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Structural and Microstructural Study on Al/Ti Intermetallic Sheets Produced by ARB

Esmaeilizadeh, Reza | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46169 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ekrami, Ali Akbar; Akbarzadeh, Abbas
  7. Abstract:
  8. Due to special physical and mechanical properties of intermetallic compounds,somehow in between of the metallic and ceramic extremes, their applications are increased in different industries. Among these materials, titanium aluminides due to their low density, high specific strength and excellent corrosion and oxidation resistance has got more attention. Because of similar high temperature properties and lower density, these compounds are suitable alternatives for nickel base superalloys. Accumulative Roll Bonding (ARB) of pure metallic sheets and the following heat treatment in production of intermetallic compounds can be considered as a manufacturing process. The goal of this study is production of composite Al/Ti intermetallic sheets by ARB method and investigation of the strain and heat treatment effects on growth and structure of the intermetallic compounds and evolution of the multilayer sheets toward uniform intermetallic sheet. By this purpose, pure aluminum and titanium sheets were used as the main components of the primary composite. The thickness of thetitanium sheet was 0.7 mm and to fix the chemical composition 0.3 mm thick aluminum sheets were used. The primary composites with the alternating layers of titanium and aluminum were produced by 50% reduction at 550 oC and then ARBed by three more cycles. To investigate the strain effect on intermetallic growth, samples from different cycles were annealed at 640 oC for a variety of times from 15 min to 32 hrs. After determination of the optimum condition to remove aluminum, the roll bonded samples were annealed at 650 oC for 48 hrs. After Al removal, the samples were annealed at 1200 oC for 3 hrs. Structural and microstructural studies were performed by optical microscope and interface investigation with EDX analyzer on composite samples. Tensile properties at different directions, with respect to the rolling direction, were determined and hardness variation is measured as well.The results show that in addition to increasing the dispersion of titanium by ARB cycles, this phase change from the continuous lamellar configuration to particles. No new phase was formed during ARB and TiAl3 is the only intreface phase beforeconsumption of aluminum.At thhe last step, high temperature annealing led to a lamellar microstructure in the final intermetallic sheets
  9. Keywords:
  10. Accumulative Roll Bonding (ARB) ; Microstructure ; Mechanical Properties ; Anisotropy ; Intermetallic Compounds ; Titanium Aluminide

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