Showing 18 results for Ashrafizadeh
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
A. Azimi Dastgerdi, F. Ashrafizadeh, M. R. Toroghinejad, F. Shahriari , H. Zahraei,
Volume 30, Issue 2 (Dec 2011)
Abstract
In this paper, bare spot defects in hot-dip galvanized sheets were studied in terms of the microstructure and their influence on the corrosion and mechanical properties. Surface characteristics and microstructural features were examined by scanning electron microscopy equipped with energy dispersive spectroscopy microanalysis system. The results showed that the major cause of the bare spots was the lack of wetability of the sheet surface due to contamination, improper heat treatment or chemical composition. Corrosion resistance was evaluated by standard salt spray test. Mechanical properties were examined by tensile testing. The time to red rust was much shorter on the bare spots as compared to other regions, but it appeared that bare spot defects had no significant effect on the mechanical properties of the galvanized steel sheets.
F. Shahriari, F. Ashrafizadeh, A. Saatchi,
Volume 31, Issue 2 (Dec 2012)
Abstract
Although titanium has been recognized for its excellent bio-compatibility with human tissues and good corrosion resistance in some specific environments, little attention has been paid to the surface enrichment of the components by titanium. In this paper, titanium diffusion coating was formed on the surface of Ni-based alloy B-1900 via pack cementation technique and the microstructure of the coatings obtained was studied. Diffusion titanizing was carried out via pack cementation technique at 850 and 950 C for 3 hours in a mixture of commercially pure titanium, Al2O3 and NH4Cl powder. Microstructure, phase composition and concentration profile of the coatings were examined using optical and electron metallography, X-ray diffraction, and glow discharge optical spectroscopy. The results showed that Ti2Ni and AlNi2Ti were the main constituents of the coating. The formation mechanism of the coatings was also evaluated.
E. Sadri, F. Ashrafizadeh, M. Ramazani,
Volume 32, Issue 2 (Dec 2013)
Abstract
In plasma sprayed nanostructured composite coatings with ceramic matrix, the feedstock must consist of nanoparticles of appropriate specifications. In this research, the procedure for production of Cr2O3-Ag agglomerated nanostructured composite powder to produce comosite coatings has been investigated. Nanopowders of Cr2O3 with 0, 2, 5, and 10 volume percentages of silver were dispersed to obtain a homogeneous aqueous dispersion appropriate for spray drying process. In the second stage, Cr2O3-Ag composite powders were produced by agglomeration process. The nanostructured composite powders were, then, used in the atmospheric plasma spray (APS) process to deposit a series of composite coatings for evaluation. The composite powders, with a granulated morphology, had uniform distribution of silver in a ceramic matrix and the coatings were composed of nanoparticles and particles of nano-sized crystallites. Experimental results indicated that presence of nanoparticle zones within the microstructure led to non-uniform porosities formed between splats and these zones. Furthermore, use of nanopowders in the feedstock caused a reduction in lamellae thickness of plasma sprayed coatings.
M.r. Dehnavi, B. Niroumand, F. Ashrafizadeh,
Volume 34, Issue 1 (Journal of Advanced Materials-Spring 2015)
Abstract
Effects of discontinuous ultrasonic treatment on the microstructure, nanoparticle distribution, and mechanical properties of cast Al413-SiCnp nanocomposites were studied. The results showed that discontinuous ultrasonic treatment was more effective in improving the mechanical properties of the cast nanocomposites than the equally timed continuous treatment. The yield and ultimate tensile strengths of Al413-2%SiCnp nanocomposites discontinuously treated for two 20 minute periods increased by about 126% and 100% compared to those of the monolithic sample, respectively. These improvements were about 107% and 94% for the nanocomposites continuously treated for a single 40 minute period. The improvement in the mechanical properties was associated with severe refinement of the microstructure, removal of the remaining gas layers on the particles surfaces, more effective fragmentation of the remaining agglomerates as well as improved wettability and distribution of the reinforcing particles during the first stage of solidification.
