Phase Transformations and Microstructural Evolution: Additive Manufacturing
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Ashley Paz y Puente, University of Cincinnati; Mark Aindow, University of Connecticut; Sriswaroop Dasari, Idaho National Laboratory; Ramasis Goswami, Naval Research Laboratory; Megumi Kawasaki, Oregon State University; Eric Lass, University of Tennessee-Knoxville; Joshua Mueller, Michigan Technological University; Eric Payton, University of Cincinnati; Le Zhou, Marquette University
Thursday 8:30 AM
March 23, 2023
Room: 25C
Location: SDCC
Session Chair: Ashley Paz y Puente, University of Cincinnati
8:30 AM
Compositional Redistribution, Phase Transformation, Microstructural Development in SS316L/IN718 Bimetallic Structure Fabricated by Laser Powder Bed Fusion: Asif Mahmud1; Nicolas Ayers1; Thinh Huynh1; Kevin Graydon1; Yongho Sohn1; 1University of Central Florida
This work reports on compositional intermixing, phase transformations, microstructural development in SS316L/IN718 bimetallic structure fabricated by laser powder bed fusion (LPBF). Fully dense and crack free SS316L/IN718 bimetallic structures (cylinders with a diameter of 10 mm, height of 12 mm and support structure 4 mm) were produced using a laser power of 200 W, laser scan speed of 800 mm/s, hatch spacing of 0.12 mm and slice thickness of 0.03 mm. The XRD pattern revealed the dominant presence of austenitic (FCC) phase. Cross-sectional microstructure near the interface of the SS316L/IN718 bimetallic structure consisted of typical cellular/columnar structure. Intermixing of primary solvents, Ni and Fe was observed for approximately 200 µm in distance, and their intermixing rate was estimated to be in the order of 10-3 m2/s based on the effective time assumption of 1.0 ms.
8:50 AM
Tracking Precipitate Evolution in an AM 316L Steel during Solid-state Thermal Cycling: A 3D Synchrotron X-ray Nanotomography Study: Steve Gaudez1; Meriem Ben Haj Slama1; Lluis Yedra2; Eva Héripré3; Mario Scheel4; Hakim Gharbi1; Simon Hallais1; Manas Upadhyay1; 1Ecole Polytechnique, LMS, CNRS; 2Universitat de Barcelona; 3CentraleSupélec, CNRS, Université Paris-Saclay; 4Anatomix beamline, Soleil synchrotron
Precipitation of oxides in stainless steels during an Additive Manufacturing (AM) process has been widely observed and reported in literature. A recent study by Upadhyay et al. Scientific Reports 11 (2021) 10393 has reported the presence of non-oxides in DED 316L steel. Until recently, oxide and non-oxide precipitation was understood to occur during rapid solidification during AM. Recently, however, precipitation kinetics simulations performed by Upadhyay et al. showed that precipitation can also occur during Solid-State Thermal Cycling (SSTC): a phenomenon occurring at every material point after its solidification and till the end of AM process. To understand precipitation kinetics during SSTC, micropillars were prepared from as-built DED 316L steel. They were subjected to SSTC inside a vacuum chamber. Between each SSTC, precipitates were mapped via 3D synchrotron X-ray nanotomography. A machine learning algorithm was employed to segment precipitates and study their evolution.
9:10 AM
Recrystallization Kinetics of 316L Stainless Steel Processed by Laser Powder Bed Fusion (LPBF): Edouard De Sonis1; Sylvain Dépinoy2; Pierre-François Giroux3; Hicham Maskrot4; Louis Lemarquis3; Olivier Hercher4; Flore Villaret5; Anne-Françoise Gourgues-Lorenzon2; 1Université Paris-Saclay, CEA, Service de Recherches Métallurgiques Appliquées; 2Mines Paris, PSL University, MAT - Centre des Matériaux, CNRS UMR 7633, BP 87; 3Université Paris-Saclay, CEA, Service de Recherches Métallurgiques Appliquées, F-91191; 4Université Paris-Saclay, CEA, Service d'Études Analytiques et de Réactivités des Surfaces, F-91191; 5EDF R&D, Département Matériaux et Mécanique des Composants (MMC), Les Renardières, F-77250
In this study, the post-manufacturing recrystallization kinetics at two temperatures for two 316L stainless steels produced by laser powder bed fusion (LPBF) were compared. The obtained as-built microstructures differed in grain size, grain boundary character distribution, and nano-inclusion population. Strong differences in recrystallization kinetics were observed. Specific thermal cycles allowed to attribute these differences to an inhibition of the formation of the first recrystallized grains in the steel initially exhibiting the finest grains, the lowest density of low angle boundaries (LABs), and the highest volume fraction of nano-inclusions. A high density of LABs, originating from solidification in the particular case of the LPBF process, favored recrystallization by locally increasing the energy stored near grain boundaries and thus promoting the formation of new recrystallized grains. This work opens a way to the development of low-density LAB microstructures with enhanced microstructural stability under high temperature.
