Plastic deformation behavior 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}(10bar 2) and (010)[001] and three twinning systems of {011}langle0bar 11rangle, {211}langlebar 1bar 0 7 13rangle and {012}langle0bar 21rangle were activated depending on the crystal orientation and tested temperature. Anomalous strengthening was observed for some orientations where (010)[100] or {201}rangle10bar 2rangle 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 minus196 to 800 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 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 APB energy on (010) and (001) in analogy with that in Ni3Al with the L12 structure