Mechanical and elastic properties of fine-grained polycrystalline scandia and erbia as determined by indentation techniques

The Young's moduli, E, and nanoindentation, NI, stress-strain curves of fine-grained scandia, Sc2O3, and erbia, Er2O3, were determined using spherical indenters with radii of 1.4 μm and 5 μm. The Young's moduli measured with the spherical indenters, were comparable to those measured by a Berkovich tip, and by ultrasound. This work further validates the use of S vs. a plots to measure the Young's moduli of polycrystalline ceramics. A major advantage of using this technique is the possibility of determining NI stress-strain curves and concomitant yield points, apparent strain hardening rates, etc. for the first time. Both the elastic moduli and the yield stresses were affected by the degree of surface polishing and tip size. The most reproducible and reliable results were obtained with the sharper nanoindenter and the best surface finish. The Vickers hardness and indentation fracture toughness values extracted from the Vickers indentations are comparable to the literature results.