A dislocation shielding prediction of the toughness transition during cleavage of semibrittle crystals

Journal Article · Mon Mar 01 04:00:00 EST 1993 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

DOI:https://doi.org/10.1007/BF02656623· OSTI ID:6310708

Gerberich, W W; Huang, H; Zielinski, W; Marsh, P G ^[1]

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1. Univ. of Minnesota, Minneapolis (United States)

An interconnected set of observations assesses current equilibrium models of the ductile-brittle-transition temperature (DBTT). This involves in situ transmission electron microscopy (TEM) studies of crack-tip dislocations in single and polycrystals and bulk fracture toughness tests at various temperatures. Beyond K[sub I] values of 8 MPa [center dot] m[sup 1/2] in both iron-base single and polycrystals, large numbers of redundant dislocations are created, as postulated recently by Weertman. Still, the necessary shielding dislocations, as required by equilibrium, can be detected at values as high as 20 and 40 MPa[center dot]m[sup 1/2] by ex situ TEM and electron channeling, respectively. In addition, the close approach of dislocations to the crack tip in some of the studies, as opposed to others, suggests that large dislocation free zones (DFZ) are a thin-film artifact. However, a failure criterion based partly on the Rice-Thomson model is both consistent with the absence of a large DFZ and observed fracture toughness variations with test temperature. It is emphasized that this toughness transition is entirely in the semibrittle regime where cleavage is the failure mode. Nevertheless, K[sub Ic] values increase from 3 to 60 MPa [center dot] with an increase in test temperature.

• DOE Contract Number: FG02-84ER45173
• OSTI ID: 6310708
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 24:3; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
BRITTLE-DUCTILE TRANSITIONS
CLEAVAGE
CRACKS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
CRYSTALS
DISLOCATIONS
ELECTRON MICROSCOPY
FRACTURE PROPERTIES
IRON ALLOYS
IRON BASE ALLOYS
LINE DEFECTS
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
MICROSCOPY
MICROSTRUCTURE
PHYSICAL PROPERTIES
POLYCRYSTALS
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
TRANSMISSION ELECTRON MICROSCOPY