STP1023

    Effects of Loading and Thermal Maneuvers on Delayed Hydride Cracking in Zr-2.5 Nb Alloys

    Published: Jan 1989


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    Abstract

    Delayed hydride crack velocities in Zr-2.5 wt% Nb alloys with different ther-momechanical treatments were measured. Materials with higher strength have higher crack velocity, and the stepwise crack propagation occurred by smaller increments associated with a smaller zone of crack tip hydrides. A series of load reduction experiments were performed on specimens with an active delayed hydride crack. An incubation period was required for the specimen to resume cracking after reducing the applied K to a level still significantly above the threshold stress intensity factor K 1H. The length of the incubation period depended on the amount of K reduction, material strength, temperature, and the final K in which cracking occurred. Crack velocity increases with the amount of hydrogen in solution in the matrix. Crack velocity increased as a function of the peak temperature reached in the initial cooldown thermal cycle. There is hysteresis in hydride solubility which results in different levels of hydrogen in solution depending upon the thermal history. The implication of this in terms of crack velocity is discussed.

    Keywords:

    zirconium alloys, delayed hydride cracking, crack velocity, strength, thermal history, loading history, striations


    Author Information:

    Shek, GK
    Metallurgical engineer and technical supervisor, Ontario Hydro, Toronto, Ontario

    Graham, DB
    Metallurgical engineer and technical supervisor, Ontario Hydro, Toronto, Ontario


    Paper ID: STP18859S

    Committee/Subcommittee: B10.05

    DOI: 10.1520/STP18859S


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