Ion bombardment of H.C.P. and F.C.C. cobalt in the electron microscope

Abstract

Visible defects having diameters ranging from 15 to 80 Å were produced in h.c.p. and f.c.c. cobalt during bombardment at about 20 °K with 100 keV O− ions in the electron microscope. The principal component of the strain field was along 〈111〉 for the majority of the defects in the f.c.c. regions and along 〈2023〉 for many of the defects in the h.c.p. regions. The strain fields are consistent with that expected for dislocation loops lying on {111} planes and having 1/3 〈111〉 Burgers vectors in the f.c.c. case and dislocation loops lying on the (0001) plane and having 1/6〈2023〉 Burgers vectors in the h.c.p. case. It is not possible, however, to differentiate between a single dislocation loop and an assembly of small narrowly spaced loops all having the same Burgers vector and the same loop habit plane. Stereo analysis of the defects produced during ion bombardment at about 20 °K was performed at 300 °K. The analysis showed that vacancy like defects were involved. It is proposed that the defects represent depleted regions formed directly in the collision cascade.

Transmission electron microscope studies of dislocation loops in heavy-ion irradiated H.C.P. cobalt

“…Dark field micrograph of an irradiated specimen with foil normal near { 1120). The marked dislocation indicates that the resolution is high enough t o detect loops on the {Oool} plane with diameters 2 3 nm Specimens of type S, when imaged with g = { 0002) are especially suitable in order to detect loops on the basal plane (n = (0001)) with b = (2023) which were assumed to be present in ion-damaged Co by other authors[5]. Their result is not confirmed in the present investigation.…”

“…can be explained better in terms of the model of Section 5.1 rather than in terms of the model of[5].With respect to other h.c.p. metals with c/a < fi we refer to the investigations ofBrimhall and Mastel [21] on Re and Bernstein and Gulden [22] and Kelly and Blake [23] on Zr.…”

“…metals fit fairly well into this concept. There is one exception: Howe and Rainville [5] reported on TEM investigations on heavy-ion bombarded h.c.p. Co (cia < 13).…”

“…Co using 60 keV Au ions for production of the vacancy type loops. I n our investigations we make use of some recent developments of the black-white contrast methodpresented in [6 to 81 and especially in [9] which were not known a t the time of the investigations of [5]. a 2.…”