Role of intensive milling in mechano-thermal processing of TiAl/Al2O3 nano-composite

Abstract

In this research a nano-composite structure containing of an intermetallic matrix with dispersed Al2O3 particles was obtained via mechanical activation of TiO2 and Al powder mixture and subsequent sintering. The mixture has been milled for different lengths of time and then as a subsequent process it has been sintered. Phase evolutions in the course of milling and subsequent sintering of the milled powder mixture were investigated. Samples were characterized by XRD, SEM, DTA and TEM techniques.The results reveal that the reaction begins during milling by formation of Al2O3 and L12 Al3Ti and further milling causes partial amorphization of powder mixture. DTA results reveal that milling of the powder mixture causes solid state reaction between Al and TiO2 rather than liquid–solid reaction. Also, it was observed that the exothermicity of aluminothermic reduction is reduced by increasing the milling time and the exothermic peak shifts to lower temperatures after partial amorphization of powder mixture during milling. Phase evolutions of the milled powders after being sintered reveal that by increasing the milling time and formation of L12 Al3Ti in the milled powder, intermediate phase formed at 500°C changes from D022 Al3Ti to Al24Ti8 phase.