Radiation Effects in Metals and Ceramics: Irradiation of Welds & Irradiation of High Entropy Alloys
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Djamel Kaoumi, North Carolina State University; Thak Sang Byun, Oak Ridge National Laboratory; Dane Morgan, University of Wisconsin-Madison; Maria Okuniewski, Purdue University; Mahmood Mamivand; Geoffrey Beausoleil, Idaho National Laboratory; Philip Edmondson, The University Of Manchester; Khalid Hattar, University of Tennessee Knoxville; Aurelie Gentils, Université Paris-Saclay; Joel Ribis, Cea

Wednesday 2:00 PM
February 26, 2020
Room: Theater A-7
Location: San Diego Convention Ctr

Session Chair: Khalid Hattar, Sandia National Laboratory; Dane Morgane, University of Wisconsin

2:00 PM  Invited
Irradiation Effects in Weld Repairs of Irradiated Stainless Steel: Janelle Wharry¹; Keyou Mao¹; Emmanuel Perez²; Yaqiao Wu³; Aaron French⁴; Paula Freyer⁵; Lin Shao⁴; Frank Garner⁴; ¹Purdue University; ²Idaho National Laboratory; ³Boise State University; ⁴Texas A&M University; ⁵Westinghouse Electric Company, LLC
    The objective of this talk is to understand how high-dose irradiation affects the microstructure of a weld repair of a previously irradiated steel. Weld repairs of irradiated reactor internal components may be necessary during life extensions of light water reactors. This work will focus on specimens of AISI 304 stainless steel, pre-irradiated in EBR-II to ~3-28 displacements per atom (dpa) at ~415°C. A single-pass laser weld was made on each specimen. Weld cross-sections were re-irradiated with Fe2+ ions to an additional 50 dpa. Compared to the as-welded microstructure, additional dislocation loops nucleate throughout the ion irradiated layer. At the ion damage peak, cavities are replaced by precipitates. The role of injected interstitials and interstitial diffusion will be discussed with respect to the cavity-to-precipitate transformation mechanism, having implications on neutron pre-conditioning studies. The talk will also discuss the consequences of these results on the viability of weld repairs of reactor internals.

2:30 PM
Microstructural Characterization of the Through-wall Thickness Pressure Vessel Weldment of the Zion NPP: Philip Edmondson¹; Thomas Rosseel¹; Mikhail Sokolov¹; ¹Oak Ridge National Laboratory
    Recently, material from the decommissioned Zion nuclear power plant Unit 1reactor pressure vessel (RPV) has become available for microstructural characterization. This unit operated from 1973-1998 and was exposed to service irradiation for approximately 13.7 effective full power years (EFPYs). Of particular interest is the circumferential beltline weld – a high Cu, high Ni Linde-80 composition that was exposed to a peak neutron fluence of ~0.75x1019 n.cm-2. In this presentation, atom probe tomography of several samples taken from different placements throughout the thickness of the RPV weld ranging from the inside to outside walls to investigate the role of neutron energy attenuation on the formation of Cu-rich and Ni-Mn-Si precipitates. This characterization will focus on the variance in composition, size and number densities of the precipitates throughout the RPV wall and place these variances into the context of mechanical property changes especially the change in ductile to brittle transition temperatures (DBTT).

2:50 PM
Irradiation of 14YWT Solid State Capacitive Discharge Welds: Calvin Lear¹; Benjamin Eftink¹; Stu Maloy¹; Thomas Lienert²; ¹Los Alamos National Laboratory; ²T.J. Lienert Consulting, LLC
    Oxide dispersion strengthened (ODS) ferritic steels show promising high temperature strength, creep resistance, and radiation tolerance, but the effects of irradiation on dispersoid stability are not fully understood. This uncertainty is compounded by the effects of joining techniques (e.g., fusion welding) that may alter, agglomerate, or redistribute nanoscale oxide particles. To minimize these effects, a solid state capacitive discharge resistance welding technique was used to seal small diameter, thin walled cladding tubes of ODS alloy 14YWT to like caps. Material from the resulting joints was irradiated with 1 MeV H⁺ and 4 MeV Fe²⁺ at various dose-temperature conditions (1-50 dpa, 350-450 şC). Microstructural and chemical evolution (e.g., oxide particle stability, radiation-induced segregation) were characterized using electron microscopy (S/TEM, EDS, EELS), while the sensitivity of these effects to the welding parameters was considered.

