1986 Volume 27 Issue 6 Pages 434-440
The plastic behaviours of a Ni3Nb single crystal are studied by tensile and compression tests. Three shear systems are found to operate. They are (010)[001] slip, (010)[100] slip and {211} ⟨‾10713⟩ twin systems, and the critical resolved shear stresses (CRSS) for these systems are obtained as 44, 51 and 56 MPa in tension, and 55, 64 and 380 MPa in compression, respectively. In case of tensile test, a brittle fracture occurs in almost all the stress orientations, since the CRSS for {211} twin in tension is comparatively low and the twin plane is easy to cleave. When the stress axis is parallel to [120], where the twin system is difficult to operate, a ductility can be expected under a tensile test. On the other hand, the CRSS for {211} twin in a compression test is considerably high, and the single crystal is plastically deformed up to strains more than 15% by the operation of the (010) slip systems. For the stress orientations parallel to [010] or parallel to the axes on the [100]-[001] great circle, however, the (010) slip systems can not be operated, and it is speculated to be brittle even in a compression test.
