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Low temperature deformation properties of crystalline mercury
Vol.
9, No.
ii
ABSTRACTS
OF ARTICLES
The transformation distortions during the B+B ' and B'+6" transformations in near equiatomic Nb-Ru alloys produce phases that have progressively lower symmetry than the CsCI type B phase and approach the packing of the hexagonal close packed structure. By the use of a simple approximation -- the superposition approximation -- a model is developed which explains all of the experimental measurements on this alloy system. The driving force for these transformations is electronic in nature. The Fermi energy ~ of the ~ phase alloys is near a sharp peak in the density of status, p (E). The transformations broaden this peak, lowering p(~) and the energy of the phase. The significant experimental measurements accounted for by this model are the variation of magnetic susceptibility with phase and Ru content, the variation of transformation temperatures and transformation distortion with Ru composition, and distortion in the B" phase with temperature and Ru composition. 8.
CHARACTERIZATION OF POINT-DEFECT CLUSTERS BY 2-I/2-D TEM J. B. MITCHELL & W.L. BELL* Lawrence Livermore Lab., University of California, Livermore CA 94550 * General Electric Co., Vallecitos Nuclear Center, Pleasonton, CA. (Received April 18, 1975)
A new transmission electron microscopy (TEM) technique for determining the vacancy of interstitial character of point-defect clusters is decribed. The technique utilizes the differences in shifts of dark field images of vacancy and interstitial clusters during defocusing of the objective lens. This shift difference produces a parallax difference when two photographs taken at different focus settings are viewed in stereo. The parallax difference separates the vacancy and interstitial cluster images into different stereo depths. This technique can also be used together with calculations of elastic displacement fields to determine the Burgers vectors of the clusters. It is shown that a significant number of vacancy super clusters with Burgers vector multiples of a/2 or a/2 are formed spontaneously at displacement cascades in 16-MeV-proton irradiated niobium. 9.
LOW TEMPERATUREDEFORMATIONPROPERTIES OF CRYSTALLINEMERCURY J. S. ABELL* Physics Dept., University of Surrey, Guildford * now at Dept. of Physical Metallurgy University of Birmingham
TO APPEAR
IN ACTA MET
xlix
(Received April 30, 1975) Single crystals of mercury of square and circular cross-section have been subjected to tensile tests at 4.2K and five distinct types of deformation mode have been identified. Three of these, {llT}slip, '{-I-35}' twinning and {i~0}'<33~>' kinking are modes which have been observed at 77K. The two new shear modes which have been detected at 4.2K are {TI3}, g = 0.47 which has been associated with the a-y phase transformation occurring in mercury at this temperature, and {TI3}, g = 0.24 for which the mechanism involved has not been determined. Metallographic observations on these shear modes are presented and the crystallography of the two new modes is discussed in detail. The orientation dependence of the occurrence of these deformation modes is interpreted using Schmid factor contour plots of the most highly stressed variants, and it is found that such an analysis can be satisfactorily extended to include the transformation shear process. It is deduced that the resolved shear stress on the transformation shear mode need only be half that on the conventional slip mode for the transformation to occur at 4.2K. The transformation habits usually occur in pairs and this feature of the transformation can be understood when the special crystallographic relationship existing for this shear mode is examined in the light of the Schmid factor analysis. I0.
GLASS TEMPERATURE AND STABILITY OF Fe, Co, Ni AND Pd BASED GLASSES: EFFECT OF CONFIGURATIONAL ENTROPY AND CRYSTALLINE SYMMETRY H. S. CHEN B e l l L a b o r a t o r i e s , Murray H i l l , New J e r s e y 07974 (Received A p r i l 30, 1975) (Revised August I, 1975)
Thermal properties of Fe, Co, Ni and Pd based glasses are investigated. The change in glass temperatures, ATe, upon alloying is evaluated from bindir~g energies of the constituents based on the quasichemical model of the solution. The calculated AT~ agrees semi-quantitatively with the experimental data. The effect of crystalline syn~netry of the constituting binary alloys on the stability of glasses upon alloying is discussed. It is the destabilization of the crystalline mixtures and not the structural stabilization of the glassy phase which dominates the formation and stability of metallic glasses.
9, No.
ii
ABSTRACTS
OF ARTICLES
The transformation distortions during the B+B ' and B'+6" transformations in near equiatomic Nb-Ru alloys produce phases that have progressively lower symmetry than the CsCI type B phase and approach the packing of the hexagonal close packed structure. By the use of a simple approximation -- the superposition approximation -- a model is developed which explains all of the experimental measurements on this alloy system. The driving force for these transformations is electronic in nature. The Fermi energy ~ of the ~ phase alloys is near a sharp peak in the density of status, p (E). The transformations broaden this peak, lowering p(~) and the energy of the phase. The significant experimental measurements accounted for by this model are the variation of magnetic susceptibility with phase and Ru content, the variation of transformation temperatures and transformation distortion with Ru composition, and distortion in the B" phase with temperature and Ru composition. 8.
CHARACTERIZATION OF POINT-DEFECT CLUSTERS BY 2-I/2-D TEM J. B. MITCHELL & W.L. BELL* Lawrence Livermore Lab., University of California, Livermore CA 94550 * General Electric Co., Vallecitos Nuclear Center, Pleasonton, CA. (Received April 18, 1975)
A new transmission electron microscopy (TEM) technique for determining the vacancy of interstitial character of point-defect clusters is decribed. The technique utilizes the differences in shifts of dark field images of vacancy and interstitial clusters during defocusing of the objective lens. This shift difference produces a parallax difference when two photographs taken at different focus settings are viewed in stereo. The parallax difference separates the vacancy and interstitial cluster images into different stereo depths. This technique can also be used together with calculations of elastic displacement fields to determine the Burgers vectors of the clusters. It is shown that a significant number of vacancy super clusters with Burgers vector multiples of a/2
LOW TEMPERATUREDEFORMATIONPROPERTIES OF CRYSTALLINEMERCURY J. S. ABELL* Physics Dept., University of Surrey, Guildford * now at Dept. of Physical Metallurgy University of Birmingham
TO APPEAR
IN ACTA MET
xlix
(Received April 30, 1975) Single crystals of mercury of square and circular cross-section have been subjected to tensile tests at 4.2K and five distinct types of deformation mode have been identified. Three of these, {llT}
GLASS TEMPERATURE AND STABILITY OF Fe, Co, Ni AND Pd BASED GLASSES: EFFECT OF CONFIGURATIONAL ENTROPY AND CRYSTALLINE SYMMETRY H. S. CHEN B e l l L a b o r a t o r i e s , Murray H i l l , New J e r s e y 07974 (Received A p r i l 30, 1975) (Revised August I, 1975)
Thermal properties of Fe, Co, Ni and Pd based glasses are investigated. The change in glass temperatures, ATe, upon alloying is evaluated from bindir~g energies of the constituents based on the quasichemical model of the solution. The calculated AT~ agrees semi-quantitatively with the experimental data. The effect of crystalline syn~netry of the constituting binary alloys on the stability of glasses upon alloying is discussed. It is the destabilization of the crystalline mixtures and not the structural stabilization of the glassy phase which dominates the formation and stability of metallic glasses.