Ion Damage Effects in Metals as Studied by Transmission Electron Microscopy

The elastic interaction of a dislocation loop with the traction‐free surface S of an elastically isotropic half‐space is calculated for arbitrary orientations of the Burgers vector of the loop, b, and the normal of the loop plane, n, with respect to S. Using the double force approximation (infinitesimal loop approximation) expressions are derived for the interaction energy and for the image force by which the loop is attracted to S.

Elastic interaction of a dislocation loop with a traction-free surface

Jäger

Rühle²,

Wilkens³

1975

Formation of vacancy-type dislocation loops in tungsten bombarded by 60 keV Au ions

Jäger

Wilkens

1975

The formation of vacancy-type dislocation loops in tungsten specimens as produced by irradiation with 60 keV Au ions is investigated by transmission electron microscopy. The majority of the loops is found to haveBurgers vectors b = -:-(111) and loop planes normal t o n = { llO} ( < ( b , n) = 35"). The 12 different loop orientations of this type are observed with significantly different frequencies depending sensitively on the crystallographic orientation of the specimen surface. The observations are explained in terms of the elastic interaction of the growing loops with the adjacent specimen surface. The proposed interpretation of the results leads to a critical resolved shear stress to of the order of magnitude of 10 N/mm2 for the onset of microslip in tungsten single crystals a t room temperature, in agreement with data reported in the literature. The specific stacking fault energy on { ll0}-planes is estimated as yllo = 0.8 x J/mm2. Die Bildung von Versetzungsringen vom Leerstellentyp in Wolfram, wie sie bei BeschuS mit Au-Ionen (60 keV) entstehen, wird elektronenmikroskopisch untersucht'. Fur die uberwiegende Mehrzahl der Ringe ergeben sich Burgersvektoren b = -:(111) und Normalen der Ringebenen vom Typ n = { 110) ( + ( b , n) = 35"). Die zu diesem Ringtyp gehorigen 12 verschiedenen Orientierungen werden mit deutlich verschiedenen relativen Haufigkeiten gefunden, wobei diese Haufigkeiten empfindlich von der kristallographischen Orientierung der Praparatoberflache abhangen. Die Beobachtungen werden mit der Annahme erklart, daD wahrend des JVachstums eines Leerstellenringes die elastische Wechselwirkung des Ringes mit der benachbarten Praparatoberflache eine spezifische Rolle spielt. Die vorgeschlagerie Deutung der Resultate ergibt eine kritische Schubspannung to von der GroBenordnung 10 N/mm2 fur den Einsatz der Mikrogleitung in Wolframeinkristallen bei Raumtemperatur in U'bereinstimmung mit Literaturwerten. Die spezifische Stapelfehlerenergie auf { 110}-Ebenen wird zu yllo = 0,8 x 10-6 J/mm2 abgeschatzt.

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

Föll¹,

Wilkens²

1977

Thin foils of h.c.p. cobalt are irradiated at room temperature with 60 keV Au ions (dose between 1011 and 1012 ions/cm2) and subsequently investigated by TEM. The dislocation loops of vacancy type (mean diameter ≈ 7 nm) produced in the cores of the displacement cascades are analysed with respect to their loop normals n and their Burgers vectors b using for the contrast analysis the first order perturbation method. For most of the loops the analysis yielded b = a/3 <1120> and n ≈ {1010}, ∢ n, b ≈ 30°. A small fraction of the loops are found to be of pure edge type with b = a/2 <1010>, n = {1010}. The results are interpreted in terms of a model of loop formation which predicts loop configurations in h.c.p. metals depending on the axial ratio c/a. It is shown that the experimental data published in the literature on dislocation loops in radiation damaged or quenched h.c.p. metals are in agreement with the model.