Diverse kinetic pathways in shock-compressed phase transitions of a metallic single crystal

Substantial gaps in solid-solid phase boundaries under hydrostatic and uniaxial compression have recently garnered great attention, though the underlying physics remains unclear. In this study, through molecular dynamics simulations of shock-compressed fcc Cu single crystals, we report pronounced orientation-dependent fcc-to-bcc phase transition pressures following the trend [100] < [110] < [111] ≈ thermodynamic phase boundary. We uncover a fundamental crystallographic law that explains these phase boundary gaps, rooted in the classical orientational relationship of martensitic transformations: the degree of alignment between loading directions and the easiest atomic moving path plays a critical role in determining phase transition pathways. The complex, orientation-dependent phase transition pathways and the observed temperature equilibrium efficiency ranking [100] > [110] > [111] further support the validity of this crystallographic law. This law is broadly applicable to fcc crystals, indicating that phase composition can be controlled by the method of compression, providing a new framework for selective polymorph formation.