better roundness... 

Many researchers favor the mesh topology as the underlying topology of the communication infrastructure of modern SoCs because of its regularity and layout efficiency. However, variability in size and shape of modules used in systems-on-chip has resulted in the use of irregular meshes for practical NoCs. In this paper, we propose a deadlock free routing algorithm for irregular mesh NoCs. Experimental results confirm that the proposed algorithm exhibits a better performance in terms of message latency and power consumption compared to other known routing algorithms for irregular mesh NoCs  

A new model is developed for the structure of nanocrystalline materials. Based on the developed model, a new approach for investigating the effect of grain size on the elastic moduli of nanocrystalline materials is introduced. The predictions of the model are strongly correlated with the experimental results reported in the existing literature  

The accumulative roll bonding (ARB) process was carried out on a high purity alloy (AA1100) and a particle containing aluminium alloy (AA3003) for up to eight cycles. The electron backscattered diffraction (EBSD) method was utilised to investigate the microstructural and microtextural evolution in ARB processed sheets. The results indicate that the lack of second phase particles in pure aluminium hinders grain refinement and leads to the formation of unrefined bands, which results in the increase of the overall texture intensity and the development of a strong texture. Asubmicrometre grain structure in this alloy develops at the final stages of the process. It was also found that the... 

In the present article, a new model for inverse Hall-Petch relation in nanocrystalline materials has been proposed. It is assumed that lattice distortion along grain boundaries can cause internal stresses and high internal stresses along grain boundaries can promote the grain boundary yielding. The designed model was then verified using the nanocrystalline-copper data. The minimum grain size for inverse Hall-Petch relation is determined to be about 11 nm for Cu. © 2008 ASM International  

In present research, nanocrystalline Fe100-xSix (x = 6.5, 10, 13.5, 20 and 25 at.%) and Fe83.5Si13.5Nb3 alloy powders were prepared by mechanical alloying using high-energy ball milling. The resulting powders mainly consist of micron-sized particles with an average grain size of less than 20 nm. According to the XRD test results, by increasing the milling time and/or the Si content the lattice parameter decreases and the internal microstrain increases. In addition, the specific saturation magnetization diminishes as Si content increases. The coercive forces of the as-milled nanocrystalline powders are much higher than those of corresponding Fe-Si bulk alloys with a minimum at 13.5 at.% Si.... 

In assessing of the effect of redundant strain factor on the microstructure inhomogeneity of the drawn wire after annealing, the Upper Bound Model based on spherical velocity field and a computer simulation based on Monte Carlo Model are utilized. Using the models, the strain, stored energy due to deformation and grain size distribution of the wires after different deformation and annealing conditions are calculated. From the achieved results the deformation and microstructure inhomogeneity are computed. It is observed that the deformation inhomogeneity as well as microstructure inhomogeneity is increased with increasing the parameter Δ and redundant strain factor. Also, the results show... 

In this paper the finite element method and Monte Carlo model are coupled to simulate the grain size distribution of inhomogeneously deformed copper wire after annealing. The wire flat rolling process is chosen as an inhomogeneous deformation. The finite element method is utilized to calculate the stored energy distribution due to deformation and is then used in Monte Carlo model to obtain the distribution of grain size. A new relationship is developed to simulate the nucleation in recrystallization phenomenon. The modeling results are compared with the experimental results and an acceptable agreement is achieved. © 2006 Elsevier B.V. All rights reserved  

With the development of computing systems for data processing, the image processing and image analyzing methods have been developed on the basis of pixel assessment. These methods can analyze and detect the images by assigning a value for each pixel and using the matrices calculations. In the present research, two methods have been used to assess the simulated material microstructures. In the first method, the vertices of the microstructure are counted to determine accurately the mean grain size by the Euler's relationship, while in the second method, the image processing and image analyzing methods are utilized to assess the microstructure image. To verify the accuracies of the methods... 

In this paper, the internal ballistics of a solid rocket motor (SRM) including a blast tube is investigated, numerically. Effects of the blast tube presence on the performance of the SRM are studied in detail using unsteady quasi one-dimensional conservation equations. These equations are discretized and solved using upwind Roe's scheme. Any two-dimensional grain configuration can be accounted for if an appropriate geometrical input file is generated using a grain analysis program. The results are presented for several blast tube geometries  

Sorption capacity as well as sorption kinetics of oil onto four different expanded perlites with different physical and surface properties were studied. In order to meticulously measure the amount of oil to be sorbed onto the adsorbents used in this study both static and dynamic methods were employed. It would be worth noting that the adsorbent, i.e., perlite can spread on the oil and float on the surface thanks to its low density. The variation of the amount of oil sorbed onto the adsorbents with time was recorded and the weight of adsorbent was monitored at each specified time. The experimental results showed that grain sizes with high surface area can sorb oil to be spread on water... 

In this investigation, fine Fe85Si10Ni5 (at.%) powders with a nanocrystalline structure were prepared by high energy ball milling. The effects of milling time on microstructure and magnetic properties of Fe85Si10Ni5 powders were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). The optimum soft magnetic properties (maximum saturation magnetization and minimum coercivity) were obtained in alloy powders with an average grain size of 8 nm after 70 h milling. © 2005 Elsevier B.V. All rights reserved