3:10 PM  Invited
Reassessment of TRIM Simulations for Damage Production in Materials: William Weber¹; Yanwen Zhang²; ¹University of Tennessee; ²Oak Ridge National Laboratory
    The TRIM code is commonly applied to predict radiation damage dose, and there is controversy over the inconsistencies (factor of 2) in determining atomic displacement numbers using full-cascade and quick (modified Kinchin–Pease) TRIM modes. Full-cascade TRIM simulations are consistent with full-cascade simulations using other modern Monte Carlo codes with the same ZBL scattering cross sections and SRIM electronic stopping powers. Furthermore, the full-cascade TRIM simulations agree with numerical solutions for displacement functions determined from coupled integro-differential equations, which supports the accuracy of full-cascade TRIM simulations. The discrepancies between full-cascade and quick TRIM simulations are due in part to misunderstandings regarding the derivation of the modified Kinchin-Pease model and limitations of the energy partition model employed, which often provides inaccurate predictions (factor of 2) of the energy loss by recoils to electrons and is not valid for polyatomic materials. This work was supported by the U.S. DOE, BES, MSED.

3:40 PM Break

4:00 PM  Invited
High Irradiation Resistance of Nanocrystalline W-based High Entropy Alloy: Enrique Martinez Saez¹; Osman El-Atwani¹; Duc Nguyen-Manh²; Matthew Schneider¹; Nan Li¹; Meimei Li³; Arun Devaraj⁴; Kevin Baldwin¹; Damian Sobieraj⁵; Jan Wrobel⁵; Stuart Maloy¹; ¹Los Alamos National Laboratory; ²CCFE; ³Argonne National Laboratory; ⁴Pacific Northwest National Laboratory; ⁵Warsaw University of Technology
    A body-centered cubic W-based refractory high entropy alloy with outstanding radiation resistance has been developed. The alloy was grown as thin films showing a bimodal grain size distribution in the nanocrystalline and ultrafine regimes and a unique 4 nm lamella-like structure revealed by atom probe tomography (APT). Transmission electron microscopy (TEM) and X-ray diffraction show certain black spots appearing after thermal annealing at elevated temperatures. TEM and APT analysis correlated the black spots with second-phase particles rich in Cr and V. No sign of irradiation-created dislocation loops, even after 8 dpa, was observed. Furthermore, nanomechanical testing shows a large hardness of 14 GPa in the as-deposited samples, with near negligible irradiation hardening. Theoretical modeling combining ab initio and Monte Carlo techniques predicts the formation of Cr and V rich second phase particles and points at equal mobilities of point defects as the origin of the exceptional radiation tolerance.

4:30 PM
Suppressing Void Swelling in NiCoFeCr-based High Entropy Alloys via Selective Doping: Zhe Fan¹; Yang Tong¹; Shijun Zhao¹; Gihan Velisa¹; Fuxiang Zhang¹; Hongbin Bei¹; Yanwen Zhang¹; ¹Oak Ridge National Laboratory
    We report the effects of doping on irradiation-induced void swelling in NiCoFeCr-based high entropy alloys (HEAs). In (NiCoFeCr)1-xPdx, the addition of Pd up to 3% leads to smaller voids with higher density, and void nucleation is largely inhibited with Pd at 5%. High-density voids form near the free surface in (NiCoFeCr)99Pd1 but not in other alloys. The suppressed void swelling and suppressed dislocation growth are attributed to enhanced sluggish diffusion due to the large size factor and local lattice distortion revealed by X-ray diffraction and total scattering measurements. Density functional theory calculations show that doping Al can substantially increase the vacancy migration energy, and experimentally we show that void swelling is better suppressed in (NiCoFeCr)99Al1 than (NiCoFeCr)99Pd1 or (NiCoFeCr)99Cu1. This study provides insights to enhance swelling resistance in HEAs through selective doping. This work was supported by EDDE, an EFRC funded by the U.S. DOE, BES.

