Exploring grain-resolved strain tensors and non-uniform lattice deformations with Laue 3DNDT

Abstract

Oligocrystalline and polycrystalline materials often display intricate grain-resolved deformation behaviours due to grain interactions, size effects, defects, and crystalline anisotropy. Gaining a deep understanding of grain deformation mechanics is essential for optimising the performance of materials in engineering and other applications. This necessitates the development of advanced experimental and theoretical tools to accurately capture and analyse these complex behaviours. Here, Laue three-dimensional neutron diffraction tomography is introduced as a high-throughput, non-destructive method to characterise grain-resolved strain and orientation changes in an oligocrystalline Co-Ni-Ga ferromagnetic shape-memory alloy during compressive deformation. Grain-resolved strain tensors were determined for 7 out of the total 11 grains indexed with a strain resolution of approximately 10⁻³, over an applied strain range of 0% – 2%. These results were obtained across various stress steps in situ, enabling direct comparisons with single-crystal models and elasto-viscoplastic Fast Fourier Transform simulations. The study demonstrates how accurate modelling of deformation behaviour, even in the elastic regime, requires detailed knowledge of the sample microstructure. Furthermore, the results reveal non-uniform deformation mechanics within individual grains, emphasising the value of Laue 3DNDT in understanding meso-scale material behaviour.