Sharif Digital Repository

To the best of our knowledge, this work presents the first successful effort to fabricate and study nanostructured Ni-based composite coatings using the electrophoretic deposition method with nanostructured SiO2 particles. In this work, Ni/SiO2 nanoparticle composite coatings were prepared by electrophoretic deposition (EPD) [1] and their hardness, wear and corrosion resistances [2] were examined. After studying the morphology of the coatings and finding the optimum conditions for uniform coating, in order to improve the mechanical properties as well as resistance to corrosion, sintering was performed. The Ni/SiO2 nanocomposite coatings show excellent hardness (∼376 HV), reduced Young's... 

An experimental study of wear characteristics of electroless Ni-10% P coating sliding against hard AISI 52100 steel pin is investigated. Experiments are carried out at room and 550°C temperatures. Heat treatment effects on tribological behavior of this coating are studied. The wear surface and the microstructure of the coatings are analyzed using optical microscopy, scanning electron microscopy, energy dispersion analysis X-ray, and microhardness testing equipment. It is observed that the forming of continuous oxide film on contacting surfaces of pin and disk improves wear resistance and decreases friction coefficient of the Ni-10% P coating. The results indicate that the wear resistance of... 

Carbide morphologies of white cast iron containing 22% Cr and 10-12% tungsten with different carbon contents (2.34-3.20. wt.%) were investigated. Results indicated that for the as-cast alloys with no heat treatments, the addition of carbon changes the morphology of carbides during air-cooling in the presence of tungsten. Light microscopy analysis revealed that for an alloy with 2.3. wt% carbon, chromium carbides possess coarse gray appearance (GA). Increasing the carbon content reduced the coarse GA zones volume fraction while a finer GA zones emerged. The coexistence of coarse and fine GA phases came to an end at 2.8. wt% carbon, at which only fine GA zones spread throughout the chromium... 

In this study, high-vanadium austenitic manganese steel (HV-AMS) alloys and the standard Hadfield steel were investigated. The microstructure of these high-vanadium alloyed Hadfield steels was studied thoroughly using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and was compared to the Hadfield steel. The hardness and unnotched Charpy impact strength of HV-AMS alloys and Hadfield steel were examined at ambient temperature in the as-cast and heat-treated conditions. A pin-on-disk wear test at linear speed of 10. m/min and a 55. N normal load was employed to evaluate the wear behavior of both steel samples. Microstructural results showed that varying... 

This study focuses on the effect of co-deposition of PTFE and/or MoS 2 particles on the morphology, wear, and corrosion properties of electroless nickel coating. The composite coating of EN-PTFE-MoS 2 was heat treated at different temperatures for hardness investigations. The surface morphology of coatings was characterized by scanning electron microscopy. Pin-on-disk and potentiodynamic polarization tests were used to study the tribological and corrosion properties of the coatings, respectively. Results of hardness analysis revealed that the hardness of electroless nickel coatings was increased by the heat treatment, and its maximum was gained at 400°C. Wear investigations showed that... 

The surface defluorination of Teflon in powdery form was performed using a chemical treatment. The reaction parameters including the reaction time, sodium, naphthalene concentrations were optimized using a Taguchi method to obtain maximum functionality on the particles surface. The surface functionality of the treated particles was analyzed by FTIR, energy dispersive X-ray analysis (EDX) and surface energy. Both treated (g-PTFE) and untreated (PTFE) Teflon were added to polyamide 66 (PA66) at various loadings up to 6 wt%. Mechanical, differential scanning calorimetry (DSC) and tribological analyses for different PA66/Teflon composites were carried out. The chemical treatment enhanced the... 

The present study was an attempt to examine the effects of carbon and cellulose fibers on the tribological characteristics of rubber-based friction materials (RBFMs). A fiber free RBFM as a reference material and a series of fiber included RBFMs at different volume fractions were prepared by two-roll mill. The friction tests were per-formed at different sliding velocities and various drum temperatures. The mechanical properties and surface microstructure of friction specimens were also examined. It was revealed that the carbon fiber infiuences slightly the coefficient of friction (COF) of RBFM but it improves the wear resistance and the fade behavior considerably. It reduces the drum... 

