Powder Materials Processing and Fundamental Understanding: Additive Manufacturing and Data-Driven Approaches
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Powder Materials Committee
Program Organizers: Kathy Lu, University of Alabama Birmingham; Eugene Olevsky, San Diego State University; Hang Yu, Virginia Polytechnic Institute And State University; Ruigang Wang, Michigan State University; Isabella Van Rooyen, Pacific Northwest National Laboratory
Tuesday 2:30 PM
March 1, 2022
Room: 263C
Location: Anaheim Convention Center
Session Chair: Kathy Lu, University of Alabama Birmingham
2:30 PM
A Bayesian Approach to the Eagar-Tsai Model for Melt Pool Geometry Predictions: Brendan Whalen1; Prasanna Balachandran1; 1University of Virginia Materials Informatics
The objective of this work is to improve melt pool geometry predictions and quantify uncertainties in the laser powder bed fusion (L-PBF) process using an adapted version of the Eagar-Tsai (E-T) model. Temperature-dependent properties of the material and powder conditions are incorporated into the conventional E-T model. Bayesian inference is employed to predict distributions for the E-T model input parameters of laser absorptivity and powder bed porosity by incorporating experimental results. Although conventionally treated as constant values in simulations and modelling, our Bayesian analysis results for 316L stainless steel (316L SS) and Ti-6Al-4V (Ti64) suggest that the absorptivity and powder bed porosity are influenced by laser power and scanning speed. Printability maps for 316L SS and Ti64 are created from the Bayesian fit adapted E-T model, which now predicts the lack of fusion and keyhole regions that were typically out of the scope for the conventional E-T model.
2:50 PM Invited
From Ultrafast Sintering with and without Electric Fields to Electrochemically Controlled Microstructural Evolution: Jian Luo1; 1University of California, San Diego
This talk will first review our recent studies on understanding the scientific questions and technological opportunities of flash sintering [Scripta 146: 260 (2018); MRS Bulletin 46: 26 (2021)]. We originally proposed that flash sintering generally starts a thermal runaway [Acta 94:87 (2015)], but it can also be activated by bulk phase and grain boundary complexion transitions [Acta 181:544 (2019)]. We further proved that ultrafast densification is enabled by ultrahigh heating rates of ~100 K/s [Acta 125:465 (2017)]. Subsequently, a generic ultrafast high-temperature sintering was reported in a collaborative study [Science 368:521 (2020)]. Other related technologies include water-assisted flash sintering (WAFS) to “flash” ZnO at room temperature [Scripta 142:79 (2018)] and two-step flash sintering (TSFS) to densify ceramics with suppressed grain growth [Scripta 141:6 (2017)]. Recent and on-going research discovered electrochemically induced grain boundary transitions [Nature Communications 12:2374 (2021)]] and is further investigating electrochemically controlled microstructural evolution occurring via several mechanisms.
3:20 PM
Surface Chemistry Changes Resulting from Ti-6Al-4V Feedstock Powder Reuse in Electron Beam Additive Manufacturing: Nicholas Derimow1; Justin Gorham1; May Martin1; Jake Benzing1; Ryan White1; Nikolas Hrabe1; 1National Institute of Standards and Technology
X-ray photoelectron spectroscopy (XPS) and electron microscopy (SEM/TEM/STEM) was carried out on Ti-6Al-4V powders used in electron beam powder-bed fusion (EB-PBF) production environments. The two objectives were to (1) investigate high oxygen containing Grade 23 Ti-6Al-4V powders which were further oxidized as a function of reuse and (2) comparing reused Grade 23 and virgin Grade 5 powders of similar oxygen content. The microstructure of the virgin Grade 23 powder was consistent with martensitic microstructure, whereas the reused powder displayed tempered Widmanstatten microstructure. XPS revealed a decrease in TiO2 at the surface of the reused powders with an increase in Al2O3. This trend is energetically favorable at the temperatures and pressures in EB-PBF machines. An unexpected amount of nitrogen was measured, with a general increase in nitride on the surface of the particles with increased reuse of the Ti-6Al-4V powder.
