Iranian Journal of Materials science and Engineering
Volume:12 Issue: 2, Jun 2015

trontium hexaferrite (SrFe 12 O 19) nanosized powders were synthesized by sol-gel auto-combustion method with and without cetyltrimethylammonium boromide (CTAB) addition in the sol with Fe/Sr ratio of 11 (using additional Sr). The resultant powders were investigated by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM) and Vibration Sample Magnetometer (VSM) techniques. Phase constituents of the synthesized samples which were heat treated at temperatures in the range of 700- 900 ◦C were studied. XRD results revealed that CTAB addition facilitates the formation of single phase strontium hexaferrite at 800 ◦C. Microstructural evaluations with FESEM represented that CTAB addition causes formation of larger particles with a narrower size distribution. VSM results represented that the highest amount of intrinsic coercivity force (i H C) was obtained in the sample without CTAB addition and with additional Sr, calcined at 800 ◦C for 1 h which was equal to 5749.21 Oe, while the value of i H C was equal to 4950.89 Oe without additional Sr. The amount of maximum magnetization (M max) was raised from 48.41 emu/g to 62.60 emu/g using CTAB and additional Sr. The microstructure and magnetic properties of the samples have been explained.

In this study, corrosion behaviour of A356-10 vol.% SiC composites casted by gravity and squeeze casting is evaluated. For this purpose, prepared samples were immersed in HCl solution for 1h at open circuit potential. Tafel polarization and electrochemical impedance spectroscopy (EIS) were carried out to study the corrosion resistance of composites. The Tafel polarization and EIS studies of the corrosion behaviour of the A356-10 vol.% SiC composites showed that the corrosion resistance of the composite casted by squeeze casting was higher than that of the composites casted by gravity in selected corrosion media. Also, the Tafel polarization and EIS studies revealed that the corrosion current densities of both composites increase with the increase in the concentration of HCl. The micrographs of scanning electron microscope (SEM) clearly showed the squeeze casting composite exhibits a good dispersion/matrix interface compared to that of the composites produced by gravity casting.

Aluminium base alloy (Al-Cu-Si) was reinforced with silicon carbide (SiC) particles, in various percentage compositions from 0-20 wt%. Silicon carbide particle size of 20µm was selected. The molten slurry of SiC reinforced base aluminium metal was casted through green and dry sand casting methods and solidification process was carried out under ambient conditions. A selected population of total casted samples were subjected to T6 heat treatment process, followed by evaluation of mechanical properties of hardness, tensile strength and impact loading. The micro sized SiC particles were preheated up to 300C prior pouring into the melted metal, for subsequent removal of residual gases and moisture content. A continuous manual stirring method was used for homogenous distribution of reinforced particle in molten slurry. The experimental results revealed that the highest parameters of hardness, impact energy and tensile strength were achieved in the T6 heat treated specimens; having highest percentage composition (20%) of Silicon Carbide (SiC) particles.

In this paper, the possibility of mechanical coating of aluminum with either Ni or SiC using planetary ball mill was studied. The Al substrate was fixed inside of the vial lid of a planetary ball mill filled with milling balls and starting powder. The phase analysis and crystallite size measurement of the coatings were carried out using X-ray diffraction (XRD) method. Scanning electron microscope (SEM) was employed to study the coating/substrate interface and coating thickness. Hardness and wear resistance of coatings were also measured. The results indicated that all coatings have relatively uniform thickness. SiC coating shows poor compaction and adhesion to the Al, while nanostructured Ni coating is well-bonded to the substrate. Moreover, Ni coating showed higher hardness and wear resistance compared to SiC coating. It was found that the balls collision will result in the grain refinement of the coating as well as Al substrate. Mechanically deposited Ni coating shows higher hardness value compared to those obtained by conventional methods. This has been related to the induced grain refinement phenomenon.

The inhibition behavior of N,N′-bis(2,4,6-trihydroxyacetophenone)-propandiimine (THAPP) as an environmentally friendly Salen Ligand on the corrosion inhibition of mild steel was studied in alkaline solution (pH=10) containing 3% NaCl. Measurements were carried out using electrochemical and surface techniques. The experimental results suggested that this compound was an effective corrosion inhibitor for mild steel and the protection efficiency was increased with the increase in inhibitor concentration. Polarization curves indicated that this organic compound was a mixed-type inhibitor. Adsorption on the mild steel surface follows the Langmuir isotherm model. Activation parameters and thermodynamic adsorption parameters of the corrosion process such as E a, ΔH, ΔS, K ads, and ΔG ads were calculated by the obtained corrosion currents at different temperatures.

In this work, TiN/TiCN & PN/TiCN multilayer films were deposited by plasma- assisted chemical vapour deposition (PACVD). Plasma nitriding (PN) and TiN intermediate layer prior to coating leads to appropriate hardness gradient and it can greatly improve the mechanical properties of the coating. The composition, crystalline structure and phase of the films were investigated by X-ray diffraction. Atomic force microscopy and scanning electron microscopy were employed to observe the morphology and structure of the films. The TiCN layer exhibited a columnar structure. The adhesion force between the film and the tool steel substrate was 30.8 MPa for TiN/TiCN and 25.4 MPa for PN/TiCN film determined by pull off tests. The hardness of TiN/TiCN film was 12.75 GPa while it was 5.4 GPa for PN/TiCN film, respectively. The improvement of the adhesion in TiN/TiCN was attributed to a less gradient hardness configuration. In addition, the mean friction coefficients of the films were about 0.2 for TiN/TiCN and 0.3 for PN/TiCN film determined by nanoindentation tests.

