Effect of specimen size and shape on strength and deformation of high-purity aluminum single-crystal micropillars

Abstract

In the present study, we have examined the compression response of single-crystal cylindrical micropillars with different diameters (approximately ranging from 1 to 10 µm) and shape parameters prepared on the sample surface of 4N purity aluminum (Al) sheets with the recrystallized microstructure. The compression tests for micropillars with various sizes demonstrated the flow stress of micropillars increases with decreasing pillar diameter. The observed size dependence of resolved shear stress for slip corresponds well to the previous studies on micropillars prepared from 3N and 5N purity Al sheets. The measured shear stress resolved onto a primary slip system (τ_i) scaled by shear modulus (G) and the pillar diameter (d) scaled by Burgers vector (b) shows the following correlation: (τ_i/G)=0.33(d/b)^−0.63. The compression response of micropillars with different d₁/d₂ (ratio of top diameter (d₁) to bottom diameter (d₂) of cylindrical micropillars) revealed higher d₁/d₂ than 0.5 is required for precisely measuring the strength of cylindrical micropillars, which was confirmed by the observations of compressed micropillars.