Combustion synthesis of FeAl-Al2O3 composites with TiB2 and TiC additions via metallothermic reduction of Fe2O3 and TiO2
(Department of Aerospace and Systems Engineering, Feng Chia University, Taichung 40724, Taiwan, China)
Abstract: Combustion synthesis involving metallothermic reduction of Fe2O3 and TiO2 was conducted in the mode of self-propagating high-temperature synthesis (SHS) to fabricate FeAl-based composites with dual ceramic phases, TiB2/Al2O3 and TiC/Al2O3. The reactant mixture included thermite reagents of 0.6Fe2O3+0.6TiO2+2Al, and elemental Fe, Al, boron, and carbon powders. The formation of xFeAl-0.6TiB2-Al2O3 composites with x=2.0-3.6 and yFeAl-0.6TiC-Al2O3 composites with y=1.8-2.75 was studied. The increase of FeAl causes a decrease in the reaction exothermicity, thus resulting in the existence of flammability limits of x=3.6 and y=2.75 for the SHS reactions. Based on combustion wave kinetics, the activation energies of Ea=97.1 and 101.1 kJ/mol are deduced for the metallothermic SHS reactions. XRD analyses confirm in situ formation of FeAl/TiB2/Al2O3 and FeAl/TiC/Al2O3 composites. SEM micrographs exhibit that FeAl is formed with a dense polycrystalline structure, and the ceramic phases, TiB2, TiC, and Al2O3, are micro-sized discrete particles. The synthesized FeAl-TiB2-Al2O3 and FeAl-TiC-Al2O3 composites exhibit the hardness ranging from 12.8 to 16.6 GPa and fracture toughness from 7.93 to 9.84 MPa·m1/2.
Key words: FeAl-based composites; self-propagating high-temperature synthesis; metallothermic reduction; activation energy