Mechanically driven grain refinement in Mo by nanoindentation pop-ins: A case of transient instability.

Manually stopping load-controlled nanoindentation immediately after the first pop-in in single-crystal molybdenum (Mo) reveals transient pop-in–induced nucleation of new highly misoriented grains at room temperature.

• Why it matters: Prior nanoindentation studies likely missed these transient transformations because continued indentation mechanically erases the newly formed grains after the pop-in.
• What they did: Experiments on single-crystal Mo with different surface orientations combined with displacement-controlled atomistic simulations show twin-boundary evolution into random high-angle grain boundaries and dislocation rearrangement into HAGBs when a preexisting grain boundary blocks glide.
• The result: Continued indentation beyond the pop-in mechanically erases the grains in both experiments and simulations, establishing pop-in as a simple platform to qualitatively probe transient microstructural evolution in defect-scarce metals.