NSUF - Nuclear Science User Facilities

Patrick Warren

Profile Information
Name
Dr. Patrick Warren
Institution
University of Texas at San Antonio
Position
Assistant Professor of Research
Affiliation
University of Texas at San Antonio
h-Index
4
ORCID
0009-0005-3384-8811
Biography

I am an assistant professor of research in the Physics and Astronomy Department at the University of Texas at San Antonio. While working at UTSA in the Extreme Environments Materials Laboratory (EEML), I have had the pleasure of working under an up-and-coming leader in nuclear materials research Dr. Elizabeth Sooby on the arc melt synthesis, heat treatment, and microstructural characterization of uranium nitride. I am also the lead on a project to evaluate the porosity and oxidation behavior of additive manufactured (AM) 316L stainless steel parts. The aim of this project is to evaluate the influence of spattering and laser energy variation on the porosity and oxidation of laser powderbed fusion (LPBF) printed parts. As the lead in the AM 316L SS project, I have mentored and supervised two undergraduate students, and one post bachelors research associate in completion of simultaneous thermal analysis (STA) steam oxidation experiments and the collection and analysis of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy data. In addition to supervising and mentoring students and researchers in the EEML, I provide training on EEML equipment including arc melt, glove box, SEM, EDS, and XRD and I assist in the editing and revisions of manuscripts for students and post-doctoral research associates. Manuscripts reporting the arc melt synthesis of uranium nitride and the porosity and oxidation behavior of AM 316L SS are currently in preparation.

Before coming to UTSA, I worked as a postdoctoral research associate at Idaho National Laboratory (INL) in the structural materials post irradiation examination group. At INL I assisted in the transmission electron microscope (TEM) characterization of irradiation creep tested HT9 samples. 

Prior to working at INL, I received my PhD in materials engineering from Purdue University in December 2022. While at Purdue, I worked under another leader in the field of nuclear materials, Dr. Janelle Wharry. In my first two semesters as a graduate student, I served as a mentor to undergraduate nuclear engineering students. My research at Purdue University involved the investigation of solute influence on the irradiated microstructures and the irradiation hardening of ferritic binary model alloys, Fe-P, Fe-N, and Fe-Cr, through SEM and TEM imaging as well as nanoindentation and TEM in situ tensile experiments. It was concluded that atomic volume differences between the solute and solvent played a significant role in the formation and evolution of irradiation induced defects as well as the hardening and deformation mechanisms in these ferritic binary model alloys. My work at Purdue University led to three first author publications, three coauthor publications, and a first author manuscript that is in the final stages of revision. 

