Superalloy 718 and Derivatives: Additive: Microsturcture & Properties
Program Organizers: Joel Andersson, University West; Chantal Sudbrack, National Energy Technology Laboratory; Eric Ott, GE Additive; Zhongnan Bi, Central Iron and Steel Research Institute
Wednesday 8:00 AM
May 17, 2023
Room: Admiral
Location: Sheraton Pittsburgh Hotel at Station Square
Session Chair: Joel Andersson, University West; Daisuke Nagahama, Honda R&D Co Ltd
8:00 AM Introductory Comments
8:05 AM
Correlating Alloy 718 and Haynes 282 Solidification Microstructures to Local Thermal History using Laser Powder Bed Fusion Process Monitoring: Andrew Wessman1; Timothy Smith2; Yi Zhang1; Fan Zhang3; Thomas Spears4; John Middendorf4; Mohammed Shafae1; Nazmul Hasan1; 1University of Arizona; 2NASA Glenn Research Center; 3Computherm LLC; 4Open Additive, LLC
Additive manufacturing processes such as laser powder bed fusion produce material by localized melting of a powder feedstock layer by layer. The small meltpools and high energy density generate very different microstructures in nickel superalloys when compared to more traditional cast or wrought processing, including features such as cellular structures and epitaxial grain growth. The features of these microstructures vary depending on local thermal history, alloy chemistry and processing parameters. In this work in-situ monitoring of a laser powder bed fusion process is used to characterize the local thermal conditions throughout an AM build for alloys IN718 and Haynes 282, and this information is correlated to observations on the microstructural features of these alloys in the as-built condition. In IN718, segregation of niobium and molybdenum are found in interdendritic regions of the 200nm wide cellular precipitate structures, while in Haynes 282 segregation of gamma prime forming elements such as titanium and aluminum segregate to the interdendtritic cell walls. In-process monitoring using thermal tomography is utilized to observe the local thermal conditions during the solidification of the AM material and correlate those conditions to the microstructures formed through computational modeling of the segregation and dendrite formation. Results for both IN718 and Haynes are compared.
8:25 AM
Understanding Annealing Behavior during Post-build Heat Treatment of Ni-based Alloys Across Additive Manufacturing Processes: Juan Gonzalez1; Yi Zhang2; Andrew Wessman2; Jonah Klemm-Toole1; 1Colorado School of Mines; 2University of Arizona
Ni-based alloys are used for high temperature structural components that span from small, highly complex, with fine feature resolution to large, simple shapes with low dimensional tolerances. Accordingly, a range of additive manufacturing (AM) processes from high precision laser powder bed fusion (LPBF) to high deposition rate wire arc additive manufacturing (WAAM) can be used to produce components. However, the microstructure evolution during post processing varies considerably between LPBF and WAAM. In this presentation, we show how the annealing responses during post build heat treatment systematically vary in LPBF and WAAM IN625 and Haynes 282. Despite suggestions in literature, primary carbides do not control the recrystallization behavior in these alloys. Differences in stored energy in the as built condition, which is heavily influence by AM process, has the greatest effect on recrystallization behavior. The implications of these results on microstructure control in AM Ni-based alloys is discussed.
8:45 AM
High-temperature Properties of Alloy 718 Made by Laser Powder-bed Fusion: David Witkin1; Tait McLouth1; Glenn Bean1; Julian Lohser1; Robert Hayes2; 1The Aerospace Corporation; 2Metals Technology, Inc.
The properties of alloy 718 made by laser powder-bed fusion have been widely reported, and while their room-temperature static properties are often similar to wrought material, elevated temperature properties have proven inferior, especially at slow strain rates. Stress rupture tests performed on LBPF 718 material after Hot isostatic Pressing (HIP) and heat treating in conformance with AMS 5663 have persistently led to brittle notch failures with limited elongation. Creep testing at 650 °C and 690 MPa shows a similar tendency, with samples showing capability of sustaining a load but with limited elongation and abrupt, transgranular failure. Alternative heat treatments performed to enhance high-temperature ductility have shown success in adjusting delta phase population but without benefit for stress rupture. Alternative HIP schedules have also been performed that led to changes in room-temperature and elevated temperature static strength but no benefit in stress rupture behavior. The root cause of this behavior is attributed to the dispersion of NbC that is a consequence of the LPBF process that results in fine-scale segregation of Nb and C during rapid solidification. Deliberately lowering the carbon content of the powder feedstock led to a greater number of smaller Y” particles and smaller size NbC particles resulting in an increase in static strength at room and elevated temperatures but no improvement in stress rupture. The presence of a large number of NbC particles leads to environmental sensitivity of LPBF 718 that is most apparent at elevated temperatures and slow strain rates.
9:05 AM
Microstructure and Mechanical Properties of Selective Laser Melting Processed TiC/GTD222 Nickel-based Composite: Rui Wang1; Zhe Zhang1; Peng Zhang1; Hailong Qin1; Zhongnan Bi1; 1Central Iron & Steel Research Institute
In this study, the microstructure and deforming mechanisms of selective laser melted GTD222 and TiC/GTD222 composite were studied. The results show that the TiC/GTD222 composite has finer grains and more precipitation phases. Meanwhile, TiC/GTD222 composite has higher yield strength both at room and high temperatures, which can be mainly attributed to the synergistic effect of the TiC strengthening and γ′ strengthening. The deformation mechanisms of TiC/GTD222 composite at 800 °C were identified as isolated stacking faults shearing the γ′ phase, continuous stacking faults shearing the γ and γ′ phases, dislocations cutting γ′ phase, and dislocation slip within the γ matrix. This study provides insights for understanding the influence of TiC particles on the deformation mechanisms of additive manufactured nickel-based alloys.
9:25 AM
Fabrication and Weldability Aspects of Ni- and Ni-Fe Based Superalloys – A Review: Joel Andersson1; 1University West
Superalloys are commonly used in structural components of aero engines. Superalloys in general, Ni- and Ni-Fe-based superalloys, belong to an important group of materials used in aerospace applications. Fabrication and associated weldability aspects of structural components for the hot section of aero-engine gas turbines continue to be of high importance to the manufacturing industry within this discipline. Cracking and specifically hot cracking as well as strain age cracking is a serious concern during the welding and additive manufacturing (AM) of these structural components. The cracking phenomena can occur during welding, AM or subsequent heat treatment of precipitation-hardening superalloys. The cracking behaviour can be influenced by several factors i.e., chemical composition in terms of hardening elements and impurities, the microstructure of base material, and weld zone, together with corresponding welding, AM and post-treatment process parameters. This paper offers a review of Ni- and Ni-Fe-based superalloys concerning fabrication and weldability aspects within the context of structural components of aeroengines.
9:45 AM Break