Crystallite formation in beryllium

Foils taken from the gauge length sections of beryllium tensile test pieces have been examined using transmission electron microscopy. The foils were taken from test pieces which had been fractured at normal ambient temperature when subjected to a constant superimposed hydrostatic pressure in the range 0.1 to 1280 MPa. An examination was made of samples taken from both extruded ingot and hot pressed powder beryllium test pieces. This was done in an effort to confirm the presence of crystal defects not normally seen in beryllium but which other workers have reported as being associated with beryllium tested in this manner. Although it was not possible to confirm the generation of such defects, nevertheless, a phenomenon was observed which had not previously been reported. This is the breakdown of the original grains into small sub-grains or crystallites. In addition, ingot and powder samples taken from specimens strained in tension to the point of instability under an applied hydrostatic pressure were microscopically examined. The presence of stabilized cracks in both grades of material was established. The relevance of these observations to the fracture of beryllium is considered. (author)