Deformation of sapphire induced by a spherical indentation on the (101̄0) plane

Abstract

This work clarifies the origin of the characteristic discontinuities registered during the deformation of the (101̄0) plane of sapphire, by means of depth sensing indentation experiments with a spherical indenter. The sudden increase of the plasticity of the crystal was found to be caused by a twinning process. The calculation and analysis of the distribution of resolved shear stresses under a spherical indenter predicted the features of the surface deformation. The high resolution microscopic examination of the residual impressions confirmed the theoretical prediction.

Nanoindentation examination of yttria-stabilized zirconia (YSZ) crystal

“…Indeed, the results of ultrasonic measurements, FEM analysis and experimental values collected in Table 1 point towards the elastic and plastic anisotropy of YSZ crystal, similarly to the recent findings by Nowak et al [10,13] who reported different elastic behavior of sapphire before and after pop-in event. The obtained results (Table 1) consistently indicate the (1 0 0) surface as the one with the highest Young's modulus and the (1 1 1) surface with the lowest stiffness.…”

“…We explored to certain extent the wide experience achieved with nanoindentation study of the Al 2 O 3 crystals [10][11][12][13], to conclude on both elastic and plastic anisotropy of the YSZ material, to discuss the pop-in event and dislocation activity. Moreover, the present authors performed the finite element (FEM) simulation of nanoindentation into different crystal planes to verify the mechanical characteristics obtained by nanoindentation measurements.…”

Berkovich indentation-induced deformation behaviors of GaN thin films observed using cathodoluminescence and cross-sectional transmission electron microscopy

“…For example, the tip-surface contact configuration and stress distribution for the Berkovich indenter tip can be drastically different from that for the spherical one or Vickers-type indenters [10,16,17]. In addition to that the multiple ''pop-in'' events behavior has been observed in materials with the hexagonal structures such as sapphire [18], single-crystal bulk ZnO [19] and GaN [20], while for materials like GaAs and InP with the cubic structure only single ''pop-in'' event was found [21]. Nevertheless, the above discussions do suggest that multiple ''pop-in'' events indeed are specific features of materials with the hexagonal lattice structure and, the geometry of the indenter tip may play an important role in determining the nanoindentation-induced mechanical responses.…”

Mechanical properties characterization of c ‐plane (0001) and m ‐plane (10–10) GaN by nanoindentation examination

“…Equation (1) coincided with not only m-plane GaN but also c-plane GaN despite the large anisotropy in mechanical properties. It may be caused by the grain boundary sliding, though it is also possible that the formation of twin is preferentially occurred on r {-1012} plane induced by both c-axis and m-axis direction indentation in covalently-bounded hexagonal crystal rather than dislocation nucleation or slip [18][19][20][21]. The derived approximation formula is suitable for evaluate the yield shear stress which affects to the life and reliability of light emitting device.…”