The analysis of dislocation networks formed in Zircaloy-4 during high temperature creep

Abstract

A TEM analysis of the Burgers vectors of hexagonal network dislocations in Zircaloy-4 crept at 800°C has shown that these networks are formed by parallel sets of predominantely screw dislocations with an 〈 a〉 type Burgers vector. These dislocations lie in intersecting 〈1010〉 prism planes, however the networks themselves form by interaction in the basal plane. The main glide system in Zircaloy-4 at 800°C is the prism system {101̄0}; 1 3 〈112̄0〉 which is also the operative system at low temperatures. Hence the networks formed in the (0001) plane are obviously non-glissile in this plane. Especially at higher temperatures however the networks can easily leave the basal plane. Mechanisms are proposed to explain the lack of edge dislocations in the crept specimens.