Investigation of damage mechanisms and short fatigue crack growth during thermomechanical fatigue loading of the nickel‐based superalloy Inconel 100

Growing demands on gas turbines, meaning lower consumption and higher efficiency, is accompanied by higher temperatures inside the turbine. Better lifetime prediction concepts for thermomechanical fatigue (TMF) loading of gas turbine components are needed to ensure safe operation. The influence of the TMF loading history - either in-phase (IP) or out-of-phase (OP) - on crack initiation and short crack growth is studied for the cast nickel-based super alloy IN100, which is commonly used as blade material. Therefore, smooth specimens are loaded at two different mechanical strain levels with, respectively, two phase relationships, using a temperature cycle T = 300-950°C and T = 300-850°C. The replica technique is used to detect cracks in the order of tens of micrometers. The differences in crack initiation and short crack growth are studied for the different loading conditions and the development of the crack length evolving from multiple short cracks is investigated.