Field‐Ion Microscopic Contrast from Partial Dislocations and Stacking Faults in B.C.C. Metals

The geometrical contrast theory of dislocated surfaces is extended to include faults in b.c.c. metals. A general approach to the problem of dislocation and fault contrast is indicated; the characteristic spiral and step configurations from any dislocation and any fault can be deduced from simple crystallographic parameters. In some cases a fault can be characterised completely by noting its line of intersection with an imaged pole and the multiplicity of associated spirals. The limitations of the theory are pointed out.