JOURNAL OF NEW MATERIALS
Year:2015 | Volume:5 | Issue:3 (19)|Papers Count:13

Silicon carbide (SiC) nano particles with high strength, hardness and electrochemical stability, are used as an ideal material in manufacturing of composites. In this study the nickel- phosphorous/ nano silicon carbide composite coating were successfully deposited on Al6061 aluminum alloy by electro less coating process. Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the coating properties. Vickers hardness measurement technique was employed to investigate the hardness of the composite coatings which contain silicon carbide nano particles and ordinary nickel- phosphorous coatings. The tribological properties of the coatings were investigated using pin on disk method. To investigate the roughness of coatings surfaces, roughness testing has been applied. The results showed that incorporation of silicon carbide particles in composite coating enhanced the hardness, roughness of surfaces, wear resistance and friction coefficient of the composite coatings. These improvements could be attributed to the superior mechanical strength of the silicon carbide nano particles in the coating.

In this study, Ni-P/Nano TiO2 coating was applied with a commercial electroless nickel bath on an aluminum substrate and various characteristics of the coating were investigated. The effects of SDS surfactant were also observed. Next the effects of Thiourea stabilizer on the coating were studied with two parameters: TiO2 content in the solution and optimized speed stirrer. Finally by using stabilizer and surfactant simultaneously, the effects of them on the morphology and micro-hardness were analyzed and compared to previous coatings. Results show that using commercial electroless nickel bath with no additives is not appropriate for applying TiO2 Nano particles and will be unstable after a short time. By adding SDS surfactant, the stability was improved slightly but micro-hardness was decreased considerably (345 HV), the reason is attributed to cauliflower morphology with high porosity structure. By adding Thiourea stabilizer, the stability was increased and at the same time, micro-hardness was improved up to a maximum quantity (792 HV). Also, the deposition rate and TiO2 content in the coating were measured 19 mm/h and 3.8 wt% respectively, which are the maximum values among all the coatings. It was also observed that using stabilizer and surfactant simultaneously, will reduce the quality of the coating.

In this research, poly (3-alkylthiophene) (p3AT) nanoparticles coated polyester fabrics are obtained by insitu-polymerization and chemical vapour deposition (CVD). The coating process cassied out in polymerization chamber at specific time and temperature (8h, 40oC insitu-coated samples) and (2h, 65oC, CVD-coated samples). Surface resistivity of coated fabrics is measured by digital multimeter. CVD coated samples conductivity is more than the other method. Scanning electron microscopy (SEM) photos shows that surface of fabrics is coated uniformly by nanoparticles in average sized of (P3MT-PES: 50 nm=CVD-coated samples, and 80 nm= insitu-coated samples) and (P3HT-PES (Polyester-poly (3- hexylthiophene): 60 nm CVD coated samples, P3MT-PES: 85 nm= insitu-coated samples). CVD method coats fabrics surface smoothly. Fourier transform spectroscopy (FTIR) is used to confirm the formation of P3AT nanoparticles. By electrochemical impedance spectroscopy (EIS) analysis surface resistance is determined which shaws (PES>PES-P3MT>PES-P3HT). Differential scanning spectroscopy (DCS) (PES-P3H=65oC Tg, 255oC=Tm, PES-P3MT 45oC=Tg 255oC=Tm). Is used to study thermal behavior of coated samples.

Alumina ceramic coating was developed on 316 L stainless steel in order to improve the surface characteristics and increase the corrosion resistance of implants used in the body by employing plasma electrolytic coating process. Electrolytic bath, containing sodium carbonate and aluminum nitrate was prepared and thereafter the samples were coated with optimal voltage and direct current. The chemical composition of the samples were studied by X-ray diffraction analysis (XRD) and the surface morphology of the coated samples was studied by scanning electron microscopy. Hardness and wear properties of coated and uncoated samples in Ringer’s solution were studied and compared. Electrochemical corrosion behavior, as an indication of corrosion resistance of samples, were evaluated in physiological solution. The results of Mechanical testing showed that improving the behavior of alumina coated samples to compare with the one. Microstructures investigation revealed that the optimal time of coating was 10 minutes. XRD analysis was showed that a-Al2O3 phase formed in the coating. The corrosion resistance of alumina coaed samples were increased due to redused corrosion current and increased potential.