4:50 PM
Effects of Chemical Complexity and Radiation Parameters on Defect Evolution in Nickel-based Concentrated Solid Solution Alloys: Pengyuan Xiu¹; Li Jiang¹; Yanwen Zhang²; Lumin Wang¹; ¹Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor; ²Materials Science and Technology Division, Oak Ridge National Laboratory
    Nickel based single-phase concentrated solid solution alloys (SP-CSA), Ni-20Fe, Ni-50Fe and NiFe-20Cr, were irradiated with 3 MeV Ni2+ ions to peak doses of 3, 16, 86 and 250 dpa at 500℃ and 580℃. High density of dislocation loops formed in three alloys under all radiation conditions, while a significant amount of Frank loops was observed only after low doses (3 dpa and 16 dpa) at 500℃. The chemically more complex NiFe-20Cr contains a higher fraction of Frank loops indicating a lower stacking fault energy compared to that of the two binary alloys. While void swelling decreases with increasing chemical complexity from Ni-20Fe to NiFe-20Cr after 250 dpa at 500℃, the trend is reversed at 580℃. Nano-indentation tests are also conducted to reveal the correlation between microstructure evolution and irradiation hardening.

5:10 PM
Advanced Electron Microscopy Characterization of Ion Radiation Damage in Bulk Metallic Glass and High Entropy Alloys: Yang Yang¹; Qin Yu¹; Jun Ding¹; Ruopeng Zhang²; Colin Ophus¹; Mark Asta¹; Robert Ritchie¹; Andrew Minor¹; ¹Lawrence Berkeley National Laboratory; ²University of California, Berkeley
     Bulk metallic glass (BMG) and high entropy alloys (HEAs) are structural materials with intriguing mechanical properties. While they have been proposed as candidate materials under irradiation environments, there is still a lack of systematic understanding of their response to radiation damage. For example, due to the limited range of ion radiation, it is difficult to perform traditional bulk-scale mechanical testing.Here, we report advanced electron microscopy characterization of ion radiation damage in BMG and HEAs. The samples are irradiated by helium ion beam at different doses and ion energies. Quantitative in-situ TEM mechanical testing has been performed to unravel the modification of mechanical performance by helium ion radiation. Energy-filtered TEM (EF-TEM), Energy-dispersive X-ray (EDX) Spectroscopy and 4D-STEM are used to characterize the structural/chemical heterogeneity and the elastic strain before and after irradiation.

5:30 PM
Irradiation Damage Behavior in Novel High-entropy Carbide Ceramics: Fei Wang¹; Xueliang Yan¹; Tianyao Wang²; Lin Shao²; Yaqiao Wu³; Michael Nastasi¹; Bai Cui¹; ¹University of Nebraska-Lincoln; ²Texas A&M University; ³Center for Advanced Energy Studies
    Novel high-entropy carbide ceramics, e.g., (Zr0.25Ta0.25Nb0.25Ti0.25)C, have been developed as a candidate material for high-temperature and irradiation extreme environments. X-ray diffraction suggests that it has a single-phase rock salt structure, in which the four metal elements likely share the cation position while the C element occupies the anion sublattice. The high-entropy carbide ceramic is thermally stable after annealing to up to 1700 şC in Ar atmosphere without phase transformation or decomposition. Irradiation damage has been evaluated by conducting heavy ion irradiation experiments. Microstructure changes, including the phase transformation, radiation-induced segregation, irradiation defect clusters, and helium bubbles, have been characterized using transmission electron microscopy as a function of temperature and irradiation dose. (Zr0.25Ta0.25Nb0.25Ti0.25)C shows exceptional structural stability in ion irradiation (at least 20 dpa) environments at 25, 300 and 500 şC.