Papers by Keyword: Zirconium-Based Alloy

Abstract: Phase transformation of the Zr-1.0Sn-0.39Nb-0.31Fe-0.05Cr alloy was investigated by high temperature X-ray diffraction (XRD). The XRD results revealed that the alloy contained two precipitates at room temperature, namely β-Nb and hexagonal Zr(Nb,Fe,Cr,)₂. β-Nb was suggested to dissolve into the α-Zr matrix at the 580oC. Thin oxide film formed at the alloy’s surface was identified as mixture of the monoclinic Zr0.93O₂ and tetragonal ZrO₂, when the temperature reached to 750oC and 850 oC. The thermal expansion coefficients of αZr in this alloy was of αa = 8.39×10^-6/°C, αc = 2.48×10^-6/°C.

Abstract: A Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5 at. %) alloy system is found to exhibit a different dependence of glass-forming ability (GFA) on atmosphere-pressure during mold casting process. High-Pd alloys (x=7.5-17.5) show a remarkable increase of critical size for glass formation (dc) as casting-atmosphere (Ar) pressure varies from vacuum to ambient. No significant change of dc, however, is observed in low-Pd alloys (x=0-5) despite the variation in atmosphere pressure. The origin of the phenomenon is unveiled by correlating the cooling characteristic during mold casting and on-cooling phase transformation characteristic of the alloy system.

Abstract: The electronic structure and phase stability of the Zr-Ni-Al ternary glassy alloys, have been systematically investigated experimentally and theoretically. Thermal stability and crystallization process have been clarified by the DSC and XRD measurements. Composition dependence of the stability parameter; Tg/Tl has been clarified. The electronic structure around the Fermi level has been investigated by using the high resolution UPS. It is found that there is a sizable pseudogap at the Fermi level of the electronic structure of the Zr65Ni20Al15 glassy alloy. The DVXα calculations for the charateristic clusters in the Zr-Ni-Al glassy alloy having high glass forming ability have been also performed. It is found that these clusters formation reduces the internal energy and can contribute to the phase stability. The LMTO-ASA band calculations for the Zr6NiAl2 compound which is the most relevant compound to the Zr60Ni25Al15 glassy alloy have been also performed. It is found that there is a sizable pseudogap at the Fermi level in its electronic structure, suggesting exiting of the pseudogap of the glassy alloy.

Abstract: Superplastic viscous deformation and thermal crystallization behavior of supercooled liquid in Zr60.0Al15.0Ni25.0 metallic glass were investigated. The temperature interval of the supercooled liquid region (∆Tx) was 83 K. The supercooled liquid showed significant viscous plasticity, resulting in large elongation and high strain rate deformation. The stress-strain behavior can be classified into three types: stress overshoot, stable viscous flow with constant flow stress and strain hardening. The strain hardening is due to the precipitation of Zr6Al2Ni crystalline phase with ellipsoidal morphology. Superplastic viscous deformation behavior is very sensitive to thermal crystallization as well as to deformation temperature and strain rate.

Abstract: As applied to tubes from Zr-based alloys, the X-ray method was developed to determine the dislocation density distribution in a-Zr depending on the orientation of Burgers vector. The method consists in registration of X-ray line profiles by each successive position of the sample in the course of diffractometric texture measurement using reflections of two orders, the following determination of coherent domain size and lattice distortion by means of the Warren-Averbach method for each orientation of reflecting planes, separate calculation of the density of c- and a-dislocations with all possible orientations of Burgers vector and presentation of results in generalized pole figures. Obtained data testify that the dislocation density varies within very wide intervals of several orders of magnitude depending on the grain orientation both in as-rolled and annealed tubes. Features of the constructed dislocation distributions are closely related to the crystallographic texture of studied tubes.