FY20 NSUF 21 Core and Structural Materials Project Award Number CFA2019122 Project Type PIE only NSUF Facility Pacific Northwest National Laboratory PI KL Murty North Carolina State University ID: 934818
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Slide1
Effect of neutron irradiation on microstructure and mechanical properties of nanocrystalline nickel
FY20 NSUF 2.1 (Core and Structural Materials)Project Award Number: CFA-20-19122Project Type: PIE onlyNSUF Facility: Pacific Northwest National Laboratory
PI: KL Murty, North Carolina State UniversityCo-PI: Ramprashad Prabhakaran, Pacific Northwest National Laboratory
2020 NSUF Annual Review Virtual MeetingNov 9-10, 2020
Slide2Outline
Introduction - Structural materials for advanced reactors - Nanocrystalline materials - Irradiation behavior of nanocrystalline materials (nickel vs. copper)
- Need to study nanocrystalline nickel vs copperNewly funded FY20 NSUF 2.1 PIE project # 20-19122 (Oct 2020 - Sep 2022) - Objectives - Materials: Conventional grained and nanocrystalline nickel - Relevance and Outcome
- NSUF Project Readiness - Previous NCSU-led NSUF Irradiation Experiment - Logical Path to Accomplishing Scope - NSUF Facility: PNNL - PIE Matrix - Roles and Responsibilities - Project Schedule & Deliverables - Summary2
Slide3Structural Materials for Advanced Reactors
3
Structural materials for the next generation nuclear reactor designs are expected to serve in more severe operating conditions (such as higher temperatures and irradiation exposures) than the current light water reactor (LWR) designs.
During irradiation, point and line defects are produced as a result of displacement cascades. At the macroscopic scale, the well-known deterioration of mechanical, thermal and physical properties of materials in radiation environments is attributed to the accumulation of radiation induced defects that lead to the formation of microscopic scale defect structures such as dislocations and voids. Hence, the ability of a material to eliminate irradiation-induced point defects determines its radiation tolerance. Thus, identifying or designing materials with a tailored response that can sustain high amounts of radiation damage while maintaining their mechanical properties is a grand challenge in materials research.
Slide4Nanocrystalline materials
One method to suppress accumulation of radiation induced defects is by annihilating them at interfaces such as grain boundaries (i.e., grain boundaries being sinks).
It has been shown that a large amount of grain boundary area will help to prevent accumulation of defects that can adversely affect mechanical properties.Nanocrystalline (NC) materials with a grain size ranging from 20-100 nm have shown to possess favorable properties in comparison to their conventional grain sized (CG) counterparts.
4In general, NC materials exhibit superior mechanical properties characterized by high values of yield and fracture strengths, hardness and superplastic deformation behavior. The general consensus identifies the difficulty of dislocation activity inside smaller grains as the underlying reason behind the high strength of NC materials. 2D model of a nanostructured material [2
]
Variation of yield stress as a function of grain size in microcrystalline, ultrafine crystalline and NC materials [1]
[1] K. Kumar, et. al., Acta Mater. 51 (2003) pp. 5743-5774.
[2] H.
Gleiter
, Progress in Mater. Sci. (1989) 33, 223
.
Slide5Irradiation behavior of nanocrystalline materials
Several studies have confirmed the enhanced radiation resistance of NC metals and alloys over a range of irradiation conditions.
In contrast, other studies have shown evidence of thermal and structural instability of NC materials under irradiation.Nita et al. [1] studied SPD (severe plastic deformation) nanocrystalline Ni and Cu-0.5Al
2O3 after proton irradiation (0.56 dpa and 0.91 dpa, respectively) at RT and observed refinement (115 nm to 38 nm) of grains in Ni while growth (178 to 493 nm) of grains in Cu-0.5Al2O3. Nita et al. [1] observed no change in the grain size for SPD Ni under ion irradiation up to 5 dpa. 5
The microstructure of nanocrystalline samples [1]: SPD Cu-Al
2
O
3
(A) unirradiated and (B) proton irradiated to 0.91 dpa; SPD Ni (C) unirradiated (D) proton irradiated to 0.56 dpa
A
B
C
D
[1] N. Nita, et. al, Philos. Mag. 85 (2005) 723.
Slide6Need to perform irradiation performance study of NC model metals
There is a disagreement in the literature regarding the radiation resistance of NC metals and alloys.
Even though NC materials present an unprecedented potential, scientific knowledge related to the effect of neutron irradiation on the mechanical properties and microstructure is still scarce. Nanocrystalline copper and nickel are typically chosen because they are commonly used as model FCC metals in studies of radiation effects.
