Phase Transformations and Microstructural Evolution: Microstructure Evolution
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Mohsen Asle Zaeem, Colorado School of Mines; Ramasis Goswami, Naval Research Laboratory; Saurabh Puri, Microstructure Engineering; Eric Payton, University of Cincinnati; Megumi Kawasaki, Oregon State University; Eric Lass, University of Tennessee-Knoxville

Monday 2:00 PM
February 28, 2022
Room: 255B
Location: Anaheim Convention Center

Session Chair: Ramasis Goswami, Naval Research Laboratory

2:00 PM  
Dynamic Microstructural Evolution of Al-Cu Alloy during Friction Stir Processing Studied Using Synchrotron Based In Situ High Energy X-ray Diffraction: Arun Bhattacharjee1; Julian Escobar Atehortua1; Jorge dos Santos2; Jan Herrnring2; Luciano Bergmann2; Peter Staron2; Benjamin Klusemann2; Bharat Gwalani1; Suveen Mathaudhu3; Cynthia Powell4; Arun Devaraj1; 1Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory; 2Institute of Materials Mechanics, Helmholtz-Zentrum Hereon; 3Metallurgical and Materials Engineering, Colorado School of Mines; 4Energy and Environment Directorate, Pacific Northwest National Laboratory
    To understand the dynamic microstructural evolution mechanisms during Friction Stir Processing (FSP) of a model Al-4 wt. % Cu alloy, in-situ high energy X-ray diffraction (HEXRD) experiments were performed at the Deutsches Elektronen-Synchrotron (DESY) using a portable FSP machine (Flexistir). The stir zone microstructural evolution was studied in two configurations. First, the x-ray beam was kept stationary at a single spot of the plate as the FSP tool moved across and away from it. In the second configuration, the x-ray beam followed the FSP tool maintaining a fixed distance in a trailing fashion while the sample was processed. Systematic analyses of the changes in lattice parameter and peak broadening were conducted as a function of FSP parameters for both measurement configurations. The in-situ HEXRD was then correlated with detailed ex-situ microscopy to understand the microstructural evolution mechanisms that operate during FSP.

2:20 PM  
Formation of Three-phase Eutectic Grains on Primary Phases: Observations from in situ and Multi-modal Imaging: George Lindemann1; Paul Chao1; Allen Hunter1; Ashwin Shahani1; 1University of Michigan
    Primary phases within off-eutectic alloys are thought to impact the surrounding eutectic microstructure. Thus, a thorough understanding of eutectic nucleation and growth in the presence of primary phases is critical to predict microstructure and its properties. Here, we investigate eutectic solidification within an off-eutectic Al-Cu-Ag alloy through in situ synchrotron X-ray radiography. The eutectic front growth velocity was found to vary based on its proximity and orientation to a neighboring primary Al2Cu rod. Ex situ 3D focused ion beam tomography, paired with scanning electron microscopy and electron backscatter diffraction analysis, revealed the eutectic Al and Ag2Al “invades” the rod surface. In between the heterogeneously nucleated Ag2Al grains, protrusions of primary Al2Cu extend into the surrounding eutectic. We propose a competitive nucleation relationship between the Al and Ag2Al phases to explain this behavior as well as the diverse neighboring eutectic microstructures.

2:40 PM  
Microstructural Evolution during Galling: Samuel Rogers1; David Dye1; 1Imperial College London
     Galling is an adhesive wear mechanism resulting from high compressive loads and low sliding speeds, and is found to occur in valves. Although characterisation of surfaces is often performed, little work has been produced which investigates the sub-surface microstructural evolution resulting from galling. The galling of self-mated 316L stainless steel results in the formation of a nanocrystalline region immediately beneath the galled surface, termed the tribologically affected zone (TAZ). Through the use of TEM, STEM-EDX and XRD the TAZ was found to contain grains of both alpha-prime martensite and austenite.By performing non self-mated galling tests of 304 against 316L stainless steel, further microstructural and macrostructural evolution was observed, most notably in the adhesive transfer of material from one surface to the other.

3:00 PM  Invited
Metallic Alloy Microstructure Evolution during Materials Processing: Amy Clarke1; Jonah Klemm-Toole1; Kester Clarke1; Alec Saville1; Christopher Jasien1; Gus Becker1; Brian Rodgers1; Jeremy Shin1; Joseph McKeown2; John Roehling2; Damien Tourret3; Sven Vogel4; Jake Benzing5; Adam Creuziger5; Adam Pilchak6; Kamel Fezzaa7; Tao Sun8; Tresa Pollock9; Alain Karma10; 1Colorado School of Mines; 2Lawrence Livermore National Laboratory; 3IMDEA Materials; 4Los Alamos National Laboratory; 5National Institute of Standards and Technology; 6MRL Materials Resources LLC; 7Argonne National Laboratory; 8University of Virginia; 9University of California Santa Barbara; 10Northeastern University
    Advanced characterization tools are generating new knowledge about phase transformations and multiscale microstructure evolution in structural metallic alloys, particularly when multiple in-situ/ex-situ techniques are used. The use of x-rays, electrons, and/or neutrons to study structural metallic alloys during/after processing is highlighted, with particular emphasis on multiscale microstructure evolution. Examples are shown that link the solidification dynamics experienced under additive manufacturing (AM) conditions (i.e., beyond equilibrium and/or during complex thermal cycling) on microstructure selection and crystallographic orientations that develop in structural metallic alloys. For example, solid-liquid interface velocities are directly measured from real-time synchrotron x-ray imaging, thermal gradients are modeled, and complementary electron microscopy and crystallographic mapping are performed and compared to solidification theory (i.e., columnar-to-equiaxed transition predictions). In-situ/ex-situ characterization of structural metallic alloys produced during/by solidification reveals possible strategies for microstructural prediction and control during AM, which will ultimately aid in the qualification and certification of parts.