ELECTRON MICROSCOPY 



lower the energy even more this extends over In other cases the interactions between 



all 4 (lll)-planes, thus forming small tetra- vacancies and dislocations produce helical 



hedra of stacking faults (Silcox and Hirsch dislocations as observed by Thomas and 



(37)), (Fig. 22). ^ATielan (38) (Fig. 23). 



,23^ 



SS78^ 



O.SfJ 



^^kem'- 



Fig. 20. Supt. : pu^cu .-lu^i^u.j; :.»...;.-. {Whelan 

 and Hirsch,^- Courtesy Philosophical Magazine) 



Fig. is. Dislocation lines traversing a twin 

 boundary {Whelan, Hirsch, Home and BoUmann,^" 

 Courtesy Royal Society) 



Fig. 19. Groups of dislocations piled up against 

 a twin boundary (Whelan, Hirsch, Home and Boll- 

 mann,^^ Courtesy Royal Society) 



Fig. 21. Dislocation loops surrounding col- 

 lapsed disks of condensed vacancies in quenched 

 aluminum. {Hirsch, Silcox, Smallman and West- 

 inacott,^^ Courtesy Philosophical Magazine^ 



302 



