Abstract
Fracture properties of micro-scale zirconium hydrides and phase boundaries were studied using microcantilever testing methods. FIB-machined microcantilevers were milled on cross-sectional surfaces of hydrided samples, with the most highly-stressed regions within the δ-hydride film, within the α-Zr or along the Zr-hydride interface. Cantilevers were notched using the FIB and then tested in bending using a nanoindenter. Load-displacement results show that three types of cantilevers have distinct deformation properties. Zr cantilevers deformed plastically. Hydride cantilevers fractured after a small amount of plastic flow; the fracture toughness of the δ-hydride was found to be 3.3 ± 0.4 MPam1/2 and SEM examination showed transgranular cleavage on the fracture surfaces. Cantilevers notched at the Zr-hydride interface developed interfacial voids during loading, at loads considerably lower than that which initiate brittle fracture of hydrides.
Highlights
Zirconium alloys are widely used as nuclear fuel cladding materials mainly because of their low neutron absorption crosssection; hydrogen formed as a product of waterside corrosion can lead to embrittlement [1]
The local stress which initiates the brittle fracture of hydride precipitates is a key input parameter to models of delayed hydride cracking (DHC) [5e7]
Fracture toughness measurements on 3.5 mm thick compact tension Zr hydride specimens obtained a value of about 1 MPam1/2 and transgranular cleavage was observed on the d-hydride fracture surfaces [8]
Summary
Zirconium alloys are widely used as nuclear fuel cladding materials mainly because of their low neutron absorption crosssection; hydrogen formed as a product of waterside corrosion can lead to embrittlement [1]. Hydrogen diffuses into the claddings to form polycrystalline zirconium hydrides when the concentration exceeds the solubility limit. Fracture toughness measurements on 3.5 mm thick compact tension Zr hydride specimens obtained a value of about 1 MPam1/2 and transgranular cleavage was observed on the d-hydride fracture surfaces [8]. These tests are on large-scale “bulk” hydrides, rather than the micron to ~100 micronescale precipitates involved in DHC. Direct loading tests on micro-scale crack-free hydrides should provide data more applicable to investigating DHC behaviour
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