Temperature and orientation dependence of yield stress and operative slip s
ystem in Ni3Nb single crystals were examined. Four slip systems of (010)[10
0], (001)[100], {201}[10 (2) over bar] and (010)[001] and three twinning sy
stems of {011}[0 (1) over bar 1], {211}[<(10)over bar> 7 13] and {012}[0 (2
) over bar 1] were activated depending on the crystal orientation and teste
d temperature. Anomalous strengthening was observed for some orientations w
here (010)[100] or {201}[10 (2) over bar] slip was operative. A remarkable
increase in the critical resolved shear stress (CRSS) for the (010)[100] sl
ip occurred over a wide temperature range from -196 to 800 degrees C. The C
RSS did not satisfy Schmid's law and the strain rate sensitivity of flow st
ress at a small plastic strain was negligible between room temperature and
700 degrees C where an anomalous stress increase occurred. The anomalous st
rengthening mechanism in Ni3Nb crystals deformed by [100] dislocations was
discussed on the basis of anisotropy of APE energy on (010) and (001) in an
alogy with that in Ni3Al with the L1(2) structure. (C) 2000 Acta Metallurgi
ca Inc. Published by Elsevier Science Ltd. All rights reserved.