Growth and transformation mechanisms of 18R and 14H in Mg–Y–Zn alloys
Growth and transformation mechanisms of 18R and 14H in Mg–Y–Zn alloys
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DOI：
10.1016/j.actamat.2012.08.022
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发表时间：
2012-11
期刊：
影响因子：
9.4
通讯作者：
Yuman Zhu;A. Morton;J. Nie
中科院分区：
文献类型：
--
作者：
Yuman Zhu;A. Morton;J. Nie
研究了Mg-8 Y-2 Zn-0.6Zr（wt.%）合金中18 R和14 H相的生长和转变。使用常规透射电子显微镜和原子分辨率高角环形暗场扫描透射电子显微镜对合金进行了检查。18 R和14 H在α-Mg基体中的生长都是通过台阶机制进行的，颗粒的厚度随着其传播而增加台阶的高度。18 R和14 H的生长台阶或断开的单位高度分别为1.563nm和1.824nm，位移矢量为a/3 <$1 <$0 10 <$α。18 R在500°C的长时间热处理过程中原位转化为14 H。18 R到14 H的转变最容易发生在18 R结构在结构单元堆叠中具有不规则性的区域，特别是一对相邻结构单元被四个而不是两个α-Mg层分开的区域。18 R向14 H的扩散-位移相变速率受Y和Zn原子向偏析层的扩散速率控制。
The growth of and transformation between 18R and 14H phases in a Mg–8Y–2Zn–0.6Zr (wt.%) alloy have been examined using conventional transmission electron microscopy and atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The growth of both 18R and 14H within the α-Mg matrix occurs via a ledge mechanism, with the thickness of the particle increasing by the height of the ledge as it propagates. The unit height of the growth ledges or disconnections is 1.563nm for 18R and 1.824nm for 14H, and the displacement vector is a/3〈1¯010〉α. 18R transforms in-situ to 14H during prolonged heat treatment at 500°C. The 18R to 14H transformation is shown to occur most readily in regions where the 18R structure has irregularities in the building block stacking, in particular where a pair of adjacent building blocks is separated by four rather than two α-Mg layers. It is proposed that the diffusional-displacive 18R to 14H transformation rate is controlled by the diffusion rate of Y and Zn atoms into the segregation layers.