In the present study, tantalum carbide nanolayer with 500 nm thickness was coated on with Ti-6Al-4V alloy surface by using physical vapor deposition technique with electron beam in order to modify the substrate surface. The surface hardness of the modified samples surface with tantalum carbide coating (Ti-6AlI-4V /Ta2C) compared to uncoated sample (Ti- 6Al-4V) was increased from 346 HV to 640 HV. Also, the corrosion test in Hank’s solution revealed that the corrosion current density of Ti-6Al-4V/ Ta2C decreased from 2 mA/cm2 to. 1.5 mA/cm2 for uncoated sample, which reflects improvements in corrosion resistance of modified sample. After the corrosion test, by investigating the release rate of Al, V and Ti ions, released elements concentration after coating reduced to loss them 50 pencil yallelantnts. Increase in the growth and proliferation of MG-67 cells (osteoblast) and their adhesion and spreading on the surface of coated samples observed compared to uncoated sample in the in vitro and cytotoxicity (MTT) tests. Finally, X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental analysis (EDXA) tests were carried out in order to identify the phases, morphological assessment and percentage of elements in the samples, respectively. the results indicated that Ti-6Al-4V coated with tantalum carbide in terms of corrosion resistance and excellent surface properties, is a betten choice for use in orthopedic implants.

In the present research, the finite element analysis of the standard hardenability test (Jominy test) was performed both thermally and metallurgically using ABAQUS finite element software. In order to predict the volume fraction of the obtained phases and the hardness profile during continuous cooling stage, the appropriate user-defined subroutine based on the Machnienko kinetic model was employed in the data flow of the software. The results obtained from the finite element analysis were compared to those extracted from the reliable references and the prediction of the kinetic model employed in the JMATPRO commercial software. The results showed the higher precision of the Machnienko model in comparison with the model4 used in the JMATPRO software. This can be attributed mainly to more accurate definition of the conditions of phase transformations and the customization of the model based on the experimental information for the materials used in this model.

In this research the effect of addition of Mo and Mo content on amorphization of Ni during mechanical alloying process was studied. A high energy planetary ball mill was utilized for mechanical alloying of powder mixtures containing elemental Ni and Mo powders. The Mo content was considered to be 20 and 35 atomic percent of the powder mixtures. Different milling energy conditions were designed by changing the milling speed and ball diameter. Evolution of the structure of powders during mechanical alloying and at different Mo contents was studied by X-ray diffractometery (XRD). Morphology and microstructure of resultant mechanically alloyed powders were observed by scanning electron microscopy (SEM). The results showed that amorphous structure in Ni can be increased by increasing Mo content during mechanical alloying at optimum milling conditions. It was also shown that in addition to high milling speed the balls diameter should decrease to increase the amorphous Ni structure.

In the present work, different kinds of gold nanostructures were fabricated using simple and inexpensive anodizing method. Key factors in fabrication of these nanostructures are pore diameter and depth of nonporous alumina template which can be controlled by anodizing conditions. Gold is deposited by physical vapor deposition and its amount has an important effect on the structure morphology. After gold deposition, if the pore depth of template is high, nonporous gold will be produced. The pore diameter of nonporous gold, in addition to pore diameter of alumina template depends on the amount of gold deposition. If the pore depth of alumina template is low, Nano rods are fabricated after gold deposition. Also, the diameter of these Nano rods depends on the pore diameter of alumina template and amount of deposition. Another nanostructure is produced by controlling nonporous alumina structure and amount sold malodors deposit. If the pore depth of alumina Nano template is about the size of pore diameter, Nano dots will be produced. This method can be used to fabricate different kinds of nanostructures with different materials which are not soluble in acidic solution used for alumina dissolution.

