Iranian Journal of Materials Science and Engineering

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The continuity and thickness of the coating layer, are the most important factors in wetting properties and strength of carbon fibers. These factors are crucial in the quality of metal matrix composites made with carbon fibers. In this research the Polyacrylonitrail base carbon fibers have been nickel coated with 0.2, 0.5, 0.8 and 11 ,u in thickness, by the electroless method. The effect of the thickness of nickel coating on surface condition and also the tensile strength of the carbon fibers has been investigated. The study of surface condition of the coated carbon fibers by SEM showed that the nickel coating at the thickness of about 0.5 pin has the best continuity oil the carbon fibers. The results of tensile tests of carbon fibers coated with different thickness of nickel showed that increasing the thickness of coating layer decreases the overall strength of fibers.

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A large number of reinforced concrete structures subjected to chloride ions. Two basicapproaches for preventing corrosion of reinforcing steel embedded in concrete are: Increasing theconsolidation of concrete and using different coating on rebars. In present research steel rebarsare coated in different ways: a) 40 µm of zinc electroplated on steel rebar b) Zinc powder withepoxy paste (zinc rich). The rebars were placed in a macrocell design according to ASTM G109-92. Concrete operations were done with mixture designs of high and normal strength concrete.The results show corrosion decrease of zinc coated rebars.

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Enhancing the properties of dental resin composites is of interest to researchers. The objective of the present investigation was to improve the strength and fracture toughness of dental composites via addition of silicon carbide whiskers and substitution of commonly used filler materials with stabilized zirconia ceramic powder. It was also intended to study the effect of powder- to- whisker ratio on mechanical properties of the resultant composites. The flexural strength and fracture toughness of composite samples with different whiskers loadings were measured. It was found that addition of whiskers to the composites enhances the mechanical properties of the composites. The strength and fracture toughness increased by increasing the amount of whiskers. The flexural strength of a composite having 60wt% whisker and 10wt% zirconia powder was about 210 MPa while that of the composite having only 60wt% ceramic powder was about 110 MPa. The microstructural examinations revealed that reinforcing mechanism was whiskers pull-out as well as crack deflection.

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In this research the influence of Ti contents on the amounts of inclusions formation and mechanical properties of a high alloy high strength steel, C300, has been investigated. For this purpose several bars were casted under the same solidification conditions, but different amounts of Ti element. All the seven casted bars were homogenized at 1200°C for a period of 2 hours. Then, they were immediately hot rolled after homogenization so that the out rolling temperature was kept in the range of 1000-1200° C. The specimens were then solution annealed at 820°C for hour and finally they were aged for a period of 3 hours at 500°C. The samples were subjected to tensile, impact and hardness tests in order to relate the variation in volume percent of inclusions due to different amount of Ti, to mechanical properties. The results showed that by increasing the amount of Ti a serious decline in toughness properties of the alloy due to increase in inclusion population occurred. So this research provides a very useful information about the relation between volume fraction of inclusions and mechanical properties of a C300 high strength steel.

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Abstract: Strength at elevated temperatures and thermal shock resistance of austempered ductile irons at high temperatures has been less intentioned, because of instability of ausferrite phase. In this research the tensile properties of this iron and pearlitic ductile cast iron have been investigated by short time high temperature tensile tests. Also thermal shock tests were done at the molten lead bath at 1000 􀁱C . In these experiments, at first samples were immersed partially in the molten lead bath for 25 seconds and then either cooled in air or quenched in water. Results of short time high temperature tensile and thermal shock tests showed that ADI samples have higher strength and shock resistance than the pearlitic ductile samples.

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Abstract: The effect of phase development on peel strength of alumina-copper metalized joint has been investigated. The alumina-copper joint was prepared in three stages. The alumina substrate was, first, metalized at 1500°C in H2-furnace by a new formulation. In the second step, a nickel layer was electroplated on the metalized layer with approximately 10µm thickness. Finally, copper strips were bonded to metalized alumina with Ag-Cu (72-28) filler metal. The peel strength of the joint was 9.5±0.5 Kg/cm which shows approximately 30% increase in comparison to previous works. By study of fracture surface and crack propagation path, it has been concluded that this increase is due to the formation of more spinel phase.

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Abstract: The use of alkali-activated cementitious materials especially over the past decades has significantly been increased. The goal of this research is to investigate the effects of silica modulus and alkali concentration on alkali-activation of blast-furnace slag. In this research, the most important physical characteristics of cementitious systems, i.e. the 28-day compressive strength and final setting time, were studied by changing influencing parameters such as silica modulus, i.e. SiO2/Na2O, (0.44, 0.52, 0.60, and 0.68) and Na2O concentration (4, 6, 8 and 10% by weight of dry binder) at a constant water-to-dry binder ratio of 0.25. Final setting time of the studied systems varies in the range between 55-386 minutes. The obtained results show that systems cured at an atmosphere of more than 95% relative humidity at room temperature exhibit relatively high 28-day compressive strengths up to 107 MPa.

