The Investigation of Additive Elements Ti, Cr on Structure and Some Mechanical Properties of Micro and Nano Composites of Iron Aluminide/Alumina

Khazraiyan Vafadar, Ali | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40204 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Abachi, Parvin; Salahi, Esmaeil
  7. Abstract:
  8. In this experiment, first the Fe and Al powders with atomic ratio of 25 and 75 were mixed by mechanical alloying process. After obtaining the optimum conditions of milling, nano structural Fe3Al powder was synthesized by 40 hours alloying with a Ball to Powder Ratio (BPR) of 20:1. The synthesized powder was then milled with different weight ratios of titanium and Cr for 30 hours. Morphological changes, size of powder particles, lattice strain, grain size and phase transitions were studied for different powders in different time spans during milling process by means of scanning electron microscopy, X-ray diffraction and grain size analyzer. The smallest grain size gained for milled powder after 40 hours was 12 nm. Also, the micro hardness changes and powder densities were measured by standard methods. After adding micro and nano size Al2O3 reinforcers and considering the importance of the compactibility effect, the compactibility behavior of composite powder mixture was evaluated in different pressures and then the yield strength of bulk was measured by extracting the equations of compactibility of powders. The specimen, containing Cr has the lowest bulk yield strength and the maximum raw density. In order to produce the compact composite specimens, raw specimens were processed under two-step sintering method. Then the microstructure, phase analysis, density and hardness of dense specimens were measured. The grain sizes of composite specimens were between 63-91 nm and the maximum density 95/1 was gained from the specimen with 8wt. % of Cr and the grain size of 77 nm. Distribution of Al2O3 reinforcer was homogenous and just a few agglomerations were observed in specimens containing 5% nanometer Al2O3. In all specimens, alloying elements such as Ti and Cr were solved in matrix and no other separate phase was observed. Finally mechanical properties such as hardness, three-point bending strength and compression strength were measured for composite specimens. By adding Ti and Cr, due to the increase in adhesion and strength of the interface between matrix and reinforcer, the bending strength was improved a lot. The maximum bending strength 414.19 MPa belonged to the specimen with 8wt. % Ti. The results of compression test also showed an improvement in compression strength after adding Cr to Iron aluminide/Alumina Composite, with the maximum increase in 8wt. % Cr composite ranging from 241.9 MPa to 542 MPa. The rate of increase in compression strength was found to be slower in specimens containing Ti compared to the specimens containing Cr
  9. Keywords:
  10. Nanocomposite ; Mechanical Alloying ; Titanium ; Chromium ; Two Step Sintering ; Bending Strength ; Compression Strength ; Tron Aluminide

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