9:30 AM
Rationalization of the Solidification Behavior in Additively Manufactured PH Steels Using In-situ Radiography, Ex-situ Orientation Image Microscopy and Thermodynamic Modelling: Rakesh Kamath1; Logan White1; Serena Beauchamp1; Kamel Fezzaa2; Eric Lass1; Hahn Choo1; 1University of Tennessee Knoxville; 2Argonne National Laboratory
In this study, a laser-AM simulator (at beamline 32-ID-B, APS) in tandem with in-situ dynamic x-ray radiography was used to investigate the effect of alloy composition on solidification microstructure in additively manufactured PH steels using conduction-mode spot melts on 17Cr-4Ni (17-4) and 15Cr-5Ni (15-5) steels. Radiography measurements showed that melting and solidification kinetics were similar for both alloys, however, it was seen that 17-4 had faster initiation and slower kinetics compared to 15-5 during solidification. Ex-situ SEM-EBSD characterization showed a fully ferritic microstructure with larger grains (~ 20 micrometers) in the 17-4 and a mostly ferritic microstructure (> 90%) with small grains (~ 5 micrometers) in the 15-5. A parent reconstruction of 15-5 resulted in full austenitic microstructure implying a primary gamma-solidification mode, in contrast with 17-4 which showed a primary delta-solidification mode. Furthermore, the experimental findings were compared to thermodynamic and kinetic modelling results obtained using the CALPHAD approach.
9:50 AM
Measurements of Retained Austenite in Additively Manufactured Nitrogen Atomized 17-4PH Stainless Steel: James Zuback1; Fan Zhang1; Daniel Gopman1; Mark Stoudt1; Maureen Williams1; Carelyn Campbell1; 1National Institute of Standards and Technology
Additively manufactured nitrogen atomized 17-4PH stainless steel is known to retain significant amounts of austenite after heat treatments that are intended to produce a fully martensitic material. Since retained austenite affects strength, ductility, and aging kinetics, accurate quantification of retained austenite is essential for establishing process-structure-property links. Here, the evolution of retained austenite in nitrogen atomized 17-4PH is probed with multiple characterization techniques from the as-deposited material to the final solutionized condition for different alloy chemistries and powder bed fusion process parameters. Bulk and surface-based measurement techniques are employed to demonstrate the advantages and disadvantages with respect to their accuracy in determining phase fractions. Depending on alloy composition and heat treatment, the volume fraction of retained austenite is shown vary by a factor up to four across measurement techniques. Further, findings suggest a universal heat treatment may not be applicable for all powder feedstock and additive manufacturing process combinations.
10:10 AM Break
10:30 AM
Phase Transformations during Laser-based Powder Bed Fusion Studied by Operando X-ray Diffraction: Steven Van Petegem1; 1Paul Scherrer Institut
Laser powder bed fusion (L-PBF) is a “layer-by-layer” additive manufacturing process, in which parts are built up by adding precursor powder layers and selectively scanning them with a high-power laser, resulting in the densification of consecutive slices of a three-dimensional object. During L-PBF, heating and cooling rates up to 10 million degrees per second have been reported, leading to far-from-equilibrium microstructures. Additionally, the thermal history of a printed component can be very complex, because each material point melts and/or heats up to high temperatures during printing successive layers. To study the evolution of the crystallographic phases during L-PBF, we have developed a dedicated miniaturized L-PBF device optimized for installation at synchrotron X-ray diffraction and imaging beamlines. In this presentation, I will demonstrate how this device was used to study the microstructure evolution in Ti and Fe-based alloys with time resolutions down to 25µs.
10:50 AM
Quantifying the Beta-to-Alpha Solid-State Phase Transformation in Additive Manufactured Ti-6Al-4V Using High-Energy X-ray Diffraction Measurements and Phase Field Modeling: Bonnie Whitney1; Anthony Spangenberger1; Dan Savage2; Donald Brown2; Travis Carver2; Diana Lados1; 1Worcester Polytechnic Institute; 2Los Alamos National Laboratory
The solid-state beta-to-alpha/alpha’ transformation in Ti-6Al-4V was studied through in-situ high-energy x-ray diffraction (HEXRD) experiments to quantify its kinetic and thermodynamic properties and support phase field (PF) modeling of the phenomenon. Additive manufactured specimens were subjected to judiciously selected thermal cycles that control the nucleation and growth rates of the alpha phase by cooling from the beta homogenization field by either quenching to an isothermal hold (between 700 and 950 °C) or continuous cooling (between 0.05 and 30 °C/s). The HEXRD data are analyzed using proven techniques to calculate volume-averaged, time-varying phase fraction, lattice stress/strain, and Al and V concentrations (specifically their segregation between alpha and beta) during heating and cooling of Ti-6Al-4V. The experimental data were further used to calibrate a PF model, and comparisons between the modeling and experimental results were made to demonstrate the viability of the approach and capabilities of the numerical technique.
11:10 AM
Structural Evolution during Nanostructuring and Heating of an Additive-Manufactured CoCrFeNi Alloys Examined by X-ray and In-situ Neutron Diffraction Analyses: Megumi Kawasaki1; Jae-Kyung Han1; Xiaojing Liu2; Klaus-Dieter Liss2; 1Oregon State University; 2Guangdong Technion - Israel Institute of Technology
Structural evolution through nanostrcuturing and relaxation upon heating are examined by X-ray diffraction and in-situ heating neutron diffraction analyses, respectively, on additive-manufactured (AM) 316L stainless steel and equiatomic CoCrFeNi high-entropy alloy (HEA). Significant structural changes occur in a very early stage of nanostructuring through the application of high-pressure torsion leading to severe lattice distortion by the excess of dislocations and defects. The sequential information on the structure relaxation during in-situ heating neutron diffraction analysis provides the texture development, linear thermal lattice expansion, and stress relaxation behaviors of the nanocrystalline steel and HEA with increasing temperature up to 1300K. Together with the hardness measurements after heating, the results of structural evolution are interpreted to describe microstructural recovery, recrystallization and grain growth behaviors and the thermal stability of the AM nanocrystalline CoCrFeNi alloys.