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Abstract: The purpose of this study is to produce scarf joint through explosive welding process (EXW). The scarf weld is a process in which the final bond interface is oblique. With applying the explosive welding technique, this joint can create a metallic bond between similar or dissimilar metals. In this study, chamfered end of aluminum and copper plates were joined explosively and named scarf joint, employing changes in chamfered angle at different stand-off distance and explosive loading. The geometry of scarf joint enables consideration of both flyer and base plate thickness and explosive loading and the effects on mechanical properties of interface such as bond shear strength and micro-hardness can be investigated. Mathematical models developed for the interface properties of scarf joint to make relationship between the bond shear strength and explosive loading ratio. To check the adequacy of developed models, mechanical properties of interface, such as bond shear strength, predicted and compared with actual values in explosive cladding process. The results show reasonable agreement with theoretical predictions. Consequently, mathematical model which is based on scarf joints, can predict bond shear strength of cladding metals under desired explosive loading and flyer plate thickness

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The effects of lower bainite volume fraction on tensile and impact properties of D6AC ultrahigh strength steel were studied in the current work. To obtain mixed microstructures containing martensite and different volume fractions of the lower bainite, specimens were austenitized at 910° C, then quenched in a salt bath of 330°C for different holding times, finally quenched in oil. In order to obtain fully martensitic and bainitic microstructures, direct oil quenching and isothermal transformation heat treatment for 24 hours were used respectively. All specimens were double tempered at 200°C for 2 hours per tempered. Microstructures were examined by optical and scanning electron microscopes. Fracture morphologies were studied by scanning electron microscopy (SEM). Results showed that both yield and ultimate tensile strength generally decreased with an increase in volume fraction of lower bainite. However, a few exceptions were observed in the mixed microstructures containing 12% lower bainite, showing a higher strength than the fully martensitic microstructure. This can be explained on the basis of two factors. The first is an increase in the strength of martensite due to the partitioning of the prior austenite grains by lower bainite resulting in the refinement of martensite substructures. The second is a plastic constraint effect leading to an enhanced strength of lower bainite by the surrounding relatively rigid martensite. Charpy V-notch impact energy and ductility is improved with increasing the volume fraction of lower bainite.

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Abstract: The linear expansion, early-age compressive strength and setting times of the binary mixtures of gypsum and Portland cement clinkers of relatively low C3A-contents were investigated. For this reason, type 1, 2, and 5 of Portland cement-clinkers were selected and a number of binary mixtures were designed. At relatively lower percentages of gypsum (about 5%), the early strength behavior is improved. Results obtained for compressive strength of mixtures with 5% gypsum confirm the possibility of achieving 28- and 90-day compressive strengths up to values higher than 100 MPa and 130 MPa, respectively. At relatively higher percentages of gypsum (more than 25%), excessive expansion caused by ettringite formation results in the formation of micro-cracks effectively weakening the strength behavior. The work suggests that type S expansive cements could be produced from Portland cement clinkers of relatively low C3Acontents.

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Metakaolinite-based geopolymer has been synthesized at about 25 °C from metakaolin which has been calcined in different temperatures (600-900 °C) and different Na2O/SiO2 ratio activator (0.3-1.1). Compressive strength and microstructure of cement pastes after 7-28 days curing at ambient temperature were measured. Compressive strength tests on the samples showed that the sample made with calcined kaolin at 700 °C and molar ratio of 0.6 has highest average compressive strength of 32 MPa after 28 days of curing. Evaluation of infrared spectroscopy (FTIR) and microstructure showed that geopolymer cement developed and new molecular structure established

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Abstract:In recent years, there have been many attempts to improve the properties of dental amalgam. The aim of the present investigation was fabrication and characterization of dental amalgams containing TiO2 nanoparticles and evaluation of their compressive strength, antibacterial and corrosion behavior. In this experimental research, TiO2 nanoparticles (TiO2 NPs) were added to reference amalgam alloy powder and then, dental amalgam was prepared. In order to investigate the effect of TiO2 NPs on properties of dental amalgam, 0, 0.5, 1, 2 and 3 wt. % of TiO2 NPs were added to amalgam alloy powder and the prepared composite powder was triturated by a given percent of mercury. Xray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) techniques were used to characterize the prepared specimens. Potentiodynamic polarization corrosion tests were performed in the Normal Saline (0.9 wt. % NaCl) Solutions as electrolytes at 37°C. The results showed that the corrosion behavior of the dental amalgam with 0.5 or 1 wt. % TiO2 NPs is similar to the corrosion behavior of the reference amalgam, while with increasing the weight percent of TiO2 NPs, the corrosion rate increases. Also, the results of this investigation indicated that adding TiO2 NPs in amounts of up to 1 wt. % to amalgam alloy powder improve compressive strength of dental amalgam and has no destructive influence on its corrosion behavior. As well as, according to antibacterial results, TiO2 NPs can increase the biocompatibility and antibacterial activity of dental amalgam. The results of present study suggest that amalgam/ TiO2 NPs nanocomposite with 1% of TiO2 NPs could be regarded as a biocompatible and bioactive dental material that provide better characters for dental applications.

