In-situ TEM studies of 150 keV W+ ion irradiated W and W-alloys: Damage production and microstructural evolution

Abstract

In-situ irradiations with 150 keV W+ ions have been performed on W and W-5wt.% (Re; Ta; V) alloys in a comprehensive study of the influences of irradiation temperature Tirr, dose, alloying elements and grain orientations on radiation damage production and microstructural evolution. For Tirr between 30 K and 1073 K, the first observable defects in pure W appeared at doses ≤0.01 dpa, and were most likely vacancy loops, with Burgers vectors predominantly of type b = ½ <111>. With increasing Tirr, the retained defect concentration decreased strongly and the maximum cluster size increased from ∼1300 point defects at 30 K to ∼2300 point defects at 1073 K. At all irradiation temperatures, the evolution of damage microstructures with dose from 0.1 to 1.0 dpa involved defect cluster migration, with mutual elastic interactions often leading to spatial inhomogeneities and loop reactions. In pure W, spatial ordering of loops was observed at doses >0.4 dpa and Tirr≥773 K in grains close to z = <001>. No such ordering was found in similar grain orientations for the W-(Re; Ta) alloys, but it was found in the non-z = <001> grains. Post-irradiation analysis on W and W-5 wt% (Re; Ta) at 1.0 dpa showed that ½ <111> and <100> loops of both vacancy and interstitial type were present, at number densities ∼ 1015 loops m−2. In all cases ½ <111> loops were dominant, the fraction of these with interstitial nature increased with Tirr, and the proportion of <100> loops decreased with increasing Tirr. Compared with pure W, microstructures in the W-(Re; Ta) alloys exhibited higher loop number densities and evolved more quickly with increasing dose towards damage saturation.