Hot Corrosion and HVOF Coatings

Hot corrosion is an aggressive form of corrosion in which metals and alloys experienced accelerated degradation when their surfaces are covered with a thin film of fused salt in an oxidizing atmosphere at elevated temperatures. This form of corrosion consumes the material at an unpredictably rapid rate. Consequently the load-carrying ability of the components reduces quickly leading eventually to catastrophic failure. Hot corrosion occurred due to the presence of salt contaminants such as Na2SO4 NaCl and V2O5 that combine to form molten deposits which damage the protective surface oxides. The inability to either totally prevent hot corrosion or at least detect it at an early stage has resulted in several accidents leading to loss of life and destruction of infrastructures. Hot corrosion has been observed in boilers internal combustion engines gas turbines fluidized bed combustion and industrial waste incinerators since 1940’s. However it became a topic of importance and popular interest in the late 1960’s when gas turbine engines of military aircrafts suffered severe corrosion attacks while operating over and near sea water during the Vietnam conflict