E. Rostamizadeh, F. Ashrafizadeh , M. H. Abbasi,
Volume 34, Issue 2 (Journal of Advanced Materials- Summer 2015)
Abstract
this study, MoSi2-TiB2 nanocomposites with 10 and 20 wt.% of TiB2 were synthesized by mechanical alloying through two different methods. In the first method, elemental powders of molybdenum, silicon, titanium and boron were milled together for 60 hours. In the second method, MoSi2 was made by 30-hours milling of Mo and Si. Then, commercial TiB2 was added to the matrix and milling was continued for another 30 hours. Heat treatment was carried out on the resultant specimens at 1000˚C for 60 min. The effect of mechanical alloying on grain size and lattice strain was investigated by Williamson-Hall method using XRD patterns. The mechanical properties of the samples were determined by hardness test. It was found that TiB2 added to MoSi2 increased hardness considerably. Agglomeration process was carried out on the powders to be used in thermal spray process. The morphology and microstructure of the milled powders before and after agglomeration process were studied by SEM. The sphericity and particle size distribution of agglomerated particles were evaluated using Clemex software. The results showed that the nanocomposite powder produced by the first method had a higher quality for thermal spray process due to its higher hardness compared to the second one. It also had adequate particles sphericity.
M. Atapour, M.m. Dana, F. Ashrafizadeh,
Volume 34, Issue 4 (Journal of Advanced Materials-winter 2016)
Abstract
In this investigation, the effect of grain size on the corrosion behavior of 304L stainless steel has been studied. Samples with grain sizes of 0.5, 3 and 12 micrometers were fabricated through formation of strain-induced martensite by 80% cold rolling of the stainless steel sheets at -15 °C and its reversion to austenite during annealing at 900 °C for 1, 5 and 180 min. The corrosion behavior of samples with different grain sizes was investigated by cyclic polarization experiments and immersion tests in 0.1 M hydrochloric acid (HCl). The polarisation tests showed no differences in uniform corrosion rates of the samples. The results of the cyclic polarisation and immersion tests showed that decreasing the grain size improved the pitting corrosion resistance from 290 mVAg/Agcl for grain size of 12 micrometers to 420 mVAg/Agcl for grain size of 0.5 micrometers.
S. Khorsand, K. Raeissi, F. Ashrafizadeh,
Volume 34, Issue 4 (Journal of Advanced Materials-winter 2016)
Abstract
Super-hydrophobic nickel and nickel-cobalt alloy coatings with micro-nano structure were successfully electrodeposited on copper substrates with one and two steps electrodeposition. Surface morphology, wettability and corrosion
resistance were characterized by scanning electron microscopy, water contact angle measurements, electrochemical impedanc spectroscopy (EIS) and potentiodynamic polarization curves. The results showed that the wettability of the micro-nano Ni and Ni-Co films varied from super-hydrophilicity to super-hydrophobicity by exposure of the surface to air at room temperature. The corrosion results revealed the positive effect of hydrophobicity on corrosion resistance of Ni coating (~10 times) and Ni-Co coating (~100 times) in comparison with their fresh coatings. The results showed that super-hydrophobic nickel coating had higher corrosion resistance than super-hydrophobic nickel-cobalt coating.
S. Pourmohamadi, M. Atapour, F. Ashrafizadeh,
Volume 35, Issue 4 (Journal of Advanced Materials-Winter 2017)
Abstract
In this study, a Cr-modified NiAl coating was fabricated by weld cladding technique using Gas- Tungsten Arc Welding (GTAW) process on 310 steel. Chemical composition and microstructure of the coating was studied by X-Ray Diffraction (XRD), optical microscopy and scanning electron microscopy equipped with an Energy Dispersive Spectroscopy (EDS). The wear behavior of the coated steel was examined through pin-on-disc tests at ambient temperature and 400 °C. The results showed that the hardness of coated steel increased remarkably due to the formation of Cr-modified NiAl on the surface. Furthermore, the wear experiments showed that the presence of Cr-modified NiAl coating caused significant improvement in wear resistance of cladding 310 steel at both ambient temperature and 400 °C. These results were discussed based on the wear mechanism obtained from examination of the worn surfaces using SEM.
