Grain Refinement and Texture Development of Zr through ECAP

초록

Sub-micrometer scale grains in the order of 200 to 400nm were obtained in Zr by equal channel angular pressing (ECAP) at room temperature as well as at 350°C. The samples ECAP-deformed at elevated temperature showed a sign of dynamic recrystallization. Electron-back-scattered-diffraction (EBSD) analysis of the deformed specimen at room temperature showed numerous tensile twins of { }< > type, which indicated a role of twinning in the grain refinement. Recrystallization heat treatment at 550°C increased the grain size to a range of 1 to 6mm during up to 48hrs of holding, indicating a relative stableness of the microstructure. The specimen ECAP-deformed at room temperature showed a (22 1)[1 00] texture in which the basal pole was inclined 80 degree from the axial (X) direction toward the transverse (Y) direction, whereas the one deformed at 350°C showed (10 2)[ 011] texture in which the basal plane was inclined 50 degree from the axial direction toward the normal direction (Z). A Monte-Carlo computer simulation code was developed to examine the microstructural evolution from the data obtained by EBSD. In the simulation, the grain boundary energy and the mobility for grain growth were continuously varied according to the grain boundary misorientation angle. During simulation the coarse grains of the initial primary texture component grew consuming the grains of minor texture components, resulting in a strengthening of the primary texture component.