Mapping dislocation densities resulting from severe plastic deformation using large strain machining

The multiplication of dislocations determines the trajectories of microstructure evolution during plastic deformation. It has been recognized that the dislocation storage and the deformation-driven subgrain formation are correlated—the principle of similitude, where the dislocation density (ρ_i) scales self-similarly with the subgrain size (δ): $(\delta):\delta \sqrt {{\rho _{\rm{i}}}} \sim $ ∼ constant. Here, the robustness of this concept in Cu is probed utilizing large strain machining across a swathe of severe shear deformation conditions—strains in the range 1–10 and strain-rates 10–10^3/s. Deformation strain, strain-rate, and temperature characterizations are juxtaposed with electron microscopy, and dislocation densities are measured by quantification of broadening of X-ray diffraction peaks of crystallographic planes. We parameterize the variation of dislocation density as a function of strain and a rate parameter R , a function of strain-rate, temperature, and material constants. We confirm the preservation of similitude between dislocation density and the subgrain structure across orders-of-magnitude of thermomechanical conditions.

位错的增殖决定了塑性变形过程中微观结构演变的轨迹。人们已经认识到，位错储存和变形驱动的亚晶粒形成是相关的——相似性原理，即位错密度（ρ_i）与亚晶粒尺寸（δ）自相似地成比例：$(\delta):\delta \sqrt {{\rho _{\rm{i}}}} \sim$ ∼常数。在此，利用在一系列剧烈剪切变形条件下（应变范围为1 - 10，应变速率为10 - 10³/秒）的大应变加工，对这一概念在铜中的稳健性进行了探究。变形应变、应变速率和温度特性与电子显微镜分析相结合，并且通过对晶体学平面的X射线衍射峰展宽进行量化来测量位错密度。我们将位错密度的变化参数化为应变以及速率参数R的函数，R是应变速率、温度和材料常数的函数。我们证实了在热机械条件的数量级范围内，位错密度和亚晶粒结构之间的相似性保持不变。