Iranian Journal of Materials Science and Engineering

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Abstract: The microstructural features of the early stage of ordering of the intermetallic compound Pt2FeCu have been examined using optical and transmission electron microscopy in conjunction with X-ray diffraction technique. It was found that the compound has similar morphological alteration to that of FePt in which the ordering cannot be suppressed by rapid quenching. The early stage of ordering transformation was initiated at temperatures above the critical value of 1178 oC, by a homogeneous nucleation of the intermediate short range ordered particles and ultra rapid directional-induced heterogeneous growth (burst type). As the result of these combined mechanisms, twin –related ordered domains have been formed which in turn minimize the strains produced by ordering reaction in polycrystalline material. The individual grain was divided up by different sizes of twin-related ordered domain bonded with {101} habit planes.

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Combustion synthesis is a special thermophysico-chemical process applied for production of intermetallic compounds. In the present work, a reaction–diffusion numerical model was developed to analyze the combustion synthesis of aluminide intermetallics by self-propagating high-temperature synthesis process. In order to verify the reliability of the numerical model, an experimental setup was designed and used to perform the combustion synthesis of nickel and titanium aluminides. The developed model was further used to determine the temperature history of a powder mixture compact during self-propagating high-temperature synthesis. The effect of compact relative density on combustion temperature and wave propagation velocity was also studied.

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Abstract: Microwave processing is one of the novel methods for combustion synthesis of intermetallic compounds and
composites. This method brings about a lot of opportunities for processing of uniquely characterized materials. In this
study, the combustion synthesis of TiAl/Al2O3 composite via microwave heating has been investigated by the
development of a heat transfer model including a microwave heating source term. The model was tested and verified
by experiments available in the literature. Parametric studies were carried out by the model to evaluate the effects of
such parameters as input power, sample aspect ratio, and porosity on the rate of process. The results showed that
higher input powers and sample volumes, as well as the use of bigger susceptors made the reaction enhanced. It was
also shown that a decrease in the porosity and aspect ratio of sample leads to the enhancement of the process.

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In this research, the nickel oxide was dissolved in cryolite at temperatures of 880, 940 and 1000°C. In order to reduce the nickel oxide, aluminum was added to the salt. Simultaneously the nickel oxide was reduced and Al3Ni2 intermetallic compound was formed. In the duration intervals of 2.5-40 minutes samples of the salt and metallic phases were taken. The variation of the nickel content in metallic and salt samples was determined by the AAS. The results indicate that increasing the temperature and duration has a positive effect on the reduction process and Al3Ni2 intermetallic compound formation. The nickel content in the metallic sample has its highest amount at 1000°C in 10 minutes. Furthermore, practical results of the studies of nickel content variations in metallic and salt samples confirm the data obtained from theoretical calculations.

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In the present study, the effect of post-rolling annealing heat treatment on the formation of intermetallic compounds between Al-Cu strips, in the presence of nickel coating on the Cu strips, was investigated. In addition, the effect of post-rolling annealing and intermetallic compounds on the bond strength of Al-Cu strips was evaluated. In order to prepare samples, Cu strips were coated with nickel by electroplating process. After surface preparing, Cu strips were placed between two Al strips and roll bonded. This method is used for producing Al-Ni-Cu composites. Then the samples were annealed at 773K for 2 h. The formation of intermetallic compounds was studied using energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Also, in order to investigate bond strength of Al-Cu after post-rolling annealing heat treatment, samples were produced using nickel powder and nickel coating. Then bond strength of strips was investigated using peeling test. The results revealed that by post-rolling annealing of layers, the bond strength between Al-Cu strips decreases dramatically.