Nucleation of Cellular Colonies in Single Crystal Ni-Based Superalloy Subjected to Previous Damage and Influence on High Temperature Fatigue Strength
Masakazu OKAZAKI, Tomoyuki HIURA and Toshio SUZUKI
Abstract:In order to get fundamental understanding to establish the refurbishment technology for advanced gas turbines, the nucleation of cellular colonies in a single crystal Ni-base superalloy, CMSX-4, was studied, supposing the case in which the material was subjected to damage associated with local plastic deformation, followed by the re-heat treatments. During the study special attention was paid to get basic understandings on it. The experimental evidences indicated that the cellular colonies was originated and developed from the damaged region, being influenced by the following many factors: the strain field by the local plastic deformation, the re-heat treatment temperature, and the microsegregation in the material. It was also shown that the cellular colonies was actually produced inside the material subjected to fatigue and thermo-mechanical fatigue damages. Furthermore, the effect of the local cellular colonies on the high temperature fatigue strength was experimentally quantified. Key Words:Refurbishment and Reheat treatments, CMSX-4, Cellular Colonies, Local Plastic Deformation, Fatigue Strength, Microsegregation, Thermo-Mechanical Fatigue Damage