The transformation behaviour of the β-phase in Zr–2.5Nb pressure tubes

Griffiths, M.; Winegar, J.E.; Buyers, A.G.

doi:10.1016/j.jnucmat.2008.08.003

Cited by 72 publications

(48 citation statements)

References 13 publications

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“…The outcomes of this investigation are consistent with earlier thermal expansion experiments and time-temperature transformation curves recently determined for Zr-2.5Nb nuclear reactor pressure tubes by using X-ray diffraction analysis. [3] In Situ AnalysisThe initial Zr-2.5Nb material is presented in Figure 2, revealing a typical fine microstrucure, composed of laths of a-phase interfacing with very fine filaments of b-phase regions between the matrix of the a phase.While undergoing heat treatments, in situ neutron diffraction tests were conducted on both the high-intensity powder diffractometer Wombat [4] and the high-resolution powder diffractometer Echidna [5] at ANSTO. Details of the sample preparation and the measurements are given further down in the Experimental Section.…”

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confidence: 99%

In Situ Characterization of Lattice Structure Evolution during Phase Transformation of Zr‐2.5Nb

et al. 2011

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As an important nuclear reactor material, Zr-2.5Nb (all concentrations in mass%, unless otherwise stated) has a low neutron absorption cross-section, high corrosion resistance, and high strength and creep resistance. [1] The phase diagram of the binary system is shown in Figure 1. [2] In thermodynamic equilibrium at room temperature it consists of a-Zr phase (hcp) and b-Nb phase (bcc), while a-Zr and Zr-rich, b-Zr(Nb) co-exist between the eutectoid temperature of T eu ¼ 893 K and the solvus temperature of T b ¼ 1 087 K in Zr-2.5Nb. A b-phase solid solution is stable above T b . The alloy has been studied widely, considering aspects of the chemistry, texture and morphology of the microstructure following different heat treatments, high temperature deformation as well as variant selection during phase transformation. However, the underlying crystal properties such as the lattice parameters and thermal expansion of the different phases during the phase transformations, have not been determined in situ and in real time.In the current study, a high-intensity neutron diffractometer in combination with a vacuum furnace has been used to determine for the first time, the crystalline properties of a Zr-2.5Nb alloy in situ during the a-b phase transformation. By combining thermal expansion and Vegard's law in a novel approach, the phase transformations and the diffusion of alloying elements can be tracked and the results compared to the phase diagram. The outcomes of this investigation are consistent with earlier thermal expansion experiments and time-temperature transformation curves recently determined for Zr-2.5Nb nuclear reactor pressure tubes by using X-ray diffraction analysis. [3] In Situ AnalysisThe initial Zr-2.5Nb material is presented in Figure 2, revealing a typical fine microstrucure, composed of laths of a-phase interfacing with very fine filaments of b-phase regions between the matrix of the a phase.While undergoing heat treatments, in situ neutron diffraction tests were conducted on both the high-intensity powder diffractometer Wombat [4] and the high-resolution powder diffractometer Echidna [5] at ANSTO. Details of the sample preparation and the measurements are given further down in the Experimental Section. ResultsA diffraction pattern obtained at room temperature is shown at the top of Figure 3. In addition to the majority of a-Zr phase, the pattern reveals a relatively large amount of retained b-Zr(Nb) phase of eutectoid composition and a small amount of b-Nb rich phase with lattice parameters of a ¼ 3.4361 and 3.3016 Å , respectively.The bottom part of Figure 3 shows a stacked sequence of such individual diffraction patterns. Temperature is shown on the vertical axis and the diffraction intensity is indicated by grayscale values. It follows that the amount of the b-Zr(Nb) phase starts to increase above T eu ¼ 893 K while the a-Zr phase vanishes totally at 1133 K, which is 46 K above T b . We attribute this sluggish behavior to the kinetics of the displace character COMMUNICATIONThe a-b phase transforma...

