STRESS INDUCED MOVEMENT OF CRYSTAL BOUNDARIES
Abstract
Single small-angle grain boundaries: small-angle boundaries we re introduced in 1.2-in. -thick disk-shaped specimens formed by cleaving spherical Zn crystals. Load was applied at the midspan of a specimen, which was supported as a simple beam and heated to 350 deg C, by a knife edge perpendicular to the basal plane. With the crystal loaded as a cantilever beam, the boundary moved toward the supports under shearing stress, and the calculated critical shear stress for the boundary shear stress for slip in Zn. Upon reversal of the stress, the motion of the boundary reversed and the boundary moved past its original position. A progressively decreaseing reduction of the critical load appeared with each reversal of the loading direction. Under a given load, the displacement was more rapid at smaller boundary angles. When 1 moving boundary overtook another, the 2 formed a single boundary which required higher stress to make it move. The motion of a boundary was retarded in the vicinity of certain imperfect regions in the crystal. The rate of movement of a boundary under a given load increased with increasing temperature. Hexagonal systems of small-angle boundaries: The system of boundaries was developed by using a conical-pointed indenter to apply a concentrated load parallel to the c axis of a disk-shaped specimen with its basal plane parallel to the surface and heated to 350 deg C. Slip occurred internally on the basal planes, and the dislocations introduced initially by the local plastic bending collected hexagonally to form low-angle boundaries. Under a constant load, the substructure growth eventually stopped. The growing hexagon of an actively enlarging system was distorted by a second, inactive hexagonal substructure.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1952
- Accession Number
- AD0000677
Entities
People
- Choh Hsien Li
- Earl R. Parker
- Eugene H. Edwards
- Jack Washburn
Organizations
- University of California, Berkeley