http:// ijmse.iust.ac.ir Iranian Journal of Materials Science and Engineering - Journal articles for year 2008, Volume 5, Number 3 Yektaweb Collection - https://yektaweb.com en 2008/9/11 http://ee.iust.ac.ir/ijmse/browse.php?a_id=138&sid=1&slc_lang=en Abstract: Thermal fatigue is a stochastic process often showing considerable scatter even in controlled environments. Due to complexity of thermal fatigue, there is no a complete analytical solution for predicting the effect of this property on the life of various components, subjected to severe thermal fluctuations. Among these components, one can mention car cylinder, cylinder head and piston which bear damages due to thermal fatigue. All these components are usually produced by casting techniques. In order to comprehend and compare the thermal fatigue resistance of cast Al alloys 356 and 413, this research was designed and performed. For this purpose, several samples in the form of disc were cast from the two alloys in sand mould. The microstructures of the cast samples were studied by light microscopy in order to choose the samples with the least amounts of defects for thermal fatigue tests. The results of thermal fatigue tests showed that the nucleation of microcracks in Al-356 alloy occurred at shorter time relative to those occurred in Al- 413 alloy under the same test conditions. In addition, the density of micro-cracks in Al-356 alloy was more than that of Al-413 alloy. The results of fractography on 356 alloy indicated that the cracks were generally nucleated from inter-dendritic shrinkage porosities and occasionally from the interface of silicon particles with the matrix. The growth of these micro cracks was along the dendrite arms. Fractography of 413 alloy fracture surfaces showed that nucleation of microcracks was often associated with silicon particles. M. Divandari, http://ee.iust.ac.ir/ijmse/browse.php?a_id=139&sid=1&slc_lang=en Abstract: The investigation is carried out to characterize welding of AISI 310 austenitic stainless steel to Inconel 657 nickel-chromium superalloy. The welds were produced using four types of filler materials: the nickel-based corresponding to Inconel 82, Inconel A, Inconel 617 and austenitic stainless steel 310. This paper describes the effects of aging treatment on the joint. The comparative evaluation was based on microstructural features and estimation of mechanical properties. While Inconel A exhibited highest thermal stability and mechanical properties (hardness and ultimate strength), Inconel 82 weld metal also showed good thermal stability and mechanical properties. On the other hand, welds produced with Inconel 617 and 310 SS filler materials showed weak thermal stability and failed in the weld metals. It is therefore concluded that for the joint between Inconel 657 and 310 stainless steel, Inconel A and Inconel 82 filler materials offered the best compromises, respectively. M. Shamanian http://ee.iust.ac.ir/ijmse/browse.php?a_id=140&sid=1&slc_lang=en Abstract: The PZT-based ceramics with a composition of Pb1.1-xLax (Zr0.53Ti0.47)O3, were prepared by conventional mixed oxide followed by mechanical alloying and sol-gel methods in which x was chosen in the range of 0.02–0.06. The samples were calcined in the range of 450 °C - 750 °C for 4h. The physical and electrical properties of the samples were determined as a function of the calcination temperature. The obtained data from two methods were compared with conventional mixed oxide method. Microstructural and compositional analyses of the samples were carried out using XRD and SEM. Dielectric properties of the samples were measured with an impedance analyzer. The ferroelectric properties of the PZT and PLZT samples were measured using the frequencies applying equipment and d33 tester. The results indicated a complete tetragonal phase prepared from both methods. It was shown that the addition of La and reduction in calcination temperature improved both the dielectric and piezoelectric properties. The dielectric constant tended to increase with doping content, giving the maximum value of about 2000 at 3 mol% La3+. In addition, the mechanical coupling factor (Qm) of the doped samples showed a significant decrease. Finally, the value of planar coupling factor (kp) reached the maximum value of 0.47 at 1 mol% La3+. A. Nemati http://ee.iust.ac.ir/ijmse/browse.php?a_id=141&sid=1&slc_lang=en Abstract: Cooling slope-casting processing is a relatively new technique to produce semisolid cast feedstock for the thixoforming process. Simple equipment, ease of operation, and low processing costs are the main advantages of this process in comparison with existing processes such as mechanical stirring, electromagnetic stirring, etc. The processing parameters of cooling slope casting are length, angle and the material of the inclined plate and their combinations, which usually affect the micro structural evolutions of the primary solid phase. In order to clarify the effect of the processing parameters on the evolution of the particle size, based on experimental investigation, Artificial Neural Network (ANN) was applied to predict the primary silicon crystals (PSCs) size of semisolid cast ingot via a cooling slope casting process of Al-20%(wt.%) Si alloy. The results demonstrated that the ANN, with 2 hidden layers and topology (4, 3), could predict the primary particle size with a high accuracy of 94%. The sensitivity analysis also revealed that material of the cooling slope had the largest effect on particle size. M. Shahmiri http://ee.iust.ac.ir/ijmse/browse.php?a_id=142&sid=1&slc_lang=en Abstract: A novel dust free alginate impression material was formulated and prepared, comprising an alginate polyvinylpyrrolidone and tetraflouroethylene resins, a mixture of liquid paraffin and dimethylpolysiloxane oil as the dust generation controlling agents and processed diatomaceous earth filler which was obtained from Iranian ore. No dusting was detected during the mixing of the powder and the conventional properties of the impression material, like working and setting times and compressive strength were in the range of the required specifications for alginate dental impressions. The compressive strength was measured to be 2.6 times of the minimum requirement for such fast setting impressions. M. Keyanpour-Rad http://ee.iust.ac.ir/ijmse/browse.php?a_id=143&sid=1&slc_lang=en Abstract: Dissolution and recovery of Mn-Al compacts with and without a chloride flux was studied by taking samples from the melt after addition of the compact. Events occurring after the addition of the compacts into the melt were studied using water quenched specimens after holding them for a specified time in molten state. The cross sections of these specimens were characterized by SEM as well as optical imaging. The results showed that an optimized amount of flux (10 to 15%wt. in this research) considerably decreases the time to reach more than 90% recovery in comparison with non-fluxed compacts. The flux caused the intermetallic forming reactions to be started considerably sooner in fluxed compacts in comparison with the non-fluxed compact. Consequently, the incubation time decreased from about 180 seconds for non-fluxed compacts to less than 3 seconds for compacts with 10%wt. flux. M. Farhani, http://ee.iust.ac.ir/ijmse/browse.php?a_id=144&sid=1&slc_lang=en Abstract: Austenitic stainless steels exhibit a low hardness and weak tribological properties. The wear behaviour of austenitic stainless steel AISI 316 was evaluated through the pin on disc tribological method. For investigating the effect of wear on the changes in microstructure and resistance to wear, optical microscopy and scanning electron microscope were used. The hardness of the worn surfaces was measured with a micro-hardness tester. Worn surfaces were analyzed through X-ray diffraction. Results showed that with increasing the sliding distance and applied load, the austenite phase partially transformed to ά martensite, and there was no trace of ε phase detected. Due to the formation of probably hard and strong martensite phase, as the sliding distance and applied load increased, the hardness and the wear resistance of the material was increased. Wear mechanism was on the base of delamination and abrasion. M. Zandrahimi