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The postirradiation tensile properties and microstructure of several vanadium alloys

Description: Tensile specimens of V-15Cr-5Ti, Vanstar-7, V-3Ti-1si, and V-20Ti were irradiated at 420)degrees)C in FFTF-MOTA to a damage level of 82 dpa. Helium was preimplanted to levels up to 480 appm in selected specimens using a modified tritium trick. Irradiation hardening was the dominant effect influencing the postirradiation tensile properties, and it markedly increased the yield strength and reduced the total elogation. The V-15Cr-5Ti alloy was very sensitive to helium embrittlement, but Vanstar-7 and V-3Ti-1Si were only slightly affected. Without helium, negligible swelling (<1%) were measured in V-3Ti-1Si and V-20Ti. Preimplanted helium increased swelling in V-3Ti-1Si by increasing cavity nucleation. 11 refs., 11 figs., 3 tabs.
Date: January 1, 1988
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

Microstructure and bend ductility of a (Fe,Ni)/sub 3/V ordered alloy irradiated in HFIR

Description: Disks of a (Fe,Ni)/sub 3/V long-range-ordered alloy were irradiated in the High Flux Isotope Reactor to 10, 21, and 42 dpa and helium levels of 1000, 2700, and 6000 at. ppM, respectively. The irradiation temperatures were 300, 400, 500, and 600/sup 0/C. The alloy remained ordered under all conditions. Swelling of the alloy was low with a peak of 1.3% occurring at 500/sup 0/C. Severe embrittlement and intergranular fracture occurred after 10 dpa at 600/sup 0/C and extended to lower temperatures as the damage level increased. Helium bubbles and a thin, continuous film of VC observed in the grain boundaries may be the cause of the embrittlement.
Date: January 1, 1983
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

The effect of neutron irradiation on the tensile properties and microstructure of several vanadium alloys. [Viewgraphs]

Description: This paper contains viewgraphs describing the effects of neutron irradiation on the tensile properties and microstructure of vanadium alloys in first wall fusion reactors. A tritium trick experiment was used to study the helium embrittlement and the stresses and strains on these materials in a controlled environment. (LSP)
Date: January 1, 1987
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

Effect of neutron irradiation on vanadium alloys

Description: Neutron-irradiated vanadium alloys were evaluated for their susceptibility to irradiation hardening, helium embrittlement, swelling, and residual radioactivity, and the results were compared with those for the austenitic and ferritic stainless steels. The VANSTAR-7 and V-15Cr-5Ti alloys showed the greatest hardening between 400 and 600/sup 0/C while V-3Ti-1Si and V-20Ti had lower values that were comparable to those of ferritic steels. The V-15Cr-5Ti and VANSTAR-7 alloys were susceptible to helium embrittlement caused by the combination of weakened grain boundaries and irradiation-hardened grain matrices. Specimen fractures were entirely intergranular in the most severe instances of embrittlement. The V-3Ti-1Si and V-20Ti alloys were more resistant to helium embrittlement. Except for VANSTAR-7 irradiated to 40 dpa at 520/sup 0/C, all of the vanadium alloys exhibited low swelling that was similar to the ferritic steels. Swelling was greater in specimens that were preimplanted with helium using the tritium trick. The vanadium alloys clearly exhibit lower residual radioactivity after irradiation than the ferrous alloys.
Date: January 1, 1986
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

Effect of neutron irradiation on the tensile properties and microstructure of several vanadium alloys

Description: Specimens of V-15Cr-5Ti, VANSTAR-7, and V-3Ti-1Si were encapsulated in TZM tubes containing /sup 7/Li to prevent interstitial pickup and irradiated in FFTF (MOTA experiment) to a damage level of 40 dpa. The irradiation temperatures were 420, 520, and 600/sup 0/C. For a better simulation of fusion reactor conditions, helium was preimplanted in some specimens using a modified version of the ''tritium trick.'' The V-15Cr-5Ti alloy was most susceptible to irradiation hardening and helium embrittlement, followed by VANSTAR-7 and V-3Ti-1Si. VANSTAR-7 exhibited a relatively high maximum void swelling of approx.6% at 520/sup 0/C while V-15Cr-5Ti and V-3Ti-1Si had values of less than 0.3% at all three temperatures. The V-3Ti-1Si clearly outperformed the other two vanadium alloys in resisting the effects of neutron irradiation.
Date: January 1, 1986
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

