2021 Technical Division Student Poster Contest: SMD 2021 Technical Division Undergraduate Student Poster Contest
Program Organizers: TMS Administration
Monday 5:30 PM
March 15, 2021
Room: RM 9
Location: TMS2021 Virtual
First Principles Study of Sigma Phase Destabilization in Compositionally-complex Stainless Steel Alloys: Anna Soper1; Savanah Diaz1; Holly Frank1; Jonas Kaufman2; Adam Shaw3; Kevin Laws4; Aurora Pribram-Jones5; Lori Bassman1; 1Harvey Mudd College; 2UC Santa Barbara; 3 California Institute of Technology; 4University of New South Wales; 5UC Merced
Stainless steels are used in industry extensively due to a combination of desirable material properties, such as corrosion resistance and strength. However, ferritic steels form a brittle sigma phase at moderately high temperatures which limits their utility. Building on experimental findings that small amounts of Al in the presence of Mn suppress the formation of the Fe-Cr sigma phase, this first principles work explores the hypothesis that Al disrupts sigma geometry by changing the electron distribution among the crystal’s molecular orbitals. In order to investigate this, a generalized cluster expansion combined with Monte Carlo simulations are used to determine the preferential placement of atomic species on each basis site. Analytical methods, including the Crystal Orbital Hamilton Population method, are used to determine the ways in which Al destabilizes the sigma structure.
Utilizing CALPHAD Methods to Determine Phases in a Compositionally Complex Fe-Cr-based Alloy: Kaitlyn Paulsen1; Alexandra Loumidis1; Patrick Conway2; Karen Privat3; Kevin Laws3; Lori Bassman1; 1Harvey Mudd College; 2Jönköping University; 3University of New South Wales
Fe-Cr-based ferritic steels exhibit excellent corrosion resistance. However, their use and application are limited by the formation of a brittle sigma phase at intermediate temperatures. Prior experiments demonstrated that the addition of Mn and small amounts of Al eliminates the sigma phase for a specific range of compositions. In this work, extrapolating from binary and ternary systems, CALPHAD methods were used to explore the boundaries of the quaternary Fe-Cr-Mn-Al composition space for which sigma is eliminated. Results from ThermoCalc’s TCFE7 (Iron) and TCHEA4 (High Entropy Alloy) databases were cross-compared with one another and with experimental results. This work helps determine the applicability of ThermoCalc predictions for this compositionally complex system and is being utilized to refine further experiments.