Iranian Journal of Materials Science and Engineering

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Dispersion and rheological behaviors of ionically stabilized aqueous alpha alumina suspensions were investigated in various pH values (3, 11) and solid volume fractions (4, 7, 10, 15) Vol% using sedimentation experiment as well as viscosity measurement. Interface separating porous-packed sediment from a relatively clear supernatant at pH 11 was measured over 20 hours with the aim of obtaining linearity range, initial settling velocity, final sediment height and suspension sensitivity factor, whilst it failed to be observed in the case of pH 3 for its turbid supernatant. Thus, the final sediment level instead of interface location was taken into consideration. For all solids loading, final sediment level in the case of pH 3 was smaller than those in pH 11. The interface was observed to be moving downward in a linear fashion, with the steady drive toward an equilibrium state, which was substantiated to be pH and solid loading dependent. As ? increased, linearity time changed in an ascending order. pH 11 suspensions showed good agreement with the well-known Richardson-Zaki equation and displayed dramatic variations in initial settling velocity, whilst it was not the case for pH 3 as understood generally by turbidity observations. In addition, pH and ? appeared to be more effective in giving stability to the suspending systems. On the other hand, rheological behaviors of these suspensions were taken into consideration for better indication of suspension stabilization degree in which suspension yield stress derived using viscosity values was focused. The results showed that ?y at pH 3 is much lower than that of at pH 11. This is a further indication of better dispersion at pH 3. It was also found that for all ? values, pH 3 suspensions were more stable than the flocculated pH 11 ones.

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The wear mechanism of plasma electrolytic nitrocarburised (PEN/C) 316L stainless steel samples was studied after a pin on disc wear test. The surface morphology of samples after application of PEN/C process was studied using scanning electron microscope technique. The sliding tracks resulting from the wear tests on the treated specimens indicated no signs of plastic deformation and adhesive wear, but the slider wear particles were trapped in the micro-craters of the counterface. The results showed that this mechanism may further improve the tribological performance of the system by increasing the wear resistance and lowering friction. PEN/C treated surfaces are therefore believed to have the potential to limit metal-to-metal wear mechanisms on a microscale, if contact pressures are sufficiently low

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In this research, nanocrystalline Co-Fe coatings were electrodeposited on copper substrate. The influence of current density on different properties of the films at two pH levels was investigated. All the coatings showed nodular structure with rougher morphology at higher current densities. Due to anomalous deposition at higher current density, the amount of iron content increased and reached its maximum value at about 50 wt.% for the coating obtained from pH 5. X-ray diffraction patterns showed hcp structure as the dominant phase. However, by increasing current density at lower pH value, a double phase structure containing fcc+hcp phases was detected. It was observed that current density has a positive effect on grain refinement. However, coarser grains would obtain at lower pH value. Microhardness measurements showed that, there is a direct relationship between grain size and microhardness. Moreover, microstructure in double phase structure films can influence microhardness more dominantly. Vibrating sample magnetometer (VSM) measurements indicated that the saturation magnetic is proportion to deposited iron content and reached its maximum value at about 1512 emu/cm³. It was cleared that grain size, phase structure and chemical composition can affect coercivity of the films effectively.