Effect of dislocation density on the ductile-brittle transition in bulk Fe-3%Si single crystals

Journal Article · Fri Apr 15 04:00:00 EDT 1994 · Scripta Metallurgica et Materialia; (United States)

DOI:https://doi.org/10.1016/0956-716X(94)90556-8· OSTI ID:5160608

Ha, K F; Yang, C; Bao, J S ^[1]

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1. Jilin Univ., Changchun (China). Dept. of Materials Science

Recently the authors have proposed a new model for the ductile-brittle transition (DBT) in bulk single crystals. The essential principle is that, according to Ohr's point of view, brittle fracture initiates by an elastic opening of the dislocation-free zone ahead of the crack tip, so the prerequisite for brittle fracture is the formation of such a dislocation-free zone. One of the conclusions obtained from this model is that the effect of dislocation density on the DBT temperature is negligibly small; they thus decided to test this result experimentally. The experimental result indicates that the effect of dislocation density in bulk Fe-3% Si single crystals on the DBT temperature is certainly very small. This means that this result is in accordance with the energy consumption rate criterion the authors proposed. On the other hand, based on Ashby and Embury thought that the increase in dislocation density by prior deformation of many b.c.c. metals, could improve the ductility of the b.c.c. metals, and hence proposed a dislocation density criterion for the DBT. However, with this criterion, the DBT temperature of these specimens with low dislocation density should be twice as high as that of the high ones. Such a discrepancy may be due to the fact that the specimens they used were single crystals, because they found that the impact DBT temperature of a polycrystalline Fe-3% Si specimen is 438 K, this value for the DBT is much higher than that for single crystals. In fact, experiments showed that the DBT temperature of the polycrystalline Fe-3% Si crystals was drastically affected by the grain size, and both Petch's (6) and Armstrong's theory of DBT also contained some grain size parameter. Therefore, they concluded that there is a different DBT mechanisms in single- and poly-crystals of the Fe-3% Si alloy.

• OSTI ID: 5160608
• Journal Information: Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 30:8; ISSN SCRMEX; ISSN 0956-716X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CRYSTALS
DATA
DUCTILE-BRITTLE TRANSITIONS
EXPERIMENTAL DATA
INFORMATION
IRON ALLOYS
IRON BASE ALLOYS
MATHEMATICAL MODELS
MONOCRYSTALS
NUMERICAL DATA
PHYSICAL PROPERTIES
SILICON ALLOYS
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE