Showing 9 results for M. Salehi
M. Salehi and A.s. Ayatollahi,
Volume 15, Issue 2 (1-1997)
Abstract
In this research the effect of volume and morphology of eutectic carbides on tribological behaviour of Ni-Hard 4 cast irons have been investigated. Therefore, as a result of the fact that the carbon content effects the carbides morphology of Ni-hard cast irons, the chemical compositions of five different specimens were kept constant with the exception of the carbon content, which was varied from 2.3 to 3.2%. The general composition of these alloys was selected according to Group D Class I of ASTM A532 standard. The microstructure and carbides morphology of homogenized specimens were examined by microhardness testings and metallographic examinations. Metallographic techniques include optical and scanning electron microscopy have been also used to characterize the predominant wear mechanism. The Ni-hard 4 cast iron surfaces worn by a process of plastic deformation and fracture to produce wear debris. SEM examination of worn surface topography and wear debris shows the tendency to plastic deformation and wear decreased as the carbon content of the specimen increased.
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.
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.
M. Salehi,
Volume 18, Issue 1 (4-1999)
Abstract
In this research, tribological behavior of Ti-Ni-P intermetallic coatings on titanium substrates have been investigated under dry reciprocating conditions. Hardness profile testing results exhibit that high surface hardness has been attained and static indentation result shows that the intermetallic coating has better adhesion strength than the conventional ceramic coatings. In this respect, these coatings have been able to protect the substrate under different loading and tribological conditions. The results show that Ti-Ni-P intermetallic coatings produced by diffusion processes have good adhesion to titanium substrate, offer a low coefficient of friction and prevent the galling of titanium to the steel counterface. The effect of increasing thickness was to increase the load-bearing capacity of the coating. Experimental findings also suggest that Ti-Ni-P intermetallic coatings would contribute to the expansion of industrial applications of titanium alloys.
M. H. Fathi, Gh. Feizi, Sb. Moosavi, Gh. Gahanshahi, M. Salehi, A. Saatchi and V. Mortazavi,
Volume 20, Issue 1 (7-2001)
Abstract
Hydroxyapatite coatings have been used on metallic substrates in a variety of applications, including modifying the surface of human implants, bone osseointegration and biological fixation. In this paper, the effects of various kinds of metallic substrate on clinical and pathological results of in vivo tests are presented. Four kinds of endodontic implants i.e, stainless steel, cobalt base alloy, plasma sprayed hydroxyapatite coated stainless steel, plasma sprayed hydroxyapatite coated cobalt base alloy were prapared and implanted in mandibular canine of
cats. After a healing period of 4 months, investigation by SEM and histopathological interpretation and evaluation showed significant differences in tissue response and osseointegration between coated and non-coated metallic implants. It was concluded that the results were affected by the kind of metallic substrate .
Keywords: Hydroxyapatite coating, Dental endodontic implant, Osseointegration, Corrosion, Stainless steel,
Cobalt base alloy
M. Shamanian, A. Saatchi, M. Salehi and T. H North,
Volume 21, Issue 2 (1-2003)
Abstract
The metallurgical and mechanical properties of Ti6Al4V/(WC-Co) friction welds have ben investigated. The microstructure close to the bondline comprised a mixture of acicular and equiaxed α plus β phases. The diffusion of elements in the welded specimens has been detected. The fracture strengths of Ti6Al4V/(WC-Co) friction welds markedly improved when the cobalt content in the (WC-Co) carbide substrate increased.
During the three-point bend testing of Ti6Al4V/WC-6wt.%Co welds, the crack initiated at the bondline region at the periphery of the weld and then propagated into the brittle (WC-6wt.%Co) substrate, while with the Ti6Al4V/WC-11 wt.%Co and Ti6Al4V/WC-24wt.%Co welds, the crack initiated and propagated at the bondline region.
Keywords: Friction welding, Ti6Al4V alloy, Cemented tungsten carbide, Microstructure, Fracture strength
M. H. Enayati and M. Salehi,
Volume 25, Issue 2 (1-2007)
Abstract
Fabrication and characterization of aluminum matrix composites containing different volume fractions of Ni3Al powder (5-40 Vol%) were investigated. Ni3Al powder was produced by mechanical alloying of elemental nickel and aluminum powder mixture. Al-Ni3Al composite parts were prepared using a powder metallurgy route involving two stages Al and Ni3Al powder mixtures were first compacted under 500MPa and then hot-pressed under 250MPa at 420 oC for 10min. The microstructure and hardness of consolidated parts were investigated by x-ray diffractometery, optical and scanning electron microscopy and
hardness measurements. Results showed that consolidated Al-Ni3Al samples included no significant porosity with a nearly uniform distribution of Ni3Al particles. Additionally, structural examinations showed that no significant reaction between Ni3Al and aluminum matrix occurred during sintering process. Al-Ni3Al composites exhibited a higher hardness value compared with pure aluminum sample prepared under identical conditions. The hardness value of Al-Ni3Al composites increased linearly as Ni3Al content increased.
S. R. Bakhshi, M. Salehi, H. Edris, G. H. Borhani,
Volume 29, Issue 1 (Jun 2010)
Abstract
In this study, Mo-14Si-10B and Mo-57Si-10B (at%) elemental powders were separately milled using an attritor mill. Mechanically alloyed powders were agglomerated and annealed. Then, powders of Mo-Si-B as alloyed (with composites) and agglomerated (without composites) were plasma sprayed onto plain carbon steels. The samples, both coated and non-coated, were subjected to isothermal oxidation tests. Metallurgical characteristics of powders and coatings were evaluated by SEM and XRD. Plasma-sprayed Mo-Si-B coatings (with phases of MoSi2, Mo5Si3, MoB and Mo5SiB2) greatly improved the oxidation resistance of the plain steel substrates, but plasma-sprayed Mo-Si-B coatings (without any phases) did not significantly improve the oxidation rate of substrates. Also, the kinetics and composition of the oxide-scale have been found to depend on the alloy composition.
M. Babashahi, M.h.enayati, M. Salehi, A. Monshi,
Volume 29, Issue 1 (Jun 2010)
Abstract
In the present study phase transformation of silicon and silica during milling in different atmospheres was investigated. The silicon powder was subjected to high energy ball milling in ammonia (25%) atmosphere. The milled powder was subsequently annealed at 1200 ◦C for 1 hour. In another test a mixture of AlN and amorphous silica (micro silica) was subjected to high energy ball milling. The milled powder mixture was subsequently annealed at 1200 ◦C for 2 hours. Phase analysis of the as milled and annealed powders was performed by X-ray diffractometery (XRD). Powder morphology was also examined using a scanning electron microscope (SEM). Results showed that ball milling of silicon in ammonia formed an amorphous phase which transformed to quartz on further milling. After annealing quartz, cristobalite and another oxide phase called O phases were developed on XRD patterns. Ball milling of AlN and amorphous silica led to the transformation of amorphous silica to stishovite phase. This process was completed after annealing..
