Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression

TL;DR

This study combines microstructure characterization, in-situ microcompression, and crystal plasticity finite element modelling to understand and predict the deformation anisotropy and internal stress build-up in lamellar TiAl alloys, with implications for improving ductility.

Contribution

It introduces a microstructure-based CP-FEM approach to analyze deformation mechanisms and internal stresses in lamellar TiAl, revealing how microstructural orientation affects anisotropy and ductility.

Findings

Longitudinal slip dominates in {25}^o microstructure.

Transverse deformation twinning can relieve internal stresses.

Internal stress build-up is detrimental to ductility.

Abstract

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 {\gamma}/{\alpha}_2 lamellar microstructure with the {\gamma}/{\alpha}_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 {\gamma}/{\alpha}_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.