Nanoindentation deformation and cracking in sapphire

Abstract Single crystal sapphire is an anisotropic material and its mechanical behavior depends on the crystallographic orientation. In this work, a systematic study is performed to investigate the effect of crystallographic orientation on the deformation and cracking of sapphire by means of nanoindentation using spherical indenters. It aims also at determining the physical origin of the ''pop-in" appearing in the nanoindentation curves. For that purpose, nanoindentations were performed where the load was increased until the detection of the ''pop-in", followed by direct unloading. After SEM and TEM observation of the indents, it is concluded that the deformation mechanisms of sapphire depend on the tip radius and the applied indentation stress: exclusively twin formation for the smaller 1 and 2 μm tip radii indenters and twin formation together with crack propagation for larger 10 μm tip radius spherical indenter. It was also determined that the cracks propagate preferentially in the ( 10 1 ¯ 2 ) ''R-plane". Therefore, this study is supplement to and enrichment of existing studies on deformation and cracking behavior of sapphire under spherical nanoindentation.