Additive Manufacturing: Nano/Micro-mechanics and Length-scale Phenomena: Monitoring and Imaging/Nanoindentation Mapping
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Meysam Haghshenas, University of Toledo; Robert Lancaster, Swansea University; Andrew Birnbaum, US Naval Research Laboratory; Jordan Weaver, National Institute of Standards and Technology; Aeriel Murphy-Leonard, Ohio State University

Wednesday 2:00 PM
March 2, 2022
Room: 260A
Location: Anaheim Convention Center

Session Chair: Aeriel Leonard, Ohio State University; Jordan Weaver, National Institute of Standards and Technology

2:00 PM Introductory Comments

2:05 PM  
Plastic Strain Visualization and Analysis of Laser Processed Nickel Single Crystals and Polycrystalline 316L: Andrew Birnbaum1; Athanasios Iliopoulos1; Anna Rawlings1; John Steuben1; John Michopoulos1; 1US Naval Research Laboratory
    The capability to characterize the mechanical response of material that has undergone laser processing is particularly relevant within the context of laser-based additive manufacturing. While there have been many efforts directed toward elastic residual field measurements, the extent of plastic deformation presents significant experimental challenges. Some efforts have focused on measuring process-induced distortion, though this only gives a global sense of geometric deviation (displacements) from the desired final form. Using a novel, data-driven approach, the present effort seeks to offer direct insight into the extent of plastic strain in ultra-high purity nickel single crystals and 316L polycrystalline materials subjected to melt-mediated laser processing. Electron backscatter diffraction-enabled orientation measurements combined with direct strain imaging techniques enabled the identification of specific slip system activation as well as surface strain measurement. These data are used as the basis of anisotropic finite element simulations of the resulting three-dimensional stress and strain states.

2:25 PM  
Deformation and Microstructure Development in DED-AM Structures via Dark Field X-ray Microscopy and In Situ Imaging: Yunhui Chen1; Yuanbo Tang2; David Collins3; Samuel Clark4; Wolfgang Ludwig5; Raquel Rodriguez-Lamaz5; Carsten Detlefs5; Roger Reed2; Can Yildirim5; Peter Lee6; Philip Withers1; 1University of Manchester; 2University of Oxford; 3University of Birmingham; 4Advanced Photon Source; 5ESRF; 6University College London
    The mechanical performance of Directed Energy Deposition Additive Manufactured (DED-AM) components are highly process condition dependent due to rapid laser induced heating and cooling rates. However, the non-equilibrium solidification process and its resulting grain structure are not easily measured by conventional techniques. Here high angular resolution Dark Field X-ray Microscopy (DFXM) is used to quantify the DED-AM microstructure including the 3D distribution of strains, lattice misorientation and Geometrically Necessary Dislocations (GNDs) in a novel nickel base superalloy. Microstructure development is explored via solidification sequence modelling, which is calibrated by in situ synchrotron imaging of the manufacturing process in real time using a unique DED-AM process replicator. Strain and crystal orientation are found to be decoupled; with sub-grain orientations correlated to thermal gradients whereas high strains are homogeneously distributed. The results presented here provide an enhanced fundamental understanding of the DED-AM process with relevance to microstructure control in AM fabricated components.

2:45 PM  Cancelled
Melt Pool-scale Monitoring of Laser Powder Bed Fusion: Jack Beuth1; Christian Gobert1; Syed Uddin1; Guadalupe Quirarte1; David Guirguis1; Luke Scime2; Conrad Tucker1; Jonathan Malen1; 1Carnegie Mellon University; 2Oak Ridge National Laboratory
    This talk gives an overview of a variety of approaches used at Carnegie Mellon to track melt pool characteristics using high speed cameras, including the analysis of high speed video frames using machine learning techniques. These include the tracking of melt pool shape as viewed from above using moderate camera speeds of 6500 fps, and its correlation to the generation of keyhole-induced flaws. Higher camera speeds near 22,000fps are used to track the emission of melt pool spatter under a variety of conditions. Ultra high speed imaging approaching 200,000 fps is being used to track variability in melt pool shape and width. Finally, color camera imaging at high speeds is being used to identify temperature fields outside of the melt pool and to some distance within it. Each of these techniques is being linked to process manipulation, modeling or other process monitoring research.

