Observation of Misoriented Tertiary Dendrite Arms During Controlled Directional Solidification in Aluminum-7 Wt pct Silicon Alloys

Electron backscattered diffraction (EBSD) examination of transverse cross sections from a directionally solidified aluminum-7 wt pct silicon alloy revealed tertiary dendrite arms that appeared in place but in reality had orientations that significantly differed from their parent arm. The maximum extent of spuriously orientated arms occurred at an intermediate growth velocity and was more pronounced at subgrain boundaries that separated uniquely oriented dendritic arrays. Mechanisms for tertiary arm misorientations are discussed, and attention is called to the practical consequences of these in-situ defects.