Influence of microstructural heterogeneity on the micro-meso deformation of a two-phase TiAl alloy investigated by nanoindentation and a numerical two scale model

Abstract

Micro and meso scale deformation behavior of a (a2+g) TiAl alloy has been investigated by multiscale modeling and nanoindentation testing using Berkovich indenter. A duplex microstructure, which consists of globular grains of g-TiAl phase and lamellar colonies of (a2Ti3Al + gTiAl) phases, has been examined. The micro-meso length scales are coupled in a previously validated FE2 multiscale approach. The constitutive behavior of the phases is described in a crystal plasticity model. The FE2 model is adjusted to capture important microstructural information, such as, volume percentage of the phases, orientation, lamellae thickness, etc. on a micro scale, and the size of grains/colonies as well as their distribution on a meso scale. The deformation behavior of the individual grains and colonies are examined by nanoindentation testing and correlated with the local microstructural heterogeneities. By means of simulations it will be shown that the model can predict the microstructure-dependent alloy response as seen from the nanoindentation testing. Furthermore, results will be shown that explain the anisotropic dependency of the yield, contribution of the dislocation-slips of the phases on the mesoscopic deformation of grains/colonies, and the influence of the microstructural heterogeneities on the local plastic strain accumulation.