Additive Manufacturing: Advanced Characterization with Synchrotron, Neutron, and In Situ Laboratory-scale Techniques: High Speed X-ray Imaging and Diffraction
Sponsored by: TMS: Additive Manufacturing Committee
Program Organizers: Fan Zhang, National Institute of Standards and Technology; Tom Stockman, Los Alamos National Laboratory; Tao Sun, Northwestern University; Donald Brown, Los Alamos National Laboratory; Yan Gao, Ge Research; Amit Pandey, Lockheed Martin Space; Joy Gockel, Wright State University; Tim Horn, North Carolina State University; Sneha Prabha Narra, Carnegie Mellon University; Judy Schneider, University of Alabama at Huntsville
Tuesday 8:30 AM
February 25, 2020
Room: 8
Location: San Diego Convention Ctr
Session Chair: Tao Sun, Argonne National Laboratory
8:30 AM Invited
Capturing Pore Formation During Laser Blown Powder Directed Energy Deposition: Peter Lee1; Yunhui Chen1; Lorna Sinclair1; CL Alex Leung1; Samuel Clark1; Sebastian Marussi1; Robert Atwood2; Martyn Jones3; Gavin Baxter3; 1University College London; 2Diamond Light Source; 3Rolls-Royce plc
Laser Blown Powder Directed Energy Deposition (LBP-DED) promises to produce and repair unique, high quality components for aerospace applications. However, the solidification mechanisms controlling the formation of continuous, pore free tracks are still poorly understood. The solidification rates during the process are 102 to 105 degrees per second, producing conditions that can lead to microstructural features (porosity, epitaxial growth) that may reduce performance. Using fast synchrotron X-ray imaging and a unique in situ and operando LBP-DED rig, we capture the mechanisms by which pores form and are pushed for a range of conditions. We find that the mechanisms of pore formation, capture by the solidification front, and motion in the pool vary significantly for different alloys and conditions, providing new insights into how to control the size and location of pores.
8:50 AM Invited
Porosity Formation and Entrapment in Directed Energy Deposition Through Highspeed In-situ Imaging: Samantha Webster1; Kornel Ehmann1; Jian Cao1; 1Northwestern University
Laser-based metal additive manufacturing (AM) has become increasingly popular due to its flexibility in materials and geometry. Inherent process defects such as porosity have limited the use of AM-fabricated components in industry, however, and the conditions under which defects form are still not fully understood across laser-based AM platforms. High-speed synchrotron imaging has been used for ¬in situ observation of melt-pool dynamics, powder entrainment, and defect formation in laser powder bed fusion (LPBF), but phenomena in powder-blown processes such as directed energy deposition (DED) will be very different due to much more stochastic and violent powder delivery. This study addresses those differences by using the X-ray imaging technique at the Advanced Photon Source and a high through-put DED set-up to measure melt-pool geometry and fluctuations over a large range of energy densities and mass flowrates. Melt-pool conditions leading to pore formation and pore entrapment are elucidated and will be discussed.
9:10 AM
Correlation of Melt Strategy Parameters to Solidification Variables During Laser Fusion Processing of Ti-6Al-4V Alloy: An In-situ Dynamic Synchrotron X-ray Radiography Study: Rakesh Kamath1; Yuan Li1; Tao Sun2; Sudarsanam Babu1; Hahn Choo3; 1University of Tennessee Knoxville; 2Argonne National Laboratory; 3University of Tennessee, Knoxville
The capability to tailor microstructural properties is critical in realizing the full potential of fusion-based metal additive manufacturing (AM) technologies; therefore, necessitating a correlation of process parameters to key physical variables governing solidification microstructure. In the present study, a laser-AM simulator (developed at beamline 32-ID-B, APS) was used to investigate effects of spot and line melt strategies on Ti-6Al-4V alloy microstructure as a function of key parameters namely laser power, line scan speed, spot dwell time and interval between successive spot melts. In-situ dynamic synchrotron x-ray radiography was used in tandem with the laser-AM simulator to obtain the liquid-solid interface velocity (V) of the liquid-solid interface. An indirect estimation of the thermal gradient across the liquid-solid interface (G) was performed using post-mortem microstructural characterization. The G & V were used to develop a heat transfer model to provide basic understanding of the development of melt pool geometry and solidification microstructure.
