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Analysis of anelastic relaxations controlled by a spectrum of relaxation times

Description: Anelastic studies, although they have provided an important method for investigating the mobility of point defects in solids, have often been difficult to analyze when a continuous spectra of relaxation times controls the anelastic response. This paper describes a new method for obtaining accurate estimates of relaxation time spectra by direct analysis (without prior assumptions) of the data using a nonlinear regression method. Applications to internal friction and anelastic creep results are described with emphasis upon the internal friction technique. 5 references.
Date: January 1, 1983
Creator: Cost, J.R.
Partner: UNT Libraries Government Documents Department

Deconvolution analysis to determine relaxation time spectra of internal friction peaks

Description: A new method for analysis of an internal friction vs temperature peak to obtain an approximation of the spectrum of relaxation time responsible for the peak is described. This method, referred to as direct spectrum analysis (DSA), is shown to provide an accurate estimate of the distribution of relaxation times. The method is validated for various spectra, and it is shown that: (1) It provides approximations to known input spectra which replicate the position, amplitude, width and shape with good accuracy (typically 10%). (2) It does not yield approximations which have false spectral peaks.
Date: January 1, 1985
Creator: Cost, J.R.
Partner: UNT Libraries Government Documents Department

Direct spectrum-analysis method for obtaining the relaxation-time spectrum from relaxation-response data: amorphous metals. [Fe/sub 40/Ni/sub 40/P/sub 14/B/sub 6/]

Description: A method is described for determining without prior assumptions the distribution of relaxation times from the experimental relaxation response curve for a system approaching equilibrium by a single-step process following first-order kinetics. By analysis of computer-generated data with simulated random experimental error, the method is demonstrated to be capable of reproducing spectra with a single lognormal peak for a broad range of peak widths. This direct spectrum analysis method is applied to previously reported results for a relaxation in the metallic glass Fe/sub 40/Ni/sub 40/P/sub 14/B/sub 6/ and the previous result that the relaxation time spectrum for this relaxation contains four relatively sharp peaks is corroborated.
Date: January 1, 1982
Creator: Cost, J.R.
Partner: UNT Libraries Government Documents Department

Radiation-induced changes in magnetic properties of Nd-Fe-B permanent magnets

Description: The high remanence and intrinsic coercivity of Nd-Fe-B magnets make them desirable for use in the accelerators. Use in the radiation environment of an accelerator requires that the sensitivity of these magnets to radiation be determined and the mechanisms responsible be understood. We present results comparing the relative radiation sensitivity of a number of commercially available Nd-Fe-B magnets. Small samples of these magnets were irradiated at the Omega West Reactor in a neutron flux of 2 x 10/sup 13/ n/cm/sup 2/s at a temperature of 350/sup 0/K (77/sup 0/C). At various time intervals during the irradiation, samples were removed from the reactor and the open-circuit remanence measured. We also measured the second quadrant demagnetization curve of samples before and after neutron irradiation to monitor changes in remanence and intrinsic coercivity. Our results show that the sensitivity to radiation varies widely among magnets from different vendors. In general, these samples showed a decrease in the remanence and an increase in the intrinsic coercivity. We present results showing that the rate of remanence decay decreases monotonically with increasing length-to-diameter (L/D) ratio for samples of the same material. Thus, it is important to compare decay rates corrected to some constant L/D ratio. 7 refs., 3 figs., 2 tabs.
Date: January 1, 1987
Creator: Brown, R.D. & Cost, J.R.
Partner: UNT Libraries Government Documents Department

Response of metallic glasses Fe/sub 40/Ni/sub 40/P/sub 14/B/sub 6/ and Fe/sub 80/B/sub 20/ to irradiation with 800-MeV protons

