Additive Manufacturing: Processing Effects on Microstructure and Material Performance: Post Processing
Sponsored by: TMS: Additive Manufacturing Committee
Program Organizers: Eric Lass, University of Tennessee-Knoxville; Joy Gockel, Wright State University; Emma White, DECHEMA Forschungsinstitut; Richard Fonda, Naval Research Laboratory; Monnamme Tlotleng, University of Johannesburg; Jayme Keist, Pennsylvania State University; Hang Yu, Virginia Polytechnic Institute And State University
Tuesday 2:00 PM
February 25, 2020
Room: 6E
Location: San Diego Convention Ctr
Session Chair: Monnamme Tlotleng, University of Johannesburg
2:00 PM
Microstructural Influence on AM 316L Mechanical Properties and Corrosion Behavior: Richard Fonda1; Jerry Feng1; Krystaufeux Williams1; 1Naval Research Laboratory
Post processing can dramatically alter the microstructures and properties exhibited by additively manufactured materials. This talk will present a systematic examination of the mechanical properties and corrosion behavior associated with characteristic microstructures produced during isothermal and HIP post processing treatments of additively manufactured AM 316L to identify the contributions arising from specific microstructural features. In particular, we will compare the behavior of the as-built material to that from three other post processing conditions to reveal the influences of i) the fine cellular structure, ii) the AM grain structure, and iii) the porosity within the build on the properties of the material.
2:20 PM
Correlative Atomic-scale Analysis of Nano-scale Precipitate Evolution in Additively Manufactured Maraging Steel: Pradeep Konda Gokuldoss1; 1Indian Institute of Technology Madras
Maraging steels are a special case of almost carbon-free type of steels where the strength depends on the formation, distribution of various types of precipitates in a Martensitic matrix. Selective Laser Melting (SLM) involves combination of rapid quenching and selective re-heating of layers resulting in metastable phase formation. This work therefore attempts to analyze correlatively the crystal structure of the nano-scale precipitates formed along with their precise local chemical composition in a high statistical manner. To achieve the above, novel correlative SEM based microscopic techniques such as TKD and STEM is utilized while the precise local chemical composition at near atomic-resolution is obtained from the investigated volume using APT. This correlative methodology applied to as-SLM and post-processed states namely, only ageing; solution treatment and ageing, provides deeper insights into the role of starting dendritic, cellular microstructures in the precipitation kinetics and hence to the final mechanical properties of the alloy.
2:40 PM
Carburization Heat Treatment of Selective Laser Melted 20MnCr5 Steel: Mei Yang1; Richard Sisson1; 1Worcester Ploytechnic Institute
Heat treatment is widely used to improve the properties of conventional manufactured steel parts. The response of additively manufactured steel parts to heat treatment may be different from conventionally manufactured steel parts. An understanding of heat treatment processes for additively manufactured steel parts is necessary to develop the heat treatment process parameters. In the present work 20MnCr5 steel is selected to investigate the carburization of additively manufactured parts. These parts were fabricated by selective laser melting. The objective of this project is to determine the carburization performance of additively manufactured steel parts. The results for the AM parts in terms of carbon concentration and microhardness profiles are compared with the results for the wrought steel. The mechanical testings including tensile and impact toughness testing are also conducted to compare the mechanical properties at the core of simultaneously carburized AM and wrought parts.
3:00 PM
Towards an Additively Manufactured, Wrought-comparable Precipitation-hardening Martensitic Stainless Steel: Fan Zhang1; Eric Lass2; Mark Stoudt1; Carelyn Campbell1; Souzan Hammadi3; Greta Lindwall3; Lyle Levine1; 1National Institute of Standards and Technology; 2University of Tennessee Knoxville ; 3KTH Royal Institute of Technology
Additive manufacturing (AM) poses unique challenges not often associated with traditional manufacturing methods. Specifically, with powders of the correct chemistry, the AM process can lead to heterogeneous microstructures of AM alloys over a wide range of length scales, mostly due to complex thermal conditions of the build at a local level. Thus, a rigorous evaluation of the as-build microstructure and its evolution during post-build heat treatment becomes a critical element in the proper understanding, modeling, and eventual certification of AM alloys. In this work, we report our progress of developing post-build processing towards making an AM precipitation-hardening martensitic stainless steel with properties comparable to its wrought counterpart. Our approach includes lab-based microscopy and mechanical measurements, in situ synchrotron scattering and diffraction experiments, and thermodynamic modeling. The impact of thermal history on the alloy properties, including martensitic fraction, precipitate size and volume fraction, and hardness will be illustrated.
3:20 PM
Effects of Thermal Processing on the Microstructure and Mechanical Properties of Additively Manufactured AlSi10Mg Parts: John Fite1; Suhas Prameela2; John Slotwinski1; Timothy Weihs2; 1Johns Hopkins University Applied Physics Laboratory; 2Johns Hopkins University
The Powder Bed Fusion (PBF) process is used for the additive manufacturing (AM) of metal parts and is capable of producing a wide variety of complex and intricate components. For AlSi10Mg, thermal post-processing is crucial to achieve the full range of material properties. This work focuses on the effects of thermal post-processing on AlSi10Mg microstructural evolution. AM AlSi10Mg coupons were fabricated by PBF, then were thermally treated using a conventional approach (with a Solution Heat Treatment (SHT)), and an alternative approach adapted for AM (without a SHT). Micro-tensile specimens were cut by EDM, and ductility and tensile strength were measured. Microstructural differences are correlated to tradeoffs in mechanical properties.
