Abstract
A high γ′ volume fraction CoNi-base superalloy with roughly equal amounts of cobalt and nickel was successfully processed through selective laser melting. The as-printed alloy has a fine cellular structure with segregation of tantalum and significant built-in misorientation within the columnar grain structure. The microstructure evolution after various heat treatments was studied by electron backscatter diffraction and scanning electron microscopy. Super-solvus solution heat treatment promotes complete recrystallization of the microstructure which degrades elevated temperature tensile ductility. Post-processing involving sub-solvus hot isostatic pressing, solution heat treatment, and aging produces a bimodal γ′ distribution while retaining a grain structure similar to the as-printed alloy. The evolution of the precipitate structure was strongly influenced by the cellular structure of the as-printed material. Peak hardness was reached after 2 hours of aging at 950 ∘C. Increasing the carbon content of the alloy promotes the formation of additional carbides on the grain boundaries. Room temperature and intermediate temperature (760 ∘C) tensile testing measured parallel and perpendicular to the build direction revealed that the new heat treatments and carbon additions to the alloy resulted in improved yield strength, ultimate tensile strength, and ductility.
| Original language | English |
|---|---|
| Pages (from-to) | 2943-2960 |
| Number of pages | 18 |
| Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
| Volume | 53 |
| Issue number | 8 |
| DOIs | |
| State | Published - Aug 2022 |
Funding
The authors gratefully acknowledge funding for this research provided by a Department of Defense (DoD) Vannevar Bush Faculty Fellowship, Grant ONR N00014-18-3031. In addition, tuition and stipend funding was provided to S.P.M. by a DoD National Defense Science and Engineering Graduate Fellowship. The research reported here made use of shared facilities of the National Science Foundation (NSF) Materials Research Science and Engineering Center (MRSEC) at UC-Santa Barbara, DMR-172025. The UC-Santa Barbara MRSEC is a member of the Materials Research Facilities Network (www.mrfn.org). A portion of this research was sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office, under contract DE-AC05-00OR22725 with UT-Battelle, LLC and performed in partiality at the Oak Ridge National Laboratory’s Manufacturing Demonstration Facility, an Office of Energy Efficiency and Renewable Energy user facility. The authors acknowledge Quintus for HIP treatments applied to alloys in this study. The authors would like to acknowledge James Lamb for developing the python script used to analyze the DTA heating curves. The authors gratefully acknowledge funding for this research provided by a Department of Defense (DoD) Vannevar Bush Faculty Fellowship, Grant ONR N00014-18-3031. In addition, tuition and stipend funding was provided to S.P.M. by a DoD National Defense Science and Engineering Graduate Fellowship. The research reported here made use of shared facilities of the National Science Foundation (NSF) Materials Research Science and Engineering Center (MRSEC) at UC-Santa Barbara, DMR-172025. The UC-Santa Barbara MRSEC is a member of the Materials Research Facilities Network (www.mrfn.org). A portion of this research was sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office, under contract DE-AC05-00OR22725 with UT-Battelle, LLC and performed in partiality at the Oak Ridge National Laboratory’s Manufacturing Demonstration Facility, an Office of Energy Efficiency and Renewable Energy user facility. The authors acknowledge Quintus for HIP treatments applied to alloys in this study. The authors would like to acknowledge James Lamb for developing the python script used to analyze the DTA heating curves. This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).
