An in-situ tem study of the thermal stability of nanocrystalline NiP

Intermittent ‘self-locking’ of grain growth in fine-grained materials

“…A second experimental example which can be used to support the present approach is provided by the observations of grain growth in nanocrystalline Ni-1.2wt.%P with an initial grain size of 5 to 10 nm [13]. In situ measurements in a transmission electron microscope demonstrated that no grain growth occurred at 473 K, while at 573 K and above discernible grain growth was recorded.…”

Evaluations of Mechanical Properties of Electrodeposited Nickel Film by Using Micro-Testing Method

“…This method used an automated system involving series of sidewall milling and rotation while the specimen tilted several degrees with respect to the beam direction. The automated system including image correlation procedures and stage manipulation steps developed by Shade and Uchic 5) . On the other hand, the fabrication method developed in our group applied two Ga ion beam directions perpendicular to axes of the pillar to fabricate non-tapered pillars with square cross-section 6,7) .…”

Phase transitions in stable nanocrystalline alloys

“…The latter mechanism is particularly promising, as substantial decreases to the grain boundary energy from grain boundary segregation could stabilize nanoscale grain sizes to higher temperatures and for longer times. [8][9][10][11][12][13] There is an even more enticing prospect when alloying to reduce the grain boundary energy: if the excess energy of the grain boundary is eliminated by grain boundary segregation, grain growth can be entirely avoided and a thermodynamically stable grain size in the nanocrystalline regime could exist. This concept was put forth by Weissmüller,14,15 with an accompanying analytical model that revealed that a system with an enthalpy of grain boundary segregation large enough to offset the pure grain boundary energy should have such a stable nanocrystalline state.…”

“…Several of these alloy systems have shown considerable nanometer-scale grain size stability in experiments, including Ni-P, Ni-W, Fe-Zr, and W-Ti. [8][9][10][11][12][13] While these models are able to identify systems with potential stability through energetic considerations of grain boundary segregation, the accurate accounting of entropic effects has been limited by assumptions needed to make the analytical models tractable, i.e., dilute limit or regular solution assumptions. A number of analytical [20][21][22][23] and atomistic models 24,25 have been developed for determining the change in free energy associated with grain boundary segregation under a variety of conditions, but typically do not allow the grain size to change during disordering.…”

“…Pure nanocrystalline materials undergo rapid grain growth into micron-scale grain sizes at relatively low homologous temperatures, [1][2][3][4] but with the addition of alloying elements grain growth can be greatly hindered. [5][6][7][8][9][10][11][12][13] Two mechanisms for suppressing grain growth by alloying have been proposed: alloying elements can either kinetically impede grain growth by increasing the activation energy for grain boundary motion (effectively decreasing grain boundary mobility) or decrease the grain boundary energy thermodynamically through grain boundary segregation (or both). The latter mechanism is particularly promising, as substantial decreases to the grain boundary energy from grain boundary segregation could stabilize nanoscale grain sizes to higher temperatures and for longer times.…”