9:30 AM
Microstructure Development in Laser Powder Bed Fusion of Superalloys via Synchrotron Radiography and TriBeam Tomography: Andrew Polonsky1; Kira Pusch1; Toby Francis1; McLean Echlin1; Jonah Klemm-Toole2; Alec Saville2; Chandler Becker2; Benjamin Ellyson2; Yaofeng Guo2; Chloe Johnson2; Brian Milligan2; Niranjan Parab3; Kamel Fezzaa3; Tao Sun3; Amy Clarke2; Tresa Pollock1; 1University of California, Santa Barbara; 2Colorado School of Mines; 3Argonne National Laboratory
Significant progress has been made in the development of advanced models that can capture the complexities of additive manufacturing processes. Advanced characterization techniques can offer insight to validate and expand these models to complex part geometries. Here we present the results of correlative studies combining both 3D microstructure characterization via TriBeam tomography with high speed radiography experiments to study the solidification process in superalloys at time and length scales relevant to additive manufacturing. Direct visualization of the solid liquid interface during solidification as well as details on the dynamics of the powder bed process will be discussed. Resulting microstructures from radiography experiments were fully characterized in 3D using Electron Backscatter Diffraction (EBSD), offering explicit measurement of grain morphology, texture, and the evolution of misorientation during solidification. The effects of base metal orientation in terms of theories developed for single crystal solidification will also be discussed.
9:50 AM
The Influence of Laser Modulation on Melt Pool Behavior in Laser Powder Bed Fusion Probed with In-situ X-ray Imaging: Nicholas Calta1; Aiden Martin1; Joshua Hammons1; Michael Nielsen1; Manyalibo Matthews1; Trevor Willey1; Jonathan Lee1; 1Lawrence Livermore National Laboratory
Temporal modulation of the laser heat source is used as an adjustable process variable in some commercially available laser powder bed fusion additive manufacturing systems. While a great deal is known regarding the melt pool fluid dynamics under continuous wave melting conditions, the relationship between this body of knowledge and laser processing under pulsed beam conditions is less clear. Here we use high speed X-ray imaging to understand the fluid dynamics of a laser powder bed fusion melt pool that arise from temporal modulation of the laser, with a particular focus on instabilities in the melt that can lead to pore formation.Prepared by LLNL under Contract DE-AC52-07NA27344.
10:10 AM Break
10:30 AM Invited
In-situ Characterization of Laser Additive Manufacturing Process Using High-speed Synchrotron X-ray Diffraction: Chihpin Chuang1; Peter Kenesei1; Jun-Sang Park1; Tao Sun1; Cang Zhao1; Niranjan Dilip Parab1; Yan Gao2; Xuan Zhang1; Anthony Rollett3; Jonathan Almer1; 1Argonne National Laboratory; 2GE Global Research; 3Carnegie Mellon University
Rapid melting and solidification during laser Additive Manufacturing (AM) process create unique microstructure that is distinct comparing to other traditional metal processing techniques. Advanced characterization tools are needed to explore the relevant temporal and thermal process regimes. In this work, we will discuss recent development in in-situ characterization capabilities at beamline 1-ID of the Advanced Photon Source that aims to better understand the effect of rapid heating and solidification on the microstructural features of engineering alloys and correlate those to AM process parameters. We utilized focused high-energy X-ray beam and a high frame rate CdTe detector to acquire position-dependent structure information around the laser scan path. The experiment demonstrates that the laser melting processes can be monitored through high-energy diffraction experiment and obtain information regarding crystal structure, phase and temperature evolution, and precipitates formation. The limitation of the current setup and the future development will also be discussed.
