Moore I J, Burke M G, Nuhfer N T, Palmiere E J
1Department of Materials Science and Engineering, The University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD UK.
2Materials Performance Centre, The University of Manchester, The Mill, Sackville Street, Manchester, M13 9PL UK.
J Mater Sci. 2017;52(14):8665-8680. doi: 10.1007/s10853-017-1091-9. Epub 2017 Apr 24.
The growth/coarsening kinetics of precipitates have been found by numerous researchers to show an apparent correspondence with the classical (Ostwald ripening) equation outlined by Lifshitz, Slyozov and (separately) Wagner for a diffusion controlled regime. Nevertheless, a significant disparity between the actual precipitate size distribution shape and that predicted by LSW is frequently observed in the interpretation of these results, the origin of which is unclear. Analysis of the literature indicates one likely cause for this deviation from LSW for precipitates is the "encounter" phenomenon described by Davies et al. (Acta Metall 28(2):179-189, 1980) that is associated with secondary phases comprising a high volume fraction. Consequently, the distributions of both precipitates described in the literature (Alloy 718) and measured in this research in Alloy 625 are analysed through employing the Lifshitz-Slyozov-Encounter-Modified (LSEM) formulation (created by Davies et al.). The results of the LSEM analysis show good far better agreement than LSW with experimental distributions after the application of a necessary correction for what is termed in this research as "directional encounter". Moreover, the activation energy for coarsening in Alloy 625 shows conformity with literature data once the effect of heterogeneous (on dislocations) precipitate nucleation at higher temperatures is accounted for.
众多研究人员发现，析出相的生长/粗化动力学与Lifshitz、Slyozov以及（独立地）Wagner提出的用于扩散控制机制的经典（奥斯特瓦尔德熟化）方程表现出明显的对应关系。然而，在对这些结果的解释中，经常观察到实际析出相尺寸分布形状与LSW预测的形状之间存在显著差异，其原因尚不清楚。文献分析表明，析出相偏离LSW的一个可能原因是Davies等人（《金属学报》28(2):179 - 189, 1980）描述的“相遇”现象，该现象与包含高体积分数的第二相有关。因此，通过采用Lifshitz - Slyozov - 相遇 - 修正（LSEM）公式（由Davies等人创建），对文献中描述的析出相（合金718）和本研究中测量的合金625中的析出相分布进行了分析。LSEM分析结果表明，在对本研究中称为“定向相遇”的情况进行必要校正后，与实验分布的一致性比LSW好得多。此外，一旦考虑到较高温度下非均匀（在位错上）析出相形核的影响，合金625中粗化的激活能与文献数据相符。
