球磨纯铁中纳米铁素体的形成机制

通过形貌观察和硬度测试研究了球磨纯铁中纳米铁素体的形成机制，结果表明，在球磨过程初期，纳米铁素体首先在球磨颗粒的表层区域形成并呈现层片状结构，扫描电镜（SEM），透射电镜（TEM）和高分辨电镜（HREM）观察表明，层片状纳米铁素体区与颗粒内部加工硬化区具有不同的微观结构，而且它们之间的界面十分明显，显微硬度测试试表明，前者的硬度数值明显高于后者，进一步的球磨过程导致颗粒细化并完成转变为纳米铁素体，分析表明，纳米铁素体的形成是由于球磨过程中加工硬化效应产生的位错胞墙结构向晶界结构转变而导致的，这也是造成加工硬化区与纳米铁素体之间存在的硬度差异的原因。

FORMATION MECHANISM OF NANOCRYSTALLINE FERRITE DURING BALL MILLING PURE Fe

Nanocrystalline ferrite formation during ball milling pure Fe (0.004%C) has been studied through morphology observation and microhardness measurements. It was found that layer- like structure consisting of nano-ferrite firstly formed at the outer surface area of the powder particle at the early stage of ball milling. The microstructures between nano-ferrite and work-hardened regions are different and the boundaries between them are quite clear under SEM and TEM. The hardness of nano-ferrite region is obviously higher than that of the work-hardened region. Further milling led to the particle refinement and formation of nano-ferrite. It has been suggested that the nanocrystalline ferrite formed through a transition from dislocation cell wall created by work hardening during ball milling to grain boundary, which is regarded to contribute to the hardness gap between the work hardened structure and the nanocrystalline ferrite.