Pyramidal glide and the formation and climb of dislocation loops in nearly perfect zinc crystals

Abstract

Abstract Zinc whiskers and platelets with a (0001) orientation and thin enough (≲ 1/2 μ) to be transparent to 100 kv electrons were deformed in tension inside the electron microscope and the motion of individual dislocations followed by the transmission technique. These observations were then related to the macroscopic properties as determined by stress–strain curves. The crystals, which were found to be initially free of dislocations, deformed mainly by twinning (which is not considered here) or by pyramidal glide on the (1122) [1 123] system. Dislocations with three types of Burgers vectors were produced: long 〈1 120〉 dislocations which were easily immobilized and contributed very little to the deformation; short 〈1 123〉 screw dislocations which caused pyramidal glide and sometimes left behind long, narrow 〈1 123〉 loops which then split up into circular loops with the same Burgers vector; and circular 〈0001〉 loops which were formed from 〈1 123〉 loops by the reaction 1/3〈1 123〉 → 1/3〈1 120〉 +〈0001〉. Both types of loops were sessile but disappeared by climb at room temperature at a rate which agreed with the predicted rate. The loops impeded the motion of dislocations and were responsible for the propagation of glide as a Lüders band.