Mechanism of nanocrystalline microstructure formation in amorphous Fe-Nb-B alloys
Mechanism of nanocrystalline microstructure formation in amorphous Fe-Nb-B alloys
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DOI：
10.1103/physrevb.74.184204
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发表时间：
2006-11
影响因子：
3.7
通讯作者：
A. Hirata;Y. Hirotsu;E. Matsubara;T. Ohkubo;K. Hono
中科院分区：
文献类型：
--
作者：
A. Hirata;Y. Hirotsu;E. Matsubara;T. Ohkubo;K. Hono
为了理解部分结晶的Fe{sub 84}Nb{sub 7}B{sub 9}合金中bcc-Fe纳米晶的高数量密度的机制，我们使用透射电子显微镜、三维原子探针和高能X射线衍射技术研究了退火非晶带的详细局部结构和成分变化。从淬火非晶带的纳米束电子衍射图案表明局部纳米级原子有序。退火时，减少干扰功能显示出明显的变化，刚好低于结晶温度（约773 K）。在这一阶段，局部成分波动开始出现，并在高分辨率电子显微镜照片中清楚地观察到具有小至2 nm的bcc-Fe结构的中程有序，具有极高的数密度。对分布函数分析表明，在这个阶段的退火，以增加在残余的非晶基体的bcc-Fe区域周围的化学键的结构变化。在剩余的非晶基体中的原子化学键的增加被认为是在退火的后期阶段的bcc-Fe MRO区域的聚结后延缓bcc-Fe纳米晶体的生长。这些结果表明，具有极高的数密度的bcc-Fe纳米晶化主要归因于（i）高密度的bcc-Fe MRO区域的存在和（ii）退火时基质原子的化学键的更多增加。«少
To understand the mechanism of the high number density of bcc-Fe nanocrystals in a partially crystallized Fe{sub 84}Nb{sub 7}B{sub 9} alloy, we have investigated detailed local structural and compositional changes on annealing amorphous ribbons using transmission electron microscopy, three-dimensional atom probe, and high-energy x-ray diffraction techniques. Nanobeam electron diffraction patterns from an as-quenched amorphous ribbon indicated a local nanoscale atomic ordering. On annealing, reduced interference functions showed a clear change just below the crystallization temperature ({approx}773 K). At this stage, local compositional fluctuations started to appear, and medium-range ordering with a bcc-Fe structure as small as 2 nm was clearly observed in high-resolution electron micrographs with an extremely high number density. Pair distribution function analyses suggested a structural change at this stage of annealing to increase the chemical bonds in the residual amorphous matrix around the bcc-Fe regions. The increase of atomic chemical bonds in the residual amorphous matrix is considered to retard the growth of the bcc-Fe nanocrystals after the coalescence of bcc-Fe MRO regions in the later stage of annealing. These results suggest that bcc-Fe nanocrystallization with the extremely high number density is ascribed to primarily (i) the presence of highly dense bcc-Fe MRO regions and (ii) themore » increase of chemical bonds of matrix atoms on annealing.« less