About this Abstract |
Meeting |
Superalloys 2024
|
Symposium
|
Superalloys 2024
|
Presentation Title |
E-2: Concurrent Improvement of Additive Manufacturing Processability and Creep Performance in a Legacy Polycrystalline Superalloy Using Grain Boundary Strengtheners |
Author(s) |
A Shaafi Shaikh, Eduard Hryha, Mohammad Sattari, Mattias Thuvander, Kevin Minet-Lallemand |
On-Site Speaker (Planned) |
A Shaafi Shaikh |
Abstract Scope |
Microcracking during processing and underperformance in creep have limited wider adoption of high γ'-fraction superalloys in additive manufacturing (AM). Certain processing issues are now understood to be related to solidification cracking caused by elements such as B and Zr, that are also essential for creep performance, particularly with fine-grained AM microstructures. A legacy γ'-strengthened polycrystalline superalloy 738LC was the subject of the current investigation. Printing trials conducted with the legacy composition and a modified version with 10 times the initial B content revealed extensive micro-cracking in the legacy composition, whereas the modified alloy produced a dense crack-free microstructure. CALPHAD-based solidification simulations and cracking susceptibility index calculations were performed to attempt to rationalise these findings. After hot isostatic pressing (1120 °C, 200 MPa, 4 hours) and ageing heat treatment (850 °C, 24 hrs), stress rupture tests showed an improvement in the rupture life of the modified alloy. Samples perpendicular to the AM building direction (typically the weaker orientation) showed a 50 % increase in rupture life compared to the conventional composition, and rupture ductility was also enhanced. Elevated temperature tensile ductility in the perpendicular direction increased to ≈ 11 El% for the modified alloy versus ≈ 6 El% for the conventional composition. These improvements are attributed to the presence of fine boride precipitates at grain boundaries of the modified alloy. The findings indicate that increasing the grain boundary strengthening element content may be a potential solution for both processing and mechanical performance issues in this superalloy. |
Proceedings Inclusion? |
Definite: At-meeting proceedings |