Abstract
The phase transformation at Ta/Zr interface in the diffusion or explosive bonded joint was clarified by employing Zr-Ta binary alloys which were synthesized the bonding interface region between Ta and Zr. Zr-10 mass%Ta and Zr-20 mass%Ta binary alloys were used for the hardness test and microstructural analyses after Formastor-testing and laser surface melting. The cooling rates of Zr-Ta alloys were varied from 0.1 (furnace cooling) to 5.3×105 K/s (laser treating). TEM observation and X-ray diffraction analyses revealed that Ta and α-Zr were identified at the cooling rates up to about 10 K/s, and that ω-Zr as well as Ta was precipitated at the cooling rates between about 100 and 104 K/s. The rapidly cooled alloys (cooling rate exceeded about 105 K/s) were transformed to the single phase of α'-(Zr, Ta) supersaturation solid solution (martensite). The hardness of Zr-Ta alloys indicated the highest value on the condition that both Ta and ω-Zr were precipitated. It could be concluded that the severe embrittlement at Ta/Zr explosive bonded interface was due to the precipitation of Ta and w-Zr attended with the phase transformation in Zr-Ta system.