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The effect of titanium dioxide addition on bonding strength of CaO-P2O5 -Na 2O-TiO2glass-ceramic system was investigated as a coating on titanium substrate. Thus, different amounts of TiO2 (2, 3.5 and 5mol %) were added to the base glass batch composition. The prepared glaze slips were applied on the substrate by dip coating method, dried and then heat treated at various temperatures. After that, bonding strength of the glass- substrates was determined via shear stress testing method. The de-bonded interfaces were analyzed by scanning electron microscopy (SEM). According to these results, the 5 mol% TiO 2 containing coating showed the best bonding strength, comparing with the other coatings. The bioactivity of the coated samples was investigated by soaking them in simulated body fluid (SBF). The surface of the samples was studied using SEM and X-Ray microprobe and it was observed that an apatite layer was grown on their surface

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The mechanical characterization of short E- glass fiber reinforced, graphite and sintered bronze filled epoxy composite was carried out in this study. The aim of the present study was to develop tribological engineering material. In this study the flexural strength, theoretical and experimental density, Hardness and Impact strength of composites was investigated experimentally. The results showed that the increased percentage of graphite (10 to 15%Vol) and Eglass fiber (10 to 15%Vol) enhanced flexural strength (149 MPa) of the composite and the maximum flexural modulus (13.3 GPa and 13.1 GPa) was obtained for composite C2 and C5 respectively. Maximum hardness (84 on L scale) and impact energy (90 Joule) was obtained for the composite C6 with increased percentage of glass fiber and graphite filler. The metallurgical electron microscopic images were discussed to interpret the effect of graphite and sintered bronze on mechanical characterization of composite

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In the present study, the effect of post-rolling annealing heat treatment on the formation of intermetallic compounds between Al-Cu strips, in the presence of nickel coating on the Cu strips, was investigated. In addition, the effect of post-rolling annealing and intermetallic compounds on the bond strength of Al-Cu strips was evaluated. In order to prepare samples, Cu strips were coated with nickel by electroplating process. After surface preparing, Cu strips were placed between two Al strips and roll bonded. This method is used for producing Al-Ni-Cu composites. Then the samples were annealed at 773K for 2 h. The formation of intermetallic compounds was studied using energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Also, in order to investigate bond strength of Al-Cu after post-rolling annealing heat treatment, samples were produced using nickel powder and nickel coating. Then bond strength of strips was investigated using peeling test. The results revealed that by post-rolling annealing of layers, the bond strength between Al-Cu strips decreases dramatically.

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This article addresses the interplay between heat of hydration and physico-mechanical properties of calcium sulfate hemi-hydrate in the presence of retarding additives such as citric and malic acids and sodium citrate. The heat of hydration was measured using a semi-isothermal calorimeter. Results proved that citric and malic acids had superior impact on hydration and mechanical properties. While the concentration of additives was increasing, the maximum heat of hydration was decreasing from 56.15 cal/g.min for blank sample to 33 cal/g.min for high concentrations of citric and malic acids. Consequently, the measured time to this maximum heat of hydration and thus the induction period were increased significantly from 5 to 105 min. Mechanical results indicated that the increase in the amounts of additive led to the reduction of the compressive strength from 16.25 MPa in the blank sample up to 74% for the highest concentration of malic acid

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Nowadays, Ni-free austenitic stainless steels are being developed rapidly and high price of nickel is one of the most important motivations for this development. At present research a new FeCrMn steel was designed and produced based on Fe-Cr-Mn-C system. Comparative studies on microstructure and high temperature mechanical properties of  new steel and AISI 316 steel were done. The results showed that new FeCrMn developed steel has single austenite phase microstructure, and its tensile strength and toughness were higher than those of 316 steel at 25, 200,350 and 500°C. In contrast with 316 steel, the new FeCrMn steel did not show strain induced transformation and dynamic strain aging phenomena during tensile tests that represented higher austenite stability of new developed steel. Lower density and higher strength of the new steel caused higher specific strength in comparison with the 316 one that can be considered as an important advantage in structural applications but in less corrosive environment

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