Resistance of (Fe,Ni)/sub 3/V long-range-ordered alloys to radiation damage

Description: The (Fe,Ni)/sub 3/V long-range-ordered (LRO) alloys (path D) are being developed at ORNL for possible application as a first-wall material for a fusion reactor. Alloys with different Fe/Ni ratios have been screened for their resistance to radiation by irradiating them with 4 MeV Ni ions to 70 dpa at temperatures from 525 to 680/sup 0/C. Helium (8 at. ppM/dpa) and deuterium ions (28 at. ppM/dpa) were simultaneously injected to better simulate fusion reactor conditions. Alloy LRO-16 (31 wt % Ni) contained sigma phase and showed swelling behavior similar to the 20%-cold-worked 316 stainless steel that was used as an internal standard. LRO-20 (39.5 wt % Ni), without sigma phase, swelled slightly less than the 316 stainless steel. Both alloys demonstrated noticeably lower swelling behavior when their composition was changed to include 0.4 wt % ti.
Date: January 1, 1980
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

Resistance of (Fe, Ni)/sub 3/V long-range-ordered alloys to neutron and ion irradiation

Description: A series of (Fe, Ni)/sub 3/V long-range-ordered alloys were irradiated with neutrons in the Oak Ridge Research Reactor (ORR) and with 4 MeV Ni ions at temperatures above 250/sup 0/C. The displacement damage levels for the two irradiations were 3.8 and 70 dpa, and the helium levels were 29 and 560 at. ppM, respectively. Irradiation in ORR generally increased the yield strength and lowered the ductility of an LRO alloy, but produced relatively little swelling. The LRO alloys retained their long-range order after ion irradiation below the critical ordering temperature, T/sub c/, and exhibited low swelling. Above T/sub c/ the alloys were disordered and showed greater swelling. Adjustment of alloy composition to prevent sigma phase formation reduced swelling.
Date: January 1, 1981
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

Vanadium alloys with improved resistance to helium embrittlement

Description: A series of experimental vanadium alloys have been designed with small MC-type carbides in their microstructures to trap helium produced during neutron irradiation, thereby reducing helium embrittlement. The tensile properties and fabricability of the alloys were strongly influenced by the amounts of MC-forming-elements, especially carbon. Alloys with 0.05 and 0.10 wt % carbon exhibited slightly lower yield strengths at 420 to 600{degree}C than vanadium alloys such as V-5Cr-5Ti, Vanstar-7, V-3Ti-1Si, and V-15Cr-5Ti. However, this characteristic may actually be an asset from the standpoint of resistance to irradiation hardening. After implantation with 300 appm {sup 3}He, both the V-Ti-C and V-Ti-Zr-C alloys exhibited less ductility losses at 600{degree}C than the other vanadium alloys tested under comparable conditions. Examination of the experimental alloy microstructures by AEM showed that the small MC-type carbides did, in fact, trap helium and that they were responsible for the increased resistance to helium embrittlement of these alloys. 16 refs., 12 figs., 2 tabs.
Date: January 1, 1990
Creator: Braski, D.N.
Partner: UNT Libraries Government Documents Department

Improved swelling resistance for PCA austenitic stainless steel under HFIR irradiation through microstructural control

Description: Six microstructural variants of Prime Candidate Alloy (PCA) were evaluated for swelling resistance during HFIR irradiation, together with several heats of type 316 stainless steel (316). Swelling was negligible in all the steels at 300/sup 0/C after approx. 44 dpa. At 500 to 600/sup 0/C 25%-cold-worked PCA showed better void swelling resistance than type 316 at approx. 44 dpa. There was less swelling variability among alloys at 400/sup 0/C, but again 25%-cold-worked PCA was the best. Microstructurally, swelling resistance correlated with development of fine, stable bubbles whereas high swelling was due to coarser distributions of bubbles becoming unstable and converting to voids (bias-driven cavities).
Date: January 1, 1983
Creator: Maziasz, P.J. & Braski, D.N.
Partner: UNT Libraries Government Documents Department

