Creep behavior of niobium-modified zirconium alloys

Charit, Indrajit; Murty, K. Linga

doi:10.1016/j.jnucmat.2007.08.019

Cited by 86 publications

(29 citation statements)

References 33 publications

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“…The activation energy estimated for regimes II and III is somewhat lesser than the activation energy for lattice self-diffusion for a-Zr determined by radioactive tracer experiments, which is 259 kJ/mol. [32] However, the value is comparable to the lattice diffusion activation energies of 213 kJ/mol and 234 kJ/mol obtained from creep experiments in Zr-1 pctNb alloys by Voeikov et al [3] and Alymov et al [17] , respectively. Further, the creep data are presented as the plot of the steady-state creep rates normalized by the lattice diffusivity…”

Section: Resultssupporting

confidence: 64%

“…In fact, the creep deformation of several Nb-added Zircaloys in n = 3 regime has been ascribed to dislocation glide-controlled mechanism arising from locking of gliding dislocations by niobium solute atoms, [3] which was as well validated by TEM micrographs revealing uniform distribution of dislocations in grain interior. Although the deformation microstructures of HANA-4 in regime II showed dislocations presented throughout the matrix, it is quite evident from the micrographs that those dislocations were pinned at the precipitates (Figure 13(a)).…”

Section: B Rate-controlling Mechanism In Regime IImentioning

confidence: 85%

“…As the applied stress becomes larger than a critical stress of about 7:5 Â 10 À4 E, which is sufficient to break away the dislocations bounded by the niobium solutes, [20] the creep deformation of Zr-Nb alloys was postulated to be controlled by dislocation climb, which is now the slower process between glide and climb acting sequentially. In this regime, the crept microstructures revealing subgrains bounded by dislocations [16] and dislocation networks [3] in TEM micrographs were ascribed to the occurrence of dislocation climb-controlled process. In addition, the activation energies determined for n = 3 and n = 5 to 7 regimes were found to be close to the lattice self-diffusion activation energy in a-Zr, since both glide and climb are controlled by solute atom diffusion and self-diffusion that are noted to have similar activation energies.…”

Section: Introductionmentioning

confidence: 99%

“…One such attempt toward realizing this goal was to add Niobium to Zircaloys for achieving an improved long-term corrosion resistance and mechanical properties without losing the neutron absorption characteristics, the attributes which are generally ascribed to the distribution of b-Nb precipitates in the microstructure. [3,4] For instance, Zr-2.5 pctNb pressure tubes are currently used in pressurized heavy water reactors (PHWR). As well, Nb-modified Zr cladding alloys such as Zirlo and M5 have been developed in USA and Europe for applications in modern PWRs.…”

Section: Introductionmentioning

confidence: 99%

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Coble, Orowan Strengthening, and Dislocation Climb Mechanisms in a Nb-Modified Zircaloy Cladding

Kombaiah

Murty

2015

Metall Mater Trans A

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BOOPATHY KOMBAIAH and KORUKONDA LINGA MURTYBiaxial creep tests on HANA-4 tubes, Nb-added Zircaloy-4 were conducted using internal pressurization of closed-end tubes to investigate the rate-controlling mechanisms over a range of hoop stresses, 8:38 Â 10 À5 E À 2:87 Â 10 À3 E, at three different temperatures 673 K, 723 K, and 773 K (400°C, 450°C, and 500°C). The mechanistic creep parameters such as stress exponent (n) and activation energy (Q C ) were then determined from steady-state creep rates. Based on the variance in stress exponent with respect to the applied stress, three regimes have been identified: a stress exponent close to 1 at low stresses that increased to 3 at the intermediate stresses, which became 4.5 at high stresses. An activation energy value of 226 kJ/mol was evaluated for the n = 3 and n = 4.5 regimes, which lies close to the activation energy for self-diffusion (Q L ) in a-Zr alloys. Further, TEM analyses of crept microstructures and comparison of experimental results with standard models were undertaken to find out the rate-controlling mechanisms. Coble creep, climbing of dislocations to bypass b-Nb precipitates, and dynamic recovery by edge dislocation climb are proposed as the rate-controlling mechanisms in the n = 1, n = 3, and n = 4.5 regimes of HANA-4, respectively.

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Section: Resultssupporting

confidence: 64%

Section: B Rate-controlling Mechanism In Regime IImentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Coble, Orowan Strengthening, and Dislocation Climb Mechanisms in a Nb-Modified Zircaloy Cladding

Kombaiah

Murty

2015

Metall Mater Trans A

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“…The broken lines denote the prediction for the ECAP processed material. Diusion data for computations of NH creep rates were taken from dierent reports [7] and [17].…”

Section: The Rate Controlling Creep Deformation Mechanism Inmentioning

confidence: 99%

Creep Behavior of a Zirconium Alloy Processed by Equal-Channel Angular Pressing

et al. 2012

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A Zr2.5 wt%Nb alloy was processed by equal-channel angular pressing and then tested under creep conditions at 623 K using a tensile stress within the range from 120 to 300 MPa. The results show conventional power-law creep with a stress exponent of n > 3 which is consistent with an intragranular dislocation process involving the glide and climb of dislocations. It is demonstrated that diusion creep is not important in these tests. For comparison purposes, the experiments were conducted using both the unprocessed alloy and after processing by equal-channel angular pressing. It was found that under same testing conditions the measured minimum creep rates in the pressed alloy with ultrane grain sizes were faster than in the same alloy in a coarse-grained unprocessed condition.

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