Influence of the high-temperature aluminizing process on the microstructure and corrosion resistance of the IN 740H nickel superalloy

Abstract

The article discusses the effect of high temperature aluminizing processes on microstructure and corrosion resistance in 0.1 M Na2SO4 solution at room temperature of the IN 740H nickel superalloy. The aluminizing processes were carried out by chemical vapor deposition (CVD): (a) in AlCl3 vapors, (b) in a mixture of AlCl3+ZrCl3 vapors under a hydrogen atmosphere as carrier gas under the same conditions (process temperature −1040 °C, time-7h under reduced pressure of 150 hPa). Observations of the surface of the produced layers showed that the additional modification of the aluminizing process with zirconium affects the morphology of the layers formed as compared to the unmodified aluminizing process. It was also found that the prepared aluminide layers unmodified and modified additionally with zirconium improve corrosion resistance of the Inconel 740H nickel superalloy. On the basis of the conducted tests, it was also found that after high-temperature aluminizing processes in the IN 740H substrate precipitates are formed at the grain boundaries containing carbide forming elements such as: Cr, Ti, Nb, which may form secondary carbides, e.g. M6C, M7C3.