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A new interpretation of flow-stress measurements of high-purity NiAl below room temperature

 
: Brunner, D.; Gumbsch, P.

Zeitschrift für Metallkunde 93 (2002), Nr.7, S.672-680
ISSN: 0044-3093
ISSN: 0179-4841
Englisch
Zeitschriftenaufsatz
Fraunhofer IWM ()
single crystal; solid solution; kink-pair theory; thermal activation; dislocation motion

Abstract
The temperature and strain-rate dependence of the critical resolved shear stress (CRSS) of high-purity NiAl single crystals in soft orientation (tensile axis near [111]) was measured in tensile tests with constant strain rate, Epsilon p = 10 (exp -4) s (exp -1), between 77 and 325 K. After pre-straining at room temperature, the crystals were plastically deformed by strain increments of Delta Epsilon p ~ 0.005 at successively decreasing temperatures. Below 325 K the CRSS on the [001] [011] slip system slowly increases with decreasing temperature, followed by a steeper increase below about 200 K. The strain-rate sensitivity of the CRSS measured by stress-relaxation experiments exhibits comparable behavior. The parameters for thermally activated dislocation motion, activation volume and activation energy, suggest that different mechanisms control the dislocation motion above and below 200 K. For low stresses, at temperatures above 200 K, an interpretation of the results within the framework of solid solution hardening theory is suggested. Below 200 K the results can be interpreted within the framework of the line-tension model of the kink-pair theory of flow stress. The evaluation of the data yields a kink-pair energy of 2Hk = 0.42 eV, a Peierls stress of 535 MPa, and a Peierls valley distance equal to the lattice constant. These data are generally compatible with a fundamental process of kink-pair formation on [110] or on [100] planes. The results are discussed with respect to recent atomistic modelling of dislocations in NiAl.

: http://publica.fraunhofer.de/dokumente/B-74400.html