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

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 have Burgers vectors b=1/2〈111〉 and loop planes normal to n ≈ {110} (∢(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 τ0 of the order of magnitude of 10 N/mm2 for the onset of microslip in tungsten single crystals at room temperature, in agreement with data reported in the literature. The specific stacking fault energy on {110}-planes is estimated as γ110≈0.8 × 10−6 J/mm2.