Interaction of noble-metal fission products with pyrolytic silicon carbide

Description: Fuel particles for the High-Temperature Gas-Cooled Reactor (HTGR) contain layers of pyrolytic carbon and silicon carbide, which act as a miniature pressure vessel and form the primary fission product barrier. Of the many fission products formed during irradiation, the noble metals are of particular interest because they interact significantly with the SiC layer and their concentrations are somewhat higher in the low-enriched uranium fuels currently under consideration. To study fission product-SiC interactions, particles of UO/sub 2/ or UC/sub 2/ are doped with fission product elements before coating and are then held in a thermal gradient up to several thousand hours. Examination of the SiC coatings by TEM-AEM after annealing shows that silver behaves differently from the palladium group.
Date: January 1, 1982
Creator: Lauf, R.J. & Braski, D.N.
Partner: UNT Libraries Government Documents Department

Modified tritium trick technique for doping vanadium alloys with helium

Description: A modified tritium trick technique was used to implant three different levels of /sup 3/He in V-15Cr-5Ti (wt %) and Vanstar-7 specimens before irradiation in the Fast Flux Test Facility (FFTF). The modifications include: (1) wrapping of the specimens with tantalum foil to minimize oxygen contamination, and (2) a 400/sup 0/C decay-time treatment to prevent vanadium tritide formation and to produce a /sup 3/He bubble distribution similar to that produced during elevated temperature irradiation. Preliminary results show that both modifications were successful. However, the tritium removal step at 700/sup 0/C was probably too excessive, especially at higher helium levels, because large /sup 3/He bubbles formed in the grain boundaries and several embrittled the V-15Cr-5Ti alloy. Reduction of the tritium removal step to 400/sup 0/C should alleviate this problem. Vanstar-7 specimens consistently absorbed about half as much tritium, and subsequently contained half as much /sup 3/He as V-15Cr-5Ti. Implanting /sup 3/He in vanadium alloys via the tritium trick offers a convenient technique to study the mechanism of helium embrittlement without irradiation and should provide a rapid screening method to help develop embrittlement-resistant vanadium alloys.
Date: January 1, 1984
Creator: Braski, D.N. & Ramey, D.W.
Partner: UNT Libraries Government Documents Department

Tensile properties of unirradiated PCA from room temperature to 700/sup 0/C

Description: The tensile properties of Prime Candidate Alloy (PCA) austenitic stainless steel after three different thermomechanical treatments were determined from room temperature to 700/sup 0/C. The solution-annealed PCA had the lowest strength and highest ductility, while the reverse was true for the 25%-cold-worked material. The PCA containing titanium-rich MC particles fell between the other two heats. The cold-worked PCA had nearly the same tensile properties as cold-worked type 316 stainless steel. Both alloys showed ductility minima at 300/sup 0/C.
Date: January 1, 1983
Creator: Braski, D.N. & Maziasz, P.J.
Partner: UNT Libraries Government Documents Department

Microstructural design of PCA austenitic stainless steel for improved resistance to helium embrittlement under HFIR irradiation

Description: Several variants of Prime Candidate Alloy (PCA) with different preirradiation thermal-mechanical treatments were irradiated in HFIR and were evaluated for embrittlement resistance via disk-bend tensile testing. Comparison tests were made on two heats of 20%-cold-worked type 316 stainless steel. None of the alloys were brittle after irradiation at 300 to 400/sup 0/C to approx. 44 dpa and helium levels of 3000 to approx.3600 at. ppm. However, all were quite brittle after similar exposure at 600/sup 0/C. Embrittlement varied with alloy and pretreatment for irradiation to 44 dpa at 500/sup 0/C and to 22 dpa at 600/sup 0/C. Better relative embrittlement resistance among PCA variants was found in alloys which contained prior grain boundary MC carbide particles that remained stable under irradiation.
Date: January 1, 1983
Creator: Maziasz, P.J. & Braski, D.N.
Partner: UNT Libraries Government Documents Department