In this research, two different carbonaceous materials (Graphite:G and Petrocoke:P) were separately compared in terms of the carbothermic reduction of hematite and anatase in order to synthesize Fe-TiC nanocrystalline composite by mechanically activated sintering method. Powders were activated in a planetary high-energy ball mill under argon atmosphere for 0, 2, 5, 10,and 20 h. Then, the activated powders were analyzed by XRD and SEM to investigate phase constituents and microstructure of the mixtures. Results proved that Fe 2 O 3 and TiO 2 were not reduced by carbonaceous materials even after 20h of milling. SEM investigations showed that G-mixture was more homogenous than P-mixture after 20h of milling, meaning that graphite-anatase-hematite was mixed satisfactorily. Thermogravimetry analysis was done on 0 and 20h milled powders. TG and DTG curves showed that mechanical activation led to almost 300°C decrease in the reduction temperature of hematite and anatase in both mixtures. In the next step, the powders were sintered in a tube furnace under argon atmosphere. In the G-mixture, anatase was reduced to titanium carbide at 1100°C; but, in the P-mixture, temperature of 1200°C was essential for completely reducing anatase to titanium carbide.Results of phase identification of the sintered powders showed that anano-crystalline ironbased composite with titanium carbide, as the reinforcement was successfully synthesized after 20 h high-energy milling of the initial powders and subsequent sintering occurred at 1200˚C for 1h.

Lead zirconate titanate (PZT) as a piezoelectric ceramic has been used widely in the fields of electronics, biomedical engineering, mechatronics and thermoelectric. Although, the electrical properties of PZT ceramics is a major considerable, but the mechanical properties such as fracture strength and toughness should be improved for many applications. In this study, lead monoxide, zirconium dioxide and titanium dioxide were used to synthesize PZT compound with chemical formula Pb(Zr 0.52, Ti 0.48)O 3 by calcination heat treatment. Planetary mill with zirconia balls were used for homogenization of materials. Two-stage calcination was performed at temperatures of 600˚C and 850˚C for holding time of 2h. In order to improve the mechanical properties of PZT, various amount of ZnO and/or Al 2 O 3 particles were added to calcined materials and so PZT/ZnO, PZT/Al 2 O 3 and PZT/ZnO+Al 2 O 3 composites were fabricated. Composites samples were sintered at 1100˚C for 2 h in the normal atmosphere. Microstructural component and phase composition were analyzed by XRD and SEM. The density, fracture strength, toughness and hardness were measured by Archimedes method, three-point bending, direct measurement length crack and Vickers method, respectively. Dielectric and piezoelectric properties of the samples were also measured by LCR meter and d33metet tester, respectively. The results showed that by addition of ZnO and Al 2 O 3 to composite materials, the relative density of PZT based composites was increased in conjunction with a signification improvement of mechanical properties such as flexural strength, toughness and hardness. Moreover, the dielectric and piezoelectric properties of PZT such as dielectric constant, piezoelectric coefficient and coupling factor were decreased while the loss tangent was also increased.

Crystallization of α – Fe phase during annealing process of Fe55Cr18Mo7B16C4 bulk amorphous alloy has been evaluated by X- ray diffraction, differential scanning calorimetric tests and TEM observations in this research. In effect, crystallization mechanism and activation energy of crystallization were evaluated using DSC tests in four different heating rates (10, 20, 30, 40 K/min). A two -step crystallization process was observed in the alloy in which α–Fe phases was crystallized in the first step after annealing process. Activation energy for the first step of crystallization process (i.e. α – Fe phase) was measured to be 276 (Kj/mole) according to Kissinger kinetic model. Furthermore, Avrami exponent calculated from DSC curves was two and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. It is also known from the TEM observations that crystalline α – Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.

The effect of anodic oxidation of a NiTi shape memory alloy in sulfuric acid electrolyte on its surface characteristics was studied. Surface roughness was measured by roughness tester. Surface morphology was studied using optical microscopy (OM) and scanning electron microscopy (SEM). Corrosion behavior was specified by recording Potentiodynamic polarization curves and measuring the content of Ni ions, released into a SBF solution using atomic absorption spectroscopy (AAS). Fourier transformation infrared radiation (FT-IR) and energy dispersive spectroscopy were employed to verify the biocompatibility of the anodized and bare alloys after submersion in SBF. It was shown that anodic oxidation in sulfuric acid significantly increases corrosion resistance and biocompatibility. This layer improves corrosion resistance and Ni ion-release resistance by impeding the direct contact of the alloy with the corrosion mediums i.e. Ringer and SBF solutions. The TiO2 oxide layer also decreases the releasing of Ni ions in to SBF solution.