Microstructure Evolution and Tensile Properties of a Selectively Laser Melted CoNi-Base Superalloy

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 53; no. 8; pp. 2943 - 2960
• Main Authors: Murray, Sean P., Raeker, Evan B., Pusch, Kira M., Frey, Carolina, Torbet, Chris J., Zhou, Ning, Forsik, Stéphane A. J., Dicus, Austin D., Colombo, Gian A., Kirka, Michael M., Pollock, Tresa M.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.08.2022; Springer Nature B.V
• Subjects: Aging (metallurgy); Carbon content; Cellular precipitates; Cellular structure; Characterization and Evaluation of Materials; Chemistry and Materials Science; Columnar structure; Ductility; Electron backscatter diffraction; Evolution; Grain boundaries; Grain structure; Heat treating; High temperature; Hot isostatic pressing; Intermetallic compounds; Laser beam melting; Materials Science; Metallic Materials; Microstructure; Misalignment; Nanotechnology; Original Research Article; Recrystallization; Room temperature; Solution heat treatment; Structural Materials; Superalloys; Surfaces and Interfaces; Tantalum; Tensile properties; Tensile tests; Thin Films; Ultimate tensile strength
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-022-06716-z

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.