The deformation behavior of (111), (110) and (001) oriented Ni 3Al single crystals was investigated by means of nano-indentation. Upon loading with the blunt and sharp indenter tips, the crystal deforms elastically in the initial stage followed by plastic deformation of which the onset was characterized by an obvious displacement burst (or pop-in) in the loading curve. This pop-in corresponds to homogeneous nucleation of dislocation loops under the indenter. When a sharp indenter tip was used, a major pop-in could be identified at a large load (̃7mN for (111) crystal) in the plastic regime on loading. The major pop-in may be correlated with the special dislocation structure of the Kear-Wilsdorf locks in the Ni3Al crystals that were formed during loading. The pop-in behavior during plastic deformation of Ni3Al crystals was found to be closely related to the crystal orientation, pre-existing dislocation density in the sample surface, loading rate, and holding (at a constant sub-critical load) time as well. Pop-ins were also observed at critical loads in unloading processes.

Deformation Behavior of Ni3Al Single Crystals during Nanoindentation. Wang, W., Jiang, C.B., Lu, K.: Acta Materialia, 2003, 51[20], 6169-80