Five-fold twin formation in face-centered cubic metals under impact loading

Five-fold twins (FFTs) are unique microstructural features in face-centered cubic (FCC) metals that significantly influence their mechanical strength. This study examines FFT formation in Cu, Au, and Ni under high-strain rate conditions induced by cold spray and compression shock impact loading, using atomistic simulations. We reveal a sequential twinning mechanism for FFT formation under impact loading, where the specific growth path varies, leading to inherently unstable FFTs that decompose post-formation. Interestingly, impact velocity had minimal influence, while elevated temperatures suppressed FFT formation, suggesting a dependency on the twinning mechanism. The stacking fault energy of the FCC metal greatly affected FFT propensity; metals with lower stacking fault energy (e.g., Au) readily formed FFTs, while those with higher stacking fault energy (e.g., Ni) encountered greater difficulty. These findings provide new insights into the behavior of FFTs under dynamic loading conditions, with implications for the design of high-strength nanocrystalline materials.