Papers by Keyword: Zr-Based Alloy

Abstract: Texture and substructure changes in cladding tubes from Zr-based alloys under neutron irradiation in the atomic reactor during 6 years were investigated by use of X-ray methods. For this aim in the “hot” laboratory the automated X-ray diffractometer was set and the technique to handle with irradiated samples was elaborated. The residual radiation activity of samples correlates with integral texture Kearns parameters of tube, so that the texture weakens as the doze of neutron irradiation grows. Because of the initial substructure inhomogeneity of cladding tubes its changes under neutron irradiation are also inhomogeneous: relatively perfect grains of texture maxima become more distorted, whereas initially distorted grains of texture minima becomes more perfect.

Abstract: In order to investigate flip-flop transitions of shear transformation zones (STZs) which are believed to be the elementary deformation sites in metallic glasses, internal friction measurements have been conducted for a commercial bulk metallic glass of a Zr-based alloy (Johnson alloy). Since the STZ is an asymmetrical two-level system, it is necessary to measure the internal friction at a high amplitude or under a bias stress condition to detect the transitions. Measurements have been made at temperatures between 130 K and 573 K at frequencies between 0.1 Hz to 10 Hz. The results showed that quite a broad peak appears between 200 K and 500 K in high amplitude internal friction measurements. The broad peak, observed for the first time in metallic glass, is interpreted to be due to flip-flop transitions of STZs having a broad spectrum, 0.5∼1.2 eV, of the activation enthalpy.

Abstract: Features of the deformation process by cold radial forging of tube billets from Zr-1%Nb alloy were reconstructed on the basis of X-ray texture data. The cold radial forging intensifies grain fragmentation in the bulk of billet and increases significantly the latent hardening of potentially active slip systems, so that operation only of the single slip system becomes possible. As a result, in radially-forged billets unusual deformation and recrystallization textures arise, differing from usual textures of a-Zr by the mutual inversion of crystallographic axes, aligned along the axis of tube.

Abstract: Deformation behavior of Zr-based alloys by forging under conditions of α↔β phase transformations was considered as applied to model samples and real semi-products. Model samples were deformed by uniaxial compression at temperatures of β- and (α+β)-regions of the phase diagram Zr-Nb. Mechanisms, responsible for plastic deformation of alloys by different temperature-rate regimes, were determined on the basis of textures, arising in deformed samples. Among these mechanisms there are crystallographic slip in grains of β-Zr and α-Zr as well as mutual displace¬ments of crystallites along interphase boundaries. The latter mechanism sharply intensifies under conditions of α«β phase transformations and lies in the basis of superplasticity. An input of each mechanism into plastic deformation of material depends on the temperature-rate regime of compression and determines its anisotropy.

Abstract: New Ti-based and Zr-based metallic wires for the future application as biomaterials were developed by arc-melting type melt-extraction method. Zr-based metallic glass wire, -Ti type Ti-Zr binary wire and -Ti type Ti-Nb-Ta-Zr (TNTZ) wire show high tensile strength and good vending ductility. Zr-based metallic glass wire shows extremely high tensile strength over 1GPa and large elastic strain limit reached approximately 2%. Ti-Zr binary alloy shows high wire-shape forming tendency during melt-extraction, and high Ti concentration Ti90Zr10 alloy wire was obtained. TNTZ wire shows superior bending ductility and full ductility is achieved.

Abstract: In Zr-Cu-Ni-Al bulk metallic glasses where there are no dislocations, localized plastic deformation in shear bands occurs largely by the formation and migration of defects such as voids, micropores, shear bands and local variations in composition. Thus, the investigation on defects is critical for the understanding and improvement of plastic deformation in metallic glasses. In this study, microstructures and nano defects in the Zr-Cu-Ni-Al BMGs are characterized by variety of techniques, such as X-ray diffractometry, high resolution transmission electron microscopy, scanning transmission electron microscopy and electron holography.

Abstract: Distinctive structure features of rods produced by hot and cold radial forging of a Zr- 2.5%Nb alloy were revealed. Most experimental data were obtained by X-ray methods. Among considered aspects, connected with the undulatory mechanism of energy transfer, there are the uniformity of bulk deformation, structure perfection under hot radial forging, the demolition of secondary phases and the oversaturation of α-Zr with Nb under cold radial forging, the role of phase transformations in deformation, and the suppression of recrystallization by annealing. Structure, texture and properties of products, produced by radial forging from Zr-based alloys, allow to consider this technology as an acceptable alternative to that usable nowadays.

Abstract: Zircaloy is commonly applied as structural element in nuclear reactors owing to the gamma radiation transparency of Zr. One of the research interests in Zr-Nb alloys is related to its behavior in H2O-rich environments due to hydrogen embrittlement. In the present work the microstructural evolution (crystallite size and microhardness), crystallography and hydrogenation behavior (after milling) due to mechanical alloying (MA) are studied for the Zr-Nb5%at and pure Zr. The MA study of Zr and the Zr-Nb system showed that frequency of rotation in a planetary mill and alloy composition play a major role on the evolution of crystallite size and microhardness. Nb addition was found to induce a partial allotropic transformation of the Zr structure (α→ω) during MA. Indeed, for milling experiments with significant Fe contamination the formation of an fcc phase was observed. Further, MA for extended times (over 5 hours) was found to reduce the hydrogen absorption capacity of Zr and the Zr-Nb system studied.

Abstract: Zr62Cu17Ni13Al8 in the supercooled liquid state is expected to be micro-formable at a relatively low stress. We used X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and quantitative high-resolution TEM (HRTEM) to investigate the microstructures of Zr62Cu17Ni13Al8 amorphous alloy after compression test. The alloy exhibited the homogeneous amorphous microstructure with some crystalline phases dispersed in the matrix. According to the XRD results, under the certain strain rate in the supercooled liquid state, the alloy showed higher crystallization at the higher heat treatment temperature. However, at the same heat treatment temperature, the alloy deformed under low strain rate showed higher crystallization. The β crystalline phase particles with spherical shape were detected by SEM and TEM. The sample with higher strain rate and temperature showed longer shear bands. Nano-voids formed by the coalescence of excess free volume in shear bands were investigated by quantitative HRTEM. Compared with the undeformed area, in the shear band, nanovoids were identified in the deformed area through quantitative HRTEM simulation.