Characterization and crystallographic analyses of new three-fold Ti(O,C) nanotwins in a hot-pressed Nb-Ti-al alloy

In this article, two new types of three-fold Ti(O,C) twins were observed, and the crystallographic relationships of the twins have been analyzed in depth. The difference in the intersection angles of primary twin boundaries derives from different crystallographic operations forming the face-centered cubic Ti(O,C) twins: two consecutive rotations of 70.5° counter-clockwise or clockwise around the [011] axis. Using double and triple Thompson tetrahedrons, the ambiguity of a three-fold twin in TEM observation is clarified by the analysis of the common [011] axis. These findings might bring about substantial insights to the crystallographic understanding of three-fold twins.