10:50 AM Invited
Quantitatively Revealing the Dynamics of Laser Powder Bed Fusion Additive Manufacturing Process by In-situ High-speed X-ray Imaging and Diffraction: Lianyi Chen1; 1University of Wisconsin-Madison
Understanding the dynamics of the laser powder bed fusion additive manufacturing process is critical for establishing location-specific processing-microstructure-property relationships. The highly localized (tens of micrometers) and very short (tens of microseconds) interaction of a laser beam with the powder bed pose a huge challenge to the characterization and understanding of this process. In this talk, I will give an overview of our research on characterizing the dynamics of powder spreading, powder spattering, melt pool evolution, melt flow, defect formation and evolution, and solidification in the laser powder bed fusion additive manufacturing process by using high-energy high-speed x-ray imaging and diffraction, with a focus on defect formation and evolution.
11:10 AM
Multi-physics Modeling of Fluid and Powder Dynamics in Laser Powder Bed Fusion Process: Xuxiao Li1; Wenda Tan1; Cang Zhao2; Niranjan Parab2; Tao Sun2; 1University of Utah; 2Argonne National Laboratory
In this work, a numerical model is established to simulate the thermo-fluidic dynamics of molten pool, metal vapor, and ambient gas as well as the powder particle motion in laser powder bed fusion (LPBF) process. The model features (a) level-set interface representation, (b) a unified framework to treat incompressible molten pool flow and compressible gas flow, and (c) a discrete element module to track particle motion. The simulations capture multiple key physical phenomena including keyhole and molten pool evolution, metal vapor expansion and ambient gas entrainment, and particle motion driven by gas flow and particle collision. The simulation results clearly reveal that the gas flow has significant effects on the powder motion, which, in turn, has significant effects on the keyhole and molten pool evolution. The results are consistent with the state-of-the-art high-speed X-ray imaging observations of the LPBF process.
11:30 AM
Study of Gas Entrapment and Its Effects on Porosity in 17-4 PH Atomized Powder Laser Powder Bed Fusion (LPBF) Parts: Ziheng Wu1; Debomita Basu1; Robin Kuo1; Jack Beuth1; Anthony Rollett1; 1Carnegie Mellon University
Gas entrapment in powder particles is nearly inevitable during the gas atomization process and is problematic because it can affect the mechanical properties of AM-built parts. In this work, several Ar and N2 atomized 17-4 PH stainless steel powders with different levels of gas entrapment are used in the laser powder bed fusion (LPBF) process with Ar and N2 building environments. Process maps for different 17-4 PH powders are also developed through process optimization. Through advanced synchrotron-based high energy X-ray techniques such as computed tomography (CT), and dynamic x-ray radiography (DXR), we can determine the formation mechanisms, the morphology, the size distribution and the spatial distribution of porosity. The results show that the level of entrapped gas and the final in-part porosity correlate with the atomization and build atmospheres.
11:50 AM
Quantification of the Effects of Deposition Parameters and Particle Size Distribution on Spatter Formation in Laser Powder Bed Fusion: Yao Xu1; Joe Pauza2; Anthony Rollett2; Sneha Narra1; 1Worcester Polytechnic Institute; 2Carnegie Mellon University
Spatter refers to the ejection of powder and molten material that can result in defects such as denudation, contamination, and porosity. The key to effectively reduce spatter is to understand the dynamics of spatter formation, of which connection between processing parameters and spatter formation is missing in the literature. Computer vision was applied on high-frequency X-ray images captured during laser melting to analyze spatter. For different laser power, velocity combinations and powder sizes, the ejection quantity, velocity, and travel distance are different. For instance, delayed ejections were observed for larger powders that can be attributed to induced chamber gas flow instead of recoil pressure. Also, spatter behavior including ejection-to-fall lifetime was quantified as a function of power and velocity for Inconel 718 and Ti-6Al-4V. This work provides insights regarding dominating mechanisms that contribute to spatter under different processing conditions. This, in turn, can provide guidance for minimizing spatter.