Experience

National Institute of Standards and Technology

Materials Science and Engineering Division • Gaithersburg, MD

Research Staff • July 2017 — Present

Extended phase-field model of Inconel 625 with more thermodynamically-consistent diffusion parameters while overhauling mathematical framework. Monitored, maintained, and upgraded shared computer hardware in the Center for Theoretical and Computational Materials Science; helped to address user concerns by building updated software versions and exploring filesystem upgrades to alleviate resource contention. Developed training materials through High Performance Computing Carpentry, created user-editable Wiki pages for CTCMS and Enki clusters, and documented major cluster features and common workflows for each.

NRC Postdoctoral Associate • July 2015 — June 2017

Implemented phase-field model for solid-state transformation in alloy systems with three components and four phases, analogous to Inconel 625. Designed initial conditions based on electron micrographs of additively manufactured Inconel 625 to simulate microstructure evolution during heat treatment. Produced thermodynamic models through simplification of quantitative CALPHAD databases while retaining key phase diagram features, using computer algebra systems to accurately generate expressions and multivariable derivatives for import into phase-field software.

Veeco Instruments

Solar Process Development Center • Clifton Park, NY

Process Engineer • July 2009 — August 2011

Part-time during master's degree. Researched non-toxic alternatives to CdS, reporting to senior management. Traveled to Helsinki to evaluate state-of-the-art atomic layer deposition reactor.

DayStar Technologies

Materials Development Group • Clifton Park, NY

Process Engineer • January 2009 — June 2009

Process Technician • July 2006 — December 2008

Researched alternatives to chemical bath deposition of CdS thin films, including nontoxic materials and novel reactor geometries. Achieved 72× scaleup in CdS deposition area with only 6× increase in waste generation.

Education

Rensselaer Polytechnic Institute

Doctor of Philosophy, Materials Engineering • • September 2011 — May 2015

Thesis: "Bias in Polycrystal Topology Caused by Grain Boundary Motion by Mean Curvature"

Performed large-scale phase field simulations of normal isotropic grain growth on high performance computing clusters including AMOS, an IBM Blue Gene/Q supercomputer. Designed and implemented algorithms to reconstruct polyhedral grain topology (faces, edges, and vertices) from diffuse interfaces in 2D and 3D phase field datasets. Found the process of triangular face elimination responsible for biasing topology in populations of polyhedral grains in synthetic, simulated, and real metal microstructures.

Master of Science, Materials Engineering • • September 2009 — May 2011

Thesis: "Effects of Magnesium(II) on Zinc Oxide Nanorod Growth From Aqueous Solution"

Designed experiments to deposit ZnO on glass substrates using a novel flow-through aqueous chemical reactor. Found minor effects of Mg2+ ions on ZnO film stress and lattice parameters.

Bachelor of Science, Chemical Engineering • • September 2002 — May 2006

Publications

D. Wheeler, T. Keller, S. DeWitt, A. Jokisaari, D. Schwen, J. Guyer, L. Aagesen, O. Heinonen, M. Tonks, P. Voorhees, and J. Warren. "PFHub: The Phase-Field Community Hub. " Journal of Open Research Software 7 (2019) 29. DOI: 10.5334/jors.276.

T. Keller, G. Lindwall, S. Ghosh, L. Ma, B. Lane, F. Zhang, U. Kattner, J. Heigel, E. Lass, Y. Idell, M. Williams, A. Allen, J. Guyer, and L. Levine. "Application of finite element, phase-field, and CALPHAD-based methods to additive manufacturing of Ni alloys. " Acta Materialia 139 (2017) 244—253. DOI: 10.1016/j.actamat.2017.05.003.

T. Keller, B. Cutler, E. Lazar, and D. Lewis. "Comparative grain topology. " Acta Materialia 66 (2014) 414—423. DOI: 10.1016/j.actamat.2013.11.039.

T. Keller, B. Cutler, M. Glicksman, and D. Lewis. "Enumeration of polyhedra for grain growth analysis. " In Proceedings of the First International Conference on 3D Materials Science (Seven Springs, PA: 2012) 97—106. DOI: 10.1007/978-3-319-48762-5_15.

Presentations*

2020

2019

2018

2017

2016

2014

2013

2012

*Presenter's name is underlined.

Posters*

  • T. Keller and D. Lewis. "Trijunction drag affects grain topology." NIST Chapter of Sigma Xi, Annual Postdoctoral Poster Session. Gaithersburg, MD: February 19, 2016.
  • T. Keller and D. Lewis. "Grain topology from 3D phase-field simulations." Eastern New York Chapter of ASM International, Spring Symposium. Troy, NY: November 18, 2014.
  • T. Keller, B. Cutler, G. Yauney, and D. Lewis. "Grain topologies in synthetic, simulated, and real microstructures." Rensselaer Moves into Petascale Computing: Celebration & Workshop. Troy, NY: October 3, 2013.
  • T. Keller, B. Cutler, G. Yauney, and D. Lewis. "Topological distributions in synthetic microstructures and grains." 8th International Conference on Porous Metals and Metallic Foams (MetFoam). Raleigh, NC: June 23-26, 2013.
  • D. Lewis, G. Saunders, S. Rock, T. Keller, J. Mao, M. Muench, J. Symons, D. Hoffman, M. Oullette, and C. LaBarre. "Development of an automated serial sectioning system." CATS/CEG Advanced Manufacturing Conference. Troy, NY: April 22, 2013.
  • T. Keller, G. Yauney, B. Cutler, and D. Lewis. "Grain populations in topological space." Eastern New York Chapter of ASM International, Spring Symposium. Troy, NY: December 5, 2012.

*Presenter's name is underlined.

Recognition

NIST Material Measurement Laboratory

MML Accolade • 2018

Nominated by multiple colleagues, "For exceptional contribution to the field of metal additive manufacturing with a focus on developing integrated simulation methods to predict microstructure evolution based on phase-field models, computational thermodynamics, and finite element analysis."

Acta Materialia and Scripta Materialia

Outstanding Reviewer Award • 2018

Outstanding Reviewer Award • 2017

Skills

Scientific Computing

  • Teaching as a Carpentries Instructor: Python, Unix Shell, Version Control.
  • Programming languages: C, C++, Python, shell (bash); CUDA, MPI-2/MPI-IO, OpenMP.

Experimental Techniques

  • Metallographic polishing and etching: Fe, Cr, Cu, Ni, Ti, and Zn alloys
  • Scanning electron microscopy (SEM) of metal and semiconductor specimens
  • X-ray diffractometry of semiconducting thin films
  • UV-visible light spectrophotometry of semiconducting thin films
  • Contact profilometry of metal, metalloid, and semiconductor thin films

Project Links