Deformation mechanisms in TiAl intermetallics - experiments and modeling

The mechanical properties of intermetallic gamma-TiAl based materials depend strongly on the microstructure, which in turn is influenced by the alloy chemistry and the applied heat treatment. First, a computational study of the room temperature deformation behavior of gamma-TiAl based two-phase alloys exhibiting a globular near-gamma microstructure is presented. The micro-mechanical model is based on the unit-cell technique using the finite element method. In the applied crystal plasticity concept crystallographic slip and deformation twinning are taken into account as the dominant deformation mechanisms. The conclusions drawn from the simulations are discussed and compared to experimental results obtained from acoustic emission measurements and transmission electron microscopy investigations. Furthermore, the creep behavior of a designed fully lamellar (DFL) gamma-TiAl microstructure is investigated. Differently spaced DFL microstructures were adjusted in order to investigate their influence on creep. The interface spacing was varied in the range of 1.2-0.14 mum by altering the cooling rates from 1 to 200 K/min, and short term creep tests were carried out in air under various temperature/load conditions. A first approach in modeling the steady state creep deformation of the fully lamellar material in question is presented. A power law description for diffusion controlled dislocation creep is proposed, and a structure factor is introduced which depends on the lamellar orientation with respect to the loading axis as well as on the mean lamellar interface spacing. (C) 2002 Elsevier Science Ltd. All rights reserved.