Journal of Advanced Materials in Engineering (Esteghlal)

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Mechanical property of porous nickel-titanium alloy produced by volumetric combustion synthesis (VCS) for bone surgery applications is reported in this paper. Stress-strain behavior of the alloy is determined by uniaxial tension test. Superelastic diagram of the porous alloy is compared with that of the solid material cooled from austenite stability temperature. Due to movements of the dislocations, growth of the nucleation sites and thinning of the martensite plates during cooling, plastic deformation and necking behavior of these materials are principally different from that of the ordinary materials. Elastic modulus and yield stress of the material have nonlinear relationship with porosity percentage and obey the following correlations  and The stress-strain curves of the alloy show more than 6 percent elongation before rupture, even with 30 percent porosity. A comparison of the cleavage surfaces of the combustion synthesis samples with those of the powder metallurgical ones indicate great influence of production process on fracture mechanism.

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In this study, the effect of Al₂O₃ addition as a diluent during mechanically activated self-propagating high temperature synthesis (MASHS) of Al₂O₃-ZrB₂ composite was investigated. For this purpose, the thermite mixture of Al, ZrO₂, H₃BO₃ and different amounts of Al₂O₃ (0, 3, 6, 9 wt.%) were used as the raw materials and mechanically activated for 5 h, then furnace sintering was performed at 650 °C. The results showed that by increasing the Al₂O₃ content up to 6 wt.%, the intensity of exothermic peak in the DSC curves increases, but for higher additive contents it decreases. In this case, more homogenous distribution of ZrB₂ particles with finer grain size was observed.

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In this research, TiAl/Al₂O₃ composite was synthesized from mechanically activated TiO₂-Al powder mixtures using microwave heating.The initial powder mixtures were mechanically activated and pressed into cylindrical tablets and then heated in a microwave oven. The effect of different amounts of excess Al and microwave susceptor material (SiC or graphite) on the ignition time and the resultant reaction products were evaluated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used for characterization of the synthesized samples. XRD patterns revealed that when there was no excess Al in the initial powder mixture, the main resulting intermetallic phase would be Ti₃Al with negligible amounts of TiAl, while with 10 wt% excess Al, TiAl phase could be formed in the composite product.The results also showed that microwave synthesis took place faster and more reproducible when samples were packed in the graphite powder than when placed between two SiC blocks.

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In this study, fabrication of an in-situ composite through aluminothermic combustion synthesis in An Al–V₂O₅-NiO system was investigated. Therefore, Al, V₂O₅ and NiO powders with stoichiometric ratio of 11:1:1, respectively, were milled for an  hour and finally the mixtures were compressed. In order to investigate the temperatures of phase transformations, Differential Thermal Analysis (DTA) was utilized. Heat treatment was applied on the raw samples according to their peak temperatures treated in DTA. X Ray Diffraction (XRD) analysis for the samples shows formation of phases such as Al₃V and Al₃Ni₂ at different sintering temperatures. Microstructure and phase analysis showed that during sintering of this sample, Al₃V phase was not formed below 700 °C, at 880 °C Al₃Ni₂ it was formed and after 950 °C, it was transformed to Al₄Ni₃ phase. In addition, after 950°C, Al₃V transformed into Al₂₃V₄ phase. Analysis of samples density and hardness showed that, due to increase of volume fraction percentages of reinforcing phase, these two parameters increase as well.