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The crystallization behaviour of amorphous rare earth-Ag thin films
Abstracts 17th Meeting Israel Society for Electron Microscopy FeTi matrix and two distinct oxide phases, namely TiO 2 rutile and cubic TiO. This latter phase appeared only in samples heat-treated at low oxygen pressure. Analysis of the diffraction rings indicated the presence of finely dispersed oxygen-stabilized Ti4Fe2Ox and Fe304. The orientation relationship of the overlying TiO 2 with respect to the matrix were determined. The results support the model according to which hydrogen penetrates bulk FeTi through the oxygenstabilized Ti4Fe20 x formed in the course of the activation treatment within the surface layer of FeTi. IDENTIFICATION OF TOUGHENING MECHANISMS IN W-Ni-Fe ALLOYS BY MEANS OF SEM FRACTOGRAPHY AND METALLOGRAPHY D. Rittel
and I. Roman
Materials Science Division, School of Applied Science and Technology, The Hebrew University, Jerusalem 91010, Israel
The present study was undertaken in order to identify the mechanisms responsible for a dramatic improvement of the tensile ductility in sintered heavy Wbase alloys as a result of post-manufacturing heat treatments. SEM fractographic studies revealed that the topography of the fracture surfaces of the alloys undergoes a drastic change as a consequence of the heat treatments, and the nature of that change is temperature dependent. Annealing treatments above 500oc were found to result in a 200% improvement in the relatively poor ductility of the as-manufactured alloys. This increase in ductility is manifest by the following SEM observations of the fractured surfaces: Poor ductility is characterized by pronounced decohesion of the tungsten grains and binding material interfaces, without any noticeable plastic deformation of the latter. This results in the exposure of numerous "binding necks" between the grains. Improved ductility is characterized mainly by the cleavage of tungsten grains and large plastic deformations of the binding material (dimpled rupture). To a lesser extent, secondary cracking of cleaved grains, precipitation on the "necks" of grains and wavy slide lines were observed in the SEM fractographs. Scanning electron microscopy metallographic studies failed to reveal significant changes, parallel to the fractographic observations, in the microstructure of the heat-treated alloys as compared with the as-sintered ones.
339
The observed toughening and its fractographic manifestations were attributed to a mechanical improvement of the ad-hesion between the grains and the binding matrix owing to the different thermal expansion of these phases during thermal treatment. THE CRYSTALLIZATION BEHAVIOUR OF AMORPHOUS RARE EARTH-Ag THIN FILMS L. Shikmanter, M. P. Dariel*
M. Talianker
and
Department of Materials Engineering, B e n - G u r i o n U n i v e r s i t y o f the N e g e v , Beersheba 84100, Israel; and *Nuclear R e s e a r c h C e n t r e - N e g e v , P. O. B o x 9001, Beersheba 84190, Israel
Thin amorphous Rare Earth-Ag thin films were evaporated in a vacuum of 10-6 Torr and their isothermal crystallization behaviour was investigated in situ by transmission electron microscopy. Electron micrographs and electron diffraction patterns were taken at fixed time intervals from the same area of the samples in order to follow the nucleation and subsequent growth of the crystalline phase within t h e a m o r p h o u s matrix from the earliest stages of its appearance. By analysis of the electron micrographs, the nucleation rate of the crystalline phase and the growth rate of the crystalline particles was determined. The size of particles increased linearly with time indicating an interface controlled growth. The kinetics of the transformation were analyzed in terms of Avrami's equation. The experimental data allowed the derivation of the values of AE = 4.60 ± 0.2 eV for the overall activation energy of the crystallization process, AEcr = i.i0 ± 0.05 for the activation energy of atomic motion.
and I. Roman
Materials Science Division, School of Applied Science and Technology, The Hebrew University, Jerusalem 91010, Israel
The present study was undertaken in order to identify the mechanisms responsible for a dramatic improvement of the tensile ductility in sintered heavy Wbase alloys as a result of post-manufacturing heat treatments. SEM fractographic studies revealed that the topography of the fracture surfaces of the alloys undergoes a drastic change as a consequence of the heat treatments, and the nature of that change is temperature dependent. Annealing treatments above 500oc were found to result in a 200% improvement in the relatively poor ductility of the as-manufactured alloys. This increase in ductility is manifest by the following SEM observations of the fractured surfaces: Poor ductility is characterized by pronounced decohesion of the tungsten grains and binding material interfaces, without any noticeable plastic deformation of the latter. This results in the exposure of numerous "binding necks" between the grains. Improved ductility is characterized mainly by the cleavage of tungsten grains and large plastic deformations of the binding material (dimpled rupture). To a lesser extent, secondary cracking of cleaved grains, precipitation on the "necks" of grains and wavy slide lines were observed in the SEM fractographs. Scanning electron microscopy metallographic studies failed to reveal significant changes, parallel to the fractographic observations, in the microstructure of the heat-treated alloys as compared with the as-sintered ones.
339
The observed toughening and its fractographic manifestations were attributed to a mechanical improvement of the ad-hesion between the grains and the binding matrix owing to the different thermal expansion of these phases during thermal treatment. THE CRYSTALLIZATION BEHAVIOUR OF AMORPHOUS RARE EARTH-Ag THIN FILMS L. Shikmanter, M. P. Dariel*
M. Talianker
and
Department of Materials Engineering, B e n - G u r i o n U n i v e r s i t y o f the N e g e v , Beersheba 84100, Israel; and *Nuclear R e s e a r c h C e n t r e - N e g e v , P. O. B o x 9001, Beersheba 84190, Israel
Thin amorphous Rare Earth-Ag thin films were evaporated in a vacuum of 10-6 Torr and their isothermal crystallization behaviour was investigated in situ by transmission electron microscopy. Electron micrographs and electron diffraction patterns were taken at fixed time intervals from the same area of the samples in order to follow the nucleation and subsequent growth of the crystalline phase within t h e a m o r p h o u s matrix from the earliest stages of its appearance. By analysis of the electron micrographs, the nucleation rate of the crystalline phase and the growth rate of the crystalline particles was determined. The size of particles increased linearly with time indicating an interface controlled growth. The kinetics of the transformation were analyzed in terms of Avrami's equation. The experimental data allowed the derivation of the values of AE = 4.60 ± 0.2 eV for the overall activation energy of the crystallization process, AEcr = i.i0 ± 0.05 for the activation energy of atomic motion.