高应变速率下等径角挤压高纯粗晶铝中的形变孪晶与退火孪晶

在室温下对铸态高纯粗晶铝进行一道次高应变率动态等径角挤压(D-ECAP)变形,利用电子背散射衍射技术(EBSD)研究挤压过程中所形成的孪晶。结果表明:利用D-ECAP能够在粗晶铝中同时制备出形变孪晶和退火孪晶,但两者在形态、Kernel平均取向差(KAM)以及与相邻晶粒的取向差三个方面存在较大差异。D-ECAP高应变率和大剪切变形使高层错能铝中形成了百微米级的形变孪晶,形变孪晶的形态为透镜状,后续变形使得孪晶界偏离∑3 60°〈111〉取向关系且KAM值主要集中于0.6°~1.8°。高应变率剪切变形下形成的大量层错和复杂的位错组态以及高形变储存能在变形温升的作用下促进了退火孪晶的形成。退火孪晶的形态较不规则,但孪晶界的取向关系更接近于∑3 60°〈111〉且KAM值主要集中于0.2°~0.5°。

Deformation twins and annealing twins in high purity coarse-grained aluminum by equal channel angular pressing at high strain rate

An as-cast high purity coarse-grained aluminum was deformed by dynamic equal channel angular pressing(D-ECAP)at high strain rate for one pass at room temperature.The twins formed during extrusion were studied with electron backscatter diffraction.The results show that deformation twins and annealing twins can be synthesized simultaneously in the coarse-grained aluminum via D-ECAP,which can be differentiated by their morphology,Kernel average misorientation(KAM)and the misorientation between adjacent grains.Due to the high strain rate and large shear deformation of D-ECAP,deformation twins with size of several hundred microns can be formed in aluminum with high stacking fault energy,and their shapes are lenticular.The twin boundaries deviate from ∑360°<111> orientation relationship as a result of subsequent deformation,and the KAM values are mainly between 0.6°-1.8°.The high strain rate shear deformation contributes to the formation of abundant stacking fault,intricate dislocation patterns,and high deformation stored energy,and thus the ensuing temperature rise facilitates the formation of annealing twins.The morphology of annealing twins is irregular,but the orientation relationship of annealing twin boundaries is more close to ∑360°<111> and the KAM values of annealing twins are mainly between 0.2°-0.5°.