Just another WordPress site - Ruhr-Universität Bochum
Influence of lattice misfit on the deformation behaviour of α2/γ lamellae in TiAl alloys
Interfaces play a significant role in the deformation behaviour of lamellar two-phase TiAl alloys and contribute to their increased strength. We study the deformation behaviour of α2/γ bilayers with either coherent or semicoherent interfaces, using atomistic simulations. We identify the nucleation sites for dislocations and decouple the effects of the microstructural parameters volume fraction and layer thickness on the yield stress and strain. Uniaxial tensile tests are carried out on bi-layer specimens with α2 and γ phases along directions parallel and perpendicular to the interface. Coherent α2∕γ bi-layers show residual stresses due to lattice mismatch which are linearly related to the volume fractions of the phases. These residual stresses, superimposed with tensile stresses during loading, lead to early yielding of the γ phase. In contrast, a semi-coherent interface leads to negligible residual stresses, but contains misfit dislocations which create localized stresses within the γ layer and thus contributes to dislocation nucleation. We show that along loading directions parallel to the interface, the layer thickness does not affect the deformation behaviour, irrespective of the type of interface, instead volume fraction is the governing parameter. When loading perpendicular to the interface, the absolute layer thickness does not affect the deformation behaviour of a bi-layer with a coherent interface, but determines the yield stress and strain in case of a semi coherent interface.