SYMPOSIA PAPER Published: 01 January 1989

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


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.

Author Information

Shek, GK
Ontario Hydro, Toronto, Ontario, Canada
Graham, DB
Ontario Hydro, Toronto, Ontario, Canada
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Developed by Committee: B10
Pages: 89–110
DOI: 10.1520/STP18859S
ISBN-EB: 978-0-8031-5084-3
ISBN-13: 978-0-8031-1199-8