Determination of critical resolved shear stresses associated with slips in pure Zn and Zn-Ag alloys via micro-pillar compression

The room-temperature plastic deformation behavior of pure Zn and Zn-Ag (0–2.2 at.%) biodegradable alloys has been investigated via uniaxial in situ micro-pillar compression tests performed within a scanning electron microscope. The critical resolved shear stresses (CRSS) were quantified as a function of micro-pillar diameter. The compression of single crystal micro-pillars was performed at various strain rates in carefully selected grains, the crystallographic orientation of which facilitates deformation either via basal 0001〈112¯0〉 or prismatic 101¯0〈112¯0〉 slip. The CRSS values increased with decreased micro-pillar diameter, revealing a more pronounced size effect in pure Zn deformed via basal slip. The observed solid solution strengthening effect in Zn-Ag alloys with increasing Ag content was associated with a CRSS increase from 26.6 MPa to 37.0 MPa (by ∼ 40 %) in the basal slip system and from 99.1 MPa to 188.4 MPa (by ∼ 104 %) in the prismatic slip system. The extraordinarily high CRSS values for basal slip activated in pure Zn and Zn-0.14Ag alloy compared to the solid solution strengthening model was attributed to the critically low dislocation density. In the Zn-Ag alloy with Ag content > 0.5 at.% higher dislocation densities are expected, which result in a more predictable plastic deformation behavior.