Additive Manufacturing: Materials, Alloy Development, Microstructure and Properties: Additive Manufacturing Process Control and Optimization
Program Organizers: Prashanth Konda Gokuldoss, Tallinn University of Technology; Zhi Wang, South China University of Technology; Jurgen Eckert, Erich Schmid Institute of Materials Science; Filippo Berto, Norwegian University of Science and Technology

Monday 2:00 PM
November 2, 2020
Room: Virtual Meeting Room 3
Location: MS&T Virtual

Session Chair: Sudhakar Vadiraja, Montana Tech


2:00 PM  
Additive Manufacturing of Nuclear Spacer Grids: Syed Zia Uddin1; Qu He1; Jack Beuth1; 1Carnegie Mellon University
    Nuclear spacer grids, an intricate consumable part of a nuclear fuel assembly, currently require lead time of more than two years from order placement to delivery using conventional fabrication methods. Laser Powder Bed Fusion (LPBF) type Additive Manufacturing (AM) process could reduce the lead time and cost significantly by printing out the structure in one major step. However, one of the main challenges in LPBF fabrication is the buckling type deformation of the tall thin walls that are abundant in the current spacer grid design. In this research, LPBF fabrication and finite element simulation of the simplified spacer grid structures with a wall thickness of 300μm and height of 47mm (~1.5inch) were performed. To eliminate the observed buckling deformation, different stiffening modifications were introduced to the thin walled cross section of the spacer grid structure. Findings in the current research would facilitate successful LPBF fabrication of tall thin wall structures.

2:20 PM  
Characterization of the Balling Ddefect during Laser Powder Bed Additive Manufacturing: Debomita Basu1; Jack Beuth1; Bryan Webler1; 1Carnegie Mellon University
    A major challenge of adopting Laser Powder Bed Fusion into an industrial setting is the relatively slow build rates characteristic of this process. While using higher laser powers and velocities increase the build rate, undesirable surface tension defects known as the balling phenomenon, or bead-up, may form along the length of the laser track. This creates uneven surfaces for subsequent layers, which can result in embedded pore-type flaws. The exact parameters at which this phenomenon occurs are not the same across different metals. In this work, 316 Stainless Steels and Ti-6Al-4V were studied to determine differences in balling behavior using optical microscopy, scanning electron microscopy, high-speed radiography, high speed imaging, and IR imaging. However, the formation mechanisms behind this defect are relatively unknown. Possible processing strategies to change melt pool shape at high powers and high velocities and mitigate balling are also discussed.

2:40 PM  
Mesoscale crystallographic texture control via beam path sequencing in electron beam melting: Patxi Fernandez-Zelai1; Michael Kirka1; Yousub Lee1; Sebastien Dryepondt1; Maxim Gussev1; 1Oak Ridge National Laboratory
    Metals additive manufacturing research is often focused on process window identification for avoiding defects and yielding desirable properties. The magnetic lens in electron beam melting fusion processes enables precise spatial-temporal control of the heat source. Prior studies have shown that this control makes possible small scale site specific microstructure manipulation. Design is therefore extended to the microstructure length scale granting overall greater flexibility in engineering and fabricating high performance components. In this presentation we discuss the role of geometry and beam path sequencing in a Ni-based superalloy manufactured via powder bed electron beam melting. Mesoscale morphology and texture are controlled by careful engineering of the melt sequence. Solidification in the build direction, which usually prefers a [001] growth texture, is continuously tilted by control of the heat flux vector. In the extreme case the resulting structure consists of epitaxial columnar crystals with a strong [011] build direction preference.

3:00 PM  
Prediction and validation of successful multi-material AM interfaces: Nicholas Jones1; Rishikesh Magar1; Amir Farimani1; Jack Beuth1; Maarten de Boer1; 1Carnegie Mellon Univ
    In metals additive manufacturing, the joining of dissimilar metals has typically been a trial-and-error process. There is a lack of research that uses a systematic approach to determine the root causes of bonding success and failure between alloys. We identified a simple base system – the iron-nickel-chromium ternary system – to test guidelines we have proposed for joining different alloys. Using CALPHAD computational techniques, we analyzed an array of these alloy pairs in order to determine precipitation of intermetallic phases between them. We fed these results into a machine-learning algorithm to quickly predict intermetallic formation across a wide range of composition and temperature. Using these results, we identified guidelines for joining two alloys without forming brittle intermetallics at the interface. These guidelines were tested via directed energy deposition on 22 material combinations. The experimental validation of these guidelines will inform future viability of many multi-material AM structures.