Grain-Growth Kinetics of Nanocrystalline Iron Studied In Situ by Synchrotron Real-Time X-ray Diffraction

Abstract

Pulsed electrodeposition (PED) is used to prepare nanocrystalline iron with an average grain size of 19 nm and thermal stability up to 550 K. At 663 K e T e 783 K the kinetics of grain growth, with respect to size and size distribution, is studied in situ by means of real-time synchrotron X-ray diffraction. The Bragg peak line shapes of the large number of diffractograms are analyzed using a Warren/Averbach procedure improved with respect to reliability and efficiency. We observe two regimes of grain growth: at less elevated temperatures grain growth is smooth and moderate up to limiting size values between 50 and 100 nm, depending on temperature. The initially rather narrow width of the size distribution increases slightly, and the activation energy of grain growth, about 100 kJ/mol, corresponds to the literature value for grain boundary self-diffusion in nanocrystalline Fe. At higher temperatures the grains grow first rapidly and then slowly up to limiting values between 200 and 400 nm, depending on temperature. The size distribution becomes rather broad, and the activation energy for grain growth, about 175 kJ/mol, corresponds to the literature value for grain boundary self-diffusion in coarse-grained polycrystalline Fe. We do not find evidence for a change of the type of distribution which indicates normal grain growth. The quality of our diffraction data allows a critical evaluation of different kinetic models of grain growth.

Role of Nanostructure in Electrochemical Corrosion and High Temperature Oxidation: A Review

“…[26][27][28][29] For example, iron and iron based-alloys resist grain growth up to 673 K to 873 K (400°C to 600°C). [12,28,[30][31][32][33][34][35] Similar behavior has been reported for other metals (e.g., Co [36] ). However, there are some inconsistencies in the literature on the temperature at which rapid grain growth is initiated.…”

“…The techniques of inert gas condensation, [3,[47][48][49][50] pulsed plasma deposition, [25] and sputtering [48] have exclusively been used for processing thin films or small amounts of nanocrystalline materials, whereas it is necessary to produce/process bulk samples for oxidation/corrosion or mechanical testing. Electrodeposition [33,34,51] and severe plastic deformation [28][29][30][31][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] have been recognized as the two relatively successful routes for processing thicker/larger sections of nanocrystalline metals and alloys. Pulsed electrodeposition has been employed successfully for processing nanocrystalline materials in bulk, [51] most notably, Ni-Fe and Ni-Co alloys.…”

Solute stabilization of nanocrystalline tungsten against abnormal grain growth

“…(1) and demonstrated that an enhanced grain boundary mobility is accompanied by a reduced activation energy for grain growth. 13,17,20 However, the onset of microstructural evolution in a range of nanocrystalline metals often transpires through an abnormal growth process, which has been observed in copper, 21,22 nickel, 21,23 iron, 24 palladium, 13 and cobalt 15 as well as a number of binary nanocrystalline alloys. [25][26][27] As the average grain size increases from the nanocrystalline to the ultrafine grain regime, abnormal grain growth widely succumbs to curvature-driven mechanisms, 28 thus underscoring the importance of stabilizing the nanostructure collectively against the initial and late stages of grain growth in nanocrystalline metals.…”

Nanocrystalline materials studied by powder diffraction line profile analysis

“…Both methods showed a wide size distribution with the mean value of 15 nm and the variance of 1.5. The graingrowth kinetics of nanocrystalline Fe was investigated in situ by synchrotron real-time X-ray diffraction during isothermal heat treatments at temperatures between 663 and 783 K [64]. Strain was expressed in terms of the meansquare-strain and the size distribution was assumed to be log-normal.…”