Solidification behavior of austenitic stainless steel filler metals

Description: Thermal analysis and interrupted solidification experiments on selected austenitic stainless steel filler metals provided an understanding of the solidification behavior of austenitic stainless steel welds. The sequences of phase separations found were for type 308 stainless steel filler metal, L + L + delta + L + delta + ..gamma.. ..-->.. ..gamma.. + delta, and for type 310 stainless steel filler metal, L ..-->.. L + ..gamma.. ..-->.. ..gamma... In type 308 stainless steel filler metal, ferrite at room temperature was identified as either the untransformed primary delta-ferrite formed during the initial stages of solidification or the residual ferrite after Widmanstaetten austenite precipitation. Microprobe and scanning transmission electron microscope microanalyses revealed that solute extensively redistributes during the transformation of primary delta-ferrite to austenite, leading to enrichment and stabilization of ferrite by chromium. The type 310 stainless steel filler metal investigated solidifies by the primary crystallization of austenite, with the transformation going to completion at the solidus temperature. In our samples residual ferrite resulting from solute segregation was absent at the intercellular or interdendritic regions.
Date: February 1, 1980
Creator: David, S.A.; Goodwin, G.M. & Braski, D.N.
Partner: UNT Libraries Government Documents Department

Proceedings of the fourth annual conference on fossil energy materials

Description: The Fourth Annual Conference on Fossil Energy Materials was held in Oak Ridge, Tennessee, on may 15--17, 1990. The meeting was sponsored by the US Department of Energy's Office of Fossil Energy through the Advanced Research and Technology Development (AR TD) Materials Program, and ASM International. The objective of the AR TD Materials Program is to conduct research and development on materials for longer-term fossil energy applications as well as for generic needs of various fossil fuel technologies. The work is divided into the following categories: (1) Ceramics, (2) New Alloys, (3) Corrosion and Erosion, and (4) Technology Assessment and Technology Transfer. Individual projects are processed separately for the data bases.
Date: August 1, 1990
Creator: Judkins, R.R. & Braski, D.N. (comps.)
Partner: UNT Libraries Government Documents Department

Effect of preinjected helium on the response of V-20Ti pressurized tubes to neutron irradiation

Description: Vanadium-205 titanium tubes, pressurized to stresses of 34 and 39 MPa, were irradiated in the Experimental Breeder Reactor (EBR-II) at 700/sup 0/C to a displacement damage level of 22 dpa. Sections of the tubes were injected with 15 appM He prior to irradiation to determine ethe effect of helium on the microstructural and creep response of this alloy to irradiation. It was found that helium promoted cavity formation, primarily within existing precipitates, but total swelling remained low. Helium also significantly enhanced creep deformation. The results indicate that the increase in creep deformation in the presence of helium may be very sensitive to stress.
Date: January 1, 1986
Creator: Vitek, J.M.; Braski, D.N. & Horak, J.A.
Partner: UNT Libraries Government Documents Department

Characterization of SiC coatings on HTGR fuel particles: preliminary report

Description: Fuel particles for the HTGR contain a layer of pyrolytic silicon carbide to act as a pressure vessel and fission product barrier. The SiC is deposited by the thermal decomposition of methyltrichlorosilane (CH/sub 3/SiC/sub 3/ or MTS) in an excess of hydrogen. Coatings deposited at temperatures from 1500 to 1700/sup 0/C and coating rates of 0.4 to 1.2 ..mu..m/min have been studied by optical microscopy, x-ray diffraction, electron microscopy, and density measurements. Transmission electron microscopy (TEM) has shown the microstructural features to be extremely complex and much finer than the ability of optical microscopy to resolve. X-ray diffraction has detected traces of ..cap alpha..-SiC in some coatings, and those conditions of deposition temperature and coating rate that give rise to this phase have been determined.
Date: August 1, 1979
Creator: Lauf, R.J.; Braski, D.N. & Tennery, V.J.
Partner: UNT Libraries Government Documents Department

