EFFECT OF PURIFICATION ON BASAL CLEAVAGE IN BERYLLIUM SINGLE CRYSTALS
The deformation of impure beryllium crystals by basal glide at room temperature invariably terminates by basal cleavage after a few percent strain. It is generally accepted that fracture of this type is caused by the splitting of low-angle boundaries, or bend planes, by obstacles that restrict the motion of the bend planes in the deforming crystal. The details of such a process have been developed by Stroh, who showed that the high tensile stress normal to the basal plane in the region where the bend plane is split results in the propagation of a basal cleavage crack, provided there is no available deformation mode having a shear component normal to the basal plane. It has been postulated that purification of beryllium might lead to increased basal ductility by the removal of barriers to bend plane motion and possibly by the activation of non- basal deformation systems. Large increases in the amount of basal glide that can be sustained prior to fracture have been observed in crystals purified by zonerefining. In each case, eventual fracture was by sharp basal cleavage, suggesting that the split-bend plane model still applies to the fracture of beryllium of reasonably high purity. Calculations are made to show to what extent basal ductility can be increased by purification while the split bend- plane fracture process remains applicable. Experimentally observed ductilities are generally somewhat lower than those predicted by calculation because of premature failure due to defects introduced during specimen preparation and testing. (auth)
- Research Organization:
- Nuclear Metals, Inc., Concord, Mass.
- Sponsoring Organization:
- US Atomic Energy Commission (AEC)
- NSA Number:
- NSA-18-005773
- OSTI ID:
- 4153436
- Report Number(s):
- CONF-339-2
- Country of Publication:
- United States
- Language:
- English
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