Incipient and regular kink bands in fully dense and 10 vol.% porous Ti2AlC

The ternary carbide Ti2AlC is a member of a large class of solids recently classified as kinking nonlinear elastic (KNE) solids because they deform primarily by the formation of kink bands. We report on the response of fully dense and 10 vol.% porous polycrystalline Ti2AlC samples to uniaxial compression and indentation by a hemispherical nanoindenter. The salient features of the kinking-induced behavior can be described by four interrelated loading parameters (stress a, nonlinear strain epsilon NL, stored nonlinear energy per unit volume U-NL, and dissipated energy per unit volume W-d) all of which can be obtained from stress-strain curves. The experimental data described are in excellent agreement with our recently proposed model for KNE solids. In the model, W-d scales with sigma(2) and U-NL with epsilon(1.5)(NL) both predictions observed over a very large stress range. Analysis of the results further indicates that the dislocation density, at the maximum stress of 350 MPa, is similar to 10(13) m(-2). From the model, the critical resolved shear stress on the basal planes can also be estimated. In the present case, it is similar to 22 MPa. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.