Investigation on surface/subsurface deformation mechanism and mechanical properties of GGG single crystal induced by nanoindentation.

In this paper, nanoindentation tests of GGG single crystal are performed on an Agilent G200 nanoindenter. The surface morphology and subsurface deformation mechanism induced by the nanoindentation are analyzed by a scanning electron microscope and a transmission electron microscope (TEM), respectively. The ductile deformation mechanism of GGG single crystal induced by the nanoindentation is a combination of "polycrystalline nanocrystallites" and "amorphous transformation." In addition, the relationships between the normal force and elastic recovery, microhardness, elastic modulus, and fracture toughness of GGG single crystal are researched. Due to the size effect caused by the tip radius of the indenter, the elastic recovery rate and fracture toughness decrease first and then tend to be stable as the normal force increases, while the microhardness and elastic modulus increase first and then decrease to be stable as the normal force increases. The stress-strain curve of GGG single crystal is developed by using the nanoindentation test with a spherical indenter. When GGG single crystal deforms from the elastic regime into the ductile regime, the original single crystal is changed into "polycrystalline nanocrystallites" and "amorphous transformation" structures verified by TEM. Therefore, the material strength decreases, which results in a discontinuity of the stress-strain curve for GGG single crystal.