The analysis of field-ion micrographs: Stacking faults in tungsten

It is shown how the images of stacking faults in b.c.c. metals can be analysed in field-ion micrographs. The method of analysis is applied to some observations in tungsten. A mixed dislocation lying close to the [142] direction and with Burgers vector a/2[11·1] is shown to have dissociated twice. The dislocation dissociated on {110} planes in accord with either the dissociation proposed by Cohen–Crussard or that proposed by Wasilewski–Foxall. A tentative value for the stacking-fault energy of tungsten of γ≃50 ergs cm−2 is obtained, in the suspected presence of some impurity segregation.