JOURNAL OF NEW MATERIALS
Year:2015 | Volume:5 | Issue:4 (20)|Papers Count:15

The martensitic transformation start and finish temperatures in steels are reduced by increasing the percentages of carbon and the alloying clements. Even in high-alloy steels with high carbon contents, the martensitic transformation finish temperatures may reach less than zero degrees Celsius. As a result, the retained austenite will exist in the steel structure after quenching to the environmental temperature. Retained austenite is a soft phase that reduces hardness, wear resistance, and dimensional stability. Therefore, one of the important issues in heat treatment of steels is the reduction or elimination of the retained austenite. One of the methods of the reduction or elimination of the retained austenite is using cryogenic treatment. The 1.3255 tool steel with its high percentage of carbon and alloy elements is one of the tool steels whose martensite finish temperature is below the zero degree temperature. The use of deep cryogenic treatment is an important method to decrease the retained austenite in this steel. The deep cryogenic treatment was proceeded by austenitizing treatment in oil media and holding on different times (1, 24, and 48 hr.) at -196oC. The effect of deep cryogenic treatment on microstructure, hardness, and wear resistance was studied by optical microscopy (OM), scanning electron microscopy (SEM), hardness test, and the pin-on-disk wear test. The obtained results showed that deep cryogenic treatment causes an increase in hardness and wear resistance levels of 6.3% and 48-60%, respectively, in holding duration times of 24 to 48 h. The increase of hardness and wear resistance during deep cryogenic treatment was related to decrease of retained austenite value, very fine carbides precipitation, and high volume fraction of the carbides. The wear mechanism was determined by scanning electron microscopy in terms of adhesive wear.

Production of grey cast iron with improved mechanical properties and low cost is an import ante challenges of these engineering materials. In this study, AISI 1045 steel chips were used for reinforcing of hypoeutectic grey cast iron and microstructure and mechanical properties of composites produced by dry sand casting has been studied. A specimen without reinforcement and two composite specimens, respectively, with 1.5 and 3 volume percent of chips were produced. Microstructural studies were carried out by light and scanning electron microscopy. Noticeable region between steel chip-reinforcement and cast iron is observed that it is a diffusion interface. In the interface, carbon and .silicon are diffused from cast iron to steel chips and this case to form of a clear interface. To determine the mechanical properties of produced specimens are used for the tensile and hardness tests. Results were shown that reinforcing of cast iron by steel chips is resulted in to increase of the strength and hardness.

In this study magnetite nonoparticles were modified with 5-amino-1,3,4-thiadiazole-thiol (AMT) molecules and evaluated as nanoadsorbent for removing nile blue as a dye from aqueous solutions. nanoparticles were characterized by X-Ray, TEM and FT-IR. The dye adsorption was examined by batch equilibrium technique. Also batch studies were performed to find various experimental parameters like pH, contact time and the amount of adsorbent. Equilibrium for adsorption on Fe304-AMT nanoparticles was reached in 30 min. Equilibrium isotherms were analyzed by Freundlich and Langmuir models. Isotherm analyzes showed the experimental adsorption data were well fitted to the Langmuir isotherm model. The Langmuir adsorption capacity was found to be 142,857 mg g-1. The adsorption data were also fitted to kinetic pseudo-first-order and pseudo second-order models. Kinetic studies show that the adsorption followed pseudo-second-order model. The nanoadsorbent can be easily separated from aqueous solution by a magnet. The reform process of magnetic nanosorbent (Fe304-AMT) was performed with ethanol.

