Quantifying Microstructure Heterogeneity for Qualification of Additively Manufactured Materials: Comparing Wrought & AM with a Focus on Ni Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Additive Manufacturing Committee, TMS: Phase Transformations Committee, TMS: Advanced Characterization, Testing, and Simulation Committee
Program Organizers: Sharniece Holland, Washington University in St. Louis; Eric Payton, University of Cincinnati; Edwin Schwalbach, Air Force Research Labroatory; Joy Gockel, Colorado School Of Mines; Ashley Paz y Puente, University of Cincinnati; Paul Wilson, The Boeing Company; Amit Verma, Lawrence Livermore National Laboratory; Sriram Vijayan, Michigan Technological University; Jake Benzing, National Institute of Standards and Technology
Wednesday 2:00 PM
March 22, 2023
Room: 24B
Location: SDCC
Session Chair: Joy Gockel , Colorado School of Mines; Sriram Vijayan, The Ohio State University
2:00 PM Invited
NASA’s Approach on the Evaluations of “Material Engineering Equivalence” Methodology in Achieving and Sustaining Efficient Qualification and Certification of AM Materials and Parts: Alison Park1; Richard Russell1; Samuel Cordner1; Mallory James1; Doug Wells1; Brian West1; Andrew Glendening1; 1NASA
The NASA Tech Standard 6030 is created with the understanding that the metallic AM parts are a unique metallurgical product form. While there are similarities to other processes, the AM product is produced in a fashion that has no true precedent. It still lacks the benefit of many years of incremental refinement, which typically provides the experiential and scientific foundation. For this reason, undiscovered failure modes remain in the metallic AM process. NASA's standard is supposed to provide the implementation approach that is heavily rooted in metallurgical understanding and respecting the evolving AM process. There are a lot of questions remain in qualification of critical spaceflight AM parts. These questions lead to considering the use of “material engineering equivalence”. The presentation will cover how it can be used to evaluate the quality of AM materials that acknowledges the range of characteristics that must be assured to meet all its expectations.
2:25 PM
Optimizing Creep Performance of Haynes 282 Printed via Laser Powder Bed Fusion through Microstructure Control: Nicholas Lamprinakos1; Junwon Seo1; Gregory Wong1; Anthony Rollett1; 1Carnegie Mellon University
As-built parts produced via laser powder bed fusion (LPBF) often have heterogeneous microstructures which can significantly affect their mechanical properties. The printed microstructure is dependent on the specific printing parameters used, so there is an opportunity to tailor the microstructure based on a part’s intended application. In this work, microstructural control of printed Haynes 282 was explored with the goal of maximizing high temperature creep performance. A modified Potts model was used to predict the printed microstructure based on input process parameters. This was correlated with experimental microstructures. Since Haynes 282 typically requires post-fabrication heat treatment, experimental heat treatments were performed on the printed parts to observe how the printed microstructures would evolve under differing heat treatment cycles. Particular interest was taken in preserving the as-printed crystallographic texture while still allowing desired precipitate structures to form. Finally, creep testing was performed to correlate the microstructure to the creep performance.
2:45 PM
Strategizing with Hot Isostatic Pressing Treatments to Increase Productivity during Post-processing of Laser-melted Inconel 718 Parts: Jake Benzing1; Orion Kafka1; Nik Hrabe1; Don Godfrey2; Philipp Schumacher2; Chad Beamer3; Frank DelRio4; 1National Institute of Standards and Technology; 2SLM Solutions; 3Quintus Technologies; 4Sandia National Laboratories
Hot isostatic pressing (HIP) treatments are typically applied to additively manufactured parts to seal internal porosity and improve reliability of the component. Ni-based super alloys require multiple heat treatments to produce a microstructure that can withstand high-temperature environments. In this work, Inconel 718 parts were manufactured by laser powder-bed fusion, subjected to a range of HIP and heat treatments, and machined into a geometry that allows for high-throughput tension testing thereby removing the following variables: surface roughness and contour microstructures. This goal of this study is to simplify heat treatment routes while maintaining satisfactory tensile performance. The tailored heat treatment avenues will attempt to accomplish the following: avoiding a stress-relief, minimizing the number of aging steps, minimizing grain growth, sealing porosity with a minimum HIP pressure, and avoiding recrystallization to retain dislocation cell networks. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
3:05 PM
Build Geometry and Parameter Influence on Alloy 718 Microstructure, Properties and Spatial Variation in Additive Manufacturing: Anna Dunn1; Dan Young1; Joy Gockel2; 1Wright State University; 2Colorado School of Mines
Additive Manufacturing (AM), particularly laser powder bed fusion, is being studied for use in critical component applications. Tensile and fatigue testing shows differences when built using different laser powers. However, when fabricated in an as-printed geometry, the gauge sections of the two specimens are different and experience different thermal behavior. This work explores microhardness, microstructure, and porosity from Alloy 718 samples made with varying laser power and different build geometry sizes representative of the gauge sections in the tensile and fatigue bars. Results show that microhardness varies spatially across the sample. Smaller diameter metallographic coupons (fatigue diameter) have a coarser microstructure and lower microhardness than the larger diameter (tensile diameter) when built using the same parameters. Therefore, the fatigue and tensile properties are not comparing the same material structure. Understanding the effect of build geometry on microstructure provides insight towards consistency in AM mechanical properties testing strategies.
