Quantification of dislocation nucleation stress in TiN through high-resolution in situ indentation experiments and first principles calculations.

N Li,N Mara,A Misra,J Wang,S.K Yadav,X.-Y Liu,R.G Hoagland

doi:10.1038/srep15813

Abstract

Through in situ indentation of TiN in a high-resolution transmission electron microscope, the nucleation of full as well as partial dislocations has been observed from {001} and {111} surfaces, respectively. The critical elastic strains associated with the nucleation of the dislocations were analyzed from the recorded atomic displacements, and the nucleation stresses corresponding to the measured critical strains were computed using density functional theory. The resolved shear stress was estimated to be 13.8 GPa for the partial dislocation 1/6 <110> {111} and 6.7 GPa for the full dislocation ½ <110> {110}. Such an approach of quantifying nucleation stresses for defects via in situ high-resolution experiment coupled with density functional theory calculation may be applied to other unit processes.

Highlights

Boundaries[36,37], interphase boundaries[38,39,40] and cracks[5]
From quantitative load–displacement measurements in polycrystalline Al film using in situ indentation in a TEM2,26,33, Minor et al estimated critical resolved shear stress for dislocation nucleation in both dislocation-free and deformed domains and found them close to the theoretical shear strength
In this Letter, we explored the nucleation mechanics at atomic scale by performing in situ indentation tests in a transmission electron microscope (TEM) at high-resolution mode

Summary

DFT stress is

(GPa) under the indenter, with the critical shear stress of 13.8 GPa for the nucleation of a partial dislocation on {111}. The possible reason for the higher nucleation stress for a partial dislocation on {111} plane than the full dislocation on {110} plane may be the larger Peierls stress for {111} < 110> To rationalize these observations, we calculated generalized stacking fault energies (GSFE) of {111}, {110}, and {100} planes using DFT as a function of shear displacements along both < 110> and < 112> directions. In this configuration, one Ti layer is displaced relative to the neighboring Ti layer in the “anti-twinning” sense. We believe that such approach can be applied to other unit phenomena, such as dislocation nucleation from boundaries or cracks, dislocation multiplication or interaction, etc

Methods

Not observed

Additional Information