CAVITATION AT TRIPLE NODES IN ALPHA-ZIRCONIUM POLYCRYSTALS

The damage mechanisms of alpha-zirconium polycrystals in tension at ro om temperature and their dependence on texture and grain size are inve stigated. Ductile damage proceeds by growth of cavities appearing at t riple nodes; at larger strain, other cavities nucleate at precipitate platelets. The cavitation kinetics depend on the tension direction; th ey are lower the coarser the grains. For a better understanding of the cavity formation at triple nodes, the internal stress held due to int ergranular plastic incompatibility is estimated. The mean stress exhib its a logarithmic singularity on the triple junction. By combining thi s property with some experimentally determined features of the cavity growth (tubular shape along the c axis and growth by activation of pri smatic glide), a crystallographic orientation-dependent cavitation cri terion is derived. The determination of the grains orientation by the E.B.S.D. technique leads to a satisfactory comparison of the model pre dictions with the observations.