Electron Transmission Through Thin Metal Sections with Appli- 

 cation to Self-Recovery in Cold Worked Aluminum 



By R. D. HEIDENREICH 



Features of the dynamical or wave mechanical theory of electron diffraction 

 pertinent to the interpretation of electron images of crystalline materials are 

 briefly discussed. It is shown that the type of image obtained depends upon the 

 local bending of the crystal, the coherent crystal size and the state of internal 

 strain. The absence of extinction contours seen in annealed aluminum is an 

 indication of the presence of internal strains. 



New data concerning the effect of temperature on the polygon or domain 

 size in cold worked aluminum is presented. These data indicate that self re- 

 covery occurs rapidly at temperatures as low as — 196°C leading to the con- 

 clusion that the process must have a low activation energy. The mechanism 

 by which dislocations leave the slip bands and redistribute and annihilate them- 

 selves during recovery is obscure. 



Introduction 



DIRECT experimental evidence for the wave nature of the electron 

 first demonstrated by Davisson and Germer was based on a prop- 

 erty unique to wave phenomena; namely, interference or diffraction. The 

 ability of a regular or periodic array of atoms to diffract electrons (just 

 as a ruled grating diffracts light) has led to the construction of quite general 

 theories of the behavior of matter, the band theory of solids being a notable 

 example. The forbidden energy zones in a crystal are simply a result of 

 diffraction of the valence electrons by the periodic structure. On the other 

 hand, the results of straight forward diffraction experiments are a conse- 

 quence of the zone or band structure of the crystal thus illustrating an 

 interesting closure or completion of the cycle. 



This paper is concerned with the interpretation of electron interference 

 phenomena occurring in thin metal sections particularly as it pertains to 

 structural changes accompanying plastic deformation. Diffraction effects 

 are observed not only in the usual electron diffraction methods but in 

 electron microscope images as well. The chief difference is that in the former 

 the diffracted rays are of primary interest while in the latter the regions of 

 the crystal in which diffraction occurs are imaged with the diffracted beams 

 removed by the objective aperture. Electron microscope images of crystalline 

 materials thus offer a high resolution method of studying variations in dif- 

 fracting power. This information can then be interpreted in terms of struc- 

 tural features. 



The structural changes accompanying plastic deformation of metals are 

 of great interest and can be profitably investigated by electron interference 



867 



