Is Smaller Stronger? Microcompression of Single-Crystal Magnesium

Size Matters! Many studies in the literature indicate that “smaller is stronger,” a concept that may sound surprising to some people. This phenomenon has been called size effects, and along with the orientation dependence of deformation mechanisms associated with single crystals under uniaxial compression, is becoming an increasingly popular area of study. Microcompression literature shows that decreasing the diameters of micro-scale pillars increases their strengths, but despite the growing collection of literature, many questions remain, especially for materials with the hexagonal close packed (hcp) crystal structure. In this study, we focus on the impact of specimen sizes and orientations on the deformation mechanisms and size effects in single-crystal magnesium. Microcompression experiments are conducted on micropillars (600 nanometers to 10 micrometers in diameter) fabricated using focused ion beam (FIB) milling. Specimens are loaded along the [0 0 0 1] c-axis and [2 -3 1 4] orientations and reveal that the angle of the basal planes with respect to the loading axis plays a large role in the material response. Post-mortem microscopy is used to examine the details of the deformation mechanisms involved.