Phase Transformations in Additively Manufactured Materials: Additive Manufacturing - Phase Transformations - Modelling
Sponsored by: TMS: Phase Transformations Committee
Program Organizers: Antonio Ramirez, Ohio State University; Ashley Paz y Puente, University of Cincinnati; Matthew Steiner, University of Cincinnati; Vijay Vasudevan, University of North Texas; Bij-Na Kim, Lancaster University/LPW Technology; Eric Lass, National Institute of Standards and Technology

Monday 2:00 PM
November 2, 2020
Room: Virtual Meeting Room 7
Location: MS&T Virtual

Session Chair: Matthew Steiner, University of Cincinnati; Vijay Vasudevan, University of Cincinnati


2:00 PM  Invited
Phase Field Simulations of Cellular-to-Dendritic Transition under Additive Manufacturing Conditions: Younggil Song1; Steve DeWitt1; Bala Radhakrishnan1; John Turner1; 1Oak Ridge National Laboratory
    Columnar dendritic microstructures are often observed during solidification of structural alloys under additive manufacturing conditions. We present large scale, high-resolution, three-dimensional, phase field simulations of the evolution of an initially flat solid-liquid interface into a cellular structure, growth competition between cells, and the initiation of the cellular to dendritic transformation (CDT) in a ternary Ni-Fe-Nb alloy that serves as a surrogate for the nickel-base superalloy 718. The simulations capture the effect of the temperature gradient and the solid-liquid interface velocity on the critical cell spacing above which CDT occurs. The mechanism by which the dendritic sidebranches emerge and grow will be examined through characterization of the evolution of the cell morphology and the solute concentration fields at the vicinity of the cell tip. Research performed at ORNL under contract DE-AC05-00OR22725 and supported by the Department of Energy’s Exascale Computing Project and the Oak Ridge Leadership Class Computing Facilities.

2:40 PM  
Development of Non-equilibrium Thermodynamic Tools for Additive Manufacturing: Kaisheng Wu1; Paul Mason1; Deepankar Pal2; 1Thermo-Calc Software Inc.; 2ANSYS Inc
    The complicated and highly non-equilibrium conditions of additive manufacturing pose a grand challenge to existing computational thermodynamic and kinetic tools that have had great values for traditional solidification and heat treatment processes. Meanwhile, increasingly sophisticated numerical algorithms in microstructural and mechanical simulations for AM applications require a variety of materials data that are not only reasonably accurate, but also deliberately processed and organized. In this work, a cooling rate dependent solute drag model for multi-component systems has been developed to account for the non-equilibrium solute partitioning during the rapid cooling AM process. It has also been embedded in Scheil model for micro segregation behavior. Work has also been done to provide well-curated materials data, e.g., heat capacity, density, etc. for facilitating subsequent mechanical analyses. These functionalities have been integrated into ANSYS additive manufacturing software to perform processing simulations. Preliminary results of some alloys have been shown to demonstrate their capabilities.

3:00 PM  
Design of Post-fabrication Heat Treatments for Ti Free Grade 300 Maraging Steel Manufactured Using Laser Powder Bed Fusion (LBPF) Process: Rangasayee Kannan1; Donovan Leonard1; Peeyush Nandwana1; 1Oak Ridge National Laboratory
    In this study, a thermodynamic and kinetic assessment of precipitation and austenite reversion during various post-fabrication heat treatments in Ti free grade 300 maraging steel manufactured using laser powder bed fusion process is conducted. A thermo-kinetic model is developed using the principles of Scheil solidification, driving force for the onset of nucleation, rule of mixtures, in combination with classical theories for nucleation and growth of precipitates to predict the precipitation and austenite reversion kinetics during various post fabrication heat treatments. The thermo-kinetic model was applied to predict the optimal post fabrication heat treatment.

3:20 PM  
Microstructure Engineering through Post-heat Treatment of Inconel 718 Superalloy Made by Laser Powder Bed Fusion: Yunhao Zhao1; Kun Li1; Noah Sargent1; Wei Xiong1; 1University of Pittsburgh
    The post-heat treatment is critical to control microstructure and property of additively manufactured (AM) Inconel 718 builds, to which work hardening is no longer applied. Therefore, dedicated investigations should be conducted to understand the heat treatment-microstructure-property relationships of AM Inconel 718. In this work, the effects of homogenization and aging heat treatments on the microstructure and property evolution in Inconel 718 made by laser powder bed fusion are studied by experiments and CALPHAD (calculation of phase diagrams) modeling. It is found the homogenization at a higher temperature than traditional methods can effectively introduce recrystallization and reduce residual strains. This can further remove anisotropic properties through microstructure engineering in the following aging processes. The effects of isochronal aging processes at various temperatures on the materials is investigated by a high-throughput approach. The present work provides a new pathway for the post-processing development of AM Inconel 718.