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In Situ Characterization of Lattice Structure Evolution during Phase Transformation of Zr‐2.5Nb

et al. 2011

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“…The surrounding beta-phase remnants may become highly enriched in Nb (>90 wt%) given high enough temperature and long enough time. The original beta-phase filaments would therefore evolve with time into a discontinuous alpha/beta interface between the alpha grains [43]. Decomposition is therefore synonymous with reduction of beta-phase filament continuity.…”

Section: Alpha-phase Line Broadeningmentioning

confidence: 99%

“…One indicator of the degree of beta-phase decomposition (or relative loss of continuity within the original beta-phase filaments) would be the enrichment of Nb in the beta-phase. This enrichment can be quantified with X-ray diffraction from the body-centred cubic lattice parameter of the betaphase [8,15,43]. The %Nb values are derived from either RN or LN reflections and may not be identical although the %Nb concentration must be.…”

Section: Alpha-phase Line Broadeningmentioning

confidence: 99%

Performance of Pressure Tubes in Candu Reactors

et al. 2016

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The pressure tubes in CANDU reactors typically operate for times up to about 30 years prior to refurbishment. The in-reactor performance of Zr-2.5Nb pressure tubes has been evaluated by sampling and periodic inspection. This paper describes the behavior and discusses the factors controlling the behaviour of these components. The Zr–2.5Nb pressure tubes are nominally extruded at 815 °C, cold worked nominally 27%, and stress relieved at 400 °C for 24 hours, resulting in a structure consisting of elongated grains of hexagonal close-packed alpha-Zr, partially surrounded by a thin network of filaments of body-centred-cubic beta-Zr. These beta-Zr filaments are meta-stable and contain about 20% Nb after extrusion. The stress-relief treatment results in partial decomposition of the beta-Zr filaments with the formation of hexagonal close-packed alpha-phase particles that are low in Nb, surrounded by a Nb-enriched beta-Zr matrix. The material properties of pressure tubes are determined by variations in alpha-phase texture, alpha-phase grain structure, network dislocation density, beta-phase decomposition, and impurity concentration that are a function of manufacturing variables. The pressure tubes operate at temperatures between 250 °C and 310 °C with coolant pressures up to about 11 MPa in fast neutron fluxes up to 4 × 1017 n·m−2·s−1 (E > 1 MeV) and the properties are modified by these conditions. The properties of the pressure tubes in an operating reactor are therefore a function of both manufacturing and operating condition variables. The ultimate tensile strength, fracture toughness, and delayed hydride-cracking properties (velocity (V) and threshold stress intensity factor (KIH)) change with irradiation, but all reach a nearly limiting value at a fluence of less than 1025 n·m−2 (E > 1 MeV). At this point the ultimate tensile strength is raised about 200 MPa, toughness is reduced by about 50%, V increases by about a factor of 6, while KIH is only slightly reduced. The role of microstructure and trace elements in these behaviours is described. Pressure tubes exhibit elongation, diametral expansion, and sag. The deformation behaviour is a function of operating conditions and the material properties that vary from tube-to-tube and as a function of axial location. Semi-empirical predictive models have been developed to describe the deformation response of average tubes as a function of operating conditions. The effect of material variability on corrosion behaviour is less well defined compared with other properties but there are instances where tube orientation and ingot source can be identified as factors that have an effect on hydrogen pick-up.

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“…The starting sample of Zr-2.5 Nb alloy consisted of elongated grains of hexagonal-close packed α-Zr, partially surrounded by a thin network of filaments of bodycentered-cubic β-Zr [7]. The microstructure of as deformed samples could not be revealed in OIM due to poor indexing of the deformed microstructure.…”

Section: Microstructure Of Recrystallized Samplesmentioning

confidence: 99%

“…This could be further Nb enrichment of β phase to the values where formation of martensite is not possible. On continuation of annealing to 14 days Nb enrichment was in the range of 8-10% [7] which on subsequent quenching resulted in formation of ω phase. The S-parameter data is shown in Fig.…”

Section: Positron Spectroscopy Of Recrystallized Samplesmentioning

confidence: 99%

Positron annihilation study of recrystallization behaviour in Zr2.5%Nb alloy

Mulki

Pujari

Srivastava

et al. 2009

Phys. Status Solidi (c)

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George Wang and co‐workers report that low dislocation density a‐plane GaN films can be grown by the coalescence of vertically‐aligned, single‐crystalline GaN nanowires on lattice‐mismatched r‐plane sapphire. In this technique, shown by the artists' rendering on the inside cover, the nanowires facilitate dramatic strain relaxation in the suspended GaN film, leading to a large reduction in defects.

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The transformation behaviour of the β-phase in Zr–2.5Nb pressure tubes

Cited by 72 publications

References 13 publications

In Situ Characterization of Lattice Structure Evolution during Phase Transformation of Zr‐2.5Nb

In Situ Characterization of Lattice Structure Evolution during Phase Transformation of Zr‐2.5Nb

Performance of Pressure Tubes in Candu Reactors

Positron annihilation study of recrystallization behaviour in Zr2.5%Nb alloy

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