Thermal creep fracture of a Zr1%Nb cladding alloy in the α and ( α+ β) phase regions

0542530 - ÚFM 2022 RIV NL eng J - Journal Article
Sklenička, Václav - Král, Petr - Kuchařová, Květa - Kvapilová, Marie - Dvořák, Jiří - Kloc, Luboš
Thermal creep fracture of a Zr1%Nb cladding alloy in the α and ( α+ β) phase regions.
Journal of Nuclear Materials. Roč. 553, SEP (2021), č. článku 152950. ISSN 0022-3115. E-ISSN 1873-4820
R&D Projects: GA TA ČR(CZ) TH02020477
Institutional support: RVO:68081723
Keywords : advanced Zr1%Nb cladding alloy * creep in tension * mechanisms of creep deformation * microstructure evolution * LOCA situation
OECD category: Materials engineering
Impact factor: 3.555, year: 2021
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S0022311521001732?via%3Dihub

The objective of the present study was to provide new relevant information on creep behaviour and fracture processes in a sponge-based modified Zr1%Nb cladding alloy (modified E110 alloy) in the α-Zr and (α+β)-Zr phase regions. To this end, constant load creep tests were carried out in argon at testing temperature intervals from 350°C to 950°C, and applied tensile stresses ranging from 5 MPa to 210 MPa, corresponding to the power-law breakdown creep regime and/or high testing temperatures, and thus to simulate disaster conditions. Creep tests were followed by
metallographic and fractographic analyses of the specimens to explain the observed creep behaviour. It was found that in the power-law region (at 350°C) the values of the stress
exponent n of the minimum creep rate ε˙ m (n = ∂lnε˙ m /∂lnσ )T , and the stress exponent m of the time to fracture tf (m = - ∂lntf /∂lnσ )T, were very high and near to each other, indicating a
close relationship between creep deformation and fracture. Further support for the idea that creep deformation and fracture are interconnected can be observed by the validity of the em-
pirical Monkman-Grant relationship. Creep tests in the α-Zr phase region revealed creep cavitation near to, and at, the fracture surface. The final fracture is a ductile dimple mode with the
synergistic effect of creep cavitation. By contrast, the final fracture in the (α+β)-Zr phase region is caused by a local strain- induced instability of the matrix leading to a loss of an external
section of specimen (necking). There is a marked difference between the values of the strain to fracture εf . In the α-Zr region, typical values of εf ~ 0.3-0.5 were found, whereas for the
(α+β)-Zr region, the value εf increases with testing temperature up to 850°C. Following drop of εf at temperatures ≥ 900°C was explain by intensive oxidation of the alloy.

Permanent Link: http://hdl.handle.net/11104/0321709