3:40 PM
The Effects of Melt Pool Geometry on Microstructure Development during Additive Manufacturing: Alexander Chadwick1; Peter Voorhees1; 1Northwestern University
During additive manufacturing, the geometry of the melt pool has a profound impact on the developed microstructure, particularly for epitaxial growth of columnar grains. Here, we compare the predicted microstructures with Rosenthal and Eagar-Tsai solutions for the temperature field. We present results from two models: a polycrystalline phase-field model with anisotropic, nonequilibrium solidification kinetics, and a novel model that considers how individual trijunctions follow the liquidus isotherm. Despite the assumption of isotropy, the empirical model predicts grain boundary trajectories, and thus grain shapes, that are in excellent agreement with the phase-field. For melt pools with similar sizes, both models predict that the Rosenthal and Eagar-Tsai solutions lead to fundamentally different grain shapes. In particular, the Eagar-Tsai model gives many more small grains following solidification than the Rosenthal model. The implications of this result are also discussed in regard to the effects of scan strategy.
4:00 PM Break
4:20 PM
Understanding of Agglomeration and Chemical Reactions of CoAl2O4 Inoculants in IN718 Processed by Selective Laser Melting: I-Ting Ho1; Kai-Chun Chang2; Dhruv Tiparti1; An-Chou Yeh2; Sammy Tin3; 1Illinois Institute of Technology; 2National Tsing Hua University; 3University of Arizona
The investigation aims to clarify the influence of laser scan parameters on the agglomeration and phase constitution of CoAl2O4 inoculants blended with superalloy Inconel 718 (IN718) powder feedstock and processed by selective laser melting (SLM). Preliminary results show that following the SLM process, CoAl2O4 inoculants were chemically reduced into Al2O3, Cr2O3, and TiO2 oxides, and Co-rich particles. Due to the multiple iterations of remelting as new layers are deposited during processing, the Co-rich particles formed as the CoAl2O4 inoculants were reduced in the melt pool did not survive and did not facilitate heterogeneous nucleation events. Additionally, the reduced oxide particles were found to agglomerate along the scan direction. Increasing the laser scan velocities were found to reduce the tendency for agglomeration but also resulted in an incomplete reduction of CoAl2O4 in the melt pool. Preliminary results will be presented and discussed.
4:40 PM
Understanding Powder Morphology and Its Effect on Flowability in Additive Manufacturing through Machine Learning Techniques: Srujana Rao Yarasi1; Anthony Rollett1; Elizabeth Holm1; 1Carnegie Mellon University
Metal powders are extensively used in additive manufacturing processes which necessitates standardized characterization methods for powder properties. The use of computer vision and machine learning tools in the additive manufacturing domain have enabled the quantitative investigation of qualitative factors like powder morphology, which affect the flowability in AM processes. Flowability is measured through rheological experiments conducted with the FT4 rheometer and the Granudrum, as well as the Hall Flowmeter. Convolutional Neural Networks (CNN) are used to generate feature descriptors of the powder feedstock, from SEM images, that describe not just the particle size distribution but also the sphericity, surface defects, and other morphological features of the particles. Powder property metrics are correlated to their performance metrics for several powder systems to characterize their performance in AM processes. This analysis approach is intended to be agnostic to the type of AM process and can be adapted to various powder forming techniques.
5:00 PM
Synthesis and Consolidation of CoCr+X (X=SiC or WC) Milled Powder for Additive Manufacturing: Madelyn Madrigal-Camacho1; Guillermo Aguilar1; Suveen Mathaudhu1; 1University of California-Riverside
The field of metal additive manufacturing (MAM) is rapidly advancing; however, it faces several challenges including the production of new alloy systems and powder composite manufacturing methods. Previous studies have investigated metal matrix composites produced by selective laser melting (SLM) which resulted in finer grains, improved hardness, and tensile strength due to the homogeneous distribution of reinforcement particles. To address some of the challenges in alloy development for MAM, this work has the intent to investigate ball milling technology and its capability of producing printable powder. Additionally, in order to obtain equiaxed, fine grained microstructures and provide useful guidance to achieve better mechanical performance for Co-Cr parts, the incorporation of carbides and their precipitation at atomic scale during the laser sintering is studied using pulsed and continuous laser. The observations point to the applicability of high energy ball milling as a platform for alloy and composite design for MAM.