In researches conducted in recent years, the nanoparticles have been used in metal matrix composites for their superior effects on the physical and mechanical properties have been much attention by researchers. The obtainment of a relatively uniform distribution of nanoparticles within the matrix during casting is difficult due to the weak wettability of nanoparticles in metallic matrix and their large surface-to-volume ratio. Accordingly, the nanoparticles tend to agglomerate and to form clusters during production process with the final detrimental effects on the strength and ductility of the particulate composites.In this investigation, the stircasting method was applied to produce composite samples with Al2O3 nanoparticles. After that composite samples were cold rolled with different levels in order to make the distribution of the particles within the matrix more uniform. Then carried out microstructure and mechanical surveys on different samples. Tensile test results and microstructure observations with optical and scanning electron microscopy approved beneficial effect of cold rolling on microstructure modification. Fulfilling annealing process removed work hardening effects caused by cold rolling and increased their strength and elongation. Toughness of rolled samples than as-cast samples raised nineteen-fold.

Composite Metal Foams (CMF) is a new generation of cellular materials. This group of materials has high energy absorption capacity in addition to their low density and weight. All these properties together make them suitable for a large number of industrial applications such as automotive industry. In presented research, aluminum matrix composite foam consist of low carbon and stainless steel hollow spheres, has been produced through gravity casting. This foam contains hollow spheres in matrix of A356 aluminum. Energy absorption of produced composite metal foam has investigated under uniaxial compression load. Results revealed that these foams not only have higher strength than current commercial foams produced from the same material, but they have higher strength to density ratio. In current commercial foams prediction of properties face some limitations due to their anisotropic structure. However, in composite metal foams this problem has addressed by more isotropic structure, which is naturally a result of similar shape, size and wall thickness of individual cells.

Carbon nanotubes (CNT) have exceptional thermal, mechanical and electrical behavior, and also low magnetic properties. Covering of CNT by ferromagnetic metal particles like iron, nickel, and cobalt could be good way to improve magnetic property. In this paper, nickel nanopartic1es via wet chemical method were deposited on the external surface of multiwaled carbon nanotubes. As low reactivity of carbon nanotubes, at first acid treatment was selected to form functional groups on the surface of CNTs. After that, by wet chemical method nickel nitrate nanoparticles deposited on the surface of CNTs, they were calcinated in air and finally product was reduced in H2/N2 atmosphere. In order to characterize the of samples, SEM, TEM, VSM, XRD and TGA instruments were used. The results indicated that good dispercity of nickel nanoparticles on the surface of CNTs, besides the mcsease in magnetic behaviour of CNTs in the presence of nickel nanoparticle were shown.

In this research, titanium sol was made by alkoxide precursor and sodium tungstate di-hydrate as tungesten oxide precursor was added to it. Dip-coating method was used by means of preparaing coatings on 316L stainless steel substrate. Crystal structure and morphology of the coatings were investigated by XRD and FE-SEM, respectively. FTIR have confirmed the bond between the Ti-O and W-O. Potentiometery method and tafel polarization tests were used to characterization of photocathodic protection properties of coatings. The XRD results showed that the entrance of tungesten oxide into titania structure decreases its crystallits size. On the other hand, the FE-SEM results indicated that the tungsten oxide addition improves the coatings morphology. In addition, it was observed that the increase of weight percentages of tungsten oxide improves the photocathodic protection properties of coatings.

In this research, the susceptibility of micro-structure of friction stir welded of 6061 aluminum alloy to intergranular corrosion was evaluated. According to ASTM G110, the immersion test was performed on the parent alloy and the weld regions. The corroded surfaces were analyzed by field-emission scanning electron microscopy (FE-SEM). After doing the immersion test on two variable times (i.e. 24 and 48 hrs.). The results of microstructural analysis showed that in the welded samples, the weld regions were susceptible to intergranular corrosion and also revealed a tendency to pitting. The susceptibility to corrosion attacks increased with increasing immersion time. The weld nugget zone showed the higher resistance to intergranular corrosion than the heat affected zone in both times of 24 and 48 hr. The parent alloy also displayed different corrosion behavior in both times. Corrosion products in the weld nugget region of welded sample were observed in unique shape (like a chimney) after immersion time of 48 hr.