Mr S. A. Razavi, Mr S. F. Ashrafizadeh,
Volume 36, Issue 2 (Journal of Advanced Materials-Summer 2017)
Abstract
Age hardening processes cause a wide range of changes in 17-4 PH stainless steel properties. Aging at 480ºC for 1 hour (A480-1) and aging at 620ºC for 4 hours (A620-4) are two most applicable heat treatment processes for this alloy. Not only the studies on fatigue behavior of this alloy in these two heat treatment conditions are few, but also the methods of fatigue test were mostly axial. In this study, after microstructure studies, hardness and tension tests, fatigue behavior at A480-1 and A620-4 conditions were evaluated by using a rotational bending fatigue test machine. Tension results showed that yield strength and ultimate tensile strength of A480-1 specimens were 40 percent more than A620-4 specimens. However, elongation of A620-4 specimens was 30 percent more than A480-1 specimens. Fatigue results revealed the endurance limit of aged specimens is 50 MPa more than overaged specimens. Overall results showed that A480-1 condition specimens are more resistant to fatigue than A620-4 condition specimens.
M. Falsafein, F. Ashrafizadeh,
Volume 37, Issue 2 (Journal of Advanced Materials-Summer 2018)
Abstract
Nitride coatings with excellent hardness and wear resistance have been deposited by physical vapor deposition (PVD) in recent years. For most applications, the load bearing and adhesion of coatings are very important and can determine the life and performance of the final components. In this study, CrN/CrAlN nanostructured coatings with different thicknesses and numberes of layers were deposited on the stainless steel AISI 420 and hot-work tool steel by cathodic arc evaporation. Nanoindentation, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) were used for the structural characterization and estimation of stress in the coatings. Adhesion of coatings was evaluated by scratch adhesion and VDI 3198 Rockwell tests. The results revealed the high values of compressive residual stress in the physical vapor deposited coatings, in the range of 500 to 1800 MPa, with a detrimental effect on coating adhesion. Load bearing capacity was observed to be dependent on the thickness and adhesion of coating, reaching the maximum at an optimum thickness. Overall, the results proved that the type of steel substrate could have a significant influence on the coating adhesion.
M. Ghasemian Malakshah, F. Ashrafizadeh, A. Eslami, F. Fadaeifard,
Volume 38, Issue 2 (Journal of Advanced Materials-Summer 2019)
Abstract
Since martensitic precipitation hardened 17-4pH stainless steel has been widely used in corrosive environments, evaluation of its corrosion fatigue behavior is important. In this research, after microstructural studies, mechanical, corrosion, fatigue and corrosion fatigue tests were performed on 17-4pH specimens. Fatigue and corrosion fatigue tests were carried out at the stress ratio of -1 and the stress frequency of 0.42 Hz (to increase the effect of corrosive solution), and corrosion fatigue tests were conducted in 3.5% NaCl solution, an environment similar to corrosive sea water. Fatigue limit of 17-4pH stainless steel was 700 MPa in air and 415 MPa in corrosive environment. Comparing the S-N curves of this alloy at the optimal heat treatment cycle in two modes of fatigue and corrosion fatigue revealed the reduction of fatigue limit up to 40 % in the presence of corrosive environment. This reduction was due to the effect of observed corrosion pits on the surface and Damaged passive layer.
P. Verdi, S. M. Monirvaghefi, F. Ashrafizadeh,
Volume 40, Issue 3 (Journal of Advanced Materials-Fall 2021)
Abstract
Regarding to the low rate of conventional Ni-P electroless plating method that needs more time to make a coating on the substrate surface, a new technique called “substrate local heating” was introduced based on the temperature parameter modification and its advantages were expressed and compared to the conventional electroless plating technique (temperature=90°C, pH=4.7). In order to provide necessary equipment making this approach practicable, electrical resistance was used as the heating source, and air injection and cooling water circulation were employed to control the solution temperature near the substrate and in the bulk solution, respectively. Considering the heater power (1000 W), the substrate and bulk temperatures were about 190°C and 80°C, respectively. This novel method could enhance the plating rate up to 32 µm/h which was about 60% greater than that of the conventional method, 20 µm/h. Moreover, benefits such as local plating, reduction of production costs, and formation of functionally graded coatings (FGC) can be achieved.