In the present study, production of Perovskite nanopowders of the proton-conducting, electrolyte material Ba0.85K0.15ZrO3-d is conducted at room temperature by mechanosynthesis. This is achieved with a planetary ball mill at 650rpm in zirconia vials, starting from BaO2, ZrO2 and KO2 precursors. The milling was done up to 420min and progression of reaction was monitored by XRD analysis of powder samples collected after each 60min of milling. By using XRD results, weight fraction of perovskite phase, crystallite size and lattice strain was estimated. Microstructure and chemical homogeneity were .analysed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) analyses respectively. Powder X-ray diffraction (XRD) reveals the formation of the perovskite phase in the early stages of milling. The perovskite crystallites are spherical in shape with an average size determined from XRD of about 20nm in agreement with transmission electron microscopy observations. EDS results shows chemical homogeneity in synthesized powder.

sintering of Al2O3- TiB2 nanocomposite Synthesized via Mechanochemical synthesis method were studied In order to improveits properties. For this purpose, First The raw materials include Al powder, TiO2 and B2O3 mixed with stoichiometric ratio were milled at room temperature under inert atmosphere at 2.5, 6 and 10h periods. In order to determine the phases formed and Crystalline grain size, X-ray diffraction analysis was used. To investigate the sintering behavior of Prepared powders were pressed at a pressure 700MP and green porosity and density was measured. Samples were sintered inside the furnace under inert at temperatures from 1100 to 1400oc for 1 to 4 hours. Finally, inorder to optimize the sintering temperature and time, The final properties in eluding compressive strength, hardness, density were studied. To study the morphology and particle size, Scanning Electron Microscope (SEM) were used. The results showed that the complete sintering is carried out at a temperature of 1400oc. At this temperature, The sample had high estdensity (3.8 gr/cm3) and alsohas a hardness 927HV and the compressive streng this 500 Mpa.

The influence of nanoscale reinforcement on the mechanical and microstructural properties of ultrafine-grained composites was studied. To evaluate structure and microstructure of the produced composites, X-ray diffraction analysis (XRD) and transmission electron microscope (TEM) was applied. Mechanical properties of the specimens were investigated by tensile and hardness tests. The result reveals that in comparing with monolithic Al (ARBed Al without ceramic particles), the presence of nanoparticles enhances strength of composites. Also, the results showed that with increasing ARB cycles, the tensile strength and microhardness of the composites increase. In addition, the tensile strength and microhardness of the composite samples are higher than those of the monolithic Al.

Electromagnetic interference occurs when electronic equipment and devices are subjected to electromagnetic radiation from unwanted sources at high intensity in the working frequency ranges of these devices. Interference interrupts and degrades the effective performance of these equipments. Electromagnetic interference shielding is the process of reaching sufficient attenuation level of the waveseither by reflection or absorption respectively at the surface and in the body of the shielding materials. In this study, the shielding effectiveness of epoxy-graphene nanoeomposites was. investigated. Graphene was first synthesized and charaeterized and graphene-epoxy nanocomposite samples upto 3wt% grapheme were fabricated by casting method. Then shielding effectiveness of samples in the 8 to 12GHz (X band) was investigated. Results showed the electromagnetic interference shielding ability of these nanocomposites such that shielding effectiveness of 22.3 and 17.6dB at 12 and 8GHz was attained respectively for 3wt% graphene sample. The dominant mechanism of shielding in the range of graphene composition and test frequencieswas absorption so that the 3wt% graphene sample showed 89.7 and 81.8 percent at 12 and 8GHz respectively. This result indicated that these nanocomposites were appropriate candidates for absorbing electromagnetic waves.

In this study Synthesis of Al3Zr intermetallic compound from The mixed powders of aluminum and zirconium and the effect of its addition to the mechanical properties of nanocompositcs aluminum was investigated. Staichiometric ratio of Al and Zr mixed and heated to 700 C under the argon atmosphere to produce Al-Zr. The densed structure that was produced grinded to produce powder. To investigate the phase and morphology of the powders, phase analysis by XRD and scanning electron microscope equipped with an EDS spectrometer was used. Results showed intermetallic Al3Zr successfully formed and no other phase was detected. Then, the powder obtained (10, 15, and 25% by weight) mixed with different percentages aluminum powder in a planetary mill. The milling was carried out under an argon atmosphere with ball to powder weight ratio of 20:1 and speed 300 rpm. The XRD results and using the Williamson-Hall method showed that after 20 hours milling the particles are diminished dramatically in size and Al3Zr intermetallic compound 56 nanometer with nanocrystal structure is formed within the aluminum matrix. Then the mixture was formed by hot pressing. To compare the mechanical properties and compressive strength tests were carried out. The results of compressive strength test and hardness test showed that yield strength and the hardness' may be increases and elongation can be decreases by addition of the Al3Zr intermetallic compound to AI. The results showed that the composite sample with 25 wt% Al intermetallic respectively, compressive strength and hardness is equal to 498MPa and 193VHN.

