MOTLEN SALTS INDUCED HOT CORROSION OF Ti_3Al INTERMETALLIC COMPOUND AND ITS ALUMINIDE COATING
Ti_3Al及其渗铝涂层的热腐蚀性能

Hot corrosion of Ti_3Al and its aluminide coating was studied by electrochemical techniques combined with physical analyses. It is observed that hot corrosion resistance of Ti_3Al is inferior to that of HK40 alloy. The corrosion product scale is of a three-layer structure with a outer scale of TiO_2 ,an intermediate layer of Al_2O_3-TiO_2 rich in Al_2O_3 and an inner layer of Nb_2O_5-TiO_2-Al_2O_3 rich in Nb_2O_5 . The inferior protectiveness of the intermediate layer may result from the presence of Ti~(4+) in Al_2O_3 , which promotes the diffusion of oxygen. Rapid outward diffusion of Ti and inward diffusion of oxygen are believed to be responsible for the fast thickening of the corrosion product scale. It is proved that aluminide coating can provide better hot corrosion resistance.This effect is attributed to the rapid formation of a thin Al_2O_3 film on its surface.