AN INVESTIGATION ON REACTIVE SINTERING OF NANO-CRYSTALLINE TiO۲ -Al POWDER PREPARED BY MECHANICAL ALLOYING

In this research an ultra-fine grained composite structure consisting of an intermetallic matrix together with dispersed nano-sized Al۲O۳ obtained via mechanical activation of TiO۲ and Al in a high energy ball mill and sintering of consolidated samples. Phase composition and morphology of the milled and sintered samples were evaluated by XRD and SEM techniques Thermal behavior of the powder sample milled for ۸ hours was evaluated by DTA technique. DTA results showed that, the reaction happens in two steps. The first step is the aluminothermic reduction of TiO۲ with Al. XRD observations reveals that minor amount of Ti۳Al phase formed during reduction reaction together with TiAl and Al۲O۳ major phases. This intermetallic phase disappeared when sintering temperature was increased to ۸۵۰ ºC. The second step in DTA is related to a reaction between residual Al in the system (partly dissolved in TiAl lattice) and the Ti۳Al phase produced earlier at lower temperatures. SEM micrographs reveal that by completion of the reduction reaction more homogeneous and finer microstructure is observable in sintered samples.

Keywords:

γ-TiAl , nano-composite , mechanical alloying , aluminothermic reduction