Journal of Materials Science

, Volume 10, Issue 3, pp 427–435 | Cite as

The influence of pressurization-induced dislocations on the plastic deformation of LiF and NaCl monocrystals

  • R. A. Evans
  • A. S. Wronski
  • B. A. W. Redfern
Papers

Abstract

Single crystals of LiF containing voids and of NaCl containing Na2SO4 precipitates were pressurized to introduce dislocations in the vicinities of the discontinuities and subsequently compressed along 〈100〉 at room temperature. The yield stress was raised in both materials; additionally, in LiF discontinuous yielding and easy glide were suppressed and work hardening rate increased by the pressurization-induced dislocations. Following pressurization at 0.85 GN m−2, for example, the 0.1 % shear flow stress of LiF was doubled to ∼ 4 MN m−2 and stage II work hardening rate quadrupled to ∼ 180 MN m−2. Pressurization of NaCl above 0.6 GN m−2 resulted in an increase in the 0.1 % flow stress from ∼ 1.2 to ∼ 2.0 MN m−2. If the slip bands in LiF were initiated by a precompression, pressurization prevented the broadening of these fresh slip bands during subsequent plastic flow. Deformation now took place at a higher stress both in LiF and NaCl. These effects resemble in some ways latent hardening in that oblique as well as conjugate dislocation intersections must take place to continue the deformation. In contrast to latent hardening data, the strain hardening rate was increased in LiF and was approximately proportional to the pressurization-induced dislocation density. This ratio, 5 to 6 dyne per dislocation, is in fair agreement with two sets of independent calculations reported by Gilman and Johnston. The results suggest, therefore, that in the present case also hardening may be due to defects left in the wakes of pressurization-induced moving dislocations.

Keywords

Plastic Deformation Dislocation Density Work Hardening Flow Stress Na2SO4 

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Copyright information

© Chapman and Hall Ltd 1975

Authors and Affiliations

  • R. A. Evans
    • 1
  • A. S. Wronski
    • 1
  • B. A. W. Redfern
    • 1
  1. 1.School of Materials ScienceUniversity of BradfordWest YorkshireUK

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