The effect of long tenn exposure (to 10.8 Ms) of Zircaloy-2 to BaO, SrO, Ceo 2 , La 2 o 3 , Gd 2 o 3 , and Y 2 o 3 at 623 and 973 K has been studied. The results of room temperature tensile tests show that the specimens were severely embrittled irrespective of the oxide environment, although annealing times longer than 3.6-5.4 Ms were needed for embrittlement at 623 K. Embrittlement is due to the presence of a nonstoichiametric double oxide on the surface, which facilitates the transfer of oxygen from the oxides to the metal.-iii- . tensile tests on Zircaloy-2 specimens after long-tenn exposure to Uniax-ial tensile tests at room temperature were perfonned on -1-Zircaloy-2 flat tensile specimens (1.016 mm thickness) which had been annealed in the individual oxide powders (purity > 99.5%) at 623 and 973 K for times from 0.18 to 10.8 Ms (50-3000 hours). The degree of embrittlement was determined by comparing the results of annealing in the oxides with those on identical specimens annealed in high-purity argon, in terms of the fracture morphology and of variation of the tensile properties with the annealing parameters.Even at the low annealing temperature of 623 K the specimens were sever.ely embrittled, irrespective of the oxide environment, although annealing times longer than 3.6 .-5.4 l' -1s (1000 -1500 hours) were needed for· embrittlement to occur (Fig. 1). The specimens broke with a reduction of area of less than 5%, as compared with over 75% for the samples annealed in the argon environment. Figures 2 and 3 show typical fracture surface morphologies of specimens from argon and the oxide environment, respectively. The fracture in argon is completely ductile. This is mostly true of the specimens annealed in the oxides for times to 3.6-Ms (1000 hours)~ although some intergranular cracks can also be observed, Fig. 3a. By contrast, the fractures are completely intergranular on ±onger exposure, Fig. 3b.Since these oxides were severely embrittling to the zircaloy specimens even at 623 K, the degree of embrittlement was expected to be greater at 973 K. Hence, all annealing at 973 K was limited to a maximum of 1. 8 Ms (500 hours)~ Not surprisingly, the specimens were completely embrittled after only 0.18 Ms (50 hours) exposure. In fact, the specimens annealed in 1a 2 o 3 , Gd 2 o 3 , Y 2 o 3 , and Ceo 2 were so brittle that they broke during clamping in the tensile testing machine and no -2-v tensile tests could be performed. Fig. 4 is an example of the fracture surface of such a specimen broken by hand. It shows a bald surface, characteristic of brittle failure due to through-section embrittlement.In the case of SrO and BaO, the specimens still retain some ductility even after 1.8 MS annealing (Fig. 5), although the fracture morphology (Fig. 6) is essentially indistinguishable from the morphology on longer exposure at 623 K (Fig. 3d).These results can be explained as follows. Thennodynamicall y the sesquioxides are more stable than Zr0 2 [3], and Zircaloy-2 should not react with these oxides. By x-ray diffra...
