EBSD Characterization of the Twinning Microstructure in a High-Damping Mn–Cu Alloy

Abstract

The {101} transformation twinning bands in Mn–Cu alloys are considered to be the dominant microstructural feature contributing to the high damping capacity of the alloys. Because the face-centered-tetragonal (fct) phase of Mn–Cu alloys has an axis ratio (c⁄a) of nearly 1, an angular resolution for Kikuchi diffraction bands of better than 0.5° is necessary to identify the twin boundaries by the electron backscattering diffraction (EBSD) method. At some angular resolutions, [100] and [001] orientations of the fct phase may be randomly recorded within the single twinning band. In contrast, the image-quality signal of EBSD shows a reflection that is sensitive to the twinning bands. The image-quality contrast is produced by the average orientation difference between the twinning bands. Therefore, the twinning bands of Mn–Cu alloys can be identified by partitioning the orientation distribution of the normal direction for the observed sample section in a range of about 1°. With the aid of {101} stereographic projection, the width of the twinning bands and the intersection morphology were analyzed for a Mn–Cu alloy. The observed intersection morphology was related to a 60° or 90° spatial intersection configuration of different groups of twinning bands. In addition, sharpened ends of twinning bands at the junction regions and secondary twinning phenomena were also characterized.