Journal of Advanced Materials in Engineering (Esteghlal)

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Fabrication and characterization of aluminum matrix composites containing different volume fractions of Ni3Al powder (5-40 Vol%) were investigated. Ni3Al powder was produced by mechanical alloying of elemental nickel and aluminum powder mixture. Al-Ni3Al composite parts were prepared using a powder metallurgy route involving two stages Al and Ni3Al powder mixtures were first compacted under 500MPa and then hot-pressed under 250MPa at 420 oC for 10min. The microstructure and hardness of consolidated parts were investigated by x-ray diffractometery, optical and scanning electron microscopy and hardness measurements. Results showed that consolidated Al-Ni3Al samples included no significant porosity with a nearly uniform distribution of Ni3Al particles. Additionally, structural examinations showed that no significant reaction between Ni3Al and aluminum matrix occurred during sintering process. Al-Ni3Al composites exhibited a higher hardness value compared with pure aluminum sample prepared under identical conditions. The hardness value of Al-Ni3Al composites increased linearly as Ni3Al content increased.

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In the present study phase transformation of silicon and silica during milling in different atmospheres was investigated. The silicon powder was subjected to high energy ball milling in ammonia (25%) atmosphere. The milled powder was subsequently annealed at 1200 ◦C for 1 hour. In another test a mixture of AlN and amorphous silica (micro silica) was subjected to high energy ball milling. The milled powder mixture was subsequently annealed at 1200 ◦C for 2 hours. Phase analysis of the as milled and annealed powders was performed by X-ray diffractometery (XRD). Powder morphology was also examined using a scanning electron microscope (SEM). Results showed that ball milling of silicon in ammonia formed an amorphous phase which transformed to quartz on further milling. After annealing quartz, cristobalite and another oxide phase called O phases were developed on XRD patterns. Ball milling of AlN and amorphous silica led to the transformation of amorphous silica to stishovite phase. This process was completed after annealing..

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In this study, TIG welding was used to clad and repair the surface of cast AZ91C magnesium alloy. Then, friction stir processing and T6 heat treatment wrer applied on the welded region. Microhardness results showed an improvement in the mean hardness of welded zone and also FSPed zone. Increase in the mean microhardness of the welded zone after T6 heat treatment to the maximum value was also concluded. The results of wear test showed that the wear resistance of the welded area was improved. Further improvement in wear properties was obtained after friction stir processing and T6 heat treatment.

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In the present study, FeAl/Al₂O₃ nanocomposite coating was produced on the carbon steel plate using mechanical alloying (MA) technique via a mechanochemical reaction. Stoichiometric ratios of Fe, Al and Fe₂O₃ as well as a substrate were mixed and milled up to 22h in a vibrating high energy mill with a 4 mm ball. Samples prepared after 18h of MA were subjected to annealing at 773 K for 1-3 h. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and microhardness measurements were carried out to study mechanochemical reaction and coating formation characterization. The results showed that mechanochemical reactions were started after 10h of MA, which finally caused the slight formation of FeAl/Al₂O₃ nanocomposite. Increasing the milling time to 18 hours led to the continuous increase of the coating thickness up to 80 μm, while the coating layer fractured and began to peel by further milling. The microhardness of the coating after 18h milling was 1050 vickers. Annealing of the 18h milled powders at 773K for 3h led to the complete formation and synthesis of the FeAl/Al₂O₃ nanocomposite. The results showed that the annealing treatment had considerable effects on the hardness increase up to 1200 vickers as well as adhesion strength of the composite coating.
 

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In the present study, the mechanical alloying process was used to produce the Ni-Nb-Si amorphous alloy. X-ray diffraction (XRD)analysis and high-resolution transmission electron microscopy (HRTEM) were used to approve the amorphous phase formation after 12 hours of mechanical alloying. The results obtained from the SEM morphological images of powder particles during mechanical alloying showed that increasing the milling time caused the reduction  of the powder particles size and uniformity in the shape of the particles. Enhancing the embrittlement and fracturing rate caused brittleness and the  increase in the  failure rate; these were followed by a decrease in the powder particle size to 1-5μm. Cold welding and flattening of the pure elemental powders after mechanical alloying for 2 hours formed a lamellar structure of the alternative layers of different elements lying over each other. SEM image of cross-section of powder particles showed that by increasing the milling time, the interlamellar spacing was decreased, the elements were distributed more uniformly, and finally, a uniform structure of theamorphous phase was completed.

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