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Title: Technique development for modulus, microcracking, hermeticity, and coating evaluation capability characterization of SiC/SiC tubes

Abstract

Driven by the need to enlarge the safety margins of nuclear fission reactors in accident scenarios, research and development of accident-tolerant fuel has become an important topic in the nuclear engineering and materials community. A continuous-fiber SiC/SiC composite is under consideration as a replacement for traditional zirconium alloy cladding owing to its high-temperature stability, chemical inertness, and exceptional irradiation resistance. An important task is the development of characterization techniques for SiC/SiC cladding, since traditional work using rectangular bars or disks cannot directly provide useful information on the properties of SiC/SiC composite tubes for fuel cladding applications. At Oak Ridge National Laboratory, experimental capabilities are under development to characterize the modulus, microcracking, and hermeticity of as-fabricated, as-irradiated SiC/SiC composite tubes. Resonant ultrasound spectroscopy has been validated as a promising technique to evaluate the elastic properties of SiC/SiC composite tubes and microcracking within the material. A similar technique, impulse excitation, is efficient in determining the basic mechanical properties of SiC bars prepared by chemical vapor deposition; it also has potential for application in studying the mechanical properties of SiC/SiC composite tubes. Complete evaluation of the quality of the developed coatings, a major mitigation strategy against gas permeation and hydrothermal corrosion, requires themore » deployment of various experimental techniques, such as scratch indentation, tensile pulling-off tests, and scanning electron microscopy. In addition, a comprehensive permeation test station is being established to assess the hermeticity of SiC/SiC composite tubes and to determine the H/D/He permeability of SiC/SiC composites. This report summarizes the current status of the development of these experimental capabilities.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE); USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1327675
Report Number(s):
ORNL/TM-2016/372
TRN: US1700312
DOE Contract Number:
AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; SILICON CARBIDES; ACCIDENT-TOLERANT NUCLEAR FUELS; ELASTICITY; FUEL CANS; TUBES; SCANNING ELECTRON MICROSCOPY; EVALUATION; IRRADIATION; PERMEABILITY; COATINGS; FIBERS; PULSES; SPECTROSCOPY; ULTRASONIC WAVES; MECHANICAL PROPERTIES; COMPOSITE MATERIALS; HYDROGEN; DEUTERIUM; HELIUM

Citation Formats

Hu, Xunxiang, Ang, Caen K., Singh, Gyanender P., and Katoh, Yutai. Technique development for modulus, microcracking, hermeticity, and coating evaluation capability characterization of SiC/SiC tubes. United States: N. p., 2016. Web. doi:10.2172/1327675.
Hu, Xunxiang, Ang, Caen K., Singh, Gyanender P., & Katoh, Yutai. Technique development for modulus, microcracking, hermeticity, and coating evaluation capability characterization of SiC/SiC tubes. United States. doi:10.2172/1327675.
Hu, Xunxiang, Ang, Caen K., Singh, Gyanender P., and Katoh, Yutai. 2016. "Technique development for modulus, microcracking, hermeticity, and coating evaluation capability characterization of SiC/SiC tubes". United States. doi:10.2172/1327675. https://www.osti.gov/servlets/purl/1327675.
@article{osti_1327675,
title = {Technique development for modulus, microcracking, hermeticity, and coating evaluation capability characterization of SiC/SiC tubes},
author = {Hu, Xunxiang and Ang, Caen K. and Singh, Gyanender P. and Katoh, Yutai},
abstractNote = {Driven by the need to enlarge the safety margins of nuclear fission reactors in accident scenarios, research and development of accident-tolerant fuel has become an important topic in the nuclear engineering and materials community. A continuous-fiber SiC/SiC composite is under consideration as a replacement for traditional zirconium alloy cladding owing to its high-temperature stability, chemical inertness, and exceptional irradiation resistance. An important task is the development of characterization techniques for SiC/SiC cladding, since traditional work using rectangular bars or disks cannot directly provide useful information on the properties of SiC/SiC composite tubes for fuel cladding applications. At Oak Ridge National Laboratory, experimental capabilities are under development to characterize the modulus, microcracking, and hermeticity of as-fabricated, as-irradiated SiC/SiC composite tubes. Resonant ultrasound spectroscopy has been validated as a promising technique to evaluate the elastic properties of SiC/SiC composite tubes and microcracking within the material. A similar technique, impulse excitation, is efficient in determining the basic mechanical properties of SiC bars prepared by chemical vapor deposition; it also has potential for application in studying the mechanical properties of SiC/SiC composite tubes. Complete evaluation of the quality of the developed coatings, a major mitigation strategy against gas permeation and hydrothermal corrosion, requires the deployment of various experimental techniques, such as scratch indentation, tensile pulling-off tests, and scanning electron microscopy. In addition, a comprehensive permeation test station is being established to assess the hermeticity of SiC/SiC composite tubes and to determine the H/D/He permeability of SiC/SiC composites. This report summarizes the current status of the development of these experimental capabilities.},
doi = {10.2172/1327675},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 8
}

