| About this Abstract |
| Meeting |
2023 AWS Professional Program
|
| Symposium
|
2023 AWS Professional Program
|
| Presentation Title |
Thermal Faceting on the Ductility-Dip Cracking Fracture Surfaces of Nickel-Based Alloys – Occurrence, Characterization, and Implications for the Cracking Mechanism |
| Author(s) |
Samuel Luther, Boian Alexandrov, Milan Heczko, Veronika Mazanova, Michael Mills |
| On-Site Speaker (Planned) |
Samuel Luther |
| Abstract Scope |
Ductility-dip cracking (DDC) fracture surfaces containing thermal faceting (TF) are extensively documented in this study. Research began with the discovery of TF on the DDC fracture surface in the weld metal of high-chromium nickel-based filler metal 52M, a valuable alloy to the nuclear industry. Fracture surfaces were generated using strain-to-fracture (STF) and simulated strain ratcheting (SSR) testing on a Gleeble® thermomechanical simulator. Initial fractography conducted in the SEM revealed faceting with preferred grain orientations, faceting interacting with void nucleation at grain boundary (GB) triple points, and faceting forming inside voids nucleated at GBs. A thin orientation- and site-specific foil was extracted from the faceted fracture surface using focused ion beam (FIB) nanofabrication. Subsequent STEM characterization down to atomic-resolution revealed that the facets have perfect crystallographic orientations parallel to close-packed directions. Atomically sharp edges and transitions between individual facets were observed. An analysis of the deformation microstructure and the chemical composition underneath the faceted surface showed a low dislocation density and no evidence of localized segregation or diffusion, respectively. These findings have led to the development of a hypothesis related to the interdependence of TF and DDC along with supporting initial claims made by Hemsworth et al. in 1969 regarding TF formation in DDC voids at elevated temperatures. |
| Proceedings Inclusion? |
Undecided |