Hot Corrosion of Gas Turbine Alloys

Abstract

Abstract Types of hot corrosion encountered in aircraft gas turbines operating in marine environments were reproduced in laboratory tests. Nickel and cobalt-base alloys were tested in the products of combustion of JP-5 and 0, 2 and 200 ppm sea salt between 1600 F (871 C) and 2000 F (1093 C). Higher chromium alloys were generally (but not always) more resistant to hot corrosion. Attack was caused by sodium sulfate, corrosion occurring only in the temperature range in which sodium sulfate was deposited in a molten state. (About 1600 F (871 C) to 1875 F (1024 C)/ 2000 F (1093 C). Effects of another alkali metal and two alkaline-earth metals, sulfur and chlorine also were evaluated. Microstructural changes were studied by metallographic techniques and chemical compositional changes and sulfides were identified by electron microprobe analyses. The nature of attack is discussed and some concepts of the hot corrosion mechanism postulated. Apparently, depletion of chromium in surface zones through the formation of oxides and sulfides reduces the corrosion resistance of depleted zones, thereby promoting severe hot corrosion.