Effects of Crystal Orientation and Temperature on the Strength of Sapphire

Abstract

The flexure and compressive strengths of sapphire are dependent on crystal orientation and temperature. Most notably, the c-axis compressive strength decreases below the tensile strength at temperatures >400°C and falls to 2% of the room-temperature compressive strength at 800°C. Loss of compressive strength complicates the interpretation of flexure tests. Four-point flexure specimens with no component of c-axis compression increase in strength at temperatures >500°C; however, specimens that have c-axis compression decrease in strength. It has been observed that c-axis compression causes twinning on rhombohedral crystal planes. Intersection of twins on different rhombohedral planes causes fracture that leads to mechanical failure.

Energy output reduction and surface alteration of quartz and sapphire tips following Er:YAG laser contact irradiation for tooth enamel ablation

“…Thus, further studies are required to clarify these questions. Regarding the sapphire material, the property of optical axis (c-axis) in the crystal is an important factor that determines the physical property [44]. Precisely speaking, it appears that the direction of the c-axis must be taken into consideration for the evaluation of sapphire products.…”

Investigations on NiAl composites fabricated by matrix coated single crystalline Al2O3-fibers with and without hBN interlayer

“…For comparison, the compressive strength of sapphire along c-axis is also given in Fig. 12 as a function of temperature [23]. Two important conclusions are deduced from the FEM calculation: Firstly, the TACS in the fiber with hBN interlayer is obviously lower than that of without an hBN interlayer and remains invariably below the compressive strength of sapphire during cooling.…”

“…It has been found that as temperature increases the tensile strength of sapphire remains fairly constant. However, its compression strength along the c-axis decreases rapidly, down to 2%-3% of the room temperature compressive strength at 600uC-800uC [23,26]. This is attributed to twinning on 10 12 À Á -planes [23].…”

“…However, its compression strength along the c-axis decreases rapidly, down to 2%-3% of the room temperature compressive strength at 600uC-800uC [23,26]. This is attributed to twinning on 10 12 À Á -planes [23]. Since twinning causes the shrinkage along the c-axis and an expansion perpendicular to the c-axis, twinning can only occur under compressing but not under tension along the c-axis.…”

“…Since twinning causes the shrinkage along the c-axis and an expansion perpendicular to the c-axis, twinning can only occur under compressing but not under tension along the c-axis. Sapphire will fracture when twins on different 10 12 À Á -planes intersect due to the uncoordinated shear of the atoms on the intersection position [23]. It is deduced according to the results of FEM analysis that the fiber damage likely occurred in a temperature range of about 680 to 790 K (about 400uC to 510uC) during cooling, because in this temperature range the TACS in the fiber is obviously larger than compressive strength of sapphire ( Fig.…”