Abstract
Mechanically alloyed Ti–25 mol%Al powders were low pressure plasma sprayed in order to produce nanostructured α2 intermetallic compound on mild steel. Rapidly quenched sprayed layers with various cooling rates were formed by changing the substrate temperature and spray distance. Mechanically alloyed powders with convoluted structure of pure Al and Ti melted in the plasma flame and completely reacted to form α2 intermetallic compound. The relative density of the sprayed layer increased with the substrate temperature and an almost 100% dense layer was obtained in the case of a substrate temperature over 650 K . The microstructure of the sprayed layer consisted of equiaxed nano α2 grains, of which size increased with substrate temperature as well. The grain size was reduced down to a minimum of about 200 nm at the substrate temperature of about 500 K . Effect of cooling rate on the grain size was estimated using Boswell’s model, which agreed well with the experimental results.
