Cr、Mn、Co、Ni掺杂对Al13Fe4相稳定性和力学性能影响的第一性原理研

采用基于密度泛函理论的第一性原理计算方法,系统地研究了不同掺杂浓度下过渡族元素Cr、Mn、Co、Ni在Al13Fe4相中的占位情况、结构稳定性和机械性能. 计算得到所有的Al13(Fe24-xMx) (M=Cr、Mn、Co、Ni;X=1,2,4)相都具有良好的热力学稳定性和机械稳定性. 相同掺杂浓度化合物的形成焓按如下顺序减小：Al78(Fe24-xCrx) > Al78(Fe24-xMnx) > Al13Fe4 > Al78(Fe24-xNix) > Al78(Fe24-xCox).形成焓的降低增加了Al13Fe4相成核驱动力,Co和Ni有利于促进Al-Fe合金中Al13Fe4相形核,细化Al13Fe4相. 过渡族元素可以改善金属间化合物的脆性,增强塑性变形能力. 并且随着掺杂浓度的增加,过渡族元素的加入对脆性的改善呈先增大后减小的趋势.     

Growth instability and surface phase transition of Ti thin film on Si(1 1 1): An atomic force microscopy study

Evolution of surface structure during the annealing of e-beam evaporated Ti films is studied by means of atomic force microscopy (AFM). Image variography and power spectral density analysis are used to study scaling properties of the films, ranging from 50 nm to 20 μm length scale. No particular grain size is observed up to 473 K. At 673 K, grain size of ∼250 nm are formed and coalesced to form bigger grain size upon further annealing. At 473 K, RMS roughness dropped at all length scale and became rougher at 673 K with an increasing trend up to 873 K. Clustering at 673 K indicates Kosterlitz-Thaouless [J.M. Kosterlitz, D.J. Thaouless, J. Phys. Chem. 6 (1973) 1181] type phase transition at the surface. The observed transition is also consistent with existing scaling laws.