3:25 PM Break
3:45 PM
Intentionally Seeding Pores in Laser Powder Bed Fusion IN718: Microstructure, Defects, and Fatigue: Krzysztof Stopka1; Andrew Desrosiers2; Tyler Nicodemus2; Nicholas Krutz2; Amber Andreaco2; Michael Sangid1; 1Purdue University; 2GE Additive
Progress towards widespread adoption and cross-industry rapid qualification standards for additively manufactured (AM) components requires a strong understanding of the influence of pervasive porosity defects on component fatigue life. In this work, we describe a robust methodology to determine processing parameters to intentionally seed three distinct types of defect structures (e.g., lack of fusion, keyhole/trapped gas, and linearly aligned defects) in AM builds alongside control specimens with minimal porosity through a design of experiments study for Ni-base superalloy IN718. Builds were then characterized using optical microscopy, electron backscatter diffraction, two computed tomography techniques with an order of magnitude difference in resolution, and strain-controlled low cycle fatigue experiments. We find that common metrics such as porosity volume fraction and size of the largest defect do not strongly correlate to fatigue resistance, motivating the need for hybrid experimental- and model-based approaches in the quest for AM qualification standards.
4:05 PM
Microstructural and Mechanical Validation of Thin-walled Additively Manufactured Inconel 625: Connor Varney1; Paul Rottmann1; 1University of Kentucky
Additive manufacturing (AM) holds tremendous promise for significantly reducing the cost to manufacture parts with complex geometries, however, realizing this promise requires development of robust process-structure-property models leaning on knowledge of individual alloys, printing techniques, and process parameters. Thin wall specimens will be fabricated with variable thickness and characterized both in the as-printed condition and after standard post-print heat treatments including HIP. This research will focus on characterizing the as-built microstructure of thin wall SLM IN625 (EDS, EBSD, XCT) to identify detrimental phases (carbides/nitrides, large dendrites), elemental segregation, and porosity that limit its mechanical reliability and the degree to which they persist after standard industry heat. These results will provide the foundation for microstructure-informed, mechanistic interpretations of the mechanical properties obtained using a custom micro-mechanical testing setup and accompanying digital image correlation system. All told, this will allow for a greater understanding of the process-properties-performance relationship of AM IN625.
4:25 PM
Microstructure Evolution According to Heat Treatment Design of Alloy 625 Produced by Selective Laser Melting: Tae-Hun Kim1; Jung Min Han2; Hyun-Uk Hong1; 1Changwon National University; 2Doosan Enerbility
This study focused on the microstructure evolution of Alloy 625 produced by selective laser melting (SLM) with different heat treatment designs. Heat treatments used in this study were RX for recrystallization and GBS for grain boundary serration. These were compared with As-built and Conventional Wrought Alloy 625 to evaluate the microstructure stability and mechanical properties. After heat treatments, mechanical properties and microstructure stability were improved than As-Built with fully recrystallized microstructures. Fracture behaviors of RX and GBS after tensile tests exhibited similar and the crack initiated at grain boundaries with precipitates. But GBS showed higher resistance to grain boundary cracking than RX. And the formation of mechanical twins was restricted due to nano-sized oxides whilst Wrought showed a high density of twins which led to higher ductility at 700 ℃. The high-temperature tensile properties of SLMed Alloy 625 with heat treatments, were discussed in terms of the unique deformation mechanisms.
4:45 PM
Quantification of Microstructural Heterogeneities in Additively Manufactured and Heat-Treated Haynes 282: Avantika Gupta1; Sriram Vijayan1; Joerg Jinschek2; Carolin Fink1; 1Ohio State University; 2Technical University of Denmark
Haynes-282 is a gamma prime (γ’) strengthened Ni-based superalloy with excellent high temperature mechanical properties for applications, e.g., in industrial gas turbine engines. Excellent thermal stability ( ̴760 ⁰C) and weldability make this alloy a promising candidate for the manufacturing of near-net shaped parts via electron beam melting (EBM) powder bed fusion (PBF) processes. To enable industrial application of EBM-deposited Haynes-282 components, a systematic understanding of its process-structure-property space is required.In this study, we used a multi-scale characterization approach to evaluate the impact of variations in EBM process parameters such as scan velocity, build height and, column thickness on size and morphology evolution of γ’, matrix gamma (γ) grains, and carbides in EBM Haynes-282. Microhardness testing was used to understand the effect of microstructural variations on mechanical properties. Further, the effect of post-process heat treatment (testing both two-step and one-step ageing) on microstructure and mechanical hardness was evaluated.
5:05 PM
Strong Impact of Minor Elements on the Microstructural Evolution of an Additively Manufactured Inconel 625 Alloy: Mo-Rigen He1; Arunima Banerjee1; Christopher Marvel2; Samuel Price3; Ian McCue3; William Musinski4; Kevin Hemker1; 1Johns Hopkins University; 2Lehigh University; 3Johns Hopkins University Applied Physics Laboratory; 4U.S. Air Force Research Laboratory
Additively manufactured metallic materials often see inhomogeneous distribution of alloying elements, which can make a strong impact on the as-built microstructure and its evolution during post-build heat treatments. In this study, an Inconel 625 alloy made with laser powder-bed fusion is characterized with comprehensive electron microscopy techniques. The as-built samples show enrichment of both major (Nb,Mo) and minor (Si,N) solutes at the columnar sub-grain cell walls, whereas stress-relief heat treatments promote formation of globular (Nb,Mo,Si,N)-rich M6X and (Nb,N)-rich MX precipitates. Absence of the detrimental needle-shaped delta-Ni3(Nb,Mo) phase is attributed to the higher Si and N contents at the cell walls and their modification of the thermodynamics of precipitate formation. The effect of sample geometry, grain texture, and precipitates on the mechanical response of the alloy is assessed with printed thin-wall elements. As demonstrated herein, rational control of minor elements requires further attention in additive manufacturing.