The deformation behavior of (111), (110) and (001) oriented single crystals was investigated by using nano-indentation techniques. Upon loading with blunt or sharp indenter tips, the crystal deformed elastically in the initial stage, followed by a plastic deformation whose onset was characterized by an obvious displacement burst (pop-in) in the loading curve. This pop-in corresponded to the homogeneous nucleation of dislocation loops under the indenter. When a sharp indenter was used, a major pop-in could be identified at high loads - about 7mN for the (111) crystal - in the plastic regime upon loading. This major pop-in could be correlated with the special dislocation structure of K–W locks that formed during loading. The pop-in behavior during plastic deformation was found to be closely related to the crystal orientation, pre-existing dislocation density in the sample surface, loading rate and holding time at a constant sub-critical load. Pop-ins were also observed at critical loads during unloading.

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