To perform a long lasting, crack-free repair welding on ultrahigh strength steels, the filler metal must be chosen and applied properly. Avoiding several short-term repairs or replacements, the repaired weldment should reveal comparative characteristics such as wear resistance, toughness and hardness to base metal. In the present study, a novel functionally graded material have been introduced to obtain enhanced wear resistance and hardness at surface as well as improved fracture toughness at fusion line of repaired weldments. A comparative study of wear resistance of repaired weld metals has been carried out by pin-on-disk apparatus at 5N normal load and 0.14ms-1 sliding speed. Fracture... 

In this study, the effects of different concentrations of SiO2 nanosized particles in the bath on deposition rate, surface morphology and wear behavior of Ni–P–SiO2 composite coatings were investigated. The rate of coating deposition was influenced by the incorporation of SiO2 particles. The observations of microstructural morphology were performed with field emission scanning electron microscopy. The amount of deposited SiO2 was examined by X-ray energy dispersive analysis. The results showed that for the coating produced at 12.5 g/L of nanoparticles, the amount of co-deposited SiO2 nanoparticles and microhardness reached their maximal... 

In the present study, regarding the theoretical and practical aspects of nanoparticle capture in liquid-state processing of aluminum composite, different volume fractions of TiB 2 and TiO 2 nanopowders were incorporated into aluminum alloy via stir casting method. Hardness and sliding wear test were carried out to evaluate the mechanical properties of composites. The effects of wear load and reinforcement content on wear rate and friction coefficient of composites were examined. Microstructural studied showed that particle distribution in A356- TiB 2 composites was more favorable than that of the A356- TiO 2 samples. Results showed that nanoparticles were partially captured by aluminum... 

Compounding electron beam irradiated polytetrafluoroethylene (PTFE or Teflon) powder with silicone rubber produced silicone rubber/PTFE composites with desired physical properties. PTFE powder was exposed to electron beam irradiation at various doses and characterized by FTIR, DSC and contact angle measurements. Irradiation of PTFE with high energy electron beam induced chain scission reactions. Irradiated PTFE showed higher degree of crystallization and lower melting point with increasing absorbed dose. Number average molecular weight of irradiated PTFE was reduced significantly at higher absorbed doses. Formation of polar groups on the surface of irradiated PTFE powder was detected by FTIR... 

In this study, the effects of simultaneous co-deposition of polytetrafluoroethylene (PTFE) and MoS 2 particles on tribological properties of electroless nickel (EN) coating were studied. The influences of specimen orientation and heat treatment on EN-PTFE-MoS 2 composite coatings were also investigated. Scanning electron microscopy was used to study the morphology of coatings and the distributions of the lubricant particles in the deposits. Chemical analyses of coatings were done by electron dispersive spectrometry. The phases of the coatings were identified by X-ray diffraction utilizing CuKα radiation. Wear and friction properties of the coatings were also determined by pin-on-disk wear... 

Controlled graphitization has become known as a practical method for improvement of wear resistance and machining properties in steels. In this paper, the effect of heat treatment on microstructure of CK45 steel has been investigated. Austenitising was carried out at 920 °C for 5 h. Besides, isothermal transformation was conducted at 750 °C in the time range of 1-20 h. In this work, full potential carbon resource was tried to be used around samples as a factor to prevent the burning of the limited carbon in steel and also to increase the percentage of sample surface carbon in order to improve wear capability and machining. The microstructure of the steel considerably changes by this heat... 

It is known that the thermomechanical processing is one of the most important techniques for improving quality and mechanical properties of microalloyed steels. In this paper, the main parameters of hot forging (preheat temperature, strain and post-forging cooling rate) on the primary austenite grain size of vanadium microalloyed steel (30MSV6) were studied. From this investigation, it was found that increasing preheat temperature from 1150 °C to 1300 °C will result in a decrease in grain size number. Furthermore, it has shown that as the strain increases, the austenite grain size number increases, as is evident for the two cooling rates of 2.5 °C/s and 1.5 °C/s for primary austenite.... 