Description: Metallic glasses with compositions of Fe/sub 40/Ni/sub 40/P/sub 14/B/sub 6/ and Fe/sub 80/B/sub 20/ were irradiated in the 800 MeV proton beam at the Los Alamos Meson Physics Facility while the electrical resistance and length changes were monitored. The resistance and the length of the first alloy were both found to increase and saturate with dose to ..delta..R/R approx. = 5 x 10/sup -3/ and ..delta..L/L approx. = 2 x 10/sup -3/. For the second alloy the total dose of 1.1 x 10/sup 19/ p/cm/sup 2/, which was calculated to give roughly 0.12 dpa, was slightly less than that required for saturation. No annealing of these increases was observed for anneals from room temperature to 250/sup 0/C. These results are interpreted in terms of a model in which collision cascades create small regions of increased atomic disorder which fully overlap each other at saturation.
Date: January 1, 1981
Creator: Cost, J.R. & Sommer, W.F.
Partner: UNT Libraries Government Documents Department

Mechanical properties of 800-MeV proton-irradiated metals

Description: Accelerator beam line components and spallation neutron targets operate in an irradiation environment where changes in mechanical properties can adversely affect component integrity. The present work presents a preliminary study of the effects of low fluences (10/sup 19/ to 10/sup 20/ p/cm/sup 2/) of 800-MeV protons on the yield strength, tensile strength, and ductility of samples of 304 stainless steel, Alloy 718, molybdenum, and tantalum. Tensile samples (0.75 or 1.6 mm thick) were directly water cooled during irradiation and were tested at room temperature. For the 304 stainless steel and annealed Alloy 718, the yield strengths increased by about a factor of 3 and 1.6, respectively, while the ductility decreased approx. 30 and 40 percent. In the bcc metals (tantalum and molybdenum) the yield strengths increased by at least a factor of 2. Tantalum samples retained significant ductility at room temperature, while several molybdenum specimens broke at less than 0.2 percent strain. These irradiation-induced changes at low proton fluences should not impair the usefulness of these materials (other than molybdenum) in accelerator environments.
Date: January 1, 1982
Creator: Brown, R.D. & Cost, J.R.
Partner: UNT Libraries Government Documents Department

Kinetics of structural relaxation in metallic glasses. [PdGe; FeNiPB]

Description: When a metallic glass is annealed at temperatures below the glass transition temperature its structure changes with time. This structural change is observed to have an irreversible component and a reversible component. Our work has concentrated on studying the reversible component of the structural relaxation. In this paper the reversible component is called chemical short-range order (CSRO) and the irreversible components topological short-range order (TSRO). It is believed important to determine if the spectrum of relaxation times has fine structure. Experiments have been carried out to obtain the maximum possible detail about the kinetic behavior of the CSRO changes. Also a new method of analysis of the response curve, referred to as direct spectrum analysis, has been used to resolve fine structure in the spectrum of relaxation times.
Date: January 1, 1983
Creator: Cost, J.R. & Stanley, J.T.
Partner: UNT Libraries Government Documents Department

Evaluation of anelastic evidence for interstitial solute binding in bcc metals

Description: A Direct Spectrum Analysis (DSA) technique has been applied to key internal friction and elastic after-effect data which are involved in the controversy over the existance of interstitial clustering in the refractory metals. It is found that at relatively high interstitial solute concentrations some of the Snoek peak broadening is due to relaxations that are distinct from the main relaxation. This finding supports the view that interstitial solutes have an interaction that produces clusters of interstitials.
Date: January 1, 1985
Creator: Cost, J.R. & Stanley, J.T.
Partner: UNT Libraries Government Documents Department

Structural relaxation rates in amorphous Metglas alloys Fe/sub 40/Ni/sub 40/P/sub 14/B/sub 6/ and Fe/sub 80/B/sub 80/

Description: Measurements made on the Metglas 2826 alloy at an anneal temperature of 250/sup 0/ are presented which again strongly indicate that the temperature-change induced reaction involves four simple first order processes. In addition, results of an unsuccessful attempt to find a similar effect in the binary metallic glass Fe/sub 80/B/sub 20/ are analyzed.
Date: January 1, 1981
Creator: Cost, J.R. & Stanley, J.T.
Partner: UNT Libraries Government Documents Department

