Studies of the Effectiveness of Certain High Performance Coatings in Preventing Hot Corrosion Degradation of Ti-Aluminide Alloys

This paper originates from a large EU programme designed to produce high performance coatings with superior mechanical and corrosion resistance properties to enhance high temperature corrosion behaviour of TiAl based alloy (Ti45Al8Nb).The paper here is concerned with studies of the hot corrosion behaviour of Ti - Aluminide alloys (Ti45Al8Nb mainly gamma-TiAl with small amount alpha(2) (Ti3Al)) coated with three coatings: (1) TiAlYN/CrN coating, (2) CrAl with 2%YN addition ([1,2]) (3) TiAlN with Al2O3 overlayer. Hot corrosion was induced by spraying salts mixture of 80%Na2SO4/20%NaCl with melting point around 700 degrees C ([1] [2]) on heated sample surfaces, and subsequently heating the sprayed samples in a furnace at 750 degrees C for various times. The extent of degradation, assessed by weight changes and examination by OM (Optical Microscope), SEM (Scanning Electron Microscope), and EDX (Energy Dispersive X-Ray Analysis) indicated that all samples suffered hot corrosion attack to various degrees. TiAlN with Al2O3 overlayer had the best corrosion resistance. We shall discuss these results within a mechanistic framework of hot corrosion degradation and describe their implications.