Plastic deformation behaviour and operative slip systems in Ni 3Nb single crystals

Abstract

Temperature and orientation dependence of yield stress and operative slip system in Ni 3Nb single crystals were examined. Four slip systems of (010)[100], (001)[100], {201}〈10 2 ̄ 〉 and (010)[001] and three twinning systems of {011}〈0 1 ̄ 1〉 , {211}〈 10 7 13〉 and {012}〈0 2 ̄ 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 ̄ 〉 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°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 Ni 3Nb crystals deformed by [100] dislocations was discussed on the basis of anisotropy of APB energy on (010) and (001) in analogy with that in Ni 3Al with the L1 2 structure.