Sharif Digital Repository

High strength Al-AlN composites were synthesized via high-energy milling and sintering technique. Al-X wt.% AlN (X = 0, 2.5, 5 and 10) composite powders were milled in a planetary ball mill for 25 h. Morphology, particle size distribution, crystallite size, micro-strain, and microhardness of milled powders were studied. Ball-milled powders were degassed at 400 °C for 30 min. After uniaxial cold compaction, composite compacts were sintered at 650 °C for 20, 30 and 60 min under N2 atmosphere. Effects of reinforcement content, degassing treatment and sintering time on the sinterability of powders were investigated. The results revealed that the sinterability was degraded by increasing the... 

In this study, a method for enhancing low-contrast images is proposed. This method, called Gaussian mixture model-based contrast enhancement (GMMCE), brings into play the Gaussian mixture modelling of histograms to model the content of the images. On the basis of the fact that each homogeneous area in natural images has a Gaussian-shaped histogram, it decomposes the narrow histogram of low-contrast images into a set of scaled and shifted Gaussians. The individual histograms are then stretched by increasing their variance parameters, and are diffused on the entire histogram by scattering their mean parameters, to build a broad version of the histogram. The number of Gaussians as well as their... 

High-energy milling technique was used to synthesize Al-10 wt.%AlN-nanostructured composite powder in a planetary ball-mill under argon atmosphere up to 25 h. To show the role of AlN particles, process was conducted for monolithic aluminum. The changes in powder characteristics were investigated by time. Microstructure of powders was studied after different milling times by scanning electron microscope (SEM). The morphological evolutions showed that relative equiaxed powder could be synthesized after 25 h milling. Structural analysis was performed by X-ray diffraction method (XRD) to determine the grain sizes and lattice strain. Furthermore, particle size analysis (PSA) revealed the... 

The compressibility behavior of Al-AlN nanostructured composite powder with different amount of reinforcement content was studied. The composite powder was synthesized by blending and high-energy milling process for 25 h. Williamson-Hall method was applied to determine the crystallite size after milling process. To investigate the role of reinforcement particles in consolidation of composite powders, monolithic aluminum powder was examined. Samples were made at different pressures and relationships were established between the compaction pressure and the density of the compacts. The modified Heckel equation was used to assume the pressure effect on yield strength and then was compared with... 

Among all active flow control methods, EHD, MHD and EMHD are the only methods which operate on the basis of body force induction on flow field. The EHD plasma actuator is the proper method which has been used in various flow control applications recently. In this paper, the effects of different body force fields on different domains have been studied for separation control on NACA 0021 and the results have been discussed. The airflow velocity has been assumed to be 35 m s-1 at a post-stall angle of attack of 23°. Three different domains have been used around the airfoil to investigate body forces with different strengths and directions and those which give the best result in separation... 

Electrophoretic technique was used to deposit micro- and nano-sized aluminum nitride coatings on stainless steel surfaces by using a well-dispersed stable suspension produced by addition of AlN powder plus a small amount of iodine to ethanol. Parabolic regime governed the deposition. Electrophoretic deposition for 240 s at 100 V resulted in formation of a uniformly dense film on the top, but a porous inhomogeneous layer at the bottom. This was attributed to fast deposition of coarse particles and/or agglomerates at large electric fields. After drying, micro-sized particles led to a uniform crack-free interface while nano-particles resulted in fragmented non-cohesive layers. Weight loss...