Technical Report:

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  • Elastic modulus of an yttria partially stabilized zirconia (YSZ) thermal barrier coating (TBC) was evaluated with a Knoop indentation technique. The measured elastic modulus values for the coating ranged from 68.4 {+-} 22.6 GPa at an indentation load of 50 g to 35.7 {+-} 9.8 at an indentation load of 300 g. At higher loads, the elastic modulus values did not change significantly. This steady-state value of 35.7 GPa for ZrO{sub 2} TBC agreed well with literature values obtained by the Hertzian indentation method. Furthermore, the measured elastic modulus for the TBC is lower than that reported for bulk ZrO{submore » 2} ({approx} 190 GPa). This difference is believed to be due to the presence of a significant amount of porosity and microcracks in the TBCs. Hardness was also measured.« less
  • The fracture and flexural behavior of monolithic SiC and SiC-whisker reinforced SiC composites (SiCw/SiC) have been investigated at room and elevated temperatures. Flexure and fracture tests were conducted in a four-point beam configuration at 230C, 800 deg C and 1200 deg C to study the effects of whisker reinforcements especially in respect of mechanical and thermal stability at high energy environments. Flexural strengths and fracture toughness data within the test temperature range are presented in graphical as well as in weibull form, and experimental observations are analyzed and discussed. Attempts have been made to predict the flexural properties of themore » composite by coupling the principle of minimization of potential energy and the rule of mixture. The deflection curve of a composite four-point beam coupon is found from an assumed Fourier series solution satisfying the geometric boundary conditions and using the rule of mixture. Strain compatibility conditions are applied to determine the axial displacement field and hence the flexural strain. Stresses on the matrix and fiber are then estimated under the assumption of isostrain conditions. Composites, Ceramics, Silicon/Carbide/Silicon Carbide, High Temperature Flexure, Fracture.« less
  • Experimental matrices were conducted to determine a suitable firing schedule for fritless tin printing ink. Considerable difficulties were encountered with oxidation. Best results were obtained with a firing cycle consisting of 400/sup 0/C for 20 minutes in nitrogen followed by 5 minutes in air at 500/sup 0/C. Elimination of oxidizing conditions impaired the adhesion of both tin and copper fritless printing inks, although adhesion of fritless copper inks was obtained when fired in nitrogen with slight oxidation.
  • Further evaluations were made on the paste formulations. All of these tests replicated the previous results of high series resistance and loss of adhesion during plating. An additional high temperature nickel formulation was tested, but could not be plated. The nickel thick films after firing were tested for stability in the cleaning and plating solutions used in the Vanguard-Pacific brush plating process. The films were found to be very sensitive to the cleaning and alkaline copper solutions. Less sensitivity was displayed to the neutral copper solution, but even with this solution reduced adhesion was observed after 30 seconds of exposure.more » Microscopic and SEM observations showed segregation of frit at the silicon nitride-thick film interface with loose frit residues after lifting off plated grid lines. Doping of the experimental pastes with silver did not affect any change in performance of the pastes. However, doping of Thick Film Systems No. 5517 nickel with 30% of EMCA No. 7069 silver paste reduced series resistance without affecting loss of adhesion during plating.« less
  • Solar cells were fabricated using the Photowatt International, Inc., production process. One hundred 3'' cells with 800 A of silicon nitride over N+/P junction, and evaporated aluminum metal (on the back side) were delivered for nickel printing. Initially two nickel pastes were defined, each lot having a different type of borosilicate frit. After application of nickel paste these solar cells were sent for brush copper plating. Electrical and mechanical data indicated a need to increase borosilicate frit and silver fluoride (AgF). Three more pastes were formulated by ESL. Electrical, mechanical and visual data were recorded for three groups of nickelmore » pastes using various fire-in temperatures and time cycles. The visual cell evaluation after brush copper plating revealed copper residue over the surface of most cells. There was an enlarging of grid lines during the copper plating. There was also an area along the edge of copper plating (approximately 1/4'') in which the nickel was removed. Several initial cells were found to have low adhesion levels when subjected to qualitative (tape test and mechanical scratching) testing. The nickel paste on some cells disclosed minor blistering after firing, but had good adhesion to tweezer-push and tape tests. Electrical and mechanical data indicate all nickel paste groups, at all temperatures and times, have ohmic contact. Quarter cells of each nickel group are being evaluated using techniques such as SEMS, SIMS and Beta-scan. (LEW)« less