Carbide and hydride formation during mechanical alloying of titanium and aluminium with hexane

Mixtures of elemental titanium and aluminium powders of overall composition Ti_xAl_1+x (x = 0.02, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, 0.8) were mechanically alloyed in a planetary-type ball mill. Hexane was added as a process control agent to reduce powder agglomeration during milling. The as-milled powders were characterized using X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. During milling, the hexane is partially dissociated, with the free carbon and hydrogen incorporated within the Ti_xAl_1−x alloy powders in increasing amounts with increasing milling time. The amount of incorporated carbon increases with the initial Ti content of the powder mixture, reaching a maximum of 12 wt.% incorporated into an initial Ti_0.8Al_0.2 powder mixture after 100 h of milling. The hydrogen is found to combine with elemental Ti to form TiH_2−x, with an initial Ti_0.5Al_0.5 powder mixture milled for 40 h incorporating 0.95 wt.% H. The milled (Ti_xAl_1−x + C) powder mixtures form a large fraction of amorphous phase near x = 0.5.
Annealing of the as-milled powders incorporating dissolved carbon and hydrogen produced a mixture of Al₂Ti₄C₂, TiC and TiAl.