Creating High Plasticity in Hard Ceramics via Coherent Twin Boundary Migration-Driven Detwinning

Lacking plasticity at room temperature is a critical limiting factor preventing the widespread use of hard ceramics, which exhibit many superior qualities but are brittle and susceptible to catastrophic failure. Coherent twin boundaries (CTBs) hold the potential to solve this difficult problem, but challenges remain. Here, we unveil a radically contrasting twin boundary migration (TBM)-driven detwinning mechanism that creates high plasticity in hard ceramics via collective motion and eventual annihilation of CTBs. Translational crystal symmetry breaking induced by CTBs allows strain concentration and energy-efficient segmented sequential local bond flipping to drive the TBM process while maintaining the intrinsic ultimate strength. Electronic structure analysis further reveals that CTBs enhance electron delocalization and weaken local bonding, thus enabling bond flipping and structural rearrangement. This work provides a conceptual breakthrough in understanding plastic deformation in hard and brittle crystals and opens a new pathway for overcoming the long-standing strength-toughness trade-off in transition-metal nitrides.