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Lamellar γ-TiAl has a microstructure that spans multiple length scales: lamellar thickness (10 nm–1 μm), γ domain length (100 nm–10 μm) and colony size (100 μm–1 mm). Only by characterizing the deformation across the different scales can one understand how the microstructure influences plasticity and damage formation in this material. Here, we use digital image correlation and electron backscatter diffraction to map strain and lattice rotation with both sub-colony and sub-lamella spatial resolution in a polycrystalline lamellar γ-TiAl alloy with TiB 2 inclusions. Two lamellar thicknesses and temperatures are tested. It is shown that the hard mode-oriented colonies undergo minimal plastic strain. However, as the temperature is increased, macroscopic deformation bands develop across colonies of different orientations, independent of their local lamellar orientations. Increasing magnification, it is apparent that some segments of these bands occur by slip or twinning parallel to the lamellae, and others by transverse lattice rotation. In the thin lamellar condition, such macroscopic deformation bands also occur along colony boundaries; this causes a significant inhomogeneity in the strain distribution. Such strain inhomogeneities are also further characterised here at the microstructural scale of single lamellae, and locally at boride particles. • Nanoscale resolution digital image correlation (HR-DIC) strain mapping up to 700 °C. • Characterisation of plastic deformation and mechanical damage across multiple length scales in lamellar γ-TiAl. • Macroscopic bands of heightened deformation developed, focused at grain boundaries. • Methods to repress deformation bands by microstructural modifications are discussed. [ABSTRACT FROM AUTHOR]

Detailed microstructure characterisation and in-situ micropillar compression were coupled with crystal plasticity-based finite element modelling (CP-FEM) to study the micro-mechanisms of plastic anisotropy in lamellar TiAl alloys. The consideration of microstructure in both simulation and in-situ experiments enables in-depth understanding of micro-mechanisms responsible for the highly anisotropic deformation response of TiAl on the intra-lamella and inter-lamella scales. This study focuses on two specific configurations of γ / α 2 lamellar microstructure with the γ / α 2 interfaces being aligned 25 o and 55 o to the loading direction. Microstructure-based CP-FEM shows that longituginal slip of super and ordinary dislocations are most responsible for the plastic anisotropy in the 25 o micropillar while the anisotropy of the 55 o micropillar is due to longitudinal superdislocations and longitudinal twins. In addition, transversal superdislocations were more active, making the deformation in the 25 o micropillar less localised than that in the 55 o micropillar. Moreover, the CP-FEM model successfully predicted substantial build-up of internal stresses at γ / α 2 interfaces, which is believed to be detrimental to the ductility in TiAl. However, as evidenced by the model, the detrimental internal stresses can be significantly relieved by the activation of transverse deformation twinning, suggesting that the ductility of TiAl can be improved by promoting transverse twins. Deformation behaviour of (ϕ = 25 o )- and (ϕ = 55 o )-pillars: in-situ observation versus CP-FEM results. Image 1 • Crystal plasticity of lamellar TiAl is studied by in-situ testing and modelling. • CP-FEM well predicts the constitutive response and localisation of lamellar TiAl. • This study reveals the micro-mechanisms of anisotropy of lamellar TiAl. • Deformation twinning significantly relieves internal stresses at γ / α 2 interfaces. [ABSTRACT FROM AUTHOR]