TRANS-MISSION ELECTRON MICROSCOPY OF METALS 



Fig. 22. Tetrahedra of stacking faults in 

 quenched gold. (Silcox and Hirsch,^ Courtesy 

 Philosophical Magazine) 



Some Metallurgical Topics^ Studied by 

 Trans.imssioii Electron Microscopy 



Transmission electron microscopy is now 

 used to a large extent to get a deeper insight 

 into metallm-gical effects. Here only a short 

 and incomplete hst can be given of work 

 achieved in this field. This kind of research 

 is in full development. 



Work hardening finds its explanation in 

 the networks of dislocations which hinder 

 the movement of further dislocations. As 

 the movement of dislocations means plastic 

 deformation, a hindrance of this movement 

 means increased resistance against plastic 

 deformation, i.e.. hardening. Metals with 

 high stacking fatilt energj* like almninum 

 work-harden less than those with low stack- 

 ing fault energy like stainless steel, because 

 of the possibUity of cross slip. Herein be- 

 longs a lot of work on dislocation reactions 

 (6, 10, 29). Thomas and Hale (39) investi- 

 gated the relation between surface structure 

 and underh-ing dislocations due to deforma- 

 tion. 



Quench hardening is explained by the 

 formation of dislocation loops (35, 36) or 



stacking fault tetrahedra by condensed 

 vacancies (37). The interaction of disloca- 

 tions and vacancy clusters has been dis- 

 cussed by Wilsdorf and Kuhlmann-Wilsdorf 

 (40^. 



Fatigue has been studied by Segall and 

 Partridge (41). In aluminimi dislocation 

 loops of condensed vacancies and compli- 

 cated shapes of dislocation fines were ob- 

 sen-ed which indicate the importance of 

 vacancies in this process (Fig. 24). In stain- 

 less steel (41) ven*' narrow sfip bands and 

 extrusions and mtrusions were seen. 



Obser\'ations on recovery and recrystalliza- 

 tion have been made by Fujita and Xishi- 

 jama (42), and Berghezan and Foudreux 

 (43) on alununum by Saulnier and Develaj'' 

 on titanium (44\ b^' Bollmann (45) on 

 nickel (Fig. 25) and by Bailey (46) on silver. 

 These studies have given an insight into the 

 poly gonizat ion and the formation of new 

 cri'stal grains in hea\ily rolled material as 

 well as into recr\'stalfization bv the move- 



...«gt 



'^^ 



I 



.^€ 



Fig. 23. Helical dislocations produced by the 

 condensation of vacancies on dislocation lines. 

 {Thomas and Whelan,^ Courtesy Philosophical 

 Magazine) 



303 



