MSE Seminar by Dr. Julian Escobar Atehortua

Wednesday, March 29, 2023
3:30 p.m.-5:00 p.m.
Room 2110 CHE
Emmanuel Duh
301 405 1935

Title: In situ thermal measurements during solid phase processing of metals: thermoelectricity and synchrotron X-ray diffraction approaches.

Abstract: Measuring temperature profiles during solid phase processing (SPP) is of fundamental interest to understand, control, and optimize the microstructure of dynamically recrystallized metals. During friction stir processing (FSP), friction stir additive manufacturing, shear assisted processing and extrusion (ShAPE), or other similar SPP techniques, the stirring microstructure cannot be directly reached as it is confined, for example, underneath a tool shoulder or inside an
extrusion die. Common approaches to measure temperature profiles include the use of non-contact infrared thermometers, or the use of thermocouples welded to FSP tools, extrusion dies, or even at the base metal as close as possible to the actively stirring microstructures. However, the accuracy of these methods is limited due to resolution or proximity issues, and often computational modeling is required to estimate the temperature of the deformed microstructure. At the Pacific Northwest National Laboratory, we are currently working on two approaches to directly measure temperature during SPP: (i) in-situ thermocouples using thermo-electric measurements during ShAPE; and (ii) in-situ observation using synchrotron X-ray diffraction during FSP. Regarding thermo-electric measurements, the voltage difference across twodissimilar materials during deformation can be translated into temperature read knowing the Seebeck coefficients of two dissimilar metals. As for synchrotron X-ray diffraction, temperature can be calculated by correlating in situ measurements of the lattice parameter and the coefficient of thermal expansion of the material of interest. These approaches have been successfully applied to measure the temperature profiles at the stirring microstructures during SPP of Al, Cu, and Ni alloys.

Bio: Dr. Escobar’s research concentrates on solid phase processing and microstructural characterization ferrous and non-ferrous alloys. His core interest is the multi-modal characterization of microstructures resulting from dynamic recrystallization processes using solid phase processing methods, such as friction stir welding and processing, and shear assisted processing and extrusion. Strong focus is given to the observation of in-situ microstructural evolution using synchrotron radiation. For this type of research, he specializes in the use of synchrotron X-ray diffraction during the simulation of thermal or thermo-mechanical processes aiming to understand, control, design, or optimize microstructures for the oil and gas, civil
construction, automotive, and the aircraft industry. Additionally, Dr. Escobar works on the development of data analysis methodologies to process large numbers of complex datasets generated by electron backscatter diffraction or X-ray diffraction techniques. Other topics of interest include the use of CALPHAD for alloy design and the advanced characterization of micro segregated microstructures produced by additive manufacturing.

Research background

  • Current Materials Scientist at the Pacific Northwest National Laboratory. Sept-2022 –Current.
  • Post-doctoral research associate at the Pacific Northwest National Laboratory. Jan-2020 –Sept-2022.
  • University of São Paulo, USP – Brazil. Postdoctoral fellowship at the Polytechnic School:Oct-2018 – Dec-2019.
  • Brazilian Nanotechnology National Laboratory, LNNano – Brazil. Invited PhD intern: 2013– 2018.
  • Ohio State University, OSU – USA. Visiting PhD. Scholar at the Welding Engineering Program: Oct-2016 – Oct-2017.
  • Karlsruhe Institute for Technology, KIT – Germany: Atom Probe Tomography Laboratory: March – 2017.
  • University of Tennessee UTK - USA: Visiting PhD. Scholar at the Mechanical, Aerospace and Biomedical Engineering Department: Oct-2014 – March-2015.
  • Oak Ridge National Laboratory ORNL: Visiting PhD. Scholar at the Manufacturing Demonstration Facility and The Center for Nanophase Materials Sciences (CNMS): Oct-2014 – March-2015.
  • Brazilian Nanotechnology National Laboratory, LNNano – Brazil. Invited MSc intern: 2011– 2013.

Audience: Graduate  Post-Docs 

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