Orientation dependence of plastic deformation in NiAl single crystals

Compression stress-strain tests were performed on NiAl single crystals of various orientations at room temperature and complemented by observations of slip traces and dislocation structures. In ‘soft’ oriented samples (far from the [100] direction), 〈100〉 slip vectors are activated at a critical resolved shear stress of ≈90 MPa. The 〈100〉 slip is very homogeneous as witnessed by a faint and uniform slip line pattern. The yield stresses of soft orientations obey the Schmid law. For ‘hard’ orientations (within 3 ° from the [100] direction), the yield stress for 〈100〉 slip becomes too large and 〈111〉 slip is activated instead. The 〈111〉 slip is highly inhomogeneous and gives rise to distinct glide bands. The strain concentrated in these bands remains constant during deformation indicating that the plastic strain is carried by mobile dislocations at the periphery of the glide bands. We suppose that the difference in the slip homogeneity is due to highly different mobilities of 〈100〉 and 〈111〉 dislocations.