Dislocation Decorrelation and Relationship to Deformation Microtwins during Creep of a Gamma' Precipitate Strengthened Ni-based Superalloy
OAK RIDGE NATIONAL LAB TN MATERIALS SCIENCE AND TECHNOLOGY DIV
Pagination or Media Count:
The evolution of microtwins during high temperature creep deformation in a gamma strengthened Ni-based superalloy has been investigated through a combination of creep testing, transmission electron microscopy TEM, theoretical modeling, and computer simulation. Experimentally, microtwin nucleation sources were identified and their evolution was tracked by characterizing the deformation substructure at different stages of creep deformation. Deformation is highly localized around stress concentrators such as carbides, borides and serrated grain boundaries, which act as sources of a2110 matrix-type dislocations. Due to fine channels between the gamma particles coupled with a low gamma matrix stacking fault energy, the a2110 matrix dislocations dissociate into a6112 Shockley partials, which were commonly observed to be decorrelated from one another, creating extended intrinsic stacking faults in the c matrix. Microtwins are common and form via Shockley partial dislocations, cooperatively shearing both the gamma and gamma phases on adjacent 1 1 1 glide planes. The TEM observations lead directly to an analysis of dislocation-precipitate interactions. The important processes of dislocation dissociation and decorrelation were modeled in detail through phase field simulations and theoretical analyses based on Orowan looping, providing a comprehensive insight into the microstructural features and applied stress conditions that favor the microtwinning deformation mode in gamma strengthened Ni-based superalloys.
- Properties of Metals and Alloys
- Solid State Physics