Synchrotron x-ray topography observations on fatigue and fracture behavior in zinc bicrystals

Technical Report · Fri May 01 04:00:00 EDT 1987

OSTI ID:6806616

Schmitz, H A

Crack propagation at 77 and 298/sup 0/K was studied for low cycle prefatigued zinc bicrystals. Synchrotron X-Ray Fractography (SXRF) and Monochromatic Bragg angle Strain Contour mapping (SCM) was used to examine the strain field of the crack in relation to the bicrystal boundary plane. Lattice curvatures due to crack opening strains were accurately determined for several pure tilt boundaries. The behavior of twist boundaries and random boundaries was also characterized by x-ray and optical examinations. The lattice curvatures were interpreted in terms of crack opening displacements. This data was then used to approximate the fracture toughness or penetration strength of the grain boundary. A boundary affected zone (BAZ), apparently a consequence of accommodation slip, was clearly discerned; the size of the BAZ was found to be strongly dependent on the test conditions. The penetration strength of the grain boundary was not strongly dependent on the size of the boundary affected zone; but earlier stages of crack nucleation and growth may be influenced by this deformed region due to the inhibition of basal slip. Pure tilt boundaries were inexplicably found to be several times tougher than a single crystal. This high toughness was attributed to a grain boundary crack tip relaxation process. Nonbasal cleavage, incompatible bicrystals, and fatigue behavior were observed.

• Research Organization: State Univ. of New York, Stony Brook (USA). Dept. of Materials Science and Engineering
• DOE Contract Number: FG02-84ER45098
• OSTI ID: 6806616
• Report Number(s): DOE/ER/45098-22; ON: TI87010227
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
BICRYSTALS
CRACK PROPAGATION
CRYSTAL STRUCTURE
CRYSTALS
ELEMENTS
FAILURES
FATIGUE
FRACTURES
GRAIN BOUNDARIES
MECHANICAL PROPERTIES
METALS
MICROSTRUCTURE
POLYCRYSTALS
ZINC