机械合金化Fe_(100-x)Cu_x体系的结构

利用XAFS和XRD方法分别研究了机械合金化 80h制备的Fe10 0 -xCux系统的晶体结构及Fe和Cu原子的局域配位环境 .结果表明 ,当x>4 0时 ,样品中Fe原子的bcc结构消失 ,Cu原子的近邻结构基本不变 ,fcc晶格参数随x的增加而减小 ;当x <30时 ,Cu原子的fcc结构消失 ,Fe原子的近邻结构基本不变 ,bcc晶格参数随Cu原子的比例减小而增大 ;而x=30左右时 ,fcc和bcc结构共存 .研究结果还表明 ,Fe原子和Cu原子的比例不是相差很大时 ,Fe原子和Cu原子的近邻配位无序度会在很大的范围内变化 ,说明Fe -Cu二元体系不可能形成均匀的过饱和固溶体 ,存在Cu富集区和Fe富集区 。

机械合金化Fe100—xCux体系的XAFS研究

本文利用XAFS方法研究机械合金化方法制备的Fe100-xCux(x=0,10,20,40,60,70,80,100,x为原子百分比）合金中Fe、Cu原子的局域环境结构随组成的变化。对于Fe100-xCux二元混合物，当x≥40时，Fe原子的近邻配位结构从bcc转变为fcc，但Cu原子的近邻结构保持其fcc不变；与之相反，当x≤20时，Fe原子的近邻配位保持bcc结构而Cu原子的近邻配位结构从fcc转变为bcc结构。XAFS结果还表明fcc结构的Fe100-xCux中Fe的无序因子σ（0．009A）比bcc结构的Fe100-xCux中的σ（0．081A）大得多；并且在同一机械合金化Fe100-xCux（x≥40）样品中Fe原子的σ（0．099A）比Cu原子的σ（0．089A）大。这表明机械合金化的Fe100-xCux样品中Fe和Cu原子可以有相同的局域结构环境但不是均匀的过饱和固溶体，而是fcc或bcc合金相同时存在Fe富集区和Cu富集区。

Local structures of mechanically alloyed Fe100—xCux solid soulutions studied by X—ray absorption fine structure

The local structures of the immiscible Fe100-xCux alloys(x=0,10,20,40,60,80and100)produced by mechanical alloying have been investigated by XAFS.For the Fe100-xCux(x≥40) solid solutions,the local structures around Fe atoms change from bcc structure to fcc one and the Cu atoms maintain the original coordination geometry after milling for 160 hours.On the contrary,the local structures around Cu atoms in both of Fe80Cu20 and Fe90 Cu10 alloys appear a transition from fcc to bcc structure.We found that the Debye-waller factor σof fcc Fe-Cu phase is larger than that of bcc F-Cu phase,and the σ(0.099A°)around Fe atoms is larger than that (0.089A°) of Cu in the Fe100-xCux(x≥40)solid solutions,This suggests that the mechanically alloyed Fe100-xCux supersaturated solid solution is not a homogeneous alloy,and consists of Fe-rich and Cu-rich regions for various compositions.A possible mechanism for bcc-to-fcc and fcc-to-bcc changes in Fe100-xCux solid solutions is discussed in relation to the interdiffusion and transition induced by the ball milling.