An investigation on reactive sintering of nano-crystalline Tio2-Al powder processed by mechanical alloying

In this research an ultra-fine grained composite structure consisting of an intermetallic matrix together with dispersed nana size Al2O3 obtained via mechanical activation of TiO2 and Al in a high energy ball mill and sintering of consolidated samples. Phase composition and morphology of milled and sintered samples were evaluated by XRD and scanning electron microscopy techniques Thermal behavior of 8 hour milled powder was evaluated by differential thermal analysis technique. Differential thermal analysis results showed that, the reaction happens in two steps. The first step is the aluminothermic reduction of TiO2 with Al. XRD observations reveals that some Ti3Al phase formed during reduction reaction together with Ti Al and Al2O3 major phases. This intermetallic phase disappeared when sintering temperature was increased to 850 and 1000degreeC. The second step in differential thermal analysis is related to a reaction between residual Al in the system (dissolved in Ti Al lattice) and the Ti3Al phase produced earlier at lower temperatures. Scanning electron microscopy micrographs reveal that by completion of the reduction reaction more homogeneous and finer microstructure is observable in sintered samples.