Additive Manufacturing: Advanced Characterization with Synchrotron, Neutron, and In Situ Laboratory-scale Techniques II: Advanced Microstructural Characterization of AM Alloys
Sponsored by: TMS Structural Materials Division, TMS: Additive Manufacturing Committee, TMS: Advanced Characterization, Testing, and Simulation Committee
Program Organizers: Fan Zhang, National Institute of Standards and Technology; Donald Brown, Los Alamos National Laboratory; Andrew Chuang, Argonne National Laboratory; Joy Gockel, Colorado School of Mines; Sneha Prabha Narra, Carnegie Mellon University; Tao Sun, University of Virginia

Wednesday 2:00 PM
March 2, 2022
Room: 258A
Location: Anaheim Convention Center

Session Chair: Fan Zhang, National Institute of Standards and Technology; Andrew Chuang, Argonne National Laboratory

2:00 PM  Invited
NOW ON-DEMAND ONLY - In-operando X-ray Scattering Diagnostics to Observe Morphological Transformations during Additive Manufacturing: Joshua Hammons1; Aiden Martin1; Aurelien Perron1; Nicholas Calta1; Hunter Henderson1; Michael Nielsen1; Trevor Willey1; Manyalibo Matthews1; Scott McCall1; Jonathan R.I. Lee1; 1Lawrence Livermore National Laboratory
     Understanding how additive manufacturing changes the microstructure of an alloy facilitates the development of new manufactured alloys with enhanced properties. While much can be learned from before-and-after ex-situ structural characterization of the microstructure, it is often difficult to elucidate the pathways to morphological changes during additive manufacturing. A high-temperature aluminum alloy (Al-8Ce-10Mg) was additively manufactured using Laser Powder Bed Fusion (LPBF) and found to have enhanced structural properties, due to the extended mesoscale aggregate structure observed by both SEM and USAXS/WAXS measurements. In operando SAXS/WAXS experiments, obtained during laser processing, reveal the formation of the extended 2-phase aggregate structure that forms upon re-solidification of the initial microstructure, which consists of different morphologies. In this way, LPBF enhances the material properties through the formation of the extended aggregate structure, as well as homogenization that is observed in operando and ex-situ. This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory (LLNL) under Contract No. DE-AC52–07NA27344 and released under document number LLNL-ABS-824857.

2:30 PM  
In-situ Heat Treatment of Additively Manufactured Ti-6Al-4V: Donald Brown1; Maria Strantza2; Gennadi Rafailov3; Eloisa Zepeda-Alarcon4; Darren Pagan5; 1Los Alamos National Laboratory; 2Lawrence Livermore National Laboratory; 3Ben Gurion University; 4Nevada Nuclear Security Site; 5Penn State University
    Additive Manufacture is currently being used for the production of metallic components because it can offer reductions in cost and waste. AM Ti64 has received attention because of the high material cost and the innate ability of AM to minimize material waste. Originally, the Ti64 alloy was developed for casting applications which have very slow cooling rates. Its property combinations are still desired for AM built parts, but the much higher cooling rates, as high as 106K/s, associated with AM result in a distinct and metastable microstructure and, subsequently, distinct material properties. Post-build heat treatments are usually used on Ti64 components produced by AM to drive the as-built microstructure closer a wrought equivalent in microstructure and properties. In this work, we have collected diffraction data during in-situ heat-treating of AM Ti64, made with various processes, in order to monitor the microstructural evolution of the material.

2:50 PM  
Precipitate Evolution in DED 316L Stainless Steel Due to Solid State Thermal Cycling: A 3D synchrotron X-ray Nanotomography Study: Steve Gaudez1; Meriem Ben Haj Slama1; Juan Guillermo Santos Macias1; Eva Héripré2; Mario Scheel3; Manas V. Upadhyay1; 1CNRS UMR7649 Ecole Polytechnique; 2CNRS UMR8579 Centrale Supélec; 3Synchrotron SOLEIL, ANATOMIX
    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. The current understanding of oxide and non-oxide precipitation is that these occur during rapid solidification of a material just after its deposition. 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 AM 316L steel. They were subjected to SSTC using a novel laser-SEM installation. Between each SSTC, precipitates were mapped via 3D synchrotron X-ray nanotomography. A machine learning algorithm was employed to segment the precipitates and study their evolution.

