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Final rept. 1 Sep 65-31 Mar 66 on Phase 3,
FRANKLIN INST RESEARCH LABS PHILADELPHIA PA
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Microstrain and etching experiments were conducted on 7030 brass single crystals to determine the effect of the presence of liquid mercury at the surface on deformation characteristics in the early stages of plastic flow. It was revealed that dislocations become mobile at stresses as low as 0.04 kg per sq mm in annealed crystals, a sharp contrast to previous observations. A model is presented to explain the microstrain characteristics. A debris layer near the surface was observed to a depth of about 20 microns after 12000 plastic shear strain, irrespective of the presence of mercury. Thus, liquid mercury is equally as effective as an oxide film in impeding the emergence of dislocations from a crystal. Since the degree to which this type of behavior inhibits crack relaxation could not be determined, it was not possible to rigorously establish this as the mechanism for liquid metal embrittlement. Author
APPROVED FOR PUBLIC RELEASE