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Friction Stir Welding of Commercially Purity Titanium and its Effect on Microstructure and Mechanical Properties using Different FSW Tools

Nasiri, Ali Mohamad | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39354 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein
  7. Abstract:
  8. The objective of this investigation was obtaining sound Friction Stir Welded (FSWed) Commercially Purity Titanium using suitable Tool’s Materials (for Shoulder and Pin) in order to be able to work in high temperature (>1000 ˚C) with great mechanical properties and minimum wear during process. Consequently, different materials and designs for Tool, such as High Speed Steel tool, Tungsten based tool, Tungsten Carbide (WC-Co) based tool and diverse tool geometry and designs like simple design, threaded design, fixed pin and inserted pin (adjustable pin) was used. The results demonstrated that using simple cylindrical WC-Co for pin and Tungsten for shoulder resulted in joints with the best quality. Also, using (1500, 32), (1500, 60), (1500, 90) and (1000, 60) (rpm, mm/min) for tool rotational rate and tool travel speed, respectively, indicates joints with the best macro and micro structure and mechanical properties with 100% welding efficiency. The FSW zones of Ti were classified by the Stirred Zone (SZ), the linear Transition Boundary (TB) and the Heat Affected Zone (HAZ). The SZ of FSWed Ti was characterized by fine equiaxed α grains surrounded by serrate grain boundaries, which were produced through the β→α allotropic transformation during the cooling cycle of friction stir welding. In the specimens with the maximum temperature of SZ during FSW less than allotropic transformation in Ti (885 ˚C), the SZ consisted of considerable amount of twins and high density of dislocations. The hardness in the SZ showed a scattered value, with higher hardness being observed in the region having denser twin structures
  9. Keywords:
  10. Friction Stir Welding ; Twinning ; Titanium ; Tool Design ; Tool Rotation Rate ; Tool Travel Speed

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