Role of cellular structure on deformation twinning and hetero-deformation induced strengthening of laser powder-bed fusion processed CuSn alloy

The sub-grain cellular dislocation structure has been reported to be the primary reason for the enhanced mechanical properties in laser powder-bed fusion (LPBF) parts. In the current work, the contribution of the cellular dislocation structure to the yield strength of LPBF processed CuSn alloy is estimated to be -45%. In addition, this work shows that the cellular dislocation structure significantly controls the deformation behavior of LPBF processed CuSn alloy by suppressing the formation of deformation twinning. Post-LPBF heat treatment with fully recrystallized microstructures devoid of cellular dislocation structure showed pronounced twinning activity. The reduced homogeneous slip length due to the fine dislocation cell structure -600 nm and increased stacking fault energy due to the cellular Sn segregation significantly increased the activation energy for the nucleation and propagation of the partial dislocations and suppressed the deformation twinning in the as-built samples. Furthermore, the present work shows that cellular dislocation structure contributes significantly to the heterodeformation induced strengthening, much higher than the heterogeneous grain structure in the LPBF samples.