Characterization of crack-tip microstructures via synchrotron fractography in Mo and Mo-Nb alloy crystals

Thesis/Dissertation · Thu Jan 01 00:00:00 EST 1987

OSTI ID:6623060

Hmelo, A B

The nature of the plastic relaxation associated with the semi-brittle cleavage fracture of a series of pre-cracked molybdenum-niobium alloy single crystals was investigated as a function of composition and temperature from 77/sup 0/ to 298/sup 0/K. Conventional optical microscopy and white-beam Synchrotron X-Ray Fractography (SXRF) were used to examined the structure of a thin layer a few microns thick at the remnant of the precursor crack plastic zone. The plastic work of fracture was evaluated by measuring the lattice curvature associated with networks of dislocations beneath the cleavage surface. Using SXRF, lattice curvature is detected as asterism on photographic plates, and is associated with an excess density of edge dislocations of one sign. The results are in qualitative agreement with a previous determination of the fracture toughness of these specimens. Excess edge-dislocation density of one sign has been shown to vary as a function of temperature and composition, in a way consistent with previous studies of total dislocation content in these materials. Unlike the etch-pit analysis that can reveal the total dislocation content only, the tensor bases analysis described here allows the activity on individual slip systems to be distinguished.

• Research Organization: State Univ. of New York, Stony Brook (USA)
• OSTI ID: 6623060
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MOLYBDENUM
MICROSTRUCTURE
MOLYBDENUM ALLOYS
NIOBIUM ALLOYS
EDGE DISLOCATIONS
FRACTOGRAPHY
FRACTURE PROPERTIES
LAYERS
ALLOYS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISLOCATIONS
ELEMENTS
LINE DEFECTS
MECHANICAL PROPERTIES
METALS
TRANSITION ELEMENTS
360102* - Metals & Alloys- Structure & Phase Studies
360103 - Metals & Alloys- Mechanical Properties