Hot corrosion influence on deformation and damage mechanisms in turbine blades made of IN-792 during service

The deformation and damage mechanisms of a gamma-prime hardened superalloy is investigated in the current paper. Two turbine blades made of precision cast polycrystalline superalloy IN-792 have been examined after service exposure under engine conditions typical for industrial gas turbines. This study is compared to a previous study with focus on deformation and damage mechanisms in IN-792 during thermal mechanical fatigue testing performed under laboratory conditions. The failure of the two turbine blades is explained as a combination of two damage mechanisms, mechanical and chemical damage. In the current investigation, type I hot corrosion and creep are the two dominant damage mechanisms. The type I hot corrosion is confirmed by the presence of Ti-sulfides and sulfur in free form at the grain boundaries, which has caused embrittlement and loss of resistance to crack growth. In turn, this has shortened the turbine blade life dramatically and intercrystalline failure is the dominant damage mechanism. Almost all cracks have propagated intercrystalline in the two turbine blades. In the previous study, mechanical damage mechanism is the dominant mechanism and for the highest temperature also oxidation give is contribution. In the previous study, almost all cracks propagated transcrystalline. When exposed to laboratory conditions, the areas around cracks are more plastically deformed compared to the area around the cracks in the turbine blades. In the two studies, dynamic recrystallization has occurred at the grain boundaries.