Structural relaxation in Pd-Ge metallic glass

Description: We have measured small reversible changes of electrical resistance which occur following a small temperature change applied to an amorphous Pd/sub 78/Ge/sub 22/ alloy. Reversibility of this relaxation was demonstrated by the resistance returning (nearly) to the original value after repeated temperature cycling and equilibration. The reversible characteristic of the relaxation suggests that the mechanism is the change in chemical short-range order with temperature. Thus the measurements provide information on atomic mobility in this metallic glass. The relaxation kinetics indicate a broad spectrum of relaxation times which is best described as lognormal but skewed towards longer times. Parameters describing the breadth and shift in this spectrum with temperature will be described. We also observed an irreversible resistance change superimposed on the reversible changes. The kinetics of the irreversible change were found to obey the equation for free volume relaxation proposed by van den Buekel. However, his ''mixed'' CSRO-TSRO kinetics model fails to describe the slowing of the CSRO kinetics that occurs early in the annealing process.
Date: January 1, 1987
Creator: Cost, J.R. & Stanley, J.T.
Partner: UNT Libraries Government Documents Department

Isothermal calorimetric investigation of a reversible reaction in rapidly solidified Fe/sub 40/Fi/sub 40/B/sub 20/

Description: A new method is described for isothermal calorimetric measurement of time-dependent reversible reactions in which the rate of heat flow is small compared to the noise and zero drift of the measurement. Results using this method are presented which measure enthalpy changes associated with reversible phase changes in a rapidly solidified Fe/sub 40/Ni/sub 40/B/sub 20/ alloy.
Date: January 1, 1983
Creator: Cost, J.R.; Elliott, R.O. & Stanley, J.T.
Partner: UNT Libraries Government Documents Department

Helium release from type 304 stainless steel

Description: Helium in very low concentration (less than 1 atomic ppB) has been introduced into type 304 stainless steel by radioactive decay of dissolved tritium. Release of this helium during subsequent annealing was monitored with a high sensitivity mass spectrometric gas analyzer. With isochronal annealing, helium is released in two temperature ranges, one near 300$sup 0$C and the other between 800$sup 0$C and the melting point. The latter release is interpreted as attributable to helium gas bubbles. The release near 300$sup 0$C was studied isothermally between 150 and 300$sup 0$C and is analyzed in terms of two stages of exponential decay. The fast and slow release stages have relaxation times near 10$sup 2$ and 10$sup 3$ s, respectively, and the fast release accounts for roughly 85 percent of the total release at low temperature. From an analysis of the temperature dependence of the release rate, it is concluded that volume diffusion is the controlling mechanism for the outgassing. (auth)
Date: September 18, 1975
Creator: Cost, J.R.; Hickman, R.G.; Holt, J.B. & Borg, R.
Partner: UNT Libraries Government Documents Department

Martensitic nature of {delta} {yields} {gamma} allotropic transformation in plutonium

Description: Isothermal and isoplethal studies using differential scanning calorimetry have been conducted to characterize the allotropic transformations of plutonium. The {delta}-{gamma} transformation (upon cooling) was observed to have a classic martensitic nature. The work described herein is the first quantitative study of this phenomena in plutonium.
Date: September 1, 1996
Creator: Lopez, P.C.; Cost, J.R. & Axler, K.M.
Partner: UNT Libraries Government Documents Department

Neutron irradiation study of Nd-Fe-B permanent magnets made from melt-spun ribbons

