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Fabrication and Characterization of Al/Al3Ti-Al2O3 Composites by Powder Metallurgy and Sol Gel and Consideration of Mechanical Properties and their Correlation with the Microstructure Evolution

Azarniya, Abolfazl | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47272 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Maddah Hosseini, Hamid Reza
  7. Abstract:
  8. In the present research, a novel method for the fabrication of Al/Al3 Ti-Al2O3 composites and nanocomposites based on the thermal degradation of the refectory ceramic “Aluminium Titanate (AT)” or Al2TiO5 by powder metallurgy route. This research encompasses some precise subsequent steps. At first stage, nanostructured aluminium titanate nanofibers and particles were synthesized via a citrate sol gel process in which citric acid was used as a chelating agent. At second step, the possible chemical reactions between Al and aluminium titanate were taken into consideration both in powder form and in bulk form. Thermal analysis results indicated that it is feasible to decompose aluminium titanate in exposure to active Al matrix at temperatures lower than 550 C. Such chemical transformations were believed to lead to the formation of in situ Al3Ti and Al2O3. However, it was found out that during the AT degradation, a large volume of oxygen gas is evolved and forms a large volume fraction of porosities in aluminium matrix. It was found that the aluminium titanate-based powder metallurgy process results in a porous structure of inferior mechanical properties (relative density of 90-95% and Vickers microhardness of 14-18 HV). In order to modify the adverse microstructure and enhance its mechanical properties, cyclic rolling and hot extrusion were employed. It was shown that among these thermomechanical treatments, hot extrusion is the more proper option for improving the mechanical properties and evolving a dense microstructure benefiting a homogenous distribution of Al2O3 and Al3Ti reinforcements. It was shown that Vickers hardness of 40-60 HV and relative density of 99% can be obtained by these complementary procedures. Also, in rolled composites, the morphology of both Al2O3 and Al3Ti reinforcements were blocky, but in hot extruded samples, the Al3Ti particles bore a sub-micron rod-like structure and Al2O3 reinforcements showed a nano-sized distribution with an average particle size less than 100 nm in a nano-grained matrix
  9. Keywords:
  10. Hot Extrusion ; Aluminum Matrix Composite ; Sol-Gel Method ; Powder Metallurgy ; Microstructure ; Hot Press ; Aluminum Titanate ; Cyclic Rolling

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