Additive Manufacturing of Metals: Complex Microstructures and Architecture Design: Microstructure Characterization and Novel Materials
Sponsored by: TMS Additive Manufacturing Committee
Program Organizers: Yu Zou, University of Toronto; Hang Yu, Virginia Polytechnic Institute And State University
Thursday 8:00 AM
November 5, 2020
Room: Virtual Meeting Room 6
Location: MS&T Virtual
Session Chair: Tao Sun, University of Virginia ; Ji Ma, University of Virginia
8:00 AM Invited
Synchrotron X-ray Studies on Additive Manufacturing and Materials: Tao Sun1; 1University of Virginia
Metal additive manufacturing (AM) is a transformative technology, which not only unleashes the design freedom by allowing the build of geometrically complex parts, but also opens up the opportunities for synthesizing novel materials with non-equilibrium structures and fabricating functionally graded architectures. AM holds the promise for completely revolutionizing the way we make thing, but building defect-free products with precisely controlled microstructures remains challenging. At the Advanced Photon Source, we recently applied high-speed x-ray imaging and diffraction techniques to in situ characterize the metal AM processes and materials. The superior penetration power of high-energy x-rays makes it possible to look into dense metallic materials and watch their dynamic structural evolution during energy-matter interaction with unprecedented spatial and temporal resolutions. In the presentation, I will introduce the new understanding gained from our synchrotron x-ray experiments, as well as their broad impact on the development of AM materials, processes, and numerical models.
8:30 AM
Application of Photodiode Sensor for Contour Extraction of Part Features in the Laser Powder Bed Fusion Process: Yuri Plotnikov1; Mark White1; Kyle Snyder1; Marcus Thoreson1; John Sions1; 1CCAM
Metal additive manufacturing (AM) allows parts of highly complex geometry to be built to near exact shape from digital drawings and build instructions. Commercial viability of using laser powder bed fusion (L-PBF) technology to repair parts or to build upon traditionally manufactured parts is challenged by difficulties in aligning the existing part with the internal coordinate system of the AM machine. A team of CCAM researchers has created a novel solution, which uses the processing laser at low power levels to extract the contour of a part and construct a virtual part position map inside the build coordinate system. This solution utilizes the surface reflection on the part from laser beam exposure, allowing the reflected light to be captured by a fast-responding photosensor. The sensor signal is digitized at a high sampling rate and parsed into a two-dimensional map that can be used to align features within print software.
8:50 AM
Control of Nanoscale Lamellae in Bulk Al-Cu Eutectic Samples Through Laser Powder Bed Fusion: Jonathan Skelton1; James Fitz-Gerald1; Jerrold Floro1; 1University Of Virginia
Eutectic alloys processed through laser powder bed fusion (LPBF) have recently generated interest as a potential class of high strength materials due to the high density of interphase interfaces that are produced. In this research, the relationship between LPBF processing parameters and the resulting microstructure of bulk Al-Cu eutectic samples is investigated as a model system. Specifically, effects of the laser velocity and power on the microstructural features such as the interphase spacing, colony width, melt pool boundary thickness, and lamellae and colony orientation are analyzed and discussed. This research demonstrates that control of the interphase spacing and microstructural orientation of eutectic alloys may be achieved through careful selection of the laser velocity and scan direction, allowing for fine tunability within each line scan, and providing potential design freedoms of bulk properties within the built part. Support for this research from the National Science Foundation grant #CMMI-1663085 is gratefully acknowledged.
9:10 AM
Mitigating Stray Grain Nucleation during the Laser Powder Bed Fusion of Single Crystal CMSX-4: Joseph Aroh1; Amir Mostafaei2; Joseph Pauza1; Runbo Jiang1; Jerard Gordon1; Anthony Rollett1; 1Carnegie Mellon University; 2Illinois Institute of Technology
Despite the rapid, nonequilibrium solidification conditions in Laser Powder Bed Fusion processing, the as-built microstructure is typically dominated by epitaxial grain growth which continues across many successive build layers/melt pool boundaries. In this work, we investigated the effects that laser processing parameters have on maintaining epitaxial growth and mitigating stray grains within a melt track on single crystal CMSX-4. Observations from electron backscatter diffraction, scanning electron microscopy, and synchrotron high energy diffraction microscopy experiments inform how the degree of epitaxy is affected in each condition. Each experiment was performed on both bare plate and with various Ni-alloy powder layers to see how powder might further promote nucleation sites. Further validation of this work included using classical nucleation theory coupled with thermal modeling to predict where nucleation has the highest probability to occur as a function of melt pool position.
9:30 AM
Microstructural Features and Mechanical Properties of a Newly Designed Steel Fabricated by Laser Powder Bed Fusion: Yuan Tian1; Robert Palad2; Clodualdo Jr. Aranas2; 1Voestalpine Additive Manufacturing Ltd.; 2University of New Brunswick
A new iron-based alloy, M789, with good printability and corrosion resistance has been recently developed and additively manufactured by laser power bed fusion process. The relationship between the microstructural features and the mechanical properties of M789 steel was studied and evaluated. In the as-printed condition, epitaxial grain growth of cellular dendritic structure inside the melt pool was observed. The primary dendrite arm spacing was measured to be 0.42±0.12 µm. The electron backscatter diffraction maps suggest the formation of elongated columnar grains with significant low-angle grain boundaries. In the solution annealed and aged samples, melt pool boundaries and scan tracks disappeared; large needle-like martensitic structures were evident with fewer LAGBs. Moreover, spherical ETA-Ni3Ti precipitates were formed during the heat-treated process, which led to significant increase in hardness, tensile and yield strength with values of 52.4±0.7HRC, 1798±4MPa and 1714±13MPa, respectively. Thermodynamic and mechanical properties simulation were consistent with the experimental data.