In this study, a novel nanocomposite thin film of Zn–SiO2 is considered. The thin film is a viable alternative for higher abrasion-resistant coatings. DLS technique revealed that the nanoparticle size is to be below 10 nm, and FE-SEM showed particle size to be below 17 nm in the obtained coating. The coating was found to be highly adhesive with an amorphous structure and hardness value above 1000HV. Corrosion resistance studies using linear polarization technique revealed that this unique nanocomposite has a lower corrosion rate than hot-dip galvanized steel at higher positive potentials. A conclusive mechanism for corrosion and erosion improvement has been proposed. Graphical Abstract:... 

Sliding friction between a pavement and tire is an important concern in traffic safety. The British pendulum test has been used worldwide to evaluate friction characteristics of pavement surfaces. However, because of considerable differences in apparatus, procedures, and operation, significant variability can occur for evaluations of British pendulum number (BPN). In this investigation, a direct shear test (DST) device is modified and proposed to determine the sliding friction coefficient between tire and pavement surface under dry and wet conditions. Dissipated energy values obtained from DST were compared with evaluations of BPN, and a high correlation was obtained. Tests were done using... 

Hybrid Cu-SiC composites have been highly considered in order to achieve a combination of electrical and thermal properties along with high strength and wear resistance. However, limited investigations have ever been conducted over the effects of using hybrid (combination of nano and micro size) particles on the wear resistance behavior of these composites. Hence, in the present study, Cu-SiC nanocomposite with 4 vol% nanosize and 4 vol% microsize SiC, and Cu-SiC microcomposite with 8 vol% micro- SiC were fabricated through mechanical milling and hot pressing process. Results revealed the homogeneous dispersion of SiC particles in the matrix, high densification, and ultrafine-grain matrix... 

In the present study, the wear behaviour of Cu-Al2O3 composites and Cu-Al alloys has been investigated. The experiment involved casting of Cu-Al alloys with 0•37, 1, 2 and 3 wt-% of aluminium under inert gas atmosphere. The composites were produced by internal oxidation of alloys at 950°C for 10 h in presence of Fe2O3 and Al 2O3 powders mixture. The microstructures of composites were studied using SEM and atomic force microscopy. To identify wear behaviour of specimens, dry sliding pin-on-disk wear tests were conducted according to ASTM G99-95a standard. The normal loads of 20, 30, and 40 N were applied on specimens during wear tests. The sliding speed and distances were selected as 0•5 m... 

The present study focuses on simultaneous influence of graphene nanoplatelets (GNP) and hydroxyapatite (HAp) nanopowder on microstructural, wear, tensile and biofunctional behavior of UHMWPE based nanocomposites used in biomedical applications, with the aim to utilize GNP's mechanical strength and wear resistance, while benefitting from HAp's biocompatibility at the same time. 0.1, 0.5 and 1 wt% GNP with 10 wt% optimized concentration of HAp were added to the UHMWPE matrix through an easy two-step approach consisting of solvent mixing and ultrasonication in ethanol as a liquid media. The dried nanocomposite samples of powder were then hot pressed at an optimized temperature and pressure to... 

In this study, SiC/Ti–Cu nanocomposite was fabricated by mechanical alloying and sintering process. Effects of SiC nano-reinforcement on phase transformation, microstructure and tribological and antibacterial properties Ti–Cu intermetallic alloy were studied. The microstructure of the powders and sintered materials was investigated using X-ray diffraction, and scanning/transmission electron microscopy. The results exhibited the formation of major TiCu and TiCu 4 , and minor Ti 2 Cu and Ti 2 Cu 3 nanocrystalline phases in the sintered Ti–Cu and SiC/Ti–Cu samples. With the addition of the nanoparticles, the amount of TiCu 4 phase increased. Reinforcing Ti–Cu intermetallic alloy by SiC...