3:05 PM  
NOW ON-DEMAND ONLY – Multi Length-scale In-situ Monitoring of AM Processes: Towards Prediction of Local Defects and Properties: Paul Hooper1; 1Imperial College London
    Microstructure and mechanical properties are governed by material composition and processing history. In additive manufacturing, this processing history is complex and varies across multiple length scales, from localised high cooling rates and thermal cycling (including remelting) to longer-term temperature trends across the wider part. In-situ process monitoring tools can quantify this processing history in unprecedented detail, across multiple length and time scales, enabling the prediction of, and potential mastery of, local microstructure and mechanical properties. This talk will describe in-situ monitoring systems to gather this data in laser powder bed fusion and demonstrate the reconstruction of 3D processing history maps to show these local variations. Relationships between processing history, defects, microstructure and properties will be shown. Opportunities and synergies with small scale characterisation methods will also be discussed.

3:25 PM Break

3:45 PM  
Mechanical Microscopy of Additively-manufactured Steels Using High-speed Nanoindentation: Jeffrey Wheeler1; Marius Wagner2; Léa Deillon2; Markus Bambach2; Ralph Spolenak2; 1FemtoTools AG, Furtbachstrasse 4, CH-8107 Buchs/ZH, Switzerland; 2ETH Zurich
    Mechanical microscopy is an emerging technique using high-speed nanoindentation to map the mechanical behavior and extract phase-level properties from complex microstructures with micron-scale lateral resolution. As such, this is an ideal method to study the mechanical behavior of additively manufactured (AM) metal microstructures and assist in the optimization of processing parameters. In this work, the microstructures of 316L stainless steel and multimaterial Cu/steel samples deposited using different AM techniques were characterized. Nanoindentation maps are observed to correlate well with bulk properties and provide insight into many microstructural features: porosity, defect phases, crystallographic orientation. Statistical analysis of the microstructural phases using Gaussian and K-means methods are compared and discussed.

4:05 PM  
A Nanomechanical Approach to Reveal the Origins of Superior Intergranular Cracking Resistance in Irradiated Additively-manufactured Stainless Steel: Xiaoyuan Lou1; Jingfan Yang1; Laura Hawkins2; Lingfeng He2; Daniel Schwen2; 1Auburn University; 2Idaho National Laboratory
    Recrystallized additively-manufactured (AM) 316L stainless steel (SS), though presenting similar grain structure like its wrought counterpart, exhibited much better resistance to irradiated-assisted stress corrosion cracking (IASCC) on the grain boundaries. Microstructure characterization observed a unique nanoscale clustering of precipitates near grain boundaries. Nanoindentation was employed to visualize the interaction between grain boundary and dislocation slip channel. Protocol was developed to conduct such measurement on the oxidized grain boundaries in tensile-tested proton-irradiated samples. The dislocation pile-up was evidenced by local hardness increase. Different from the irradiated wrought 316L SS, the nanoscale clustering near grain boundary region in irradiated AM 316L SS created barrier for dislocations and prevented the direct interaction between grain boundary and slip channels, resulting in strain localization away from grain boundaries. The local stress applied to grain boundaries was reduced. The study demonstrates the ability of nanoindentation to probe the localized phenomenon of mesoscale interfaces.

4:25 PM  
Micromechanical Study of Microstructurally Heterogenous and Hierarchical Additive Manufactured Material Using High-resolution Nanoindentation Mapping: Abhijeet Dhal1; Rajiv Mishra1; 1University of North Texas
    Apart from maximizing design flexibility, additive manufacturing (AM) also enables broad microstructural and compositional flexibility due to its unique process thermodynamics. It is possible to engineer distinctive heterogeneous and hierarchical microstructures in AM processed material. Due to the activation of multiple strengthening mechanisms, paradoxical mechanical responses such as high strength-ductility synergy are observed in such microstructures. Conventional macro-mechanical testing cannot delineate complex deformation behavior at various length scales. The presentation introduces a unique combination of high-resolution nanoindentation mapping and microstructural analysis to provide insight into the strengthening mechanisms occurring at the microscopic length scale. This approach serves as an efficient and high-throughput tool to understand the underlying micro-mechanisms in the AM processed materials. The values obtained by nanoindentation are unaffected by AM processing defects and helps to evaluate the full strengthening potential of the material.