1Cr18Ni9Ti不锈钢剪切变形诱发的表面纳米化

Surface Nanocrystallization of 1Cr18Ni9Ti Stainless Steel Induced by Shear Deformation

对1Cr18Ni9Ti板材进行球磨处理,利用光学显微镜、X射线衍射和透射电镜研究剪切变形方式下深度方向的组织演变.结果表明,剪切变形可以在1Cr18Ni9Ti中诱发表面纳米化,其过程包括:奥氏体内通过位错的增殖、运动、湮灭和重组形成具有亚微米尺度的、取向差较小的位错胞;位错胞壁不断吸收位错而转变成小角度和大角度晶界,将原始粗晶分割成亚微晶;应变量和应变速率的增加诱发机械孪生,形成纳米量级的板条状马氏体;细化组织重复上述过程使晶粒尺寸减小、取向差增大,最终形成等轴状、取向呈随机分布的纳米晶组织.外力作用方向并未改变纳米化过程,但会影响变形层的厚度.

1Cr18Ni9Ti stainless steel sheet was treated by ball milling. The microstructural evolution induced by shear-stress along the depth was examined by using optical microscopy, X- ray diffraction and transmission electron microscope, respectively. The results showed that shearstress can induce surface nanocrystallization in 1Crl8Ni9Ti sheet. The grain refinement procedure is summarized as follows： the formation of dislocation ceils through the propagation, slip, annihilation and recombination of the dislocations in the austenite matrix; the transformation of dislocation walls into small and large angle boundaries to refine the initial coarse grains into submicro-grains; the strain-induced mechanical twinning and nano-scale lamellar martensite; further subdivision of refined grains by dislocation activities and mechanical twinning leading to the formation of equiaxed nanoscale grains with random orientations. The direction of external loads does not affect the grain refinement procedure, but can change the thickness of deformation layer.