Kinetics and mechanisms of low temperature deformation in high purity niobium single crystals

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:5283002

Karam, N H

This study included three main aspects: (1) an extensive examination of the temperature and strain rate dependence of the flow stress without any thermodynamic analysis; (2) detailed thermodynamic analysis of the experimental data with no specific models involved, and (3) testing the results against specific models as well as modification of Seeger's model (1981-1983) to account for the results. The temperature and strain rate dependence of the tau/sub f/, tau/sup */, and tau/sub ..mu../ was experimentally determined over the temperature range 300 to 4.2 K with intervals ..delta..T less than or equal to 20K. The value of tau/sub ..mu../(T/sub k/) was found experimentally by decremental unloading, stress relaxation, and back extrapolation techniques giving tau/sub ..mu../(T/sub k/) = 19 MPa in agreement with the analytical analysis. The knee temperature was found T/sub k/ = 300K and the Peierls stress was determined as taup = 370 MPa. The strain rate sensitivity lambda was evaluated using both strain rate cycle and stress relaxation techniques which were in excellent agreement. lambda reached its maximum at 77K. Experimental data are best described by double kink nucleation models where deformation occurs by the formation of double kinks on <111> screw dislocations that are resisted by a lattice friction arising from the periodic lattice potential.

• Research Organization: North Carolina State Univ., Raleigh (USA)
• OSTI ID: 5283002
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals &amp; Alloys-- Mechanical Properties
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
CRYSTALS
DEFORMATION
DISLOCATIONS
ELEMENTS
LINE DEFECTS
METALS
MONOCRYSTALS
NIOBIUM
NUCLEATION
SCREW DISLOCATIONS
STRAIN RATE
TEMPERATURE DEPENDENCE
TRANSITION ELEMENTS