Microstructural Processes in Irradiated Materials: Fusion Materials
Sponsored by: TMS Structural Materials Division, TMS/ASM: Nuclear Materials Committee
Program Organizers: Thak Sang Byun, Pacific Northwest National Laboratory; Dane Morgan, University of Wisconsin-Madison; Yasuyoshi Nagai, Tohoku University; Zhijie Jiao, University of Michigan-Ann Arbor; Christine Guéneau, CEA-Saclay

Wednesday 2:00 PM
March 6, 2013
Room: 203A
Location: Henry B. Gonzalez Convention Center

Session Chair: Roger Stoller, Oak Ridge National Laboratory; Steven Zinkle, Oak Ridge National Laboratory

2:00 PM  Invited
Radiation Effects on a High Strength, High Conductivity Copper Alloy: Steven Zinkle1; 1Oak Ridge National Laboratory
    High-strength, high-conductivity copper alloys are being considered for first wall heat sink and divertor structural applications in fusion energy systems. Two heats of CuNiBe alloys with room temperature yield strengths of 630-725 MPa and electrical conductivities of 65-72% IACS were irradiated with fission neutrons at 100 - 240˚C. The irradiation produced a slight increase in strength and a significant decrease in ductility. The measured tensile elongation increased with increasing irradiation temperature, with a uniform elongation of ~3.3% observed at 240˚C. The data indicate that CuNiBe alloys may be suitable for certain fusion energy structural applications at temperatures <250˚C. However, ductile intergranular fracture and low uniform elongation occurs for test temperatures above 350˚C. The change in deformation behavior from intragranular to intergranular was analyzed using an Ashby-type deformation map. The possible implications for other precipitation hardened alloys such as superalloys are discussed.

2:30 PM  
Effect of Grain Boundary Characters on Sink Efficiency: Weizhong Han1; Michael Demkowicz2; Engang Fu1; Yongqiang Wang1; Amit Misra1; 1Los Alamos National Lab; 2MIT
    The dependence of the width of void-denuded zones (VDZs) on grain boundary (GB) characters was investigated in Cu irradiated with Helium ions at elevated temperature. Dislocation loops and voids formed near GBs during irradiation were characterized by transmission electron microscopy, and GB misorientations and plane normals were determined by electron backscatter diffraction. The VDZ widths at Σ3 <110> tilt GBs ranged from 0 to 24 nm and increased with the GB plane inclination angle. For non-Σ3 GBs, VDZ widths ranged from 40 to 70 nm and generally increased with misorientation angle. Nevertheless, there is considerable scatter about this general trend, indicating that the remaining crystallographic parameters also play a role in determining the sink efficiencies of these GBs. Voids were also observed within GB planes and their density and radius also appeared to depend on GB character. We conclude that GB sink efficiencies depend on the complete GB character, including both misorientation and GB plane orientation. This research is supported by US DOE, Office of Science, Office of Basic Energy Sciences.

2:50 PM  
Correlation between Irradiation Hardening and Microstructural Evolution in High Purity Reference V-4Cr-4Ti Alloy for Fusion Reactor: Takuya Nagasaka1; Takeo Muroga1; Hideo Watanabe2; Takeshi Miyazawa3; Masanori Yamazaki4; 1National Institute for Fusion Science; 2Research Institute for Applied Mechanics, Kyushu University; 3The Graduate University for Advanced Studies; 4International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University
    Vanadium alloys are recognized as a candidate structural material for fusion reactor blanket. The present study seeks the correlation between the neutron irradiation hardening and the microstructural evolution for vanadium alloys to understand the mechanisms of irradiation hardening and effects of interstitial impurities on it. Base metal and weld metal of NIFS-HEAT-2, a reference high-purity V-4Cr-4Ti alloy, were irradiated in JMTR, JOYO, HFIR and BR-II reactor up to 1.3 x 10^26 n m^-2 (E > 0.1 MeV, 5.3 dpa). Irradiation temperature varied from 333 to 723 K. Observed irradiation hardening of the base metal ranged from 16 to 92 VHN compared with the hardness before irradiation, 144 VHN. Some irradiations exhibited additional hardening likely due to interstitial impurity contamination. Welding also enhanced the irradiation hardening. The irradiation hardening was recovered by post-irradiation annealing at around 873 K. Hardening factors in microstructures were identified as dislocation loops, tangle and irradiation-induced precipitates.

3:10 PM  
A Replica Technique for Extracting Precipitates from Neutron-Irradiated or Thermal-Aged Vanadium Alloys for TEM Analysis: Ken-ichi Fukumoto1; Masahiro Iwasaki2; 1RINE/Univ. of Fukui; 2Univ. of Fukui
    A carbon replica technique has been developed to extract precipitates from vanadium alloys. Using this technique, precipitation phases can be extracted from neutron-irradiated or thermal-aged V-4Cr-4Ti alloys. Precipitate identification using EDS X-ray analysis and electron diffraction was facilitated. Only NaCl type of Ti(OCN) precipitate was formed in the thermal-aged V-4Cr-4Ti alloys in the temperature regime from 800 to 1000°C and cation sub-lattice was only occupied by Ti atoms only. However the thin plate of precipitates with NaCl type of crystallographic structure could be seen in the V-4Cr-4Ti alloys irradiated in the temperature from 400 to 600°C at the JOYO fast reactor in Japan. The precipitate contained chromium and vanadium atoms on the cation sub-lattice as well as titanium atoms. It is considered that the phase of MX type (M = Ti, V, Cr and X=O, N, C) is metastable phase under neutron irradiation.