Ti3SiC2:: A damage tolerant ceramic studied with nano-indentations and transmission electron microscopy

Nano-indentations into Ti3SiC2 grains with their basal planes either oriented parallel or perpendicular with respect to the surface were performed. These grains were selected on the basis of orientation imaging microscopy (OIM). Scanning electron microscopy analysis of the indentations clearly showed that for grains whose basal planes are oriented parallel to the surface the elastic recovery and hardness values are lower, the plastic deformation larger, and the pile up around the indents larger than for the perpendicular orientation. These observations are explained by the deformation mechanism, i.e. kink-band formation that operates at room temperature in Ti3SiC2. Kink bands are more easily formed during indentations when the basal planes are parallel to the surface. For comparison indentations were also performed in 6H-SiC with the basal planes parallel and perpendicular to the surface. For 6H-SiC the results are identical for both orientations, apart from the initial peak hardness and modulus that occur during loading for small indenter depths. In both Ti3SiC2 and 6H-SiC these initial peak values for both properties are lower when the basal planes are oriented perpendicular or edge on to the surface. This is attributed to the cleavage fracture between basal planes that occur under the indenter tip for the perpendicular orientation initially during loading. Some results of the High Resolution Transmission Electron Microscopy analysis of stacking faults in Ti3SiC2 and Conventional TEM analysis of dislocation walls in kink bands invoked during indentation are also shown. From the TEM observations of wedge cracks, the shear and normal stresses that resulted in these cracks are estimated and found to be in agreement with the estimates derived from the nano-indentation experiments. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.