Bending-induced phase transformations and penta-twinning in molybdenum: From nano to microscale

Understanding phase transformations (PT) under bending is essential for designing ductile refractory nanomaterials. Here, we systematically investigate deformation mechanisms in single-crystalline molybdenum (Mo) nanowires through molecular dynamics simulations and microcantilever bending experiments. Under monodirectional bending, we uncover a sequential bcc 1 → quasi-stable fcc → bcc 2 transformation, with fcc Mo acting as a lubricating layer that facilitates lattice rotation and relative motion. This quasi-stable fcc phase, maintained under high stress but disappearing upon unloading, reveals a stress-stabilized intermediate structure in bcc systems. Geometrically necessary dislocation calculations further confirm that dislocations alone cannot account for the observed bcc reorientation, establishing PT as the dominant deformation mechanism. Next, in bidirectional bending simulations, we discover { 112 } penta-twin formation in both the tensile and compressive regions of the Mo nanowire—behavior often seen in fcc systems. Unloading simulations further demonstrate the persistence of these twins under stress-free conditions. Our simulations and experiments bridge nanoscale and microscale observations, highlighting how bending-driven PT can be harnessed to enhance strength and ductility. These insights open pathways toward designing ductile, flexible refractory nanomaterials through controlled-PT engineering.