Plasticity and fracture of sapphire at room temperature: Load-controlled microcompression of four different orientations

We report the mechanical behavior and deformation mechanisms in sapphire (Al2O3) studied using ~1 µm diameter micro-pillar compression experiments performed in situ in a scanning electron microscope (SEM) at room temperature. Four crystallographic orientations: 〈10 –10〉, 〈1 –210〉, 〈0001〉 and 〈−1012〉 corresponding to M, A, C and R planes respectively, were studied. The residual deformations of the four planes were analyzed using Schmid law and geometric observations. Several deformation mechanisms such as cracking and plasticity were observed in our tests, and their probability of occurrence were strongly orientation dependent. Thus, for the same pillar size, pillars oriented along 〈1 −210〉 are more prone to deform plastically than those 〈10 –10〉 oriented. For pillars exhibiting plasticity, the resolved shear stress achieved just before the load drop was close to one thirtieth of the shear modulus and was consistent with heterogeneous nucleation mechanisms.