3:10 PM  
In Situ Synchrotron Analysis of Aging in Commercial High Strength 7000 Series Additive Aluminum Alloys: John Martin1; Darby LaPlant1; Fan Zhang2; David Beaudry3; Patrick Callahan4; 1HRL Laboratories LLC; 2NIST; 3John's Hopkins University; 4NRL
    HRL Laboratories has commercialized the high strength (>600MPa Yield Strength) 7000 series alloy, registered as 7A77, utilizing unique zirconium based functionalization to eliminate hot cracking. The resulting as-built microstructure is highly distinctive from typical wrought 7000 alloys containing fine grains (<5 microns) and grain boundary segregation of strengthening elements (e.g. Zn,Cu,Mg). Experimental results have indicated a more rapid aging response than wrought alloys. For the first time high strength 7000 series alloys produced by additive manufacturing were subjected to in-situ aging under synchrotron radiation to obtain small and ultra-small angle x-ray scattering (SAXS and USAXS) information over 24 hours. Aged coupons were subsequently analyzed via atom probe tomography to quantify size and shape distribution of precipitates. This presentation will highlight the aging behavior of this alloy, the unique aspects observed, and recommendations for improved aging regimes.

3:30 PM  
Effect of Heat Treatments on Fabricated Wire and Arc Additive Manufacturing Parts of Stainless Steel 316: Microstructure and Synchrotron X-ray Diffraction Analysis: Joao Oliveira1; 1FCT-UNL
     Large metallic parts can now be fabricated by wire and arc additive manufacturing (WAAM). Undesired phases may appear during the multiple thermal cycles of WAAM. In this work, 316L stainless steel walls were fabricated by WAAM and submitted to several heat treatments to understand the precipitation kinetics of secondary phases and observe the δ-ferrite dissolution with synchrotron X-ray diffraction measurements. The as-built samples presented δ–ferrite dendrites in an austenite matrix. In-situ observations showed σ precipitation during the first minutes of isothermal holding at 950 °C, from direct precipitation on the δ-ferrite islands.Solubilization heat treatments at 1050 and 1200 °C resulted in an undissolved amount of ferrite of approximately 6.5 and 0.4 %, respectively. The amount of δ–ferrite showed a direct relationship with the hardness values. We combine advanced materials characterization and thermodynamic calculations to rationalize the microstructure evolution during heat treatment of WAAM-fabricated 316L stainless steel parts.

3:50 PM Break

4:05 PM  
In-situ Characterization of Residual Strain Relaxation of Additively Manufactured Inconel 625 through Energy-resolved Neutron Imaging: Anton Tremsin1; Yan Gao2; Ade Makinde2; Hassina Bilheux3; Jean Bilheux3; Ke An3; Takenao Shinohara4; Kenichi Oikawa4; 1University of California at Berkeley; 2General Electric Global Research Center; 3ORNL; 4Japan Atomic Energy Agency
    The release of residual stresses in Inconel 625 materials during post-build annealing is investigated with the help of neutron imaging. The 25 x 15 x 6 mm3 samples were printed using the powder-bed metal laser melting additive manufacturing technique. With the help of energy-resolved neutron imaging we measure, in-situ, the strain map distribution within as-built samples and during their subsequent stress relief annealing in a vacuum furnace at 700°C and 875°C. Despite the limited accuracy of in-situ lattice strain reconstruction during annealing, the results indicate that most of the strain relaxation occurs at 700°C within 2-3 hours. Relaxation of the strain at 875°C happened at a much faster rate. We also performed simulations of the AM build process to predict the residual stress distributions as a function of the build process parameters. The simulation results are in a good agreement with experiments, confirming their usefulness for simulation validation.

