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Mechanical and Microstructural Behavior of Al1050/TiO2-Gr Nano-Composite Produced via Friction Stir Processing

Farshbaf Ahmadi Pour, Mohammad | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48384 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Movahedi, Mojtaba; Kokabi, Amir Hossein
  7. Abstract:
  8. In the presented research, feasibility of producing hybrid nano-composite on the surface of Al1050 with TiO2 (~15 nm) and Graphite (~100 μm) reinforcement particles via Friction Stir Processing (FSP) has been investigated. 1.93%, 1.68% and 1.44% are the weight percentage of added reinforcement particles in the nano-composite. Rotational and travelling speeds (and their ratio, ω/v) and volume fraction of the embedded reinforcement particles, mentioned as variable parameters in this research. Despite, effect of these parameters on the microstructural evolution and mechanical properties such as strength, hardness and wear, were studied. Results in the ratio of Gr/TiO2 = 1/3, revealed that by increasing ω/v and subsequent increase in heat input, fine dispersion and homogenous distribution of particles in the matrix was acquired. Moreover, by increasing Gr/TiO2 ratio up to 1 and 3/1 levels, finely dispersed particles led to more homogenous distribution in the structure. Severe plastic deformation during FSP, decrease activation energy of reaction between particles and matrix. As a result, formation of secondary compounds is susceptible. Considering tensile strength values, increasing volume fraction of graphite led to increase in tensile strength. In a specific volume fraction of reincement particles, increase in heat input that induces fine dispersion of particles in the matrix beside its effect on the microstructure and grain size, tensile strength may vary by mutual effects of these two phenomena. At lower amounts of heat input, strength may increase as a result of fine grain size. By increasing heat input, coarsening of grains may occur, in spite of that may led to obtaining more homogenous distribution of particles in the matrix, which can increase strength by Orowon mechanism and pinning effect of nano-sized reinforcement particles. Consideration of hardness test results indicates that homogenous distribution of particles in the matrix, increases hardness values. Moreover, by increasing graphite volume fraction in composite, hardness value decreased but then increased. Decrease in hardness value by increasing graphite volume fraction is due graphite's lower module. Subsequent increase in hardness value as graphite volume fraction increases, is attributed to possible reaction between particles and formation of secondary compounds such as Al3Ti, Al2O3, Al4C3 and TiC, as a consequent of synthesizing is-situ nano-composite. Region between TMAZ and SZ represented lowest value of hardness, considering hardness transverse profile. Moreover, transverse tensile strength specimens also failed in this region. This results indicates that mechanical properties is deteriorated in this region. Wear test revealed that by increasing volume fraction of graphite, coefficient of friction decreases, as well as wear rate. Squeezind out and presence of flake shaped graphite between the sliding pairs, enhances wear properties. Therefor, optimum heat input is required to least the raction between graphite and titanium oxide, so graphite operates as solid lubricant on the surface
  9. Keywords:
  10. Aluminum Alloy 1050 ; Friction Stir Welding ; Hybrid Nanocomposite ; In-Situ Synthesis ; Titanium Dioxide-Graphite

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