3:40 PM Break
4:00 PM
Microstructural Development in Additively Manufactured and Heat Treated IN625: Holden Hyer1; Ryan Newell2; Daniel Matejczyk3; Sinsar Hsie2; Mason Anthony2; Le Zhou1; Catherine Kammerer2; Yongho Sohn1; 1University of Central Florida; 2Aerojet Rocketdyne - WPB; 3Aerojet Rocketdyne - CP
Laser powder bed fusion (LPBF) has been demonstrated to produce dense, complex parts from IN625 powder feedstock. As built microstructures include a cellular-solidification sub-structure with ~1 micron cell diameters and cell walls that may or may not contain carbides and Laves AB2 phases. The cellular structure and presences or absence of second phase particles affect subsequent heat treatment. In this study, IN625 components were manufactured via LPBF and heat-treated that consisted of stress-relief, hot isostatic press and anneal. The microstructure was examined with optical, scanning electron, and transmission electron microscopy techniques. Changes in phase constituents and microstructure were documented as a function of heat treatment and component geometry (i.e., solidification and/or heat transfer characteristics). Results will be discussed with respect to the process-microstructure relationship in LPBF-manufactured IN625.
4:20 PM
Stimulating the Evolution of γ’/γ” Precipitates in the Inter-dendritic Regions of Additively Manufactured IN718 Due to Post-processing Heat Treatments: Younggil Song1; Bala Radhakrishnan1; Ranadip Acharya2; 1Oak Ridge National Laboratory; 2United Technologies Research Center
We present simulations of microstructure evolution during post-process annealing of Inconel alloy 718 (IN718) made by powder bed laser additive manufacturing. Additively manufactured IN718 forms finer dendrites, steeper Nb gradients, and finer Laves phase distributions compared to traditional cast materials, and thus requires custom post-processing heat treatments. The heat treatment leads to dissolution of Laves phase within inter-dendritic regions, followed by the formation of γ’, γ”, and δ precipitates in the Nb-rich areas, and further evolution to equilibrium volume fractions of these phases. We perform multi-phase-field simulations using a quaternary surrogate alloy to investigate the above phase evolution, which are compared to post-process-annealed microstructures of AM IN718. The simulation results are used to design efficient heat procedures for AM IN718 to achieve target mechanical properties. Research performed at ORNL under contract DE-AC05-00OR22725 and the Advanced Manufacturing Office through the High Performance Computing for Manufacturing Program at the Department of Energy.
4:40 PM
Modified Post-processing Thermal Treatments Designed to Relieve Notch Sensitivity in SLM Inconel 718: Tait Mclouth1; Julian Lohser1; David Witkin1; Glenn Bean1; Rafael Zaldivar1; 1The Aerospace Corporation
Most accounts of Inconel 718 processed by laser powder-bed fusion have used a range of post-build thermal treatments, but typically employ standardized solution treatment and aging schedules developed for mill products. Although the alloy was designed for high-temperature service, descriptions of resulting mechanical properties are often limited to room-temperature tensile tests. A wider range of tests, including room-temperature tensile, creep rupture and notched stress rupture at 650 C showed that quasi-static properties were similar to wrought material but slower strain rates revealed differences, and in particular high notch sensitivity. To address this sensitivity, heat treatments that target specific aspects of the SLM microstructure are proposed, including high-temperature homogenization and an intermediate heat treatment prior to aging to further enhance δ phase precipitation. Elevated temperature mechanical testing allows for comparisons between typical heat treatments used for SLM IN718 and the novel heat treatments.
5:00 PM
Study of Deformation Mechanisms in Various Heat-treated AM-IN718 Using Transmission Electron Microscopy: Thomas Gallmeyer1; Jack Dale1; Behnam Aminahmadi1; Aaron Stebner1; 1Colorado School of Mines
Previous work by the authors explored the structure-property relationships of AM-IN718 after the application of various post-processing heat treatment. It was shown that the coexistence of preserved dislocation cell substructures from the AM process, in conjunction with nanoprecipitation from aging, led to increased yield strength and ultimate tensile strength without a significant decrease in ductility. In an effort to better understanding the influence of the AM-specific microstructural aspects, the microstructure of each sample was examined using transmission electron microscopy after monotonic tensile deformation. Results show various deformation mechanisms for each heat treatment, including shear band formation, dislocation pileups, precipitate shearing, and nanotwin formation along slip traces. In addition, interaction of the shear bands with the preserved dislocation cells and nanoprecipitation is also discussed at the atomic scale.
5:20 PM
Effects of Post-heat Treatments on the Microstructure Evolutions, High Temperature Oxidation and Mechanical Properties of IN738LC Fabricated by Selective Laser Melting: Kyu-Sik Kim1; Myeong-Se Kim2; Kee-Ahn Lee1; 1Inha University; 2Auratech Co. Ltd.
Effects of different heat treatments on the microstructure evolution, oxidation behavior, and mechanical properties of additively manufactured IN738LC were studied. Three different post-heat-treatments were performed respectively: standard heat-treatments, direct aging, hot isostatic pressing. Changes in amounts of defects and microstructure characteristics were analyzed quantitively by OM, SEM, EBSD, and TEM. Oxidation behavior was investigated by high-temperature isothermal oxidation tests from 800 to 1100°C. The influence of microstructures on the oxidation mechanism is discussed in the perspective of local chemical-compositions. Mechanical properties were evaluated from room temperature up to 1000°C. As a result, the direct-aged sample showed the highest yield strength of 1170.3 MPa at room temperature. Interestingly, the serrated stress flow is observed only in the as-built sample due to a dynamic strain aging at intermediate temperatures. Deformed microstructures were analyzed to discuss the effects of post-heat-treatments on strengthening mechanisms and deformation behaviors of IN738LC fabricated by selective laser melting.