对纯铝(高层能金属)进行表面机械研磨处理(SMAT),在试样表面形成纳米层。利用透射电子显微镜(TEM)对表面层的微观结构进行了表征。实验结果表明,晶粒细化的主要微观特征为:在原始晶粒和细化晶粒内部形成位错缠结(DTs)、位错胞(DCs)和高密度位错墙(DDWs)、亚晶、显微带(MBs)、层状结构,并随着应变和应变速率的进一步增加,逐渐在表面形成随机取向的纳米晶。分析可见,高应变速率和高应变是形成纳米晶的必要条件。
A nanostructured surface layer was formed on pure A1 (high stacking-fault energy)by means of the surface mechanical attrition treatment (SMAT). The microstructure of the surface layer of the SMATed sample was characterized by using transmission electron microscope (TEM). The grain refinement process on the surface layer involves formation of dislocation tangles(DTs) ,dislocation cells(DCs) and dense dislocation walls (DDWs) in original grains and in the refined cells (under further straining) as well, transformation of DTs and DCs into subboundaries with small misorientations separating individual cells and forming microbands(MBs) cut by incidental dislocation boundaries (IDBs) grain boundaries. Experimental evidences that high strains with a high strain rate , and evolution of subboundaries to highly misoriented and analysis of the grain refinement mechanism indicate are necessary for formation of nanocrystallites during SMAT.