Revealing the grain size-dependent microstructural evolution of Cu-Sn-P polycrystals via in-situ EBSD

This study employed in-situ electron backscatter diffraction (EBSD) to systematically investigate the microstructural evolution of CuSn10P1 polycrystalline alloy as tensile strain increased from 0 % to 15.3 %. The results and findings are as follows: (1) With increasing strain, the fraction of LAGBs (2°–10°) rose sharply from an initial 2.79 % to 28.4 % at 15.3 % strain, predominantly forming within the fine-grain regions and near HAGBs in coarse grains. Analysis of the Nye tensor α 13 component revealed that significant back-stress accumulation is exclusively associated with LAGBs, whereas HAGBs contribute negligibly to GND accumulation, providing direct microscale evidence for hetero-deformation-induced strengthening. (2) A pronounced grain-size-dependent deformation mechanism was identified: coarse grains accommodate deformation mainly through intragranular multiple-slip activation, non-uniform lattice rotation, and subgrain formation, resulting in large intragranular orientation gradients and a dispersed pole figure distribution; in contrast, fine grains, strongly constrained by grain boundaries, deform via collective, coherent grain rotation, exhibiting uniform internal orientation changes and almost no slip traces, thus demonstrating a collective deformation characteristic. (3) GND density analysis showed that the average dislocation density in the fine-grain region consistently exceeds that in the coarse-grain region throughout deformation, reaching 11.6 × 10 14 m -2 at 15.3 % strain, underscoring the superior dislocation storage capacity of fine grains under constraint. These results provide an important theoretical foundation for the strength-toughness balance in this class of alloys.