Powder Materials Processing and Fundamental Understanding: Additive Manufacturing I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Powder Materials Committee
Program Organizers: Kathy Lu, Virginia Polytechnic Institute and State University; Eugene Olevsky, San Diego State University; Hang Yu, Virginia Polytechnic Institute and State University; Ruigang Wang, The University of Alabama; Isabella Van Rooyen, Pacific Northwest National Laboratory

Monday 2:00 PM
February 28, 2022
Room: 263C
Location: Anaheim Convention Center

Session Chair: Eugene Olevsky, San Diego State University; Hang Yu, Virginia Polytechnic Institute and State University

2:00 PM  Invited
Laser-based, Machine-learning Guided, Additive Manufacturing of Ceramics with Designed Microstructure and Hardness: Xiao Geng1; Jianan Tang1; Dongsheng Li2; Yunfeng Shi3; Jianhua Tong1; Hai Xiao1; Fei Peng1; Rajendra Bordia1; 1Clemson University; 2Advanced Manufacturing LLC; 3Rensselaer Polytechnic Institute
    We report ultra–fast sintering of alumina under scanning laser irradiation, and a machine learning approach to predict the microstructure and hardness of sintered alumina. We developed an elegant machine learning (ML) algorithm to predict the microstructure under arbitrary laser power. This algorithm realistically regenerates the SEM micrographs under the trained laser powers. Further, it also accurately predicts the alumina’s microstructure under unexplored laser power. Using this approach, we can simultaneously fabricate a sample array that contains hundreds of individual sample units. Micro-indentation was carried out to measure the hardness of the sample units. The microstructure of selected sample units was characterized. Finally, using these results (of hardness as a function of microstructure), we developed an ML algorithm to not only accurately predict the microstructure of alumina of arbitrary hardness, but also predicts the hardness based on the observed microstructure.

2:30 PM  
Influence of Powder Reuse in LPBF on the Attributes of SS316L Particles and Powder Beds: Timothee Delacroix1; Fernando Lomello1; Frédéric Schuster1; Hicham Maskrot1; Jean-Paul Garandet1; 1CEA
    In Laser Powder Bed Fusion (LPBF), a significant amount of metallic powder is not solidified by the laser beam. The ability to reuse metal powder efficiently strongly impact costs and material yield. However, some of the recovered powder is exposed to high temperatures during the manufacturing process in an imperfectly controlled environment. Therefore, there is a need to study and understand powder degradation during the process and the effect after multiple reuses. One batch of gas-atomized 316L stainless steel powder was used, recovered, sieved and reused to produce 15 successive LPBF prints without addition of virgin powder. Recycled powders were characterized throughout each iteration to investigate changes in particles morphology, rheology, crystal structure and chemical composition. A gradual increase of oxygen content was observed, along with the presence of colored and oxidized particles. Powder bed layers were also studied with scan acquisitions at very high spatial resolution.

2:50 PM  
Understanding Surface Roughness on Vertical Walls in Laser Powder Bad Fusion Additive Manufacturing: Tianyu Zhang1; Lang Yuan1; 1University of South Carolina
    In the laser powder bed fusion (LPBF) additive manufacturing process, parameters such as laser scanning speed and power have overarching effects on the development of melt pool and surface roughness, all of which contribute significantly to the final material integrity and mechanical properties. In this study, a wide range of energy densities (calculated based on the laser power, scanning speed, and hatch spacing) on stainless steel 316L powder were systematically investigated experimentally and numerically for cubic samples in LPBF. The correlations between energy density and surface roughness on vertical walls were discussed in detail via examining the melt pool dimensions, microstructural characteristics and surface topography. Mechanisms that drive surface roughness on vertical walls were proposed based on the analysis of partially attached particles and isolated balling effect. Methods to control the surface roughness on vertical walls based on the mechanisms were established and demonstrated in LPBF.

