On the intrusion-like co-zone twin-twin structure: An in situ observation

Abstract

An in situ optical microscopy combined with ex situ electron backscatter diffraction testing was applied to a pristine single-crystal magnesium specimen under monotonic tension along the c-axis. An intrusion-like co-zone twin-twin structure is observed for the first time at the micron scale. In situ observation reveals that the intrusion-like twin-twin structure consists of multiple twin-twin boundaries (TTBs) and incoherent twin boundaries (I-CTBs) following energetically favorable formation sequences. The initial interaction results in the impinging TTBI and the acute-angle TTBA. In the local junction region on the obtuse angle side, the impinging twinning dislocations (TDs) further deposit near TTBI due to the preferred local twinning shear stress, leading to the incoherent curve of the impinging twin boundary adjacent to TTBI. Shortly after, the barrier twin boundary on the obtuse angle side migrates and encompasses the incoherent impinging twin boundary. The combination of sequential TTBI, TTBA, and I-CTBs formed locally on the obtuse angle side shapes the final configuration of the intrusion-like twin-twin structure at the micron scale.