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Direct observations of vacancies and vacancy-type defects in molybdenum following uniaxial shock-wave compression

Acta Metallurgica, ISSN: 0001-6160, Vol: 24, Issue: 3, Page: 261-270
1976
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Metrics Details

  • Citations
    42
    • Citation Indexes
      42
  • Captures
    7

Article Description

Molybdenum sheet and small diameter wire samples were simultaneously shock-loaded to pressures of 150 and 250 kbar at a constant shock-pulse duration of 2 μsec. Thin foils and emission end-forms prepared from annealed as well as the shock-loaded samples were simultaneously examined by transmission electron and field-ion microscopy respectively. Dislocation loop densities were observed to increase from an annealed value of 5 × 10 9 −4 × 10 14 cm −3 and 7 × 10 14 cm −3 at 150 and 250 kbar, respectively, and the corresponding average loop diameters were measured to be 57, 104 and 152 Å, respectively. A full determination of the relevant diffraction conditions and Burgers vectors of the loops in the electron microscope showed that 75% of the loops at 150 kbar and 80% of the loops at 250 kbar were vacancy type. By comparison, direct observations of vacancies and small vacancy aggregates in the field-ion microscope by systematic field-evaporation of atom layers showed a vacancy concentration of 1.2% in the annealed wires as compared with 2.2 and 6.0% vacancies in the 150 and 250 kbar shock-loaded wire samples respectively. Since the corresponding increase in dislocation density was determined to be 1.0 × 10 10 −1.2 × 10 10 cm −2 between 150 and 250 kbar for a concomitant increase in average residual microhardness from 514 to 770 kg/mm 2 in the same pressure range, it is shown that shock induced vacancies contribute significantly to residual shock hardening.

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