Correlation between dislocation hardening and the geometrically-necessary-dislocation densities in a hexagonal-close-packed Zr-2wt%Ti alloy

Geometrically necessary bands (GNBs) that are reflected by variations in the geometrically necessary dislocation densities (GNDDs) often appear at early stages of deformation. Studying the hardening variation inside and outside of GNBs is helpful for understanding how GNBs are formed to accommodate deformation heterogeneity. The former requires an accurate estimation of the slip activities at the mesoscale. Making use of the facts that the lattice rotation induced by prismatic <a> slips does not affect the <0001> direction, and one resulting from basal <a> slips does not influence an axis ⊥ <0001>, the slip activities identified by both the crystal plasticity model and slip traces for the electron backscatter diffraction microstructures after compression were verified. An abundance of GNBs was observed. The hardening/softening effect in the GNBs is always compensated by a softening/hardening behavior near the GNBs. Such microstructural features are also reflected in the profiles of frequency as a function of strength for both high and low GNDD regions: they share the same shape and peak positions. This confirms that the high GNDD region is always accompanied by a low GNDD region, and the GNDDs are independent of grain strength. Strong dependence of slip activities on grain orientations was identified, while the GNDDs are independent of orientations. The present paper provides experimental evidences of the identified slip activities and a way to explore the correlation between dislocation hardening and the GNDDs.