Grain Growth Behaviour Of Nanocrystalline Nickel

Abstract

The thermal stability of electrodeposited nanocrystalline Ni-1.2%P and Ni-0.12%S alloys is evaluated by in-situ electron microscopy studies. Isothermal grain size versus annealing time curves at 573K and 623K show an unexpected thermal stabilization in form of a transition from rapid initial grain growth to negligible grain growth. This behaviour is discussed in terms of the various grain boundary drag mechanisms which may be operative in these alloys.

Grain boundary migration during abnormal grain growth in nanocrystalline Ni

“…An earlier in situ TEM annealing study of electrodeposited nanocrystalline Ni [9] reported very different annealing behaviour from that presented in Fig. 3.…”

“…3. In that study, 10 nm starting grain size Ni was annealed at 573 K for a period of 20.5 h; the grain size increased from the 10 nm starting size to ∼30 nm after 90 min, and stabilized at that size through the remaining 1140 min of the experiment [9]. It is likely that a thin foil effect was responsible for this stabilizing behaviour, considering that it has not been observed in any bulk ex situ annealing experiment of nanocrystalline Ni produced by the same synthesis method (e.g.…”

“…In situ TEM annealing has been used to investigate grain growth of nanocrystalline materials in a number of studies [9,[20][21][22][23][24][25][26][27][28], but most [9,[20][21][22][23][24][25][26][27] have not reported this type of migration behaviour. One possible explanation stems from differences in sampling rates.…”

“…[9][10][11][12][13][14]). Calorimetric studies have shown a broad, low energy exotherm followed by a main heat release peak [10], having an activation energy similar to that of grain boundary self-diffusion [11].…”

“…Calorimetric studies have shown a broad, low energy exotherm followed by a main heat release peak [10], having an activation energy similar to that of grain boundary self-diffusion [11]. Transformation mechanisms have generally been inferred by characterizing annealed microstructures and tracing the structural evolution back to the initial state [9][10][11][12][13][14]. This approach has shown that the structure initially undergoes pronounced abnormal grain growth in which a few growth centers become activated, consuming an otherwise stable nanocrystalline matrix [10,11].…”