3:10 PM  
NOW ON-DEMAND ONLY - Optical Analysis of Powder Oxygen Content in Metal Powder Bed Fusion: Tan-Phuc Le1; Xiaogang Wang1; Nick Weeks2; Matteo Seita1; 1Nanyang Technological University; 2Carpenter Additive
    Powder recycling is key to reducing material wastage and improving the sustainability of powder bed fusion processes. However, the quality of the powder is known to progressively decrease as it is recycled due to particle oxidation and to the incorporation of other contaminants, which have detrimental effects on part quality. In this work, we employ a “powder bed scanner” to capture particle-level resolution, colored-images of different powder batches, which we use to assess the particle oxidation state in recycled powder. Because particles change color as they are exposed to the high processing temperature, we devise a numerical image analysis technique to quantify the fraction of oxidized particles and correlate it to the actual oxygen content, benchmarked by inert gas fusion measurements. Our method provides a rapid and inexpensive means to estimate the ‘age’ of recycled powders and inform powder mixing strategies to maintain powder feedstock consistency and build quality.

3:30 PM Break

3:50 PM  
Synchrotron X-ray Imaging of Cracking during Laser Powder Bed Fusion (LPBF) of Aged CM247 Powder with Varying Oxygen Content: David Rees1; Chu Lun Alex Leung1; Thomas Kellock1; Gowtham Soundarapandiyan2; Sebastian Marussi1; Saurabh Shah1; Robert Atwood3; Ben Saunders4; Gavin Baxter5; Peter Lee1; 1University College London; 2National Structural Integrity Research Centre; 3Diamond Light Source Ltd; 4Rolls-Royce plc.; 5MAPP EPSRC Future Manufacturing Hub
    Laser powder bed fusion (LBPF) of Ni-based superalloys enables the production of geometrically complex components for operation in high-temperature, high-stress environments. However, precipitation hardened alloys such as CM247 are highly susceptible to cracking during processing (hot-, liquation-, and ductility-dip cracking) and during heat-treatment. The underlying phenomena causing cracking, and how to prevent it, remains unclear but it is known that both the feedstock composition and complex thermal history are key factors. Here, we investigated the effect of different levels of oxidized CM247 powder on cracking during LPBF to identify a suitable trade-off between build quality and economic value. To observe crack evolution, we performed high-speed synchrotron X-ray radiography of the LPBF process over a range of processing parameters, and post-build synchrotron computed tomography. Our results show that high oxidized powder exacerbates crack formation and demonstrates that for a given defect size criteria, a tolerable oxidation level can be determined.

4:10 PM  
Inconel 718 Contamination in Ti6Al4V during Powder Bed Fusion: Cory Groden1; Kellen Traxel1; Amit Bandyopadhyay1; 1Washington State University
     Contaminating other metal powders is a critical problem in additive manufacturing, especially in powder bed fusion (PBF) metal printers. This occurs as some powder may remain on the printer components even after a thorough cleaning and/or may get mixed in the bulk powder at the start. When this contaminated powder is printed, the contaminant metal may cause unwanted intermetallic compounds that can cause microcracks to form. Also, a contaminant powder with a higher melting point could cause microcracks and other printing issues. In this work, Ti6Al4V powder was contaminated with 0.5%, 1.5%, and 2.5% Inconel 718 and printed using the same printing parameters of uncontaminated Ti6Al4V as it is assumed that we are unaware of the contamination. It was found that contamination with 1.5% Inconel 718 reduced the ductility by about 50% and contamination with 2.5% Inconel rendered the specimen unable to undergo any plastic deformation without catastrophic failure.

4:30 PM  
Electromigration Behavior of Additively Manufactured Copper Wirings: Hugo Ramirez Grijalba1; Ping-Chuan Wang1; Dan Freedman1; 1SUNY New Paltz
    Characterized by its excellent electrical and thermal conductivities, copper is widely used in the electronics industry for circuitry and thermal management applications. As it becomes more readily available as a material of choice for additive manufacturing (AM), wide adoption of AM copper components can be anticipated to produce complicated designs that are otherwise costly or even impossible to realize. In this study, AM copper wirings are fabricated using bound metal deposition on a Desktop Metal Studio system, where the microstructure is characterized with scanning electron microscopy and electron backscatter diffraction at different stages through the debinding and sintering processes. Electromigration, a degradation process in circuit interconnects due to biased mass depletion under excessive electrical current, is applied to the specimens at various stress conditions to investigate the wear-out process and mechanism. The relationship among the microstructure, surface morphology, and electromigration behavior will be discussed in this presentation.