Microyielding in tantalum single crystals. I. Microflow parameters

Journal Article · Wed Jun 01 04:00:00 EDT 1977 · Acta Metall.; (United States)

DOI:https://doi.org/10.1016/0001-6160(77)90006-2· OSTI ID:7295281

Cowling, M J; Bacon, D J

The microflow parameters of tantalum single crystals of three purity levels have been determined from uniaxial compression tests at temperatures in the range 77 295K. The parameters measured were the elastic limit sigma/sub e/, the microyield stress sigma/sub mys/, the activation volume ..nu.. and the activation energy ..delta..H. Specimens were tested in the as-annealed state or after a 1/sup 0///sub 0/ prestrain at 77K, which increased the density of dislocations near the screw orientation, and the data show that the mechanism of dislocation motion in these two states is different. In both cases interstitial impurities increase sigma/sub e/ by an athermal process, but at sigma/sub mys/ dislocations overcome interstitial barriers by thermal activation. The possible mechanisms of dislocation motion are discussed, and it is suggested that screw dislocations can be mobile in the microflow region above about 200K. Tests on crystals of different orientation produced results which were ambiguous. It is concluded that further interpretation of the data may be possible if reference is made to the results of internal friction experiments.

• Research Organization: Liverpool Univ.
• OSTI ID: 7295281
• Journal Information: Acta Metall.; (United States), Journal Name: Acta Metall.; (United States) Vol. 25:6; ISSN AMETA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
CRYSTALS
DISLOCATIONS
ELEMENTS
FLOW STRESS
LINE DEFECTS
LOW TEMPERATURE
MEDIUM TEMPERATURE
METALS
MICROSTRUCTURE
MONOCRYSTALS
REFRACTORY METALS
STRESSES
TANTALUM
TRANSITION ELEMENTS