Nickel is an FCC metal with a high stacking-fault energy (~125 mJ/m2) compared to copper (~45 mJ/m2).The stacking fault energy plays a significant role in the formation of SFTs (stacking fault tetrahedra) in metals and alloys. The stacking fault energy (SFE) is one of the most important properties of FCC crystals that affect mechanical behavior, defect structure and dislocation behavior.6D
Slide7Irradiation behavior of
conventional-grained Cu and Ni
Vacancy clusters in FCC metals can be either a SFTs, Frank loops, voids or perfect loops depending on the SFE and other factors. SFTs are frequently observed in FCC metals and alloys with low SFE, such as Ag, Au, Cu and stainless steels.
The lower proportion of SFTs [1] formed in Ni relative to those formed in Cu might be due to the higher stacking fault energy for Ni. 7A B
C
D
(Left):
TEM weak beam images showing SFTs (bright contrast characterized by a triangular shape) in conventional-grained Cu and Ni irradiated (
590 MeV protons)
at room temperature at a dose of 0.046 dpa and 0.0083 dpa, respectively;
(Right)
Size distributions of irradiation-induced defects in Cu and Ni for an irradiation dose around 10E-2 dpa. Black, SFTs; white, loops; grey, unidentified defects (black dots); Cu presents 90% of SFTs while Ni present values of 40-50% [
1
]
[1] R.
Schäublin
, et al., Phil. Mag. (2005) 85:4-7, 769
Slide8Project Objectives
To characterize the effect of neutron irradiation on microstructure and mechanical properties of nanocrystalline nickel and compare with conventional grain sized Ni. As a part of a NCSU NSUF Irradiation Experiment project, conventional and nanograined Cu, ECAP steel and Ni were irradiated in ATR (1 and 2 dpa).
The selection of these materials was based on the motivation to investigate the effect of crystal structure (FCC vs BCC) as well as stacking fault energy (Cu vs Ni). Among these 3 materials, work was completed on Cu [1]
and ECAP steel [2] which clearly revealed the influence of ultra-fine grain size on radiation hardening as well as microstructures while irradiated conventional and nanograined Ni samples were not tested in detail. This study will investigate the changes in mechanical properties and microstructures of irradiated Ni with particular attention to examine whether nanograined Ni is relatively more radiation resistant. Efforts will be made to understand the microstructural evolution and the concomitant changes in mechanical properties of nanocrystalline Ni in order to be considered for nuclear applications.8[1] W. Mohamed, B. Miller, D. Porter and K.L. Murty, Materials (2016) 9, 144, pp. 1-23. [2] A. Alsabbagh, A. Sarkar, B. Miller, J. Burns, L. Squires, D. Porter, J. Cole and K.L Murty, Mat. Sci. Eng., A615 (2014)128-138 (2014 ANS Mark Mills Award).
Slide9Key questions to answer
What is the effect of neutron irradiation on the mechanical properties of nanocrystalline nickel (radiation hardening and ductility)?What is the effect of neutron irradiation on the grain size of nanocrystalline nickel?
What is the effect of higher stacking fault energy on the irradiation behavior? Will the behavior be different from Cu?What is the number density of stacking fault tetrahedra (SFT) and mean size?
Does nanocrystalline nickel show significant reduction of defect clusters, when compared with conventional Ni?9
Materials
Conventional grained nickel (unirradiated and neutron irradiated)
Nanocrystalline nickel (unirradiated and neutron irradiated)
Slide10Nanocrystalline Nickel (unirradiated)
10
The nanocrystalline nickel investigated in this work was acquired from a vendor -synthesized via the electrodeposition technique.
The conventional grained (micrometer size grains) nickel samples were legacy materials from NCSU. In order to evaluate the microstructure and mechanical properties, samples of different geometries were prepared for hardness, tensile and TEM.
Slide11Conventional grained vs nanocrystalline nickel (unirradiated)
11
Vickers microhardness and tensile tests were performed to evaluate the mechanical properties of conventional grained and nanocrystalline Ni.
Tensile tests were performed at room temperature at a strain rate of 10-3 s-1.NC nickel has higher yield and ultimate tensile strength values compared to conventional grained nickel as expected from grain refinement.
Slide12Conventional grained vs nanocrystalline nickel (unirradiated)
12
The average grain size of conventional grained and nanocrystalline nickel were 12 μm (optical) and 25 nm (TEM and XRD), respectively.
The broad XRD peaks indicate a smaller grain size and the enhanced intensity of the (200) peak signifies the presence of a preferred orientation in the electrodeposited nanocrystalline Ni foil. Conventional grained nickelNanocrystalline nickel
Slide13NSUF Irradiation Experiment (08-96)
13
Advanced Test Reactor
MaterialSample Type
ATR Insertion
Irradiation Temperature
Target Dose
Nanocrystalline Ni
Mini-Tensile
Hardness/TEM
2009
75-100°C
1 and 2 dpa
Conventional Ni
Mini-Tensile
Hardness/TEM
2009
75-100°C
1 and 2 dpa
Slide14Logical Path to Accomplishing Scope
14
The six major tasks of the NCSU-led NSUF project are:
Task 1: Transfer neutron irradiated nano and conventional grained Ni samples from NSUF library (INL) to PNNL (NSUF facility) Task 2: Tensile testing of neutron irradiated nano and conventional grained Ni samples at PNNLTask 3: Sample preparation of control and neutron irradiated nano and conventional grained Ni samples at PNNL for indentation and microstructural studiesTask 4: Vickers microhardness testing of control and neutron irradiated nano and conventional grained Ni samples at PNNL Task 5: SEM/EBSD and TEM studies of control and neutron irradiated nano and conventional grained Ni samples at PNNL Task 6: Understand the effect of neutron irradiation on the microstructure and mechanical properties of nanocrystalline and conventional grained nickel.
Slide15NSUF Project’s PIE Test Matrix
15
No irradiation is required.
NSUF PIE facility: Pacific Northwest National LaboratoryTensile testing will be performed on sub-size tensile specimens (3 specimens per condition). Microhardness, SEM/EBSD and TEM studies will be performed on samples (one per condition). Number of specimens: 18 (neutron irradiated: 16 and control: 2)
Slide16NSUF PIE Facility: PNNL
16
The neutron irradiated nano and conventional grained Ni samples are currently at INL (NSUF library).
These samples would be shipped from INL to PNNL. Sample preparation, mechanical and microstructural characterizations will be performed at PNNL. Pacific Northwest National Laboratory: - PNNL has the capability to perform post irradiation examination of irradiated structural materials. - Mechanical and microstructural characterizations will be performed using the following equipment: Sample preparation equipment F-M microhardness tester Instron servo hydraulic mechanical test frame FEI Quanta 3D FEG dual beam FIB SEM Aberration corrected JEOL ARM200 atomic resolution TEM High resolution JEOL 7600F field emission gun SEM/EBSD
Slide17Roles and Responsibilities
17Staff/Organization
Role
PI: KL Murty, NCSU • Lead the project and manage various experiments and data analysis. • Provide unirradiated materials. • Work with the Co-PI and study the effect neutron irradiation of nanocrystalline and conventional grained nickel.
• Coordinate with the Co-PI and develop microstructure-property-dose correlations.
Co-PI: Ramprashad Prabhakaran, PNNL
• Request, coordinate and obtain neutron irradiated materials from NSUF library.
•
Perform mechanical characterization - tensile and microhardness testing.
• W
ork with SEM/TEM instrument scientists to obtain microstructural information.
Dan Edwards,
PNNL NSUF Instrument Scientist
• P
erform microstructural characterization (SEM/EBSD and TEM).
Collin Knight, NSUF
• Work with the INL staff to identify neutron irradiated samples at the INL
hotcell
and ship samples to PNNL.
Our team has the necessary expertise (irradiated sample preparation, tensile testing, microhardness testing, SEM/EBSD, TEM, radiation effects, developing structure-property-dose correlations) to successfully complete the project.
Slide18Project Schedule
18
Slide19Milestones and Deliverables
19Identify and transfer neutron irradiated samples from INL to PNNL: Dec 31, 2020Complete sample preparation for indentation and microstructural studies at PNNL: Sep 30, 2021Complete tensile and microhardness testing at PNNL: Sep 30, 2021Submit the first-year annual report: Sep 30, 2021
Complete SEM/EBSD and TEM studies of neutron irradiated samples at PNNL: Mar 31, 2022
Understand the effect of neutron irradiation on the microstructure and mechanical properties of nanocrystalline and conventional grained nickel: July 31, 2022Present the work at a major conference: Summer 2022Submit a final report and peer-review journal manuscript: Sep 30, 2022
Slide20Summary
20
This study will investigate the changes in mechanical properties and microstructures of irradiated Ni with particular attention to examine whether nanograined Ni is relatively more radiation resistant compared to conventional grained Ni.
The study will also yield the following information about nanocrystalline nickel: - The effect of grain size on radiation hardening (changes in microhardness and strength). - The effect of neutron irradiation on the grain size of nanocrystalline nickel. - The effect of higher stacking fault energy on the irradiation behavior. - The number density of stacking fault tetrahedra (SFT) and mean size. - Defect clusters in Nano vs conventional Ni. - Annual reports to DOE; conference presentations and peer-review journal publicationsEfforts will be made to compare the results with the literature data and our previous work on conventional grained and nanocrystalline Cu and ECAP steel; establish structure-property-dose correlations.
Slide21Acknowledgements
21
The neutron irradiation and PIE are supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07-051D14517 as part of Nuclear Science User Facilities (NSUF) experiments:
- NSUF Irradiation Experiment Project Title: “Influence of fast neutron irradiation on the mechanical properties and microstructure of nanostructured metals/alloys” (Project # 08-96) - CINR NSUF Project Title: “Effect of neutron irradiation on microstructure and mechanical properties of nanocrystalline nickel” (Project # CFA-20-19122)The researchers would like to thank Douglas Porter and Collin Knight (INL) for their assistance in performing irradiation and PIE studies, respectively.The End