Description: Radiation-induced changes in the magnetization of sintered Nd-Fe-B permanent magnets are known to vary widely among specimens produced by different manufacturers. Samples of Nd-Fe-B MAGNEQUENCH magnets, which are made from melt-spun ribbons, have now been studied and show a much reduced sensitivity to neutron irradiation than do sintered Nd-Fe-B magnets. All melt-spun ribbon-based MAGNEQUENCH magnets, i.e., epoxy-bonded, hot-pressed, and die-upset magnets, show essentially the same slow decrease in magnetic remanence with neutron dose. Measurements of the open-circuit remanence B/sub r//B/sub ro/ at various times during the irradiation show a decay of only 1.5% of the preirradiated value for the MAGNEQUENCH magnets after 1 hour of irradiation, or a dose of 1.4 /times/ 10/sup 16/ neutrons/cm/sup 2/, compared to a 4.6% drop in remanence for the best sintered Nd-Fe-B magnet (Sumitomo 3OH) with the same irradiation dose. Moreover, after 5.3 hours of irradiation, the remanence drops by only 3% for the MAGNEQUENCH magnets. Magnets made from melt-spun ribbons are thus the least sensitive to neutron irradiation so far measured for Nd-Fe-B permanent magnets, but are somewhat more sensitive than samarium-cobalt magnets. 12 refs., 1 fig.
Date: January 1, 1988
Creator: Brown, R.D.; Cost, J.R.; Meisner, G.P. & Brewer, E.G.
Partner: UNT Libraries Government Documents Department

Radiation effects in rare-earth permanent magnets. [Nd-Fe-B; Sm-Co]

Description: Nd-Fe-B and Sm-Co permanent magnets have been irradiated with fission neutrons and gamma rays. Irradiated samples were periodically removed for room temperature measurements of the open-circuit remanence. Hysteresis loops were measured before and after irradiation. For neutron irradiation, two magnets showed a rapid loss of remanence, while a third decayed more slowly. Irradiation in the Omega West Reactor at Los Alamos with fast neutrons caused the fast-decay samples to have an initial loss of remanence of 1% for irradiation at 350 K to a fluence of 10/sup 15/ n/cm/sup 2/. Both SmCo/sub 5/ and Sm/sub 2/Co/sub 17/ magnets showed excellent resistance to radiation-induced loss of remanence for neutron irradiation to a fluence of 2.6 x 10/sup 18/ n/cm/sup 2/. Results for gamma irradiation are presented and discussed in terms of possible mechanisms for radiation-induced loss of magnetic properties.
Date: January 1, 1987
Creator: Cost, J.R.; Brown, R.D.; Giorgi, A.L. & Stanley, J.T.
Partner: UNT Libraries Government Documents Department

Radiation damage in YBa/sub 2/Cu/sub 3/O/sub 7/ by fast neutrons

Description: The superconducting transition temperature of sintered YBa/sub 2/Cu/sub 3/O/sub 7/ decreases at a rate of 2.7 K/10/sup 18/ n/cm/sup 2/ (E > 0.1 MeV) for fast neutron irradiation. The critical current density J/sub c/ increases a factor of three at zero field and more than three at nonzero fields for fluences up to 2 x 10/sup 18/ n/cm/sup 2/. At both 7 and 75 K, J/sub c/ is decreasing with fluence near 3 x 10/sup 18/ n/cm/sup 2/.
Date: January 1, 1987
Creator: Willis, J.O.; Cost, J.R.; Brown, R.D.; Thompson, J.D. & Peterson, D.E.
Partner: UNT Libraries Government Documents Department

Phase transformations, stability, and materials interactions

Description: The proceedings of the Materials Sciences Workshop on Phase Transformations, Stability, and Materials Interactions are divided into sections according to the following topics: (I) workshop scope and priorities; (II) study group reports--ERDA mission needs; (III) study group reports--technical area research priorities. (SDF)
Date: July 1, 1977
Creator: Morris, J.W. Jr.; Brewer, L.; Cost, J.R. & Shewmon, P.
Partner: UNT Libraries Government Documents Department

