The influence of oxide coatings on the ductility of zircaloy-4

In the upper range of the α-phase field, ZrO2 coatings on zircaloy substantially increase the ductility of tensile as well as of tube specimens. The increase in ductility is accompanied by a reduction in cavitation which is responsible for internal necking. The protective influence of the oxide layer against cavitation is most effective when plastic deformation occurs in an oxidizing environment. This unexpected influence of oxidation upon ductility results from the fact that cavitation can be suppressed by an isostatic pressure which is superimposed on the tensile stress. As follows from the model for a single fibre composite in the present case a compressive stress component can result when the composite zircaloy/ZrO2 is elastically strained. This depends essentially on the difference in the respective Poisson's ratios for both the components. (Auth.)