In this Study, the effects of heat treatment parameters on the microstructure and mechanical properties of interfacial intermetallic that was produced during explosive welding of 321 austenitic stainless steel and 1230 aluminum alloy were investigated. The interfacial intermetallic were evaluated by optical microscopy (OM), Scanning electron microscope (SEM), micro hardness testing and tensile-shear test. The diffusion of aluminum, iron, nickel and chromium elements were studied by linear energy-dispersive X-ray spectroscopy method. The interface before heat treatment changed from smooth to wavy shape with increasing the stand-off distance from 1 mm to 2.5 mm. The intermetallic layers thickness also raised from 3.5 mm to 102.3 mm. The micro hardness of the samples with 1 mm stand-off distance was 766 HV that increased to 927 HV in the samples with 2.5 mm stand-off distance which was related to the amount of intermetallics. The proportional amount of strength were 103.2 MPa and 214.5 MPa in the above samples respectively. Heat treatment at 45oC for 6 hr. resulted in intermetallic thickness reaching to 4.4 mm in the samples with 1 mm stand-off distances and to 118.5 mm in the samples with 2.5 mm stand-off distances. These results showed that the increase in heat treatment temperatures and times reduced the micro hardness and strength level.

High heat flux exposes of convergent - divergent nozzle may lead to melt the internal wall, thereby the performance of the nozzle have deteriorated significantly. In order to solve this problem, in this study, functionally graded Yttria Stabilized Zirconia (YSZ)/NiCrAlY coating was deposited on the internal wall using air plasma spray technique. Coated and uncoated specimens were subjected to high heat flux acetylene-oxygen combustion flame and were then characterized by optical microscope, Scanning Electron Microscopy (SEM) and microhardness test. SEM observation into the functionally graded layers showed that selective oxidation occurred during atmosphericplasma spray of the YSZ-NiCrAIY. Mixing these oxides with zirconia at molten state produced ceramic composites regions, which contain undissolved zirconia granules embedded in the liquid matrix of zirconia + the oxides. It was observed that the bare sample melted during high heat flux beating. For the coated specimen, it was found that the test causes changes in the coating, leading to a denser microstructure and development of cracks in the YSZ top coat, even though no visible differences in appearance between the exposed and unexposed coated samples were observed.

In this study, poly (s-caprolactone)/hydroxyapatit scaffold were produced by micro and nano hydroxyapatite. Different weight fractions of 5, 10 and 15% of the HA were added to the PCL. PCL-HA scaffolds were prepared by solvent casting/particulate leaching method. Sodium chloride (NaCl) particle was used as a porogen with diameters 250-400 mm. Structural, chemical, mechanical and biodegradation properties of scaffolds were evaluated. The pore morphology, size, and distribution of the scaffolds were characterized using a scanning electron microscope (SEM). X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to determine the phase structure, chemical composition and functional groups of scaffolds. Porosity of the scaffolds was measured using Archimedes' Principle according to a known method. These scaffolds were evaluated for their compressive mechanical properties. In vitro degradation was studied by immersing of scaffolds in phosphate buffered saline (PBS) up to 30 days. The changes of pH of the PBS and the changes of the weight loss of the scaffolds were measured. Results showed compressive strength and biodegradation of scaffolds increased with the increasing the weight ratio of HA. Also, the compressive strength of the scaffolds with nano hydroxyapatite was greater than with micro hydroxyapatite. But, biodegradation of the scaffolds with nano hydroxyapatite was lesser than with micro hydroxyapatite.