Expertise
Additive Manufacturing, Corrosion, Crystallography, Irradiation Damage, Mechanical Properties, Microstructural Characterization, Uranium Nitride (UN)
Publications:
"Comparison of ion irradiation effects in PM-HIP and forged alloy 625" Caleb Clement, Patrick Warren, Yangyang Zhao, Xiang Liu, David Gandy, Janelle Wharry, Sichuang Xue, Journal of Nuclear Materials Vol. 558 [unknown] Link
The nuclear industry has growing interest in replacing forgings with structural components fabricated by powder metallurgy with hot isostatic pressing (PM-HIP), owing to their chemical homogeneity, uniform grain structure, and near-net shape production. This study compares the ion irradiation response of PM-HIP and forged Alloy 625, over 50 and 100 dpa, 400 °C and 500 °C. Microstructure is characterized using down-zone bright-field scanning transmission electron microscopy (DZBFSTEM), and hardening is characterized using nanoindentation. PM-HIP Alloy 625 has a lower initial dislocation line density, resulting in a more rapid onset of dislocation loop growth and unfaulting than the forged material. But the total defect population (i.e. loop line length plus dislocation density) is insensitive to fabrication method. This finding shows promise for the eventual qualification of PM-HIP alloys for nuclear applications.
"Ion Implantation-Induced Plastic Phenomena in Metallic Alloys" Patrick Warren, Janelle Wharry, Caleb Clement, Yang Yang, Yongwen Sun, Jim Ciston, Colin Ophus, Journal of Materials Vol. [unknown] Link
Ion implantation is widely used for doping semiconductors or electroceramic materials and probing material behaviors in extreme radiation environments. However, implanted ions can induce compressive stresses into the host material, which can induce plasticity and mesoscopic deformation. However, these phenomena have almost exclusively been observed in brittle ionic and/or covalently bonded materials. Here, we present transmission electron micro- scopy observations of unusual implantation-induced plasticity in two metallic alloys. First, Fe2+ ions induce dislocation plasticity below the implanted layer in a model Fe-P alloy. Next, He+ ions form pressurized cavities which activate the fcc-to-hcp strain-induced martensitic transformation in Alloy 625. In both cases, the plasticity can be explained by a combination of implanted ions being incorporated into the lattice and the creation of irradiation defects. These findings have significant implications for mechanical testing of ion-implanted layers, while also opening pathways distributions in metallic alloys.
"Method for Fabricating Depth-Specific TEM in situ Tensile Bars" Patrick Warren, Yaqiao Wu, Janelle Wharry, George Warren, Megha Dubey, Jatu Burns, Journal of Materials Vol. 72 [unknown] 2057 - 2064 Link
The growing use of ion irradiation to assess degradation of nuclear materials has created a need to develop novel methods to probe the mechanical response of shallow ion-irradiated layers. Transmission electron microscopy (TEM) in situ mechanical testing can isolate the ion-irradiated layer from its unirradiated substrate. However, there is a lack of established procedures for preparing TEM in situ mechanical testing specimens from bulk materials requiring depth-specific examination, e.g., target dose on the ion irradiation damage profile. This study demonstrates a new method for extracting depth-specific TEM in situ tensile bars from a bulk specimen of Fe-5 wt.%Mo. Measured yield stress, ultimate tensile stress, Young’s modulus, and elongation are consistent with those properties obtained from similarly sized Fe and Mo single-crystal nanowires. Results are discussed in the context of the specimen size effect.
"The Role of Cr, P, and N solutes on the irradiated microstructure of bcc Fe" Patrick Warren, Caleb Clement, Chao Yang, Amrita Sen, Wei-Ying Chen, Yaqiao Wu, Journal of Nuclear Materials Vol. 583 [unknown] Link
The objective of this study is to understand irradiation-induced and assisted defect evolution in binary body center cubic (bcc) Fe-based alloys. The broader class of bcc ferritic alloys are leading candidates for advanced nuclear fission and fusion applications, in part due to their exceptional void swelling resistance. However, their irradiated microstructure evolution is sensitive to solute species present, since these solutes can act as traps for irradiation-induced defects due to the surrounding tensile or compressive stress fields. Here, three alloys (Fe- 9.5%Cr, Fe-4.5%P, and Fe-2.3%N) are selected for study because they systematically exhibit varying solute sizes and solute positions (i.e., substitutional or interstitial). Ex situ and in situ ion irradiations reveal that Fe-P has a considerably finer and denser population of irradiation-induced defects than Fe-Cr and Fe-N at the same irra- diation conditions, which is attributed to strong defect trapping at undersized substitutional P, consequently hindering the development of extended defects. Meanwhile, oversized substitutional solutes (e.g., Cr) and interstitial solutes (e.g., N) may also suppress dislocation loop development due to weak solute-defect trapping.
Presentations:
"A New Method for TEM in situ Tensile Testing of Ion Irradiated Alloys" Patrick Warren, George Warren, Nuela Enebechi, Jatu Burns, Megha Dubey, Janelle Wharry, MiNES Conference October 6-10, (2019)
"A standards perspective on nano mechanical testing to accelerate nuclear materials development and qualification" Janelle Wharry, Priyam Patki, George Warren, Patrick Warren, JB Hall, TMS 2021 March 15-18, (2021)
"High Temperature Steam Oxidation of Additive Manufactured 316L Stainless Steel" Patrick Warren, Scott Schier, Allyssa Batemen, Michelle Voges, Cyana Zaragosa, Elizabeth Sooby, TMS 2024 March 3-7, (2024)
"Mechanical Martensites in Nuclear Steels" Janelle Wharry, Patrick Warren, Haozheng Qu, TMS 2023 March 19-23, (2023)
"Role of Phosphorus in Irradiated Microstructure Evolution of a Binary Fe-P Model Alloy by TEM in situ Irradiation" Patrick Warren, Wei-Ying Chen, Amrita Sen, Ling Wang, Janelle Wharry, TMS Conference February 27-3, (2022)
"The Influence of Nanoindentation Orientation on Deformation Mechanisms in Irradiated Fe-P and Fe-N" Patrick Warren, Janelle Wharry, TMS 2023 March 19-23, (2023)
"The Role of Alloying Species on Radiation Tolerance of BCC Fe Binary Alloys" Patrick Warren, MiNES Conference November 8-11, (2021)

About Us

The Nuclear Science User Facilities (NSUF) is the U.S. Department of Energy Office of Nuclear Energy's only designated nuclear energy user facility. Through peer-reviewed proposal processes, the NSUF provides researchers access to neutron, ion, and gamma irradiations, post-irradiation examination and beamline capabilities at Idaho National Laboratory and a diverse mix of university, national laboratory and industry partner institutions.

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