Behavior of branch cracking and the microstructural strengthening mechanism of polycrystalline Ni-base superalloy, IN100 under creep condition

Recently, the development of the high-efficiency technology for gas turbine and jet engine is required to minimize carbon dioxide and nitrogen oxide emission. It is effective way to increase the operational temperature to develop the high-efficiency technology for high temperature instruments. To increase the operating temperature, advanced Ni-base superalloys have been developed as a turbine blade material. Even though a Ni-base superalloy is used for a structural component, creep damages and creep cracks may be caused due to the external tensile load under high temperature conditions. Therefore, a predictive law of creep crack growth life is necessary to maintain operational safety. This study is aimed to clarify the branch cracking behavior due to the microstructural strengthening mechanism of polycrystalline Ni-base superalloy IN100 under the creep condition. The creep crack growth tests were conducted at a temperature of 900°C. The creep crack growth behavior and creep damage formulation were observed by in-situ observational system and FE-SEM/EBSD. Additionally, two-dimensional elastic-plastic creep finite element analyses were conducted for the model which describes the experimental results. The creep crack growth behavior and the creep damage progression were found to be affected by the distribution behaviors of grains and grain boundaries around the notch tip. By comparison of experimental results with mechanical analysis using FEM analyses, mechanisms of the creep crack growth and the creep damage formulation were clarified.