An instrumented spherical indentation study on high purity magnesium loaded nearly parallel to the c-axis

Instrumented spherical indentation has been used to extract information on the deformation behaviour of (0001) oriented grains in commercial purity magnesium. Reproducible discontinuities were found in the loading and the unloading curves and these have been interpreted as the nucleation and growth of {101¯2} extension twins during loading and their subsequent retreat during unloading. Detailed three-dimensional electron backscatter diffraction-based orientation microscopy (3D-EBSD) revealed that the presence of residual deformation twins depended on the depth of the indent. Analysis of residual geometrically necessary dislocation density using the EBSD data showed that residual basal 〈a〉 dislocations were dominant in the deformation zone. The crystallographic misorientation observed below the indent can be rationalized by the presence of these basal 〈a〉 dislocations and this is shown to be consistent with crystal plasticity finite element method calculations. Finally, a schematic view of the different stages of deformation during loading and unloading is proposed to rationalize the experimental observations.