Influence of grain orientation on hardness anisotropy and dislocation behavior of AlN ceramic in nanoindentation

Abstract The anisotropic hardness, elastic modulus, and dislocation behavior of AlN grains were investigated by Berkovich nanoindentation. Grain orientation had a strong correlation with hardness and elastic modulus. The hardness of the basal plane (0001) was higher than those on the two prismatic planes ( 10 1 ‾ 0 ) and ( 1 ‾ 2 1 ‾ 0 ), while the modulus was showing the opposite trend. Further investigation on the deformation behavior of AlN revealed that pop-in, pile-up and slip lines only occurred on the two prismatic planes ( 10 1 ‾ 0 ) and ( 1 ‾ 2 1 ‾ 0 ). Through molecular dynamics (MD) simulation, the mechanisms of anisotropic pop-in events and dislocations were disclosed. The activation of the slip system for different grain orientations was presented by Schmid factor. The method of using Schmid factor to determine the activated slip system was verified by the observation of pile-up and slip lines around the indent, and proven to be accurate in identifying the grain orientation of AlN ceramic. Lower hardness and higher modulus were found to be related to more plastic events like pop-in, pile-up and slip lines, and the crystalline orientation could be roughly determined by the observation of plastic activities from nanoindentation.