Nano-scale precipitation and phase growth in Mg-Gd binary alloy: An atomic-scale investigation using HAADF-STEM

Publication date: 5 January 2018
Source:Materials & Design, Volume 137
Author(s): Jingxu Kent Zheng, Ruichun Luo, Xiaoqin Zeng, Bin Chen
In the present study, nanoscale precipitation and phase growth in Mg-15Gd(wt%) binary alloy are comprehensively studied by atomic-resolution high angle annular dark field - scanning transmission electron microscopy (HAADF-STEM). Various nanoscale precipitate structures, including βH, β^′, βT′, βM and β^′′-like structure, assembled by the "basic unit" as building block, are observed, reconstructed and discussed in detail. In the early stage of precipitation, the precipitate growth basically follows y (nm)=1.53x−2.68 (nm) and protrusions start to grow when the size of a precipitate reaches a threshold value. Long-range diffusion of Gd solute preferentially proceeds along <101¯0>Mg directions and protrusions are formed. A large number of fine β^′ precipitates exist and act as the key strengthening structures. The formation of precipitate-free zones in the over-age condition is attributed to the intertwining of precipitates.

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