| Abstract Scope |
Plastic deformation in body-centered cubic refractory metals is traditionally interpreted through dislocation motion and twinning. In this talk, I will show that stress-induced metastable phase transformations constitute an equally important deformation pathway in molybdenum under extreme mechanical loading. Combining large-scale atomistic simulations with nanoindentation and microcantilever experiments, we reveal a previously unrecognized bcc→fcc→bcc transformation that mediates lattice reorientation, enables penta-twin formation, and promotes remarkable deformation behavior across multiple loading conditions. Under bending, the transient fcc phase acts as a stress-stabilized intermediate that accommodates large lattice rotations, while under ultrahigh strain-rate nanoindentation pop-ins, massive dislocation nucleation and transformation-assisted mechanisms drive room-temperature new grains formation in a material that normally recrystallizes only above ~900 °C. Together, these results establish metastable phase transformations as a governing mechanism for extreme deformation in molybdenum and provide new opportunities to engineer strength, ductility, and microstructural evolution in refractory metals through transformation-assisted plasticity. |