High Rate
Deformation
Group

In-Situ TEM Straining of Pre-Deformed Materials to Determine Constraints of Dislocation-Boundary Interactions

Small strain perturbations on pre-deformed material can be observed in-situ in the TEM.

Primary focus is to provide fundamental information on the processes of dislocation interaction with grain boundaries and to determine these constraints for different crystal structures (HCP, BCC, FCC) and for different loading conditions.

This information will be used as the basis for developing a constitutive model of the response of the grain boundary, and ultimately as a test of the predictions of the model.

Dislocation Buildup at Grain Boundaries

In titanium (HCP) In 310 stainless steel (FCC)

Figure 1: Dislocation pileups at grain boundaries indicate these boundaries are very strong obstacles to dislocation motion

Slip Transfer Conditions

Figure 2: Slip transfer conditions must be satisfied:

Intersection angle a must be a minimum

Locally resolved shear stress should be a maximum

must be a minimum

Slip Transfer Through a Grain Boundary

Figure 3: Example of slip transfer through a sigma=3 grain boundary in stainless steel.

Grain Boundary Sources

Figure 4: Example of grain boundary sources. One slip system enters the grain boundary, and three grain boundary sources produce dislocations in the adjacent grain.

Future Work

Detailed study of the interaction of dislocations with various types of grain boundaries formed in high strain rate deformed FCC, BCC, and HCP materials.