Abstract
The mechanism of embrittlement at Ta/Zr diffusion bonded interface was clarified by employing Zr-Ta binary alloys which were synthesized the bonding interface region between Ta and Zr. Zr-3 mass%Ta, Zr-10 mass%Ta and Zr-20 mass% Ta binary alloys were used for the hardness test and microstructural analyses after solution and/or annealing treatments. The hardness of Zr-Ta alloys increased quickly with increasing the annealing time at the early stage of aging and fell down after long term aging. TEM observation revealed that α'-(Zr, Ta) supersaturation solid solution (martensite) was formed in as solution treated specimens, and that Ta and ω-Zr were precipitated in the aged specimens. The hardening of Zr-Ta alloys at the early stage of aging was due to the precipitation of Ta and ω-Zr from the ω' martensite, and the overaging was subsequently occurred with coarsening the Ta precipitates. It was deduced that the precipitation of Ta which was attributable to the spinodal decomposition of supersaturation solid solution of Zr, and that Ta was the main cause of embrittlement at Ta-Zr diffusion bonded interface.
