Additive Manufacturing: Advanced Characterization with Synchrotron, Neutron, and In Situ Laboratory-scale Techniques II: High-speed X-ray Imaging
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

Tuesday 8:00 AM
March 1, 2022
Room: 258A
Location: Anaheim Convention Center

Session Chair: Tao Sun, University of Virginia

8:00 AM  Invited
Utilising High-speed Synchrotron X-ray Imaging to Understand the Response of AM Alloys under Realistic Processing Conditions: Peter Lee1; Chu Lun Alex Leung1; Yunhui Chen1; Sebastian Marussi1; Samy Hocine1; Elena Ruckh1; Yuze Huang1; Maureen Fitzpatrick1; Marta Majkut2; Alexander Rack2; Veijo Honkimaki2; Robert Atwood3; Sam Clark4; Ben Saunders5; Martyn Jones5; 1University College London; 2European Synchrotron Radiation Facility; 3Diamond Light Source; 4Argonne National Laboratory; 5Rolls-Royce plc
    High speed in situ synchrotron x-ray imaging in real and reciprocal space is now an established tool for gaining understanding of the laser-matter interaction during a range of additive manufacturing (AM) process. However, replicating realistic build conditions on a beamline remains a challenge. Many of the studies in powder bed are just on the substrate or using a single layer of powder, rather than looking at multi-layer builds. For both powder bed and blown powder experiments, the processing parameters and hence pool size have not always matched the typical values use commercially. This talk will first review the benefits and limitations of using idealised conditions, and then show examples of how some of the limitations can be overcome through second and third generation in situ process replicators that have many of the features of industrial machines allowing multi-layer builds and even multi-lasers coupled with optical and IR imaging.

8:30 AM  Cancelled
In-situ Dynamic Synchrotron X-ray Radiography Study on the Effect of Laser Power on Melt Pool Dynamics and Solidification Kinetics during Laser Spot Melting of Ti-6Al-4V Alloy: Rakesh Kamath1; Ryan Heldt1; Yuan Li1; Meiyue Shao2; Sriram Vijayan2; Joerg Jinschek2; Tao Sun3; Hahn Choo1; 1University of Tennessee; 2Ohio State University; 3Argonne National Laboratory; University of Virginia
    A key determinant in establishing the process-structure correlations in fusion-based additive manufacturing (AM) processes is the liquid-to-solid phase transformation. In-situ dynamic synchrotron x-ray imaging technique was used in tandem with a laser-AM simulator (at beamline 32-ID-B, APS) to investigate the dynamics of the melt pool and vapor cavity produced during laser spot melting as well as subsequent solidification kinetics of Ti-6Al-4V alloy. The dynamics were mapped as a function of laser power (80 to 310 W) for a constant spot dwell time of 0.5 ms. The velocity of the liquid-solid interface (R), a key physical variable which determines the solidification microstructure, was obtained from the analysis. Further, post-mortem microstructural characterization was performed using EBSD to obtain an indirect estimation of the thermal gradient (G). The G & R values will be used to inform and improve high-fidelity, high-performance methods used to simulate melt pool solidification in AM.

8:50 AM  
Grain Morphology Prediction in AM Simulated Beta-Titanium: Chris Jasien1; Alec Saville1; Jonah Klemm-Toole1; Kamel Fezzaa2; Tao Sun2; Amy Clarke1; 1Colorado School of Mines; 2Advanced Photon Source, Argonne National Laboratory
    The continued development of metal additive manufacturing (AM) has expanded the metallic alloys for which these processes can be applied. To understand the response of beta-titanium alloys to AM processing, solidification and microstructure evolution needs to be investigated. In particular, thermal gradients (G) and solidification velocities (V) experienced during AM are needed to link processing to microstructure development, including the columnar to equiaxed transition (CET). In-situ synchrotron x-ray radiography of the beta-titanium alloy Ti-10V-2Fe-3Al during simulated laser-powder bed fusion (L-PBF) was performed at the Advanced Photon Source at Argonne National Laboratory, allowing for direct determination of Vs. Since Gs cannot be readily measured, simulation tools were used. The Gs and Vs obtained from computational modeling and experiments are compared to solidification modeling and observed grain morphologies obtained by complementary post-mortem microstructural characterization. These results are then used to develop a solidification map for beta-titanium alloys.

9:10 AM  
NOW ON DEMAND ONLY: Comparison of Benefits and Limitations of High Temporal Versus Low Temporal Resolution of In Situ In Operando AM Imaging of Superalloys: Maureen Fitzpatrick1; Yunhui Chen1; Marta Majkut2; Bratislav Lukic2; Kudakwashe Jakata2; Sebastian Marussi1; Alexander Rack2; Peter Lee1; 1UCL; 2ESRF
    As additive manufacturing (AM) finds importance in industries with stringent compliance regulations such as aerospace and biomedical, developing an understanding of the limitations of AM is critical for successful implementation of additive manufactured components. When superalloys undergo rapid melting with high power lasers, steep thermal gradients can introduce microstructural features which can be detrimental to product performance. These mechanisms occur on the scale of microseconds, which makes them difficult to characterise and therefore difficult to understand. Since the ESRF’s new upgrade, EBS, we are able to achieve ultrafast radiography of the build process with framerates reaching 200kHz. This high temporal resolution data allows us to study defect mechanisms that occur on short timescales while complementary lower temporal resolution data (1kHz framerate) yields information about the laser-matter interactions and the effects on the overall build. Pixel sizes of four microns were achieved, enabling observation of defects with fine spatial resolution.

