Effect of Grain Orientation on Indentation Induced Creep in Pure Zinc

The study presents the anisotropy in the indentation creep response of zinc. Indentation creep tests were conducted on grains with three different orientations, namely, 〈0001〉, $⟨112¯0⟩$⁠, and $⟨101¯0⟩$⁠. Indentation creep along the 〈c〉 axis showed a pronounced creep exhibiting a 25% higher creep displacement as compared with indentation perpendicular to the 〈c〉 axis. However, the recovery observed was the highest for basal-oriented grains wherein a recovery of 50% to its indented depth was observed, whereas for $⟨112¯0⟩$ the recovery observed was 30%. The stress exponent, n, was obtained by employing two different approaches for each of the orientations and a difference in the stress exponent value was also observed, highlighting the anisotropic creep response. Basal and non-basal oriented grains showed a lower (n ≅ 1.6) and higher stress exponent (n ≅ 5), respectively, highlighting the different operable creep mechanism. Surface topography using atomic force microscope (AFM) revealed twinning and sink-in for $⟨112¯0⟩$ and $⟨101¯0⟩$⁠, whereas uniform pile up was observed for basal grain.