Showing 7 results for Rafizadeh
M. Shamanian, M. Salehi and F. Ashrafizadeh,
Volume 16, Issue 2 (1-1998)
Abstract
The use of Fe-Al intermetallic compound coatings has been investigated in order to improve the tribological behaviour of carbon tool steel. The coatings were formed by a pack cementation process and subsequently diffusion annealing at 900˚C in an argon controlled atmosphere. The optimum diffusion time was selected on the basis of optimum thickness and tribological behaviour.
The microstructure and the phases developed on the surface were identified by metallography, microhardness, X-ray diffraction (XRD), microanalysis (EDX) and glow discharge optical spectroscopy (GDOS) techniques. Experimental results indicate that a three layer coating is formed on the surface of the aluminized specimens, the outermost layer being identified as Fe2Al5 and the underlying layers as FeAl and Fe3Al. A two layer coating was formed on the surface of the aluminized and subsequently diffusion annealed specimen at the optimum time. The FeAl and Fe3Al have been formed on and below the surface, respectively.
The results from wear testing indicate that these coatings improve the wear and frictional behaviour of carbon steel significantly. The predominant wear mechanisms of diffusion annealed specimens were identified as delamination and oxidative wear.
F. Ashrafizadeh, M. R. Toroghinezhad,
Volume 17, Issue 1 (7-1998)
Abstract
In this study carburizing and boronizing processes were applied to powder metallurgy steel specimens and the mechanical and tribological properties of the substrate and coatings were evaluated under various process conditions.
The specimens, made from industrial test pieces, were carburized in a powder pack for a duration of 2-5 hrs at 850-950 ˚C. Similar specimens were pack boronized for 4 hrs at 950 ˚C. The effect of austenitization-quench treatment was also investigated on some specimens. The wear tests were carried out by means of a pin-on-disc tribotester against ball bearing steel.
The results indicate that by appropriate selection of process parameters it is possible to obtain high wear resistance together with moderate toughness. Boride layers with hardness values of 1700HV are properly formed on PM samples. The wear resistance, therefore, is significantly increased with practically no reduction in impact resistance. It is concluded that boronizing treatment can be more suitable for some PM parts under tribological conditions.
S. R. Bakhsi, M. Salehi, F. Ashrafizadeh,
Volume 17, Issue 2 (4-1998)
Abstract
A study for optimizing of siliconizing and borosiliconizing processes on carbon steels has been carried out. The process parameters, i.e, time and powder mixture, were considered for optimization of the case depth, surface quality and the hardness profile.
Time and temperature of the processes were 4 hr and 950˚C, respectively. Powder mixture in siliconizing process was 2.5% ferrosilicon, 2.5% NH4Cl and Al2O3, while the optimum simultaneous borosiliconizing process was obtained in a mixture of 90% boronizing powder and 10% siliconizing powder. These powders had already been optimized, individually. This is a depth of layer of about 150μm and maximum hardness value of 600HV0.1 in siliconized steels, and a depth of layer of about 100μm and a hardness value of greater than 3000 HV0.1 in borosiliconized steels. Microscopical tests by light microscopes, XRD and EDAX analyses indicated Fe3Si and Fe5Si3 phases within the surface layers of siliconized steel, and B(FeSi)3, Fe4.9Si2B, FeSi, FeB and Fe2B phases within the surface layers of borosiliconized steels.
R. Mozaffarinia, F. Ashrafizadeh, M. A. Golozar,
Volume 22, Issue 2 (1-2004)
Abstract
The purpose of this work was to production of ceramic thin films by using of Sol-Gel process. For this purpose deposition of SiO2 on substrates of soda-lime glasses has been carried out. Coating treatments on prepared specimen were conducted in a Sol solution by means of dipping at various times. After drying and performing appropriate heat treatment on each sample, the thickness of coated layer was measured by means of roughness method. Some of the specimens were also exposed to heat and chemical environment to evaluate the coating resistance in such media. SEM examination and EDAX and XRD analysis of coating layers was also conducted on some samples.
The results indicated that by Sol-Gel method, it is easily possible to achieve thin layers in the scale of one hundredth micron meter. Any change of the thickness layer on the surface is negligible and the quality of the coating is excellent. Also, experiments indicated that deposited coatings by Sol-Gel process, are stable and give enough durability in various environments.
M. Talebi, E. Shirani, and M. Ashrafizadeh,
Volume 25, Issue 2 (1-2007)
Abstract
In this study, turbulent flow around a tube bundle in non-orthogonal grid is simulated using the Large Eddy Simulation (LES) technique and parallelization of fully coupled Navier – Stokes (NS) equations. To model the small eddies, the Smagorinsky and a mixed model was used. This model represents the effect of dissipation and the grid-scale and subgrid-scale interactions. The fully coupled NS equations with the multiblock method was parallelized. Parallelization of the computer code was accomplished by splitting the calculation domain into several subdomains and using different processors in such a way that the computational work was equally distributed among processors. The discretized governing equations are second order in time and in space and the pressure is calculated by Momentum Interpolation Method (MIM) to prevent the checkerboard problem. The results are obtained for the turbulent flow over five parallel tube rows. The computational efficiency, flow patterns, and flow properties are also determined. The results showed high parallelization efficiency and high speed up for the computer code. The flow characteristics were determined and compared with experimental results which showed good agreement. Also, the results showed that the mixed model is better than the Smagorinsky model for evaluation of flow characteristics and lift and drag forces on tubes.
S. Vahabzadeh, M. A. Golozar, F. Ashrafizadeh and A. Ghasemi,
Volume 27, Issue 2 (1-2009)
Abstract
S. M. Zandi, A. Rafizadeh,
Volume 37, Issue 1 (9-2018)
Abstract
In this article, a meshless method based on exponential basis functions (EBFs) is presented to simulate the harmonic waves with moving free-surfaces generated by the piston-type wave maker. Accordingly, velocity potential is adopted in a Mixed Eulerian-Lagrangian (MEL) approach. Boundary conditions are met through a point-wise collocation approach. In order to update the geometry in the simulation time, the free surface points are only moved vertically. To reduce the reflection in the wave flume, a damping zone is added at the far end opposite to the wave maker, where the velocity is modified by adding an artificial damping term. The results indicated the ability of this numerical method in simulating free surface flow problems like non-linear waves with a good accuracy, as well as suitable performances and the least run time calculation.