9:30 AM Break

9:45 AM  
Characterization of the Healability of Aluminium Alloys Produced by Laser Powder Bed Fusion (L-PBF) Using X-ray Nanoholotomography at Synchrotron (ESRF): Julie Gheysen1; Mariia Arseenko1; Grzegorz Pyka1; Florent Hannard1; Julie Villanova2; Aude Simar1; 1UCLouvain; 2ESRF
     In aeronautic applications, overloads can damage parts and lead to their replacement. Self-healing materials, i.e. with the ability to repair internal damage, could increase the part’s lifetime. While polymer-based systems have dominated the field of self-healing materials, self-healing of metals remains an important challenge because of the slow diffusion at room temperature. In this research, two healable aluminum alloys produced by L-PBF are developed based on: - diffusion of healing agents towards the free surfaces of the damage voids during heat treatment; - melting of an eutectic phase which flows towards the damage.The healability of these two strategies was studied on damaged specimens using in-situ heating coupled with X-ray nanoholotomography at European Synchrotron Radiation Facility (ESRF). This 4D nano-imaging highlighted the progressive filling of the damage sites, allowing to optimise the healing temperature and showing the potential of these two healable aluminum alloys.

10:05 AM  
Building Links between Laser Melting Phenomena Observed with In Situ X-ray Imaging and Laboratory-based Process Monitor: Nicholas Calta1; Aiden Martin1; Jenny Wang1; Jean Baptiste Forien1; Maria Strantza1; Manyalibo Matthews1; 1Lawrence Livermore National Laboratory
    In situ X-ray probes have provided a wealth of information about process dynamics during laser powder bed fusion (LPBF) over the past few years. This has included studies of the melt pool fluid flow, defect formation, and post-solidification cooling behavior. These studies, while essential for a thorough understanding of the LPBF process, cannot be applied in a typical industrial setting because they require a synchrotron X-ray source. Away from a synchrotron, process monitoring approaches to detect defect formation or process stability typically use optical or acoustic approaches to infer melt pool behavior. In this talk I will outline our efforts to connect these two areas by comparing thermal emission to X-ray imaging data. I will describe experiments that measure the melt pool emission during synchrotron X-ray imaging experiments as well as comparisons between X-ray imaging and 3D part fabrication in the laboratory. Prepared by LLNL under Contract DE-AC52-07NA27344.

10:25 AM  Invited
Melt Pool Oscillations at Keyhole Transition as a Precursor to Pore-generating Turbulence: Brian Simonds1; Tao Sun2; Saad Khairallah3; 1National Institute of Standards and Technology; 2University of Virginia; 3Lawrence Livermore National Laboratory
    Detection of pore-generating events during additive manufacturing is the first step towards implementing feedback control for creating fully dense AM parts. Several researchers have successfully used high-speed synchrotron X-ray imaging to witness and describe these events but deploying this technology during actual AM builds is problematic. By combining ultrahigh-speed (25 MHz) light scattering methods with X-ray imaging, we have found that there is a regime of natural periodic melt pool fluctuations (25 – 60 kHz) that precedes pore-generating melt pool turbulence. High-fidelity multiphysics simulations were used to describe the mechanisms that drive these oscillations and found excellent quantitative agreement with respect to the measured frequency and absolute absorptance value. Light scattering presents a promising approach as a deployable platform for real-world AM build monitoring as it is easily capable of the very high detection rates necessary to observe these phenomena while also producing a readily processable one dimensional data stream.

10:55 AM  
Pairing X-ray Synchrotron Imaging, In-situ Absorption Measurements, Thermal Modeling, and Post-mortem Metallography Towards the Understanding of the Solidification Microstructures in Ti-6Al-4V for Additive Manufacturing Applications: Nicholas Derimow1; Edwin Schwalbach2; Jake Benzing1; Alexandria Artusio-Glimpse1; Nikolas Hrabe1; Brian Simonds1; 1National Institute of Standards and Technology; 2Air Force Research Laboratory
    X-ray synchrotron imaging was carried out in conjunction with in-situ integrating sphere radiometry for real-time energy absorption measurements during the melting of Ti-6Al-4V alloy. The resulting post-mortem solidification microstructures were then studied via electron microscopy and electron backscatter diffraction (EBSD) to elucidate the changes in microstructure resulting from the laser melting process. We report on the solidification and microstructural evolution of Ti-6Al-4V resulting from the imaging/absorption melting experiments. In particular, there were significant changes to the alpha/beta phase fraction in the unmelted heat-affected zone (HAZ) across all test cases. A thermal conduction model incorporating the in-situ absorption data is used to calculate the thermal histories and diffusion distances along the HAZ in these alloys in order to gain insight into the solid-state phase transformations that occurred beneath the melt pool in these alloys.