STP824

    Cracking Zirconium Alloys in Hydrogen

    Published: Jan 1984


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    Abstract

    We have loaded precracked double-cantilever-beam specimens of coldworked Zircaloy-2 and Zr-2.5Nb to a constant displacement in a hydrogen atmosphere at 290 to 420 K and measured the characteristics of crack propagation using optical and acoustic emission techniques. With cold-worked Zr-2.5Nb at 293 K the Stage II crack velocity, V, was almost independent of stress-intensity factor, KI, at about 3 × 10−6 m/s, between about 70 and 20 MPa√m. As KI decreased with crack extension to below 20 MPa√m, V diminished and approached zero at ≈14 MPa√m. The crack surfaces were covered with a layer of hydride up to 300 μm thick in places. The main fractographic features were cleavage typical of hydride cracking. At 350 K, the Stage II crack velocity was 2 × 10−5 m/s, and the critical value of KI remained at ≈14 MPa√m. At 420 K, only limited crack propagation at high KI-values has been observed. In the pressure range 100 to 10 kPa at 293 K, the V versus KI curves were indistinguishable but at 1 kPa cracking was difficult to initiate, once started V (in Stage II) was 1.5 × 10−6 m/s and KIH was 22 MPa√m. This apparent effect of hydrogen pressure may result from traces of contaminants, since deliberate small additions of oxygen to a 10-kPa hydrogen atmosphere stopped the cracking. Additions of helium up to 10 kPa had no effect on cracking. The implications of the results are that zirconium alloys exposed to gaseous hydrogen at room temperature will crack only if the hydrogen is very low in oxidizing impurities. If zirconium alloys are used to store tritium, then helium from transmutation will not impede tritium absorption.

    Keywords:

    Zircaloy-2, Zr-2.5Nb, cracking, hydrogen gas, stress-intensity factor, temperature, oxygen, helium


    Author Information:

    Coleman, CE
    Metallurgist, Metallurgical Engineering Branch, and head, Materials Science Branch, Atomic Energy of Canada Ltd., Chalk River Nuclear Laboratories, Chalk River, Ont.

    Cox, B
    Metallurgist, Metallurgical Engineering Branch, and head, Materials Science Branch, Atomic Energy of Canada Ltd., Chalk River Nuclear Laboratories, Chalk River, Ont.


    Paper ID: STP34501S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP34501S


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