Plastic deformation behaviour and operative slip systems in Ni3Nb single crystals

Temperature and orientation dependence of yield stress and operative slip system in Ni3Nb single crystals were examined. Four slip systems of (010)[100], (001)[100], {201}[10 (2) over bar] and (010)[001] and three twinning systems 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 tested temperature. Anomalous strengthening was observed for some orientations where (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] slip occurred over a wide temperature range from -196 to 800 degrees C. The CRSS did not satisfy Schmid's law and the strain rate sensitivity of flow stress at a small plastic strain was negligible between room temperature and 700 degrees C where an anomalous stress increase occurred. The anomalous strengthening mechanism in Ni3Nb crystals deformed by [100] dislocations was discussed on the basis of anisotropy of APE energy on (010) and (001) in analogy with that in Ni3Al with the L1(2) structure. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.