The development of small-scale quadrupoles to operate at 20 to 50K

Description: The development of cryogenically cooled, high-frequency linacs at Los Alamos necessitates that small quadrupoles be developed to operate inside the drift tubes at temperatures as low as 20 K. A program has been undertaken to procure some of these quads, designed to critical specifications, and to test them for field-gradient and harmonic- distortion changes when taken down to the 20- to 50-K operating range and cycled many times back to room temperature. In this application SmCo/sub 5/ and Sm/sub 2/Co/sub 17/ will be used. Both low-temperature operation and resistance to radiation damage are required of these critical components; therefore, the test program also involves exposure to high radiation fluxes in the Omega West reactor at Los Alamos, coupled with post-irradiation field tests. 2 refs., 3 figs., 1 tab.
Date: January 1, 1988
Creator: Liska, D.J.; Kraus, R.H.; Brown, R.D. & Cost, J.R.
Partner: UNT Libraries Government Documents Department

The kinetics of the beta to alpha transformation in unalloyed plutonium using differential scanning calorimetry

Description: Differential scanning calorimetry measurements, both isothermal and on cooling, were made during the {beta} {yields} {alpha} transformation of unalloyed plutonium. The calorimetric measurements, because they directly measure the rate of heat flow, provide a direct quantitative measure of the rate of the reaction. Isothermal measurements at temperatures from 56{degree} to 68{degree}C showed that the reaction required incubation times, presumably for nucleation of the alpha phase, of from 300 to 550 seconds. The reaction rate increased with decreasing temperature in agreement with results of prior studies. The measured value for the heat of the reaction also corroborated earlier findings. The fraction-transformed curves were analyzed using the Johnson, Mehl, Avrami model. Analysis showed clearly that the reaction kinetics do not fit this model. The Avrami exponent, instead of being constant as predicted, decreased continuously (by more than a factor of four) during the first 80% of the reaction. Possible reasons for this apparent deviation from classical transformation kinetics are discussed. Measurements in the temperature-scanning mode were made on a sample consisting of ten separate pieces of plutonium. With successive cooling cycles through the {beta} {yields} {alpha} transformation, the heat release peak changed in shape, width, and position. This effect is believed to be due to changes in the residual stresses in different pieces of the sample.
Date: December 31, 1993
Creator: Cost, J. R. & Soderquist, S. D.
Partner: UNT Libraries Government Documents Department

Mechanical after-effect studies of oxygen relaxation in YBa sub 2 Cu sub 3 O sub 7-. delta

Description: YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} has an anelastic relaxation involving motion of an oxygen atom or defect. This relaxation has been studied with good agreement by more than seven investigating teams over the temperature range from 200 to 550{degrees}C using internal friction techniques. We have extended measurements of this relaxation to a new regime of temperature and relaxation time using the mechanical after-effect method. Our results cover an additional three orders of magnitude in relaxation time over the temperature range from 50 to 110{degrees}C. The Arrhenius plot, when combined with internal friction results, now covers eleven orders of magnitude in relaxation time. The fit gives an activation energy, Q=1.12 ({plus minus}0.015) and pre-exponential, {tau}{sub 0}=1.9 {times} 10{sup {minus}13} s. The isothermal mechanical relaxation curves we measured always spanned longer times than predicted for a simple exponential relaxation. This indicates that the process is controlled by a relatively wide spectrum of relaxation times. We have calculated best approximations of this spectrum by deconvoluting the mechanical after-effect curves. The resulting distribution is symmetrical in logarithm of the relaxation time with a width at half-height which is a factor of 20 in relaxation time. The significance of these findings is discussed in terms of our understanding of oxygen mobility in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. 16 refs., 5 figs.
Date: January 1, 1991
Creator: Cost, J.R. (Los Alamos National Lab., NM (United States)) & Stanley, J.T. (Arizona State Univ., Tempe, AZ (United States))
Partner: UNT Libraries Government Documents Department