Abstract

Ti_52Al_48 and (Ti_52Al_48)_100-xB_x(x=0.5, 2, 5) alloys have been Produced by mechanical milling in an attritor mill using prealloyed powders. Microstructure of binary Ti_52Al_48 powders consists of grains of hexagonal phase whose structure is very close to Ti_2Al. (Ti_52Al_48)_95B_5 powders contains TiB2 in addition to matrix grains of hexagonal phase. The grain sizes in the as-milled powders of both alloys are nanocrystalline. The mechanically alloyed powders were consolidated by vacuum hot pressing (VHP) at 1000°C for 2 hours, resulting in a material which is fully dense. Microstructure of consolidated binary alloy consists of gamma-TiAl phase with dispersions of Ti_2AlN and A1_2O_3 phases located along the grain boundaries. Binary alloy shows a significant coarsening in grain and dispersoid sizes. On the other hand, microstructure of B containing alloy consists of gamma-TiAl grains with fine dispersions of TiB_2 within the grains and shows the minimal coarsening during annealing. The vacuum hot pressed billets were subjected to various heat treatments, and the mechanical properties were measured by compression testing at room temperature. Mechanically alloyed materials show much better combinations of strength and fracture strain compared with the ingot-cast TiAl, indicating the effectiveness of mechanical alloying in improving the mechanical properties.