疲劳裂纹尖端的位错结构

在双相钢物理短裂纹门槛区，观察到稳定的位错胞和墙结构；长裂纹门槛区，在铁素体／马氏体相界堆垛位错密度大，有形成位错胞的趋势．长裂纹扩展第二阶段，铁素体晶粒内具有单向滑移线（Ｒ＝０，－１）和正交网状（Ｒ＝－１）的位错结构，长裂纹扩展第三阶段，位错稀少，但单滑移、双交滑移位错线明显拉长，说明裂纹尖端位错组态是应变历史的产物．疲劳裂纹扩展门槛区形成的位错胞和墙是一亚稳态结构，与门槛循环应力应变处于动态平衡，也是一微观结构参数．

DISLOCATION STRUCTURE OF FATIGUE CRACK TIP

It was observed first in this test that the stabilized dislocation cell and wall structures had been formed on near fatigue threshold of physcial short crack in dual-phase steels. There was a probability of forming dislocation cell on ferrite-martensite interfaces in long crack growth threshold. where the dislocation lines were more dense, there were the dislocation lines of single(R = 0,-1) and cross slip(R=-1) in the second stage of long crack growth ;there were obviously rare and lengthened dislocation lines of single and cross slip in the third stage of long crack growth. It is indicated that the dislocation morphologies of fatigue crack tip were the products of strain history. The dislocation cell and wall structures were substable on near physical short crack threshold. it was constituted into dynamic balance with cyclic stress-strain on threshold, and also was one of microstructural parameters.