Dislocations in Stainless Steel 



W. BOLLMANN 



Battelle Memorial Institute, Geneva 



The first experiments on the study of metals by 

 electron microscopy in transmission were under- 

 taken by Heidenreich (5) on aluminium- and alu- 

 minium-4 ",, copper alloy; he mainly investigated 

 cold working and the formation of precipitates using 

 an electropolishing technique for the preparation of 

 the specimen. In the same paper, this author gives 

 a theory on some diffraction effects occurring in the 

 electron microscopy of thin crystal foils. 



Castaing (3) used, in addition to the electro- 

 polishing, an ion bombardment for the preparation 

 of transparent specimens of the same metals as 

 studied by Heidenreich. 



The present work was undertaken with the aim 

 of studying creep in certain austenitic temperature- 

 resistant steels. To develop the preparation technique, 

 (18 %) chrome- (8 %) nickel-steel was chosen. 



The raw specimen, a circular disc (2 cm diameter, 

 0.2 mm thick) insulated around the edge with varnish 

 was attacked electrolytically from both sides. Thecathodes 

 consisted of pointed electrodes which were insulated 

 except for the points. At the start the electrodes were 

 placed at a distance of 1-2 mm from the disc and the 

 attack was continued up to the moment when a central 

 hole appeared. Then the cathodes were placed at about 

 1 cm from the specimen. Under these conditions, the 



specimen was preferentially attacked near the insulated 

 edge and there a second hole opened. The attack was 

 continued until the space between the two holes was 

 about 1 mm. Then the current was applied in pulses up 

 to the moment when the two holes joined. In that region 

 the specimen showed fairly large areas which could be 

 observed by transmission. 



The electrolytic solution consisted of 40 °o sulfuric and 

 60 °o orthophosphoric acid. The current applied was 

 about 3 amp. 



Much attention had to be paid to the cleaning of the 

 specimen; it was rinsed as soon as possible, first in hot 

 running water, then in a hot sequestrol solution in order 

 to dissolve all the salts and finally in hot distilled water. 



ExperiiiK'itts with ion hoiiihardmetit. — Some experi- 

 ments were undertaken to apply the method of 

 Castaing (3) on stainless-steel specimens. In the 

 first trials the ion bombardment was applied through 

 a small ion gun (ca. 1 //A 1500 Volt). The ions of air 

 and of pure nitrogen produced a strong corrosion of 

 the specimen; so the experiments were continued with 

 argon. Here, the specimien was directly placed as 

 cathode into a gas-discharge. The current in this gas 

 discharge proved to be practically independent of the 

 gas pressure in a wide range (1-0.05 mm Hg). As 

 the current density is the product of the ion density 

 multiplied by the mean velocity of the ions, this ve- 



Fig. 1. Rows of dislocation lines crossing a steel foil (piled 

 up against obstacles). 



Fig. 2. Network of dislocation lines in lightly rolled steel. 



