Use of electron channelling contrast imaging to assess near-surface mechanical damage

Electron channelling contrast imaging (ECCI) is a scanning electron microscopy method that forms contrast from crystallographic orientation information in the near-surface region; because of this, ECCI is useful for imaging crystal defects in the near-surface region. As a consequence of this sensitivity to surface condition, ECCI is well suited as a non-destructive method to evaluate the surface quality of prepared samples. Here, ECCI has been used to show the dislocation structure underlying the surface of a mechanically polished NiAl single crystal, and the evolution of this structure with depth when revealed by electropolishing. It is shown that for single crystal intermetallic compounds such as NiAl, simple mechanical polishing may leave a surface damage layer of depths greater than 100 mu m.