Microstructure of Zr Grain-refined through Equal Channel Angular Pressing

초록

Equal Cannel Angular Pressing(ECAP) is a means of producing nano-scale grains through severe plastic deformation without changing the shape of work piece. In this study, pure Zr was grain-refined via ECAP method and the crystallographic texture and grain boundary character distribution were analyzed with electron back-scattered diffraction and x-ray diffraction analysis. A grain refinement in the order of 1/100-1/1000 times the original grain size was obtained by using 90/20 as well as 135/45 die design at 350oC and RT, respectively. In the as-ECAPed condition, the average grain size was about 200-400nm with large angle grain boundaries and profuse number of deformation twins. The stability of the microstructure was maintained up to 40min. at 500oC but grain coarsening occurred up to 600nm during a 550oC/48hr-heat treatment. Grain boundary misorientation angles shifted toward low angle side in the ECAPed sample compared with the random case. A mild pyramidal texture was observed after ECAP and a slight rotation of the basal poles occurred during subsequent heat treatment. A computer simulation was employed to study the microstructural and texture evolution upon normal grain growth.