IMX Seminar Series - Predicting deformation behaviour in structural alloys with electronic structure calculations

Ni-based superalloys can exhibit a wide range of deformation behavior depending on alloy composition, microstructure, temperature, strain rates, and applied stresses. Characterizing the deformation behavior often requires time consuming and potentially expensive experiments, but new models and increased computational power combined with density functional theory have enabled electronic structure calculations to predict deformation behavior in Ni-based superalloys and other structural alloys. In the first example in this presentation, our attempts to model solute segregation behavior to planar defects during deformation, known as Suzuki Segregation, will be shown. In this work, we utilized a combination of cluster expansion and Monte Carlo techniques housed within the a Clusters Approach to Statistical Mechanics (CASM) software to determine equilibrium concentrations of solute in Co-Ni disordered FCC alloys and Ni3Al-based ordered alloys [1]. We extended this work to investigate the segregation tendency across all Ni-X and Co-X transition metal binaries and uncovered the complex interactions that are responsible for controlling segregation or depletion tendencies to stacking faults in these alloys. Recent experimental validation of these predictions will also be presented. In the second example, we show how calculation of the generalized stacking fault energy (GSFE) surface can be used to predict deformation in a novel -Ni2(Cr,Mo,W)-strengthened superalloy, Haynes® 244®. Owing to its lower symmetry, the phase presents itself as 6 different orientation variants coherently embedded in the disordered FCC matrix and exhibits two close-packed planes and three unique deformation pathways. We show that the combination of these characteristics leads to the formation of microtwins at temperatures and strain rates ranging from 23 – 760 ºC and 10-3 –
10-9 s-1, respectively [2]. These results suggest that new structural alloys could be designed with unique precipitates that enable favorable deformation mechanisms for improved ductility and work hardening over a wide range of temperatures.
[1] Wen, D., & Titus, M. S. (2021). First-principles study of Suzuki segregation at stacking faults indisordered face-centered cubic Co-Ni alloys. Acta Materialia, 221, 117358. [doi]
[2] Mann, T., Fahrmann, M. G., & Titus, M. S. (2022). Ab Initio Investigation of Planar Defects inImmm-Ni2 (Cr, Mo, W) Strengthened HAYNES 244 Alloy. Metallurgical and Materials Transactions A,53(12), 4188-4206. [doi]
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Bio: Prof. Michael Titus is a tenured Associate Professor and Technical Director of the Purdue Heat Treating Consortium at the School of Materials Engineering at Purdue University in West Lafayette, IN, USA. Prior to joining Purdue University in 2016, he earned his B.S. in Engineering Physics at The Ohio State University, 2010 and Ph.D. in Materials at the University of California Santa Barbara, 2015. From 2015 to 2016 he was an Alexander von Humboldt Postdoctoral Fellow at the Max Planck Institute for Iron Research in Dusseldorf, Germany. Prof. Titus Prof. Titus is the recipient of the NSF CAREER award (2018) and many professional society awards including the TMS SMD Young Leaders Professional Development Award (2017), TMS-JIM Young Leaders International Scholar
(2020), and the ASM Bradley-Stoughton Award for Young Teachers (2021). He has co-authored over 35 peer-reviewed publications, has supervised 10 Ph.D. and Masters thesis students, and is currently advising 7 Ph.D. students