Wolfram Schillinger

Micromechanical mechanism of texture formation in γ-TiAl

Abstract Texture evolution in TiAl depends on the type of deformation such as uniaxial compression, tension or rolling as well as on the initial microstructure. Cast TiAl shows a lamellar microstructure with an alignment of the lamellae and exhibits a strong texture. Deformation parallel to the aligned lamellae results in a plane-strain deformation which leads to a brass type texture. From room temperature up to 700 °C, compression tests of TiAl specimens with equiaxed microstructures result in -fiber textures where the component is shifted to . At higher temperatures the orientation is caused by dynamic recrystallization. In rolled sheets of TiAl with equiaxed microstructure the main texture component is a modified cube texture {100} where the tetragonal c-axis is aligned in transverse direction of the sheet. This texture component is caused by dynamic recrystallization and appears to be stable against further rolling.

Strain Rate Dependence of the Deformation Mechanisms in a Fully Lamellar γ-TiAl-Based Alloy

Abstract The intention of this study was to investigate the mechanical properties of an engineering γ-TiAl-based alloy with fully lamellar microstructure under quasistatic and dynamic compression at room temperature and strain rates ranging from 5.0 × 10-3 s−1 to 4.0 × 103 s−1. The microstructure of undeformed and deformed specimens was investigated by means of optical and electron microscopy. The results of the compression tests exhibit a slight strain rate sensitivity of the postyield stress. The fracture behavior of the studied γ-TiAl alloy strongly depends on the applied strain rates. Transmission electron microscopy observations conducted on deformed specimens revealed the existence of a high number of tangled ordinary dislocations, curved superdislocations and mechanical twins. The analysis of the deformation texture confirms the high activity of superdislocations and mechanical twinning during dynamic compression testing.