摘要:

Sheet samples of pure nickel and Inconel 600 alloy (76% Ni, 16% Cr, 7% Fe) containing a fine precipitate were simultaneously shock loaded in sandwich assemblies at pressures of 50, 100, 150, 200, and 370 kbar by a planar pulse of roughly 2‐&mgr;sec duration explosively initiated by a flying plate. The residual microhardness of the nickel was observed to saturate above 300 kbar while that for Inconel continued to increase steadily. Examination of the nickel substructures by transmission electron microscopy revealed a steadily decreasing cell size with increasing shock pressure; with almost no evidence of deformation twins at 370 kbar. The Inconel substructure was characterized by planar dislocation arrays which included an increasing concentration of dipoles and elongated loops to 200 kbar; while at 370 kbar deformation twins having an average thickness of 150 Å and occupying 19% of the volume were observed. The coherent precipitates in the Inconel matrix were observed to become incoherent at pressures above 50 kbar, with the concomitant production of dislocation tangles and loops at the particle‐matrix interface. The precipitates were observed to enhance shock hardening by acting as sources for dislocation dipoles and elongated loops.

ISSN:0021-8979    

DOI:10.1063/1.1658274

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A vaporization experiment is described in which both vaporization and condensation coefficients can be accurately determined. The technique involves rate measurements under various degrees of undersaturation and supersaturation and shows that for silver both the vaporization and growth processes are ideal and independent of surface orientations. Low pressures of vapor phase reactants,p<10−5Torr of O2, CO2, N2, H2S, Cl2, acetone vapor, or CH4, were found to have no influence upon the kinetics of the process. Through the process of adsorption several of these gases markedly influenced the surface morphology of the specimens without appreciably disturbing the concentration of the desorbing silver species. Mechanistically, these results imply that there is a free interchange of silver between surface and bulk sites and that the desorption of silver from the surface is the controlling step in the vaporization process. In a similar way, the gas results show that the absorption or desorption of surface impurities characteristic of normal vacuum environments maintains the surface concentration of all impurities below a value where they could impede the vaporization process.

ISSN:0021-8979    

DOI:10.1063/1.1658275

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Certain morphological features developed during the vaporization of solid silver have been found to correlate with crystallography and environment. Through the results obtained in related kinetic measurements, capillarity forces are shown to be responsible for the hill and valley roughness that is developed. On the basis of the deduced origin, a model for the roughening process is developed. An orientation dependence of the surface morphology, vaporization faceting, is shown to demonstrate the presence of cusped minima in the surface‐energy‐orientation relationship for silver at the {111} and {100} orientations. Evidence for the adsorption of O2, acetone, CH3, H2S, and Cl2on Ag during vaporization was obtained. The results indicate that a C impurity is deposited on the surface by the interaction between carbon‐bearing gases and the vaporizing silver and that the C impurity adsorbs preferentially at surface defects and tends to blunt the surface‐energy cusps at the low‐index orientations. Absorbed oxygen was found to react with other impurities to form desorbable surface species.

ISSN:0021-8979    

DOI:10.1063/1.1658276

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The formation of oxide layers on fresh {100} cleavage faces of uranium monocarbide (UC) single crystals during exposure to air at room temperature is studied using the channeling technique and Rutherford backscattering of 1‐MeV He+ions. The thickness of the layers increases with humidity and, for exposure times of about 1 week, ranges between 20 and 80 Å.

ISSN:0021-8979    

DOI:10.1063/1.1658277

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Work‐function changes during the desorption of cesium from three tungsten surfaces, polycrystalline foil, (100), and (110) oriented single crystals, have been measured in the region of the work function minimum. A modification of the vibrating capacitor technique which made contact‐potential difference on electron emitting surfaces possible was developed for these experiments. For different arrival rates of cesium, the minimum work function occurred at different temperatures and decreased in magnitude with temperature. Values at 295°K were 1.78 eV for polycrystalline foil, 1.795 eV for the (100), and 1.955 eV for the (110). For all specimens the decrease in magnitude with temperature was of the order of 10−3eV·K0−1. These data were compared with thermionic values for the work function minimum and with theoretical predictions. We note especially that the sign of the variation is opposite to that predicted by the Rasor‐Warner theory in every case.

ISSN:0021-8979    

DOI:10.1063/1.1658278

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Results are presented for the thermal oxidation behavior of four types of sputtered tantalum films between 100° and 525°C. These films are bcc tantalum, &bgr;‐tantalum, a porous &bgr;‐tantalum, and tantalum nitride (Ta2N). All four types of films show parabolic oxidation kinetics and the formation of adherent Ta2O5(tantalum oxy‐nitride for Ta2N films) with bright interference colors. The first three types of films dissolve about 12 at.% oxygen, which is much higher than the oxygen solubility found in bulk tantalum, and the films show a different degree of suboxide formation than bulk tantalum. The activation energies for oxygen diffusion in the metal and for oxide growth are 1.2 and 1.4 eV, respectively. The dielectric properties of the thermal oxide are discussed in terms of the defects in the oxide.

ISSN:0021-8979    

DOI:10.1063/1.1658279

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is shown that in a cryostat the use of an isothermal path leading out of an applied magnetic field will ensure insensitivity of thermocouples to the magnetic field. Tests in liquid helium in such a cryostat were conducted on a number of thermocouples with the applied field ranging up to 100 kG. The results showed that Cu‐constantan, Cu&sngbnd;Au 0.03 at.% Fe, and Cu&sngbnd;Au 2.1 at.% Co thermocouples are not affected by magnetic fields. In subsequent work up to 300 K the first two thermocouples listed were still insensitive to magnetic fields. The third thermocouple was not tested at the higher temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1658280

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The photoelectric and Compton response to &ggr; rays for a detector made from semi‐insulating material (i.e., a monocrystalline semiconductor containing trapping centers) was calculated for the case of charge transport by one type of carrier (electron or hole), and also for the case of two‐carrier transport (electron and hole) with each carrier having the same mean free path. Approximate expressions were then derived for the observable &ggr;‐ray efficiency of the detector as a function of material parameters for CdTe crystals used in the fabrication of surface barrier detectors; this efficiency is dependent upon temperature and electric field intensity for specified values of the carrier mobility‐trapping time product and the threshold used in the recording of spectra. Spectra and values for efficiency were determined at room temperature for &ggr; rays at energy values from 0.393 to 1.33 MeV, and also as a function of temperature over the range 24° to 68°C for &ggr; rays from a60Co source. The observations show behavior corresponding to a trap‐limited response, and the presence of charge detrapping.

ISSN:0021-8979    

DOI:10.1063/1.1658281

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The reddish color seen in photographs of exploding copper wires was assumed to be due in part to the scattering of the blue and green wavelengths of the BH6 mercury lamp used. Accordingly, this scattered light was used to measure particle size by the dissymmetry method. The average value of the predominant particle dimension was found to be time dependent with a value of (12±3)×102Å occurring 0.6 &mgr;sec before the voltage peak.

ISSN:0021-8979    

DOI:10.1063/1.1658282

出版商:AIP    

年代:1969

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1658284

出版商:AIP    

年代:1969

数据来源: AIP