In this study, the NiO/Al203-MgO nanocrystalline with 20 wt% Ni were synthesized by using the modified sol-gel method. The aim of this study is in vestigation of influence molar ratio of AI: Mg on structural properties such as phases of nanocatalyst, the crystalline size and nanoparticles, the morphology, the surface area, the pore volume and pore size distribution. For this purpose, seven nanocrystals with different Al: Mg molar ratios (Al: Mg: 1: 1, 2: 1, 3: 1, 4: 1, 1 :2, 1 :3, 1 :4) were synthesized. The prepared powders were characterized by XRD, FTIR, TGA-DSC, FESEM with the energy dispersive Xvray spectroscopy (EDX), TEM and BET-BJH. The results of X-ray analysis showed that increasing the molar ratio of Al to Mg, the solid solution of MgO. NiO was replaced by NiO phase and the crystal size of NiO reduced with increasing this molar ratio. The crystalline size of NiO in the molar ratio of Al to Mg: 3: 1 was about 11 nm. But with increasing Mg to Al molar ratio from 1: 1 to 4: 1, the NiO phase wasn't observed and the crystalline size, with increasing Mg to Al molar ratio from 1: 1 to 4: 1 was increased from 6.7 to 9.8 nm. Also, with increasing molar ratio of Al to Mg 2: 1 to 3: 1, the specific surface area of nanocatalysts were reduced from 120 m2/g to 100m2/g .TEM image and the selected area diffraction pattern of nanoparticles with molar ratio of 2: 1 confirmed mesopore stfucture and nanocrystalline of catalysts synthesized.

In this research, diamond like carbon thin film was deposited on silicon solar cell by plasma enhanced chemical vapor deposition method using methane and hydrogen gases. The adhesion, crystal structure, chemical bonding, SP2/SP3 hybridation ratio, surface roughness and surface morphology of the diamond like carbon thin film was investigated by tape test, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, atomic force microscopy and field emission scanning electron microscope, respectively. Current-voltage characteristics and efficiency of the silicon solar cell with diamond like carbon thin film and without it was measured by solar simulator. The results indicated the surface roughness of the silicon solar cell decreased by deposition of the diamond like carbon thin film. In addition, the solar simulator results indicated that the short current density in silicon solar cell increased by deposition of the diamond like carbon thin film. The Efficiency of the silicon solar cell increased to 37% of the original value by deposition of the diamond like carbon thin film.

In the present study, Cr2O3 nanostructured and conventional (microstructured) coatings have been prepared by atmospheric plasma spraying (APS) on carbon steel substrates. Phase composition and structural properties of coatings were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Also, the mechanical properties of coatings such as microhardness were evaluated. Nanostructured Cr2O3 coating exhibited a bimodal microstructure consisting of nanosized particles retained from the powder and microcolumnar grains formed through the resolidification of the molten part of powder, whereas the microstructure of conventional Cr2O3 coating consisted of columnar-grain splats. The results revealed that nanostructured coating, due to unique microstructure container of nanozones, presented improved microhardness and fracture toughness as compared to the conventional coating.

Theoretical studies in the analysis of sheet metal failures are referred to obtain the Forming Limit Diagrams (FLD). Since necking in some processes such as hydroforming can occur at locations where in addition to the in-plane stresses a through thickness compressive stress acts, the plane stress assumption is not proper for these processes. Therefore, in this study, determination of the forming limit diagram with existence of the normal stress is based on the generalized Marciniak and Kuczynski model. Newton-Raphson method has been used to find the set of variables. The structure of FLD prediction algorithm is in a way that it is possible to apply Von Mises and Hill48 yield criterions and different hardening laws. The results show that existence of the normal stress shifts up the forming limit diagram. The increase of limit strain in plane strain state has been investigated quantitatively for better understanding of this effect. The theoretical results have been verified by comparing them with the published experimental data.