Loading...

Effect of Heat Treatment on the Mechanical Properties of In-situ Al-Al3Ti Nanocomposite Fabricated by Mechanical Alloying and Hot Extrusion

Tamizi, Mohammad Reza | 2019

435 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51790 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Madaah Hosseini, Hamid Reza
  7. Abstract:
  8. In the present work, at first Al-20 wt% Ti nanocomposite was fabricated via mechanical alloying in high energy vibratiory mill for 1-4 hours. Particles morphology, crystallite size changes and phases transformation were investigated during mechanical alloying. Next, the powders which mechanically alloyed for 2 and 4 hours was compressed by hot extrusion at 500 ℃. The extruded specimens were investigated by different tests such as density, hardness, tensile and differential scanning calorimetry (DSC). Microscopic analysis and phases transformation were also investigated by optical microscopy (OM), field emission electron microscope (FESEM) and X-ray diffraction. Then, the samples were heat treated at different time periods and temperatures and similar tests were performed on them and investigated thermal effects on mechanical and microstructural properties. The results indicated that after 4-hours period use of vibratiory mill, aluminum crystallite size reaches 63 nm and Al3Ti phase identified by XRD. After extrusion, under mechanical and thermal conditions of the process, the volume percentage of Al3Ti increased. For extruded sample of 4 hours milling powders, density, failure stress, and strain-to-failure was 2.91 g/cm3, 300Mpa and respectively, and the mechanical properties of this specimen were higher than the other extruded specimen. After heat treatment of this specimen at different temperatures and time periods, it was found that, after 8 hours and 4 hours of heat treatment at temperatures of 600 ℃ and 630 ℃ the respectively, Al3Ti layer was clearly observed around the titanium micro particles and with thickening of this layer, the amount of voids in the structure increased. In best condition of heat treatments, the failure stress and strain-to-failure of specimens reached 293Mpa and 0.132 respectively. Also, the average value of Young modulus reached to 130 GPa in best condition. Depending on the type of hardness measurement, different results were obtained. This is because of the variation of the affected area on each sample in each of the hardness measurement methods
  9. Keywords:
  10. In-Situ Nanocomposite ; Intermetallic Compounds ; Mechanical Alloying ; Hot Extrusion ; Mechanical Properties ; Heat Treatment

 Digital Object List

 Bookmark

No TOC