Journal of Advanced Materials in Engineering (Esteghlal)

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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.

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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.

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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.

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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.

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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

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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

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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.

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In this paper, properties of slab deformation in sizing press mill as one of the slab reduction processes in hot rolling mills have been evaluated using the elastoviscoplastic finite element method with explicit formulation. Effect of prarameters such as initial slab width and thickness, reduction, feed pitch, and anvil speed on factors such as dogbone formation, head and tail fishtail profile, width necking at the leading end of slab, and slab edge quality have been studied. Furthermore, a comparison has been made between the two common width reduction methods, i.e. Vertical Rolling (Edging) and sizing Press, in order to determine their differences and the efficiency of each process. The amount of width return (back spread), one of the most important factors related to width reduction efficiency and also slab formation after the first horizontal rolling pass, has been evaluated. Also, in order to validate the applied finite element method, the results obtained have been compared with experimental ones found in the literature. The results show that deformation in sizing press is more favourable and that its efficiency is better than that of the vertical rolling mill.

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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..

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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.

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The addition of ZrO2 particles to the HA coating has received considerable attention because ZrO2 particles increase the bonding strength between HA coating and substrate. In this study, nanostructured hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) coatings were prepared by a sol–gel method. It was found that at 950ºC, the dominant phases were HA and tetragonal (t)-zirconia in 3YSZ, cubic (c)-zirconia in 8 YSZ and t-c-Zirconia in 5YSZ phases with the small amounts of β-tricalcium phosphate (β-TCP) and CaZrO3. The crystallite size of the coating was about ~20-30 nm for tetragonal and cubic zirconia grain size and 40-80 nm for hydroxyapatite grain size. Crack-free and homogeneous HA/YSZ composite coatings were obtained with no observable defects. In vitro evaluation in 0.9% NaCl showed that Ca2+ dissolution rate of composite coatings was lower than that of pure HA coatings. The decrease in electrochemical performance of these coated samples in comparison with the uncoated type 316L St.St could be associated with chloride ion and water penetration into the coating, transport of ions through the coating, and the subsequent electrochemical reactions at the coating–metal interface.

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In the present work, thermal and mechanical behaviors of phenolic resin are investigated. This polymer can be used as a matrix for carbon-carbon composites. To find out the best heating process, five different cycles are used for curing the polymer and flexural strength of the specimens are obtained. The cycle with maximum strength is used for the next steps. Then, the oxidation behavior of specimens is studied at different temperatures. The results show that the polymer can withstand temperature about 350°C without significant weight changes. Carbonization of phenolic resin is studied by four different cycles at 1100°C. Oxidation of carbon obtained from carbonization cycle is analyzed extensively and shows no weight change until 550°C. The microstructure of specimens is also investigated by SEM. By additining SiC micro particles to phenolic polymer, the strength change is achieved.

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Carbon fiber composite is one of the most important materials in aerospace engineering applications. For fabrication of this composite, optimum polymerization and carbonization cycles of phenolic resin were obtained [1]. Then, carbon/phenolic composite was fabricated by mixing different weight percentages of T700 carbon fiber with phenolic resin, and the flexural strength of specimens was examined.The samples were pyrolyzed at 1100°C to form high temperature phenolic matrix. Because of high porosity of samples, the composite was impregnated to increase the density and reduce porosity. The maximum flexural strength of samples was obtained with 40 wt. % of fiber. With addition of TiO2 and ZrO2 nanoparticles to carbon/phenolic composite, thermal and mechanical improvement was measured. The samples were examined by ablation test and microstructures of composites were analyzed by SEM.

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In this study, electrical wire explosion has been used to produce aluminum carbon nanotube (Al-CNT) nanocomposite particles in acetone medium. In order to synthesize Al-CNT nanocomposites, initially, CNTs were ultrasonically dispersed. Then, aluminum wire was exploded in this medium. Synthesized samples were characterized by Fourier Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM) methods. The results exhibited formation of spherical nanoparticles in the medium. The average diameter of nanoparticles was 4 nm. Moreover, attained nanoparticles remained stable in acetone. Results revealed a good interaction between aluminum nanoparticles and CNTs in this medium. It is concluded that acetone is a suitable medium for synthesizing Al-CNT nanocomposite as appropriate dispersion of Al-CNT nanoparticles can be achieved in this medium.

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In this research, investigation of the microstructure and magnetic properties of doped barium hexaferrite with cobalt, chromium and tin with BaCo_xCr_xSn_xFe_12-3xO₁₉ (x=0.3,0.5) formula, was performed using solid state method. Phase and structural investigation by X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy respectively, confirmed the formation of barium hexaferrites single phase without the presence of non-magnetic secondary phase after heat treatment for 5 h at temperature of 1000 °C. Also, according to scanning electron microscopy (SEM) images, morphology of particles was perfectly hexagonal with average particle size 200-250 nm. Based on magnetic parameters measured by Vibrating Sample Magnetometer (VSM), both samples were soft magnetic and the highest saturation magnetization was obtained for the sample with composition of BaCo_0.3Cr_0.3Sn_0.3Fe_11.1O₁₉. The values of saturation magnetization (M_s) and the coercivity (H_c) were 42.21 emu/g and 656 Oe respectively for this compound.

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