# Molybdenum grains nucleated at room temperature by nanoindentation pop-in, Rochester and Technion report

- Published: 2026-11-15 15:58 UTC
- Section: Machines & Making › Materials science
- Tags: molybdenum recrystallization, room temperature grain nucleation, nanoindentation pop-in, high-angle grain boundaries, twinning in molybdenum, dislocation nucleation, single-crystal molybdenum, atomistic simulations, Niaz Abdolrahim
- URL: https://realtech.media/news/rt-19ac74ed5a566b0de5216380_molybdenum_grains_nucleated/

**Stopping a nanoindenter right after the first pop-in produced new highly misoriented grains in single-crystal molybdenum at room temperature, with no furnace annealing.**

![Molybdenum grains nucleated at room temperature by nanoindentation pop-in, Rochester and Technion report](https://realtech.media/media/2026/11/d05be61610dd59a0.jpg)
*chip.pl*

Engineers from the University of Rochester and the Technion–Israel Institute of Technology report that new grains can be nucleated in molybdenum at room temperature by mechanical loading alone. The results were published in Proceedings of the National Academy of Sciences. The experiments used single-crystal molybdenum with different surface orientations and a nanoindenter; the group was led by Prof. Niaz Abdolrahim. [1]

Molybdenum is used in nuclear reactor shielding, jet engine turbine blades and rocket nozzles, and its melting point exceeds 2600°C. At ambient temperature it is brittle. Recrystallization, the rebuilding of boundaries and formation of new grains, normally occurs in molybdenum only above about 1000°C.

## Pop-in as a window into transient deformation

In load-controlled nanoindentation of pristine metals, homogeneous dislocation nucleation appears as a sudden displacement burst, a pop-in. It is associated with shear stresses approaching the theoretical strength, massive dislocation nucleation and rapid, uncontrolled penetration of the indenter. [1] The authors terminated indentation manually immediately after the first pop-in, which gave direct access to the transient deformation. According to the experiments and simulations, a depth of only a few nanometers is enough to produce the pop-in. [1]

After the pop-in, new, highly misoriented grains were found at room temperature. The authors attribute this to two mechanically driven processes. In the first, twinning is activated and the twin boundaries evolve into random high-angle grain boundaries. In the second, dislocations rearrange into high-angle grain boundaries in regions of high local dislocation density. [1]

## Simulations and erasure of new grains

Displacement-controlled atomistic simulations reproduced both twin- and dislocation-mediated grain nucleation within an individual grain when a preexisting grain boundary blocked dislocation glide. Without such a boundary, the nucleated dislocations glided into the surrounding crystal and did not form new grains. [1]

Continued indentation beyond the pop-in mechanically erases the newly formed grains. This was confirmed in both experiments and simulations, and the authors say it explains why the phenomenon was not detected in earlier studies. [1] They describe the pop-in as a simple, widely accessible platform for qualitative study of transient microstructural evolution in metals with few defects. [1]

Doctoral student Afnan Mostafa said the technique removes the need to heat whole components to temperatures near 1000°C and allows local changes in the crystal structure without affecting the rest of the sample.

## Sources

1. [Proceedings of the National Academy of Sciences](https://doi.org/10.1073/pnas.2612140123)
2. [chip.pl](https://www.chip.pl/2026/11/rekrystalizacja-molibdenu-przypadkowe-odkrycie-otwiera-droge-do-miniaturyzacji-procesorow-nowej-generacji)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-19ac74ed5a566b0de5216380_molybdenum_grains_nucleated/