XRD analysis of cell size and dislocation density in Twin Parallel Channel Angular Extrusion

Equal Channel Angular Extrusion (ECAE) is a processing method in which a metal is subjected to an intense plastic deformation through simple shear to achieve UFG structures. To eliminate the shortcomings of conventional ECAE, a new development of ECAE in parallel channels, named Twin Parallel Channel Angular Extrusion (TPCAE), is presented. In this study, capability of using this technique to produce billets with least waste of materials is investigated. Microstructural evolution is studied employing XRD measurements. Crystallite size was assessed according to the modified Williamson-Hall method and Rietveld refinement analysis. Considering Rietveld analysis, cell size of 91 nm was achieved after the 4th pass. Although Williamson -Hall method underestimates the cell size in comparison to the Rietveld method, good agreement was achieved between both methods in prediction of crystallite size variation trend through straining. Also, dislocation density was obtained by modified Williamson-Hall method in different passes. The predicted trend of dislocation density variation shows a maximum causing by the two compensating mechanism of dislocation generation and dislocation annihilation.

Keywords:

TPCAE , ultrafine grain structures , crystallite size , dislocation density