Texture development and Monte-Carlo simulation of microstructure evolution in pure Zr grain-refined by equal channel angular pressing

The evolution of the grain boundary character distribution (GBCD) of severely deformed commercial purity Zr was studied by experiment as well as computer simulation. The severe plastic deformation was performed by equal channel angular pressing (ECAP) at 350degreesC using a die with 90degrees/20degrees. Through a repetitive operation, it was possible to reduce the grain size of specimens from 20mum to about 300nm with high angle grain boundaries. During the severe deformation, it strong texture developed in specimens, which could be traced through a viscoplastic self-consistent (VPSC) model. Combination of prism slips and mechanical twinning were presumed to operate during the severe deformation that was predominantly shear in character. Grain growth kinetics of severely deformed specimens were studied by optical microscopy as well as by Monte-Carlo computer simulation, which showed a grain growth exponent, n. ranging from 0.25 to 0.44. For the computer simulation, a direct mapping method was developed such that the orientation image map (OIM) obtained by electron back scattered diffraction (EBSD) was digitized and planted into the simulation microstructure grid. The grain growth, which can be characterized as normal growth, was accompanied by unaltered distribution characteristics of the boundary misorientation angles and tenacious trait of the texture.