EFFECT OF CARBIDES ON THE HYDRIDING AND OXIDATION BEHAVIOR OF A ZR-2.5NB ALLOY

The surface carbide layer, interior chain-like carbide arrangements an d the carbide/matrix interfaces present in an initial Zr-2.5Nb alloy w ere studied in hydriding and oxidation experiments. Hydriding performe d by cathodic charge in 0.1 M H2SO4 solution showed that neither the i nner carbide chains nor the corresponding interfaces offered short cir cuit paths for hydrogen diffusion, while the surface carbide layer act ed as a protective layer. The oxidation tests performed in autoclaves during 24 h in deaerated steam at 400-degrees-C and 105 bar showed wei ght gains higher than one order of magnitude with respect to the sampl es free of carbides. The surface carbides promoted the accelerated oxi dation of the surrounding matrix and were stripped during the experime nts. Evidence was found of the oxidation of the inner carbides, probab ly due to the transformation strain energy produced by the former oxid ation of the surrounding matrix. Moreover, the carbide/matrix interfac es acted as short circuit paths for oxygen diffusion.