4:25 PM  
High-throughput Surface Characterization to Identify Processing Defect Boundaries in Additively Manufactured Materials: Ankur Kumar Agrawal1; Dan Thoma1; 1University of Wisconsin-Madison
    In laser powder bed fusion (LPBF), porosity defects can be minimized by controlling the melt pool geometry and improving interlayer bonding. Thus, a careful examination of the melt pool tracks can provide insights into different processing regimes. This study presents a new high-throughput (HT) surface methodology that is capable as an emerging in situ process monitoring tool for different types of porosity defects in LPBF. Processing maps in metal additive manufacturing are typically shown as laser power-velocity plots, where lack-of-fusion, keyholing, and balling regimes can be estimated from analytical models, or more rigorously defined with high-throughput synthesis of samples by evaluating density and hardness. However, validation of the types of defects has been limited to traditional, low-throughput metallographic techniques on a select set of samples. The new surface analysis permits direct linkages to the porosity defects in the process maps. Applications to other alloy systems will be discussed.

4:45 PM  
Multimodal Characterization of L-PBF 316L Stainless Steel: David Sprouster1; M Ouyang1; W Cunningham1; G Halada1; D Olds2; A Pattammattel2; H Yan2; Y Chu2; E. Dooryhee2; S. Storck3; J Trelewicz1; 1Stony Brook University; 2Brookhaven National Laboratory; 3Johns Hopkins University
    The hierarchical nature of AM materials necessitates a multiscale approach for quantifying structural features and corresponding chemical heterogeneities that form during rapid solidification. In this work, we describe our recent multimodal characterization efforts as applied to (i) pulsed, (ii) continuous laser deposited 316L, as well as (iii) compositionally tailored 316L. We specifically employ synchrotron-based; X-ray diffraction; scanning nano-X-ray microscopy; X-ray photoemission electron microscopy, in concert with correlative transmission electron microscopy. The combination of these techniques has been crucial in unravelling the role of microstructure across various length scales on performance as functions of printing conditions. The sensitivity of the different techniques highlights their exceptional ability to build a detailed picture of the trends in atomic structure and microstructural properties with printing conditions. Finally, the surface sensitive techniques have shown that passive films contain complex inhomogeneous microstructures that potentially have non-negligible effects on the corrosion performance.

5:05 PM  
In-situ TEM Heating-cooling Experiments to Study Precipitate Evolution in DED 316L Steel: Meriem Ben Haj Slama1; Eva Héripré2; Lluís Yedra3; Manas Upadhyay4; 1LMS, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris & MSSMat, CNRS, CentraleSupelec, Universite Paris-Saclay; 2MSSMat, CNRS, CentraleSupélec, Université Paris-Saclay; 3IN2UB, Department of Electronics and Biomedical Engineering, University of Barcelona & MSSMat SPMS, CNRS, CentraleSupélec, Université Paris-Saclay; 4LMS, CNRS, Ecole Polytechnique, Institut Polytechnique de Paris
     In this work, we perform in-situ TEM experiments to understand the evolution of precipitates in DED 316L stainless steel due to Solid-State Thermal Cycling (SSTC) that occurs during AM. It is important to study the role of SSTC on microstructure evolution because the microstructural features affected by SSTC determine the material response. Due to the intractability of probing microstructure evolution via electron microscopy during AM, we subject pre-built DED 316L steel samples to SSTC inside a TEM. The results of a series of such in-situ TEM SSTC experiments performed on pre-built DED 316L steel lamellae are presented. These experiments help us distinguish the role of (i) maximum temperature and (ii) maximum temperature rates occurring due to SSTC during AM, as well as the role of (iii) the type and number of SSTCs and (iv) post-process annealing, on the evolution of precipitates in DED 316L steel.