SUSCEPTIBILITY OF ZIRCONIUM AND ZIRCONIUM ALLOYS TO DELAYED FAILURE HYDROGEN EMBRITTLEMENT

The susceptibility of zirconium and certain zirconium alloys to delayed failure (static fatigue), as caused by a combination of absorbed hydrogen and applied stress, was determined. Specimens of unalloyed zirconium, Zircaloy-2, Zr- - 1.25 Al--1 Sn--l Mo, and Zr--2.5 Nb were hydrogenated in a Sieverts apparatus and evaluated in static tests at room temperature. For unnotched and notched specimens of unalloyed zirconium and Zircaloy-2 containing up to 500 ppm hydrogen, no time-dependent, brittle frictures occurred that could be attributed to the delayed failure phenomenon. The high-strength Zr--Al--Sn--Mo alloy with 500 ppm hydrogen, however, exhibited a high degree of susceptibility to delayed failure at room temperature. Data for heat treated Zr--2.5 Nb containing 500 ppm hydrogen indicated that this material is moderately susceptible to delayed failure. The results are explained in terms of dislocation pile-up at hydride platelets and the ability of these matrices to allow crack propagation. (auth)