XPS study of Ni-Fe manganite thermistor material

Description: The resistivity of the as-fabricated thermistor material, nickel-iron-manganite, changes during initial aging in the temperature range of 150-300{degrees}C before becoming stable. X-ray photoelectron spectroscopy (XPS) was used to determine if any valency change or chemical shift of the cations or oxygen occurred after aging. The goal of the study was to identify any ionic changes that might affect thermistor stability. The only observed changes in 2p{sub 3/2} peaks due to aging were those related to Ni ions; the same peaks for Mn, Fe, and O remained unchanged. The changes in the Ni 2p{sub 3/2} peak may be related to: (a) the migration of Ni{sup 2+} ions from octahedral to tetrahedral sites, (b) subtle changes in the energy states of Ni{sup 2+} which promoted a more stable ionic structure, and/or (c) the presence of Ni{sup 3+} ions, some of which revert back to Ni{sup 2+}.
Date: March 1, 1995
Creator: Braski, D.N.; Osborne, N.R. & Zurbuchen, J.M.
Partner: UNT Libraries Government Documents Department

Au microstructure and the functional properties of Ni/Au finishes on ceramic IC packages

Description: Ni/Au plated finishes used on thick-film metallized multilayer ceramic packages for integrated circuits must meet functional requirements such as bondability, sealability, and solderability. Their ability to do so is dependent, among other things, on the ability of the Au deposit to inhibit the grain boundary diffusion and subsequent surface oxidation of Ni. In this study, the relation between functional performance, Ni diffusionr ate, and Au microstructure was examined. Extent of Ni diffusion during heating was determined by Auger electron spectroscopy for several electrolytic and electroless Ni/Au finishing processes. Results were correlated with differences in Au microstructures determined by SEM, atomic force microscopy, and XRD.
Date: December 31, 1995
Creator: Winters, E.D.; Baxter, W.K.; Braski, D.N. & Watkins, T.R.
Partner: UNT Libraries Government Documents Department

Interface modification during oxidation of a glass-ceramic matrix/SiC fibre composite

Description: Oxidation heat treatments between 375{degrees}C and 600{degrees}C for 100 hours in air, have been performed on the calcium aluminosilicate glass-ceramic matrix/SiC fibre reinforced composite CAS/Nicalon (manufactured by Coming, USA). Using a commercial nano-indentation system to perform fibre push-down tests, the fibre-matrix interfacial debond fracture surface energy (G{sub i}) and frictional shear stress ({tau}) have been determined. Modification of interface properties, compared to the as fabricated material, was observed at heat treatment temperatures as low as 375{degrees}C, where a significant drop in G{sub i} and an increase in {tau} were recorded. With 450{degrees}C, 525{degrees}C and 600{degrees}C heat treatments, an increase in G{sub i} but a dramatic increase in {tau} were recorded. Under four-point flexure testing, the as fabricated and the 375{degrees}C heat treated materials displayed tough, composite behaviour with extensive fibre pull out, but at {le}450{degrees}C, brittle failure with minimal fibre pull out, was observed. This transition from tough mechanical response to one of brittleness is due to the large increase in {tau} reducing fibre pull out to a minimum and therefore reducing the total required work of fracture. The large increases in {tau} and G{sub i} have been attributed to the oxidative removal of the lubricating, carbon interface and the compressive residual stresses across the interface.
Date: April 1, 1996
Creator: Daniel, A.M.; Martin-Meizoso, A.; Plucknett, K.P. & Braski, D.N.
Partner: UNT Libraries Government Documents Department

Environmental aging degradation in continuous fiber ceramic composites

Description: The thermal stability of two-continuous fiber ceramic composites (CFCC`s) has been assessed. A Nicalon/CaO-Al{sub 2}O{sub 3}-SiO{sub 2} (CAS) glass-ceramic composite has been subjected to unstressed, oxidation heat treatments between 375 and 1200{degrees}C, after which the material was tested in flexure at room temperature. The static fatigue behavior of a chemical vapor infiltrated (CVI) Nicalon/SiC ceramic matrix composite has been assessed in air, between 425 and 1150{degrees}C, both with and without protective seal coating. Severe property degradation was observed due to oxidation of the graphite fiber/matrix interlayer in both CFCC`s.
Date: December 31, 1995
Creator: Plucknett, K. P.; Lin, H. T.; Braski, D. N. & Becher, P. F.
Partner: UNT Libraries Government Documents Department