Effects of Crystal Orientation on the Crack Propagation of Sapphire by Sequential Indentation Testing

Abstract

Single-crystal sapphire (α-Al 2 O 3) is a hard and brittle material. Due to its highly crystalline nature, the fracture behavior of sapphire is strongly related to its crystal structure, and understanding the effects of crystal structure on the crack propagation of sapphire is essential for the successful application of this important material (e.g., as wafers in the electronics industry). In the present work, crack propagation that is induced by sequential indentation was investigated on the A-plane and C-plane of sapphire using a Vickers indenter on a micrometer scale. It was found that increasing indentation depth obviously increases the rate of crack propagation on the A-plane, but this effect is not so obvious on the C-plane because of the different slip systems induced by indentation on the different crystal planes of sapphire. Moreover, some parallel linear traces along the A-plane, which fracture with increasing indentation depth, are observed from the residual indentation on the A-plane. The fracture toughness of both A-plane and C-plane sapphire is smaller after indentation testing than that obtained using conventional testing methods. The subsurface damage was detected by transmission electron microscopy (TEM).

Mechanical characterisation of the protective Al2O3 scale in Cr2AlC MAX phases

“…O 3 -Cr 7 C 3 interface, and 3.55 MPa √ m for the Cr 7 C 3 -Cr 2 AlC interface. In comparison, single crystal alumina when measured by indentation cracking[49] is around 1.5 MPa √ m, very similar to that of the alumina-based interface. Hirota measures, in a 97% Cr 7 C 3 -3% Cr 2 O 3 sample, a fracture toughness of[12], it is promising to see that without any design or im-provement of the interfaces, they are nevertheless in line with typical literature values.…”

Orientation Dependence of Hardness and Reduced Modulus of Single Crystal Sapphire Surface Measured by Nanoindentation

“…When the indenter was indented to enough depth of the specimen, the stress is transmitted from the apex of indenter to the specimen. It was reported that the stress was concentrated along the ridge line of the indenter [14]. Therefore, if the ridge line of indenter was oriented to m -axis, the stress was concentrated to the fragile m -axis, and eventually the hardness along m -axis became low.…”

Nanoindentation deformation and cracking in sapphire

“…It is well known that during nanoindentation experiments, when using non-spherical indenters, the deformation and crack patterns are not only dependent on the crystallography of the sample, but it is also influenced by the tip geometry; e.g. cracks always start at the tip edges due to stress concentration at these locations [22]. Hence, spherical indenters were chosen to avoid the influence of the tip geometry in the stress distribution on the sample during the test and so to measure the true deformation and fracture behavior of sapphire.…”