3:40 PM  
Rapid Solidification of Aluminium 6061 Using Fast Scanning DSC: Lakshmi Ravi Narayan1; Cain Hung1; Rainer Hebert1; 1Department of Materials Science and Engineering, University of Connecticut
    In order to model and predict solidification cracking during additive manufacturing, the fraction of solid must be known during rapid solidification as well as the microstructure formation. Fast-scanning Differential Scanning Calorimetry (DSC) was used in this study to determine the fraction of solid of aluminum alloy AA6061 during rapid solidification as a function of temperature and at cooling rates up to 40,000 Ks-1. The experimentally determined solid fractions were compared with analytical predictions. Microstructural analysis was performed on samples of these alloys after solidification at different cooling rates. The liquidus and solidus temperatures decrease by nearly 20 K and 300 K, respectively at the highest cooling rates over near-equilibrium freezing while the microstructure reveals a significant grain refinement. The changes in solidification and in microstructural behavior during rapid cooling are interpreted based on existing theories for their impact on solidification cracking.

4:00 PM  
Real-time Observation of the Competition between Ferritic vs Austenitic Solidification in Micro-laser Welding of 316L Using Synchrotron X-ray Diffraction: Joseph Aroh1; Seunghee Oh1; Benjamin Gould2; Andrew Chuang2; P. Pistorius1; Anthony Rollett1; 1Carnegie Mellon University; 2Argonne National Laboratory
    It is generally accepted that, at high interfacial velocities, austenite becomes the primary solidification phase in stainless steels with low Cr/Ni ratios (e.g. 316L) for kinetic reasons. Recent developments at the Advanced Photon Source allowed us to critically examine this notion via in-situ synchrotron x-ray diffraction studies of the phase transformation kinetics that occur in micro-laser welding of 316L. A Pilatus 2M detector was employed to capture multiple complete Bragg cones during the relevant phase evolution with acquisition rates of up to 500 Hz allowing solidification rates to range from 1 to 200 mm/s. The experimental results from in-situ XRD were compared to both the predictions from an interface response function model and post-mortem microstructural characterization of the retained ferrite. The insights from these experiments can be advantageous in materials processing such as Laser Powder Bed Fusion which features microstructures completely comprised of micro-laser weld pools.

4:20 PM  
Laser Powder Bed Fusion of Stainless Steel 15-5PH: Microstructure Analysis and Process Optimization: Cameron Lucas1; Nathalia Diaz Vallejo1; Holden Hyer1; Brandon McWilliams2; Kyu Cho2; Yongho Sohn1; 1University of Central Florida; 2US Army Research Laboratory
    Microstructure development in 15-5PH stainless steel was investigated over a wide range of laser bed fusion (LPBF) processing parameters (e.g., laser power, scan speed, and hatch spacing) that were independently varied on the SLM 125HL. The starting powders, sourced from SLM Solutions (Lubeck, Germany), had a size distribution of D10 = 22 um; D50 = 36 um; D90 = 50 um, and composition of (in wt.%) 18.24Cr–4.35Ni–4.31Cu–0.86Si-Fe. Use of energy density between 58 and 278 J/mm3 produced nearly fully dense (≥ 99.9 %) 15-5PH, including the SLM recommended parameter set: power = 200 W; scan speed = 800 mm/sec; hatch spacing = 0.12; slice thickness = 0.03; energy density = 69 J/mm3). Microstructure analysis, including quantification of melt pools and cellular structure within melt pools, were coupled with the Rosenthal equation to understand the LPBF process in terms of cooling and solidification rates.

3:40 PM  Cancelled
Modelling of Microstructure Evolution of Ni-based Additively Manufactured Parts: Guilherme Abreu Faria1; Kamalnath Kadirvel2; Antonio Ramirez2; Xuesong Gao2; Yunzhi Wang2; Wei Zhang2; 1Helmholtz-Zentrum Geesthacht; 2Ohio State University
    Laser powder bed fusion (L-PBF) additive manufacturing (AM) of Ni-based superalloy components has shown great advantages for the aerospace industry. Such advanced materials require complex and carefully performed heat treatments to provide optimal performance. However, if the heat treatment schedules used for conventionally manufactured cast or wrought materials is applied on AM parts, undesirable microstructures and poor performance are not uncommon. This is due the unique solidification microstructure arising from the AM process. In this work, we present a hierarchical modelling approach to predict the solidification microstructure and follow how such microstructure will evolve during the build process and with following heat treatments. The modelling approach was applied on L-PBF of alloy 718 and verified against microstructural characterization of as-built material. The solidification model is shown to match morphology and segregation profiles observed on the microstructure.