6th World Congress on Integrated Computational Materials Engineering (ICME 2022): Applications: Advanced Manufacturing – Additive Manufacturing II
Program Organizers: William Joost; Kester Clarke, Los Alamos National Laboratory; Danielle Cote, Worcester Polytechnic Institute; Javier Llorca, IMDEA Materials Institute & Technical University of Madrid; Heather Murdoch, U.S. Army Research Laboratory; Satyam Sahay, John Deere; Michael Sangid, Purdue University
Monday 1:30 PM
April 25, 2022
Room: Regency Ballroom AB
Location: Hyatt Regency Lake Tahoe
Session Chair: Katherine Sebeck, US Army Ground Vehicle Systems Center
1:30 PM Break
1:40 PM
Modeling Microstructural Evolution in Laser Powder Bed Fusion with Kinetic Monte Carlo and Lattice-Boltzmann Cellular Automata Methods: Joseph Pauza1; Guannan Tang1; Joseph Aroh1; Anthony Rollett1; Gregory Wong; 1Carnegie Mellon University
Although the basics of solidification driven microstructural evolution is well understood, Laser Powder Bed Fusion produces components with complex grain structures which vary with laser settings and material properties. Because the grain formation occurs locally within the melt pool which is rastered in three dimensions and evolves with time, it adds to the difficulty of predicting the final microstructure. In this talk, we present a kinetic Monte Carlo (KMC) code which enables fast simulation of 3D solidification textures for a variety of processing parameters and scan strategies. It is discovered that the melt pool shape and the preferred growth direction relationship are the two fundamental factors to achieving reasonable microstructures that match with experiments. Another code based on a coupled Lattice Boltzmann and Cellular Automata approach considers more physics such as melt pool fluid flow and growth kinetics to simulate grain structures which will be compared with the KMC code.
2:00 PM
An ICME Framework for Heat Treating Additively Manufactured Nitrogen Atomized 17-4PH Stainless Steel: James Zuback1; Mark Stoudt1; Daniel Gopman1; Maureen Williams1; Carelyn Campbell1; 1National Institute of Standards and Technology
The presence of nitrogen hinders the ability of additively manufactured 17-4PH stainless steel to form martensite during conventional post-process heat treatment. Here, an ICME approach is used to guide exploratory work for designing heat treatments with the goal of tailoring martensite fractions. Calphad based tools are used to reveal post-processing pathways for redistributing nitrogen in the form of precipitates and allowing the formation of martensite without cryogenic treatment. The calculated phase stabilities and transformation temperatures guide targeted heat treatment experiments, and post-processed materials are extensively characterized to provide validation and feedback for improving model predictions. Post-processing procedures are tested with multiple heats of nitrogen-atomized 17-4PH to identify necessary modifications to account for compositional variations. Findings suggest that although alternative heat treatment temperatures and times can be used to achieve desirable microstructure and properties, a universal protocol may not be suitable for all powder feedstock and additive manufacturing process combinations available.
2:20 PM
Full Field Modeling of Austenitic Stainless Steel Solidification Features in Laser Powder Bed Fusion Melt Pools: Joseph Aroh1; P. Chris Pistorius1; Anthony Rollett1; 1Carnegie Mellon University
Laser Powder Bed Fusion (LPBF) prints with a rastered laser which produces microstructures comprised of multiple weld pools in each layer. Due to the rapid speed of the welds, it is possible that metastable austenite becomes the primary solidification phase in austenitic stainless steels due to growth kinetics and potentially limited chemical segregation because of solute trapping. A computational framework consisting of a numerical thermal model, computational thermodynamics, and a dendrite growth model was developed to understand the location dependence of dendrite growth kinetics and segregation trapping at the full field melt pool scale for several stainless steels. The model was compared to both in-situ synchrotron x-ray diffraction experiments and post-mortem characterization of cross-sectioned single beads. This work aims to elucidate the location dependent microstructural evolution of sub-grain features at the melt pool level to inform future alloy properties, laser parameters, and scan strategies tailored specifically for the LPBF process.